U.S. patent number 3,566,871 [Application Number 04/736,181] was granted by the patent office on 1971-03-02 for hydrophilic medical sponge and method of using same.
This patent grant is currently assigned to American Cyanamid Company. Invention is credited to Charles Teets Riall, Ferdinand Joseph Richter.
United States Patent |
3,566,871 |
Richter , et al. |
March 2, 1971 |
HYDROPHILIC MEDICAL SPONGE AND METHOD OF USING SAME
Abstract
A hydrophilic polyurethane sponge adapted for medical usage, in
which the sponge pores contain a surfactant coating to accelerate
absorption of body fluids into the pores at medically preferred
rates, the fluids being retained therein by capillarity to affect
removal of the fluids from the body. The sponge is flexible, and
substantially free from lint, toxicity, and abrasiveness, making it
particularly suitable for use as a surgical laparotomy pad.
Inventors: |
Richter; Ferdinand Joseph
(Danbury, CT), Riall; Charles Teets (Danbury, CT) |
Assignee: |
American Cyanamid Company
(Stamford, CT)
|
Family
ID: |
24958838 |
Appl.
No.: |
04/736,181 |
Filed: |
June 11, 1968 |
Current U.S.
Class: |
604/362;
604/369 |
Current CPC
Class: |
A61L
15/425 (20130101); C08J 9/40 (20130101); C08J
2375/04 (20130101) |
Current International
Class: |
A61L
15/42 (20060101); A61L 15/16 (20060101); C08J
9/00 (20060101); C08J 9/40 (20060101); A61f
013/00 () |
Field of
Search: |
;128/285,290,296,156 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; Charles F.
Claims
I claim:
1. A hydrophilic sponge, adapted for medical usage, comprising a
flexible polyurethane foam:
a. the surfaces of said foam being nonabrasive towards internal
body organs;
b. said foam containing at least one zone of intercommunicating
pores extending inwardly from a surface of the foam;
c. said pores are of sufficiently small dimension to insure
retention of body fluids therein substantially by capillarity;
d. the surface of said pore zone is substantially free from
obstructions which inhibit flow of fluids into the pores;
e. substantially all of the internal surfaces of said pores having
a coating of at least one surfactant;
f. said surfactant being substantially nonfoaming when the sponge
is moistened;
g. said surfactant being nontoxic to living tissue;
h. said surfactant being a nonflowing liquid at room
temperature;
i. the thickness of said surfactant coating being insufficient to
cause a substantial reduction in pore volume, but sufficient to
initiate, without compression of said sponge, flow of body fluids
in contact with said sponge into the pore volume at a medically
preferred rate, said pores functioning as a reservoir for said
fluids; and
j. the quantity of surfactant is about 0.1 percent to about 25
percent by weight, based on the dry weight of the foam whereby
substantial amounts of fluid, based on the dry weight of the
sponge, are removable from their environment upon contact of said
fluid with said pore zone and subsequent removal of the sponge from
said environment.
2. The sponge of claim 1, having an X-ray opaque therein.
3. The sponge of claim 2, wherein the quantity of surfactant is
about 5 percent to about 10 percent by weight, based on the dry
weight of the foam, and said sponge is sterile at time of use.
4. The sponge of claim 3, wherein said surfactant contains a
hygroscopic agent uniformly dispersed throughout.
5. A medical sponge package comprising a sterile enclosure
containing therein the sponge of claim 2 in sterile condition.
6. A medical sponge package comprising an internally sterile
strippable outer envelope containing at least one sponge, as
defined in claim 2, in sterile conditions, in a sterile inner
envelope, whereby on stripping the outer envelope, the separate
sterilely wrapped sponges are sterilely released.
7. A hydrophilic sponge, adapted for medical usage, comprising a
flexible polyurethane foam:
a. the surfaces of said foam being nonabrasive towards internal
body organs;
b. said foam containing at least one zone of intercommunicating
pores extending inwardly from a surface of the foam;
c. said pores are of sufficiently small dimension to insure
retention of body fluids therein substantially by capillarity;
d. the surface of said pore zone is substantially free from
obstructions which inhibit flow of fluids into the pores;
e. substantially all of the internal surfaces of said pores having
a coating of at least one surfactant;
f. said surfactant being substantially nonfoaming when the sponge
is moistened;
g. said surfactant being nontoxic to living tissue;
h. said surfactant being a nonflowing liquid at room
temperature;
i. the thickness of said surfactant coating being insufficient to
cause a substantial reduction in pore volume, but sufficient to
initiate, without compression of said sponge, flow of body fluids
in contact with said sponge into the pore volume at a medically
preferred rate, said pores functioning as a reservoir for said
fluids;
j. the quantity of surfactant is about 5 percent to about 10
percent by weight, based on the dry weight of the foam;
k. said surfactant contains a hygroscopic agent uniformly dispersed
throughout; and
l. the surfactant is polyoxyethylene sorbitan mono-oleate and the
hygroscopic agent is glycerine and wherein said sponge comprises,
in its entirety, a single zone of intercommunicating pores, said
foam being polyurethane of the polyester type, being about 100
percent reticulated, and having about 100 pores per inch, whereby
substantial amounts of fluid, based on the dry weight of the
sponge, are removable from their environment upon contact of said
fluid with said pore zone and subsequent removal of the sponge from
said environment.
8. The sponge of claim 7, having an X-ray opaque therein, and being
sterile at time of use.
Description
BACKGROUND OF THE INVENTION
During surgery, there is frequent need for sponging various
portions of the body to remove body fluids such as blood, serum,
plasma, lymph, spinal fluid, tissue fluid, urine, sweat, bile
juice, and digestive juice. For example, during an initial surgical
incision it is common practice to blot the incision and the area
adjacent to the incision with sponges to remove blood and other
fluids emanating from the incision. After entering the thoracic
cavity, abdominal cavity, or other operating field, it is customary
to use sponges which have been moistened in saline solution to
isolate various organs from the operating field. This is done by
packing the organs with sponges to restrain them from entering the
operating field and thereby interfering with the operation. The
sponges are moistened in saline solution to prevent drying out
organs or tissue with which they come into contact.
Sponges are also used in specialized areas of surgery such as
ophthalmic surgery, neurosurgery, and spinal surgery, such sponges
often having a configuration especially adapted for these
particular uses.
GAUZE PAD PRIOR ART
At the present time, gauze pads are the most commonly used medical
sponges. These pads are prepared from modified cellulose or rayon
and are comprised of multilayers of sheets woven from multifilament
yarns. A radiopaque marker, such as barium sulfate dispersed in a
suitable carrier, is usually attached to the pad to assist in
locating the pad by X-ray should it be inadvertently left in the
body after surgery.
These pads have many disadvantages. Their edges often fray and they
tend to shed large amounts of lint. The lint is particularly
undesirable. It may pick up bacteria from nonsterile sections of
the operating room and then serve as a carrier of bacteria into the
exposed body cavity of the operative patient. Furthermore, the lint
particles, upon entering the body cavity, may create undesirable
foreign body reaction such as granulomata or adhesions, as
discussed in greater detail by Sturdy et al. in Annals of Surgery
165, pgs. 128--134 (1967 ).
Dry gauze pads may accumulate electrical charges, adding to the
explosion hazard in the operating room when anesthetics, such as
ether, are being used.
Gauze pads, particularly when dry, are highly abrasive towards
sensitive internal body organs. Since these pads are used to sponge
these organs and to pack the organs during surgery, the pads are
necessarily in intimate contact with the organs and can cause
serious trauma to the organs because of their abrasiveness. As the
pads absorb blood and other body fluids, they become progressively
less pliable and harder thus tending to continue their undesirable
abrasive affect upon organs even after becoming moist. In
considering the seriousness of the abrasive character of gauze
pads, it should be remembered that the surgeon or his assistant may
reposition the pad in the course of an operation, and may
frequently remove used pads and insert new ones.
During an operation, the surgeon may desire to cut a pad to a
smaller size for a special use. Not only are gauze pads difficult
to cut but, after cutting, they tend to fray extensively and to
shed lint.
A further disadvantage of the gauze pad is the risk of cross
contamination, arising from the common hospital practice of
rewashing and reusing the pads several times before they are
discarded. After the first laundering, the size of the pad may be
reduced as much as 30 percent. Shrinking continues in subsequent
washings, but at a reduced rate. The softness and flexibility
progressively diminish during repeated laundering. Before pads can
be reused, they must be resterilized as well as rewashed.
This invention envisions elimination of the above disadvantages by
providing a novel hydrophilic polyurethane sponge which is
eminently suitable for usage in medical applications such as those
described hereinabove.
POLYURETHANE SPONGE PRIOR ART
Prior art on hydrophilic or otherwise modified polyurethane foams
is voluminous. However, it can be conveniently broken down into
four categories.
The first category comprises foams which have been rendered
hydrophilic by chemical modification. This is commonly done by
adding a hydrophilic agent to the reaction mixture from which the
foam is prepared. For example, in U.S. Pat. No. 3,326,823, a
hydrophilic polymer is added to a reaction mixture containing a
polyisocyanate, a polyether having a monomer of hydrophilic
character grafted thereon, and an activator mixture to produce a
hydrophilic foam capable of absorbing up to 3.1 grams of water per
gram of dry sponge (measured by passing the sponge over the surface
of water without pressure), an amount unsuitable for use as a
medical sponge wherein water pick up of from 20 to 25 times the dry
sponge weight is desirable. U.S. Pat. No. 3,098,048 describes a
similar procedure for preparing a sponge containing an ethylene
oxide content of 30 to 80 percent. Unfortunately, this sponge foams
when wetted to release surfactant over long periods of time;
clearly, such a sponge would be unsuitable for medical use,
especially within a body cavity.
The second category comprises polyurethane foams which have been
impregnated with a hydrophilic agent. For example U.S. Pat. No.
3,224,889 describes a foam whose pores are coated with fine silica.
The sponge is capable of absorbing from 9.5 to 17 grams of water
per gram of dry sponge. Were this sponge to be used in surgery, it
is possible that silica solids could spill into the body cavity and
cause tissue poisoning which could develop into silicosis.
Furthermore, this sponge loses wettability when washed in hot or
cold water containing fatty acids soaps, thus restricting reuse of
the sponges unless special care is taken during laundering. U.S.
Pat. No. 3,149,000 describes a polyurethane foam impregnated with
polyacrolein. However, acrolein monomer is a known body irritant
and the possibility of some monomer being present in the
polyacrolein would be a deterent to the medical usage of the
sponge.
The third category comprises polyurethane foams impregnated with
various substances for the purpose of releasing the substance from
the sponge at a controlled rate upon wetting of the sponge.
Generally, the pores of such sponges are substantially filled with
impregnant, the pores functioning primarily as a reservoir for the
impregnant. Obviously, when the pores of the foam are so filled,
any substantial inward flow of fluids such as would be required
with a medical sponge, could not be achieved. This third category
of polyurethane foam is amply illustrated by U.S. Pat. No.
3,088,158 which describes a sponge impregnated with an emulsion
suitable for washing and waxing auto finishes upon wetting, and by
U.S. Pat. No. 3,262,450 which describes a moistened foam containing
a layer of foaming surfactants which, when repeatedly compressed,
produces foam for a cleaning purpose. Also included in this
category are polyurethane foams impregnated with a germicide and
soap solution, having at least one surface sufficiently abrasive
for surgical scrubbing so that upon moistening and squeezing the
sponge, foam will be produced at the abrasive surface for
scrubbing. U.S. Pat. No. 3,002,937 describes a sponge containing
zones of fine pore size and zones of much coarser pore size, the
sponge containing a detergent. In addition to foaming upon wetting,
the size of the large pores (up to one-half inch in diameter) tends
to make the sponge excessively abrasive. Furthermore, these large
pores, particularly when they appear on the surface of the sponge,
will not retain fluids by capillarity when the sponge is disengaged
from the environment of the fluid. None of the sponges within this
third category would be suitable for medical usage because fluids
either are blocked from entering the foam in substantial amounts or
because the foam is incapable of retaining sufficiently large
amounts of liquids, or because they foam excessively upon
wetting.
The fourth category comprises polyurethane foam having an external
surface coating of a detergent or disinfectant. Such a product is
shown in U.S. Pat. No. 3,283,357 in which the polyurethane foam
contains a substantially impermeable outer layer of a
germicide-detergent mixture which foams upon wetting. Although the
inner pores of the sponge are unfilled, access to these pores is
blocked by the continuous impermeable surface layer. As a result,
this sponge would be unsuitable for medical use.
SUMMARY OF THE INVENTION
This invention relates to novel hydrophilic polyurethane sponges
which are particularly suitable for use as medical sponges. More
particularly, this invention relates to a flexible hydrophilic
polyurethane foam whose surfaces are nonabrasive towards exposed
internal body organs and which contains at least one zone of pores
extending inwardly from a surface of the sponge. The sponge is
rendered hydrophilic by a thin coating on the internal surfaces of
the pores of at least one surfactant which is a nonflowable liquid
at room temperature. It is important that substantially all of the
internal pore surfaces be coated with surfactant to insure
uniformity of fluid absorption throughout the entire zone of pores.
An amount of surfactant is required which accelerates absorption of
body fluids into the pores, without compression of the sponge, at a
medically preferred rate, while not simultaneously causing any
substantial reduction in the volume of the pores so as to interfere
with the capacity of the sponge to absorb fluid.
Once fluids have entered the pores of the sponge, they are retained
therein primarily by capillary action and are thereby conveniently
removed from their body environment when the sponge is so removed.
The sponge pores must be properly dimensioned to insure said
capillary retention of fluid therein.
It is important that the surfactant be nontoxic to the body and
also that it not foam when the sponge is wetted with body fluids.
It is also important that there be no substantial blockage of
access to the pores whereby body fluids are prevented from entering
the pores.
The sponges of this invention are conveniently prepared in many
different sizes and can be tagged with radiopaque markers, if
desired. They can be used in a variety of surgical applications as
described hereinbelow. The sponges of this invention are
substantially free from toxicity, abrasiveness, and lint; they
resist fraying and can be readily cut to any size desired.
Although the sponges are designed for disposibility after being
used once, thereby eliminating the risk of cross contamination,
they may be washed, resterilized, and reused many times without
noticeable shrinkage or diminishment of their hydrophilic
properties. Repeated autoclaving of the sponges, for example,
enhances their surgical handleability.
Despite the presence of surfactant in the sponges, the sponges are
free from a greasy texture. The sponges will rapidly absorb up to
about 20 t0 25 times their dry weight of fluids. Furthermore, they
will absorb such fluids merely by contacting the fluids with the
sponge; compression of the sponge is not required to achieve
absorption.
It is an object of this invention to provide a novel hydrophilic
polyurethane medical sponge which eliminates the numerous
disadvantages of the currently used gauze pads as described
hereinabove.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a typical disposable polyurethane
sponge of this invention, the sponge having a radiopaque tracer
attached thereto.
FIG. 2 is an enlarged cross sectioned view of the sponge taken
along plane 2-2 of FIG. 1, and illustrates the nature of the
surfactant coating upon the pore walls of the sponge.
FIG. 3 shows graphically the affect of the surfactant concentration
in the sponge upon blood absorption rate and the amount of blood
retained per weight of dry sponge.
FIG. 4 is a schematic diagram illustrating a preferred method of
preparing the sponges of this invention.
FIGS. 5 and 6 illustrate sponge configurations which are
particularly suitable for use in ophthalmic surgery.
FIG. 7 is a cubed configuration of the sponge of this invention
which finds general utility in surgery.
FIGS. 8 and 9 illustrate configurations of the sponge of this
invention which are particularly useful in neurosurgery.
FIG. 10 is a frontal sectional view of a patient on an operating
table and illustrates usage of the sponge of this invention for the
removal of body fluids during an initial surgical incision.
FIG. 11 is a frontal sectional view of a patient of an operating
table and illustrates usage of the sponge of this invention for
packing internal organs in the body cavity during surgery for
purposes of maintaining a clear surgical field.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polyurethane foam suitable for preparing the sponges of this
invention may be either the polyester or the polyether type.
Polyurethane polyester foams such as those supplied by Scott Paper
Company, Chester, Pa., under the names of Scott "Z" or Scott "Q"
polyurethane foam, having about 100 pores per inch, said pores
being fully reticulated, i.e., open pores, are preferred. A
polyurethane polyether foam such as that supplied by Nopco Chemical
Co., Newark, N.J., under the name Nopco ST-1840 polyurethane foam,
having about 60 to 100 pores per inch, said pores being about 60
percent reticulated, is also quite suitable. Although reticulated
or nonreticulated foam is generally acceptable, 100 percent
reticulated foam is preferred. Reticulated foam may be prepared by
a physical or chemical reticulation process. A typical physical
reticulation process involves blowing out connecting windows in the
foam matrix under high pressure; a typical chemical reticulation
process involves removing the connecting windows by treating the
foam with a dilute aqueous caustic solution.
The size of the pores of the foam must be sufficiently small to
insure retention of fluids therein substantially by capillary
action. Foams having from about 60 to about 150 pores per linear
inch meet this requirement, with about 100 pores per inch
representing a preferred pore density. Should the foam contain less
than about 60 pores per inch, the sponge surfaces are too abrasive
for medical usage and the pores are too large to retain fluid by
capillary action. When foam contains more than 150 pores per inch,
pore size becomes too small to permit flow of fluids into the pores
at a medically preferred rate.
Since the sponges are frequently used in a bloody surgical field,
it is desirable to dye the polyurethane foam a color which will
offset the sponges from the surgical field. Blue and green are
particularly suitable colors for this purpose and polyurethane foam
dyed with these colors is readily available commercially. The dye
selected should be nontoxic and generally innocuous toward living
tissue.
For medical usage, it is important that the foam be extremely
flexible and pliable to permit the surgeon to wrap and contour the
foam around various internal organs or to otherwise use the foam to
pack such organs with assurance that the foam will stay in place
during the operation. To achieve the desired flexibility, coupled
with the required foam free volume for adequate absorbency, foam
thicknesses of from one thirty-second to one-half of an inch give
good results with a thickness of about one-eighth of an inch
preferred for many application.
An acceptable polyurethane foam typically has a void fraction of
about 97 percent; were all the voids to be filled with a fluid such
as water, the foam would be capable of retaining about 30 times its
dry weight of water.
The sponges can be conveniently cut to a variety of sizes, the size
depending on the particular application of the sponge. For example,
4" .times. 4" and 4" .times. 8" sponges are particularly suitable
for sponging during an initial surgical incision. Larger size
sponges are preferred for packing internal organs once the body
cavity has been opened and exposed. Sponge sizes suitable for this
latter purpose are 4" .times. 12", 4" .times. 30", 14" .times. 14",
and 16" .times. 16"; the 4" .times. 30" sponge, for example, is
typically rolled into a cylindrical configuration for use in
packing body organs. The other sized sponges may be similarly used,
or they can be used as is, i.e. without rolling or forming into
special configurations.
Sponges suitable for other types of surgery such as ophthalmic and
neurosurgery, for example, are of different sizes and
configurations as discussed hereinbelow.
FIG. 1 depicts a typical sponge of this invention. Attached to
sponge 1 is a radiopaque tracer 2 to permit X-ray detection of the
sponge should it be inadvertently left in the body following
surgery. A suitable radiopaque tracer is a black polyvinyl chloride
filament containing not less than 60 percent of X-ray grade barium
sulfate. This filament is conveniently attached to polyurethane
foam by conventional heat sealing techniques whereby the filament
is compressed into a ribbon and affixed to the foam as shown in
FIG. 1. A tracer material could also be incorporated into the foam
during its formation by addition of a suitable amount thereof to
the reaction mixture.
The foam is rendered hydrophilic by coating the pore walls of the
foam with a thin layer of a surfactant which is a nonflowable
liquid at room temperature. Nonflowability eliminates the danger of
the surfactant dripping out of the sponge and into the body cavity.
The surfactant must be nontoxic to human tissue and, furthermore,
must not foam when the sponge is wetted with water, blood, or other
body fluids. Surfactants of the anionic, nonionic, and cationic
variety are suitable for imparting the desired hydrophilicity to
the polyurethane foam. More particularly, surfactants such as
lauryl sulfate (anionic), stearamido
propyldimethyl-.beta.-hydroxyethyl ammonium nitrate (cationic),
alkylaryl polyethoxylated glycol ethers (nonionic) and
polyoxyethylene sorbitan mono-oleate (nonionic) have been
successfully used.
A preferred surfactant is polyoxyethylene sorbitan mono-oleate;
this surfactant is sold by Atlas Incorporated, under the trademark
of Tween-80. This surfactant is preferred because it is known to be
physiologically innocuous and has already been approved by the
Federal Food and Drug Administration for internal consumption in
such items as food and candy. It has also been approved for use in
intravenous and intramuscular pharmaceutical preparations such as
those of tetracycline and chlortetracycline. This surfactant is
listed under the name of Polysorbate 80 in the Merck Index, 7th ed.
(1960 ) at pg, 833 and in the U.S. Pharmacopoeia XV at pg, 566,
said publications being incorporated herein by reference.
Two important considerations arise in determining the preferred
amount of surfactant. First, sufficient surfactant must be provided
to insure accelerating the absorption of body fluids into the
sponge, without compression to the sponge, at a medically preferred
rate. A "medically preferred rate" exists when there is no undue
lag time between contact of the sponge with the fluid and the
disappearance of the fluid into the sponge. It is difficult to
precisely define such a rate since it varies depending upon the
application in which the sponge is being used. For example, when a
surgeon desires to have the cutting field cleared of blood during
an initial surgical incision, almost instantaneous removal of blood
by the sponge is required. On the other hand, when the sponge is
inserted into the body cavity for purposes of preventing blood and
other body fluids from cascading into the surgical field,
instantaneous fluid absorption is not necessarily required provided
the rate of absorption is sufficient to prevent the fluids from
noticeably obscuring the surgeon's view of the operating field.
The second consideration is that the free volume of the sponge must
be maintained at a sufficiently high value to provide a reservoir
for a substantial amount of fluid flowing into the sponge. The
sponge should have the capability of absorbing at least 20 times
its dry weight of water as discussed hereinabove. While increasing
the surfactant concentration increases hydrophilicity of the
sponge, it tends to decrease the free volume of the sponge by
increasing the thickness of surfactant coating on the pore walls.
This is best understood by reference to FIG. 2 which is a greatly
enlarged cross-sectional view of the foam showing the network of
pores 3 within sponge 1 and the thin layer of surfactant coating 4
on the walls of pores 3.
The thin continuous surfactant coating shown in FIG. 2 is
illustrative only. The nature of the coating can vary provided its
function of accelerating absorption of fluids into the sponge is
retained. For example, the coating could be a network of fine beads
of surfactant resting on the internal pore surfaces; or it could be
a continuous or partially continuous thin film of surfactant.
FIG. 3 shows graphically the effect of surfactant concentration in
the sponge upon the average time required to absorb a single drop
of blood. FIG. 3 also shows the effect of surfactant concentration
in the sponge upon the average quantity of blood retained by the
sponge. Generally, a surfactant concentration of from about 0.1
percent to about 25 percent, based on dry sponge weight, is
operable. Surfactant concentrations below 2 percent, while
acceptable for less demanding medical applications, would be not be
generally acceptable because of the reduced rate of fluid
absorption. Surfactant concentrations above 25 percent do not
noticeably enhance hydrophilicity of the sponge. However, such high
surfactant concentrations tend to decrease the quantity of fluid
retained by the sponge and, furthermore, tend to impart an
undesirable greasy texture to the sponge. A surfactant
concentration of about 3 to about 15 percent, based on the dry
weight of the sponge, is quite acceptable with a surfactant
concentration of from about 5 to about 10 percent preferred.
Hygroscopic agents may also be incorporated with the surfactant
into the foam, the purpose of such agents being to pick up
sufficient moisture from the environment to impart antistatic
properties to the foam thereby minimizing any explosion hazard as
heretofore discussed.
Generally, any well-known nontoxic drying agent or humectant is
suitable, although liquid agents are preferable because they may be
readily and uniformly mixed with the liquid surfactant for
convenient impregnation into the sponge. Illustrative hygroscopic
agents are propylene glycol, diethylene glycol, or other homologs
of glycol. A highly preferred hydroscopic agent in U.S.P. grade
glycerin since it is known to be nontoxic and readily assimilable
by the body. Glycerine is listed in the Merck Index, 7th ed. (1960
) at pages 489--490 and in the U.S. Pharmacopoeia XV at pages
309--310, said publications herein incorporated by reference.
The hygroscopic agents have substantially no effect upon
hydrophilicity of the sponge. The amount added is not critical;
however, sufficient hygroscopic agent must be provided to achieve
the desired degree of antistatic behavior while, at the same time,
if an excessive amount of hygroscopic agent is added, the quantity
of fluid retained by the sponge will be accordingly decreased due
to the reduction in available pore volume, The incorporation of
equal amounts of surfactant and hygroscopic agent, or of a minor
amount of hygroscopic agent based on the amount of surfactant, has
been found quite suitable.
Other additives, particularly germicidal and therapeutic agents
such as, for example, hexachlorophene, chlorotetracycline,
neomycin, and penicillin can also be incorporated into the
sponges.
A preferred method for preparing the sponges of this invention is
shown in FIG. 4. Referring to FIG. 4, surfactant and water are fed
to mixing tank 5 where the surfactant is uniformly dispersed
throughout the water. The surfactant-water dispersion is then
pumped to impregnation tank 6. The radiopaque tracer is applied at
8 to a continuously advancing ribbon of polyurethane foam 7. Foam 7
advances through compression rolls 9 into impregnation bath 10
which is contained in tank 6. As foam 7 expands, bath 10 rushes
into the foam pores to impregnate foam 7. Recirculating line 11
containing filter 12 is provided to remove loose pieces of foam
introduced into bath 6 by the mechanical working of foam 7 by rolls
9. These loose particles must be removed to prevent their
appearance in the final product. Immediately prior to emerging from
bath 10, foam 7 passes through compression rolls 13 wherein a
portion of impregnant is squeezed out of foam 7. Foam 7 then
emerges from bath 10 and tank 6 prior to any substantial expansion
thereof and passes under infrared lamps 14 whereby water is
vaporized and removed from foam 7. The dry sponge is then cut by
cutting blade 15 into the desired size. Sponge pieces 16 are then
packaged 17 and sterilized 18.
The amount of surfactant in the final product can be controlled in
several ways. The concentration of bath 10 may be fixed to insure
impregnation of the required amount of surfactant into the pores of
foam 7, in which case foam 7 would bypass rolls 13, proceeding
directly to lamps 14 where water would be vaporized and removed. On
the other hand, bath 10 may contain a higher surfactant
concentration in which case foam 7 passes through rolls 13 which
are preset at an experimentally determined setting whereby
excessive impregnant is squeezed from foam 7 prior to removal of
water by lamps 14. The latter method is preferred since less water
must be evaporated with consequent savings in manufacturing
costs.
Bath 10 should not contain more than about 10 percent surfactant in
order to avoid imparting a greasy surface to foam 7. When it is
desired to add a hygroscopic agent to the foam, the agent can be
conveniently added to mixing tank 5 along with water and surfactant
to produce a uniform impregnation bath. A preferred impregnation
bath composition is 95.5 percent water, 3 percent surfactant, and
1.5 percent hygroscopic agent. When a hygroscopic agent is not
desired, the composition of the above bath becomes 3 percent
surfactant and 97 percent water. Foam impregnation is preferably
performed with bath 10 at room temperature.
The sponges are conveniently marketed in conventional dual envelope
packages wherein an inner envelope containing one or more sponges
is contained in an outer strippable envelope. An illustrative
package of this type is described in U.S. Pat. No. 2,949,181.
Alternatively, the sponges can be wrapped in one or more layers of
tissue paper which would then be packaged in a strippable outer
envelope. Up to 8--10 pound tissue paper is satisfactory. A
suitable outer envelope is a peelable bleached microporous kraft
paper (up to 30 pounds) zone coated with a cold sealable
adhesive.
The packaged sponges can be sterilized using conventional methods
such as heat sterilization, X-rays, beta or gamma radiation, or
various liquid and gaseous chemical sterilants. A preferred method
of sterilization is by gaseous ethylene oxide. For example, the
packaged sponges are sterilized by placing them in an oven,
evacuating the oven under 15" vacuum for 30 minutes and then
filling the oven with a mixture of 20 percent ethylene oxide and 80
percent carbon dioxide vapor for 18 hours at an oven temperature of
124.degree. F., a pressure of 40 psia, and 50--65 percent relative
humidity (steam charged to oven separately); the oven is then
evacuated for 90 minutes, after which the oven pressure is raised
to atmospheric pressure by the admittance of carbon dioxide.
Sterile packaged sponges are then removed from the oven.
The sponge of this invention is may be cut, shaped or otherwise
fabricated into various configurations suitable for a host of
applications. FIG. 5 shows a sponge of suppository configuration
having two slightly rounded narrow ends 19 and a relatively thick
central portion 20 for grasping with the hand. Points 19, due to
their small size, can be readily inserted into the eye during
ophthalmic surgery to remove fluids therefrom.
FIG. 6 shows another embodiment of a sponge useful in ophthalmic
surgery. The sponge 21 is in the shape of a triangular wedge having
a fine point 22, which can be inserted into the eye. Sponge 21 is
mounted on shaft 23 which is provided for ease of handling.
FIG. 7 is a sponge cube useful in general surgery and in a variety
of other medical applications such as surgical prepping, swabbing,
sponging, etc.
FIGS. 8 and 9 illustrate sponges particuarly suitable for use in
neurosurgery. These sponges are typically offered in smaller sizes
ranging anywhere from as small as 1/2" .times. 1/2" to as large as
3" .times. 3". Attached to each sponge is thread 23a which, in view
of the relatively small size of these sponges, is provided for easy
removal of the sponges from the operating field. Thread 23a
ordinarily contains a radiopaque tracer material as a
precaution.
Other sponge configurations and embodiments designed in accordance
with particular medical and surgical applications also fall within
the scope of this invention although not shown in this
specification. For example, the sponges with a proper impervious
backing can be used as a catamenial bandage or napkin to absorb
menstrual fluid, or as a catamenial tampon for insertion into the
vaginal cavity for a similar purpose. The sponges of this invention
may also be used as aerated bandages or wound dressings. To be
useful in such an application, the sponge surface in contact with
the wound should not stick to the wound when the bandage is
removed. Small amounts of a release agent or a nonsticking agent
may be applied to the bandage surface for this purpose. Cosmetic
grade silicones are effective release agents for this purpose.
Other additives such as germicides and therapeutic agents may also
be incorporated into such bandages.
FIG. 10 is a front sectional view of a patient 24 lying on
operating table 25 and illustrates use of the sponges of this
invention to remove blood and other body fluids during a surgical
incision. Sponge 26 is grasped with forceps 27 by the surgeon 28 or
other operating room personnel and applied to the external body
surfaces 29 immediately adjacent to incision 30. Sponge 26 is also
inserted into incision 30 to provide a clear cutting field for the
surgeon as he continues incision 30 until he gains entry into body
cavity 31.
FIG. 11 illustrates the use of the sponges of this invention within
body cavity 31. Once the surgeon has gained entry into cavity 31 it
is necessary to push aside internal organs 32 which cover the
diseased organ. To insure that organs 32 remain out of the
operative field and do not interfere with the surgery, sponges 33
are inserted into cavity 31 and packed against organs 32 to retain
them in the desired position. Organs 32 may be conveniently packed
either by rolling a sponge into a cylindrical configuration such as
is shown at 34 or by placing the sponges directly over organs 32
without rolling or otherwise altering their configuration as shown
at 35.
Prior to inserting sponges in the body cavity, the dry sponges are
usually placed in a basin containing saline solution and it is
desirable for the sponges to be sufficiently hydrophilic to sink
immediately. Untreated polyurethane foam floats for days on the
surface of such solutions; however the treated polyurethane sponges
of this invention sink rapidly into the solution (see Example 3
hereinbelow). Immediately before insertion of the sponge into the
body cavity, the sponge is removed from the saline solution and
squeezed to remove most of the liquid. It is then inserted in the
body cavity as described hereinabove. The presence of some saline
solution in the sponge minimizes drying out of tissue with which
the sponge comes into contact. On the other hand, the sponge
retains sufficient porosity to serve as a reservoir for blood and
other free flowing fluids within the body cavity which could
otherwise cascade into the operating field to obscure it.
The following examples are provided to further illustrate the
invention.
EXAMPLE 1
RATE OF BLOOD ABSORPTION AND QUANTITY OF BLOOD RETAINED BY THE
NOVEL SPONGES
Sponges were prepared in accordance with the process described
above and contained varying amounts of impregnated Tween-80 and
glycerine. The rate of blood absorption was measured by placing a
drop of blood on a 4" .times. 4" .times. 1/8" pad and measuring the
time for the blood bubble to completely soak into the foam. When a
drop of blood is placed on untreated polyurethane foam, it remains
as a spherical bubble on the surface of the foam for about 30
minutes whereupon the blood begins to thicken and coagulate.
Blood retention of the sponges was determined by weighing a dry
treated sponge, then completely wetting the sponge with blood by
immersion therein, draining for 40 seconds, and then weighing to
determine the amount of blood in the sponge.
Data are presented below in Table I which clearly show the rapid
rate of blood absorption and high degree of blood retention
demonstrated by the sponges of this invention. The relationship
between surfactant concentration and the average absorption times
of Table I is shown graphically in FIG. 3.
Surfactant and glycerine concentrations listed in Table I and shown
in FIG. 3 were calculated by measuring the total amount of
impregnant and then apportioning this amount between surfactant and
glycerine based on the proportion of surfactant to glycerine in the
impregnating bath used to prepare the sponges. ##SPC1##
##SPC2##
EXAMPLE 2
RATE OF WATER ABSORPTION OF THE NOVEL SPONGES
The hydrophilicity of the inventive sponges as indicated by rate of
water absorption was demonstrated by taking four 2" .times. 2"
squares of untreated polyurethane foam and foam which had been
prepared in accordance with the process described hereinabove,
stacking the four squares vertically and placing them on the
surface of 25 ml. of water in a petri dish. A penny was placed on
the top of the sponges to increase their weight. The amount of time
required for complete absorption of the 25 ml. of water in a petri
dish. A penny was placed on the top of the sponges to increase
their weight. The amount of time required for complete absorption
of the 25 ml. of water was measured for both treated and untreated
foam. These results are summarized in Table II and clearly show the
improvement in the rate of absorption resulting when the foam is
treated according to the present invention. Treated sponges in
Table II contain from about 0.09 to about 1.28 percent total
impregnant, i.e. Tween-80 and glycerine, said sponges prepared
using an impregnation bath containing 1.5 percent Tween-80, 1.5
percent glycerine, and 97 percent water. ##SPC3##
EXAMPLE 3
WETTING TIME IN WATER AND QUANTITY OF WATER RETAINED BY THE NOVEL
SPONGES
The quantity of water retained was measured by placing a square of
both treated and untreated polyurethane foam on the surface of
water. The wetting time, defined as the time required before the
last corner of the square had submerged in the water, was recorded.
The sample was then removed from the water, drained one minute, and
weighed. The resultant data are presented in Table III and indicate
that wetting time is substantially decreased with treated foam. The
results further indicate that the sponges of this invention can
absorb up to about 23 times their dry weight of water. Treated
sponges in Table III contain from about 0.09 to about 1.28 percent
total impregnant, i.e. Tween-80 and glycerine, said sponges
prepared using an impregnation bath containing 1.5 percent Tween-80
1.5 percent glycerine, and 97 percent water. ##SPC4##
* * * * *