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
  • A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
  • A61L31/04—Macromolecular materials
  • A61L31/043—Proteins; Polypeptides; Degradation products thereof
  • A61L31/045—Gelatin
• • 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
  • A61L24/00—Surgical adhesives or cements; Adhesives for colostomy devices
  • A61L24/04—Surgical adhesives or cements; Adhesives for colostomy devices containing macromolecular materials
  • A61L24/10—Polypeptides; Proteins
  • A61L24/104—Gelatin

Definitions

• the present invention relates generally to collagen and gelatin compositions and methods for their preparation and use.
• the present invention relates to a gelatin film having characteristics suitable for application to tissue for a variety of purposes.
• gelatin or collagen films have been applied to tissue for tissue sealing.
• Specific gelatin materials are described in parent application Serial Nos. 08/303,336 and 08/481,712, the full disclosures of which have previously been incorporated herein by reference.
• biocompatible adhesives including dialdehyde starch (DAS)
• DAS dialdehyde starch
• US 5,281,660 protein polymer surfaces
• DAS has also been utilized as an integral cross-linker in the preparation of shaped collagen/chitin composite materials that may have biomedical applications such hemostasis (US 4,378,017).
• collagen or gelatin films should possess a number of characteristics. They should be sufficiently thin so that (if desired) they can be effectively bonded to the underlying tissue by the subsequent application of energy. They should be sufficiently pliable so that they can conform to the tissue, further enhancing bonding to the tissue upon subsequent application of energy. They should possess low moisture, enhancing their preservation and permitting rehydration upon application to tissue. They should be sufficiently elastic, still further enhancing conformability to tissue. They should be sufficiently strong so that they can be bonded to tissue (with or without the application of energy) and can provide the desired sealing after bonding.
• WO 93/17669 describes particular hydrogel materials that may be applied to tissue, cross-linked by exposure to UV, and relied on for inhibiting tissue adhesion.
• U.S. Patents relating to materials and methods for inhibiting tissue adhesion include 5,422,376; 5,410,016; 5,380,536, 5,366,735; 5,364,622; 5,365,883; 5,321,113; 5,266,326; 5,264,540 . 5,194,473; 5,156,839; 5,135,751; 5,134,299; 5,126,141, 5,068,225; 5,017,229; 4,937,270; 4,937,254; 4,911,926, 4,889,772; 4,674,488; and 4,603,695.
• the present invention provides improved film compositions composing gelatin and/or collagen are useful for a variety of purposes, including immobilization over tissue for tissue sealing and/or inhibition of tissue adhesion.
• the films are characterized by a film thickness in the range from 0.03 mm to 0.2 mm, preferably being from 0.055 mm to 0.075 mm, and a pliability in the range from 1.0 mN to 4.0 mN, preferably from 2 mN to 3.5 mN.
• the gelatin films will be further characterized by at least one characteristic selected from the group consisting of (1) a moisture content in the range from 11% to 16%, preferably from 13% to 15%, (2) an elasticity in the range from 30% to 150%, preferably from 40% to 130%, (3) a tensile strength in the range from 150 N/cm 2 to 260 N/cm 2 , preferably from 170 N/cm 2 to 250 N/cm 2 , (4) a melting temperature in the range from 33°C to 40°C, preferably from 34°C to 37°C, (5) a collagenase digestion time in the range from 1 minute to 100 minutes, usually from 10 minutes to 40 minutes, preferably from 15 minutes to 35 minutes, and (6) a degree of swelling (V/V 0 ) in the range from 4.5 to 6.5, preferably from 5 to 6.
• Such films may be cross-linked or non-cross-linked, preferably being cross-linked.
• the gelatin films may further be granular or non-granular, preferably being granular.
• the films may comprise a plasticizer or be free from plasticizers .
• the films may comprise a cross-linking agent, preferably DAS which acts as a cross- linker if applied to one or both surfaces.
• the films will preferably comprise mostly or entirely gelatin, with collagen being present at less than 10% by weight, more preferably less than 1% by weight.
• Preferred gelatin films according to the present invention will be cross-linked, granular, include a plasticizer as described in greater detail below.
• the films may comprise a cross-linking agent over a portion or all of their surfaces.
• the particularly preferred cross-linking agent is a dialdehyde starch (DAS) .
• gelatin and/or collagen films according to the present invention comprise a sheet of granular, cross-linked gelatin and/or collagen (preferably gelatin) having a plasticizer content in the range from 5% by weight to 40% by weight, and a thickness in the range from 0.03 mm to 0.2 mm.
• Such films will usually consist essentially of gelatin and/or collagen, preferably gelatin, and the plasticizer, more preferably where the gelatin has been produced from collagen and residual collagen may be present to a low level, typically below 30% by weight, preferably below 1% by weight.
• Suitable plasticizers include polyethylene glycol, sorbitol, glycerine, and the like.
• the preferred plasticizer is polyethylene glycol with an average molecular weight of 400 (PEG 400) , present in the film from 5% by weight to 40% by weight.
• a solution containing a suitable biocompatible cross-linking agent can be applied over at least a portion of a surface of the gelatin and/or collagen film of the present invention.
• Films incorporating the cross-linker can be immediately applied wet to the tissue surface or (with an appropriately stable cross-linker) can be dried and stored for future tissue attachment.
• Suitable cross-linking agents include aldehydes obtained by oxidative cleavage of carbohydrates and their derivatives such as oxidized oligosaccharides, e.g. malto-dextrins and cellulose derivatives of various molecular weights, while poly- or di- aldehydes are more preferable, and dialdehyde starch is most preferable.
• the preferred cross-linker is dialdehyde starch with an oxidation degree of from 75% to 98%, applied to the film as an aqueous solution of from (0.5 mg/ml to 5 mg/ml) , most preferably at a concentration of 3%.
• the present invention provides packages comprising gelatin or collagen films as described above present in a container.
• the container maintains the sterility and moisture of the film, so that the films are ready for surgical use immediately upon being removed from the containers.
• Virtually any type of sterile medical container would be suitable, with sterile pouches and trays formed from moisture-impermeable materials, such as spun olefin, mylar, and the like, being exemplary.
• a method for sealing tissue comprises positioning the film as described above over a target region in tissue. Energy is then applied to the film while positioned over the region in an amount sufficient to immobilize the film on the tissue.
• the target region will typically be a surgical site, and the target tissue be any of a wide variety of tissue types such as muscle, skin, epithelial tissue, connective or supporting tissue, nerve tissue ophthalmic and other sense organ tissue, vascular and cardiac tissues, gastrointestinal organs and tissue, pleura and other pulmonary tissue, kidney, endocrine glands, male and female reproductive organs, adipose tissue, liver, pancreas, lymph, cartilage, bone, oral tissue, mucosal tissue and the like.
• the methods will be particularly useful for treating surgical sites in a target region, where the surgical site may be open or may have been sutured, stapled, or otherwise closed prior to permitting the tissue surface to engage an adjacent tissue surface.
• the method of the present invention for positioning the gelatin or collagen film over a surgical site is intended primarily for sealing the site or for inhibiting or preventing the occurrence of tissue adhesions between adjacent tissue surfaces.
• the terms "inhibiting”, and “inhibition” will denote both total inhibition (i.e. prevention) and partial inhibition of adhesion.
• the methods of the present invention may utilize an application of energy from a wide variety of sources, including electromagnetic energy, particularly electric energy, e.g. radio frequency (RF) energy and microwave energy, infrared (heat) energy, and ultraviolet energy; optical energy, e.g. laser; mechanical energy, e.g. ultrasonic; and the like.
• electromagnetic energy particularly electric energy, e.g. radio frequency (RF) energy and microwave energy, infrared (heat) energy, and ultraviolet energy
• optical energy e.g. laser
• mechanical energy e.g. ultrasonic; and the like.
• RF energy which can be provided by conventional electrosurgical power supplies operating at frequencies typically in the range of 200 kHz to 1.2 MHz.
• RF energy can be applied using applicators which provide a uniform, dispersed energy flux over a defined area, such as inert gas beam RF energy sources, more particularly argon beam RF energy sources .
• a preferred RF energy applicator comprises a spherical electrode surface as described
• the film will not be bound directly to the tissue, but will remain immobilized as a result of those areas where the film or sheet of material is bound.
• the energy may be applied about the periphery of the preformed film or sheet in order to attach the edges of the sheet to tissue. Additional locations within the periphery may also be tacked by applying spots or other small areas of energy to the material. It will also be possible to apply the energy uniformly to the film or sheet, thus resulting in substantially uniform bonding of the material to underlying tissue.
• a cross- linking agent applied to the gelatin and/or collagen film it may be possible to obtain adhesion and immobilization of the preformed film or sheet to the underlying tissue without the application of energy or with lower energy thresholds.
• the methods of the present invention may be performed in conventional open surgical procedures, i.e. where access to internal body tissues and/or organs is provided through a relatively large percutaneous surgical incision which permits the introduction of conventional surgical instruments.
• the gelatin and/or collagen films of the present invention may thus be introduced by the surgeon while directly viewing the target region through the incision and manipulating the film using conventional graspers and the like.
• the methods of the present invention for sealing tissue may be performed via less invasive surgery, e.g. laparoscopically, thoracoscopically, arthroscopically, or the like. Such procedures typically rely on forming small percutaneous penetrations and accessing the target region through cannulas placed within such penetrations. The target region is viewed through an associated viewing scope. In both open surgical procedures and less invasive procedures, the films will typically be cut into a desired configuration and dimensions prior to application over the tissue.
• gelatin and/or collagen preferably gelatin films are prepared by combining collagen and a plasticizer in an aqueous solution.
• the collagen is at from 60% by weight to 95% by weight, preferably from 70% by weight to 90% by weight, and the plasticizer is present at from 5% by weight to 40% by weight, preferably from 8% by weight to 20% by weight.
• the solution is then heated to a temperature and for a time sufficient to convert the collagen to gelatin, preferably with at least about 90% by weight of the collagen being converted.
• the solution will be heated to a temperature in the range from 65°C to 75°C, preferably about 70°C for a time in the range from 40 minutes to 60 minutes, preferably about
• the converted solution is then formed into a thin layer and dried to produce a film.
• the film is then cross- linked, typically by exposure to radiation, such as ultraviolet radiation at a power from 100 mJ/cm 2 to 7000 mJ/cm 2 , preferably from 2800 mJ/cm 2 to 4000 mJ/cm 2 .
• a cross-linking agent may then be painted, sprayed, dipped, rolled, or otherwise applied to the film. If the cross-linker is sprayed it may be sprayed as an aerosol, a foam, or the like.
• the cross-linker comprises a dialdehyde starch with a degree of oxidation in the range from 75% to 98%, which can be applied to the film as an aqueous solution of from (0.5 mg/ml to 5 mg/ml), most preferably at a concentration of 3% by weight (3 mg/ml) .
• Such collagen/gelatin films with the addition of the cross-linker can be immediately applied wet to the tissue surface or with an appropriately stable cross-linker formulation, dried preferably at a temperature of from about (room temperature to 65°C) and then stored for future tissue attachment.
• the methods may further comprise packaging the films (uncoated or coated with the cross- linking agent) in sterile, moisture-tight containers, where the moisture is maintained in the range from 10% to 17%, preferably from 11.5% to 16% by weight .
• the preferred dialdehyde starch cross-linking material can be incorporated into or coated over tissue-cover films in addition to the preferred gelatin films described above.
• the films may comprise collagen/gelatin having characteristics outside the ranges set forth above and/or may be composed of materials other than gelatin/collagen, such as other proteins including albumin, hemoglobin, fibrinogen, fibrin, fibronectin, elastin, keratin, laminin, and combinations thereof.
• Other suitable biologic polymers include polysaccharides, such as glycosaminoglycans, starch derivatives, xylan, cellulose derivatives, hemicellulose derivatives, agarose, alignate, chitosan, and combinations thereof.
• Suitable non-biologic polymers will be selected to be degradable by either of two mechanisms, i.e. (1) break down of the polymeric backbone or (2) degradation of side chains which result in aqueous solubility.
• Exemplary nonbiological polymers include synthetics, such as polyacrylates, polymethacrylates, polyacrylamides, polyvinyl resins, polylactide-glycolides, polycarprolactones , polyoxyethylenes, and combinations thereof.
• Other film materials which may be coated with dialdehyde starch are described in the following co-pending applications which are hereby incorporated herein by reference: 08/303,336; 08/746,052; PCT US 96/17854; PCT US 96/17846; and 08/758,267.
• Fig. 1 illustrates the dimensions of test films used to measure the force in the Experimental section below.
• Figs. 2A-2D depict the DSC of various tissues and granular film. Heating rate: 5°C/min. for Fig. A and 10°C/min. for Figs. 2B, C, and D.
• Fig. 2A Granular film. 1.2 mg film at 11% moisture plus saline to 13 mg total, enthalpy of denaturation, 15.7 J/g.
• Fig. 2B Beef muscle; 11 mg hydrated.
• Fig. 2C Porcine lung pleura; 9 mg hydrated. Porcine lung pleura and parenchyma; 8.5 mg hydrated. Films were hydrated with 0.9% aq. sodium chloride.
• Fig. 3 shows the melting temperature as a function of moisture content for non-granular film.
• Figs. 4A-4C Non-granular film properties as a function of the degree of cross-linking.
• Fig. 4A Swelling (V/V 0 ) as a function of cross-linking time in UV.
• Fig. 4B Collagenase digestion time vs. swelling (V/V 0 ) .
• Fig. 4C Peak melting temperature in DSC vs. (V/V D ) . Approximate errors in swelling ratio, collagenase digestion time, and DSC melting temperature were 3%, 18%, and 3%, respectively.
• Figs. 5A-5C Granular film after attachment to beef heart tissue by the argon beam coagulator. An untreated region of the film is visible in the lower part of the figure. Holes created in the film by the argon beam are darker, lighter areas of film are evident between holes.
• Fig. 5B Film as in Fig. 5A removed from the beef heart. Holes in film clearly visible.
• Fig. 5C Beef heart muscle underlying argon-beam treated film. Lighter areas are coagulum. Darker regions appear to be unaffected by the beam; i.e. these areas have the same appearance as untreated beef heart. Images from Bausch and Lomb Stereo Zoom 7 dissecting microscope at 30X.
• Figs. 6A-6C Bonding of apposed films pressed between heated brass blocks. All tests were on granular films, cross-linked with UV light for 20 min. Points marked with a vertical arrow represent films which failed cohesively at that force; i.e. the peel bond strength was higher than the measured point.
• Fig. 6A Peel bond strength vs. hydration, smooth side to smooth side apposition, 100°C, 20 sec.
• Fig. 7 illustrates a gelatin film according to the present invention packaged in a sterile surgical package.
• gelatin refers to denatured collagen.
• Gelatin is a heterogenous mixture of high molecular weight water-soluble proteins, usually obtained by heating aqueous solutions of collagen or collagen-containing materials, such as skin, tendons, ligaments, etc.
• Gelatins may be commercially obtained from suppliers, such as Hormel foods, (Austin, MN) .
• the gelatin films of the present invention will be prepared by heating aqueous solutions of at least partially purified collagens, as described in detail in the Experimental section hereinafter.
• Collagen may be obtained from commercial suppliers, such as Kensey Nash (Type F, Exton, PA) .
• a preferred collagen starting material is Type F collagen obtained from Kensey-Nash corporation.
• film refers to sheet, layer, membrane, patch, or other generally planar configuration of the gelatin material.
• the films or at least a substantial portion thereof, will have a thickness in the range from 0.01 mm to 0.20 mm, preferably from 0.04 mm to 0.08 mm.
• the thickness will usually be uniform, but not necessarily so. That is, the film thickness may vary within the aforestated ranges, and certain portions of the film may have thicknesses outside of these ranges, where the portions having such non-conforming thicknesses will generally not be intended for application to tissue. That is, they may be intended merely to facilitate handling of the films, or for other purposes.
• Film thickness may be measured by conventional means, such as a Mitutoyo Thickness Gauge Model, IDC Mitutoyo Corp., Japan or by weighing the film and calculating the thickness given the surface area of the film and the film density.
• pliability refers to the force required to bend the film through a defined distance. Pliability is measured in units of milliNewtons (mN) , and specific methods for measuring pliability are set forth in the Experimental section hereinbelow.
• moisture content refers to the amount of water present in the gelatin films after preparation.
• the moisture content will be in the range from 10% by weight to 17% by weight, preferably being in the range from 11.5% by weight to 16% by weight.
• Moisture content can be measured in a variety of ways, such as weight loss on drying.
• the relatively dry collagen films of the present invention will typically hydrate when applied to tissue.
• the capability of the films hydrating may be assessed by the "degree of swelling” which is defined as V/V Q , where V Q is volume when dry and V is volume when fully hydrated.
• the gelatin films of the present invention have a degree of swelling of at least 4.5, usually being in the range from 4.5 to 6.5, preferably in the range from 5 to 6.
• tensile strength refers to the force required to induce tensile failure in the film. Tensile strength is measured in Newtons (N/cm 2 ) and particular methods for measuring tensile strength are set forth in the Experimental section hereinafter.
• peel strength refers to the force required to separate the film bonded to itself or to the tissue attachment site. Peel strength is measured both in peak force (N) and normalized energy (N/cm 2 ) by the particular methods as described in the experimental section hereinafter.
• melting temperature refers to the denaturation temperature (DSC peak), i.e. the temperature at which the gelatin components of the gelatin and/or collagen films denature. Specific techniques for measuring such melting temperatures are set forth in the Experimental section hereinafter.
• collagenase digestion refers to digestion of the protein films in a collagenase enzyme solution. Film samples having a particular size are placed in a collagenase solution having a particular activity. The time necessary for disintegration of the film samples is then determined. Specific techniques for measuring collagenase digestion times are set forth in the Experimental section hereinafter.
• the gelatin and/or collagen films of the present invention may be cross-linked or non-cross-linked.
• the films are preferably cross-linked in a conventional manner, typically by exposure to radiation, such as ultraviolet (UV) radiation for a time and at a power level sufficient to achieve a desired level of cross - linking .
• the films are cross-linked sufficiently to enhance tensile strength, handling characteristics, and resistance to degradation in the surgical environments in which they are used, without being cross-linked to the extent that the ability to fuse the films to underlying tissue is diminished.
• gelatin and/or collagen films of the present invention may also be granular or non-granular.
• granular it is meant that the solution of denatured collagen has not been filtered or centrifuged prior to casting into films.
• the granular films will include collagen particles having a size greater than 0.01 mm, usually greater than 0.1 mm, prior to the heat conversion to gelatin.
• non-granular gelatin films will be produced by filtration or by centrifugation of the collagen solutions to remove particles having sizes above 0.1 mm, usually above 0.03 mm, prior to film formation.
• Granular collagen films have been found to possess a significantly greater tear strength.
• Granular films are generally preferred for use as sealants because, for example, they shrink less with application of energy.
• Non-granular films are generally preferred for use as anti-adhesive barriers.
• the gelatin and/or collagen, preferably gelatin, films of the present invention will preferably further include plasticizers, such as polyethylene glycol, sorbitol, glycerine, or the like.
• the plasticizers may be combined with the collagen solutions prior to heating and conversion to gelatin.
• the plasticizers enhance the pliability of the resulting gelatin films.
• the preferred plasticizer is polyethylene glycol having a molecular weight of about 400 which is present in the gelatin film at from 5% by weight to 40% by weight.
• the films may preferably further include a cross- linking agent on one or more surfaces.
• the cross-linking agent will usually be applied as a coating or layer over either of both surfaces, in whole or in part, preferably being present over at least one entire surface.
• the layer or coating will typically be absorbed into the film after its initial application over the surface.
• the cross-linking agent may be impregnated into the collagen/solution film, with or without a separate layer over a surface or surfaces thereof.
• the cross-linking material will typically be applied in an amount equal to from 0.1% to 5% by weight of the film, usually from 0.5% to 4% by weight.
• the cross- linkers may be applied to the gelatin and/or collagen films immediately prior to attachment of the film to the tissue target or alternatively may be a preformed component of the film in its sterile container.
• the cross- linker enhances the adhesion and immobilization of the film to the tissue site prior to the application of energy sufficient to fuse the gelatin to the underlying tissue.
• the coated film may function to seal the tissue or prevent adhesion formation in the absence of applied energy or with lower energy thresholds.
• the preferred cross- linker is dialdehyde starch which is applied to the film as a solution, usually an aqueous solution of from 0.5% to 4%, more usually from 1% to 3% by weight.
• the films of the present invention may be applied to tissue without the use of an energy source (particularly when they incorporate the cross-linking agent) or using energy of a type and in an amount sufficient to fuse the gelatin material to underlying tissue.
• Suitable energy sources include electromagnetic energy, particularly electrical energy, e.g. radio frequency (RF) energy and microwave energy, infrared (heat) energy, and ultraviolet energy; optical energy, e.g. laser; mechanical energy, e.g. ultrasonic; and the like.
• RF energy sources such as those available as electrosurgical power supplies from companies such as Valleylab, Boulder, Colorado, and Birtcher Medical Systems, Irvine, California, employing conventional RF- applying probes.
• an electrosurgical probe sold under the tradename SilverBulletTM by Fusion Medical Technologies, Inc., Mountain View, California, assignee of the present application, may be used.
• radio frequency energy sources which provide for a dispersed or distributed current flow from a hand-held probe to the tissue.
• One such radio frequency energy source referred to as an inert gas beam coagulator, relies on flow of an inert ionizable gas, such as argon, for conducting current from the probe to the tissue.
• lower temperature energy sources may be used to attach the film of the present invention to the underlying tissue, particularly with films having a cross-linker coating.
• One such low temperature energy source is a heat annealing probe that is applied to the surface of the film or uses thermal energy to produce attachment and sealing.
• lower temperature energy sources may not need to be in direct contact with the cross-linker coated film or sheet as in instances where the energy source includes infrared, microwave or optical energy e.g. laser applicators.
• Energy from the energy source will typically be manually directed to the fusible material overlying the tissue using a probe connected to an external power supply.
• the treating physician will manually direct the probe to apply energy over the surface of the fusible material and will visually confirm that fusion has been achieved.
• the probe may use conventional electrosurgical power supplies having an energy output from 2 W to 100 W, preferably from 20 W to 60 W.
• the fusible material will typically be exposed to the energy for a total time from about 5 seconds to 120 seconds, usually from 10 seconds to 40 seconds, for material having an area from 1 cm 2 to 10 cm 2 . The precise timing will depend on the physician's visual assessment that fusion of the material to the underlying tissue has been achieved.
• Films according to the present invention may be prepared by first combining a collagen starting material, e.g. a commercial grade of collagen, with a plasticizer in a aqueous solution.
• Collagen starting materials may be obtained from any of the commercial sources listed above, and the preferred polyethylene glycol 400 plasticizer may be obtained from, for example, Polysciences, Inc., Warrington, Pennsylvania.
• the collagen is typically present at from 70% by weight to 90% by weight and the plasticizers present in from about 8% by weight to 20% by weight.
• Collagen and plasticizer are combined in a sterile water source, such as distilled water, deionized water, or the like.
• the collagen suspension may be filtered or centrifuged after heating as described in detail in the Experimental section hereinafter.
• aqueous solution is heated to a temperature and for a time efficient to convert collagen largely or completely to gelatin.
• the solution is heated to a temperature in the range from 65°C to 75°C, preferably about 70°C, for a time in the range from 40 minutes to 60 minutes. Any conventional heating vessel may be used for this reaction.
• the solution is dried and formed into a film, preferably by pouring the solution into an appropriate receptacle, usually a square or rectangle.
• the solution may be dried at room temperature or an elevated temperature, preferably at room temperature at a moderate humidity, e.g. RH 50%.
• the films are then preferably cross-linked as described above.
• the films may then preferably have a cross-linking agent applied to one or more surfaces as described above. Referring now to Fig.
• a gelatin film 10 according to the present invention may be packaged in any conventional sterile packaging, such as a sterile pouch 12 comprising a moisture-impermeable material, such as mylar film.
• sterile packages are ready for use by the treating physician in the surgical environment .
• Example 1 MATERIALS AND METHODS FOR GELATIN FILM
• Formulation A 451 g grams of collagen (Kensey Nash
• Formulation C 36.1 g of collagen (Kensey Nash Type F) were dispersed with 960 ml WFI and 3.6 g PEG 400 MW and heated at 70°C for 50 min. The dispersion was then homogenized as described in Formulation A and B. The homogenized dispersion without filtration or addition of water was cooled to 35°C and cast into gels, dried, and cross-linked with 3000 mJ/cm 2 as described above.
• Formulation D 58.8 g of collagen as above were dispersed with 1850 ml WFI and 7.2 g PEG 400 MW and heated at 70 °C for 50 min. The formulation was then homogenized as in A & B above. The homogenized dispersion without filtration or the addition of water was then cooled to 35 °C and aliquots of 14.7 ml were cast into 100 x 100 x 15 mm sterile square polystyrene petri dishes. The gelled solution was dried as above, then cross-linked with 3300 mJ/cm 2 as above.
• a Mitutoyo Thickness Gauge Model IDC Mitutoyo Corp., Japan was used to determine the thickness of collagen/gelatin films. Using the release cable or the lifting lever, the thicknesses at each corner and at the center of the film were measured, for a total of 5 measurements on each film.
• the amount of saline absorbed by collagen/gelatin during a 22 ⁇ 1 hour incubation was determined as follows. Saline solution (0.9% w/w; 5 mL) was added to each scintillation vial containing a test sample. The films were hydrated for 22 + 1 hours at 20-25°C. The degree of swelling was expressed as V/V 0 , where V is the hydrated volume (weight) and V 0 is the dry volume (weight) .
• the denaturation temperature of the collagen/gelatin components of the test films and collagen raw material were determined using a DSC 2910 Differential Scanning Calorimeter (DSC), TA Instruments, New Castle, Delaware. 1.0-3.0 mg of film sample plus 0.9% w/w sodium chloride and hermetically sealed. Heating rates were 5°C/min. or 10°C/min. Peak temperatures and enthalpy of melting were recorded.
• DSC Differential Scanning Calorimeter
• each collagen/gelatin film was determined as follows. The force required to bend the collagen/gelatin film through a defined distance was measured, and the bending modulus calculated from the equation given in the Machinery's Industrial Press, Inc., NY, 21st Edition, 1980. A film sample was placed in the clamp on a Swiss Height Gauge so that 8 mm of patch was free. The force required to bend the patch through a deflection of 2 mm was measured. 5 . TEAR TEST
• the forces required to propagate a tear in the collagen/gelatin films were calculated using a 3.8 x 2.5 cm rectangular piece from the test film having the shape and dimensions shown in Fig. 1.
• the force to tear between tabs A and B was measured using a Chatillon tester (TDC 200 test stand fitted with 250 g or 2.25 N load cell, DGGS 250 g digital force gauge) .
• Tests were performed with a Chatillon TCD 200 fitted with a digital force gauge (Chatillon Instruments, Greensboro, NC) , connected to an XY plotter. Film samples were typically 1 x 3 cm and were glued to polystyrene tabs with cyanoacrylate (Superglue) . Films and tabs were hydrated for precisely
• Weight loss on drying of collagen/gelatin films, raw material collagen, slurries, and solutions were determined by placing the test samples into an oven which had been set at 120°C ⁇ 5°C. The sample remained in the oven for at least 20 minutes after the oven had reached its set temperature.
• the gauge With the patch under no tension, the gauge was set to zero force, and then the gauge was raised manually at a rate of approximately 1 cm/sec or automatically using a Chatillon test stand at a rate of 50 mm/min. to effect a peeling detachment of the film. The gauge was lifted until the film was separated from the tissue. The maximum force registered during the peeling operation was recorded as Newtons of force or Newtons/force per cm width of film. Where the Chatillon test stand was used, the total energy required to peel the patch was recorded as millijoules. Films were welded to warm excised tissue, such as porcine lung or bovine heart muscle which was warmed or incubated at 37°C. Peel strength measurements were typically commenced at 3 minutes and 20 minutes after welding to tissue.
• Example 3 Three additional formulations were produced according to the methods set forth in Example 1. These formulations were tested according to the methods set forth in Example 2 and had similar results. The formulations had various starting ratios of collagen and PEG and are summarized in Table 3 below. Table 3
• a collagen/gelatin film was produced according to the methods set forth in Example 1.
• the smooth side of the film was coated using a foam brush with a thin film of a 3% by weight solution of dialdehyde starch.
• Dialdehyde starch (DAS) with degrees of oxidation of 75% and 98% was prepared from potato starch by periodate oxidation after heating at 70°C for 30 minutes, according to METHODS IN CARBOHYDRATE CHEMISTRY, Vol. 4, (Whistler, R. , et al . , eds . , 1964).
• the films were either allowed to dry, or were left wet.
• the coated films were tested according to the tensile peel strength and tensile strength methods described in Example 2 and according to the In vitro Tissue Welding test and In vitro Patch Attachment tests described below.
• Tissue welding with argon beam coagulator and peel strength measurements on porcine lung in vi tro were performed as follows. Film samples were placed on the tissue of interest, typically porcine lung (see below) or beef heart slices (purchased from a local market.) The tissue of interest was placed in contact with the return electrode of the argon beam coagulator, usually on the underside.
• the film began to hydrate. Welding was preferably performed within 20 sec after placing on tissue, since bonding was a function of film hydration.
• the spark discharge from the tip of the coagulator was then directed onto a patch at a distance of a few mm between tip and film.
• the coagulator was typically set at 40 W of power and 2-4 liters/min. of argon gas flow. Other settings were explored, but the strength of the bond achieved was less.
• the spark discharge was maintained for 2-5 sec per cm 2 of film. Application of the argon spark was terminated when the film became desiccated or showed signs of carbonization .
• the porcine lung model for in vi tro welding tests was as follows. Porcine lung was received on ice from a slaughterhouse, usually within a day of slaughter. The lung was divided at the main bronchus, and one side was used for each test series. A tube was fitted to the largest bronchus, and air was pumped into the lung using a pump (Air Cadet Model 7059-42, Cole-Parmer Instruments, Niles, IL) to achieve inflation. The lung was housed in a chamber of clear acrylic, which was mounted on a heated platform. The air pressure lines were also passed through a heated circulating bath. Heated 0.9% aq. sodium chloride was sprayed on the lung tissue at intervals. Tissue temperatures were maintained between 29°C and 40°C, preferably between 37°C and 40°C.
• films were bonded with a heated brass platen.
• the test device utilized was constructed as follows. Brass blocks with an exposed contact area of 1 cm 2 were placed in contact. The lower block was connected to a digital heating controller, which permitted temperature control within 1°C. The upper block was connected to a lever arm to which weights could be attached to vary the compressive force between the blocks. Heating was first applied with the upper and lower blocks in contact. The upper block was heated by conduction from the lower. Two film samples (1 cm x 2 cm) were glued to plastic tabs, as described above for tensile testing. The films were then hydrated in 0.9% aq.
• V/V 0 hydration ratio
• the foil wrapper prevented the films from sticking to brass blocks. Heating of the apposed, hydrated films was conducted for 10 to 30 seconds. Approximately 100 g of compressive force (IN) was applied during the weld. At the completion of the weld, the apposed film samples were removed from the foil wrapper, mounted in the tensile test apparatus, and the force to peel apart was measured within 5 to 20 min. At the time of the peel test, the sample was at room temperature and the hydration level (V/V 0 ) was still approximately two.
• a thoracotomy was performed at the level of the mid-chest of an intubated domestic pig. A five to six inch incision was made using sharp dissection and electrocautery. A chest tube or Foley ® catheter of appropriate size was carefully inserted into the thoracic cavity. A purse-string suture was placed around the chest tube to ensure integrity of the thorax. Baseline thoracic air flow measurements were then performed under constant suction pressure (approximately 20 cm water at the chest tube) . On completion of the baseline measurements, the chest tube was removed, the thoracotomy completed, the ribs retracted and the lung surface exposed.
• the lower lung lobe was carefully grasped with a padded forceps and brought to the thoracotomy for the resection and patching procedure. Using a sharp scalpel blade or scissors, a partial resection of the lower lung was performed. A section at least 1 cm wide of the apical portion of the lung lobe was resected yielding approximately 4-6 cm 2 exposure of parenchymal surface. Tissue hemorrhage was controlled with a combination of electrocautery and gauze sponge pressure .
• Example 4 Approximately 2 cm x 4 cm of the coated films prepared in Example 4 were then applied over the resected surface in a shingling pattern. The shingles were placed with approximately 5 mm overlapping adjacent patches. The number, formulation, and exact size of the films applied were recorded. The films were then welded to the resection site using argon-enhanced coagulation as described in Example 5. On completion of the film application, the covered surfaces were carefully tested for air leaks by pouring sterile saline over the site and watching for any air bubbles as the lung was inflated. The thoracotomy was then closed after reinsertion of the chest tube and aspiration of liquid and air to produce the required the negative pressure needed to maintain lung expansion.
• Air flow from the pleural cavity was measured by connecting the chest tube to the following equipment series: Vacuum aspiration bottle, desiccator column, digital flow meter, electronic vacuum transducer, Pleur-evac ® unit and vacuum source. Air flow through the chest tube was recorded at 15 second intervals for the first two minutes and then at 1 minute intervals until the 10 minute mark and at 10 minute intervals thereafter for the next 4 hours. The films were considered to effectively seal the lung defect if a "zero" air flow was recorded within the time taken to evacuate the pleural cavity (1-5 minutes) and the integrated air flow between 5 and 240 minutes did not exceed
• Table 2 summarizes the properties of granular films prepared by the process of the present invention.
• Non- granular films were similar.
• the melting temperatures in DSC confirmed that the collagen had been converted to gelatin during the extended heating step (see below) .
• Resistance to collagenase and the high swelling percentages were consistent with cross-linked gelatin resulting from UV treatment.
• Films were quite thin to enhance pliability, which was critical for good apposition to irregular tissue sites.
• Granular films were somewhat opaque in appearance, had a roughened texture on the upper surface, and contained fibrous inclusions up to 1 mm in diameter when viewed in a light microscope.
• Non-granular films were transparent, were smooth both on upper and lower surfaces, and possessed no inclusions greater than a few microns in diameter.
• the DSC of the cross-linked gelatin of the present invention was compared with that of known collagen and gelatin samples.
• films may be hydrated to different extents on tissue as a function of time of tissue contact, we also examined the effect of hydration level on peak melting temperature (Fig. 3) . Film characteristics were greatly affected by the extent of cross-linking (Fig. 4) . In general, films swelled less, resisted collagenase more, and melted at higher temperatures as the degree of cross-linking increased.
• the film changed in appearance, becoming more opaque and melting and shrinking to a limited extent in response to the thermal energy. Tissue underneath the patch was also "melted” or denatured. The material of the patch and the tissue appeared to have intermingled or flowed together during the application of the argon beam. Immediately upon cessation of argon treatment, the temperature of the weld site declined rapidly and returned to that of the surrounding tissue within seconds, resulting in a coagulum, or congealed mixture, of the two components. The fusion of tissue and film elements was easily observed when the bonded film was peeled away from the tissue, the film-tissue interface being visualized in a dissecting microscope at 10-20 X.
• tissue protein appeared to have penetrated into holes in the film and solidified there, creating a mechanical bond (Figs. 5A, 5B, and 5C) .
• Tissue appeared to be denatured to a depth of 0.2 to 0.7 mm, depending on the duration of energy application and the power setting.
• DSC of lung and heart tissue showed that these tissues have components which denature over a wide range of temperatures from 50°C to 150°C. (See, Figs. 2B, 2C, and 2D.) Although it is difficult to determine the temperature of tissue subjected to the argon beam, vaporization of water is evident, and for long exposures, points of carbonization appear, which suggests temperatures above 100 °C in localized domains.
• films less than about 0.04 mm thick were easy to weld, but they partially disintegrated during the application of the argon beam, and they failed cohesively in peel bond tests.
• Films greater than 0.2 mm thick presented a conductive barrier to the argon beam, and the spark could only find a conductive path at the edge of the film.
• Such films were only bonded to tissue at the edges, and once the edge bond was broken, they were readily detached from the tissue. Apposition to tissue appeared to be essential for achieving a good bond.
• the effect of UV cross-linking was also examined. Films which were not cross-linked bonded very well and with a shorter duration of argon beam application. Such films, however, had poor cohesive strength during peel tests.
• the ideal duration of application of the argon beam was about 2- 5 sec/cm 2 for granular films with the properties given in Table 2. For non-granular films between 0.04 and 0.06 mm thick, 1-3 sec/cm 2 gave better bonds. For films which were thicker or more granular (less homogenization) or more highly cross-linked, the optimal weld duration was 5-7 sec/cm 2 . Power settings higher than 40 W tended to cause disintegration of films and deeper denaturation of tissue. Lower power settings were not possible with the Birtcher coagulator. With other argon beam instruments which permitted lower power, it was found that melting and intermingling of film and tissue were inadequate to produce a satisfactory bond. Granularity of films also affected the optimum welding time. Granular films required longer energy application times compared to non-granular films. Non-granular films had poor cohesive strength during peel test experiments, compared to granular films.
• Tissue Welding test (Example 5) .
• Table 4 summarizes the results of this comparison, where it can be seen that DAS- coating of films prior to tissue welding enhanced bonding to lung tissue both at 3 minutes and 20 minutes post welding when compared to identical material without the DAS cross-linker.
• DAS Dialdehyde Starch
• Sheet stock of implantable grade polypropylene, polyethylene, silicone, and Gortex ® Soft Tissue Patch were unsuitable. Holes were created in the sheets if they were thin enough, but no bonding resulted. Meshes and fluted tubes of the above materials and of Dacron ® , intended for vascular grafts or hernia repair, were also unsatisfactory.
• ND Not Done
• collagen films that did not pass the Air leak test i.e. zero air flow achieved from between 1 and 5 minutes after sealing the thoracotomy and inducing negative pressure, and total air leakage of less than 500 ml over the 4 hour observation period (Example 6) were converted to films that passed the Air Leak test by the application of DAS cross-linker prior to tissue welding.
• zero air flow was achieved in 1 minute and 20 seconds and total air leak over the 240 minute observation period was only 4 ml .
• In vivo bond strength scores for these DAS coated films ranged from 2.5-3.0.

Landscapes

• Health & Medical Sciences (AREA)
• Surgery (AREA)
• Epidemiology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Heart & Thoracic Surgery (AREA)
• Vascular Medicine (AREA)
• Materials For Medical Uses (AREA)

Priority Applications (2)

Applications Claiming Priority (6)

Publications (1)

Family

ID=27363346

Family Applications (1)

Country Status (3)

Cited By (9)

Citations (11)

Family Cites Families (3)

• 1997
  • 1997-10-15 EP EP97910940A patent/EP0959795A4/de not_active Withdrawn
  • 1997-10-15 WO PCT/US1997/018518 patent/WO1998016165A1/en not_active Application Discontinuation
  • 1997-10-15 AU AU48198/97A patent/AU4819897A/en not_active Abandoned

Patent Citations (11)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events