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PubMed1979

ESCA studies of surface chemical composition of segmented polyurethanes.

Surface chemical analysis of two commercially available polyurethanes, i.e., Avcothane and Biomer was carried out by electron spectroscopy for chemical analysis (ESCA). The depth which is subject to analysis is in the range of 50-100 A. The variables studied in this study are the difference in exposure to air or to the mold substrate during the solvent casting process. Model compounds such as a pure polydimethylsiloxane, polyether soft segment and hard segment copolymer were used to identify and assign various ESCA peaks. The air facing surface of Avcothane which is the blood contacting surface is found to be covered mostly with polydimethylsiloxane polymer, with a small amount of polyether soft segment mixed with silicone. Therefore, the hard segment of the polyurethanes is hidden beneath the blood contact surface in Avcothane. In Biomer films, the air facing surface contains a greater concentration of polyether soft segment than the substrate surface. These results are consistent with our previous results obtained by Fourier transform IR internal reflection and Auger electron spectroscopy.

Carbon↗

PubMed1979

Evaluation of sunlight stability of polyurethane elastomers for maxillofacial use. II.

The effect of selected UV stabilizers on the stability of mechanical properties of a polyurethane material, Calthane ND2300, was evaluated. The addition of UV stabilizers prolonged the service life of the systems studied but did not achieve completely satisfactory results. The tensile strength and modulus of elasticity decreased after extended exposure to UV. The rate of decrease, however, was much less for the specimens with UV stabilizers. The polyurethane system that contains a mixture of a UV stabilizer and an antioxidant is considered to be the best of the groups tested, in terms of the percentage of retention of tensile strength and modulus of elasticity. It was also found that elongation at break was increased when the duration of UV aging was increased. This phenomenon occurred in all the systems, with or without UV stabilizers, and can be understood in terms of the concepts of the fragmentation of macromolecules that resulted from UV aging. The physical appearance in conjunction with mechanical property tests are needed to ensure the successful performance of any UV stabilizer.

Chemical Phenomena↗

PubMed1988

Albumin adsorption on alkyl chain derivatized polyurethanes: I. The effect of C-18 alkylation.

The initial adsorption rate of delipidized Human Serum Albumin (HSA) is increased by addition of C-18 alkyl chains to a polyurethane. The presence of alkyl chains does not appear to influence the total amount of HSA adsorbed after one hour exposure to a 5.0 mg/mL HSA solution. Neither does the desorption following one hour of adsorption appear to be influenced by the presence of alkyl chains. A study of the effects of solution concentration and temperature showed that the initial adsorption rates on both polymers are proportional to the protein concentration raised to the 0.36 power, and that alkylation of the polymer increases the activation energy of the initial adsorption rate above the 14 kJ/mol observed for the underivatized polyurethane. A new technique is presented to quantify the mass of adsorbed protein using Fourier transform infrared spectroscopy and attenuated total reflection optics. This technique uses the absorbance of bulk protein as an internal calibration reference, and appears to be as accurate and perhaps more precise than radiolabeling techniques.

Adsorption↗

PubMed1989

Properties and biological interactions of polyurethane anionomers: effect of sulfonate incorporation.

In order to investigate the factors affecting the interaction of polyurethanes and blood, a series of poly(tetramethylene oxide)-based polyurethane block copolymers was synthesized with systematically varying levels of ion incorporation in the hard segment block. A bimolecular nucleophilic substitution reaction was used to replace up to 20% of the urethane hydrogens with propyl sulfonate groups. Bulk and surface characterization was performed, and a canine ex vivo arteriovenous shunt was used to monitor initial platelet and fibrinogen deposition on these surfaces. The microphase separation and bulk physical properties were found to vary with ionic content. Surface analysis using both in vacuo (ESCA) and water-equilibrated (contact angle) methods indicated that these polymers, and especially the highly sulfonated materials, could rearrange to minimize their interfacial tension, depending on the contacting environment. Platelet deposition onto these materials decreased as the level of sulfonation increased, with the highly sulfonated polymer showing substantially less platelet spreading and activation than previously seen in the same experiment with other polymers.

Anions↗

PubMed1990

Series shunt evaluation of polyurethane vascular graft materials in chronically AV-shunted canines.

Well characterized, laboratory-synthesized polymeric materials which have been extensively tested for biocompatibility via initial platelet and protein deposition in an acute ex vivo canine model were placed as interpositional series shunts in canines with chronically implanted iliac arteriovenous shunts ex vivo. Platelet deposition was measured on a base polyurethane block copolymer, a sulfonated ionic derivative, an alkyl grafted (C18) derivative, Biomer, polyethylene, and polydimethylsiloxane for 24 h using radiolabeled platelets. Platelet survival and in vitro aggregation were determined to investigate the effects of the shunting procedure on experimental animals. The viability of adopting a chronic arteriovenous (iliac) shunted canine model for use with series shunts to evaluate polyurethanes having applications as materials in vascular graft construction was investigated and the results compared with acute model data.

Animals↗

PubMed1991

Effect of soft segment chemistry on the biostability of segmented polyurethanes. I. In vitro oxidation.

A series of segmented polyurethanes (SPUs) containing various polyol soft segments was prepared and their resistance to oxidative degradation was investigated after aging in AgNO3 solution. The SPU with the polyether soft segment showed a large reduction in mechanical strength after exposure to the oxidative environment. Surface cracking was often observed for these specimens. XPS measurements revealed that scission of the ether linkage occurs upon oxidation. The oxidative resistance of SPUs containing aliphatic hydrocarbon soft segments was significantly improved over the poly(tetramethylene oxide) (PTMO) based polyurethane.

Calorimetry, Differential Scanning↗

PubMed1992

Polyurethanes bearing pendant amino acids: fibrinogen adsorption and coagulant properties.

Segmented polyurethanes based on 4,4'-diphenylmethane diisocyanate and polypropylene oxide and chain extended with a sulfonated diamine were derivatized by reaction of sulfonate groups in the polymer with amino acids. The chemical composition of the derivatized polymers was determined by elemental analysis. Tensile stress-strain measurements indicated a slight increase in modulus and elongation with incorporation of amino acids. Water uptake at room temperature showed little change following derivatization, but at 70 degrees C increased significantly. Water contact angles were not influenced by the presence of amino acids, but electron spectroscopy for chemical analysis data showed an increase in hard segment content in the near-surface layers so that bulk and surface compositions were more nearly the same in the amino-acid-containing materials. Fibrinogen adsorption from plasma, shown previously to be high on the sulfonated polyurethanes, was reduced by derivatization, due probably to the decrease in free sulfonate content. Thrombin times of plasma in contact with these materials were essentially the same for the derivatized and underivatized materials.

Adsorption↗

PubMed1992

Porous polyurethane vascular prostheses with variable compliances.

A new technique for the preparation of porous vascular prostheses was investigated. Polyurethane solution (5 to 15 wt%) was injected into a mold. After freezing at low temperature (0 degrees C-196 degrees C), solvents were dissolved out with water at 0 degrees C to form porous tubes. The average pore size (several microns to 70 microns), pore occupation (10% to 51%), and compliance (3% to 35%) were easily changed by changing polyurethane concentration, freezing temperature, and freezing methods. Compliances could be decreased gradually by heat treatment. This technique can give a proper pore size (30-60 microns) for tissue ingrowth, and a suitable compliance for matching with arteries and veins. This method might give a desired compliant graft for artificial implantation with the presently valid medical polymers.

Blood Vessel Prosthesis↗

PubMed1993

Enzyme-biomaterial interactions: effect of biosystems on degradation of polyurethanes.

Enzyme-induced liberation of hard-segment-containing components from polyurethanes was evaluated using two 14C-labeled polyurethanes. A polyester urea-urethane and polyether urea-urethane were synthesized from toluene-2,4-diisocyanate (TDI)/polycaprolactone diol (PCL) or TDI/polyethylene glycol (PEO) with 14C-labeled ethylene diamine. Both materials were characterized using electron spectroscopy for chemical analysis (ESCA), differential scanning calorimetry (DSC), size exclusion chromatography, and material chemistry by Fourier transform infrared (FTIR) spectroscopy. Biodegradation assays were carried out using cholesterol esterase (CE), collagenase (CO), cathepsin B (CB), and xanthine oxidase (XO) at the pH optimum conditions for each enzyme at 37 degrees C. Biodegradation was analyzed by monitoring the release of radiolabel, by weight change, and by surface analysis using scanning electron microscopy. The polyester urea-urethane was shown to be susceptible to enzymatic degradation above the effect of the buffer control solution by the CE but not by the other enzyme systems as monitored by radiolabel released. In the initial period of incubation, the rate of degradation was increased for all systems, including buffer controls; however, the rates dropped off rapidly by day 28. The change in weight data for the polyester urea-urethane and polyether urea-urethane showed no enzyme-dependent biodegradation above the buffer controls. However, in sodium acetate buffer at pH = 5, the polymers showed a significant weight loss relative to other buffers. In conclusion, this study showed that the biological component responsible for the onset of the biodegradation process is more likely the result of a multitude of biologically mediated compounds acting synergistically, with the process being enhanced by physical parameters such as material dissolution. In addition characterization of surface and bulk chemistry as well as material structure evaluation have been shown to be essential to interpret degradation data.

Biocompatible Materials↗

PubMed1993

Degradation of medical-grade polyurethane elastomers: the effect of hydrogen peroxide in vitro.

Treatment of Pellethane 2363-80A--a medical-grade poly(tetramethylene oxide)-based polyurethane elastomer--with 25% (w/w) hydrogen peroxide at 100 degrees C for times ranging from 24 h to 336 h led to significant decreases in ultimate tensile properties and decreases in molecular weight, both at the surface and in the bulk. IR spectral changes were similar to those observed after degradation in vivo. Differential scanning calorimetry showed that hydrogen-peroxide-induced degradation was associated with greater order in the hard domain and greater mobility in the soft domain. Studies conducted with low-molecular-weight model compounds for the hard and soft segments confirmed that methylene groups adjacent to oxygen were susceptible toward oxidation. The extent of degradation of a series of commercial polyurethanes on treatment with hydrogen peroxide (25%, 24 h, 100 degrees C) correlated well with their reported susceptibility to environmental stress cracking in vivo.

Hydrogen Peroxide↗

PubMed1993

Compliance effects on small diameter polyurethane graft patency.

Microporous compliance matched and noncompliant grafts were compared in a dog carotid artery interposition model. We fabricated 4 mm diameter sponge type polyurethane (Biomer) tubes 5 cm in length with a 0.5 mm wall thickness. The luminal surface was covered with a 50 microns coating of cross-linked gelatin. Compliance was measured in vitro and in vivo by volume and vessel diameter changes. Over a mean arterial pressure range of 55-155 mm Hg, the diameter changes of grafts and stump arteries were measured in situ using an ultrasonic Hokanson device. Compliance matched grafts were found to have the same in vitro compliance values as the natural canine carotid at a mean arterial pressure of 100 mm Hg. Compliance matched and noncompliant grafts had values of 10.3 +/- 1.3 and 0.9 +/- 0.1 x 10(-2) mm Hg, respectively. End to end arterial anastomoses were constructed between the graft and the host arteries. The use of synthetic grafts with matched compliance to the adjacent natural vessels has been advocated as the ideal solution to circumvent the problems of graft failure. These studies indicate that compliance values for compliance matched grafts decreased immediately after implantation (from 10.3 to 6.5 x 10(-2) %/mm Hg) and within 6 weeks decreased to 3.6 x 10(-2) %/mm Hg. The compliance values for noncompliant grafts remained constant throughout the test period. At autopsy all grafts showed a tightly adhered tissue capsule. The thickness of the anastomotic hyperplasia at the distal sites of compliance matched grafts was significantly different (P < .05) than that of the adjacent artery. The patency for compliant and noncompliant grafts was 64% and 50%, respectively. Evidence for polyurethane graft degradation was obtained by Fourier transform infrared spectroscopy and gel permeation chromatography analysis of patent explants. Compliance mismatch alone does not contribute to graft failure, however, material degradation, suture technique and/or capsule formation can play a contributory role although these were not tested directly.

Animals↗

PubMed1995

Glass wool-H2O2/CoCl2 test system for in vitro evaluation of biodegradative stress cracking in polyurethane elastomers.

Environmental stress cracking (ESC) in polyetherurethanes has been demonstrated in animal models. However, duplication of this phenomenon in vitro has been a challenge. The glass wool-H2O2/CoCl2 test system was designed to provide oxidation components found in vivo, i.e., hydroxyl radical (HO.), molecular oxygen (O2), and superoxide (O2-.) required for auto-oxidation of polyetherurethanes. The in vitro test is not only reliable in duplicating the characteristics of in vivo stress cracking in polyetherurethanes at 37 degrees C, but also accelerates ESC as much as seven times. The test results on several types of polyurethanes showed that Tecothane 80A was as vulnerable to biodegradative stress cracking in vitro as Pellethane 2363-80A, while the new generation of polyurethanes, Corethane, demonstrated great resistance against stress cracking.

Biodegradation, Environmental↗

PubMed2003

A biodegradable polyurethane-ascorbic acid scaffold for bone tissue engineering.

A novel, nontoxic, biodegradable, sponge-like polyurethane scaffold was synthesized from lysine-di-isocyanate (LDI) and glycerol. Ascorbic acid (AA) was copolymerized with LDI-glycerol. Our hypothesis was that the AA-containing polymer foam would enhance the biological activity of the osteoblastic precursor cell (OPCs). The LDI-glycerol-AA matrix degraded in aqueous solution to the nontoxic products of lysine, glycerol, and AA. The degradation products did not significantly affect the solution pH. The physical properties of the polymer network supported the cell growth in vitro. Mouse OPCs attached to the polymer matrix and remained viable. OPCs produced multilayered confluent cultures, a characteristic typical of bone cells. Furthermore, AA release stimulated cell proliferation, type I collagen, and alkaline phosphatase synthesis. Cells grown on the LDI-glycerol-AA matrix also showed an enhancement of mRNA expression for pro-alpha1 (I) collagen and transforming growth factor-alpha1 after 1 week. Data were tested for significance with an analysis of variance model and multiple comparison test (Fisher's Protected Least Significant Difference) at p < or = 0.05. The observations suggest that AA-containing polyurethane may be useful in bone tissue engineering applications.

Alkaline Phosphatase↗

PubMed2003

Vascularization and tissue infiltration of a biodegradable polyurethane matrix.

Urethanes are frequently used in biomedical applications because of their excellent biocompatibility. However, their use has been limited to bioresistant polyurethanes. The aim of this study was to develop a nontoxic biodegradable polyurethane and to test its potential for tissue compatibility. A matrix was synthesized with pentane diisocyanate (PDI) as a hard segment and sucrose as a hydroxyl group donor to obtain a microtextured spongy urethane matrix. The matrix was biodegradable in an aqueous solution at 37 degrees C in vitro as well as in vivo. The polymer was mechanically stable at body temperatures and exhibited a glass transition temperature (Tg) of 67 degrees C. The porosity of the polymer network was between 10 and 2000 microm, with the majority of pores between 100 and 300 microm in diameter. This porosity was found to be adequate to support the adherence and proliferation of bone-marrow stromal cells (BMSC) and chondrocytes in vitro. The degradation products of the polymer were nontoxic to cells in vitro. Subdermal implants of the PDI-sucrose matrix did not exhibit toxicity in vivo and did not induce an acute inflammatory response in the host. However, some foreign-body giant cells did accumulate around the polymer and in its pores, suggesting its degradation is facilitated by hydrolysis as well as by giant cells. More important, subdermal implants of the polymer allowed marked infiltration of vascular and connective tissue, suggesting the free flow of fluids and nutrients in the implants. Because of the flexibility of the mechanical strength that can be obtained in urethanes and because of the ease with which a porous microtexture can be achieved, this matrix may be useful in many tissue-engineering applications.

Animals↗

PubMed2005

Improving the blood compatibility of polyurethane using carbon nanotubes as fillers and its implications to cardiovascular surgery.

Blood compatibility has been an occlusion for biomaterials used in the cardiovascular system. In this work, a multiwalled carbon nanotubes-polyurethane composite (MWNT-PU) was prepared through a controlled co-precipitation. The surface chemical composition of treated carbon nanotubes was analyzed with XPS and the thermal behaviors of composite were characterized by DSC. The platelet adhesion and activation caused by the composite were evaluated by using SEM and flow cytometric analysis, respectively, and the disruption of red blood cells was analyzed through measuring the absorbance of free hemoglobin. The experimental results demonstrated that: (1) Multiwalled carbon nanotubes (MWNTs) with oxygen-containing functional groups could be well dispersed in polyurethane matrix through a controlled coprecipitation; (2) the composite surface displayed a significantly improved anticoagulant function, which can be indicative of the promising potentials of carbon nanotube-based materials in the implants and medical devices applied in blood-contacting environments.

Biocompatible Materials↗

PubMed2006

In vivo biostability of polysiloxane polyether polyurethanes: resistance to metal ion oxidation.

Polyether polyurethanes are subject to oxidation catalyzed by and through direct (redox) reaction with transition metal ions (cobalt), released by corrosion of metallic parts in an implanted device. Replacing part of the polyether with polysiloxane appears to reduce susceptibility to metal ion oxidation (MIO). In vitro studies indicated that polyurethanes containing 20-35% polysiloxane (PS-20 and PS-35) are about optimum. We implanted tubing samples containing cobalt mandrels in the subcutis of rabbits for periods up to 2 years. After 2 years, only traces of microscopic cracks were seen on half the PS-35 samples, PS-20 significantly delayed MIO, while the polysiloxane-free control was very severely degraded. Infrared spectroscopy established that polyether soft segment oxidation was occurring in PS-20. We could not directly evaluate oxidation in PS-35 because siloxane bands mask the aliphatic ether. Indirect FTIR evidence suggests that there is very slight polyether oxidation that develops early, and then seems to stabilize. The molecular weight of degraded PS-20 decreased. That of microcracked PS-35 decreased negligibly while that of undamaged PS-35 increased slightly after 2-year in vivo. The polysiloxane-free control was profoundly degraded. PS-20 has much improved MIO resistance, while that for PS-35 is highly MIO resistant compared with its polysiloxane-free control.

Animals↗

PubMed2006

In vivo biostability of polysiloxane polyether polyurethanes: resistance to biologic oxidation and stress cracking.

Polyether polyurethanes are extremely interesting for use in implantable devices. They are, however, susceptible to autoxidative degradation and stress cracking. One approach to improving biostability is to replace some of the polyether with polysiloxane. Shore 80A polyether polyurethanes with 20% (PS-20) and 35% (PS-35) polysiloxane were strained to 400% elongation and implanted in rabbits. Twelve weeks implant showed that both were significantly more biostable than their polysiloxane-free controls. After 18 months implant, PS-20 developed some localized tensile fractures. PS-35 showed no sign of visual damage. Infrared surface analysis does not allow direct evaluation of autoxidation because the Si--O--Si stretch peaks mask the polyether bands. Secondary indicators suggest possible very slight autoxidation of both PS-20 and PS-35 surfaces, but not enough to develop cracks. The polysiloxane-free controls did show substantial infrared evidence of autoxidation. Molecular weights of long-term PS-20 and PS-35 explants were negligibly lower. In comparison, the polysiloxane-free control suffered 35% molecular weight loss. Positive and negative controls performed as expected. PS-20 is recommended for devices that do not sustain high fixed loads. PS-35 is dramatically more biostable than its unmodified polyether analogues and is recommended for use in chronically implantable devices.

Animals↗

PubMed2006

Regeneration of bicortical defects in the iliac crest of estrogen-deficient sheep, using new biodegradable polyurethane bone graft substitutes.

Porous scaffolds for cancellous bone graft substitutes were prepared from new experimental biodegradable aliphatic polyurethane elastomers with varying hydrophilicity. The ratios of the hydrophilic-to-hydrophobic content in the polymers were 30-70, 50-50, and 70-30%, respectively. The hydrophilic component consisted of poly(ethylene oxide) diol and the hydrophobic component of poly(epsilon-caprolactone) diol. To promote the materials' biological performance, the calcium complexing moiety, the polysaccharide, and vitamin D(3) were incorporated into the polymer chain upon synthesis. The scaffolds had an interconnected porous structure with an average pore size in the range of 300-2,000 microm and pore-to-volume ratios of (85 +/- 5)%. The bone substitutes were implanted (press-fit) in biocortical 10 x 10 mm(2) defects created in the tuber coxae of 21 skeletally mature Warhill ewes, which were ovariectomized 12 months prior to implantation. At the time of euthanasia at 18 and 25 months, all the defects in the ilium implanted with polyurethane bone substitutes had healed with new bone. The extent of bone healing depended on the chemical composition of the polymer from which the implant was made, although for the same material there were animal-related differences in healing. The structure of the newly formed cancellous bone was radiographically and histologically similar to the native bone. The implants from polymers with the incorporated calcium-complexing additive were the most effective promoters of bone healing, followed by those with vitamin D(3) and polysaccharide-containing polymer. There was no bone healing in the control defects.

Absorbable Implants↗