Method for preparing a porous polyurethane vascular graft prosthesis

BACKGROUND
The present invention relates to a method for preparing porous polyurethane vascular graft prostheses, and in particular to a method for preparing porous polyurethane vascular grafts by placing polyurethane coated mandrel in a coagulant consisting of water, ethanol and optionally aprotic solvent.
Vascular graft prostheses have been used in clinical applications for many years to replace diseased arteries or, to act as shunting for blocked arteries, or to serve as graft fistula for blood dialysis.
Commercial available vascular graft prostheses include woven or knitted polyester fiber (Trademark Dacron) tubes and microporous expanded polytetrafluoroethylene (PTFE, tradename Teflon) tube, such as Gore-Tex(Gore & Associates, Inc.) or Impra Teflon(IMPRA, Inc.) vascular graft prostheses. When vascular graft prostheses made from Dacron or Teflon tubing have a relatively large diameter, good clinical results are obtained because the blood flow rate is high and therefore does not lead to thrombus formation on the luminal surface therein. However, when the Dacron or Teflon tubings have a relatively small diameter, the clinical performance are unsatisfactory because the blood flow rate is usually slow and therefore causes thrombus.
In view of the above mentioned drawbacks to vascular graft prostheses made from Dacron or Teflon, vascular graft prostheses made from polyurethane material have already been developed and have proven to be suitable for this purpose because they possess good blood compatibility.
For example, David Annis, Thien V. How and A. C. Fisher disclose a porous polyurethane vascular graft which is prepared by an electrostatic spinning and winding method. The method includes extruding polyurethane resin "Biomer" (tradename, Ethicon, Inc.) through a spinneret to form filaments and winding the filaments on a rotating mandrel by electrostatic force to form a porous polyurethane tubing having an internal diameter of 10mm ("A compliant small diameter arterial prosthesis," CRC press, 1987; "The design of a small diameter arterial replacement," in Polymers in medicine: Biomedical and pharmacological applications Emo Chiellini & Paolo Giusti Eds, Plenum Press, 1983; "Recent Advances in the development of artificial devices to replace diseased arteries in man: A new elastomeric synthetic artery graft," in Polyurethanes in Biomedical Engineering, Elsevier Science Publishers, 1984; " The design of a small diameter arterial replacement, in Polymers in medicine: Biomedical and Pharmacological Applications Emo Chiellini & Paolo Giusti Eds, Plenum Press, 1983).
The exact components of the above-mentioned "Biomer" polyurethane resins are not known, however, according to Michael D. Lelah, such resins are solvent type polyurethanes synthesized from polytetramethylene glycols having a molecular weight of 2000, 4,4'-diphenylmethanee diisocyanate(MDI), mixture of diamines and silicon compounds (Polyurethane in medicine, CRC press, Inc. 1986).
S. Gogolewski and A. J. Pennings disclose a biodegradable vascular graft prosthesis having an internal diameter of 10 mm and an average pore size of 40-50 .mu.m. The biodegradable vascular graft is prepared by dipping a fluorizated stainless steel mandrel in a mixed resin of a polyurethane resin dissolved in a mixed solvent of DMF and THF and a polyacetide resin dissolved in DMF solvent, followed by placing the coated mandrel in a coagulant consisting of ethanol and water (volume ratio=1:1) ("Compliant, Biodegradable vascular prosthesis" in Polyurethanes in biomedical engineering, Elsevier Science Publishers, 1984).
J. G. F. Bots, L. Van der Does, A. Bantjes disclose a blood vessel prosthesis having pore size of 5-200 .mu.m, which is prepared by forming filaments from a solution of polyethylene oxide, polypropylene oxide and dicumylperoxide, followed by winding the filaments on a rotating mandrel and irradiating them with UV light for 60 minutes. The solvents for dissolving the resins are a mixture solvent of dichloromethane and dichloroethane ("Small diameter blood vessel prostheses from polyethers," in Polymers in medicine II, edited by E. chielline, et al, 1986).
Thomas E. Brothers, James C. Stanley, William e. Burkel and Linda M. Graham disclose a vascular graft. The method for preparing the vascular graft includes forming a polyurethane tubing from a PU resin, B. F. Goodrich Estane 5714 (tradename) to which are added salts, by using the principle of phase inversion, and extracting the salts from the PU resin. The detailed manufacturing procedures are not disclosed ("Small caliber polyurethane and polytetrafluoroethylene grafts: A comparative study in a canine aortoiliac model" Journal of Biomedical Materials Research, vol. 24, pp 761-771, 1990).
Rajagopal R. Kowligi, Wolf W. Von Maltzahn and Robert C. Eberhart disclose a polyurethane tubing fabricated by using the precipitation-flotation method. The method includes premixing polyurethane resin with nitrogen gas in a spray nozzle, spraying the premixture on a flowing water bath in which a rotating mandrel is immersed, causing the polyurethane resin to form into filaments and to coagulate on the water bath and be taken up by the mandrel to form a porous polyurethane tubing. The polyurethane material used is a polyurethane resin with a tradename, "Surethane" and a solid content of 2-5%. The exact components of the polyurethane resin is not disclosed ("Synthetic vascular graft fabrication by a precipitation-floation method," Trans Am Soc Artif Intern Organs, Vol. XXX IV, pp 800-803(1988)).
White et al disclose a microporous polyurethane vascular graft prepared by using replamineform method. The method includes coating a reactive liquid polyurethane resin over a cylindrical mandrel which is formed by mechanically polishing a needlelike protrusion of sea urchin having the composition of calcite, carrying out the polymerization in situ and dipping the mandrel together with the polyurethane tubing formed thereon in a hydrochloride solution to dissolve the mandrel. The resultant polyurethane tubing has an average pore size of 15-20 .mu.m(Michael d. Lelah,"Polyurethane in Medicine", CRC Press, Inc 1986)
Lyman et al also disclose a method of fabricating polyurethane tubing. Their method uses polyurethane resin synthesized from MDI and polypropylene oxide having a molecular weight of 1078 and ethylene diamine. The polyurethane tubing is obtained by using repeated dipping and precipitation method. The precipitating solution used is consisted of water and Dimethyl Formamide(DMF)(Michael d. Lelah, "Polyurethane in Medicine", CRC Press, Inc. 1986) ,
Leidner et al also disclose a method of fabricating porous polyurethane tubings. The method for this fabrication includes extruding polyurethane solution or melt into filaments, stretching the filaments and winding on a rotating mandrel to form a porous tubing(Michael d. Lelah,"Polyurethane in Medicine", CRC Press, Inc 1986)
Kozaburo Hayaski, Tomoyuki Saito et al synthesized a polyurethane resin by using MDI, polytetramethylene glycol(PTMG), polyethylene oxide-polydimethylsiloxanepolyethylene oxide(PES) and ethylene glycol as raw material and reported that a porous polyurethane vascular graft was fabricated. However, the actual procedures and conditions for this fabrication have not been disclosed ("Elastic properties and strength of a novel small-diameter, compliant polyurethane vascular graft," J. Biomed, Mater Res: Applied Biomaterials, vol 123, No. A2, p229-244, 1989).
Shu Qin Lin and Makoto Kodama et al used an aliphatic polyurethane resin, tradename, Tecoflex Sc 80A, having a solid content of 5-10% and solvent 1,4-dioxane, to produce porous polyurethane vascular prostheses. The polyurethane resin is injected into a cavity of a mold, frozen at a temperature of 0.degree. to -196.degree. C. and thawed to obtain a porous polyurethane vascular prosthesis with a pore size form several .mu.m to 70 .mu.m ("Porous polyurethane vascular prostheses with variable compliances", Journal of Biomedical Materials Research, Vol. 26, 1489-1502(1992)).
SUMMARY OF THE INVENTION
The object of the invention is to provide a method for producing a vascular graft prosthesis made of porous polyurethane polymer tubing which has superior biocompatability, in particular, blood compatability and uniform porous structure.
The object is achieved by providing a method including the steps of coating a solvent type polyurethane resin over the outer surface of a cylindrical mandrel; within 30 seconds immediately after the coating, placing the coated mandrel in a static coagulant having a temperature of 15.degree.-40.degree. C. for 2 to 12 hours to form a porous polyurethane tubing surrounding the mandrel, and followed by placing the mandrel surrounded with the porous polyurethane tubing in a swelling agent for 5 to 60 minutes. The solvent type polyurethane resin, according to the present invention, is prepared from polytetramethylene glycol, glycols and 4,4'-diphenylmethane diisocyanate, and has a solid content of 15-45 percent by weight and a viscosity of 10,000 to 150,000 centipoises.
The solvent type polyurethane resin is prepared from 1 mole of polytetra-methylene glycol, from 0.8 to 4 moles of glycol, and from 1.8 to 5 moles of 4,4'-diphenylethane diisocyanate. The coagulant according to the invention consists of water, ethanol and optionally an aprotic solvent. The aprotic solvent is N,N-dimethyl formamide(DMF) or N,N-dimethyl acetamide(DMAc). The swelling agent according to the invention should include at least 90 percent by weight of ethanol. The swelled porous polyurethane tubing, after being removed from the mandrel, is rinsed with a solution containing at least 80 percent by weight of ethanol for 5 to 120 minutes, and then dried.
According to an aspect of the method of the invention, in order to obtain porous vascular graft prosthesis with uniform porous structure, it is important that the coagulant consists of 10 to 50 percent by weight water and 90 to 50 percent by weight solvent selected from ethanol and aprotic solvent. The weight fraction of the ethanol is between 1.0 and 0.4 and the weight fraction of the aprotic solvent is between 0 and 0.6.

BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be more fully understood by reference to the following detailed description and accompanying drawings, which form an integral part of this application.
FIG. 1A is a scanning electron microphotograph of a cross-section of the wall of the porous polyurethane tubing 1WA100-0705, showing the morphology of the pore distribution;
FIG. 1B is a scanning electron microphotograph of a cross-section of the wall of the porous polyurethane tubing 1WA9010-0705, showing the morphology of the pore distribution;
FIG. 1C is a scanning electron microphotograph of a cross-section of the wall of the porous polyurethane tubing 1WA8020-0705, showing the morphology of the pore distribution;
FIG. 1D is a scanning electron microphotographs of a cross-section of the wall of the porous polyurethane tubing 1WA7030-0705, showing the morphology of the pore distribution;
FIG. 1E is a scanning electron microphotographs of a cross-section of the wall of the porous polyurethane tubing 1WA6040-0705, showing the morphology of the pore distribution;
FIG. 2A is a scanning electron microphotographs of a cross-section of the wall of the porous polyurethane tubing 2WE9010-1211, showing the morphology of the pore distribution;
FIG. 2B is a scanning electron microphotographs of a cross-section of the wall of the porous polyurethane tubing 2WE7030-1211, showing the morphology of the pore distribution;
FIG. 2C is a scanning electron microphotographs of a cross-section of the wall of the porous polyurethane tubing 2WE5050-1211, showing the morphology of the pore distribution; and
FIG. 2D is a scanning electron microphotographs of a cross-section of the wall of the porous polyurethane tubing 2WE3070-1211, showing the morphology of the pore distribution.

DETAILED DESCRIPTION OF THE INVENTION
According to the method of the invention, the solvent type polyurethane resin is prepared by solution polymerization, i.e. polymerizing the necessary ingredients for the synthesis of polyurethane, that is, diisocyanate, chain extender and long chain polyol in an aprotic solvent, for example N, N-dimethyl formamide or N,N-dimethyl acetamide. Either one-shot process or prepolymer process can be used. It is essential for the method of the invention that the diisocyanate is an aromatic diisocyanate, i.e. 4,4'-diphenylmethane diisocyanate (MDI), because MDI has good reactivity, and therefore in synthesizing polyurethane, it is not necessary to add any catalyst to facilitate the polymerization reaction. If an aliphatic diisocyanate is used, organic metals or amine must be added as a catalyst which remains in the fabricated polyurethane product after the polymerization, causing cytotoxicity problems when the polyurethane polymer is used as the material for vascular graft prosthesis. Another advantage of using MDI is that the synthsized polyurethane polymers demonstrate superior mechanical strength, and therefore are able to provide a tough vascular graft prosthesis so as to reduce the possibility of distoration of the vascular graft prosthesis after they have been implanted in human body.
The chain extenders suitable for use in the method of the invention are short chain glycols. Examples of these short chain glycols are ethylene glycol, 1,4-butylene glycol and 1,6-hexamethylene glycol. The advantage of using short chain glycols as the chain extender is that homogeneity of the final product can be obtained. If diamines are used as chain extender in the solution polymerization of polyurethane, nonhomogeneity of the final product results because the polymerization normaly proceeds too quickly and a crosslinking side reaction occurs. Using short chain glycols can eliminate this drawback.
The long chain polyols suitable for use according to the method of the invention include various polyesters, polyethylene oxides, polypropylene oxides, polycaprolactons, polysulfides, polysilicone and polytetramethylene glycols. Among these, polytetramethylene glycol is preferred because it has superior mechanical properties, hydrolysis resistance and biocompatibility and blood compatibility.
It is also important to the method of the invention that the solid content and viscosity of the resultant polyurethane resin should be controlled in a specific range so that the polyurethane resin can be uniformly coated over the outer surface of a cylindrical mandrel. The resultant polyurethane resin should have a solid content of 15 to 45 percent by weight and a viscosity of 10,000 to 150,000 centipoises when measured by a Brookfield viscosimeter at room temperature (25.degree. C.). The cylindrical mandrel is preferably a metal mandrel with an outer diameter of 2 mm to 15 mm. In addition, according to the present invention, the coating of polyurethane resin over the mandrel should be conducted at a temperature of 10.degree. to 40.degree. C.
According to the invention, the coating is conducted by dropping the mandrel to be coated through a vertically mounted cylindrical container which is filled with the polyurethane resin, from its top open end to its bottom. A hole having a size suitable for the passing of the mandrel is formed at the bottom of the cylindrical container and positioning screws are provided at lower part of the container to ensure the passing of the mandrel through the hole. After the coating, the coated mandrel is placed in a coagulant to form a porous polyurethane tubing surrounding the mandrel. Note that the coated mandrel should be placed in the coagulant within 30 seconds immediately after the coating and the coagulant should be in a static state when the mandrel is placed in. According to the invention, a vessel containing coagulant is mounted below the coating cylinder so that the coated mandrel can be directly and quickly dropped into the coagulant within 30 seconds.
The coagulant suitable for use in the present invention consists of water, ethanol and optionally, an aprotic solvent, for example N,N-dimethyl formamide or N,N-dimethyl acetamide. In order to obtain a porous polyurethane tubing, the fraction of the ingredients of the coagulant must be properly controlled. The amount of each ingredients of the coagulant should be accorded with the following two equations:
W+(100-W)(ESF+ASF)=100(%)
ESF+ASF=1
wherein
W=wt % of water (nonsolvent) in coagulant
ESF=weight fraction of ethanol solvent based on the total solvent used in the coagulant
ASF=weight fraction of aprotic solvent on the total solvent used in coagulant, ##EQU1##
It has been found that in order to obtain a polyurethane tubing with a uniform distribution of pore size and without large cavities formed on the tubing wall, the parameter W should be in the range of 10-50, S should be in the range of 90 to 50, ESF should be in the range of 1.0 to 0.4 and ASF should be in the range of 0 to 0.6.
The coated mandrel is placed in the above-mentioned coagulant for a period of 2 to 12 hours according to the method of the invention. The coagulant should be maintained at a temperature of from 15.degree. C. to 40.degree. C.
The porous polyurethane tubings are separated from the mandrels by first placing the mandrel surrounded with the porous polyurethane tubing in a swelling agent to swell the polyurethane tubing and then removing the porous polyurethane tubings from the mandrel. The swelling agent suitable for use in the method of the invention should contain at least 90 percent by weight ethanol. A swelling agent consisting of 90 percent by weight ethanol and 10 percent by weight water is preferred for use in the invention. To facilitate the separation, the mandrel is placed in the swelling agent for 5 to 60 minutes.
The separated polyurethane tubings are then rinsed with a solution. The rinsing should last for 5 to 130 minutes to remove any possible PU oligomer remaining thereon. The solution for this purpose should contain at least 80 percent by weight ethanol. An aqueous solution contains 80 percent by weight ethanol and 20 percent by weight water is preferred for use according to the method of the invention.
After drying at, for example 20.degree.-50.degree. C., the porous polyurethane vascular grafts of the invention are obtained. The drying can be conducted by any method known to those skilled in this art.
This invention is more specifically described by the following illustrative examples.
Example 1
Synthesis of the solvent type polyurethane resins
In this example, solvent type polyurethane resins No. 1-16 of Table 1 below were prepared by one-shot process or prepolymer process. For one-shot process, polytetramethylene glycols, glycols, 4,4'-diphenylmethane diisocyanates in an amount as specified in Table 1, and suitable amount of aprotic solvents, were fed into a reactor, stirred and allowed to polymerize at a temperature of 70.degree.-75.degree. C. When the viscosity of the polyurethane reached the specific value as respectively indicated in Table 1, NCO terminators were added to the polymerization system to terminate the reaction. For prepolymer process, theoretical amount of polytetramethylene glycols(PTMG), 4,4'-dimethylmethane diisocyanates(MDI) and suitable amount of aprotic solvents were added to a reactor first to react to a prepolymer with NCO groups at its terminals, then chain extender, i.e. short-chain glycols, were added to allow the viscosity to increase to the specific value, and followed by adding NCO terminators to terminate the polymerization reaction.
TABLE 1__________________________________________________________________________PU resin PTMG:Glycol:MDI Solid content Viscosity Polymerization AproticNo. (mole ratio) (%) (.times.10.sup.-3 cps) method solvent__________________________________________________________________________1 PTMG (Mw = 1000) 30 8.0 one-shot DMF PTMG:BG:MDI 1:3:42 PTMG (Mw = 1000) 30 12.8 one-shot DMF PTMG:BG:MDI 1:2:33 PTMG (Mw = 1000) 30 10.6 one-shot DMF PTMG:BG:MDI 1:1.5:2.54 PTMG (Mw = 1000) 30 8.8 one-shot DMF PTMG:BG:MDI 1:1.2:2.25 PTMG (Mw = 1000) 30 6.7 one-shot DMF PTMG:BG:MDI 1:1:26 PTMG (Mw = 1000) 30 5.1 one-shot DMF PTMG:BG:MDI 1:0.8:1.87 PTMG (Mw = 1000) 45 16.0 one-shot DMAc PTMG:BG:MDI 1:1:28 PTMG (Mw = 1000) 30 13.2 prepolyner DMF PTMG:BG:MDI 1:1:29 PTMG (Mw = 1000) 30 12.0 prepolyner DMF PTMG:EG:MDI 1:1:210 PTMG (Mw = 1000) 30 18.2 prepolymer DMF PTMG:HG:MDI 1:1:211 PTMG (Mw = 2000) 30 7.6 one-shot DMF PTMG:BG:MDI 1:4:512 PTMG (Mw = 2000) 30 7.2 one-shot DMF PTMG:BG:MDI 1:3:413 PTMG (Mw = 2000) 30 8.2 one-shot DMF PTMG:BG:MDI 1:2.7:3.714 PTMG (Mw = 2000) 30 6.0 one-shot DMF PTMG:BG:MDI 1:2:315 PTMG (Mw = 2000) 30 2.1 one-shot DMF PTMG:BG:MDI 1:1:216 PTMG (Mw = 2000) 15 4.6 one-shot DMAc PTMG:BG:MDI 1:1:2__________________________________________________________________________ Note: BG = Butylene Glycol EG = Ethylene Glycol HG = Hexamethylene Glycol PTMG = polytetramethylene glycol MDI = 4,4Diphenylmethane diisocyanate DMF = N,NDimethyl Formamide DMAc = N,NDimethyl Acetamide
Example 2
Polyurethane resin No. 1 of Table 1 was coated over the outer surfaces of a cylindrical metal mandrel having an outer diameter of 8 mm with a thickness of 0.5 mm. Within 30 seconds immediately after the coating, the coated mandrels were placed in static coagulants having the components as set forth in Table 2.1. Porous polyurethane tubings 1WA100-0705, 1WA9010-0705, 1WA8020-0705, 1WA7030-0705, and 1WA6040-0705 were prepared by following the procedures of the invention and the conditions as indicated in Table 2.1.
Certain physical properties of these prepared tubings are summarized in Table 2.2. Scanning electron microphotographs of the porous polyurethane tubings of the invention are shown in FIGS. 1A-1E. It can be seen from Table 2.2 that the burst pressure of the porous polyurethane tubings of the invention in every case exceeds 2280 mmHg, indicating that the blood pressure that the porous polyurethane tubings of the invention can endure is about 19 times that of the physiologic systolic pressure, if normal average human physiologic systolic pressure is considered to be 120 mm Hg. In addition, the cytotoxicities and hemolytic indexes as set forth in Table 2.2 indicate that the porous polyurethane tubings of this example show no cytotoxicity response or hemolytic phenomenon, and therefore can be used as vascular graft prostheses with superior results.
TABLE No. 2.1__________________________________________________________________________Coagulant No. WA 100 WA 9010 WA 8020 WA 7030 WA 6040__________________________________________________________________________Composition of Coagulant 100/0 90/10 80/20 70/30 60/40(Water/DMF, wt/wt %)Temperature of Coagulant (.degree.C.) 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2Coagulating Time (hour) 6 6 6 6 6Composition of Swelling Agent 10/90 10/90 10/90 10/90 10/90(Water/Ethanol, wt/wt %)Temperature of Swelling Agent (.degree.C.) 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2Swelling Time (min) 10 10 10 10 10Composition of Rinsing Solution 20/80 20/80 20/80 20/80 20/80(Water/Ethanol, wt/wt %)Rinsing Time (min) 30 30 30 30 30Drying Temperature (.degree.C.) 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2Porous PU tubing No. 1WA100- 1WA9010- 1WA8020- 1WA7030- 1WA6040- 0705 0705 0705 0705 0705__________________________________________________________________________
TABLE 2.2__________________________________________________________________________ Porous PU tubingPU Tubing 1WA100- 1WA9010- 1WA8020- 1WA7030- 1WA6040-Characteristies 0705 0705 0705 0705 0705__________________________________________________________________________Internal Diameter (mm) 7.5 .+-. 0.2 7.5 .+-. 0.2 7.5 .+-. 0.2 7.4 .+-. 0.2 7.4 .+-. 0.2Wall Thickness (mm) 0.48 .+-. 0.03 0.48 .+-. 0.03 0.48 .+-. 0.03 0.44 .+-. 0.03 0.42 .+-. 0.03Pore Homogeneity [1] non-homogenous non-homogenous non-homogenous non-homogenous non-homogenousBurst Pressure (mmHg) [2] 2280 .+-. 76 2295 .+-. 76 2356 .+-. 76 2320 .+-. 76 2508 .+-. 76ASTM F895 Cytotoxicity [3] 0/0 0/0 0/0 0/0 0/0Hemolytic Index % [4] .largecircle. .largecircle. .largecircle. .largecircle. .largecircle.__________________________________________________________________________ Note: (1) Pore homogeneity is determined by observing the pores distribution in wallthickness direction by using a scanning electron microscope. (2) Burst pressure is measured by increasing the internal pressure of the polyurethane tubing specimen with its one end sealed until tubing bursts. The final pressure at which the burst occurs is the burst pressure. (3) Cytotoxicity is measured by the method described in ASTM F895 Standar Test for agar diffusion cell culture or cytotoxicity, and is represented by the Zone index/Lysis index. A result of 0/0 indicates that the test specimen shows no cytotoxicity response. (4) Hemolytic index is an index of the degree of hemolysis caused by contacting the test specimen with blood. The hemolytic index is measured by the method described in the ASTM F756 "Standard practice for assessmen of hemolytic properties for materials." A result of 0% indicates no hemolysis occurs.
Example 3
Polyurethane resin No. 2 of Table 1 was coated over the outer surfaces of cylindrical metal mandrels having an outer diameter of 13 mm and thickness of 1.2 mm. Within 30 seconds immediately after the coating, the coated mandrels were placed in static coagulants having the components as set forth in Table 3.1. Porous polyurethane tubings 2WE9010-1211, 2WE7030-1211, 2WE5050-1211, and 2WE3070-1211 were prepared by following the procedures of the invention and the conditions as indicated in Table 3.1.
Certain physical properties of these prepared tubings are summarized in Table 3.2. Scanning electron microphotographs of the porous polyurethane tubings of the invention are shown in FIGS. 2A-2D. As shown in these photographs, porous polyurethane tubings having uniform porous structure can be obtained when water/ethanol solution is used as the coagulant, and the amount of the weak solvent, i.e. the ethanol, exceeds 50 wt %. Also it can be seen from Table 3.2 that the burst pressure of the porous polyurethane tubings of the invention in every case exceeds 2350 mmHg, indicating that the blood pressure that the porous polyurethane tubings of the invention can endure is about 20 times that of the systolic pressure, if normal average human systolic pressure is considered to be 120mm Hg. In addition, the cytotoxicity and hemolytic indexes as set forth in Table 3.2 indicate that the porous polyurethane tubings of this example show no cytotoxicity response or hemolytic phenomenon, and therefore can be used as vascular graft prostheses with superior results.
TABLE 3__________________________________________________________________________ Porous PU TubingPU Tubing 2WE9010- 2WE7030- 2WE5050- 2WE3070-Characteristies 1211 1211 1211 1211__________________________________________________________________________Internal Diameter (mm) 12.0 .+-. 0.2 12.0 .+-. 0.2 12.0 .+-. 0.2 11.8 .+-. 0.2Wall Thickness (mm) 1.13 .+-. 0.05 1.13 .+-. 0.05 1.13 .+-. 0.05 1.10 .+-. 0.02Pore Homogeneity non-homogenous non-homogenous homogenous homogenousBrust Pressure (mmHg) -- 2350 .+-. 76 2660 .+-. 76 2710 .+-. 76ASTM F895 Cytotoxicity 0/0 0/0 0/0 0/0ASTM F756 Hemolytic Index .largecircle. .largecircle. .largecircle. .largecircle.(%)__________________________________________________________________________
TABLE 3.1__________________________________________________________________________Coagulant No. WE9010 WE7030 WE5050 WE3070__________________________________________________________________________Composition of Coagulant 90/10 70/30 50/50 30/70(Water/Ethanol, wt/wt %)Temperature of Coagulant (.degree.C.) 20 .+-. 2 20 .+-. 2 20 .+-. 2 20 .+-. 2Coagulating Time (hour) 4 4 4 4Composition of Swelling 5/95 5/95 5/95 5/95Agent (Water/Ethanol, wt/wt %Temperature of Swelling 30 .+-. 2 30 .+-. 2 30 .+-. 2 30 .+-. 2Agent (.degree.C.)Swelling Time (min) 5 5 5 5Composition of Rinsing 15/85 15/85 15/85 15/85Solution (Water/Ethanol,wt/wt %)Rinsing Time (min) 5 5 5 5Drying Temperature (.degree.C.) 30 .+-. 2 30 .+-. 2 30 .+-. 2 30 .+-. 2Porous PU tubing No. 2WE9010- 2WE7030- 2WE5050- 2WE3070- 1211 1211 1211 1211__________________________________________________________________________
Example 4
Polyurethane resin No. 3 of Table 1 was coated over the outer surfaces of cylindrical metal mandrels having an outer diameter of 6 mm and a coating thickness of 1.1 mm. Within 30 seconds immediately after the coating, the coated mandrels were placed in static coagulants having the components as set forth in Table 4.1. Porous polyurethane tubings 3WEA1010-0510, 3WEA1082-0510, 3WEA1064-0510, 3WEA3010-0510, 3WEA3064-0510, 3WEA5010-0510 and 3WEA5064-0510 were prepared by following the procedures of the invention and the conditions as indicated in Table 4.1.
Certain physical properties of these prepared tubings are summarized in Table 4.2. As it can be seen from Table 4.2 that when water/ethanol/DMF solutions are used as coagulants, and W is increased from 10 to 50, if ESF and ASF are controlled at an appropriate value, the resultant porous polyurethane tubings have uniform porous structure. It can also be seen from Table 4.2 that the porous polyurethane tubings all have a burst pressure larger than 2100 mm Hg, a pore size from 1-26 .mu.m and an area pososity of 25-42%. The cytotoxicity and hemolytic indexes as set forth in Table 4.2 indicate that the porous polyurethane tubings of this example show no cytotoxicity response or hemolytic phenomenon.
TABLE 4.1__________________________________________________________________________Coagulant No. WEA1010 WEA1082 WEA1064 WEA3010 WEA3064 WEA5010 WEA5064__________________________________________________________________________Composition W [1] 10 10 10 30 30 50 50parameters of S = 100-W 90 90 90 70 70 50 50coagulants [2] ESF [3] 1.0 0.8 0.6 1.0 0.6 1.0 0.6 ASF [4] 0.0 0.2 0.4 0.0 0.4 0.0 0.4Temperature of Cougulant 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2(.degree.C.)Coagulating Time (hour) 10 10 10 12 12 12 12Composition of Swelling 10/90 10/90 10/90 10/90 10/90 10/90 10/90Agent (Water/Ethanol,wt/wt %)Temperature of Swelling 20 .+-. 2 20 .+-. 2 20 .+-. 2 20 .+-. 2 20 .+-. 2 20 .+-. 2 20 .+-. 2Agent (.degree.C.)Swelling Time (min) 10 10 10 10 10 10 10Composition of Rinsing 20/80 20/80 20/80 20/80 20/80 20/80 20/80Solution (Water/ethanol,wt/wt %)Rinsing Time (min) 30 30 30 30 30 30 30Drying Temperature (.degree.C.) 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2Porous PU Tubing No. 3WEA1010- 3WEA1082- 3WEA1064- 3WEA3010- 3WEA3064- 3WEA5010 3WEA5064- 0510 0510 osto 0510 0510 0510 0510__________________________________________________________________________
TABLE 4.2__________________________________________________________________________ Porous PU TubingPU Tubing 3WEA 1010- 3WEA 1082- 3WEA 1064- 3WEA 3010- 3WEA 3064- 3WEA 5010- 3WEA 5064-Characteristics 5010 0510 0510 0510 0510 0510 0510__________________________________________________________________________Internal Diameter (mm) 5.1 .+-. 0.2 5.1 .+-. 0.2 5.1 .+-. 0.2 5.2 .+-. 0.2 5.2 .+-. 0.2 5.3 .+-. 0.2 5.3 .+-. 0.2Wall Thickness (mm) 1.05 .+-. 0.05 1.05 .+-. 0.05 1.05 .+-. 0.05 1.05 .+-. 0.05 1.05 .+-. 0.05 1.05 .+-. 0.05 1.05 .+-. 0.05Pore Homogeneity [1] homogenous homogenous homogenous homogenous homogenous homogenous homogenousBurst Pressure (mmHg) 2150 .+-. 76 2200 .+-. 76 2250 .+-. 76 -- -- 2100 .+-. 70 2180 .+-. 76ASTM F895 Cytoxicity 0/0 0/0 0/0 0/0 0/0 0/0 0/0ASTM F756 Hemolytic .largecircle. .largecircle. .largecircle. .largecircle. .largecircle. .largecircle. .largecircle.Index (%)Pore size .mu.m [1] 1-15 2-10 2-12 4-16 5-19 5-23 4-26Area Porosity %, [2] 25 28 33 39 -- 42 39__________________________________________________________________________ Note: (1) Pore size is determined by measuring the pore image taken by SEM in the crosssection of the wall of the porous polyurethane tubing specimen b using a computer image analysis technique. ##STR1##? The pore area and unit area are determined by calculating a unit image taken by SEM in the cross-section of the wall of the porous polyurethane tubing by using computer image analysis system.
Example 5
Polyurethane resins Nos. 4,5,6,7,8,9, and 10 of Table 1 were coated over the outer surfaces of cylindrical metal mandrels having an outer diameter of 6 mm and a coating thickness of 0.8 mm. Within 30 seconds immediately after the coating, the coated mandrels were placed in static coagulants having the components as set forth in Table 5.1. Porous polyurethane tubings 4WEA15955-0508, 5WEA15955-0508, 6WEA15955-0508, 7WEA15955-0508, 8WEA15955-0508, 9WEA15955-0508 and 10WEA15955-0508 were prepared by following the procedures of the invention and the conditions as indicated in Table 5.1.
Certain physical properties of these prepared tubings are summarized in Table 5.2. As it can be seen from Table 5.2 that when water/ethanol/DMF solutions are used as coagulants, and W is controlled at 15%, ESF is 0.95 and ASF is controlled at 0.05, the resultant porous polyurethane is controlled at 0.05, the resultant porous polyurethane tubings have uniform porous structure. It can also be seen from Table 5.2 that the porous polyurethane tubings all have a high burst pressure, a pore size from 2-32 .mu.m and an area pososity of 17-40%. The cytotoxicity and hemolytic indexes as set forth in Table 5.2 indicate that the porous polyurethane tubings of this example show no cytotoxicity response or hemolytic phenomenon.
TABLE 5.1__________________________________________________________________________Coagulant No. WEA15955 WEA15955 WEA15955 WEA15955 WEA16965 WEA15955 WEA15955__________________________________________________________________________Compostion W [1] 15 15 15 15 15 15 15Parameters of S = 100-W [2] 85 85 85 85 85 85 85Coagulants ESF [3] 0.95 0.95 0.95 0.95 0.95 0.95 0.95 ASF [4] 0.05 0.05 0.05 0.05 0.05 0.05 0.05PU Resin No. 4 5 6 7 8 9 10Temperature of Coagulant (.degree.C.) 30 .+-. 2 30 .+-. 2 30 .+-. 2 30 .+-. 2 30 .+-. 2 30 .+-. 2 30 .+-. 2Coagulating Time (hour) 6 6 6 6 6 6 6Composition of Swelling Agent 10/90 10/90 10/90 10/90 10/90 10/90 10/90(Water/Ethanol, wt/wt %)Temperature of Swelling Agent (.degree.C.) 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2Swelling Time (min) 50 50 50 50 50 50 50Composition of Rinsing Solution 20/80 20/80 20/80 20/80 20/80 20/80 20/80(Water/Ethanol, wt/wt %)Rinsing Time (min) 120 120 120 120 120 120 120Drying Temperature (.degree.C.) 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2Porous PU Tubing No. 4WEA159 5WEA159 6WEA159 7WEA159 8WEA159 9WEA159 10WEA159 55-0508 55-0508 55-0508 55-0508 55-0508 55-0508 55-0508__________________________________________________________________________
TABLE 5.2__________________________________________________________________________ Pourous PU tubingPU Tubing 4WEA15955- 5WEA15955- 6WEA15955- 7WEA15955- 8WEA15955- 9WEA15955- 10WEA15955-Characteristics 0508 0508 0508 0508 0508 0508 0508__________________________________________________________________________Internal Diameter (mm) 5.2 .+-. 0.2 5.2 .+-. 0.2 5.2 .+-. 0.2 5.2 .+-. 0.2 5.2 .+-. 0.2 5.2 .+-. 0.2 5.2 .+-. 0.2Wall Thickness (mm) 0.76 .+-. 0.05 0.76 .+-. 0.05 0.76 .+-. 0.05 0.76 .+-. 0.05 0.76 .+-. 0.05 0.76 .+-. 0.05 0.76 .+-. 0.05Pore Homogeneity homogenous homogenous homogenous homogenous homogenous homogenous homogenousBurst Pressure (mmHg) 1950 .+-. 76 1880 .+-. 76 1800 .+-. 76 2450 .+-. 76 1960 .+-. 76 -- --ASTM F895 Cytotoxicity 0/0 0/0 0/0 0/0 0/0 0/0 0/0ASTM F756 Hemolytic .largecircle. .largecircle. .largecircle. .largecircle. .largecircle. .largecircle. .largecircle.Index (%)Pore Size .mu.m [1] 5-15 4-20 4-30 2-13 2-18 2-32 2-18Area Porosity % [2] 30 32 33 17 33 40 34__________________________________________________________________________
Example 6
Polyurethane resins Nos. 11-16 of Table 1 were coated over the outer surfaces of cylindrical metal mandrels having an outer diameter of 4 mm and a coating thickness of 0.4 mm. Within 30 seconds immediately after the coating, the coated mandrels were placed in static coagulants having the components as set forth in Table 6.1. Porous polyurethane tubings 11WEA208515-0304, 12WEA208515-0304, 13WEA208515-0304, 14WEA208515-0304, 15WEA208515-0304, and 16WEA208515-0304 were prepared by following the procedures of the invention and the conditions as indicated in Table 6.1.
Certain physical properties of these prepared tubings are summarized in Table 6.2. As it can be seen from Table 6.2 that when water/ethanol/DMF solutions are used as coagulants, and W is controlled at 20%, ESF is 0.85 and ASF is controlled at 0.15, the resultant porous polyurethane tubings have uniform porous structure. It can also be seen from Table 6.2 that the porous polyurethane tubings have a pore size from 2-23 .mu.m and an area pososity of 23-31%. The cytotoxicity and hemolytic indexes as set forth in Table 6.2 indicate that the porous polyurethane tubings of this example show no cytotoxicity response or hemolytic phenomenon.
TABLE 6.1__________________________________________________________________________ WEA WEA WEA WEA WEA WEACoagulant No. 208515 208515 208515 208515 208515 208515__________________________________________________________________________Composition W 20 20 20 20 20 20Parameters of S = 100-W 80 80 80 80 80 80Coagulants ESF 0.85 0.85 0.85 0.85 0.85 0.85 ASF 0.15 0.15 0.15 0.15 0.15 0.15PU Resin No. 11 12 13 14 15 16Temperature of Coagulant (.degree.C.) 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2Coagulating Time (hour) 8 8 8 8 8 8Composition of Swelling Agent 5/95 5/95 5/95 5/95 5/95 5/95(Water/Ethanol, wt/wt %)Temperature of Swelling Agent (.degree.C.) 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2 25 .+-. 2Swelling Time (min) 30 30 30 30 30 30Composition of Rinsing Solution 15/85 15/85 15/85 15/85 15/85 15/85(Water/Ethanol, wt/wt %)Rinsig Time (min) 60 60 60 60 60 60Drying Temperature (.degree.C.) 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2 40 .+-. 2Porous PU Tubing No. 11WEA2085 12WEA2085 13WEA2085 14WEA2085 15WEA2085 16WEA2085 15-0304 15-0304 15-0304 15-0304 15-0304 15-0304__________________________________________________________________________
TABLE 6.2__________________________________________________________________________ Porous PU tubingPU Tubing 11WEA2085 12WEA2085 13WEA2085 14WEA2085 15WEA2085 16WEA2085Characteristics 15-0304 15-0304 15-0304 15-0304 15-0304 15-0304__________________________________________________________________________Internal Diameter (mm) 3.2 .+-. 0.2 3.2 .+-. 0.2 3.2 .+-. 0.2 3.2 .+-. 0.2 3.2 .+-. 0.2 3.2 .+-. 0.2Wall Thickness (mm) 0.37 .+-. 0.05 0.37 .+-. 0.05 0.36 .+-. 0.05 0.36 .+-. 0.05 0.37 .+-. 0.05 0.37 .+-. 0.05Pore Homogeneity homogenous homogenous
Example 7
In this example, several porous polyurethane tubings prepared in the previous examples were implanted in dogs for a chronic animal test to survey the biocompatibility. The survey method and results are summarized in Table 7 below.
TABLE 7______________________________________ implanted PU tubingAnimal Nos. position implanted______________________________________dog (#1) iliac artery 1WA5050-0705(25 Kg) of left leg I.D. (7.5 mm)results:no blocking, taken out and checked by observation, 2 yearsafter the implantationdog (#2) iliac artery 1WA5050-0705(20 Kg) of left leg I.D. (7.5 mm)results:no blocking, taken out and checked by observation, 2 yearsafter the implantationdog (#3) femoral artery 5WEA15955-0508(25 Kg) I.D. (5.2 mm)results:no blocking, checked by angiography, 2 years after theimplantationdog (#4) right femoral artery PU tubing prepared(20 Kg) by using PU resin No. 2 and coagulant WA5050, I.D. (3 mm)results:no blocking, checked by angiography, 2 years after theimplantationdog (#4) left femoral artery PU tubing prepared(20 Kg) by using PU resin No. 2 and coagulant WA5050, I.D. (3 mm)results:no blocking, checked by angiography, 2 years after theimplantationdog (#5) right femoral artery PU tubing prepared(20 Kg) by using PU resin No. 2 and coagulant WA5050, I.D. (3 mm)results:no blocking, checked by angiography, 2 years after theimplantationdog (#5) left femoral artery PU tubing prepared(20 Kg) by using PU resin No. 2 and coagulant WA5050, I.D. (3 mm)results:no blocking, checked by antjiography, 2 years after theimplantationdog (#6) right femoral artery PU tubing prepared(20 Kg) by using PU resin No. 5 and coagulant WEA15955, I.D. (3 mm)results:no blocking, checked by angiography, 1.5 years after theimplantationdog (#6) left femoral artery PU tubing prepared(20 Kg) by using PU resin No. 5 and coagulant WEA15955, I.D. (3 mm)results:no blocking, checked by angiography, 1.5 years after theimplantation______________________________________
It can be seen from the above illustrative examples and tables that the porous polyurethane tubings fabricated by the method of the invention have homogeneous pore structure and superior blood compatibility and therefore are suitable for being used as vascular graft prostheses.

Method for preparing a porous polyurethane vascular graft prosthesis

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

US Referenced Citations (1)