U.S. patent application number 12/173044 was filed with the patent office on 2009-01-15 for carbon dioxide removal from whole blood by photolytic activation.
This patent application is currently assigned to BATTELLE MEMORIAL INSTITUTE. Invention is credited to Eric C. Burckle, Bruce F. Monzyk.
Application Number | 20090017128 12/173044 |
Document ID | / |
Family ID | 40352089 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090017128 |
Kind Code |
A1 |
Monzyk; Bruce F. ; et
al. |
January 15, 2009 |
CARBON DIOXIDE REMOVAL FROM WHOLE BLOOD BY PHOTOLYTIC
ACTIVATION
Abstract
Apparatus and methods for removing carbon dioxide from whole
blood. Hydrogen ions are generated from water in the blood,
resulting in the formation and release of carbon dioxide from the
blood.
Inventors: |
Monzyk; Bruce F.; (Delaware,
OH) ; Burckle; Eric C.; (Dublin, OH) |
Correspondence
Address: |
FAY SHARPE LLP
1100 SUPERIOR AVENUE, SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Assignee: |
BATTELLE MEMORIAL INSTITUTE
Columbus
OH
|
Family ID: |
40352089 |
Appl. No.: |
12/173044 |
Filed: |
July 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11130047 |
May 16, 2005 |
7399717 |
|
|
12173044 |
|
|
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|
Current U.S.
Class: |
424/529 ;
435/1.1; 604/6.08 |
Current CPC
Class: |
A61M 1/32 20130101; A61M
1/3683 20140204; A61M 1/3681 20130101; A61M 1/327 20140204 |
Class at
Publication: |
424/529 ;
604/6.08; 435/1.1 |
International
Class: |
A61M 1/32 20060101
A61M001/32; A01N 1/02 20060101 A01N001/02; A61K 35/14 20060101
A61K035/14 |
Claims
1. A process for removing carbon dioxide from the whole blood of a
patient, comprising: a) providing blood containing a base amount of
carbon dioxide from a patient to a photolytic device wherein the
photolytic device comprises: an inlet for receiving blood from a
patient and transporting the blood to a photolytic cell; a
photolytic cell having a light transparent substrate and a
photo-reactive surface, said photo-reactive surface comprising (i)
a layer of a light activated photolytic catalyst and (ii) an
electrically conductive layer, wherein said photo-reactive surface
has the ability to release hydrogen ions from water in the blood
upon light activation; a light source for providing light photons
to said light transparent substrate of the photolytic cell and
activating said photolytic catalyst to initiate a series of
chemical reactions that result in hydrogen ion generation by the
photo-reactive surface of the photolytic cell; a gas sorption
device for capturing carbon dioxide released from the blood; and an
outlet for transporting the blood out of said photolytic cell; b)
activating the light source to release carbon dioxide from the
blood to form blood containing a lower amount of carbon dioxide;
and c) returning the carbon dioxide poor blood to the patient.
2. The process of claim 1, wherein the light activated photolytic
catalyst is a metal oxide.
3. The process of claim 2, wherein the metal oxide substantially
comprises TiO.sub.2 (anatase), WO.sub.3, ZnO, and combinations
thereof.
4. The process of claim 1, wherein the light source is an
ultraviolet laser light that emits light at 350-390 nm.
5. The process of claim 1, wherein the photo-reactive surface
further comprises a layer of a disproportionation catalyst disposed
on the photolytic catalyst layer.
6. The process of claim 5, wherein said disproportionation catalyst
comprises MnO.sub.2.
7. The process of claim 1, wherein the photo-reactive surface is
disposed upon the light transparent substrate, the photolytic
catalyst layer is a layer of TiO.sub.2, and the photo-reactive
surface further comprises a layer of MnO.sub.2 disposed upon the
layer of TiO.sub.2.
8. The process of claim 1, wherein the photolytic cell further
converts water into dissolved oxygen.
9. Oxygenated whole blood produced by the process of claim 1.
10. The process of claim 1, wherein the whole blood is mammalian
whole blood.
11. The process of claim 1, wherein there is also an increase in
oxyhemoglobin in the blood containing a lower amount of carbon
dioxide.
12. A process for enhancing the viability of an organ to be
transplanted comprising: a) providing to an organ to be
transplanted whole blood and a photolytic device, wherein the
photolytic device comprises: i. an inlet for receiving blood from
the organ and transplanting the blood to a photolytic cell; ii. a
photolytic cell having a light transparent substrate and a
photo-reactive surface, said photo-reactive surface comprising (A)
a layer of a light activated photolytic catalyst and (B) a layer of
a disproportionation catalyst disposed on the photolytic catalyst,
wherein said photo-reactive surface has the ability to release
hydrogen ions from water in the blood upon light activation; iii. a
light source for providing light photons to the light transparent
substrate of the photolytic cell and activating said photolytic
catalyst to initiate a series of chemical reactions that result in
hydrogen ion generation by the photo-reactive surface of the
photolytic cell; iv. a gas sorption device for capturing carbon
dioxide released from the blood; and v. an outlet for transporting
the blood out of said photolytic cell; b) providing blood
containing a base amount of carbon dioxide from the organ to the
photolytic device to lower the amount of carbon dioxide in the
blood; and c) returning the blood containing a lower amount of
carbon dioxide to the organ.
13. The process of claim 12, wherein the light activated photolytic
catalyst is a metal oxide.
14. The process of claim 13, wherein the metal oxide substantially
comprises TiO.sub.2 (anatase), WO.sub.3, ZnO, and combinations
thereof.
15. The process of claim 12, wherein the light source is an
ultraviolet laser that emits light at 350-390 nm.
16. The process of claim 12, wherein the disproportionation
catalyst comprises MnO.sub.2.
17. The process of claim 12, wherein the photolytic cell also
converts water in the whole blood into dissolved oxygen.
18. The process of claim 12, wherein there is also an increase in
oxyhemoglobin in the blood containing a lower amount of carbon
dioxide.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation application of
U.S. patent application Ser. No. 11/130,047, now U.S. Pat. No.
7,399,717. The disclosure of this application is hereby fully
incorporated by reference.
[0002] This application is also related to U.S. patent application
Ser. Nos. 10/485,455; 10/485,476; and, 10/485,934, all filed on
Jan. 30, 2004. The disclosures of those applications are also fully
incorporated herein by reference.
BACKGROUND
[0003] The present disclosure, in various embodiments, is directed
to a photolytic apparatus that utilizes light energy to achieve
physiological gas exchange in whole blood, such as in the blood
stream of a patient experiencing respiratory difficulties, whole
blood utilized to transport organs, etc., and to a photolytic cell
or module used for the same. The disclosure finds particular
applications in conjunction with the field of artificial organs and
the medical arts. However, it is to be appreciated, that the
embodiment disclosed herein will also find applications in related
fields due to the photo-electro chemical transformations involved
therein.
[0004] In this regard, despite major reduction in disease mortality
experienced over the past several decades, the mortality associated
with chronic lung disease has continued to rise. This is largely
due to a lack of emerging treatments, and inadequate technology for
providing intermediate ("bridge" therapy) or long-term respiratory
support. Numerous technical solutions have been proposed and
implemented. Moreno-Cabral R J, Dembitsky W P, Adamson R M, Daily P
O., Percutaneous extracorporeal membrane oxygenation. Adv Card
Surg, 5: 163-179, 1994; Funakubo A, Higami T, Sakuma I, Fukui Y,
Kawamura T, Sato K, Sueoka A, Nose Y., Development of a membrane
oxygenator for EXMO using a novel fine silicone hollow fiber,
ASAIO, 42: M837-840, 1996; Naganuma S, Nitta S, Yambe T, Kobayashi
S, Tanaka M, Hashimoto H., Gas exchange efficiency of a membrane
oxygenator with use of a vibrating flow pump, Artif Organs, 19:
747-749, 1995; Yamane S, Ohashi Y, Sueoka A, Sato K, Kuwana J, Nose
Y., Development of a silicone hollow fiber membrane oxygenator for
ECMO application, ASAIO, 44: M384-387, 1998; Stammers A H, Fristoe
L W, Alonso A, Song Z, Galbraith T., Clinical evaluation of a new
generation membrane oxygenator: a prospective randomized study,
Perfusion, 13: 165-175, 1998; Kitano Y, Takata M, Miyasaka K,
Sasaki N, Zhang Q, Liu D, Tsuchida Y., Evaluation of an
extracorporeal membrane oxygenation system using a nonporous
membrane oxygenator and a new method for heparin coating, J
Pediatric Surgery, 32: 691-697, 1997; Sueda T, Fukunmaga S, Morita
S, Sueshiro M, Hirai S, Okada K, Orihashi K, Matsuura Y.,
Development of an intravascular pumping oxygenator using a new
silicone membrane, Artif Organs, 21: 75-78, 1997; Mortensen J D,
Berry G., Conceptual and design features of a practical, clinically
effective intravenous mechanical blood oxygen/carbon dioxide
exchange device (IVOX), Int J Artif Organs, 12: 384-389, 1989; and,
Babley B, Bagley A, Henrie J, Fooerer C, Brohamer, J, Burkart J,
Mortensen J D., Quantitative gas transfer into and out of
circulating venous blood by means of an intra-vena caval
Oxygenator, ASAIO Trans, 37: M413-415, 1991. However, none are
believed, to this point, to provide sufficient yield, safety, and
ease of use to support broad clinical deployment.
[0005] Furthermore, numerous improvements in lung transplantation
have occurred due to advances in procurement, preservation, and
implantation. Stammers A H, Fristoe L W, Alonso A, Song Z,
Galbraith T., Clinical evaluation of a new generation membrane
oxygenator: a prospective randomized study, Perfusion, 13: 165-175,
1998; Kitano Y, Takata M, Miyasaka K, Sasaki N, Zhang Q, Liu D,
Tsuchida Y., Evaluation of an extracorporeal membrane oxygenation
system using a nonporous membrane oxygenator and a new method for
heparin coating, J Pediatric Surgery, 32: 691-697, 1997; Sueda T,
Fukunmaga S, Morita S, Sueshiro M, Hirai S, Okada K, Orihashi K,
Matsuura Y., Development of an intravascular pumping oxygenator
using a new silicone membrane, Artif Organs, 21: 75-78, 1997; and,
Mortensen J D, Berry G., Conceptual and design features of a
practical, clinically effective intravenous mechanical blood
oxygen/carbon dioxide exchange device (IVOX), Int J Artif Organs,
12: 384-389, 1989. However, the large discrepancy between the
numbers of donors and recipients, the low yield of usable lungs,
and the absence of temporizing methods for patients awaiting
transplantation, make this option outside the reach of many
patients.
[0006] Prior artificial lung technologies have been based on the
delivery to the bloodstream of oxygen gas via hollow fibers,
followed by back-and-forth diffusion across permeable membranes.
Golob J F, Federspiel W J, Merrill T L, Frankowski B J, Kitwak K,
Russian H, Haftler B G., Acute in vivo testing of an intravascular
respiratory support catheter, ASAIO J, 47: 434-437, 2001;
Federspiel W J, Hewitt T J, Hattler B G., Experimental evaluation
of a model for oxygen exchange in a pulsating intravascular
artificial lung, Ann Biomed Eng, 28: 160-167, 2000; and,
Swischenberger J B, Anderson C M, Cook K E, Lick S D, Mockros L H,
Bartlett R H., Development of an implantable artificial lung:
challenges and progress, ASAIO J. 47: 316-20, 2001. These systems
are attractive since gas exchange, analogous to that of the normal
lung, is reliant on diffusivity and differential gas pressure on
opposite sides of the membrane to drive O.sub.2/CO.sub.2 exchange.
The principal weakness, however, of these systems is that they
require the presence of major diffusion boundary layers, which
results in slowed mass transport and the need for a large surface
area to achieve sufficient flux of gases. In addition, these
systems require a continuous source of exogenous pressurized
O.sub.2 gas, generally via a tank or system of tanks.
[0007] The present disclosure seeks to circumvent one or more of
the limitations set forth above by considering the problem of
intravascular oxygenation from a fundamentally different
perspective. Rather than delivering oxygen gas to the blood (or
removing carbon dioxide against a back pressure of O.sub.2), the
present disclosure uses photolytic energy to generate dissolved
oxygen directly from the water already present in the blood,
thereby eliminating the need for exogenous gas delivery, gas or
liquid selective diffusion boundary layers, and the requirement for
operating at or near equilibrium (FIG. 1). This approach thus
constitutes a direct mechanism by which photolytically driven
oxygenation of whole blood can occur.
[0008] It has previously been shown by Applicants that it is
possible to generate dissolved oxygen directly from the water
content of synthetic serum, based on the interaction of UV light
with a semi-conducting titanium dioxide thin film. Dasse K A,
Monzyk B F, Burckle E C, Busch J R, Gilbert R J., Development of a
photolytic artificial lung, Preliminary concept validation, ASAIO
Journal, 48:556-563, 2003. The opto-electronic interaction of a
metal chelate chromophores with transition metal oxides is believed
to be the basis for the well known phenomenon in nature, the
light-dependent oxygen generation occurring in photosynthetic (PS)
organisms, cyanobacteria, and, higher plants and algae. Limburg J,
Vrettos J S, Liable-Sands L M, Rheingold A L, Crabtree R H, Bredvig
G W., A functional model of O-O bond formation by the
O.sub.2-evolving complex in photosystem II, Science, 283:
1524-1527, 1999; Vrettos J S, Brudvig G W., Water oxidation
chemistry of photosystem II, Philos Trans Royal Society of London B
Biol Sci, 357: 1395-1404, 2002; Yachandra V K, DeRose V J, Latimer
M J, Mukerji I, Sauer K, Klein M P., Where plants make oxygen: a
structural model for the photosynthetic oxygen-evolving manganese
cluster, Science, 260: 675-679, 1993; and, Yachandra V K, Sauer K,
Klein M P., Manganese cluster in photosynthesis: Where plants
oxidize water to dioxygen, Chem Rev, 96: 2927-2950, 1996. The
proposed photolytic lung technology disclosed herein thus builds
upon the known ability of the metal oxide, the anatase form of
titanium dioxide, TiO.sub.2, to serve both as the chromophore and
the charge separation center. Fernandez-Ibanez P, Blanco J, Malato
S, de las Nieves F J., Application of the colloidal stability of
TiO.sub.2 particles for recovery and reuse in solar photocatalysis,
Water Res. 37(13):3180-8, 2003; Topoglidis E, Campbell C J,
Palomares E, Durrant J R., Photoelectrochemical study of Zn
cytochrome-c immobilized on a nanoporous metal oxide electrode,
Chem Commun (Camb). 21; (14): 1518-9, 2002; Hagfeldt A, Gratzel M.,
Molecular photovoltaics, Acc Chem. Res. 33(5):269-77, 2000; and,
Tsai P, We C T, Lee C S., Electrokinetic studies of inorganic
coated capillaries, J Chromatography B Biomed Appl. 657(2):285-90,
1994. The present disclosure describes and provides for the
generation of dissolved oxygen, and the resulting increase of
oxyhemoglobin, via photolytic means, in whole mammalian blood.
BRIEF DESCRIPTION
[0009] Disclosed herein, in various embodiments, is a process and
apparatus for using photolytic energy to generate dissolved oxygen
from whole blood, thus providing an increase of oxyhemoglobin as a
function of the metal oxide (i.e., TiO.sub.2) surface illumination.
In one embodiment, the disclosure includes flowing mixed
arterial-venous whole blood in a recirculating loop in a device
having a nanocrystalline metal oxide TiO.sub.2 thin film. Following
light exposure of the metal oxide or TiO.sub.2 film only (while not
exposing the blood to the light), the fraction of oxy-hemoglobin in
the blood rapidly increases and remains substantially stable
thereafter. The fraction of dissolved oxygen contained in the serum
phase of the blood increases in a parallel manner with
oxyhemoglobin as a result of light induction, indicating that near
complete oxygenation of the blood's hemoglobin content has been
achieved. The present disclosure demonstrates that it is feasible
to photolytically oxygenate the hemoglobin contained in whole blood
with oxygen derived from the blood's own water content by only
providing energy at mild conditions.
[0010] In another embodiment, the present disclosure is directed to
a process and a photolytic apparatus or device for oxygenating
whole blood. The device has a photolytic cell having a
photo-reactive surface. The photo-reactive surface comprises a
light-activated catalyst and a disproportionate catalyst which
converts water in the whole blood into dissolved oxygen upon light
activation.
[0011] In this regard, the photo-reactive surface comprises a light
transparent substrate and a photolytic coating. The photolytic
coating comprises a layer of light-activated catalyst and a layer
of disproportionate catalyst. The light-activated catalyst
converts, when photo irradiated, water (H.sub.2O) in the blood into
hydrogen ions, electrons and active oxygen. The hydrogen ions
formed during photolysis can be removed or reacted with carbonate
ions in the whole blood to form carbonic acid. The carbonic acid
then reacts with carbonic anhydrase in the blood to form water and
carbon dioxide which is subsequently removed. The active oxygen
formed during photolysis is then converted by a disproportionate
catalyst (such as MnO.sub.2, etc.) into dissolved oxygen. The
electrons generated during photolysis are subsequently electrically
conducted away to avoid reversal of the conversion reaction. This
results in the oxygenation of whole blood without the need of
exogenous gas delivery, etc.
[0012] In a further embodiment, the disclosure relates to a process
and device for enhancing the viability of an organ to be
transplanted. The process comprises adding to an organ to be
transplanted and/or transported whole blood. The whole blood is
then oxygenated. This is by a photolytical device which generates
dissolved oxygen, and a resulting increase in oxyhemoglobin, from
water present in the whole blood by photolytic means.
[0013] These and other non-limiting characteristics of the
disclosure are more particularly described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The following is a brief description of the drawings, which
are presented for the purposes of illustrating the exemplary
embodiments disclosed herein and not for the purposes of limiting
the same.
[0015] FIG. 1 is a diagram showing the fundamental mechanism of a
photolytic cell or chamber. The photolytic technology is based on
the ability of transition metal oxides to convert light energy to
electric current; the resulting charge separation is used to
generate oxygen from adjacent (non diffusion) water molecules
supplied from serum. The photochemical materials are designed to
produce dissolved oxygen directly in an aqueous fluid (blood),
without involving the gaseous phase, which is freely available for
binding with hemoglobin. The photolytic technology utilizes a
semi-conducting metal oxide material, such as TiO.sub.2, WO.sub.3,
ZnO, or combinations thereof. Those skilled in the art will
appreciate that various dopants can be added to the metal oxide
layer. The light energy produces charge separation (electron-hole
pairs) in the semi-conductor, which results in the production of
active oxygen, hydrogen ions and free electrons. DO stands for
dissolved oxygen.
[0016] FIG. 2 is a graph showing photolytic generation of dissolved
oxygen and enhanced oxyhemoglobin in whole blood. The vertical
scale is in percent of the measured amount and the horizontal scale
is time in minutes. A modified FM01-LC Electrolyser, operating in a
divided cell mode using a NAFION.TM. membrane was used to separate
catholyte and anolyte solution. The anode was optically
transparent, and illumination was achieved side-on by UV light (354
nm) using a filter and UVA fiber optic lamp source. The catholyte
was Locke's-Ringer solution, and the anolyte was anticoagulated,
fresh whole blood at 37.degree. C. using an in-line jacket. Flow
was regulated by a peristaltic pump at 80 cc/min. Oxyhemoglobin,
(represented in the figure as FO.sub.2Hb) rapidly increased with
laser illumination from 83% to 92% and remained stable throughout
the trial. The term FO.sub.2Hb indicates the percent of hemoglobin,
which contains bound oxygen, i.e. hemoglobin saturation. The term
sO.sub.2 indicates the extent to which dissolved oxygen is
contained in the water phase of blood; in effect the degree to
which dissolved oxygen may be contained in water before it
separates out as O.sub.2.
[0017] FIG. 3 shows a perspective view of an embodiment of a
photolytic device for oxygenated whole blood designed for external
or extra-corporeal usage.
[0018] FIGS. 4A-4D illustrate the various embodiments of the
photolytic device set forth in FIG. 3. FIG. 4A shows a general
illustration of the photolytic artificial lung connected externally
to a patient. FIG. 4B shows an interior view of the components of
one embodiment of the photolytic device. FIG. 4C also shows an
inside view of an alternative embodiment of the photolytic device,
and FIG. 4D illustrates the chemical reactions occurring
therein.
[0019] FIG. 5 shows a schematic view of the model photolytic cell
apparatus. Among other things, this view depicts the relative
positions of the coated test surface, light source, and the
chemical sensor in place to monitor the chemical yield of the
system.
[0020] FIG. 6 shows an overall schematic diagram of the photolytic
device disclosed herein.
DETAILED DESCRIPTION
[0021] The unrelenting nature of chronic lung disease has long
energized the pulmonary community to seek technologies to replicate
the capacity of the lungs to exchange oxygen for carbon dioxide.
While most such artificial lung technologies work by delivering
pressurized oxygen gas to the blood through a system of hollow
fibers or tubes, the present disclosure employs photolytic energy
to generate dissolved oxygen in blood directly from the water
already present in blood, thus eliminating the need for gas
delivery.
[0022] In one embodiment, the present disclosure is directed to the
use of the photolytic cell in a novel respiratory assist device and
process. The respiratory assist device includes one or more
photolytic cells having photochemically active material and
associated components for the production of oxygen and, optionally,
the regulation of pH, the removal of carbon dioxide, and the
co-production of electrical energy in whole blood. The electrical
energy can be used to produce additional chemical changes or
reactions. The embodiment may include a photolytic chamber to house
or hold a sufficient number of stacked or assembled photolytic
cells to perform the rate of gas exchange desired.
[0023] The respiratory assist device can be an extracorporeal
device, or a highly miniaturized, intracorporeal device, capable of
achieving physiological gas exchange in patients. Utilizing the
device, oxygen is photolytically generated from water in whole
blood at a catalyst center, using photolytic energy under mild
conditions of pressure, temperature and pH, while releasing
hydrogen ions. Hydrogen ions, which may be removed or released into
solutions of bicarbonate ion, present in the blood, cause
conversion of these ions into carbonic acid, which spontaneously
dissociates into water and CO.sub.2 in the presence of carbonic
anhydrase, a natural component of blood.
[0024] In another embodiment, a semi-conducting metal oxide is
utilized as the photo-absorption element, such as the anatase form
of titania, or TiO.sub.2 Photolysis of this oxide results in the
generation of active oxygen in whole blood. The light energy
associated with activation by a light source, such as a 354 nm UV
laser light, selectively excites the TiO.sub.2 semiconductor
electronic transition (350-389 nm band, or about 3.2 eV) with
minimal wasted radiation or transmission. Special dopants may
adjust this wavelength, in order to reduce the energy requirement
and even to allow activation within the range of visible light. UV
energy produces charge separation in the anatase, which then
produces active oxygen and free electrons, the latter being
electrically conducted away. Diffusion layers are minimized through
the use of electron conductance to and from the photolytic site (as
is done in natural photosynthesis) by photolytic transparency and
by electrochemical conduction. The active oxygen is then converted
to dissolve oxygen through the use of a disproportionation catalyst
such as MnO.sub.2.
[0025] Preferably, the device comprises a blood inlet cannula, a
pump, at least one photolytic cell, a light source that irradiates
the photolytic cells, an oxygenated blood outlet cannula and an
optional carbon dioxide vent and/or absorption device. A power
source and/or batteries can be present to power the pump or light
source. One or more in-line sensors and processors can be present
to monitor and optimize the blood flow through the system, the
amount of oxygen and/or carbon dioxide generation, the presence of
toxins, etc. Desaturated blood circulating through the device will
be pumped through the photolytic cells where light activation will
result in dissolved oxygen generation and, in some embodiments,
carbon dioxide removal.
[0026] A more complete understanding of the components, processes
and apparatuses disclosed herein can be obtained by reference to
the accompanying drawings. These figures are merely schematic
representations based on convenience and the ease of demonstrating
the present development, and are, therefore, not intended to
indicate relative size and dimensions of the devices or components
thereof and/or to define or limit the scope of the exemplary
embodiments.
[0027] Although specific terms are used in the following
description for the sake of clarity, these terms are intended to
refer only to the particular structure of the embodiments selected
for illustration in the drawings, and are not intended to define or
limit the scope of the disclosure. In the drawings and the
following description below, it is to be understood that like
numeric designations refer to components of like function.
[0028] More particularly, FIG. 3 shows an embodiment of a device 10
developed as an extra-corporeal respiratory assist system. The
device 10 includes a blood inlet 12 that cannulates blood from the
patient into the device 10. The blood inlet 12 is connected to a
pump 14 that draws blood from the patient into the device 10. The
pump 14 directs desaturated blood through one or more photolytic
cells 16 where light activation (for example, laser at 350-390 nm)
results in oxygen generation and ultimate carbon dioxide removal
via a carbon dioxide sorption device 24 or external ventilation. A
power supply 18 or optional battery 19 activates the light source
20. The light source 20 emits light photos 21 which irradiate the
photolytic cells 16. In turn, the photolytic cells 16
photochemically initiate a series of chemical reactions that
produce oxygen and remove carbon dioxide from the blood. Oxygenated
blood travels from the artificial lung 10 back to the patient by
way of a blood outlet 22. Consequently, the artificial lung 10
takes blood from the venous circulation of a patient and returns it
to the arterial circulation.
[0029] The device omits the gaseous state that causes problems
which have limited other blood oxygenation technologies, while
optionally consuming carbon dioxide. Also, the device does not
require the careful control of temperature or pressure. As briefly
mentioned above, the materials for use in the present photolytic
device are generally biocompatible and prevent blood contamination.
Blood contact with the coatings is also minimized. Diffusion
layers, which can decrease oxygenation rates, are minimized using
electrical conduction of electrons and cations to and from the
photolytic site by incorporating thin films having good photolytic
transparency, and electrical and electrochemical conduction.
[0030] The wave length, beam size, pulse duration, frequency and
fluency of the light source are adjusted to produce maximum and/or
efficient gas exchange. Similarly, pump rate, flow-through
capacity, etc. of the photolytic cells are also so adjusted. This
can be accomplished by sensors and regulators which also monitor
reaction chemistry, toxins, etc. The sensors and regulators have
the capacity to auto-regulate various parameters of the system in
response to the conditions monitored by the sensors.
[0031] The photolytic device can be designed so that it is an extra
corporeal device or an intra-corporeal device. For example, the
photolytic device can be designed as a miniaturized, implantable
unit. Such a unit is configured to be implantable and it uses a
transcutaneous energy transmission system and/or an internal light
source for energy conversion.
[0032] FIG. 4A shows a simple representation of a patient attached
to a device 10 as an extra-corporal device. Most preferably, the
device is designed to provide at least about 150 ml of dissolved
oxygen per minute at 5 L/min of blood flow through the system for a
human patient. FIGS. 4B and 4C are enlargement views showing the
components of various embodiments of the device 10. FIG. 4D shows
the chemical transformations which occur in each compartment of the
various embodiments of the device.
[0033] The device 10 pumps venous blood from the patient through a
blood inlet 12. The venous blood enters by means of a flow
distributor 25 into one or more photolytic cell(s) 16. The
photolytic cell(s) may be optionally arranged to form a stack of
photolysis cells 27. The amount of blood entering and leaving the
photolytic cell(s) 16 is controlled by flow distributor 25. See
FIG. 4B.
[0034] A light source 20 irradiates the photolytic cell(s) 16,
thereby initiating the photochemical reactions within the
photolytic cell(s) 16 that ultimately form dissolved oxygen that
binds to blood hemoglobin (Hb). Excess carbon dioxide and hydrogen
formed from the chemical reactions in the photolytic cell(s) 16
enter one or more gas sorption devices 24 for storage and/or
eventual venting through a venting outlet 28. Once the blood has
been oxygenated, and the carbon dioxide removed, the blood returns
to the artery of a patient by way of blood outlet 22. Among the
components of the photolytic device not illustrated in this
embodiment is the blood pump, power supply, control electronics and
sensory technology for monitoring reaction chemistry, the amount of
oxygen, carbon dioxide, etc. generated the presence of potential
toxins, etc.
[0035] The main component of the device is the photolytic cell 16.
See, for example, FIG. 4C. Light energy 21 from a light source 20
enters the photolytic cell 16 through a transparent substrate or
window 30 and activates a layer of light-activated catalyst 32. As
discussed in more detail below, an example of such a light
activated catalyst is anatase (TiO.sub.2). Depending on the
catalyst 32 used, the light-activated catalyst 32 converts water in
the blood into intermediate active oxygen, hydrogen ions and excess
electrons, or directly converts water into dissolved oxygen. An
optional second catalyst, i.e. a disproportionation catalyst, 34
can be used to convert the intermediate active oxygen to dissolved
oxygen, O.sub.2. An example of such a second catalyst is manganese
dioxide (MnO.sub.2). Excess electrons are formed during the
conversion of water to dissolved oxygen and are conducted out from
the catalyst 32 to an anode conductor layer 36 such as gold or
titanium metal film. In chamber 37, the dissolved oxygen binds to
hemoglobin (Hb) in the blood and the oxygenated blood returns to
the patient via an arterial blood outlet 22.
[0036] Additionally, in chamber 37, bicarbonate ions which are also
present in the deoxygenated blood react with the hydrogen ions
generated above to form carbonic acid. The carbonic acid is then
converted to water and carbon dioxide by carbonic anhydrase. The
water formed reacts with electrons at the cathode 38 to form
hydrogen gas (H.sub.2) and hydroxyl groups. The hemoglobin also
releases carbon dioxide when the oxygen binds to the hemoglobin.
The excess carbon dioxide and hydrogen created from the reactions
occurring in the photolytic cell 16 enter one or more gas sorption
devices 24 for storage or venting.
[0037] FIG. 5 shows a flow-through embodiment of the photolytic
cell 16. In the flow-through cell embodiment, the following main
components of the photolytic cell 16 are assembled, i.e. a
conductive coating of vacuum deposited Ti metal 36, a coating of
adherent TiO.sub.2 (anatase) 32, an optional MnO.sub.2 particulate
layer 34, and then tested using a bicarbonate solution. A UV laser
light 20 was shown on the transparent glass or quartz substrate 30
so to initiate the reactions. As discussed below, this cell was
utilized to collect pH and data as a function of laser U.V.
irradiation demonstrating the effectiveness of the disclosure.
[0038] In this regard, the photolytic cell 16 of FIG. 5 includes a
transparent window 30 or wave guide for the entry of light energy
in the form of photons 21 from a light source 20 such as an
ultraviolet laser light. On one side of the glass slide is an anode
conductor layer 36, such as titanium (Ti) metal film. Attached to
the anode conductor layer 36, is a layer of a light activated
catalyst 32 such as anatase (TiO.sub.2). An optional catalyst layer
34, such as manganese dioxide, is adjacent to the light activated
catalyst layer 32. The photolytic cell 16 includes one or more
layers of silicone gaskets or spacers 40 and an acrylic housing 42.
A pair of anolytes 44 (in/out) is connected to the light activated
catalyst layer 32 or optional catalyst layer 34 and extend through
the photolytic cell 16 away from the transparent window 30. The
photolytic cell 16 further includes a cation exchange member 46,
such as a NAFION.RTM. membrane from DuPont. A pair of catholytes 48
(in/out) is connected to the cation exchange member 46 and extends
outwardly through the photolytic cell 16 generally away from the
transparent window 30. The photolytic cell 16 further includes a
cathode layer 38, such as Pt foil, adjacent to the cation exchange
member 46.
[0039] FIG. 6 is a schematic drawing showing the electrical and
chemical transformations which occur in the photolytic cell 16 of
the device 10. Venous blood (low in oxygen and high in carbon
dioxide) from a patient enters the photolytic cell 16 through inlet
12 by way of a peristaltic pump 14. Light photons (hv) 21 generated
by light source 20 enter through a transparent window 30 or
waveguide and activate the light activated catalyst 32 such as 100
.mu.m TiO.sub.2 (anatase). The light activated catalyst 32 either
directly converts water to dissolved oxygen or converts water to
active oxygen and hydrogen ions and an optional second catalyst 34,
such as manganese dioxide (MnO.sub.2) on a porous film, converts
active oxygen (e.g. H.sub.2O.sub.2) into dissolved oxygen (DO). The
dissolved oxygen then binds to hemoglobin present in the blood.
[0040] The electrons released from the conversion of water to
oxygen are collected in an anode conductor layer 36. An optional
electrical bias voltage formed from a battery 49 facilitates
electron flow from the layer 36 to the cathode 38 (such as
stainless steel, copper, graphite or nickel), so that the electrons
do not react with the active oxygen to cause a back reaction and
the reformation of water.
[0041] The electrical current and electron flow can be regulated by
a current regulator 50 or resistor 52. The electrons can react with
water to form hydrogen gas, H.sub.2, and a hydroxyl ion (OH--). The
hydrogen gas formed is moved to a gas sorption device, where it is
stored and/or released (i.e., expired). Sodium (Na+) ions from the
blood migrate across the cation exchange membrane 46 and react with
hydroxyl ions to form sodium hydroxide (NaOH) in the catholyte 48.
The hydrogen ions formed from the conversion of water at the light
activated catalyst reacts with bicarbonate ions to form carbonic
acid, which is converted by carbonic anhydrase enzyme present in
the blood or added to form carbon dioxide and water. The carbon
dioxide formed in the photolytic cell 16 along with the carbon
dioxide released from the blood is moved to one or more gas
sorption devices 24 or vented. The oxygenated blood exits the
photolytic cell 16 via an outlet 22 and returns to the artery of
the patient.
[0042] The various particular components and/or processes of the
flow through photolytic cell embodiment of the present invention
are described in more detail below:
[0043] 1. Transparent Substrate or Window 30
[0044] The transparent window 30 can be formed from glass, quartz
slides, quartz, etc. Glass is useful in forming the transparent
window provided that the UV transparency is adequate at the
wavelength needed. Quartz slides are also useful because of its
high UV transparency. For the transparent window, light entry into
and through the transparent window can be from the back, side, or
bottom. Edge illumination through the transparent window can
optionally include a lens or wave guide.
[0045] The transparent window can further include a wave guide. A
wave guide uniformly distributes photons (hv) from the light over
the surface of the light activated catalyst. Particularly, the wave
guide causes the light photons to travel in a path so that the
photons maximally contact the entire layer of the light activated
catalyst. Light enters the wave guide in the side of the
transparent window generally parallel to the surface of the light
activated catalyst that is attached to the transparent window. The
wave guide allows for maximal light photon contact with the light
activated catalyst without directly illuminating the side of the
entire light activated catalyst attached to the transparent window.
The wave guide also allows form maximal photolytic cell staking
because light is not required to directly illuminate the light
activated catalyst but rather can be indirectly illuminated by side
or edge entry in the transparent window. The wave guide provides
additional efficiency to light used in the photolytic cell because
the light can be spread across the entire surface of the light
activated catalyst.
[0046] 2. Anode Conductor Layer 36
[0047] The anode conductor layer 36 conducts electrons formed from
the reaction of water to oxygen out of the anode. The anode
conductor layer prevents the electrons from reacting back with the
oxygen to reform water, thereby allowing maximal formation of
oxygen. The anode conductor layer is applied or attached to at
least one side of the transparent window.
[0048] The anode conductor layer can be formed at least two
different ways. The anode layer can be formed by attaching a thin
film of uniform metallic conductor to the transparent window using
vapor deposition. The film preferably has a thickness of less than
about 0.2 .mu.m. Preferably, the film is formed from gold,
titanium, or indium tin oxide or other conductive material that is
light transparent when thinned. Gold remains metallic at all
conditions but can be very efficient at UV light blockage or
reflection. Titanium can be oxidized to TiO.sub.2 by adding O.sub.2
to the deposition chamber to yield a possible catalyst layer with
excellent adhesion.
[0049] The anode conductor layer 36 can also be formed by using
photo-resist technology. Under photo-resist based technology, grids
or vias are prepared with masks using vapor deposition, etching,
and electroless plating. Conductor line spacing, width and
thickness optimization may be required to prevent excessive
attenuation, and provide sufficiently close conductive areas to
sweep electrons away from the light activated catalyst layer.
[0050] 3. Catalysts 32 and 34
[0051] A light activated catalyst 32 is coated onto the anode
conductor layer. The light activated catalyst is photochemically
activated and reacts with water to form dissolved oxygen or a free
radical oxygen intermediate that is ultimately converted to
dissolved oxygen. The term active oxygen (AO) in the present
application defines any free radical oxygen intermediate formed in
the photolytically catalyzed reaction of water that is ultimately
converted to dissolved oxygen. The active oxygen formed is in the
form of a peroxide, such as hydrogen peroxide, H.sub.2O.sub.2, or
peroxide ion salt, hydroxyl free radical, super oxide ion, etc.,
and is converted into dissolved oxygen in the presence of a
catalyst. The active oxygen formed depends on the light activated
catalyst used. Also, depending on the light activated catalyst
used, water may be photolytically converted directly into dissolved
oxygen without first forming an active oxygen.
[0052] Several different catalysts can be employed for producing
dissolved oxygen photochemically. One catalyst that can be used to
photochemically produce oxygen is zinc oxide. By using zinc oxide,
peroxide (H.sub.2O.sub.2) is produced directly from water at blood
pH. H.sub.2O.sub.2 is an excellent form of active oxygen for
providing sufficient potential diffusion distance, and also for the
disproportionate reaction to dissolved oxygen and water via a solid
MnO.sub.2 catalyst (similar to green plant O.sub.2 generation site)
occurring photochemically at <340 nm by way of metal ion
assisted disproportionation with catalase and other
hydroperoxidases. Zinc oxide film has other positive attributes
including, known film formation technology (e.g. via the
zinc/nitrate/glycine reaction), low toxicity concerns, and low
cost.
[0053] An additional catalyst that can be used to photochemically
produce dissolved oxygen is tungstate (WO.sub.3) that is exposed to
visible light and using e-scb removal. WO.sub.3 yields oxygen
(O.sub.2) directly from water without the need to first produce an
active oxygen species. Oxygen is generated stoichiometrically and
the "back reaction" is unfavored so that there is not significant
competition to the direct formation of dissolved oxygen. Only
visible light is needed to generate dissolved oxygen from WO.sub.3,
no more than about 496 nm. WO.sub.3 films present low toxicity
concerns. Preferably, the use of WO.sub.3 further includes the
removal of excess e-scb formed during oxygen formation from
water.
[0054] Another catalyst suitable for reacting with water is
TiO.sub.2 (anatase) irradiation with, followed by dissolved oxygen
production at a metal catalyst, such as a MnO.sub.2 catalyst, or
other similar catalyst. TiO.sub.2 removes the e-scb efficiently
from the production area in order to ultimately obtain good
dissolved oxygen production and minimize any back reaction to
reform reactants. The removal of e-scb is performed through
conduction via the semi-conductor property of the TiO.sub.2(a) with
enhancement via application of a small DC bias voltage. TiO.sub.2
irradiation also presents low toxicity concerns. TiO.sub.2 provides
very high insolubility and kinetic inertness to minimize
dissolution and fouling during use and maintenance. Preferably, UV
light is chopped or pulsed during TiO.sub.2 irradiation to allow
time for the chemical reactions to occur since with continuous
irradiation causes the e-scb to accumulate and force a back
reaction to form water. A pause in the irradiation allows time for
the slower, but still extremely fast irradiation in the range of
.mu. sec to msec to occur.
[0055] A further catalyst for reacting with water to ultimately
form dissolved oxygen is a semiconductor powder (SCP)-filled UV/VIS
light transparent thermoplastic film. SCP-filled thermoplastic film
is relatively inexpensive to manufacture and form into shape. SCP
film is easily moldable, extrudable, cut and machined. SCP can be
used very efficiently in surface applied only form. Also, SCP has
low toxicity concerns. Optimized commercial products (conductive
plastic filler powders) are available with good properties for
dispersion, particle-to-particle electrical conductivity (for e-scb
removal), and resistance to sloughing off that can be used with the
present photolytic artificial lung.
[0056] The following additional preferred conditions may be used
for each of the above-mentioned catalysts. First, an application of
a small (e.g. up to a few volts DC) bias voltage can be applied to
help ensure that the e-sch is quickly conducted away from the
production site. Second, a chopped illumination, instead of a
continuously applied illumination, may allow secondary chemical
reactions to occur since the secondary chemical reactions are
slower than the photochemical reactions and enhance photo yields by
allowing the excited electrons to exit the system and not be
present for regeneration of starting material, i.e., water.
[0057] Of the above-mentioned catalysts, the TiO.sub.2 (anatase)
catalyst followed by a second metal catalyst for disproportionation
is the most preferred. When the TiO.sub.2 catalyst is used, the
light-titania interaction is the first step in the ultimate
formation of dissolved oxygen. It is known that surface hydrated
particulate TiO.sub.2 (anatase) solid, TiO.sub.2(a)-OH.sub.2 or
TiIVO.sub.2(a)-OH, is an efficient UV light (h.nu.) acceptor at
wave lengths <390 nm, resulting in active oxygen formation from
sorbed water and hydroxyl groups. The most probable reaction is
believed to be:
Ti.sup.IVO.sub.2(a)--OH+h.nu..fwdarw.Ti.sup.III--.OH*
[0058] It is noted that other bonds to Ti have been omitted for
clarity. The reactant and product of the above reaction are solid
materials. In the above reaction, H.sub.2O is already bonded to the
surface of the TiO.sub.2(a) catalyst as H.sub.2O or as hydroxyl ion
(OH--), i.e. TiIVO.sub.2(a)-OH.sub.2 or TiIVO.sub.2(a)-OH,
respectfully. Hence, no atoms are required to move during the very
fast photon absorption process. The * represents a low lying
excited electronic state where the energy of the photon is used to
transition or excite an electron from a nonbonding orbital on the
oxygen to a molecular orbital centered on the titanium ion, hence
converting the titanium into a trivalent oxidation state. The
molecular orbital centered on the titanium ion is known to be a
part of the semiconduction band ("scb"), and so the electron is
readily conducted away from the site to form a bipolar charged
grain, or, if connected to a closed DC electrical circuit,
resulting in full charge separation, i.e.,
Ti.sup.III--.OH*.fwdarw.[Ti.sup.IV--.OH].sup.++e.sup.-.sub.(scb).uparw.
[0059] If the e-scb is not conducted away or otherwise removed by
reaction with an oxidant present in the solution, the e-scb could
react with the hydroxyl free radical and reverse or back react so
that the system would return to its original state and form water.
In this latter case there would be no net reaction and the
photolytic energy will appear as a small amount of heat. Hence the
charge separation process and removal of e.sup.-.sub.scb is
considered an important first step of the photolytic cell dissolved
oxygen generation process.
[0060] The hydroxyl free radical (.OH) group present is used to
represent the initial form of the active oxygen generated by the
photolytic process. It is not certain that .OH is the dominant
species present when TiO.sub.2(a) is photolyzed. The active oxygen
formed could generally be in the form of a superoxide, hydrogen
peroxide, or a hydroxyl free radical. However, the form of this
active oxygen produced has sufficient thermodynamic driving force
to form active oxygen from water. For the TiO.sub.2(a) catalyst at
neutral pH, these highly reactive hydroxyl free radicals either
back react as described above, or rapidly dimerize to form
(.mu.-peroxo) titanium (IV) and hydrogen ions, i.e.
##STR00001##
[0061] These H+ ions are valuable for blood-CO.sub.2 level control.
The rate of dissolved oxygen production is the rate at which the
active oxygen splits out to form O.sub.2(aq) and reforms
TiO.sub.2(a), i.e.
Ti.sup.IV--O--O--Ti.sup.IV-----.fwdarw.Ti.sup.IV--O--Ti.sup.IV+1/2O.sub.-
2(aq) (as dissolved oxygen)
[0062] In an unwanted but unharmful second side reaction, any
O.sub.2(aq) produced can react with e-scb previously produced but
not yet conducted away. These e-scb negative charges tend to reside
on the surfaces of the TiO.sub.2 particles so that the negative
charge are most separated. Therefore, these e-scb electrons are
available for reduction reactions with O.sub.2 or the .mu.-peroxide
linkage to produce species such as O.sub.2--, O.dbd., O--, etc.,
thereby decreasing dissolved oxygen yields. In order to minimize
side reaction, the illumination is pulsed instead of continuous.
The delay caused by illumination pulsation allows the e-scb to be
conducted away in one direction and the dissolved oxygen to diffuse
away in another (E. Pelizzetti, M. Barbeni, E. Pramauro, W. Erbs,
E. Borgarello, M. A. Jamieson, and N. Serpone, Quimica Nova
(Brazil), 288 (1985)). Also, illumination pulsation prevents the
local populations of O.sub.2(aq) and e-scb from becoming so high
that reaction between them becomes fast. The pulse rates involved
are extremely short in the .mu.sec-msec range so that there is
little effect on O.sub.2(aq) production rates. Enhanced yields are
also possible for photolytically established charge separation when
a bias voltage is present across the coating. (X. Z. Li, H. L. Liu,
and P. T. Yue, Envison-Sci-Technology, 2000, 34, 4401-4406.) A
small bias voltage may also be used to further reduce the amount of
e-scb present and produce more dissolved oxygen.
[0063] Another way to increase the amount of dissolved oxygen
production in the TiO.sub.2(a) system is to provide a means to
speed the rate of release of the trapped .mu.-peroxide as hydrogen
peroxide as to active oxygen.
Ti.sup.IV--O--O--Ti.sup.IV+H.sub.2O-----.fwdarw.Ti.sup.IV--O--Ti.sup.IV+-
H.sub.2O.sub.2(aq)
[0064] H.sub.2O.sub.2 is an excellent form for the active oxygen
species as it readily migrates and is easily catalyzed to
disproportionate into dissolved oxygen and water.
##STR00002##
[0065] Stable free radicals (SFRs) can be used to release the
trapped @-peroxide as hydrogen peroxide. SFRs can exist as free
radicals for extended periods of time relative to the hydroxyl free
radical SFRs have been found useful for promoting electron transfer
reactions. They electronically and reversibly rearrange into
reduced or oxidized species one electron at a time as set by the
reaction conditions. Biological systems are known to use SFRs as
respiratory carriers, such as quinone coenzymes including
ubiquinone, vitamin K, etc. The SFR shuttles the reactivity from
the point of generation to the point of H.sub.2O.sub.2 production,
or even directly to the metal ion MnO.sub.2 catalyst for dissolved
oxygen production. Components found in biological systems such as
vitamins E, C, K, etc. also may function in the role of SFRs except
without recycle. At least four classes of SFRs exist from which a
suitable agent can be selected: hindered hydroxylated aromatics
(quinones, substituted phenolics); organic peroxide precursors
(alcohols, etc.); peracid precursors (acylating agents, etc.); and
nitroxides, RN.fwdarw.O.
[0066] Therefore, for the TiO.sub.2(a) photocatalyst to be useful,
a means for releasing the .mu.-peroxide energy is needed, such as
soluble H.sub.2O.sub.2, since H.sub.2O.sub.2 can diffuse to the
MnO.sub.2 for dissolved oxygen production, or by conducting the
oxidizing power to another active oxygen form, such as SFRs in the
adjacent solution that can be used in dissolved oxygen production,
or using the TiIV--O--O--TiIV content to electronically remove
electrons from the MnO.sub.2 cluster/particle (as is done in green
plant photosynthesis by the "D" protein). In the last means, only
an electron flows from the water through the MnO.sub.2 to the
.mu.-peroxo linkage through delocalized bonds. This electron
replaces the e-lost from the TiO.sub.2(a)-OH system as e-scb.
[0067] The formation of H.sub.2O.sub.2 as the active oxygen is
valuable since H.sub.2O.sub.2 can be rapidly converted to dissolved
oxygen in 100% yield using many different methods: thermally; metal
ion catalysis; particulate/surface catalysis; base catalysis; and
free radical reaction with reductant initiation. Preferably, metal
ion catalysis, such as, MnO.sub.2(s), provides an efficient
catalyst for H.sub.2O.sub.2 disproportionation to water and
O.sub.2, on thin film substrate constructs.
##STR00003##
[0068] Photo catalyst systems such as zinc oxide, ZnO, release
peroxide as the active oxygen more readily than does TiO.sub.2.
Less acidic metal ions under the Lewis acid/base theory definition
cannot sufficiently stabilize the highly alkaline peroxide ion
relative to water protonation (pKa1 of H.sub.2O.sub.2 is 11.38
(25.degree. C.)) to form it within the solid phase, and so hydrogen
peroxide, H.sub.2O.sub.2, is readily formed from ZnO:
##STR00004##
[0069] ZnO films and particles can be prepared in a number of ways
with varying but controlled composition, morphology and porosity.
For example, mirrors of zinc, doped zinc, and zinc alloys and can
be sputtered down onto an optically transparent support, followed
by oxidation with O.sub.2(g). This treatment produces a metal/metal
oxide (Zn/ZnO) film. Another highly effective approach to
semiconducting ZnO-based films is to utilize a process for optical
glass coatings. (L. R. Pederson, L. A. Chick, and G. J. Exarhos,
U.S. Pat. No. 4,880,772 (1989).) The optical glass coating
technique is based on applying a zinc nitrate/glycine aqueous
solution as a dip or spray, followed by drying (110.degree. C. for
15 min), then heating (450-500.degree. C. for 3 min) to initiate a
self-oxidation reaction during which the carbon and nitrogen exits
as gases leaving an adherent yet porous film bonded to the
underlying surface (e.g. glass) and is referred to as the glycine
nitrate process. (L. R. Pederson, L. A. Chick, and G. J. Exarhos,
U.S. Pat. No. 4,880,772 (1989).) The ZnO film is normally produced
doped with alumina by including aluminum nitrate in the aqueous
formulation for the initial dip. Many other metal ion blends are
also possible with this technique.
[0070] Tungstate only requires visible light to produce dissolved
oxygen, and produces dissolved oxygen directly without requiring a
second catalyst to form dissolved oxygen. The lower photon energy
requirement for WO.sub.3 is due to the smaller band gap of 2.5 eV
versus at least 3 eV for TiO.sub.2(a). As with the TiO.sub.2
anatase system, high yields are possible with the WO.sub.3 catalyst
if the e-scb is removed. The production of O.sub.2 increases very
significantly if RuO.sub.2 (ruthenium oxide) is placed on the
surface of the WO.sub.3. This is consistent with the fact that
RuO.sub.2 is a known good catalyst for O.sub.2 production and so
represents a route to improving other approaches.
[0071] An advantage may exist if the dissolved oxygen producing
film could be a filled plastic. Such materials are often
inexpensive and manufactured easily. Commercial sources exist for
semi-conducting, low light absorbing, inorganic fillers for
plastics which are supplied in ready made condition for
incorporation into plastics, making the plastics electrically
conductive. For example, E.I. DuPont Nemours, Inc. sells
electroconductive powders (EPC) under the trade name ZELEC.RTM. ECP
for such purposes. The conductive substance in ZELEC.RTM. ECP is
antimony-doped tin oxide (SnO.sub.2:Sb). The bulk of these
materials, onto which the conductor is coated, are familiar
inorganics such as mica flakes, TiO.sub.2, and hollow silica
shells, or ECP-M, ECP-T and ECP-S respectively. Pure
SnO.sub.2:Sb-based material is designated ECP-XC and is a much
smaller particle than the other materials. About 25-45% by weight
of the ECP products are used so that the particles are sufficiently
close to each other to provide internal electrical connections
throughout the otherwise non-conducting plastic. ECP-S and ECP-M
normally perform best for lower concentrations. Thin films of
ECP-XC can provide an attractive coating because they are very fine
grained and strongly light absorbing.
[0072] The TiO.sub.2 layer can be formed a variety of ways. The
TiO.sub.2 layer can be formed by sol gel, drying and baking. A
product under the trademark LIQUICOAT.RTM. from Merck & Co.,
Inc., which hydrolyzes Ti(OR)4 type material in water to form
TiO.sub.2 and 4ROH can be used to form the TiO.sub.2 layer under a
sol gel/drying/baking process. TiO.sub.2 can also be formed from
preparing an anatase suspension from dry powder, then dipping,
drying, and baking the suspension to form the TiO.sub.2 layer.
Another way the TiO.sub.2 layer can be formed is by e-beam
evaporating titanium and subsequently exposing the titanium to
O.sub.2 within a deposition chamber. The TiO.sub.2 layer can also
be formed by adding titanium salt to water and adjusting the pH to
.about.2-7 to form a suspension, then dipping the suspension and
allowing the suspension to dry.
[0073] Active oxygen is created from TiO.sub.2 by irradiation with
UV light, but the chemical form of the active oxygen is very
reactive and can be lost by side reaction occurring in close
proximity to the TiO.sub.2 particle surface where active oxygen is
generated. There are at least three ways to minimize the loss of
active oxygen to unwanted side reaction: 1) move the active oxygen
to dissolved oxygen conversion point closer to the active oxygen
generation point, i.e. move the metal ion catalyst as close as
possible to the TiO.sub.2, which may require intimate contact
between these two materials, in the order of angstroms; 2)
electrically connect the two points, as is done in photosynthesis
by a protein capable of conducting electrons; or 3) convert the
active oxygen into a longer lived intermediate active oxygen
species that has time to migrate to more distant MnO.sub.2 centers
for conversion to dissolved oxygen.
[0074] The amount of active oxygen lost by side reactions can be
minimized by introducing an active oxygen carrier molecule into the
media, or "D," by analogy to a photosynthetic system. Agents for
use with species D can be selected from two groups, those that
readily form organic peroxides, and those that form "stable" (i.e.
long-lived) free radicals. Organic peroxides are useful because
they easily produce dissolved oxygen when contacting MnO.sub.2, and
readily form by oxygen insertion. The organic peroxide reactions
are as follows:
[TiO.sub.2]--Ti.sup.IV--OH+hv->{[TiO.sub.2]--Ti.sup.III.OH}
where the excited electronic state corresponds to the
ligand-to-metal charge transfer (free radical pair), and is
followed by the reaction:
{[TiO.sub.2]--Ti.sup.III.OH}+H.sub.2O->[TiO.sub.2]--Ti.sup.IV--OH+H.s-
up.++.OH
where conduction of the e- into the semiconductor conduction band
and away from the side of the particle near the .OH prevents
recombination of that e.sup.-. As shown in the reaction above, the
TiO.sub.2 anatase is regenerated. The above reaction produces a
hydrogen ion for eventual CO.sub.2 removal. Also, the active oxygen
produced in the above reaction is in close proximity to TiO.sub.2
as a free radical hydroxyl groups, .OH.
[0075] As .OH is extremely reactive, lasts only for a very short
time and does not diffuse far. One way to increase the amount of
time that .OH is present is by introducing a species that
stabilizes the .OH. Similar to photosynthesis, a species "D" is
introduced into the test system to capture the hydroxyl free
radical in a longer lived species. The species D is generally shown
the in following chemical reaction:
D+.OH->D*
where D can be RC(O)OH:
##STR00005##
or D can be R.sub.3COH:
##STR00006##
[0076] or D can be a free radical scavenger that forms a stable
free radical:
##STR00007##
or D can be 2,6-di-tertbutyl phenol:
t-Bu--Ar--OH+.OH->t-Bu--Ar--O.+H2O
[0077] The 2,6-di-tertbutyl phenol is the most desired D species,
as a strongly reducing .H radical is not formed that would consume
OH-- and [TiO.sub.2]--TiIII in wasteful reactions, regenerate the
starting materials, and result in a low photochemical yield.
[0078] The catalyst used to convert active oxygen into dissolved
oxygen includes metal ions capable of redox cycling, such as FeII,
FeIII, CuI, CuII, CoII, CoIII, MnII, MnIII, MnIV, etc., or metal
oxides formed from metal ions capable of redox cycling, such as
manganese dioxide, MnO.sub.2. The present reaction produces
dissolved oxygen directly from water and by-passes the gaseous
state. The MnO.sub.2 catalyst is most preferred because it forms
dissolved oxygen efficiently and is not highly selective of the
active oxygen form.
[0079] One way to facilitate the conversion of active oxygen to
O.sub.2 is by doping the surface of the TiO.sub.2 anatase with
manganese (Mn). Surface doping the TiO.sub.2 with Mn provides a
highly productive active oxygen to O.sub.2 conversion catalyst.
Active oxygen disproportionation is rapid when dropped on a
Mn-doped anatase. Alternatively, active oxygen can also be
converted to O.sub.2 by placing MnO.sub.2 on the surface of the
anatase in conductive form. In this form, electrons are
catalytically passed from water to the active oxygen region of the
anatase. Such an arrangement more closely mimics photosynthesis
O.sub.2 production.
[0080] Another way to convert active oxygen to O.sub.2 in the
photolytic cell is by using a MnO.sub.2 octahedral molecular sieve
(MOMS) material as the dissolved oxygen catalyst. The MOMS material
has an open gel-like structure and is closely related to zeolites
in structure. The MOMS material is easily formed from manganese
salts through precipitation and drying.
[0081] Active oxygen may also be converted to O.sub.2 in the
photolytic cell by a superoxide dismutase (SOD) catalyst. SOD
catalyst is already available in the human body and can provide the
required conversion of active oxygen, e.g. as O.sub.2--, into a
dissolved oxygen precursor, i.e. H.sub.2O.sub.2, to supplement the
photolytic cell and Mn-doped anatase.
[0082] Blood is routinely exposed to active oxygen forms and blood
already has built-in measures for self protection against low
levels of excessive active oxygen. ("Inorganic Biochemistry", G. L.
Eichhorn (Ed)., Chap. 28, p 988 (Elsevier, Scientific Publ., NY
(1975), and "Advances in Inorganic and Bioinorganic Mechanisms", A.
G. Skes (Ed), p 128 (1986) (Academy Press, NY)) Active oxygen forms
within the body in the form of species such as peroxides
(R--O--O--H) and superoxide (O.sub.2-(aq)), which are
disproportionated to dissolved oxygen and H2O respectively by
hydroperoxidases, such as catalase which contains zinc ion,
peroxidase which contains iron ion, etc., and superoxide dismutase
metal ion-based enzymes, such as ferriprotophyrin IX.
Alternatively, these enzymes can utilize active oxygen forms to
oxidize a wide range of chemical reductants such as ascorbic acid
and other vitamins such as such as vitamin E and vitamin K.
Although the photolytic artificial lung does not rely on such
protection mechanisms, it is noteworthy that low levels of such
molecules are not new to body chemistry and that conventional
mechanisms for handling such exposures exists.
[0083] 4. Blood Exchange
[0084] Hemoglobin from blood follows the following steps of
reactions within the photolytic cell.
Hb(h.s. Fe.sup.II)+O.sub.2.delta.Hb(I.s. Fe.sup.II)O.sub.2
HbO.sub.2+2H.sup.+ (pH 6.8-7.6) .delta.
H.sub.2Hb2.sup.++O.sub.2
N-- of two alpha-chains (pKa 8.0) and His .beta.146
(pKa 6.5) residues are bases for H.sup.+ reaction
CO.sub.2+H.sub.2O .lamda. H.sub.2CO.sub.3 .lamda.
H.sup.++HCO.sub.3.sup.-
Hb(R--NH.sub.2)+CO.sub.2 .lamda. R--NH--COO.sup.-+H.sup.+
[0085] When water reacts with a light activated catalyst, the
hydrogen ion that is released rapidly reacts with an HCO3- ion and
forms H2CO3. The photolytic cell has excess HCO.sub.3- ions to
react with hydrogen ions.
[0086] The photolytic cell allows the blood to achieve the proper
mass balance. The mass balance of blood traveling through the
photolytic cell is as follows:
##STR00008##
[0087] Alternatively, quinone can be replaced with
Fe(CN).sup.6.sup.3-. The quinone or Fe(CN)63- Q could be in
homogeneous solution or film form.
[0088] 5. Cation Exchange Membrane 46
[0089] The cation exchange membrane 46 allows for the diffusion of
cations in the photolytic cell. Particularly, the cation exchange
membrane allows a cation, such as a sodium ion (Na+) from blood to
diffuse through the membrane and subsequently form sodium hydroxide
(NaOH) in the catholyte. The cation exchange membrane is
commercially available under the trademark NAFION.RTM. and is
available from E.I. DuPont Nemours Inc. NAFION.RTM. cation exchange
membranes are a perfluorosulfonic acid/PTFE copolymer in an acidic
form. Although NAFION.RTM. cation exchange membranes are the
preferred membrane, one skilled in the art would recognize that
other cation exchange membranes are also suitable in the photolytic
cell.
[0090] The anodic compartment of the photolytic cell has the
following series of reactions:
##STR00009##
[0091] The overall net anodic reaction from the above reactions is
as follows:
h.nu.+1/4Hb+2NaHCO.sub.3.fwdarw.2CO.sub.2(g).mu.+H.sub.2O+1/2Hb.sub.0.5O-
.sub.2+2e.sup.-+2Na.sup.+
[0092] The two electrons formed in the anodic reaction are
conducted away to the cathode via the anode conductor layer. The
two Na+ ions are moved to a catholyte via a cation exchange
membrane.
[0093] 6. Catholyte 48
[0094] Sodium hydroxide (NaOH) builds in the catholyte during the
series of reactions in the photolytic cell. It is preferred that
the NaOH is purged occasionally from the catholyte. If sodium
chloride (NaCl) is used in the catholyte instead of NaOH, NaCl(s)
may eventually form within the catholyte and would periodically be
purged.
[0095] The reactions occurring in the cathode of the photolytic
cell are as follows:
2NaHCO.sub.3.lamda.2Na.sup.++2HCO.sub.3.sup.-
2e.sup.-+2H.sub.2O+H.sub.2(g)+2OH.sup.-
2OH.sup.-+2HCO.sub.3.sup.-2CO.sub.3.sup.=+2H.sub.2O
4Na.sup.++2CO.sub.3.sup.2-.lamda.2Na.sub.2CO.sub.3
[0096] The overall net cathodic reaction is as follows:
2e.sup.-+2Na.sup.++2NaHCO.sub.3.fwdarw.H.sub.2(g).mu.+2Na.sub.2CO.sub.3
[0097] The Na2CO3 that is produced causes pH to rise. Based upon
the overall anodic and cathodic cell reactions, the overall net
photolytic cell reaction is:
h.nu.+1/4Hb+4NaHCO.sub.3.fwdarw.H.sub.2(g)+2Na.sub.2CO.sub.3+2CO.sub.2(g-
)+H.sub.2O+1/2Hb.sub.0.5O
[0098] 7. Battery/Current Regulator
[0099] As shown in FIG. 4, the photolytic cell can include a
battery 49, current regulator 50, or resistor 52. An electrical
current formed from a battery 49 allows electrons to flow from the
anode 36 to the cathode 38. The initial bias voltage caused by the
current supplied from the battery initiates the removal of
electrons formed during the conversion of water to dissolved oxygen
and prevents the electrons from reacting with the active or
dissolved oxygen to reform water. The initial bias voltage also
allows more dissolved oxygen to be produced as the removal of the
electrons minimizes the reformation of water. Additional external
electrical contacts can monitor or apply a particular voltage to
the photolytic cell.
[0100] The current regulator and resistor help control the flow of
electrons from the anode to cathode, thereby controlling the amount
of dissolved oxygen formation. The resistor creates a fixed control
in the current flow, whereas the current regulator can be adjusted
to increase or decrease the resistance of the current flow.
Increasing the resistance of the current lowers the number of
electrons flowing from the anode to the cathode, thereby lowering
the overall production of dissolved oxygen. Decreasing the
resistance of the current increases the flow of electrons from the
anode to the cathode, thereby increasing the amount of dissolved
oxygen produced.
[0101] 8. Optimal Gas Sorption Device 24
[0102] Continual venting of carbon dioxide gas out of the
photolytic cell presents the problem of potential infection. A gas
sorption device minimizes and provides control over potential
infection risks by avoiding continuous venting of the CO.sub.2 to
the atmosphere. The gas sorption device captures CO.sub.2 gas
released from the oxygenated blood in a concentrated form. The
concentrate can be processed or disposed of occasionally so that
the sterility of the photolytic cell is not continuously subjected
to possible contaminants due to the continual venting of the
CO.sub.2 gas.
[0103] CO.sub.2 can be captured using a number of different ways by
a gas sorption device 24. The gas sorption device can use the
process of chemi-absorption and convert CO.sub.2 into a
concentrated solid or solution form. The concentrate formed in the
gas sorption device can then be disposed of as disposable
cartridges having liquid or solid CO.sub.2, or regenerated.
[0104] 9. Light Supply 20
[0105] The light supply is used in the photolytic cell to provide
the photon energy necessary to activate the catalyst converting
water into oxygen. The light source can be from any known light
source including, but not limited to, sunlight, UV light, laser
light, incandescent light, etc., depending on the activation
requirement for the light activated catalyst used. Preferably, the
blood flowing through the photolytic artificial lung is not exposed
to the light in order to prevent irradiation of the blood.
[0106] The light source may provide a particular wavelength of
light depending upon the catalyst used. When tungstate (WO.sub.3)
is used as a light activated catalyst, the light source exposes
visible light in order to activate WO.sub.3. When TiO.sub.2 or ZnO
is used as a light activated catalyst, the light source used has a
wavelength in the UV range.
[0107] Preferably, the light source used in the photolytic
artificial lung is a laser light. The wavelength of laser light can
be manipulated in order to attain a higher efficiency in exciting
the light activated catalyst and forming active oxygen. Also, laser
light allows the photolytic artificial lung to dissipate less
overall heat. The laser light can be directed in a small area to
energize the light activated catalyst and avoid contact or
irradiation with other components of the photolytic artificial
lung. A particularly preferred laser light that can be used to
activate TiO.sub.2 is an argon laser at 364 nm (400 mwatts/cm2),
which has a total power of about 2 watts, although other UV
sources, including an HG arc lamp at 365 nm line, are also
available.
[0108] It is preferred that the light from the light source be
evenly spread within the photolytic cell. The even spreading of the
light from the light source allows for maximal excitation of the
catalyst in order to convert more water into either active oxygen
or dissolved oxygen. Along these lines, light from the light source
can enter the photolytic cell through the transparent window from
many positions. Light from the light source can enter directly
through the transparent window and come into contact with the
catalyst. Alternatively, light can enter the transparent window
from a side, back, bottom, or corner position and move through the
transparent window by a wave guide to provide photon energy and
excite the light activated catalyst. Side entry of light into the
transparent window of the photolytic cell occurs at about at least
a 68.degree. angle. Preferably, side entry of light into the
transparent window occurs at an angle of from about 70.degree. to
about 80.degree..
[0109] 10. Pump
[0110] A peristaltic pump or some other simple pump drives blood
through the photolytic artificial lung. The pump draws venous
deoxygenated blood from a patient and moves the blood through the
photolytic artificial lung. Preferably, the photolytic artificial
lung only requires a pump to draw blood from a patient, as the flow
produced by the pump drawing blood from the patient also moves the
blood through the photolytic cell for oxygenation and back into the
patient.
[0111] 11. Sensors Monitoring Reaction Chemistry
[0112] The photolytic artificial lung can include one or more
sensors that monitor the different chemical reactions occurring
within the photolytic cell. The sensors can be used to measure for
potential toxins and toxin levels. Various sensors and sensor
systems can be used including visual observations of color changes
of redox indicator dyes or gas bubble formation, closed electrical
current measurements and pH measurements, and dissolved oxygen
probe analysis. Gas chromatography assays can also be performed. A
dissolved oxygen probe can be used to test and monitor O.sub.2
generation, as dissolved oxygen, in real time. Also, the photolytic
artificial lung can incorporate one or more portals to insert a
dissolved oxygen probe, CO.sub.2 probe, pH monitor, etc. in
different locations if necessary. The photolytic artificial lung
can also incorporate separate sampling chambers to trap gas bubbles
for testing. These sampling chambers could also incorporate a
device, such as a septum for a hypodermic needle for instance, to
obtain a sample for further testing. One skilled in the art would
recognize numerous sensors could be used for monitoring the
reaction chemistries occurring within the photolytic cell.
[0113] The photolytic device and photolytic cell can also include
one or more process regulator devices that respond to the readings
provided by the sensors. The process regulator devices increase or
decrease the amount of dissolved oxygen or CO.sub.2 output, lower
toxin levels, etc., depending on the requirements of the patient or
of the photolytic cell. It is within the purview of one utilizing
the photolytic artificial lung to determine what process regulator
devices are required.
[0114] All of the seals in the photolytic artificial lung are made
of an inert material that properly seals blood flowing through the
photolytic artificial lung from accidental contamination. The seals
of the photolytic lung should also be formed of a material that
does not interact with the blood. Preferably, the seals are formed
of a silicone-based material.
[0115] Laminar flow is minimized within the photolytic artificial
lung. Minimization of laminar flow is accomplished by using current
commercial cells, such as electrodialysis, electrodeionization,
etc. Commercially available cells accommodate electrodes,
membranes, and thin liquid chambers with flow distributors, and
provide good seals and corrosion resistance. The cells are
available in lab scale units for process development work. A
particularly preferred commercial cell is the FM01-LC device from
ICI Chemicals and Polymers, Electrochemical Technology, Cheshire,
UK.
Multiple Photolytic Cells
[0116] Preferably, the photolytic artificial lung uses a plurality
of photolytic cells in a stacked formation. The plurality of
photolytic cells receives blood flow from the venous circulation
and is exposed to photo-activation via a directed laser light
source. The stacking of a plurality of photolytic cells allows for
a large overall surface area for blood to receive maximal exposure
to dissolved oxygen. Also, stacking a plurality of photolytic cells
allows the overall photolytic artificial lung to achieve a smaller
size, thereby allowing the photolytic artificial lung to be
miniaturized.
[0117] Moreover, it has been found that one is able to control
material properties of the photolytic surface, resulting in an
expression of the maximal rate by which dissolved oxygen is
increased (or carbon dioxide decreased) as a function of reaction
surface area and laser power. If desired one can use the materials
described herein to create a photolytic chamber, which incorporates
optimal reaction kinetics and fluid mechanical modeling of blood
flow in relation to the photolytic surface. The selected materials
can be used in selecting the boundary conditions for the full
chamber, emulating the fundamental relationship between the
alveolar surface and the pulmonary capillary.
[0118] The following examples are for the purposes of further
illustrating photoactive layers for whole blood oxygenation in
accordance with the present disclosure. The examples are merely
illustrative and are not intended to limit photoactive layers in
accordance with the disclosure to the materials, conditions, or
process parameters set forth therein. All parts are percentages by
volume unless otherwise indicated.
EXAMPLES
Example 1
[0119] This example illustrates the fabrication of photoactive
layers. Oxide materials were added to a substrate using a spin
coating technique. Glass slides containing the conducting layer
were placed on a vacuum. For the TiO.sub.2 coating, 0.5 g of the
acid treated material was added to 40 ml isopropanol and mixed for
30 minutes. 0.050 ml H.sub.2O and 0.100 ml titanium(IV)
tetra(isopropoxide) (TTIP), a sol-gel reagent, was added to this
solution. After mixing for 30 minutes, the solution was added
drop-wise to the rotating substrate for a total volume of about 12
ml. In the case of the constructs containing MnO.sub.2, following
the addition of 9 ml of TiO.sub.2 slurry, 0.20 g MnO.sub.2 was
added to the remaining slurry. Exactly four ml of the resulting
solution was then added drop-wise to the substrate at spin coating
conditions. As a modification of this technique, RuO.sub.2/Pt doped
TiO.sub.2 (0.125 g) was added to 10 ml isopropanol. After 15
minutes of mixing, 50 uL water and 25 uL TTIP was added and allowed
to mix for an additional 15 minutes. The solution was then added
drop-wise to the substrate for a total volume of 9 ml. The sol-gel
coated samples were all allowed to air dry at room temperature
overnight. They were then placed in a preheated tube furnace and
heated for 45 minutes at elevated temperature under a 1 L/min. flow
of nitrogen. Samples containing conducting layers of Ti or indium
tin oxide were heated at 350.degree. C., while samples containing
Ni or Cr (metallic conducting films) were heated at 209.degree.
C.
Example 2
[0120] In addition to batch cells, a flow-through test cell was
constructed to associate flowing liquids (such as blood) with
photolytic output. A modified FM01-LC Electrolyser, operating in a
divided cell mode with a Nafion.TM. cation exchange membrane was
used. The anode was optically transparent, and illumination was
achieved side-on by UV light (354 nm) using a filter and UVA fiber
optic lamp source. The catholyte was Locke's-Ringer solution, and
the anolyte fresh whole bovine blood containing anticoagulant. The
photolytic surface was TiO.sub.2 on a quartz plate. Fluids were
maintained at 37.degree. C. using an in-line heat exchange jacket,
and flow was 80 cc/min by a peristaltic pump. The flow-through cell
consisted of a 3 ml photolytic chamber, with a single active
surface of vacuum deposited Ti metal, a coating of TiO.sub.2
(anatase) and optionally a MnO.sub.2 layer. These films were
prepared as described above for the batch test films, except on
larger glass and quartz substrates (effective area .about.5 in2).
The uncoated glass/quartz side of the plates was illuminated by
filtered UV light.
[0121] Data collected were pH, electrical current, dissolved oxygen
(DO), pO.sub.2, pCO.sub.2, SO.sub.2, and oxyhemoglobin as a
function of laser irradiation and the presence or absence of bias
voltage.
Example 3
[0122] This example illustrates real-time measurement of dissolved
oxygen (DO): A liquid phase in line reaction chamber was used to
monitor dissolved oxygen production. This device utilized a Clark
Electrode to measure dissolved oxygen (DO). A two-point calibration
procedure was used to calibrate the dissolved oxygen sensor. Dasse
K A, Monzyk B F, Burckle E C, Busch J R, Gilbert R J., Development
of a photolytic artificial lung: Preliminary concept validation,
ASAIO Journal, 48:556-563, 2003. A low bias voltage was applied to
the cell through a DC power source, sufficient to insure proper
anode-to-cathode electron flow direction, to promote immediate
removal of photo-generated electrons, but insufficient to drive
electrochemical side reactions, as evidenced by the lack of current
flow in the absence of illumination. Dasse K A, Monzyk B F, Burckle
E C, Busch J R, Gilbert R J., Development of a photolytic
artificial lung: Preliminary concept validation, In press, ASAIO
Journal, 2003. Electrical current was measured with a
high-impedance VOM multimeter. The light was directed to the
reaction chamber through a liquid light pipe, and filtered to
produce light of only 365 nm; the intensity at this wavelength was
88.1 mW/cm2 at the exit point of the light pipe. It would be
preferred to make measurements to record actual photon flux
impinging on the photolytic surface as substantial light losses
occur at this interface. Heating of the solution during
illumination was prevented by use of a light filter at the 365 nm
wavelength light that is efficiently absorbed by the anatase film.
A water-jacketed surrounding the reaction chamber was used to
maintain a physiologically significant and constant 36.degree. C.
throughout the experiments.
Example 4
[0123] This example illustrates the measurement of blood gas
parameters. Conventional blood gas analyses were made using a blood
gas analyzer. Precise volumes of blood samples (.about.0.25 ml)
were withdrawn at specific times by needle fitted syringe from an
in-line septum access port and analyzed using the NPT7 Blood-Gas
Analyzer (Radiometer, Inc). This instrument gives readout of
concentration measurements of total hemoglobin, oxyhemoglobin,
deoxyhemoglobin, methemoglobin, partial pressure of O.sub.2,
partial pressure of CO.sub.2, SO.sub.2, and pH. As described above,
a Clark electrode was also used to monitor for total dissolved
oxygen (DO) in real time, thus comprising an independent
verification and measurement of this key parameter.
[0124] Filtered UV illumination of the metal oxide light-absorbing
surface opposite the blood in the flow-through cell described above
resulted in near complete oxygen saturation of the blood
circulating on the opposite side of the photolyzed surface (see
FIG. 2). The fraction of oxyhemoglobin (represented in the FIG. 2
as FO.sub.2Hb) rapidly increased from 83% to 92% and remained
stable throughout the trial period. The extent to which dissolved
oxygen is dissolved in the serum phase of the blood, represented as
a percentage, is depicted by the term SO.sub.2, or "soluble
O.sub.2." by the blood gas instrument. SO.sub.2 is that portion of
the total O.sub.2 resident in the blood that is normally supplied
through the alveolar membrane/pulmonary capillary wall interface,
and is equal to 100*(DO/DOmax), where DO is the amount of dissolved
oxygen, and DOmax is the maximum solubility of O.sub.2 in blood
serum at the temperature of the blood, a reference value
automatically calculated from an algorithm pre-programmed into the
blood gas analyzer. This is the percent of maximum O.sub.2 that is
ready to diffuse into red blood cells and bind to hemoglobin.
SO.sub.2 also predicts when O.sub.2 gas bubbles can form due to
super-saturation, i.e. when dissolved oxygen reaches levels such
that SO.sub.2.gtoreq.1.0. Such bubbles would be 100% O.sub.2,
saturated with humidity, and so would re-dissolve quickly and
completely by the tissue as the demand for O.sub.2 by the tissue
consumes it and if production of dissolved oxygen is slowed. Hence
excessive dissolved oxygen production is easily controlled in the
envisioned process. The fact that the FO.sub.2Hb and SO.sub.2
curves varied in a parallel manner (see FIG. 2) confirm the O.sub.2
generation results, and demonstrates that near complete oxygenation
of hemoglobin content of the blood was achieved. It also replicates
previous results 18 in a complex matrix, that of whole blood.
[0125] The effect of UV light illumination on pH, the partial
pressures of O.sub.2 and CO.sub.2, oxygen saturation in the blood
serum, fraction of hemoglobin saturated with oxygen, and the
percent of blood methemoglobin were determined at various time
points, from 16 to 460 minutes, in a recirculating flow loop (Table
1). Significantly, blood pH and the partial pressures of O.sub.2
and CO.sub.2 stabilized at approximately 60 minutes, and remained
so for the duration of the experiment. It should be noted that the
pH of the anolyte dropped only during the initial formation of
oxyhemoglobin, which can be understood using conventional blood
chemistry coupled with the previously described photochemistry 18
by the following reaction:
2H.sub.2O+Hb+h.nu.(light).fwdarw.O.sub.2Hb+4H.sup.++4e.sup.-
[0126] These electrons provide the basis for the observed
electrical current, and the H+ ions caused the observed small drop
in pH. The drop in pH is small as most of the H+ ion are
immediately consumed through CO.sub.2 formation from the bloods'
bicarbonate buffer, as follows:
##STR00010##
resulting in the stabilization of blood pH and enables the release
of CO.sub.2 from the blood, the second major requirement for
complete blood gas control by the lung. The percent dissolved
oxygen of saturation in the water phase of the blood (SO.sub.2) and
oxyhemoglobin (FO.sub.2Hb) increased in parallel in the flowing
blood with continuous laser illumination of the photoactive
surface, reaching maximum values at 58 minutes, then remaining
stable to the end of the trial. It was additionally considered that
the exposure of the TiO.sub.2 surface to continuous UV light (even
without direct exposure of the blood) could have toxic oxidant
effects, resulting in an increased percent of hemoglobin in which
the iron of heme was oxidized to the ferric form, or methemoglobin.
Gibson Q H., The reduction of methemoglobin in red blood cells and
studies on the cause of ideopathic methemoglobinemia, Biochemical
Journal, 42: 13-23, 1948; and, Beutler E., Methemoglobinemia and
other causes of cyanosis, In Beutler E, Lichtman M A, Coller B W,
Kipps T S, eds, Williams Hematology, 5.sup.th Edition, New York:
McGraw-Hill, pp 654-662, 1994. However, the percent methemoglobin
measured was generally low and remained stable throughout the
trial, in the range of 2-3%. Hence, degradation of the blood was
not observed in these tests.
TABLE-US-00001 TABLE Measurement of gases generated by photolytic
activation in flowing blood. Time pCO.sub.2 pO.sub.2 SO.sub.2
FO.sub.2Hb FMetHb (min) PH (kPa) (kPa) (%) (%) (%) 16 6.75 48.7
12.6 81.1 80.1 2.9 25 7.16 27.7 9.9 85.3 83.6 2.4 36 7.56 13.7 7.7
88.0 85.9 2.3 58 7.45 16.6 8.6 88.9 86.3 2.8 110 7.44 16.8 9.0 91.5
89.1 2.5 158 7.45 16.0 9.3 92.5 89.6 2.7 258 7.45 16.3 9.6 93.6
90.4 3.1 357 7.44 16.0 9.6 93.6 90.0 3.2 412 7.44 16.0 9.3 92.8
90.5 2.2 436 7.44 16.1 9.0 91.6 88.2 3.4 460 7.44 16.3 8.8 90.6
87.4 3.2
[0127] Blood gas analyses for the Table were made using the NPT7
Blood-Gas Analyzer (Radiometer, Inc). This instrument provided a
readout of concentration measurements of the percent oxyhemoglobin
(FO.sub.2Hb), the saturation of dissolved oxygen in the liquid
phase of serum (SO.sub.2), the percent methemoglobin (FinetHb),
partial pressure of O.sub.2 (kPa) and CO.sub.2 (kPa), and pH as
function of laser illumination in a recirculating blood loop
configuration.
[0128] The present disclosure applies photolytic principles to the
development of a novel respiratory surface which generates an
increase in intravascular oxygen and augments oxyhemoglobin
formation without the physical delivery of oxygen gas. For the
inventive system, a well-characterized semi-conducting metal oxide
film was designed as the photo-absorption element, the anatase form
of titania, TiO.sub.2. Chen F, Xie Y, Zhao J, Lu G., Photocatalytic
degradation of dyes on a magnetically separated photocatalyst under
visible and UV irradiation, Chemosphere, 44: 1159-1168, 2001; Asahi
R, Morikawa T, Ohwaki T, Aoki K, Taga Y., Visible-light
photocatalysis in nitrogen-doped titanium oxides, Science, 293:
269-271, 2001; and, Garcia Rodenas L A, Weisz A D, Magaz G E, Blesa
M A., Effect of light on the electrokinetic behavior of TiO.sub.2
particles in contact with Cr (VI) aqueous solutions, J Colloid
Interface Sci, 230: 181-185, 2000. Importantly, the light energy
associated with activation by a 354 nm UV laser light selectively
excites the electronic transition of the TiO.sub.2 semiconductor
(350-389 nm band, or at least 3.2 eV), thus resulting in minimal
wasted radiation or transmission (and unwanted heating).
[0129] As noted earlier, in initial work, Dasse K A, Monzyk B F,
Burckle E C, Busch J R, Gilbert R J., Development of a photolytic
artificial lung: Preliminary concept validation, ASAIO Journal,
2005, it was demonstrated that photoactivation of the proposed thin
film in contact with surrogate serum induced the following set of
high-yielding reactions within the oxide film, which have now been
replicated here with whole blood: [0130] 1) UV light is absorbed
into the TiO.sub.2 layer, thus energizing the material by producing
electrical charge separation. [0131] 2) Charge separation drives
the conversion of water, present in large excess from the serum, to
form the "active oxygen" (AO) intermediate in the nanoporous metal
oxide film. The use of wavelengths >340 nm was chosen to prevent
this active oxygen species from reforming H.sub.2O directly. The
solid state configuration results in the physical separation of
active oxygen from the red blood cells and blood proteins. [0132]
3) Active oxygen spontaneously (and completely) disproportionates
directly into O.sub.2 as dissolved oxygen, and, in a similarity to
photosynthesis, can be facilitated by a MnO.sub.2 catalyst film,
without forming a gaseous phase. [0133] 4) Dissolved oxygen
diffuses into the aqueous phase (blood serum), exiting the
nanoporosity of the metal oxide film into the flowing blood raising
its SO.sub.2 value, and is thus available to diffuse into red blood
cells. [0134] 5) Simultaneously, in order to avoid recombination
with active oxygen the freed electrons are conducted away to the
cathode and so are available to effect other useful changes. Such
recombination would result in the re-formation of water, a harmless
event except it results in decreased energy efficiency (the
"quantum efficiency, .PHI..sub.DO value is reduced, where
DO=dissolved oxygen) (i.e. the "back reaction"). [0135] 6) The
freed H.sup.+ rapidly combines with bicarbonate ions in the serum
by a protonation reaction (see above) yielding initially carbonic
acid, which is rapidly converted (facilitated by endogenous
carbonic anhydrase) into dissolved CO.sub.2(aq), as per normal lung
function, ready for elimination (see above reactions). In another
embodiment of the disclosure, in some applications it, it appears
advantageous to combine these hydrogen ions with the bicarbonate
ions using the freed electrons (electrochemical reduction at the
cathode) to form a biocompatible organic compound easily eliminated
through the urine, the gut, or by other means, or utilized by the
body as food, i.e. a reduced sugar. In either case, note that the
H.sup.+ ions are not required to diffuse from the point of
formation, but use the well-known proton "hopping" mechanism. Voth
G A., The computer simulation of proton transport in biomolecular
systems, Frontiers Bioscience, 8: S1384-1379-1384, 2003. This
eliminates another potential diffusion boundary layer. [0136] 7) In
lieu of CO.sub.2 "fixation" (electrochemical reduction) the final
step, CO.sub.2(aq) is believed to be eliminated by releasing it
CO.sub.2 gas by perevaporation via a gas selective membrane into
the trachea or lung cavity, similar to that done by the natural
lung, or through some other blood to air vent route.
[0137] In the present disclosure, it is shown that the
photolytically-driven artificial lung approach can be used to
generate sufficient dissolved oxygen (as a function of unit area
and recirculation time) to yield a measurable increase of
oxyhemoglobin in flowing whole blood. To determine appropriate
upscaling of the disclosed results and to determine desirable
dissolved oxygen production rates, the following calculations were
performed. Assuming that one molecule of O.sub.2 would be formed
for every four electrons produced (see above reaction
stoichiometry), the measured electrical current was used to
calculate that the maximum rate of oxygen generation with the
disclosed laboratory scale apparatus is 1.08 mL
O.sub.2/m.sub.2/min. Projecting this result to an alveolar surface
area of 75 m.sub.2, as is the case for the human lung, the output
of this system would be approximately 81.0 ml O.sub.2/m.sub.2/min.
This value is a significant fraction of the net oxygen flux
traversing the normally functioning pulmonary capillary membrane,
that is, 250 ml O.sub.2/m.sub.2/min. Since the slow process of
liquid dissolution of oxygen gas is not required, a major
impediment faced by current artificial lung technologies is
avoided. In addition the requirement for natural lung operation of
being near gas/solid equilibrium for both air and exhaled CO.sub.2,
to allow their flow in opposite directions during a breath, is
avoided by separating these two components. Instead, owing to the
fact that dissolved oxygen flux is not dependent on diffusion
across a gas/liquid boundary and against an outflow of diffusing
CO.sub.2, a high dissolved oxygen flux entering the blood is
conceivable with the inventive photolytic process. In addition, the
TiO.sub.2 semi-conductor material is considerably more durable than
PS pigments (i.e., naturally occurring chlorophyll) and,
importantly, is selectively excited by light of a narrow UV
bandwidth, thus minimizing heat production and the potential
exposure of blood cells to UV light. The catalyst film, which
converts active oxygen into dissolved oxygen is located within the
photoactive film, and buried within the nano-porosity so that
oxygen enters water within the nanopores, and only dissolved oxygen
exits the surface pores that are exposed to blood.
[0138] While the forms of the disclosure herein disclosed
constitute presently preferred embodiments, many others are
possible. It is not intended herein to mention all of the possible
equivalent forms or ramifications of the disclosure. It is to be
understood that the terms used herein are merely descriptive,
rather than limiting, and that various changes may be made without
departing from the spirit of the scope of the disclosure.
* * * * *