U.S. patent application number 17/307504 was filed with the patent office on 2021-09-02 for method for separating charged biologically active substances from liquids and the recovery thereof.
This patent application is currently assigned to i3 MEMBRANE GMBH. The applicant listed for this patent is i3 MEMBRANE GMBH. Invention is credited to Stephan BRINKE-SEIFERTH.
Application Number | 20210268442 17/307504 |
Document ID | / |
Family ID | 1000005583438 |
Filed Date | 2021-09-02 |
United States Patent
Application |
20210268442 |
Kind Code |
A1 |
BRINKE-SEIFERTH; Stephan |
September 2, 2021 |
METHOD FOR SEPARATING CHARGED BIOLOGICALLY ACTIVE SUBSTANCES FROM
LIQUIDS AND THE RECOVERY THEREOF
Abstract
The present invention relates to a method for the at least
temporary retention of charged biologically active substances such
as endotoxins, viruses, and proteins from liquids, and optional
later release for better determination. The object is achieved by a
method for the at least temporary separation and/or detection of
charged biologically active substances in a liquid by means of
electrosorption and/or electrofiltration, comprising the following
steps: a. providing a polymer membrane with a flat and porous metal
coating at least on a first side of the polymer membrane; b.
providing a counterelectrode; c. applying a voltage between the
metal coating of the polymer membrane and the counterelectrode; d.
bringing the polymer membrane and the counterelectrode into contact
with the liquid, with the contacting being performed such that the
liquid generates at least one connection between the polymer
membrane and the counterelectrode.
Inventors: |
BRINKE-SEIFERTH; Stephan;
(Hamburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
i3 MEMBRANE GMBH |
Hamburg |
|
DE |
|
|
Assignee: |
i3 MEMBRANE GMBH
Hamburg
DE
|
Family ID: |
1000005583438 |
Appl. No.: |
17/307504 |
Filed: |
May 4, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16473640 |
Jun 26, 2019 |
11027238 |
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PCT/EP2017/084721 |
Dec 28, 2017 |
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17307504 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2313/345 20130101;
B01D 67/0088 20130101; G01N 27/44756 20130101; B01D 2313/24
20130101; B01D 61/425 20130101; B01D 65/02 20130101; B01D 69/12
20130101; B01D 71/68 20130101 |
International
Class: |
B01D 61/42 20060101
B01D061/42; B01D 65/02 20060101 B01D065/02; B01D 67/00 20060101
B01D067/00; B01D 69/12 20060101 B01D069/12; B01D 71/68 20060101
B01D071/68; G01N 27/447 20060101 G01N027/447 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2016 |
DE |
102016125818.0 |
Claims
1. A method for the at least temporary separation and/or detection
of charged biologically active substances in a liquid by means of
electrosorption and/or electrofiltration, comprising the following
steps: a. providing a polymer membrane with a flat and porous metal
coating at least on a first side of the polymer membrane; b.
providing a counterelectrode; c. applying a voltage between the
metal coating of the polymer membrane and the counterelectrode; d.
bringing the polymer membrane and the counterelectrode into contact
with the liquid, with the contacting being performed such that the
liquid generates at least one connection between the polymer
membrane and the counterelectrode.
2. The method as set forth in claim 1, wherein step c takes place
after steps a and b and before step d, or wherein step d takes
place after steps a and b and before step c.
3. The method as set forth in claim 1, wherein, after steps a to d,
the liquid is removed at least partially and/or the liquid is
allowed to pass through the membrane at least partially.
4. The method as set forth in claim 1, wherein, the rinsing of the
membrane is performed before or after the polarity reversal or
reduction in the voltage.
5. The method as set forth in claim 1, wherein the polymer membrane
with a flat and porous metal coating and the counterelectrode are
accommodated in a housing, which has a small hold-up volume of no
more than 10 ml and the liquid to be filtered is conducted through
the housing.
6. The method as set forth in claim 5, wherein the housing has a
small hold-up volume of no more than 10 ml and no more than 2
mm.sup.3/mm.sup.2 of metal coating on the polymer membrane.
7. The method as set forth in claim 5 wherein the liquid is pressed
out of a syringe and through the housing through actuation of the
syringe.
8. The method as set forth in claim 1, wherein the counterelectrode
is formed either by an additional flat, porous metal coating on a
second side that is situated opposite the first side, the
two-dimensional metal coatings being isolated from each other by
the polymer membrane, or through arrangement of a permeable
electrode.
9. The method as set forth in claim 8, wherein the permeable
electrode is formed by a metallic mesh with interposition of an
insulating and permeable spacer.
10. The method as set forth in claim 1, wherein the porosity of the
polymer membrane with metal coating is reduced by between 1% and
50% relative to the initial bubble point pore and/or the mean pore
size compared to the uncoated polymer membrane.
11. The method as set forth in claim 10, wherein the porosity of
the polymer membrane with metal coating is reduced by between 1%
and 20% relative to the initial bubble point pore and/or the mean
pore size compared to the uncoated polymer membrane.
12. The method as set forth in claim 1, wherein the thickness of
the metal coating is from 5 to 50 nm and the pore size of the
uncoated polymer membrane is greater than 0.01 .mu.m.
13. The method as set forth in claim 1, for determining the
occupancy of the binding sites of the polymer membrane with a flat
and porous metal coating or for determining at least one
concentration in the liquid, wherein the current flow caused by the
applied voltage is detected or evaluated, and an alarm is triggered
in the case of an undershoot or an overshoot.
14. The method as set forth in claim 13, wherein the current flow
caused by the applied voltage is evaluated with regard to falling
below a limit or exceeding a positive or negative rate of change.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 16/473,640 filed Jun. 26, 2019, which is a
National Stage Entry of PCT/EP2017/084721 filed Dec. 28, 2017,
which claims priority from German Patent Application Serial No.
102016125818, filed Dec. 28, 2016, the entire disclosures of which
are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a method for the at least
temporary retention of charged biologically active substances such
as endotoxins, viruses, and proteins from liquids, and optional
later release for better determination.
BACKGROUND
Background Information
[0003] Endotoxins are lipopolysaccharides (LPS) and components of
the outer membrane of the cell wall of Gram-negative bacteria. They
consist of a lipophilic lipid that is anchored in the membrane and
a hydrophilic polysaccharide, which represents the antigenic
properties. Endotoxins are released upon lysis of the bacterial
cell. They are extremely heat-stable and can even be detected after
sterilization--that is, after the bacteria have been killed.
Because of their ability to induce an immune response, endotoxins
are among the pyrogens. Endotoxins in a quantity of 1 ng/kg body
weight are considered sufficient to cause a febrile response
(ARDUINO (1989)). Besides fever as a result of inflammation, they
can cause numerous physiological reactions in humans after contact
with mucous membranes and especially upon passing into the
bloodstream. These include hypotension, blood coagulation, and
complement activation, as well as life-threatening states of
shock.
[0004] Endotoxins are usually detected in rabbits or by means of a
Limulus amebocyte lysate (LAL) test. The LAL test is based on the
blood of the horseshoe crab, which reacts extremely sensitively to
endotoxins of Gram-negative bacteria. Due to its sensitivity, the
LAL test is the most widely used test in the fields of pharmacology
and medicine. However, endotoxins can only be determined in clear,
undyed fluids when using this test. Direct determination of
endotoxins in human blood is therefore not possible. It is for this
reason that the so-called monocyte activation test was developed in
recent years. This works by using different levels of enzymatic
reactions that mimic the human fever response. It also requires the
creation of a standard curve for each determination, since the
reactants of each test kit react differently. This test requires
special training, has high specific costs, and also takes much
longer than the LAL test.
[0005] Microporous membranes have long since been known. These are
made primarily of polymers and used for water treatment
(wastewater, drinking water, industrial waters) as well as in the
pharmaceutical industry for the production of ultrapure water and
in medical technology as sterile filters or respiratory filters.
The areas of application are numerous and very divergent.
Microporous membranes typically have a pore size between 0.01 .mu.m
and 10 .mu.m and retain substances according to these pore
sizes.
[0006] Microporous filters are typically used to separate
substances that are dissolved in water and to obtain a clear
filtrate. This is generally done mechanically through the pore
size. All substances that are larger than the size of the pores are
mechanically retained. In addition to this property, there is
another mechanism that takes place in order to retain substances
when they pass through the membrane. This is an undefined
adsorption by the materials making up the membrane itself, such as
polyether sulfone, polypropylene, or polyvinylidene fluoride
(PVDF), for example. Different materials adsorb different solutes
to different degrees ("Analyte loss due to membrane filter
adsorption as determined by high-performance liquid
chromatography," M. Carlson and R. D. Thompson, Journal of
Chromatographic Science, Vol. 38, February 2000).
[0007] Targeted adsorption of substances smaller than the pore size
of the microporous membrane by means of the material properties of
the membrane material is achieved through treatment of the chemical
composition of the membrane material. A positive charge is
generated, for example, by combining the membrane material with
positively charged quaternary ammonium compounds. Positively
charged membranes are known from U.S. Pat. No. 5,282,971 or from
U.S. Pat. No. 7,396,465 B2, while negatively charged membranes are
known from U.S. Pat. No. 7,132,049 B2. For example, positively
charged microporous membranes are used to mechanically retain
bacteria and allow positively charged material to pass through in
order to avoid nontargeted, unquantifiable adsorption by the
membrane material. However, positively and negatively charged
membranes are also used to bind and concentrate proteins by
adsorption. Positively charged microporous membranes are also used
to bind endotoxins and viruses through adsorption in addition to
filtration, as is disclosed in DE 1999981099947 A1, for
example.
[0008] CH 678403 discloses a metal-coated membrane with optionally
slightly porous passages between macropores on one side and
micropores on the metallic side. In addition, metal membranes with
tunnel-like passages are known from DE 101 64 214 A1, for example.
These differ from passages that are porous in the parlance of the
application, such as those which are known from porous polymer
membranes, for example, in that they form no cavities outside of
the actual passage channel within the membrane. Therefore, "porous"
is not to be equated with the characterization that the membrane
has pores, i.e., passages, like in DE 101 64 214 A1, for example.
Porous passages thus have a surface area within the membrane that
substantially exceeds the surface area of a circular tunnel with
the same pore size through a membrane of equal thickness, at least
by 50%, particularly by a multiple, more particularly by at least
threefold.
[0009] Moreover, it is known from WO 1999/22843 A1 to sputter a
polymer membrane with metal.
[0010] It is also known from U.S. Pat. No. 4,857,080 to seal a
membrane with a metal coating.
[0011] Another form of adsorption is electrosorption.
Electrosorption is accomplished by forming an electrically charged
field on surfaces by applying a positive and negative voltage to
two electrodes. A combination of electrosorption and ultraporous
filtration is described in "Removal of arsenic and humic substances
(HSs) by electro-ultrafiltration (EUF)" (Weng, Y.-H. et al., Chem.
Eng. R&D Vol. 77, July 1999, pages 461-468). In that case, an
increase of 30% to 90% in the adsorption of negatively charged
arsenic (V) during the filtration of arsenic-contaminated water is
achieved by ultrafiltration by establishing an electric field by
means of an external electrode that is positioned near an
ultrafiltration membrane. A similar use of electrosorption in
combination with membranes is described in US 2013/0240361 A1. The
purification of dialysis water is described in a combination of
substances with highly adsorptive properties and the regeneration
thereof by electrical charging. The method is carried out in
conjunction with a dialysis membrane filter.
[0012] An electrosorption membrane is described in EP 0872278 A1.
Here, a ceramic membrane is provided with a conductive layer of
pyrolytic carbon. The pores are sealed with pyrolytic carbon, and
the ceramic surface is then rendered conductive through
high-temperature conversion of the ceramic surface to carbide. With
this ceramic membrane, salts were adsorptively bound on the surface
by electrosorption. Possible electrosorption on the conductive
surface of a ceramic membrane allows for a more flexible sorption
of substances but is very expensive to achieve. The pores of the
membrane are sealed during the process for producing the conductive
surface, and the ceramic surface is provided with a conductive
carbide layer in a subsequent production step by means of very high
temperatures.
[0013] In addition to the advantages of membranes that have been
positively or negatively charged by chemical treatment--namely the
combination of mechanical filtration and adsorption--they also have
a drawback. Since the charge cannot be varied, the substances that
have been adsorptively bound can be removed again or recovered once
the membrane has been loaded only by shifting the charge through a
solution to be filtered, generally by means of a change in pH. In
particular, this represents an additional expense during the
recovery of active substances such as proteins through
concentration. Endotoxins are denatured by shifting the pH into the
basic range. But this pH shift would be necessary in order to
recover endotoxins from a positively charged membrane. It is
therefore not possible to obtain endotoxins--from blood, for
example--by means of permanently charged membranes in order to
subsequently convert them into a colorless liquid and forward them
for easier analysis.
SUMMARY
[0014] The object is to establish a method for the at least
temporary separation and/or detection of charged biologically
active substances, particularly endotoxins, from liquids,
particularly from colored liquids.
[0015] The object is also to establish a method for the at least
temporary retention of charged biologically active substances,
particularly endotoxins, in order, for example, to enable the
content of endotoxins to be determined independently of the other
substances of the original fluid.
[0016] It is also the object to provide a corresponding device.
[0017] The objects are achieved by a method for the at least
temporary separation and/or detection of charged biologically
active substances in a liquid by means of electrosorption and/or
electrofiltration, comprising the steps of a. providing a polymer
membrane with a flat and porous metal coating at least on a first
side of the polymer membrane; b. providing a counterelectrode; c.
applying a voltage between the metal coating of the polymer
membrane and the counterelectrode; and d. bringing the polymer
membrane and the counterelectrode into contact with the liquid,
with the contacting being performed such that the liquid generates
at least one connection between the polymer membrane and the
counterelectrode. The objects are further achieved by an
electrofiltration and/or electrosorption device comprising at least
one polymer membrane with a flat and porous metal coating on at
least one side of the polymer membrane and a contact of the metal
coating and a counterelectrode and, in particular, an additional
electrode, wherein the polymer membrane and the counterelectrode
are arranged in a housing that is embodied particularly as a
syringe attachment and/or has a small hold-up volume, particularly
of no more than 10 ml and/or no more than 20 mm.sup.3/mm.sup.2 of
metal coating on the polymer membrane, particularly no more than 2
mm.sup.3/mm.sup.2 of metal coating on the polymer membrane, and/or
wherein the polymer membrane and the counterelectrode are connected
to a voltage source that is configured to form a voltage between
polymer membrane and counterelectrode, wherein the voltage source
with the polymer membrane and the counterelectrode are arranged
particularly in a common housing, and/or a current-measuring device
is provided that measures the current flowing between polymer
membrane and counterelectrode and/or the rate of change thereof
and/or compares it with a limit value, and/or the voltage source is
configured to reverse and/or reduce the polarity of the
voltage.
[0018] Advantageous developments include a method wherein step c
takes place after steps a and b and before step d, and/or wherein
step d takes place after steps a and b and before step c. Further
advantageous developments include a method wherein, after steps a
to d, the liquid is removed at least partially and/or the liquid is
allowed to pass through the membrane at least partially. The method
may further include that after steps a to d, a polarity reversal
and/or reduction of the voltage takes place, with rinsing of the
membrane being performed particularly before and/or after the
polarity reversal and/or reduction. The polymer membrane with a
flat and porous metal coating and the counterelectrode are
accommodated in a housing, which, in particular, has a small
hold-up volume, particularly of no more than 10 ml and/or no more
than 20 mm.sup.3/mm.sup.2 of metal coating on the polymer membrane,
particularly no more than 2 mm.sup.3/mm.sup.2 of metal coating on
the polymer membrane, and the liquid to be filtered is conducted
through the housing. In the method, the liquid is pressed out of a
syringe against the polymer membrane with a flat and porous metal
coating or through the polymer membrane with a flat and porous
metal coating and/or through the housing through actuation of the
syringe. The counterelectrode is formed either by an additional
flat, porous metal coating on a second side that is situated
opposite the first side, the two-dimensional metal coatings being
isolated from each other by the polymer membrane, or through
arrangement of a permeable electrode that is formed particularly by
a metallic mesh with interposition of an insulating and permeable
spacer. The method is characterized in that the porosity of the
polymer membrane with metal coating is reduced by between 1% and
50%, in particular 1 and 20% relative to the initial bubble point
pore and/or the mean pore size compared to the uncoated polymer
membrane. The method is further characterized in that the thickness
of the metal coating is from 5 to 50 nm and the pore size of the
uncoated polymer membrane is particularly greater than 0.01 .mu.m.
The method is used for determining the occupancy of the binding
sites of the polymer membrane with a flat and porous metal coating
and/or for determining at least one concentration in the liquid,
wherein the current flow caused by the applied voltage is detected
and/or evaluated, particularly evaluated with regard to falling
below a limit and/or exceeding a positive and/negative rate of
change, and an alarm is triggered particularly in the case of an
undershoot or overshoot.
[0019] Further advantageous developments in the electrosorption
and/or electrofiltration device include that the counterelectrode
is either formed by an additional flat, porous metal coating on a
second side that is situated opposite the first side or by a
permeable electrode that is formed particularly by a metallic mesh
with interposition of an insulating and permeable spacer. In the
electrosorption and/or electrofiltration device, the porosity of
the polymer membrane with metal coating is reduced by between 1%
and 50%, in particular 1 and 20% relative to the initial bubble
point pore and/or the mean pore size compared to the uncoated
polymer membrane. Furthermore, in the electrosorption and/or
electrofiltration device, the thickness of the metal coating is
from 5 to 50 nm and the pore size of the uncoated polymer membrane
is particularly from 0.01 .mu.m to 15 .mu.m.
[0020] The production of a polymer membrane with a flat and porous
metal coating for use in the method and/or the device can be
achieved through deposition by means of magnetron sputtering. This
allows for the large-scale production of thin layers with a
homogeneous layer thickness as well as a complex layered structure.
The basis of the magnetron deposition is a plasma discharge in an
inert gas atmosphere, e.g., argon, that is amplified by a static
magnetic field (A. Anders, Handbook of Plasma Immersion Ion
Implantation and Deposition, Wiley-VHC, 2004). The ions of the
process gas are accelerated cathode, knocking atoms out of the
cathode on impact. Consequently, the cathode (target) must be made
of the material that is to be deposited. The atoms knocked out of
the target then condense on the substrate to be coated and form a
continuous thin layer. This layer thickness can be produced in a
controlled manner so as to be from few nanometers to several
micrometers. Besides round magnetrons, rectangular variants that
are several meters in length are widely used above all for coating
large surfaces, for example in architectural glass coating.
Surfaces of membranes can be coated in this way.
[0021] In order to produce the polymer membrane with a flat and
porous metal coating, a polymer membrane (for example, polysulfone,
polyethersulfone, polypropylene, or polyvinylidene fluoride) can be
provided with a thin layer of metal by means of the magnetron
sputtering process. The residence time of the membrane in the
process is selected so as to be short enough that the temperature
remains below 200.degree. C., particularly below 100.degree. C.,
and the original chemical structure of the polymer membrane is not
affected. As an example, a polyethersulfone membrane having a
microporous structure was provided with a 20 nm-thin layer of
aluminum. Porosity analyses were performed on this membrane. The
following table shows the results of the porosity measurement of
the membrane in the original state on the one hand and with a layer
of aluminum with a defined thickness of 20 nm on the other
hand.
TABLE-US-00001 TABLE 1 Pore size of a microporous polyethersulfone
membrane in the original and with a 20 nm-thick layer of aluminum.
Polyethersulfone membrane Difference 20 nm coating Al Original %
Bubble point pore size (.mu.m) 0.51 0.56 8.5 Mean pore size (.mu.m)
0.41 0.43 6.1 Smallest pore size (.mu.m) 0.37 0.39 5.5
[0022] It can be seen that the porosity of the membrane is
influenced to below 10%.
[0023] The metal coating is applied at least two-dimensionally to a
first side of the polymer membrane and/or at least to the surfaces
that can be accessed from one side, particularly until the layer
thickness of the metal coating of the polymer membrane is between
1% and 45% relative to the initial bubble point pore and/or the
mean pore size of the uncoated polymer membrane.
[0024] Particularly with a preferred coating up to a thickness of
up to 200 nm, it is possible to hardly influence the pore size of
the polymer membrane, in particular the polysulfone membrane,
particularly in the range from 0.1 .mu.m to 10 .mu.m, and to thus
leave it largely unchanged.
[0025] The coating is particularly porous and, in particular,
applied directly.
[0026] Copper, aluminum, silver, gold, nickel, platinum, and/or
tungsten or alloys containing copper, aluminum, silver, gold,
nickel, platinum, and/or tungsten can be used as the metal for the
coating.
[0027] Membranes of polysulfone, polypropylene, polyethersulfone,
polyetherimide, polyacrylonitrile, polycarbonate, polyethylene
terephthalate, polyvinylidene fluoride (PVDF), and/or
polytetrafluoroethylene or membranes containing polysulfone,
polypropylene, polyethersulfone, polyetherimide, polyacrylonitrile,
cellulose, polycarbonate, polyethylene terephthalate,
polyvinylidene fluoride (PVDF), and/or polytetrafluoroethylene can
be used as the polymer membrane, for example.
[0028] It is with particular advantage that metal is deposited
until the layer thickness of the metal coating of the polymer
membrane is between 1% and 45% relative to the initial bubble point
pore and/or the mean pore size of the uncoated polymer
membrane.
[0029] These values enable good conductivity to be combined with
good throughput and high porosity.
[0030] Preferably, metal is deposited until the porosity of the
polymer membrane with metal coating is reduced by between 1% and
50%, in particular 1 and 20% relative to the initial bubble point
pore and/or the mean pore size compared to the uncoated polymer
membrane. These values also enable good conductivity to be combined
with good throughput and high porosity.
[0031] Preferably, metal is deposited until the initial bubble
point pore and/or the mean pore size of the polymer membrane with
metal coating and/or aluminum oxide is 0.01 to 10 .mu.m. For this
purpose, the polymer membrane is selected so as to have an initial
bubble point pore and/or mean pore size of greater than 0.01 to 10
.mu.m.
[0032] Advantageously, the polymer membrane is coated on the first
side and on a second side that is situated opposite the first side
porously and directly with metal. In particular, the
two-dimensional coatings, including metallizations, are
electrically insulated from one another.
[0033] Through omission of the coating of the porous passages and
of the edges to the extent that no conductive connection is formed
between the two sides, a membrane with two electrically conductive
and mutually insulated surfaces can be produced.
[0034] Advantageously, metal has been deposited until the thickness
of the metal coating or the mean thickness of the metal coating is
at least 1 nm, particularly at least 5 nm, and no more than 50 nm.
These values of at least 5 nm enable good conductivity to be
combined with good throughput and high porosity.
[0035] Advantageously, the pore size of the uncoated polymer
membrane is selected so as to be between 0.01 and 15 .mu.m,
particularly up to 10 .mu.m, and/or greater than or equal to 0.1
.mu.m. This enables a sealing of the pores with metal to be
prevented particularly well.
[0036] Advantageously, metal has been deposited until the thickness
of the metal coating of the pores within the membrane or the mean
thickness of the metal coating of the pores within the membrane is
at least 1 nm and no more than 50 nm.
[0037] The object is also achieved through the use of a
metal-coated polymer membrane having porous passageways, the
metal-coated polymer membrane having an internal polymer membrane
with porous passages and a metal coating, characterized in that the
polymer membrane is completely encapsulated by the metal coating
and the metal coating has a thickness of from 1 nm, particularly 5
nm, to 500 nm.
[0038] In particular, the coating is applied directly to the
polymer membrane. In particular, the coated polymer membrane
consists exclusively of the polymer membrane and the metal
coating.
[0039] To special advantage, the polymer membrane with metal
coating thus has a porosity that is reduced by between 1% and 50%,
particularly 1% and 20% relative to the initial bubble point pore
and/or the mean pore size compared to the uncoated polymer
membrane.
[0040] For example, the membrane can also be folded and/or used in
folded form as is known in conventional membranes. In particular,
at least one insulating folding aid is used and/or included,
particularly on each side of the membrane. These allow for passage
of liquid and, in particular, provide for insulation of the
individual folds from one another.
[0041] In particular, the at least one folding aid is arranged on
one or both sides of the membrane prior to folding and folded
together with the membrane. The folding aids need not be made
completely of insulating material; for instance, a polymer fleece
can be used that is particularly coated in an electrically
conductive manner on one side or both sides, but the fleece itself
provides for insulation.
[0042] According to the method, in order to achieve the object of
the at least temporary separation and/or detection of charged
biologically active substances, [0043] a. a polymer membrane with a
flat and porous metal coating, particularly as described above, is
provided at least on a first side, particularly on both sides, of
the polymer membrane; [0044] b. a counterelectrode is provided;
[0045] c. a voltage is applied between the metal coating of the
polymer membrane and the counterelectrode; [0046] d. the polymer
membrane and, in particular, the counterelectrode are brought into
contact with the liquid, with the contacting being performed
particularly such that the liquid generates at least one connection
between the polymer membrane and the counterelectrode.
[0047] By means of such a method, it is possible to adsorb and/or
retain, and hence particularly to separate charged substances,
particularly biologically active charged substances, as well as
other charged substances at least temporarily from liquids--for
example from blood--through binding to the polymer membrane with
metal coating. At the same time, a much more customized and
flexible process control can be achieved than is possible with
known (ionically) charged membranes. Detachment into another
liquid, for example--for the purpose of recovery, for example--can
also be facilitated, particularly without the need to change a pH
value, by reversing the voltage, which does not presuppose the same
level of voltage with an reversed sign, but rather can also be of a
lower or higher magnitude, and/or by decreasing the voltage.
[0048] The amount of voltage is advantageously no more than 1.5 V.
In particular, the amount of voltage is no more than 1.5 V even
after a polarity reversal. The voltage or the energy required to
generate it can be transferred capacitively, inductively, and/or by
cable, for example. In particular, the voltage or the energy
required to generate it can be transferred, especially inductively,
into a housing that encloses the polymer membrane and the
counterelectrode. For example, the voltage or the energy required
to generate it can be inductively coupled into the housing and
applied to the polymer membrane and the counterelectrode within the
housing via cables.
[0049] The expression "charged biologically active substances" is
to be understood as referring to a variety of substances. A more or
less specific retention, separation, and/or a more or less specific
detection of individual or numerous substances can be made
possible, for example, through targeted selection of the voltage
and/or of the membrane surface. A retention and/or an adsorption
against/by the membrane of more highly charged particles is already
possible at lower voltages than for less-highly charged particles.
This allows for a certain selectivity through selection of the
voltage. It is not imperative that only a single substance be
separated and/or detected. Examples of suitable biologically active
substances include viruses, bacteria, endotoxins, proteins, amino
acids, zwitterions, substances with an isoelectric point, exosomes,
and/or vesicles. They need not have a charge in every environment
in order to be regarded as charged. It is sufficient that they have
a charge in a state in which they are or can be brought into
contact with the membrane; in particular, they are present in the
liquid at least partially in a charged state. Thus, separation
and/or detection, particularly of proteins, more particularly
viruses, is performed particularly in a solution having a pH at
which the substances to be retained and/or adsorbed have the
greatest possible charge, particularly relative to substances that
are not to be retained or adsorbed.
[0050] In general, polymer membrane with metal coating and, in
particular, the counterelectrode as well are extensively brought
into contact with the liquid, particularly wetted over a large
area. A contact or connection over a small area--by means of a drop
between the counterelectrode and polymer membrane with metal
coating, for example--is already sufficient, however. Contacting
can also be achieved by filling one or a plurality of pores of a
two-sided metallically coated polymer membrane, one side of which
is used as a counterelectrode.
[0051] To special advantage, the counterelectrode is formed either
by an additional flat, porous metal coating on a second side that
is situated opposite the first side, the two-dimensional metal
coatings being isolated from each other by the polymer membrane, or
through arrangement of a permeable electrode that is formed
particularly by a metallic mesh and/or a rod electrode with
interposition of an insulating and permeable spacer and/or with
spacing.
[0052] Advantageously, the porosity of the polymer membrane with
metal coating is selected so as to be reduced by between 1% and
50%, in particular 1 and 20% relative to the initial bubble point
pore and/or the mean pore size compared to the uncoated polymer
membrane. This provides reliable conductivity and large porosity at
the same time.
[0053] Advantageously, the polymer membrane is selected such that
the thickness of the metal coating is 1 nm, particularly 5 to 50
nm, and/or the pore size of the uncoated polymer membrane is
particularly greater than 0.01 .mu.m and particularly less than 15
.mu.m. This provides reliable conductivity and large porosity at
the same time.
[0054] To special advantage, a reference electrode is provided for
measurement purposes and the potential at the reference electrode
is measured.
[0055] Advantageously, in addition to the polymer membrane with
metal coating that is used according to the invention as an
electrode and counterelectrode and, optionally, as a reference
electrode, at least one additional electrode is provided,
particularly at least one additional polymer membrane with a metal
coating or an additional side of the polymer membrane with a metal
coating, particularly as explained above, provided as an additional
electrode. In particular, this additional electrode is likewise
arranged in the common housing and is insulated electrically from
the polymer membrane with metal coating and the counterelectrode.
The common housing can also be an outer housing that encloses an
inner housing in which polymer membrane and counterelectrode are
arranged.
[0056] In particular, a voltage is applied to the at least one
additional electrode that is selected such that the potential of
the counterelectrode comes to lie between the potential of the
polymer membrane with metal coating and of the at least one
additional electrode. In particular, the counterelectrode is
arranged in the housing between the polymer membrane with metal
coating and the at least one additional electrode.
[0057] In this case, it can also be expedient to use a plurality of
reference electrodes and to respectively arrange them between the
electrodes and/or counterelectrode.
[0058] Electrosorption experiments were conducted on a
polyethersulfone membrane with a pore size of 0.2 .mu.m in an
arrangement as shown in FIG. 1. A laboratory filtration membrane
with a diameter of d=47 mm was provided for this purpose with a 15
nm layer of aluminum by means of magnetron sputtering. A copper
cable was glued to the aluminum surface and provided with an
insulating varnish. The remaining cable was about 30 cm long and
insulated. The membrane was placed in a commercial vacuum
filtration unit. The receiving vessel was filled with pure water
and a platinum counterelectrode introduced therein.
[0059] Endotoxins were introduced into the pure water in the
receiving vessel so that an endotoxin concentration of 1,000 IU
(international units endotoxin) was achieved. Filtration was
carried out without pressure. Filtration was performed with the
membrane in the original state without a coating and with a
membrane with a 15 nm coating. A voltage of 500 mV was applied to
the coated membrane. The results are shown in the following
table.
TABLE-US-00002 Concentration of ml endotoxin in IE/ml Sample feed
collecting vessel volume Filter without coating 1000 952.5 100
Filter with coating at +500 mV 1000 0.3 50
[0060] It can clearly be seen that endotoxins are retained,
particularly adsorbed almost completely via the charged aluminum
coating, so that the concentration in the collecting vessel is
close to zero. Little was adsorbed not only the polymer membrane in
the original state without metal coating, but also the metal-coated
polymer membrane without voltage.
[0061] The adsorbed endotoxins can be released again and removed
from the membrane by reversing the polarity of the voltage and
rinsing the membrane.
[0062] Similar to the endotoxin retention experiment described
above, virus retention can also be achieved. It is known that
viruses have a negative charge above their isoelectric point and
can be adsorbed on surfaces with a positive charge (Adsorption of
viruses to charged modified silica, Zerda et al., Applied and
Environmental Microbiology, January 1985, p. 91-. Using the same
experimental setup as described above in relation to the retention
of bacteria, experiments were conducted on the retention of
viruses. Bacteriophages MS2 with a size (diameter) of 25 nm were
used. The isoelectric point of these bacteriophages is at pH 3.9.
15 ml of an aqueous solution of 10.sup.5 PFU/ml (plaque-forming
units/ml) were filtered through the membrane; the pH of the
solution was 7. Membranes of polyethersulfone 0.2 .mu.m without a
coating and with a coating of titanium (20 nm) and a coating of
gold (20 nm) were investigated. The following table shows the
results of the experiments:
TABLE-US-00003 Coating Voltage in volts Retention in Log 10 without
0.0 0.1 Titanium 0.0 0.05 Titanium 1.0 1.4 Gold 0.0 <0.01 Gold
1.0 2.4
[0063] It is apparent from the results of the retention
experiments--particularly for adsorption, without a coating, and
without voltage--that a low level of virus retention is achieved on
the membrane without a coating. Polymer membranes have a zeta
potential (surface tension) without a coating. Titanium and gold
have a lower zeta potential (near zero). So it is understandable
that without voltage on the membrane without a coating, the most
viruses are adsorbed in comparison to the coated membranes, since a
gold or titanium coating of the membrane reduces the zeta potential
and thus the charge of the membrane.
[0064] Considering the results of the tests for adsorption under a
voltage of 1.0 volts, virus retention on the order of 1.4
log.sub.10 (i.e., a retention of >95%) is achieved with the
titanium coating, and virus retention on the order of 2.4
log.sub.10 (i.e., >99% retention) is achieved with a gold
coating. It was able to be shown that, by means of a membrane that
is provided with a metal layer and an applied voltage of 0.5 volts
or 1.0 volts, a significant improvement of the retention,
particularly adsorption, of endotoxins as well as of viruses can be
achieved in comparison to an uncharged membrane.
[0065] In addition, after switching the voltage in the experiments
for the retention of endotoxins from +500 mV to -500 mV, at least
50% of the adsorptively bound endotoxins were able to be recovered
back into the water by rinsing the membrane with water. This
demonstrates that at least some of the endotoxins are desorbed by
reversing the voltage.
[0066] The object is also achieved by a method for determining the
occupancy of the binding sites of the polymer membrane with a flat
and porous metal coating and/or for determining at least one at
least relative concentration in the liquid, this method building on
the method for the at least temporary separation and/or detection
of charged biologically active substances in a liquid and can make
use of all advantageous embodiments and is characterized in that
the current flow caused by the applied voltage is detected and/or
evaluated, particularly evaluated with regard to falling below a
limit and/or exceeding a positive and/negative rate of change
and/or its time course, and an alarm is triggered particularly in
the case of an undershoot or overshoot. This enables concentration
limits or rates of change of concentrations to be monitored, for
example.
[0067] Such monitoring can be performed very closely and even in
real time. For instance, it is possible to monitor the endotoxin
concentration in the blood. The current flow is dependent on the
occupancy of the binding sites on the membrane. If fewer binding
sites are available, the current flow drops. The concentration need
not be determined as an absolute value, however; it is also
sufficient to detect under- or overshooting of reference values,
and the reference values can also be indicated in the form of
current flows.
[0068] For instance, an alarm can occur when certain concentration
limits and/or rates of change are exceeded, particularly measured
as the rate of change of the current flow, e.g., acoustically,
optically, and/or electrically.
[0069] The object is achieved by electrosorption and/or
electrofiltration device comprising a counterelectrode and a
polymer membrane with a flat and porous metal coating on at least
one side of the polymer membrane, particularly as described above,
and a contact of the metal coating for the purpose of applying a
voltage to the counterelectrode. The above applies here to the
device as well, particularly with regard to electrode, membrane,
coating, counterelectrode, reference electrode, and/or
arrangement.
[0070] The polymer membrane and, in particular, the
counterelectrode as well are arranged in a housing that is embodied
particularly as a syringe attachment and/or has a small hold-up
volume, particularly of no more than 10 ml and/or no more than 20
mm.sup.3/mm.sup.2 of metal coating on the polymer membrane,
particularly no more than 2 mm.sup.3/mm.sup.2 of metal coating on
the polymer membrane, and/or the polymer membrane and the
counterelectrode are configured to be or are connected to a voltage
source that is set up to form a voltage between the polymer
membrane and the counterelectrode, the voltage source being
arranged particularly in a common housing with the polymer membrane
and the counterelectrode and/or a current-measuring device being
provided that measures the current flowing between the polymer
membrane and the counterelectrode and/or measures its rate of
change and/or compares it with a limit value, and/or the voltage
source being configured to reverse the polarity of the voltage.
[0071] For the purpose of connecting to a voltage source and/or
contacting the metal coating, the metal coating of the membrane
can, for example, be connected directly to and/or brought into
contact with an electrical conductor, e.g., a cable, for example by
soldering or welding. In addition or alternatively, however, it can
also be brought into contact with other electrically conductive
components--e.g., with a cage into which the membrane is inserted
and/or with at least one conductive coated folding aid--and
connected to the voltage source by means of these and, optionally,
additional components and/or cables and/or contacted by same.
[0072] It is also possible to incorporate an inductive and/or
capacitive coupling into the connection to the voltage source so
that it is also possible, for example, to connect the voltage
source through a closed housing without corresponding cable
feedthroughs.
[0073] The common housing can also be an outer housing that
encloses an inner housing in which polymer membrane and
counterelectrode are arranged.
[0074] In particular, a residence volume for liquid is provided in
the housing in which liquid can dwell or through which liquid can
be moved. The flat and porous metal coating of the polymer membrane
and, in particular, the counterelectrode are then arranged within
this volume. This residence volume is arranged particularly in
liquid-permeable connection with at least one, particularly two
connections for hoses and or syringes, particularly in the form of
a Luer-lock connection. In particular, this residence volume
together with the volume of the at least one, particularly two
connections and the liquid-permeable connection represents the
hold-up volume.
[0075] The device can also include a device for generating a
voltage, e.g., a battery, particularly in the common housing, that
is particularly arranged and/or contacted such that it can generate
a potential between metal coating of the polymer membrane and
counterelectrode.
[0076] The device is embodied particularly as a pre-filter and/or
syringe attachment.
[0077] In particular, counterelectrode and polymer membrane with a
flat and porous metal coating are electrically insulated from one
another.
[0078] Electrosorption and/or electrofiltration device particularly
has a vessel and/or housing for the purpose of arranging and
conducting liquid through as well, the polymer membrane and the
counterelectrode being arranged so as to be electrically insulated
from one another.
[0079] The electrosorption and/or electrofiltration device can
include one or more reference electrodes.
[0080] It can also advantageously contain at least one additional
electrode as described above in relation to the electrosorption
and/or electrofiltration process.
[0081] The other features described in relation to this method can
also be advantageously implemented in the electrosorption and/or
electrofiltration device.
[0082] The polymer membrane with metal coating is advantageously a
metal-coated polymer membrane as described above. These are
especially suitable, particularly if the porous passages are also
coated with metal. Since the electrically active surface is then
substantially larger. However, other metal-coated polymer membranes
can also be used.
[0083] To special advantage, the counterelectrode is either an
additional flat, porous metal coating on a second side that is
situated opposite the first side or a permeable electrode that is
formed particularly by a metallic mesh with interposition of an
insulating and permeable spacer.
[0084] In particular, the device for carrying out the method for
the at least temporary separation and/or detection of charged
biologically active substances is advantageously configured with
some or all advantageous features. In particular, it is also
configured to carry out the method for determining the occupancy of
the binding sites of the polymer membrane with a flat and porous
metal coating and/or for determining at least one concentration in
the liquid. The method is carried out particularly with a device
according to the invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0085] Additional advantageous embodiments are to be explained
below purely for the sake of example with reference to the
schematic drawing that follows. In the drawing:
[0086] FIG. 1 shows an electrofiltration device according to the
invention;
[0087] FIG. 2 shows an electrofiltration device according to the
invention as a syringe attachment filter; and
[0088] FIG. 3 an electrofiltration device according to the
invention with a folded membrane that is embodied as a cartridge in
a housing.
DETAILED DESCRIPTION
[0089] FIG. 1 shows an electrofiltration device according to the
invention. The electrofiltration method according to the invention
can be carried out with this.
[0090] A liquid is introduced into the receiving vessel (5) and
filtered into the collecting vessel (3) through the membrane (6),
which is formed by a metal-coated polymer membrane, with
application of a voltage, applied by a potentiostat (4), between
the membrane (6) that is embodied as an electrode, and
counterelectrode (2). The frit (7) serves the purpose of
stabilizing the membrane.
[0091] FIG. 2 shows an electrofiltration device according to the
invention in the form of a syringe attachment filter. Shown is a
circular membrane (8) made of polymer material and metallized on
one or both sides. The metallization can be applied to one side,
upstream from the membrane (top of the figure) or downstream from
the membrane (bottom of the figure), or to both sides. In the case
of application to both sides, the metallized sides are particularly
insulated from one another.
[0092] In principle, FIG. 2 shows two possible embodiments in one
figure. Either all parts that are designated by the suffix b are
omitted, or all parts that are designated by the suffix a.
[0093] In particular, the filter also has at least one
counterelectrode (10a or 10b, 12a or 12b). This can be embodied as
a metal mesh, for example.
[0094] Electrically insulating but permeable release films (9a or
9b) that allow the flow of a liquid in the direction indicated by
the arrows, but provide electrical insulation between the circular
membrane (8) and counterelectrode (10a or 10b) can be included.
However, an embodiment without such a dividing line is also
possible if insulation is ensured by means of other constructive
measures.
[0095] The syringe attachment filter has a filter inlet (13). It
also has a filter outlet (14). These can include feedthroughs for
contacting. These can be achieved by cable but also inductively,
capacitively, by means of plugs, and/or the like.
[0096] Electrical conductors (12a or 12b and 11a or 11b) are also
included. The conductors (12a or 12b) themselves can also serve as
counterelectrodes and thus replace the counterelectrodes (10a or
10b).
[0097] Filter inlet and filter outlet are particularly part of a
housing for the hermetic sealing of the entire filter, so that a
loss of liquid is only possible between the filter inlet and filter
outlet and only by passing through the elements that are arranged
in the liquid flow, such as circular membrane, trend film, and
counterelectrode, insofar as they are embodied as a permeable or
mesh.
[0098] The syringe attachment filter is embodied so as to enable a
potential to be applied between metallization of the circular
membrane and counterelectrode. For this purpose, it particularly
has corresponding conductors, feedthroughs, and/or contacting
and/or transmission devices (in particular inductive and/or
capacitive). The voltage can be applied, for example, via a voltage
source (15a or 15b) and electrical conductors (12a or 12b and 11a
or 11b).
[0099] With the aid of such a syringe attachment filter with a
voltage source (15a or 15b), substances contained in the liquid,
such as endotoxins, can be adsorbed on the circular membrane (8)
under a first polarization of the voltage source when liquid,
particularly blood, is passed through the syringe attachment
filter.
[0100] Later, the substances can be discharged, particularly under
reverse polarization or without voltage and with the passage of
another liquid, e.g., water, particularly counter to the direction
of flow shown by the arrows.
[0101] FIG. 3 shows a cartridge according to the invention in a
housing with a folded membrane (16). According to the prior art,
such fluted filter cartridges are prepared as follows: [0102] 1.
The membrane (16) is positioned and folded between two folding aids
(17a and 17b), which are particularly made of a polymer fleece
and/or film. [0103] 2. The finished folded membrane is pressed into
a round cage (18) so that it does come unfolded again and is
provided with a core. Cage and core are particularly made of
plastic and, in particular, configured such that liquid can pass
through, particularly provided with rectangular or round holes.
[0104] 3. The membrane with folding aid and cage and core are
welded to the upper closure of a sealed plastic cap and then welded
to the lower closure (plate with opening).
[0105] The same procedure was also used in this exemplary
embodiment and can generally be used with the membrane that is
included and/or used according to the invention.
[0106] FIG. 3 shows a circular membrane (16) made of polymer
material and metallized on one or both sides. The metallization can
be applied to one side, upstream from the membrane (on the outside
in the figure) or downstream from the membrane (on the inside in
the figure), or to both sides. If it is applied to both sides, the
metallized sides are particularly insulated from one another by the
membrane itself. The membrane is folded particularly by means of
folding aids that are folded with the membrane and consist
particularly of a polymer fleece (17a, b). The polymer fleece can
be embodied both as a conductive fleece (with metal coating on both
sides) or as a voltage-insulating fleece.
[0107] In principle, FIG. 3 shows two possible embodiments in one
figure. Either all parts that are designated by the suffix b are
omitted, or all parts that are designated by the suffix a. In the
variant in which the parts that are denoted with the suffix a are
included, the membrane is contacted directly via an electrical line
as an electrode, or in the variant in which the parts that are
denoted with the suffix b are included, the membrane is contacted
as an electrode via an electrically conductive folding aid (17b)
and via an electrically conductive core that holds the folded
membrane.
[0108] In particular, the filter also has at least one
counterelectrode (25a or 25b). This can be embodied as a metal mesh
and/or rod electrode, for example.
[0109] The filter that is embodied as a cartridge with folded
membrane has a filter inlet. It also has a filter outlet (23).
These can include feedthroughs for contacting. These can be
achieved by cable but also inductively, capacitively, by means of
plugs, and/or the like.
[0110] Electrical conductors (24a and 25a or 24b and 25b) are also
included. The conductors (25a or 25b) can serve as
counterelectrodes and thus replace the counterelectrodes.
[0111] Filter inlet and filter outlet are particularly part of a
housing for the hermetic sealing of the entire diaphragm so that a
loss of liquid is only possible between the filter inlet and filter
outlet and only by passing through the elements that are arranged
in the liquid flow, such as membrane and counterelectrode, insofar
as they are embodied as a permeable or mesh.
[0112] The cartridge with folded membrane is embodied so as to
enable a potential to be applied between metallization of the
membrane and counterelectrode. For this purpose, it particularly
has corresponding conductors, feedthroughs, and/or contacting
and/or transmission devices (in particular inductive and/or
capacitive). The voltage can be applied, for example, via a voltage
source (26a or 26b) and electrical conductors (25a or 25b and 24a
or 24b).
[0113] With the aid of such a cartridge with folded membrane with a
voltage source (26a or 26b), substances contained in the liquid can
be adsorbed on the folded membrane (8), for example under an
initial polarization of the voltage source upon passage of liquid
through the cartridge with folded membrane.
[0114] Later, the substances that were previously bound
electrosorptively to the folded membrane of the filter can be
desorbed, particularly under reverse polarization or without
voltage and, in particular, with the passage of another liquid,
e.g., water, particularly counter to the direction of flow
indicated by the arrows.
LIST OF REFERENCE SYMBOLS
[0115] 1 cable [0116] 2 counterelectrode [0117] 3 collecting vessel
[0118] 4 potentiostat [0119] 5 receiving vessel [0120] 6 diaphragm
[0121] 7 frit [0122] 8 circular membrane (polymer) with
metallization on one side (upstream or downstream) or on both sides
[0123] 9 a and b electrically insulating, permeable release film
[0124] 10 a and b counterelectrode upstream (a) and downstream (b)
from the switchable circular membrane 1 in the form of a permeable
metal mesh [0125] 11 a metal wire for contacting of the
upstream-side metallization of the circular membrane 8 [0126] b
metal wire for contacting of the downstream-side metallization of
the circular membrane 8 [0127] 12 a and b electrical conductor to
the counterelectrode/metal mesh 10a and 10b [0128] 13 filter inlet
with feedthrough(s) for electrical contacting of electrode/membrane
and counterelectrode [0129] 14 filter outlet, optionally with
feedthrough for electrical contacting of the counterelectrode/metal
mesh [0130] 15 a voltage source for applying electrical potential
to electrode and counterelectrode [0131] b voltage source for
applying electrical potential to electrode and counterelectrode
[0132] 16 folded membrane [0133] 17 a and b electrically
insulating, permeable release film in front of or behind the
membrane [0134] 18 conductive outer sleeve of the cartridge [0135]
19 conductive inner sleeve of the cartridge [0136] 20 upper closure
member and baffle plate of the cartridge [0137] 21 lower closure
member and outlet of the cartridge [0138] 22 22 filter inlet and
filter housing [0139] 23 filter outlet and filter housing [0140] 24
a contact bushing for electrical contacting of the upstream
metallization of the membrane 16 [0141] b contact bushing for
electrical contacting of the downstream metallization of the
membrane 16 [0142] 25 a contact bushing and counterelectrode on the
upstream side of the metallized membrane 16 [0143] b contact
bushing for electrical contacting of the counterelectrode [0144] c
counterelectrode on the downstream side of the metallized membrane
16 [0145] 26 a voltage source for applying electrical potential to
electrode and counterelectrode [0146] b voltage source for applying
electrical potential to electrode and counterelectrode
* * * * *