CA1066466A - Polyurethane foam surgical dressing - Google Patents
Polyurethane foam surgical dressingInfo
- Publication number
- CA1066466A CA1066466A CA243,581A CA243581A CA1066466A CA 1066466 A CA1066466 A CA 1066466A CA 243581 A CA243581 A CA 243581A CA 1066466 A CA1066466 A CA 1066466A
- Authority
- CA
- Canada
- Prior art keywords
- foam
- modified
- wetting agent
- microporous
- absorbent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/42—Use of materials characterised by their function or physical properties
- A61L15/48—Surfactants
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/42—Use of materials characterised by their function or physical properties
- A61L15/425—Porous materials, e.g. foams or sponges
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S521/00—Synthetic resins or natural rubbers -- part of the class 520 series
- Y10S521/905—Hydrophilic or hydrophobic cellular product
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S521/00—Synthetic resins or natural rubbers -- part of the class 520 series
- Y10S521/918—Physical aftertreatment of a cellular product
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S602/00—Surgery: splint, brace, or bandage
- Y10S602/90—Method of making bandage structure
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
- Y10T428/249961—With gradual property change within a component
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
- Y10T428/249978—Voids specified as micro
- Y10T428/249979—Specified thickness of void-containing component [absolute or relative] or numerical cell dimension
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
- Y10T428/268—Monolayer with structurally defined element
Abstract
ABSTRACT OF THE INVENTION
The invention is directed to an open celled poly-urethane foam article which initially is generally non-absorbent, the surface of which is subsequently rendered absorbent by decreasing the average pore cell size to a critical range while preferably also simultaneously or subsequently achieving a critical range of a wetting agent in such surface. This can be accomplished in either of two ways. The first method is to permanently collapse the cells in the surface region of the original foam so that the concentration of any residual wetting agents initially present in the structure increases in the compressed surface region, thus rendering said surface more readily absorbent. For a surgical dressing, the surface cells should be permanently but only partially collapsed to substantially less than the original size to form a microporous skin. According to the second method substantially all residual wetting agents which may be present in the original foam material are extracted from the polyurethane either before or after forming the microporous skin surface. Preferably, the extraction comes after formation of the skin so that a controlled amount of a desired wetting agent(s) can then be reapplied to the microporous surface for better controlling absorbency into the structure. As the invention relates primarily to surgical dressings, a critical range for the amount of wetting agent(s) and the average cell pore size in the collapsed surface have been found which are related to the wicking, absorbency rate, and non-adherence characteristics of the resulting structure. These characteristics in turn are directly related to critical and measurable differences in the rate of epithelization, wound healing performance and wound healing quality.
The invention is directed to an open celled poly-urethane foam article which initially is generally non-absorbent, the surface of which is subsequently rendered absorbent by decreasing the average pore cell size to a critical range while preferably also simultaneously or subsequently achieving a critical range of a wetting agent in such surface. This can be accomplished in either of two ways. The first method is to permanently collapse the cells in the surface region of the original foam so that the concentration of any residual wetting agents initially present in the structure increases in the compressed surface region, thus rendering said surface more readily absorbent. For a surgical dressing, the surface cells should be permanently but only partially collapsed to substantially less than the original size to form a microporous skin. According to the second method substantially all residual wetting agents which may be present in the original foam material are extracted from the polyurethane either before or after forming the microporous skin surface. Preferably, the extraction comes after formation of the skin so that a controlled amount of a desired wetting agent(s) can then be reapplied to the microporous surface for better controlling absorbency into the structure. As the invention relates primarily to surgical dressings, a critical range for the amount of wetting agent(s) and the average cell pore size in the collapsed surface have been found which are related to the wicking, absorbency rate, and non-adherence characteristics of the resulting structure. These characteristics in turn are directly related to critical and measurable differences in the rate of epithelization, wound healing performance and wound healing quality.
Description
1066~6~.
This invention relates to an integral, non-laminated, non-rigid, open cell polyurethane foam article for use as a surgical dressing and also to the method of producing such an article.
A dressing material for a wound must ideally possess several properties. Such a dressing should be absorbent to remove excess exudate from the wound and at the same time be capable of protecting the wound from mechanical injury as well as reducing the risk of infection thereof by bacteria. Preferably, it should be non-adherent to the wound so as not to disturb I healing during periods of inspection of the wound or removal of the dressing. Furthermore, a dressing material must be free of toxic substances which may be absorbed into the wound. While all dressings must preform certain basic functions, it has been well documented that the pattern of healing (speed and quality) can be profoundly affected by the kind of dressing used.
Commonly known cellulosic dressings, such as cotton lint, cotton gauze, cotton wool pads and cotton/rayon wool pads faced with non-woven materials demonstrate good absorbent qualities, but their surface fibers tend to adhere to the wound or to absorb the scab-forming serum so that they actually become embedded in the scab as it coagulates and hardens. Thus, if these dressings are removed to allow inspection or treatment of the wound, the wound tissue or scab may be damaged, retarding the healing process and even re-opening the wound. Furthermore, the open weave construction of these dressings and the uncontrolled absorbency rate of the cellulosic fibers causes the serous exudate on the wound surface to dry out. The epidermis regenerating from the wound edges and from cut surfaces of hair follicles within the wound is then forced to move through the fibrous tissue beneath the dry layer which fo~led the scab and the epitherlization rate is thus substantially slower than if the ywl/ ~
-^ 106646i6 epithelium were allowed to move through a moist fluid layer.
Attempts have been made to provide wound dressings of fully occlusive materials, such as polyethylene, in order to keep the wound area from dehydrating. Such dressings provide a satisfactory environment for skin regeneration by preserving a fluid layer of serum in the vicinity of the wound.
Epithelization rate under these occlusive conditions has been shown to be at least twice as rapid as with the fibrous oellulosic dressings. However, it is essential to apply such fully occlusive dressings in a sterile state and under sterile conditions to prevent harmful bacteria from entering the wound area and breeding close to or in the wound. Furthermore, such dressings do not absorb exudate, thus causing pooling in the wound which is not desirable.
The use of polyurethane foam as a partially occlusive dressing has been attempted in the past as well. Such dressings-however made from Bowater-Scott's "Sterafoam ~ .M.)" and Harrison and Jones' "Supersoft(T-M )" have an open-cell structure with ~elati~ely enormous pores (greater than 200 micrometers) compared to the tissue fibers and cell~ on the wound surface. The serous exudate will penetrate theSe dressings only under pressure, filling the large open cells with proteinaceous fluid, erythrocytes, and leucocytes. Histological evidence shows that the exudate on the wound surface will generally remain moist for at least a few days with the regenerating epidermis migrating through the moist exudate between the wound surface and the over-lying dressing. ~y preserving this moist environment while epidermal migration is taking place, epithelization is relatively rapid compared to wounds covered with conventional celluslosic dressings. However due to the excessive cell pore size of such foam, relative to the tissue cell size, it is necessary to press such nonmodified open-celled polyurethane foam dressing ywl/~3 ~ 2 -1066~t~6 against the wound to physically drive serum into the dressing to overcome the surface tension of the serum and allow excess exudate to be removed. The polyurethane foam cell structure becomes impressed into the dermis, indenting the collagenous tissue, and causing numerous inflammatory cells to be attracted to this foreign material. The relative difference between foam cell size and tissue cell size also allows the regenerating epidermis to grow around the particles of polyurethane foam. This stimulates hyperplasis resulting in bizarre epidermal tissue. In some cases, particles of foam are broken away from the large open-celled dressing and come to lie in the developing connective tissue under the new epidermis causing foreign body reactions. In addition such indentation of the wound surface with inclusion of particles of polyurethane within the epidermis and dermis may also lead to excess fibrosis, granuloma and scarring.
In some cases, non-adherent wound dressings have been made by placing a normally occlusive material, such as poly-ethylene, over the front surface of an absorbent pad, such as cotton gauze. To perform properly, the occlusive surface contains perforations or is spatially apertured to allow exudate to migrate into the absorbent backing. Nhile such a structure partially overcomes the problems of adherence to the wound as commonly found in cotton gauze dressings and of foam particles embedding in the wound, the uncontrolled absorption of the pad causes the wound area to dry out, scab formation to occur, and the epithelization rate to be retarded by forcing the regenerating epithelium to migrate beneath the dry necrotic region.
ywl/,~ ~~ _ 3 _ .~
- 1066~6 It i9 therefore an ob~ect of the present invention to provide improved polyurethane surgical dressings which allow for a more satisfactory microclimate for tissue regeneration and a process for producing the same.
In one particular aspect the present invention provides an integral, non-laminated, non-rigid, open cell polyurethane foam article comprising at least one modified surface with essentially all of said surface having a microporous structure of an average pore cell size between about 0.2 to 200 micrometers in contrast to the remaining un-modified macroporous portions of the foam having an average pore cell size range between about 200 - 2,000 micrometer~, said modified, microporous surface further character-ized by an inherently absorbent structure of permanently but only partially collapsed or compressed open foam cells as contrasted to the said non-modified macroporous foam cell portions which are substantially uncollapsed and inherently non-absorbent.
In another particular aspsct the present invention provides the procesq for producing an absorbent structure on a surface of an essentially non-absorbent, non-rigit, open-cell polyurethane foam material having an average pore cell size range between about 200-2000 micrometers comprising applying sufficient heat and pressure to said foam surface to result in permanently but only partially collapsing the surface cells into a motifiet microporous integral structure having an average pore cell size range between about 0,2 to 200 micrometers whereby essentially all of said motifiet surface structure is inherently absorbent as contrasted to the remaining untreated and non-modified macroporous foam cell portions.
Various other objects and advantages will be apparent to one skilled in the art upon reading the following disclosure and the novel features will be particularly pointed out hereinafter in connection with the appended claims. It is understood that ~ -4-, 10~6~66 the details may be modified without departure from the principles of the invention which is readily understood when taken in con-nection with the accompanying description and examples.
Various processes for subjecting polyurethane foams to heat and pressure are well known in the prior art and it is understood that the present invention does not claim as novel such processes in general or articles produced thereby. Rather the preferred embodiment provides a polyurethane foam article, the foam cells on at least one surface being permanently but only I0 partially collap~ed compared to the remaining portions ~ 4a--` 1066~66 of the foam article and wbich surfaoe is further rendered more readily absorbent by conoentrating or adding an am~unt of wetting agent per unit surfaoe into the collapsed membrane surfaoe relative to cells in the remaining portions of the foam article; the cell pore siæ of said surface being critically controlled preferably in conjunction with the conoentration of wetting agent(s) to produce a unique wound dressing which pmvides a satisfactory microclimate for tissue regeneration and improved wound healing.
The article described in this present invention is fabricated fmm an original b~e material of an open-celled polyurethane foam having oe lls of an average pore siæ in the range of about 200 to about 2,000 mincrometers and containing in one of the preferred enbodiments of the invention a residual conoe ntration of wetting agent(s). The article further compri æs a microporous surfaoe region of oFen cells which bave been permanently partially collapsed from that of the original ba æ cells so that the average p~re cell si æ in said surfaoe region is between about 0.2 to 200 micrcmeters and preferably containing a conoe ntration of wetting agent in said microporous surfaoe of no greater than about 1% and preferably no less than about 0.01 percent by weight.
It is found that if the average pore cell siæ of the original foam base material is less than about 200 micrometers the entire structure including the modified and nonimDdified portions will continue to wick l~p exudate and the modified micropor~us polyurethane surfaoe next to the wDund will dry out, thus substantially preventing development of the proper environment for epithelization and tissue regeneration. In contrast should the oe 11 pore size of the original foam structure employed to fabricate the unique dressing material of the present invention be greater than about 2000 micrometers, it is found that exoe ss exudate will not be held in the non-mcdified foam portion of the dressing and will instead tend to flow out into the environment making the article an unsatisfactory wound dressing. The critical range of,about between 200 to 2,000 micrometers for the original non-mDdified foam portion was found in practioe to be the ideal range for maintaining the adjaoe nt modified microporous surfaoe in a reasonably moist ywl/ ~ ~ 5 ~066466 state with the non-modified back up foam further functioning as a reservoir for holding excess exudate therein. The pore size of polyurethane cellular material may be oontrolled or varied as desired by well kn~wn and conventional means such as for example in the case of isocyanate derived polymers by the addition of foam stabiIizing or ooalescing agents.
It is further found that if the wetting agent(s) on the m~dified microporous polyurethane foam surfaoe oonstitute less than the preferred minimNm of about 0.01~ by weight, the article will not readily absorb exudate into its structure thereby tending to cau æ pooling of ser~m below the microporous foam surfaoe cover which further causes maoe ration of tissue in the wound area. Should the wetting agent(s) contained in the microporous foam surface be~c~e greater than about 1% by weight, it is found in tests conducted on pigs that wounds dry exoe ssively and the rate of epithelization is increasing sJower as the level of wetting agent(s) increaæs above the 1~ level.
The foam cells oo~prising the microporous surface have been defined as "permanently but only partially collapsed". It is known that polyurethane foam can be reversibly deformed or compressed to reduoe thickness up to a oe rtain extent but will esæntially recover its original thickness upon washing or steam heating. The present invention relates to compression of the surfa oe of the foam at an extended temperature beyond thds pre-determined extent, that is, to an "irreversible" (pe~manent) process. The open oe lls defined as "partially oollapsed" have their standard structural me~bers (polymer strands) distorted to produce smaller cells or pores, but it is i~portant that the cells are not completely collapsed or fused. So as not to have an average pore cell size less than about 0.2 micrometers, the temperature of the polyurethane foam employed in the present process may exceed its second order transition point or glass temperature but n~t exoeed the fi s t order transition temperature for the specific polymer and pressure applied. Such an effect is produoe d by controlling the temperature and pressure parameters employed.
The foam article of the present invention is preferably in the YWV ~ C` - 6 -` ~66~66 form of a sheet, strip or ribbon and one or both of the major surfaces of the foam thereof may be increased in density. Where hoth surfaces of the foam are of increased density, the densities of the two surfaces may be the same or different.
According to a further aspect of the invention there is provided a process for making an open-celled polyurethane foam article which comprises applying pressure and heat to at least a surface of the foam to permanently (irreversibly) partially collapse the foam cells on said surface to an extent such that said surface is or may be rendered absorbent. The cells on said surface must be permanently but only partially collapsed to produce a micro-porous surface having an average pore size no greater than about 200 micro-meters and preferably containing therein at least about 0.01% by weight of wetting agent to overcome the surface tension of blood, serum, water, and other fluid exudate. The surface pores must also be larger than about 0.2 micrometers to allow proper wicking and absorption of said exudate to pass through the collapsed surface membrane. The foam cells remote from said surface remain unchanged at a pore size greater than about 200 micrometers . . ~ .
so as not to be readily absorbent but to still allow excess exudate to be rejected from said collapsed microporous surface into the remote, unchanged cell8 of the original foam and held therein as if in a reservoir.
The surface of the foam which is to be partially collapsed must be heated to a temperature near the softening point of the foam. This varies with foam composition and the surface temperature may suitably be from 300 F
to 450 F depending on the time the foam is subjected to heat and pressure.
It is important not to exceed the fusion temperature of the particular foam since this would cause complete collapse of the cells. The pressure applied may, for example, be up to 200 pounds per square inch and is preferably from 50 p.s.i. to 100 p.s.i.
This heat and pressure may be applied to said surface by conventional means such as a heated plate or roller. During the pressure and heat treat-ments, a release material, for example, silicone coated paper or a sheet of Teflon fluorocarbon, may be placed between the heatinq means and the said surface of the foam to prevent adhesion of the foam material to the plate dg/~ -7-1066~66 or roller and maintain the smooth micrcporous me~brane surface thus created.
The initial or starting piece of foam may be of any thickness but is preferably from about 0.1 cm to about 10 cm and is preferably modified by heat and pressure to a final thickness of fram about 0.05 cm to about 5 cm, preferably with a compressed micrcporous surface thickness up to about 5 mm.
Fram a practical standpoint, to obtain a one sided micraporws surface in the desired pore siæ range, the foam material is usually reduoed to ab~ut half its original thickness. Hawever, this is not essential; very thin pi e s of foam material, approximately 0.1 cm in thickness, can be } red absorbent by this pr~cess and it is only n e ssary to modify the s~lrfaoe to a depth of about 0.04 mm to achieve a satisfactory result.
The foam sheet, strip or ribbon may be similarly modified on both faoe s for which purpose the foam, after being removed from betwsen the plate or roller and the relea æ material, (if present) conveniently is reversed and the operation repeated. Alternatively, the pressure plate may be heated to the foam modifying temperature so that both surfaoe s of the foam or even the full thickness of the foam may be modified by heat and pressure in one or more pressing and heating operations.
m e foam which is e~ployed in the invention may be a reticulated or nonrreticulated, open-oe ll polyurethane foam based on polyester or polyether which foam is essentially non-absorbent in that any residual wetting agent(s) remaining in the foam during manufacture does not exoeed 1 percent by weight of the foam. By peDmanently but only partially collapsing the surfaoe of such an open-oe lled foam to a microporous me~brane structure of the critical pQre siæs as previously defined, the density or surfa oe area per gram weight of foam is decreased. m is modification in density also increa æs the con oentration of any residhal wetting agent present in the original foam, thus rendering said surface more readily absorbent. By reducing the original piece of foam to approximately one half its initial overall thickness by partially collapsing the oe lls of one surface, the weight of residual wetting agent(s) per unit surfaoe in the said modified surfaoe can be increased approximately up to ten times its original weight ywl/~ - 8 -10669~6fi per unit surface.
m e use of the article of the present invention as a surgical dressing in animal research on pigs indicates that the level of wetting agent(s) oont~;n~d in the microporous surface of the polyurethane foam should preferably not exceed about 1 peroe nt by weight. ~eyond that level, most wetting agents appear to be at least slightly toxic to epidermal oe lls on the wDund surface and to impair epidermal regeneration. While epidermal regeneration is still significantly more rapid under the p~lyurethane foam article at slightly above the said 1 percent level than wounds ccvened under cellulosic ootton dressings, the quality of wound healing is progressively degraded as the ccr~ ]}ltion of wetting agents in the surface increase above such con oe ntration level.
Wbund healing can also be impaired if ex oe ss exudate from a w,ound does not flow relatively freely into the microporous foam surfa oe but is allowed to pool in the vicinity of the wound. If pooling is prolonged, ma oe ration of the wound may occur and healing will break down and the wcund ~ecorls unmanageable. Therefore, although certain improved h~ling characteristics attributable to the article of this invention may at timeæ
be obtained in the absen oe of any appreciable wetting agent, (prDvided of course that the critical porosity range is maintained) however the nunim~m level of wetting agent(s) desired in the said microporous surface of the polyurethane foam dressing is still preferably akove the 0.01 per oe nt by weight to penmit the exudate to be immediately absorbed into the microporous membrane surfa oe at a relatively controlled, even rate.
Applicants have attempted to determine the physical and chemical characteristics which will predict that a particular open-celled poly-urethane foam which is generally essentially non-absorbent can be rendered to produce a surgical dressing that will provide a proper microclimate for tissue regeneration and enhan oe wound healing. In general, it is necessary to perform preliminary tests with any given sample of foam, but preferred formulations of reticulated or non-ret iculated, polyester and polyether open-cell polyurethane foams are cited in the examples. The bulk density, ywl/ j.~ r~ 9 1066~6~;
cell size, and thickness of the initial foam material may be chosen for the particular application for which the absorberit product is required, but the average pore cell size of the initial material should be maintained in the critical range of from about 200 to about 2,000 micrometers. If polyurethane foams are selected having residual levels of wetting agent(s) which fall out-side the critical or preferred range, the level can be easily adjusted. This readjustment can be made by substantially completely extracting any residual wetting agent(s) remaining in the original polyurethane foam after manufacture.
The desired concentration of wetting agent can be reapplied to at least the modified surface area and dispersed therein in an even omnidirectional pattern substantially throughout the microporous region. Suitable examples of wetting agents include anionic, nonionic and cationic surfactants singly or as mixtures, such as long chain hydrocarbon sulfates or sulfonates, e.g., sodium laurel sulfate, or long chain hydrocarbon radicals attached to polyethylene oxide radicals, such as nonylphenal poly (ethyleneoxy) ethanol (e.g. Igepal C0-730).
A particularly satisfactory wetting agent is the ammonium salt of a sulfate ester of a alkylphenoxypoly ethanol sold under the trademar~ Alipal C0-416 (Antura Chemical Co.). For use especially in a surgical dressing article, the wetting agent could be for example polyvinyl pyrollidone, ~Propylan 8123) polyoxypropylene glycol, (Carbowax 200) polyethylene glycol, (Alipal C0-436) or similar F.D.A. approved wetting agents capable of enhancing the absorption of serum exudate from a wound. A satisfactory method of applying the wetting aqent to the foam is by dipping the foam in the desired solution of a wettinq agent and carefully wringing out the excess and drying in a vacuum at 110 C.
The concentration of wetting agent in the dried foam can be determined by the volume of solution dried out in the foam.
As previously stated the foam articles of the present invention are particularly advantageous for use as surgical dressing materials. In this respect, the product can be readily sterilized, for example, by means of steam autoclave, gamma irradiation, or ethylene oxide. Also, the body of the aressing material is suitable for incorporating a medicament such as an dg/; ~' -10-1066~6fi anti-bacterial and~or antiseptic. m e dressing may be impregnated with such a medicament after the heat and pressure treatment but prior to sterilization. The dressing may be treated by depositing a film of medicated material on to the dressing or by dipping the dressing into a-solution of medication material and then drying the material.
For purpDses of this disclosure the term "resid~al" wetting agent is a wetting agent which may be found present in the original foam material after manufacture. For example, in the manufacture of a polyether based polyurethane, an excess amount of a polyether polyol such as polyo~ypr~pylene glycol may be employed in the formula mix. After polymerization of the mix into the foam material there will be found resid~al or excess polyol that did not react. mus the amount of residual (unreacted) polyol (wetting agent) in the foam may be brought to various levels by controlling the am~unt included in the initial mix or formulation.
However it is difficult to exactly oontrDl the quantity of unreacted wetting agent that will remain in the newly manufactured foam by the "residual"
method. It is therefore preferre~d that the fcam material be first treated by a solvent extraction process to rem~ve all wetting agents present if any and then to reapply the wetting solution therein under controlled conditions up to any amount desired.
The following examples show, by illustration and not ky limitation, the methods and materials which can be utilized in fabricating op~nrcelled FDlyurethane foam articles of the present invention ky employing an original foam material having average oe ll pore sizes of more than about 200 micrometers but less than about 2,000 micrcmeters and which initial foam material is generally non-absorbent, the surfaoe of which is subseguently rendered absorbent by decreasing the average cell pores si æs to the critioal range between about 0.2 to about 200 micrometers and preferably simultaneously or subsequently achieving a concentration of wetting agent(s) in said modified surface of between about 0.01% to 1.0% by weight.
ywv,9 .f - 11 -1066~66 Example I
A loaf of polyurethane foam based on polyether is n~nufactured from the following formulation by means well known in the art:
Ingredients Parts ky Weight PolyoxyprDpylene glycol 100 (a polyether polyol) Stannous Octoate 0.25 Water 4.0 Dimethylethanolamine 0.5 Silicone Surfactant 2.0 Trichloromonofluoromethane 15.0 Toluene diisocyanate (80% 2,4- 82.5 20% 2,6 isomer) By pho~amicroscopy the average pore siæ of the foam so produced is found to be in the critiaal range of between about 200 to about 2,000 micrometers. A residual wetting agent of polyol remained in the foam after manufacture as determined by extraction with ethanol in a Soxhlet extractor.
A sheet of foam is cut from the loaf in a conventiona manner.
. .
A silicone coated release paper is plaoe d on one surfaoe of the sheet which is then plaoe d in contact with a metal platen heated to a temperatwre in the range bebween 380 to 410F. A cold pressure plate is foroed against the free faoe of the foam, pressing the foam against the heated platen. A
pressure of about 70 p.s.i. is maintained for about 20 seconds, at which time the cold pressure plate is remoNed and the sheet of modified foam is stripped from the siliaone paper. The temperature employed in the heated platen is adjusted to result in the formation of a permanently, ~ut only partially collapsed skin having an average pore siæ in the critical range of from about 0.2 to about 200 micrometers and a skin concentration by weight of polyol wetting agent falling within the critical range of 0.01 to 1.0%.
Example 2 m e heat and temperature proce~lre of Example 1 is repeated using a polyether foam manufactured fr~m a slightly modified formulation:
ywl/~ 12 -106~46fi Ingredients Parts by Weight Polyox,opropylene glyool (a polyol) 100 Stannous Cctoate 0.4 Water 2.8 Dimethylethanolamine 0.7 Silic~ne oil 1.6 Trichloromonofluoromethane 13.0 ~oluene diisocyanate (80/20 isomer) 36.9 It is found that the resulting article has pore cell size and ooncentration of polyol wetting agent in the required and preferred critical ranges.
Example 3 The original non-modified polyether foams of Examples 1 and 2 containing a residual polyol wetting agent of less than 1% by wei~ht are found substantially non-absorbent in that water when applied to the foam beads up and stands on the surface theneof. As previously stated the average pore siæ of the original open-celled foam structure is greater than about 200 micrometers. After the heat and press~re treatment described in Example 1, approximately half of the foam sheet thickness is permanently but cnly partially collapsed into a microporaus surface skin having cell pore sizes in the range of between about 0.2 to about 200 micrometers. After the heat and pressure treatment, the concentration of wetting agent in the modified surface is found by extraction to be above 0.01% ky weight but less than 1.0% by weight. The t~me, temperature, and pressure applied to the foam surface during oompression, is previously determined by prelimunary tests so as to allow the foam to pass into its second order transition te~perature but not to substantially exceed its first order transition temperature whic~
could lead to fusing. A standard wet-out test is performed by applying water an the partially collapsed surface of the foam which is significantly smcother than the original surface of the parent foam. Absorption is readily apparent with the water diffusing rapidly into the microporous surface within a matter of several seconds after application. m e standard wet-out test is repeated on the non-m~dified side of the original foam and such foam is shown to remain ywl/~ 13 -1066~66 substantially non-absor~ent.
The surfaces of the microporous modified foams are completely wetted by the continuous application of water onto the surface after initial wet-out. The water is absorbed uniformly along the total surfa oe indicating no differential in the x or y direction (width or length direction) and no fluid paths are found further f m m the center of the water application in any direction along the surface indicating uniformity of pore size distribution. Upon suFersaturation of the smooth mDdified surface, the water is subsequently rejected therefrom and passed into the adjacent macro-celled portions of the un-modified foam. As water continues to be ap1plied onto the microporous surface, it will continue to pass into the reservDir por-tion of theun- modified foam indicating a one~way valving effect, possibly the result of the foam density differential in the z direction (the direction of thickness of the foam). Possibly the density differential creates a capill~rity effect throughout the modified structures, the force of which is sufficiently large to overcome the surface tension of the liquid or water against the non-absor~ent macroporous foam oells to allow liquid to penetrate these large open cells by displacing the air previcusly occupying them. It is significant to note that the modified foam surface continues to absorb water and reject and pass only excess liquid into the adjacent non-absorbent macro-cells. It is substantially shcwn by experiments on pigs that pooling of serum in the vicinity of a wound with resultant maceration iA avoided as the mcdified surfaoe of the foam dressing exhibits rapid absorptive capacity while still allowing the microporcus surface in contact with the wound to remain moist, thus prDviding a proper microclimate for epithelization.
Example 4 The same heat and temperature procedure of Example 1 is repeated using a polyether based.polyurethane foam manufactured from the following foLmulation:
ywl/d ~ ' - 14 -~0~6~66 - ngredl;ents Parts by Weight OKypropylated glycerin (a polyether) 100 Stannous Octoate 0.25 Water 4.0 Dimethylethanolamine 0.1 Silicone Surfactant 1.5 Toluene Diisocyanate (80/20 isomer) 49.8 Again the procedure employed is found to produoe a product in the critical cell size but containing wetting agent outside the critical range.
Example 5 ffle same heat and temperature of Example 1 is repeated using a fo~m based on a polyester manufactured from the following formulation:
Ingredients Parts-k~ Weight Polyester of adipic acid, trimethyl prDpane & diethylene glycol 100 Toluene diisocyanate (80% 2,4 - 20~
This invention relates to an integral, non-laminated, non-rigid, open cell polyurethane foam article for use as a surgical dressing and also to the method of producing such an article.
A dressing material for a wound must ideally possess several properties. Such a dressing should be absorbent to remove excess exudate from the wound and at the same time be capable of protecting the wound from mechanical injury as well as reducing the risk of infection thereof by bacteria. Preferably, it should be non-adherent to the wound so as not to disturb I healing during periods of inspection of the wound or removal of the dressing. Furthermore, a dressing material must be free of toxic substances which may be absorbed into the wound. While all dressings must preform certain basic functions, it has been well documented that the pattern of healing (speed and quality) can be profoundly affected by the kind of dressing used.
Commonly known cellulosic dressings, such as cotton lint, cotton gauze, cotton wool pads and cotton/rayon wool pads faced with non-woven materials demonstrate good absorbent qualities, but their surface fibers tend to adhere to the wound or to absorb the scab-forming serum so that they actually become embedded in the scab as it coagulates and hardens. Thus, if these dressings are removed to allow inspection or treatment of the wound, the wound tissue or scab may be damaged, retarding the healing process and even re-opening the wound. Furthermore, the open weave construction of these dressings and the uncontrolled absorbency rate of the cellulosic fibers causes the serous exudate on the wound surface to dry out. The epidermis regenerating from the wound edges and from cut surfaces of hair follicles within the wound is then forced to move through the fibrous tissue beneath the dry layer which fo~led the scab and the epitherlization rate is thus substantially slower than if the ywl/ ~
-^ 106646i6 epithelium were allowed to move through a moist fluid layer.
Attempts have been made to provide wound dressings of fully occlusive materials, such as polyethylene, in order to keep the wound area from dehydrating. Such dressings provide a satisfactory environment for skin regeneration by preserving a fluid layer of serum in the vicinity of the wound.
Epithelization rate under these occlusive conditions has been shown to be at least twice as rapid as with the fibrous oellulosic dressings. However, it is essential to apply such fully occlusive dressings in a sterile state and under sterile conditions to prevent harmful bacteria from entering the wound area and breeding close to or in the wound. Furthermore, such dressings do not absorb exudate, thus causing pooling in the wound which is not desirable.
The use of polyurethane foam as a partially occlusive dressing has been attempted in the past as well. Such dressings-however made from Bowater-Scott's "Sterafoam ~ .M.)" and Harrison and Jones' "Supersoft(T-M )" have an open-cell structure with ~elati~ely enormous pores (greater than 200 micrometers) compared to the tissue fibers and cell~ on the wound surface. The serous exudate will penetrate theSe dressings only under pressure, filling the large open cells with proteinaceous fluid, erythrocytes, and leucocytes. Histological evidence shows that the exudate on the wound surface will generally remain moist for at least a few days with the regenerating epidermis migrating through the moist exudate between the wound surface and the over-lying dressing. ~y preserving this moist environment while epidermal migration is taking place, epithelization is relatively rapid compared to wounds covered with conventional celluslosic dressings. However due to the excessive cell pore size of such foam, relative to the tissue cell size, it is necessary to press such nonmodified open-celled polyurethane foam dressing ywl/~3 ~ 2 -1066~t~6 against the wound to physically drive serum into the dressing to overcome the surface tension of the serum and allow excess exudate to be removed. The polyurethane foam cell structure becomes impressed into the dermis, indenting the collagenous tissue, and causing numerous inflammatory cells to be attracted to this foreign material. The relative difference between foam cell size and tissue cell size also allows the regenerating epidermis to grow around the particles of polyurethane foam. This stimulates hyperplasis resulting in bizarre epidermal tissue. In some cases, particles of foam are broken away from the large open-celled dressing and come to lie in the developing connective tissue under the new epidermis causing foreign body reactions. In addition such indentation of the wound surface with inclusion of particles of polyurethane within the epidermis and dermis may also lead to excess fibrosis, granuloma and scarring.
In some cases, non-adherent wound dressings have been made by placing a normally occlusive material, such as poly-ethylene, over the front surface of an absorbent pad, such as cotton gauze. To perform properly, the occlusive surface contains perforations or is spatially apertured to allow exudate to migrate into the absorbent backing. Nhile such a structure partially overcomes the problems of adherence to the wound as commonly found in cotton gauze dressings and of foam particles embedding in the wound, the uncontrolled absorption of the pad causes the wound area to dry out, scab formation to occur, and the epithelization rate to be retarded by forcing the regenerating epithelium to migrate beneath the dry necrotic region.
ywl/,~ ~~ _ 3 _ .~
- 1066~6 It i9 therefore an ob~ect of the present invention to provide improved polyurethane surgical dressings which allow for a more satisfactory microclimate for tissue regeneration and a process for producing the same.
In one particular aspect the present invention provides an integral, non-laminated, non-rigid, open cell polyurethane foam article comprising at least one modified surface with essentially all of said surface having a microporous structure of an average pore cell size between about 0.2 to 200 micrometers in contrast to the remaining un-modified macroporous portions of the foam having an average pore cell size range between about 200 - 2,000 micrometer~, said modified, microporous surface further character-ized by an inherently absorbent structure of permanently but only partially collapsed or compressed open foam cells as contrasted to the said non-modified macroporous foam cell portions which are substantially uncollapsed and inherently non-absorbent.
In another particular aspsct the present invention provides the procesq for producing an absorbent structure on a surface of an essentially non-absorbent, non-rigit, open-cell polyurethane foam material having an average pore cell size range between about 200-2000 micrometers comprising applying sufficient heat and pressure to said foam surface to result in permanently but only partially collapsing the surface cells into a motifiet microporous integral structure having an average pore cell size range between about 0,2 to 200 micrometers whereby essentially all of said motifiet surface structure is inherently absorbent as contrasted to the remaining untreated and non-modified macroporous foam cell portions.
Various other objects and advantages will be apparent to one skilled in the art upon reading the following disclosure and the novel features will be particularly pointed out hereinafter in connection with the appended claims. It is understood that ~ -4-, 10~6~66 the details may be modified without departure from the principles of the invention which is readily understood when taken in con-nection with the accompanying description and examples.
Various processes for subjecting polyurethane foams to heat and pressure are well known in the prior art and it is understood that the present invention does not claim as novel such processes in general or articles produced thereby. Rather the preferred embodiment provides a polyurethane foam article, the foam cells on at least one surface being permanently but only I0 partially collap~ed compared to the remaining portions ~ 4a--` 1066~66 of the foam article and wbich surfaoe is further rendered more readily absorbent by conoentrating or adding an am~unt of wetting agent per unit surfaoe into the collapsed membrane surfaoe relative to cells in the remaining portions of the foam article; the cell pore siæ of said surface being critically controlled preferably in conjunction with the conoentration of wetting agent(s) to produce a unique wound dressing which pmvides a satisfactory microclimate for tissue regeneration and improved wound healing.
The article described in this present invention is fabricated fmm an original b~e material of an open-celled polyurethane foam having oe lls of an average pore siæ in the range of about 200 to about 2,000 mincrometers and containing in one of the preferred enbodiments of the invention a residual conoe ntration of wetting agent(s). The article further compri æs a microporous surfaoe region of oFen cells which bave been permanently partially collapsed from that of the original ba æ cells so that the average p~re cell si æ in said surfaoe region is between about 0.2 to 200 micrcmeters and preferably containing a conoe ntration of wetting agent in said microporous surfaoe of no greater than about 1% and preferably no less than about 0.01 percent by weight.
It is found that if the average pore cell siæ of the original foam base material is less than about 200 micrometers the entire structure including the modified and nonimDdified portions will continue to wick l~p exudate and the modified micropor~us polyurethane surfaoe next to the wDund will dry out, thus substantially preventing development of the proper environment for epithelization and tissue regeneration. In contrast should the oe 11 pore size of the original foam structure employed to fabricate the unique dressing material of the present invention be greater than about 2000 micrometers, it is found that exoe ss exudate will not be held in the non-mcdified foam portion of the dressing and will instead tend to flow out into the environment making the article an unsatisfactory wound dressing. The critical range of,about between 200 to 2,000 micrometers for the original non-mDdified foam portion was found in practioe to be the ideal range for maintaining the adjaoe nt modified microporous surfaoe in a reasonably moist ywl/ ~ ~ 5 ~066466 state with the non-modified back up foam further functioning as a reservoir for holding excess exudate therein. The pore size of polyurethane cellular material may be oontrolled or varied as desired by well kn~wn and conventional means such as for example in the case of isocyanate derived polymers by the addition of foam stabiIizing or ooalescing agents.
It is further found that if the wetting agent(s) on the m~dified microporous polyurethane foam surfaoe oonstitute less than the preferred minimNm of about 0.01~ by weight, the article will not readily absorb exudate into its structure thereby tending to cau æ pooling of ser~m below the microporous foam surfaoe cover which further causes maoe ration of tissue in the wound area. Should the wetting agent(s) contained in the microporous foam surface be~c~e greater than about 1% by weight, it is found in tests conducted on pigs that wounds dry exoe ssively and the rate of epithelization is increasing sJower as the level of wetting agent(s) increaæs above the 1~ level.
The foam cells oo~prising the microporous surface have been defined as "permanently but only partially collapsed". It is known that polyurethane foam can be reversibly deformed or compressed to reduoe thickness up to a oe rtain extent but will esæntially recover its original thickness upon washing or steam heating. The present invention relates to compression of the surfa oe of the foam at an extended temperature beyond thds pre-determined extent, that is, to an "irreversible" (pe~manent) process. The open oe lls defined as "partially oollapsed" have their standard structural me~bers (polymer strands) distorted to produce smaller cells or pores, but it is i~portant that the cells are not completely collapsed or fused. So as not to have an average pore cell size less than about 0.2 micrometers, the temperature of the polyurethane foam employed in the present process may exceed its second order transition point or glass temperature but n~t exoeed the fi s t order transition temperature for the specific polymer and pressure applied. Such an effect is produoe d by controlling the temperature and pressure parameters employed.
The foam article of the present invention is preferably in the YWV ~ C` - 6 -` ~66~66 form of a sheet, strip or ribbon and one or both of the major surfaces of the foam thereof may be increased in density. Where hoth surfaces of the foam are of increased density, the densities of the two surfaces may be the same or different.
According to a further aspect of the invention there is provided a process for making an open-celled polyurethane foam article which comprises applying pressure and heat to at least a surface of the foam to permanently (irreversibly) partially collapse the foam cells on said surface to an extent such that said surface is or may be rendered absorbent. The cells on said surface must be permanently but only partially collapsed to produce a micro-porous surface having an average pore size no greater than about 200 micro-meters and preferably containing therein at least about 0.01% by weight of wetting agent to overcome the surface tension of blood, serum, water, and other fluid exudate. The surface pores must also be larger than about 0.2 micrometers to allow proper wicking and absorption of said exudate to pass through the collapsed surface membrane. The foam cells remote from said surface remain unchanged at a pore size greater than about 200 micrometers . . ~ .
so as not to be readily absorbent but to still allow excess exudate to be rejected from said collapsed microporous surface into the remote, unchanged cell8 of the original foam and held therein as if in a reservoir.
The surface of the foam which is to be partially collapsed must be heated to a temperature near the softening point of the foam. This varies with foam composition and the surface temperature may suitably be from 300 F
to 450 F depending on the time the foam is subjected to heat and pressure.
It is important not to exceed the fusion temperature of the particular foam since this would cause complete collapse of the cells. The pressure applied may, for example, be up to 200 pounds per square inch and is preferably from 50 p.s.i. to 100 p.s.i.
This heat and pressure may be applied to said surface by conventional means such as a heated plate or roller. During the pressure and heat treat-ments, a release material, for example, silicone coated paper or a sheet of Teflon fluorocarbon, may be placed between the heatinq means and the said surface of the foam to prevent adhesion of the foam material to the plate dg/~ -7-1066~66 or roller and maintain the smooth micrcporous me~brane surface thus created.
The initial or starting piece of foam may be of any thickness but is preferably from about 0.1 cm to about 10 cm and is preferably modified by heat and pressure to a final thickness of fram about 0.05 cm to about 5 cm, preferably with a compressed micrcporous surface thickness up to about 5 mm.
Fram a practical standpoint, to obtain a one sided micraporws surface in the desired pore siæ range, the foam material is usually reduoed to ab~ut half its original thickness. Hawever, this is not essential; very thin pi e s of foam material, approximately 0.1 cm in thickness, can be } red absorbent by this pr~cess and it is only n e ssary to modify the s~lrfaoe to a depth of about 0.04 mm to achieve a satisfactory result.
The foam sheet, strip or ribbon may be similarly modified on both faoe s for which purpose the foam, after being removed from betwsen the plate or roller and the relea æ material, (if present) conveniently is reversed and the operation repeated. Alternatively, the pressure plate may be heated to the foam modifying temperature so that both surfaoe s of the foam or even the full thickness of the foam may be modified by heat and pressure in one or more pressing and heating operations.
m e foam which is e~ployed in the invention may be a reticulated or nonrreticulated, open-oe ll polyurethane foam based on polyester or polyether which foam is essentially non-absorbent in that any residual wetting agent(s) remaining in the foam during manufacture does not exoeed 1 percent by weight of the foam. By peDmanently but only partially collapsing the surfaoe of such an open-oe lled foam to a microporous me~brane structure of the critical pQre siæs as previously defined, the density or surfa oe area per gram weight of foam is decreased. m is modification in density also increa æs the con oentration of any residhal wetting agent present in the original foam, thus rendering said surface more readily absorbent. By reducing the original piece of foam to approximately one half its initial overall thickness by partially collapsing the oe lls of one surface, the weight of residual wetting agent(s) per unit surfaoe in the said modified surfaoe can be increased approximately up to ten times its original weight ywl/~ - 8 -10669~6fi per unit surface.
m e use of the article of the present invention as a surgical dressing in animal research on pigs indicates that the level of wetting agent(s) oont~;n~d in the microporous surface of the polyurethane foam should preferably not exceed about 1 peroe nt by weight. ~eyond that level, most wetting agents appear to be at least slightly toxic to epidermal oe lls on the wDund surface and to impair epidermal regeneration. While epidermal regeneration is still significantly more rapid under the p~lyurethane foam article at slightly above the said 1 percent level than wounds ccvened under cellulosic ootton dressings, the quality of wound healing is progressively degraded as the ccr~ ]}ltion of wetting agents in the surface increase above such con oe ntration level.
Wbund healing can also be impaired if ex oe ss exudate from a w,ound does not flow relatively freely into the microporous foam surfa oe but is allowed to pool in the vicinity of the wound. If pooling is prolonged, ma oe ration of the wound may occur and healing will break down and the wcund ~ecorls unmanageable. Therefore, although certain improved h~ling characteristics attributable to the article of this invention may at timeæ
be obtained in the absen oe of any appreciable wetting agent, (prDvided of course that the critical porosity range is maintained) however the nunim~m level of wetting agent(s) desired in the said microporous surface of the polyurethane foam dressing is still preferably akove the 0.01 per oe nt by weight to penmit the exudate to be immediately absorbed into the microporous membrane surfa oe at a relatively controlled, even rate.
Applicants have attempted to determine the physical and chemical characteristics which will predict that a particular open-celled poly-urethane foam which is generally essentially non-absorbent can be rendered to produce a surgical dressing that will provide a proper microclimate for tissue regeneration and enhan oe wound healing. In general, it is necessary to perform preliminary tests with any given sample of foam, but preferred formulations of reticulated or non-ret iculated, polyester and polyether open-cell polyurethane foams are cited in the examples. The bulk density, ywl/ j.~ r~ 9 1066~6~;
cell size, and thickness of the initial foam material may be chosen for the particular application for which the absorberit product is required, but the average pore cell size of the initial material should be maintained in the critical range of from about 200 to about 2,000 micrometers. If polyurethane foams are selected having residual levels of wetting agent(s) which fall out-side the critical or preferred range, the level can be easily adjusted. This readjustment can be made by substantially completely extracting any residual wetting agent(s) remaining in the original polyurethane foam after manufacture.
The desired concentration of wetting agent can be reapplied to at least the modified surface area and dispersed therein in an even omnidirectional pattern substantially throughout the microporous region. Suitable examples of wetting agents include anionic, nonionic and cationic surfactants singly or as mixtures, such as long chain hydrocarbon sulfates or sulfonates, e.g., sodium laurel sulfate, or long chain hydrocarbon radicals attached to polyethylene oxide radicals, such as nonylphenal poly (ethyleneoxy) ethanol (e.g. Igepal C0-730).
A particularly satisfactory wetting agent is the ammonium salt of a sulfate ester of a alkylphenoxypoly ethanol sold under the trademar~ Alipal C0-416 (Antura Chemical Co.). For use especially in a surgical dressing article, the wetting agent could be for example polyvinyl pyrollidone, ~Propylan 8123) polyoxypropylene glycol, (Carbowax 200) polyethylene glycol, (Alipal C0-436) or similar F.D.A. approved wetting agents capable of enhancing the absorption of serum exudate from a wound. A satisfactory method of applying the wetting aqent to the foam is by dipping the foam in the desired solution of a wettinq agent and carefully wringing out the excess and drying in a vacuum at 110 C.
The concentration of wetting agent in the dried foam can be determined by the volume of solution dried out in the foam.
As previously stated the foam articles of the present invention are particularly advantageous for use as surgical dressing materials. In this respect, the product can be readily sterilized, for example, by means of steam autoclave, gamma irradiation, or ethylene oxide. Also, the body of the aressing material is suitable for incorporating a medicament such as an dg/; ~' -10-1066~6fi anti-bacterial and~or antiseptic. m e dressing may be impregnated with such a medicament after the heat and pressure treatment but prior to sterilization. The dressing may be treated by depositing a film of medicated material on to the dressing or by dipping the dressing into a-solution of medication material and then drying the material.
For purpDses of this disclosure the term "resid~al" wetting agent is a wetting agent which may be found present in the original foam material after manufacture. For example, in the manufacture of a polyether based polyurethane, an excess amount of a polyether polyol such as polyo~ypr~pylene glycol may be employed in the formula mix. After polymerization of the mix into the foam material there will be found resid~al or excess polyol that did not react. mus the amount of residual (unreacted) polyol (wetting agent) in the foam may be brought to various levels by controlling the am~unt included in the initial mix or formulation.
However it is difficult to exactly oontrDl the quantity of unreacted wetting agent that will remain in the newly manufactured foam by the "residual"
method. It is therefore preferre~d that the fcam material be first treated by a solvent extraction process to rem~ve all wetting agents present if any and then to reapply the wetting solution therein under controlled conditions up to any amount desired.
The following examples show, by illustration and not ky limitation, the methods and materials which can be utilized in fabricating op~nrcelled FDlyurethane foam articles of the present invention ky employing an original foam material having average oe ll pore sizes of more than about 200 micrometers but less than about 2,000 micrcmeters and which initial foam material is generally non-absorbent, the surfaoe of which is subseguently rendered absorbent by decreasing the average cell pores si æs to the critioal range between about 0.2 to about 200 micrometers and preferably simultaneously or subsequently achieving a concentration of wetting agent(s) in said modified surface of between about 0.01% to 1.0% by weight.
ywv,9 .f - 11 -1066~66 Example I
A loaf of polyurethane foam based on polyether is n~nufactured from the following formulation by means well known in the art:
Ingredients Parts ky Weight PolyoxyprDpylene glycol 100 (a polyether polyol) Stannous Octoate 0.25 Water 4.0 Dimethylethanolamine 0.5 Silicone Surfactant 2.0 Trichloromonofluoromethane 15.0 Toluene diisocyanate (80% 2,4- 82.5 20% 2,6 isomer) By pho~amicroscopy the average pore siæ of the foam so produced is found to be in the critiaal range of between about 200 to about 2,000 micrometers. A residual wetting agent of polyol remained in the foam after manufacture as determined by extraction with ethanol in a Soxhlet extractor.
A sheet of foam is cut from the loaf in a conventiona manner.
. .
A silicone coated release paper is plaoe d on one surfaoe of the sheet which is then plaoe d in contact with a metal platen heated to a temperatwre in the range bebween 380 to 410F. A cold pressure plate is foroed against the free faoe of the foam, pressing the foam against the heated platen. A
pressure of about 70 p.s.i. is maintained for about 20 seconds, at which time the cold pressure plate is remoNed and the sheet of modified foam is stripped from the siliaone paper. The temperature employed in the heated platen is adjusted to result in the formation of a permanently, ~ut only partially collapsed skin having an average pore siæ in the critical range of from about 0.2 to about 200 micrometers and a skin concentration by weight of polyol wetting agent falling within the critical range of 0.01 to 1.0%.
Example 2 m e heat and temperature proce~lre of Example 1 is repeated using a polyether foam manufactured fr~m a slightly modified formulation:
ywl/~ 12 -106~46fi Ingredients Parts by Weight Polyox,opropylene glyool (a polyol) 100 Stannous Cctoate 0.4 Water 2.8 Dimethylethanolamine 0.7 Silic~ne oil 1.6 Trichloromonofluoromethane 13.0 ~oluene diisocyanate (80/20 isomer) 36.9 It is found that the resulting article has pore cell size and ooncentration of polyol wetting agent in the required and preferred critical ranges.
Example 3 The original non-modified polyether foams of Examples 1 and 2 containing a residual polyol wetting agent of less than 1% by wei~ht are found substantially non-absorbent in that water when applied to the foam beads up and stands on the surface theneof. As previously stated the average pore siæ of the original open-celled foam structure is greater than about 200 micrometers. After the heat and press~re treatment described in Example 1, approximately half of the foam sheet thickness is permanently but cnly partially collapsed into a microporaus surface skin having cell pore sizes in the range of between about 0.2 to about 200 micrometers. After the heat and pressure treatment, the concentration of wetting agent in the modified surface is found by extraction to be above 0.01% ky weight but less than 1.0% by weight. The t~me, temperature, and pressure applied to the foam surface during oompression, is previously determined by prelimunary tests so as to allow the foam to pass into its second order transition te~perature but not to substantially exceed its first order transition temperature whic~
could lead to fusing. A standard wet-out test is performed by applying water an the partially collapsed surface of the foam which is significantly smcother than the original surface of the parent foam. Absorption is readily apparent with the water diffusing rapidly into the microporous surface within a matter of several seconds after application. m e standard wet-out test is repeated on the non-m~dified side of the original foam and such foam is shown to remain ywl/~ 13 -1066~66 substantially non-absor~ent.
The surfaces of the microporous modified foams are completely wetted by the continuous application of water onto the surface after initial wet-out. The water is absorbed uniformly along the total surfa oe indicating no differential in the x or y direction (width or length direction) and no fluid paths are found further f m m the center of the water application in any direction along the surface indicating uniformity of pore size distribution. Upon suFersaturation of the smooth mDdified surface, the water is subsequently rejected therefrom and passed into the adjacent macro-celled portions of the un-modified foam. As water continues to be ap1plied onto the microporous surface, it will continue to pass into the reservDir por-tion of theun- modified foam indicating a one~way valving effect, possibly the result of the foam density differential in the z direction (the direction of thickness of the foam). Possibly the density differential creates a capill~rity effect throughout the modified structures, the force of which is sufficiently large to overcome the surface tension of the liquid or water against the non-absor~ent macroporous foam oells to allow liquid to penetrate these large open cells by displacing the air previcusly occupying them. It is significant to note that the modified foam surface continues to absorb water and reject and pass only excess liquid into the adjacent non-absorbent macro-cells. It is substantially shcwn by experiments on pigs that pooling of serum in the vicinity of a wound with resultant maceration iA avoided as the mcdified surfaoe of the foam dressing exhibits rapid absorptive capacity while still allowing the microporcus surface in contact with the wound to remain moist, thus prDviding a proper microclimate for epithelization.
Example 4 The same heat and temperature procedure of Example 1 is repeated using a polyether based.polyurethane foam manufactured from the following foLmulation:
ywl/d ~ ' - 14 -~0~6~66 - ngredl;ents Parts by Weight OKypropylated glycerin (a polyether) 100 Stannous Octoate 0.25 Water 4.0 Dimethylethanolamine 0.1 Silicone Surfactant 1.5 Toluene Diisocyanate (80/20 isomer) 49.8 Again the procedure employed is found to produoe a product in the critical cell size but containing wetting agent outside the critical range.
Example 5 ffle same heat and temperature of Example 1 is repeated using a fo~m based on a polyester manufactured from the following formulation:
Ingredients Parts-k~ Weight Polyester of adipic acid, trimethyl prDpane & diethylene glycol 100 Toluene diisocyanate (80% 2,4 - 20~
2,6 isomer) 53.5 N-ethylmorpholine 2.0 Water 4 3 Anncnium oleate 1.5 Coupling agent (Witco EC~Z~ 77-86 non-ionic/anionic surfactant blend oonkaining poly~l, alcohol, carboxylic acid esters and oil soluble sulfonates 1.5 The finished polyester based $Dam article is founa to oontain cell siæs that fall in the critical range required for the prDper functioning of koth the mDdified and non-m~dified portion of the foan.
Example 6 m e same procedure of Example 1 is reFeated using reticulated (skeletoni æd) palyurethane foams having as much as 97% void area and available commercially under the trademark Scottfoam from Foam Division, Scott Paper Co., Chester, Pa. The samples of reticulated foams are identified by the manufacturer as polyester and polyether polyurethane foams. m e foam samples as obtained from the manufacturer are all found ywl/ j ~ A ~ ~, 15 106i6466 to have average pore sizes within the critical range of 200 to 2,000 micro-meters. The heat and temperature procedure is successful in partially collapsing a surfa oe into a micrDporDus structure possessing oe ll sizes falling within the preferred ranges.
Example 7 The modified foams of Exa~ples 1, 4, 5 and 6 are subsequently extracted with ethanol in a Soxhlet type extractor to substantially remDve all wetting agents oontained therein. Such treatment does not change the pDre size of the modified surfaces of the foams. Standard wet-out tests can be performed and the mDdified surfaces will be found to absorb but not very readily. Various am w ntS and kinds of wetting agents are re-applied to the surfa oe s in measured doses to establish the critical minimum level at which the structures readily absorb fluids within a matter of several seconds. It is found that a minimum dose level approxImately equivalent to not less than 0.01% of the weight of the mDdified surfa oe is required to onoe again render the surfa oe membranes very readily absorbent. Various wetting agents used include Lankno Chemical, Ltd.'s PropylanTM8123, Union Carbide's CarbowaxTM
200, and Antara Chemical's Alipal(TM)C0-436. The wetting agents are preferakly applied ~y first dissolving in a suitable solvent such as a 90/10 ethanol/
water mixture and applying the desired amDunt to the foam before or after heat treatment. A measured volume of the wetting agent solution may be rked into a weighed amount of foam to obtain the required ooncentration.
Alternatively, the foam may be immersed in the sDlution and the ex oe ss pressed or wrung out. In any case, the solvent is allowed to evaporate leaving the detergent substantially evenly distributed thrDughout the foam or thnDughout the micr,oporous surface of the foam depending upon the manner of application of the solution. The concentration of wetting agent in the foam is oontrolled by adjusting the concentration of such asent in solution and/or by adjusting the amount of solution applied per unit weight of foam or per unit weight of micropor~us surfa oe . The wet-out tests shcw the samples to be very readily absorbent on their modified microporous surfa oe s.
ywl/~ 16 -~ 1066~;~; `
Example 8 The m~dified foams described in Example 7 are dc~ed with levels of various wetting agents above the 1% con oentration for subsequent testing on pigs to determune the effect on w~und healing at the increased ooncentra-tions. It is found that in using dressings made fram samples of higher concentrations, epithelization is n~t as rapid when co~pared to dressings containing less than about 1% by weight of wetting agent(s) in the micro-ponous surface. No fundamental differenoe s are found among samples oortaining different wetting agents at substantially the same doping levels.
Example 9 ~ he Soottfoam(l~ polyether and polyester poly~rethane foams of Exa~ple 6 which are found to have the preferred averaged pore si æ range of about between 200 micmmeters and 2,000 micrometers, are nDdified on their surfaoe by heat and pressure as described in Example 1 until the oell pore si æ is in the preferred range of 0.2 micromters to 200 micrameters. The level of wetting agent is found to be outside the preferred range. me material is subsequently extracted of substantially all wetting agents and a desired v~lume of a wetting agent solution is re-applied in the preferred range of about 0.01% to 1% by weight. After drying, the samples are subjected to wet-out tests and found to be accept~ble.
ywl/~ 17 -
Example 6 m e same procedure of Example 1 is reFeated using reticulated (skeletoni æd) palyurethane foams having as much as 97% void area and available commercially under the trademark Scottfoam from Foam Division, Scott Paper Co., Chester, Pa. The samples of reticulated foams are identified by the manufacturer as polyester and polyether polyurethane foams. m e foam samples as obtained from the manufacturer are all found ywl/ j ~ A ~ ~, 15 106i6466 to have average pore sizes within the critical range of 200 to 2,000 micro-meters. The heat and temperature procedure is successful in partially collapsing a surfa oe into a micrDporDus structure possessing oe ll sizes falling within the preferred ranges.
Example 7 The modified foams of Exa~ples 1, 4, 5 and 6 are subsequently extracted with ethanol in a Soxhlet type extractor to substantially remDve all wetting agents oontained therein. Such treatment does not change the pDre size of the modified surfaces of the foams. Standard wet-out tests can be performed and the mDdified surfaces will be found to absorb but not very readily. Various am w ntS and kinds of wetting agents are re-applied to the surfa oe s in measured doses to establish the critical minimum level at which the structures readily absorb fluids within a matter of several seconds. It is found that a minimum dose level approxImately equivalent to not less than 0.01% of the weight of the mDdified surfa oe is required to onoe again render the surfa oe membranes very readily absorbent. Various wetting agents used include Lankno Chemical, Ltd.'s PropylanTM8123, Union Carbide's CarbowaxTM
200, and Antara Chemical's Alipal(TM)C0-436. The wetting agents are preferakly applied ~y first dissolving in a suitable solvent such as a 90/10 ethanol/
water mixture and applying the desired amDunt to the foam before or after heat treatment. A measured volume of the wetting agent solution may be rked into a weighed amount of foam to obtain the required ooncentration.
Alternatively, the foam may be immersed in the sDlution and the ex oe ss pressed or wrung out. In any case, the solvent is allowed to evaporate leaving the detergent substantially evenly distributed thrDughout the foam or thnDughout the micr,oporous surface of the foam depending upon the manner of application of the solution. The concentration of wetting agent in the foam is oontrolled by adjusting the concentration of such asent in solution and/or by adjusting the amount of solution applied per unit weight of foam or per unit weight of micropor~us surfa oe . The wet-out tests shcw the samples to be very readily absorbent on their modified microporous surfa oe s.
ywl/~ 16 -~ 1066~;~; `
Example 8 The m~dified foams described in Example 7 are dc~ed with levels of various wetting agents above the 1% con oentration for subsequent testing on pigs to determune the effect on w~und healing at the increased ooncentra-tions. It is found that in using dressings made fram samples of higher concentrations, epithelization is n~t as rapid when co~pared to dressings containing less than about 1% by weight of wetting agent(s) in the micro-ponous surface. No fundamental differenoe s are found among samples oortaining different wetting agents at substantially the same doping levels.
Example 9 ~ he Soottfoam(l~ polyether and polyester poly~rethane foams of Exa~ple 6 which are found to have the preferred averaged pore si æ range of about between 200 micmmeters and 2,000 micrometers, are nDdified on their surfaoe by heat and pressure as described in Example 1 until the oell pore si æ is in the preferred range of 0.2 micromters to 200 micrameters. The level of wetting agent is found to be outside the preferred range. me material is subsequently extracted of substantially all wetting agents and a desired v~lume of a wetting agent solution is re-applied in the preferred range of about 0.01% to 1% by weight. After drying, the samples are subjected to wet-out tests and found to be accept~ble.
ywl/~ 17 -
Claims (16)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An integral, non-laminated, non-rigid, open cell poly-urethane foam article comprising at least one modified surface with essentially all of said surface having a microporous structure of an average pore cell size between about 0.2 to 200 micrometers in contrast to the remaining un-modified macroporous portions of the foam having an average pore cell size range between about 200-2000 micrometers, said modified, microporous surface further character-ized by an inherently absorbent structure of permanently but only partially collapsed or compressed open foam cells as contrasted to the said non-modified macroporous foam cell portions which are substantially uncollapsed and inherently non-absorbant.
2. The foam article of Claim 1 comprising a non-retriculated open cell structure.
3. The foam article of Claim 1 comprising a reticulated open cell structure.
4. The article of Claim 1 wherein the said modified sur-face portion contains a wetting agent in a concentration by weight of between about 0.01 to 1%.
5. The article of Claim 4 wherein the wetting agent is selected from the group consisting of an anionic, nonionic and cationic surfactant or mixtures thereof.
6. The article of Claim 4 wherein the non-modified foam portion also contains a wetting agent and wherein the concentration of said wetting agent in said modified surface portion is between one to ten times the concentration contained in the said non-modified foam.
7. The article of Claim 1 including, incorporated therein, a medicament.
8. The process for producing an absorbent structure on a surface of an essentially non-absorbent, non-rigid, open-cell polyurethane foam material having an average pore cell size range between about 200-2000 micrometers comprising applying sufficient heat and pressure to said foam surface to result in permanently but only partially collapsing the surface cells into a modified microporous integral structure having an average pore cell size range between about 0.2 to 200 micrometers whereby essentially all of said modified surface structure is inherently absorbent as con-trasted to the remaining untreated and non-modified macroporous foam cell portions.
9. The process of Claim 8 wherein the original non-absorbent, macroporous polyurethane foam starting material contains residual wetting agents therein and which agents by the application of heat and pressure forming the collapsed microporous surface become concentrated therein in an amount between about 0.01 to 1%
by weight of the resulting microporous polyurethane surface structure whereby said surface becomes more readily absorbent.
by weight of the resulting microporous polyurethane surface structure whereby said surface becomes more readily absorbent.
10. The process of Claim 9 wherein the foam material is treated by solvent extraction to remove residual wetting agents which may be present and thereafter reapplying a controlled amount of the desired wetting agent therein.
11. The process of Claim 10 wherein the amount of desired wetting agent is applied after the formation of said modified microporous surface in an amount between about 0.01 to 1% by weight.
12. The process of Claim 10 wherein the solvent extraction is performed on the original foam material prior to the formation of the said microporous surface.
13. The process of Claim 10 wherein the solvent extraction is performed on the foam material after the formation of the said microporous surface.
14. The process of Claim 10 wherein the wetting agents are selected from the group consisting of an anionic, nonionic and cationic surfactant or mixtures thereof.
15. The process of Claim 8 wherein the heating of the foam is between said foams second and first order transition temper-atures.
16. The process of Claim 10 wherein the wetting agent is selected from the group consisting of polyethylene glycol, polyoxypropylene glycol, oxypropylated glycerin, polyvinyl pyrollidone and mixtures thereof.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/541,809 US3978855A (en) | 1975-01-17 | 1975-01-17 | Polyurethane foam surgical dressing |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066466A true CA1066466A (en) | 1979-11-20 |
Family
ID=24161147
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA243,581A Expired CA1066466A (en) | 1975-01-17 | 1976-01-14 | Polyurethane foam surgical dressing |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US3978855A (en) |
| CA (1) | CA1066466A (en) |
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-
1975
- 1975-01-17 US US05/541,809 patent/US3978855A/en not_active Expired - Lifetime
-
1976
- 1976-01-14 CA CA243,581A patent/CA1066466A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US3978855A (en) | 1976-09-07 |
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