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PubMedDate not supplied

Synthesis and characterization of novel blood-compatible soluble chemically cross-linked polyurethanes with excellent mechanical performance for biomedical applications.

A controlled cross-linking polymerization system was designed, and soluble chemically cross-linked polyurethane was synthesized using laurylamine, n-octylamine, n-pentylamine, and ethylenediamine chain extenders. The mechanical analysis showed that the polyurethane materials synthesized in this paper have very excellent mechanical properties with a breaking elongation of 1914% and a tensile strength of 4303 N/cm(2). Such good mechanical properties must enable it to have good longevity when used as biomaterials. The polyurethane materials with n-pentylamine and n-octylamine chain extenders show reduced platelet adhesion than that with an ethylenediamine chain extender after sustaining 200 000 times of load cycles, indicating that polyurethanes introduced with an alkyl side chain onto the hard segments keep good antithrombogenic properties after sustaining load cycles. This might be because the hard segments are shielded by the alkyl side chain when the micro-phase-separation structure is destroyed in the repeated deformation of the polyurethane materials. The present investigation reveals that the influence of introducing long alkyl side chains into the backbone of the polyurethane macromolecule has been shown to reduce platelet deposition and to enhance in vitro albumin adsorption. However, in this paper, it has been observed that the polyurethane material introduced with a proper-length alkyl side chain onto the hard segment has the best antithrombogenic properties after the fatigue test.

Biocompatible Materials↗

PubMedDate not supplied

Structure and properties of polyurethanes prepared from triglyceride polyols by ozonolysis.

Ozonolysis was used to obtain polyols with terminal primary hydroxyl groups and different functionalities from trilinolein (or triolein), low-saturation canola oil, and soybean oil. The functionality of the model polyol from triolein (trilinolein) was 3.0 and that of soy polyol was 2.5, due to the presence of unreactive saturated fatty acids, while canola gave a polyol with a functionality of 2.8. All polyols exhibited a high tendency to crystallize at room temperature. The resulting waxes had melting points comparable to that of paraffin and very low viscosities in the liquid state. The polyols were cross-linked using 4,4'-methylenebis(phenyl isocyanate) to give polyurethanes. Glass transitions (T(g)) for the model-, canola-, and soy-based polyurethanes were 53, 36, and 22 degrees C, respectively. The about 30 degrees C lower T(g) of the soy-based polyurethane than that of the model polyurethane was the result not only of lower functionality but also of the presence of saturated fatty acids in the former. Polyurethane from the canola polyol had intermediate cross-linking density and properties. These polyurethanes displayed excellent mechanical properties and higher glass transition temperatures compared to polyurethanes from epoxidized and hydroformylated polyols of the same functionality, presumably due to the absence or lower content of dangling chains in the former.

Ozone↗

PubMed2003

Longevity of silicone and polyurethane catheters in long-term enteral feeding via percutaneous endoscopic gastrostomy.

BACKGROUND: As percutaneous endoscopic gastrostomy (PEG) is often used for many months or years, the longevity of the feeding tubes plays an important role in the global outcome and costs of PEG. AIM: A retrospective study to evaluate the longevity of silicone and polyurethane PEG catheters. METHODS: The records of 297 patients who were fed via PEG for over 90 days were evaluated. The material of the PEG catheter, duration of follow-up, local complications, need to remove PEG because of tube deterioration or local complications and time from PEG placement to PEG removal were recorded and compared. RESULTS: Two hundred and twenty-eight patients had polyurethane and 69 had silicone PEG catheters. The follow-up ranged from 116 to 3207 days for the polyurethane group and from 98 to 1861 days for the silicone group. No differences were observed in either local complications or PEG removal because of local complications. Tube deterioration causing PEG removal occurred in 36 of the 228 polyurethane PEG catheters and in 25 of the 69 silicone PEG catheters (P = 0.0005). Tube deterioration occurred significantly earlier in the 25 silicone catheters than in the 36 polyurethane catheters. The mean time from PEG placement to PEG removal was 287 days (95% confidence interval, 239-335) for silicone tubes and 573.9 days (95% confidence interval, 425-723) for polyurethane tubes (P = 0.0024). CONCLUSION: Polyurethane PEG catheters seem to be more resistant to deterioration than silicone PEG catheters, and at present they should be preferred for long-term enteral feeding via PEG.

Adolescent↗

PubMed1994

The capsule quality of saline-filled smooth silicone, textured silicone, and polyurethane implants in rabbits: a long-term study.

Recently, there have been many new designs in both the surface texture and chemical composition of breast implants that claim reduced constrictive capsular formation. The purpose of this study was to utilize a quantitative method to determine the firmness of capsules formed around saline-filled smooth silicone, textured silicone, and polyurethane implants in an experimental rabbit model 1 year after implantation. Our objective was to analyze the histologic, biologic, and biochemical content of the respective capsules to account for any differences in physical behavior. Forty-five smooth silicone, textured silicone, and polyurethane implants were placed in one of three positions beneath the panniculus carnosus muscle of New Zealand White rabbits. After 1 year, all capsules were palpated and classified according to firmness. Intracapsular static and dynamic pressure measurements were obtained by placing a pressure monitor (Stryker) in an injector port attached to the individual implants. Capsular firmness was significantly greater in the textured silicone implants than in the smooth silicone or polyurethane implants after 1 year. The dynamic qualities of the periprosthetic soft tissues were measured while saline was injected into the implants. The capsules around the textured silicone implants generated significantly higher pressures than the smooth silicone or polyurethane counterparts. The capsules around the polyurethane implants were the softest and most compliant in all categories. Histologically, there is a significant inflammatory response surrounding the textured silicone implants that does not exist in the capsules around the smooth silicone implants. The capsules around the polyurethane implants have the least fibrous tissue deposition. There is a decrease in the proportion of type III collagen in the capsules around the textured silicone implants versus smooth silicone or polyurethane implants. The in vitro contraction patterns of the fibroblast-populated collagen lattices do not reveal the contraction differences observed in vivo in rabbits. However, there are many components that determine contractility. This area deserves further investigation.

Animals↗

PubMed2002

Elastomeric biodegradable polyurethane blends for soft tissue applications.

Four biodegradable polyurethane blends were made from segmented polyurethanes that contain amino acid-based chain extender and diisocyanate groups. The soft segments of these parent polyurethanes were either polyethylene oxide (PEO) or polycaprolactone (PCL) diols. The blends were developed to investigate the effect of varying soft segment compositions on the overall morphological, mechanical, and degradative properties of the materials, with a view to producing a family of materials with a wide range of properties. The highly hydrophilic PEO material was incorporated to increase the blend's susceptibility to degradation, while the PCL polyurethane was selected to provide higher moduli and percent elongations (strains) than the PEO parent materials can achieve. All four blends were determined to be semi-crystalline, elastomeric materials that possess similarly shaped stress-strain curves to that of the PCL-based parent polyurethane. As the percent composition of PEO polyurethane within the blend increased, the material became weaker and less extensible. The blends demonstrated rapid initial degradation in buffer followed by significantly slower, prolonged degradation, likely corresponding to an initial loss of primarily PEO-containing polymer, followed by the slower degradation of the PCL polyurethane. All four blends were successfully formed into three-dimensional porous scaffolds utilizing solvent casting/particulate leaching methods. Since these new blends possess a range of mechanical and degradation properties and can be shaped into three-dimensional objects, these materials may hold potential for use in soft tissue engineering scaffold applications.

Absorbable Implants↗

PubMed1992

Biostability and blood-contacting properties of sulfonate grafted polyurethane and Biomer.

Sulfonate-containing polyurethanes were evaluated for in vivo biodegradation using subcutaneously implanted tensile bars. In addition, these anionically charged polyurethanes were evaluated for in vivo activation of human complement C3a and ex vivo platelet deposition in arteriovenously-shunted canines. The sulfonate derivatized polymers included laboratory synthesized polyurethane and Biomer. Other polymers used for references included Intramedic polyethylene, Silastic and a poly(ethylene oxide) based polyurethane. The biodegradation results indicated that Biomer and the laboratory sulfonated Biomer (both manufactured with stabilizers), remained mechanically stable, retaining both tensile strength and elasticity after 4 weeks of subcutaneous implantation. The unstabilized polyurethanes (with or without sulfonation), however, showed marked cracking and a loss of mechanical properties after the same period of subcutaneous implantation. Sulfonated polyurethanes depressed human complement C3a activation in plasma, as indicated by decreased levels of anaphylatoxin production. The results of canine ex vivo blood contacting experiments were conducted in both an acute and chronic model and demonstrated decreased platelet deposition and activation for the sulfonated polyurethanes.

Absorption↗

PubMed1989

Polyurethane support films: structure and cellular adhesion.

It is desirable to examine the cytobiology of cell adhesion to the same materials which are contemplated for use in biomedical and biotechnological devices. It is also of fundamental interest to examine adhesion to substrates with properties which are likely to influence adhesion in controlled ways. In many of these applications the materials of choice are polyurethane elastomers due to their physical properties and resistance to biodegradation. Polyurethanes have a two phase microstructure consisting of hydrophilic hard segments and hydrophobic soft segment domains. Variations of both the chemistry and the morphology of these microdomains may be produced. It is well understood that the hydrophilic/hydrophobic nature of surfaces affects cellular adhesion and the adsorption of extracellular proteins. Since polyurethane microdomains have dimensions in the range of 10-100 nm, hence the size of proteins and cell-surface receptors, polyurethane microdomain structure could influence order at the cell-material interface. Polyurethanes may be prepared as thin films with excellent properties for use as specimen supports in High Voltage transmission Electron Microscopy (HVEM) at 1 MeV. This permits the imaging of the cytoskeleton and other internal features of whole mounts of adherent cells, rather than tedious thin sectioning required for conventional TEM. Subsequently the surface morphology of these preparations may be imaged with high resolution SEM. Finally, the polyurethane itself may be stained and imaged by either HVEM or high resolution SEM in order to relate polyurethane micro-morphology to cellular features.

Biocompatible Materials↗

PubMed1994

Interactions of enzymes and fungi with crosslinked polyurethanes prepared for biomedical applications.

Shelf life and long-term environmental stability of polyurethanes intended for percutaneous applications and various biomedical applications are largely depend on their resistance to fungal attack and growth. Two classes of aliphatic crosslinked polyurethanes based on hexamethylene diisocyanate (HDI) and bicyclo-hexyl-methane diisocyanate (SM DI) were subjected to cell-free enzymatic degradation using hydrolytic and oxidative enzymes and to fungal attack and fungal growth using Aspergillus niger and Penicillium Sp. The present crosslinked polyurethanes are not susceptible to degradation by hydrolytic enzymes. The marginal loss of tensile strength in buffered solution of papain is attributed to plasticization by the absorbed components of the enzyme solution. The PEG based crosslinked polyurethanes are marginally susceptible to degradation by lactic dehydrogenase solution. The present polyurethanes are resistant to fungal attack. The fungal growth was not observed with PTMG and PPG based Polyurethanes, however, a marginal growth was observed with PEG based polyurethanes.

Cross-Linking Reagents↗

PubMed1996

In vitro function and durability of a polyurethane heart valve: material considerations.

BACKGROUND AND AIMS OF THE STUDY: Flexible trileaflet polyurethane heart valves can be designed which have good hydrodynamic function in vitro. The choice of polyurethane for fabrication of such valves is not simple; several similar polyurethanes are available, but relatively minor differences in their structure and composition may have profound effects on long term fatigue behavior with little effect on their short term mechanical properties. METHODS: The relative functional characteristics of flexible trileaflet polyurethane valves made from two different polyetherurethanes were compared before and after long term fatigue testing. The polyetherurethanes had similar gross mechanical properties, differing in that one was chain-extended with butanediol (PEU) and the other with ethylene diamine (PEUE). Six valves of each type, with similar leaflet thickness distributions, were studied. RESULTS: Hydrodynamic function of both valve types was similar to a similarly sized porcine aortic valve. Mean pressure drop across the open valve was higher in PEU valves than in PEUE valves, although PEUE valves had greater energy losses during closure and when closed. Reverse flow decreased with time in the fatigue tester. In long term fatigue tests, all six PEU valves failed by 307 million cycles, with failure primarily by development of holes at the coaptation region of the leaflets associated with localized calcification. Three PEUE valves exceeded 800 million cycles without failure and all PEUE valves exceeded 450 million cycles. CONCLUSIONS: A combination of good phase separation of polyurethane soft and hard segments with good rubbery characteristics can explain the better results achieved in the PEUE valves compared with similar PEU valves. These results suggest the general type of polyurethane structure suitable for heart valve fabrication and have implications for development of novel polyurethanes for this application.

Animals↗

PubMedDate not supplied

Breakage and acceptability of a polyurethane condom: a randomized, controlled study.

CONTEXT: Although the first commercial polyurethane condom was approved for use several years ago, no U.S. clinical trial has compared its performance to that of the latex condom. METHODS: In a masked crossover study, 360 couples were randomized to use three polyurethane condoms and three latex condoms. After each use, couples recorded condom breaks, condom slips and other aspects of performance. At completion of the study, couples compared the sensitivity, ease of use, fit and lubrication of the two types of condoms. RESULTS: The clinical breakage rate of the polyurethane condom was 7.2%, compared with 1.1% for the latex condom (relative risk of 6.6, 95% confidence interval of 3.5-12.3). The complete slippage rate (combining incidents during intercourse and withdrawal) of the polyurethane condom was 3.6%, compared with 0.6% for the latex condom (relative risk of 6.0, 95% confidence interval of 2.6-14.2). Most male users preferred the sensitivity provided by the polyurethane condom to that of the latex condom. CONCLUSIONS: The clinical breakage rate of the polyurethane condom is significantly higher than that of the latex condom. However, nearly half of the users preferred the polyurethane condom, which provides an option for couples who have rejected conventional condoms or who cannot use latex products.

Adolescent↗

PubMed2001

Synthesis and Surface Property of Aqueous Fluorine-Containing Polyurethane.

A novel aqueous fluorine-containing polyurethane was prepared with a hydrophobic macromonomer of a perfluoroalkyl group. Two representative properties of the polyurethane, initial particle diameter dispersed in water and surface free energy of coating films, were investigated. The macromonomer was synthesized by radical copolymerization of perfluoroalkylethyl acrylate and methyl methacrylate with a diol of chain-transfer agent in order to attenuate solubility and hydrophobic property. Anionic aqueous polyurethane was obtained with a good hydrophobic film property by one-step condensation polymerization of the macromonomer with hydrophilic comonomers and successive ionization. The polyurethane showed an initial average diameter of less than 1100 nm in water and surface free energies of less than 19 dyn/cm. The water dispersion property and hydrophobic surface property of the polyurethane can be controlled by controlling the content and hydrophobic property of the macromonomer. The incorporation of the macromonomer in the polyurethane backbone did not show a significant effect on the glass transition temperature, or the softness, of the polyurethane. Copyright 2001 Academic Press.

Journal Article↗

PubMed2002

Surface characterization and platelet adhesion studies of aliphatic polyurethanes grafted by fluorocarbon oligomers: effect of fluorocarbon chain length and carboxylic acid group.

The surfaces of aliphatic polyurethane films, which were synthesized by 1,6 hexamethylene diisocyanate, poly(tetramethylene glycol) and 1,4 butanediol, were modified by grafting different chain length of fluorocarbon oligomers. The fluorocarbon oligomers on polyurethane surfaces were terminated with trifluorocarbon or carboxylic acid functionality. The alkyl groups were also grafted onto polyurethane surfaces for comparison. The surface characterization and platelet-contacting property were studied using electron spectroscopy for chemical analysis (ESCA), static contact angle analysis and in vitro platelet adhesion experiments. The effects of fluorocarbon oligomers and their terminal functionalities are discussed. The ESCA results demonstrate the fluorocarbon enrichment at the outmost layer in fluorocarbon oligomer grafted polyurethanes. The fluorocarbon content at the surface increases with increasing the chain length of fluorocarbon oligomers. The fluorocarbon oligomer grafted polyurethanes exhibit highly hydrophobic surfaces, while alkyl groups grafted polyurethanes show relatively hydrophobic surfaces compared with the untreated polyurethane. The in vitro platelet adhesion experiments indicated that the fluorocarbon oligomer and carboxylic acid functionality significantly reduced the number and the degree of activation of the adherent platelets.

Journal Article↗

PubMed1995

Split-thickness skin graft donor site management. A randomized prospective trial comparing a hydrophilic polyurethane absorbent foam dressing with a petrolatum gauze dressing.

OBJECTIVE: Traditionally, skin graft donor sites have been covered with fine-mesh gauze dressings, and a dry eschar has been allowed to form. Newer dressings that can provide a moist wound environment may facilitate reepithelialization. We compared a hydrophilic semipermeable absorbent polyurethane foam dressing that provides a moist wound environment with a petrolatum gauze dressing for donor sites. DESIGN: Prospective randomized trial; follow-up at 14 days. SETTING: Department of head and neck surgery in a tertiary care center. PATIENTS: Sixty-eight eligible patients received one of the two dressings. Harvested skin grafts were 0.375-mm (0.015-in) thick; donor site surface areas were recorded. At postoperative day 14, the dressings were removed, and wound epithelialization was scored: 1, none; 2, scattered or spotty; and 3, complete. Donor site and operative site pain intensities were assessed by a visual numeric scale: none (0) to the worst (100) experienced over the preceding 24-hour period. Pain scores were available for 58 patients. MAIN OUTCOME MEASURES: Dressings were compared based on these criteria: healing at 14 days, infection, and donor site and operative site pain. RESULTS: A healing score of 3 was seen in 37% (14/38) of patients with hydrophilic semipermeable absorbent polyurethane foam dressings and in 17% (5/30) of patients with petrolatum gauze dressings (P = .06) by day 14. Overall, however, mean healing scores were similar in both groups. Mean healing scores for the patients who received a hydrophilic semipermeable absorbent polyurethane foam dressing was 2.3 (SD = 0.6) vs 2.2 (SD = 0.6) for patients who received the petrolatum gauze dressing (P = .20). Numbers of days required for complete epithelialization in these groups were 20.6 (SD = 10.1) and 19.3 (SD = 5.1), respectively (P = .49). One infection occurred in the group who received the petrolatum gauze dressing. The mean maximum pain intensity scores were lower for those who were given the hydrophilic semipermeable absorbent polyurethane foam dressing on postoperative days 1 through 3 (P = .003, .03, and .04, respectively). Pain increased with a larger donor site surface area for the patients with the petrolatum gauze dressing but not for the patients with the hydrophilic semipermeable absorbent polyurethane foam dressing. CONCLUSIONS: The hydrophilic semipermeable absorbent polyurethane foam dressing appears to have potential advantages over the petrolatum gauze dressing; it produces less initial patient donor site discomfort and tends to produce more complete donor site healing by postoperative day 14.

Absorption↗

PubMed1997

Ex vivo and in vivo evaluation of the blood compatibility of surface-modified polyurethane catheters.

Catheter model tubes were prepared from a medical-grade polyetherurethane and their outer surfaces modified by surface-graft polymerization of acrylamide and dimethyl acrylamide (DMAA). The surface-graft layer was characterized by means of dry staining, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and protein adsorption. Ex vivo evaluation for the blood compatibility of the surface-modified polyurethane was carried out using the polyurethane tube as an arterio-venous shunt between the carotid artery and the jugular vein of rabbits. When the surface density of grafted polymer was in the range of 10-30 microg/cm2, the in vitro adsorption of IgG exhibited a minimum value and platelet adhesion to the grafted polyurethane surface was insignificant, in marked contrast with that to the virgin (nonmodified) surface. The in vivo blood compatibility of polyurethane was evaluated by implanting the catheter tube in the inferior vena cava of rabbits from the femoral vein after ligation of a distal site of the exposed femoral vein. After remaining there for predetermined periods of time, the implanted catheters were taken out together with the veins of the rabbits that had been heparinized and sacrificed just prior to excision of the veins. After exchange of the blood in the veins for saline, the excised veins were opened by cutting longitudinally to inspect for clot formations on the surfaces of the implanted catheters. Occlusion of the inferior vena cava was not observed for any of the catheters, nor was there any apparent damage or microembolizations in the lungs and kidneys. Many small-sized clots were observed on the surfaces of the nonmodified polyurethane tubes after a 2-week implantation whereas the catheter surfaces grafted with DMAA polymer chains had a much smaller number of clots. When the blood compatibility of polyurethane surfaces was graded for relative evaluation from one (marked clotting) to five (no clotting) based on the size and number of the clots, the evaluation results were as follows: 3.1 (virgin, 2 weeks), 4.0 (grafted, 1 week), 4.1 (grafted, 2 weeks), and 3.5 (grafted, 1 month).

Acrylamides↗

PubMed1997

Use of surface-modifying macromolecules to enhance the biostability of segmented polyurethanes.

Polyurethanes are widely used as biomaterials for medical implants because of their excellent mechanical properties and moderate biocompatibility. However, the demand for more bioresistant and biocompatible polyurethanes to meet the needs of long-term implant devices still remains an important issue. Since most biological interactions with materials occur at the interface, a significant number of studies for improving the biocompatibility of polyurethanes have concentrated on surface modification. It is well known that additives used in polymeric materials as processing aids, mold releasing agents, antioxidants, etc., migrate to the surface and change the surface properties of the material. Under certain conditions polymeric additives may also migrate toward surfaces. This study describes two fluorine-containing, surface-modifying macromolecules (SMMs) that have been evaluated for their ability to inhibit polyurethane degradation. These materials actively migrate to the upper surface of a material film when they are mixed with a base polymeric materia. Contact angle measurements for the mixture of SMM with base polyurethane indicate that the surface becomes more hydrophobic after adding the SMMs, while X-ray photoelectron spectroscopy analysis shows an enrichment of fluorine on the polymer surfaces. Differential scanning calorimetry thermograms indicate that the micro-structure, as defined by the thermal transitions of the base polymer, are not altered by the addition of SMMs. Enzyme-induced biodegradation tests exhibit a significant reduction of polyurethane degradation in the presence of these surface-resident materials. The results indicate that the SMMs have the potential to resist hydrolytic degradation mediated by lysosomal enzymes while generating a surface chemistry on the native elastomer which is similar in nature to that of a fluoropolymer, e.g., Teflon.

Absorptiometry, Photon↗

PubMed1984

Determination of extractable methylene dianiline in thermoplastic polyurethanes by HPLC.

Polyurethanes are finding increasing utilization in biomedical applications. Recently, the reported finding of methylene dianiline (4,4'-diaminodiphenylmethane, MDA) in the aqueous extracts of autoclaved 4,4'-diphenylmethane diisocyanate-based polyurethanes promoted our investigation of the origin and extent of extractable methylene dianiline in polyurethanes. A high-pressure liquid chromatography procedure using precolumn derivatization is utilized to selectively monitor the appearance of this diamine in the aqueous extracts of polyurethanes subjected to water immersion, heat aging, and various sterilization techniques. No MDA was found in the aqueous extracts of the treated polyurethane except for the case of prolonged steam autoclaving. The appearance of 3-5 ppb MDA in the extract under these conditions is attributed to hydrolysis of the polymer. The stability of the polyurethanes under most conditions renders these materials useful in biomedical applications.

Aniline Compounds↗

PubMed1995

Studies on the tumor-promoting activity of polyurethanes: depletion of inhibitory action of metabolic cooperation on the surface of a polyalkyleneurethane but not a polyetherurethane.

Methanol extracts prepared from three polyetherurethanes (PEUs), namely PU4, PU6, and PU8, which were synthesized using 4,4'-diphenylmethanediisocyanate, poly(tetramethylene oxide), and 1,4-butanediol, showed an inhibitory action on the gap-junctional intercellular communication in a V79 metabolic cooperation (MC) test system. However, the inhibitory potentials of methanol extracts did not correlate with the tumorigenic potential of the polyurethanes in 1-year rat implantation studies. When the MC test was carried out using glass dishes partly coated with low molecular weight PEU, the inhibitory activity was clearly detected on the surface of the polyurethane coating but not on that of the noncoated glass area. The inhibitory activity of the three PEUs investigated using polyurethane-coated dishes correlated with the values of the polyurethane's tumorigenic potential in the rat implantation study. Various polyurethanes containing polybutadiene (PBD), hydrogenated polybutadiene (HPBD), or a fluoropolyether glycol (FPEG) as the soft segment were also tested using coated dishes in the MC assay. The threshold inhibitory response of FPEG-PU was 10-fold less than that of PU4, and neither PBD-PU nor HPBD-PU showed any inhibition in the MC test system. Both the FPEG and aliphatic soft segment containing polyurethanes decreased, and had minimal influence on the gap junctional intercellular communication. Thus, the tumor-promoting potential of PBD-PU, HPBD-PU, and FPEG-PU was considered to be lower than those of the PEUs based on these in vitro test results.

Animals↗

PubMed1993

Effect of hand segment chemistry and strain on the stability of polyurethanes: in vivo biostability.

We investigated four polyurethanes that were synthesized with different hard segments and four commercial polyurethanes for in vivo biostability. The four polyurethanes with the varying hard segments were based on a 3:2:1 mole ratio of methylene diphenylene diisocyanate (MDI) or methylene dicyclohexane diisocyanate (H12MDI), butanediol (BD) or ethylene diamine (ED) and polytetramethylene oxide (PTMO) (MW = 1000). Four commercial polyurethanes were also used: Biomer, Pellethane, Medtronic experimental C-19 (C-19) and Medtronic experimental C-36 (C-36). Films of the polymers were implanted subcutaneously in rats for up to 12 wk to assess their biostability. Polymer films were implanted either with a 100% strain applied or in the unstrained state. Measurement of tensile properties, molecular weight and surface properties before and after implantation assessed the stability of each of the polymers. Surface cracking was observed with scanning electron microscopy and the extent and depth of cracking were determined. Pellethane, C-19 and C-36 showed the least evidence of degradation, although all underwent strain-induced phenomena that decreased their tensile elongation when an external force was applied. After implantation, the BD chain-extended polymers retained their tensile properties better than ED chain-extended polymers. H12MDI-based polyurethanes were more susceptible to surface cracking and molecular weight changes than MDI-based polyurethanes, possibly due to the lack of a crystallizable hard segment.

Animals↗