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At least 37 records · Page 2Linked to original sources

PubMed1997

In vivo biocompatibility and biostability of modified polyurethanes.

Modified segmented polyurethanes were examined for biostability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS endcapped polyether polyurethane (SPU-S), and two polycarbonate polyurethanes (SPU-PCU and SPU-C) were investigated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress-strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively describe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC densities and cell coverage on SPU-S were attributed to the hydrophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attributed to hydrolysis of the carbonate linkage.

Animals↗

PubMed2001

Bisphosphonate derivatized polyurethanes resist calcification.

Calcification of polyurethane cardiovascular implants is an important disease process that has the potential to compromise the long-term function of devices such as polymer heart valves and ventricular assist systems. In this study we report the successful formulation and characterization of bisphosphonate-derivatized polyurethanes, hypothesized to resist implant calcification based on the pharmacologic activity of the immobilized bisphosphonate. Fully polymerized polyurethanes (a polyurea-polyurethane and a polycarbonate polyurethane) were modified (post-polymerization) with bromoalkylation of the hard segments followed by attachment of a bisphosphonate group at the bromine site. These bisphosphonate-polyurethanes resisted calcification in rat 60 day subdermal implants compared to nonmodified control polyurethane implants, that calcify. Bisphosphonates-modified polyurethanes were also studied in circulatory implants using a pulmonary valve cusp replacement model in sheep. Polyurethane cusps modified with bisphosphonate did not calcify in 90 day implants. compared to control polyurethane cusps implants, that demonstrated nodular surface oriented calcific deposits. It is concluded that bisphosphonate modified polyurethanes resist calcification both in subdermal implants and in the circulation. This novel biomaterial approach offers great promise for long-term blood stream implantation with calcification resistance.

Animals↗

PubMed2004

Localized gene delivery using antibody tethered adenovirus from polyurethane heart valve cusps and intra-aortic implants.

The present study investigated a novel approach for gene therapy of heart valve disease and vascular disorders. We formulated and characterized implantable polyurethane films that could also function as gene delivery systems through the surface attachment of replication defective adenoviruses using an anti-adenovirus antibody tethering mechanism. Our hypothesis was that we could achieve site-specific gene delivery to cells interacting with these polyurethane implants, and thereby demonstrate the potential for intravascular devices that could also function as gene delivery platforms for therapeutic vectors. Previous research by our group has demonstrated that polyurethane elastomers can be derivatized post-polymerization through a series of chemical reactions activating the hard segment amide groups with alkyl bromine residues, which can enable a wide variety of subsequent chemical modifications. Furthermore, prior research by our group investigating gene delivery intravascular stents has shown that collagen-coated balloon expandable stents can be configured with anti-adenovirus antibodies via thiol-based chemistry, and can then tether adenoviral vectors at doses that lead to high levels of localized arterial neointima expression, but with virtually no distal spread of vector. Thus, we sought to create two-device configurations for our investigations building on this previous research. (1) Polyurethane films coated with Type I collagen were thiol activated to permit covalent attachment of anti-adenovirus antibodies to enable gene delivery via vector tethering. (2) We also formulated polyurethane films with direct covalent attachment of anti-adenovirus antibodies to polyurethane hard segments derivatized with alkyl-thiol groups, thereby also enabling tethering of replication-defective adenoviruses. Both formulations demonstrated highly localized and efficient transduction in cell culture studies with rat arterial smooth muscle cells. In vivo experiments with collagen-coated polyurethane films investigated an abdominal aorta implant model in pigs using a button configuration that simulated the blood contacting environment of a vascular graft. One week explants of the collagen-coated polyurethane films demonstrated 14.3+/-2.5% of neointimal cells on the surface of the implant transduced with green fluorescent protein - adenovirus (AdGFP) vector loadings of 1 x 10(8) PFU. PCR studies demonstrated no detectable vector DNA in blood or distal organs. Similarly, polyurethane films with direct attachment of antivector antibodies to the surface were used in sheep pulmonary valve leaflet replacement studies, simulating the blood contacting environment of a prosthetic heart valve cusp. Polyurethane films with antibody tethered AdGFP vector (10(8) PFU) demonstrated 25.1+/-5.7% of attached cells transduced in these 1 week studies, with no detectable vector DNA in blood or distal organs. In vivo GFP expression was confirmed with immunohistochemistry. It is concluded that site-specific intravascular delivery of adenoviral vectors for gene therapy can be achieved with polyurethane implants utilizing the antivector antibody tethering mechanism.

Adenoviridae↗

PubMed2005

Plasma treatment of polyurethane coating for improving endothelial cell growth and adhesion.

The advantage of helium plasma treatment in enhancing endothelial cell growth and adhesion on polyurethane film coated on glass substrate is demonstrated with experimental data. Human coronary artery endothelial cell (HCAE) growth and attachment was studied on (1) bare glass substrate, used as control, (2) coated glass, with and without helium plasma treatment and (3) collagen-treated polyurethane-coated glass substrates. The untreated polyurethane film surface was rough (RMS = 690 nm) and highly hydrophobic (contact angle theta = 90 degrees). Cell growth on the untreated polyurethane surface was poor (cell concentration approximately 3750/cm2) compared to glass surface (cell concentration approximately 17 665/cm2). The atmospheric helium plasma treatment of the polyurethane film resulted in oxidation of the surface, a slight increase in roughness (RMS = 735 nm) and a significant drop in hydrophobicity (contact angle theta = 79 degrees). The critical surface tension (gamma c) of polyurethane film was also increased by 2 dynes/cm due to helium plasma treatment. These changes resulted in enhanced HCAE cell growth in polyurethane film (cell concentration approximately 16 230/cm2) compared to the untreated polyurethane film. The cell growth was also comparable to cell growth on a glass surface (17 665/cm2) and the collagen-treated polyurethane film surfaces (cell concentration approximately 21 645/cm2), respectively. Moreover, the strength of cell attachment on a plasma-treated surface (cell retention R = 89%) under laminar flow was significantly higher than that on a glass surface (R = 71%). While the collagen-treated polyurethane surface had the highest number of HCAE cells, the cell adhesion was found to be poor (R = 42%) compared to that of a plasma-treated surface. Thus, the overall performance of the plasma-treated polyurethane film surface on endothelial cell growth was better than other substrates studied here.

Cell Adhesion↗

PubMed2001

A new design for polyurethane heart valves.

BACKGROUND AND AIM OF THE STUDY: The synthetic flexible tri-leaflet heart valve offers considerable potential for improvement in both hydrodynamic and biomechanical performance of replacement heart valves. To date, success with the synthetic leaflet heart valve has been limited, partly due to limitations in the biostability of the polyurethanes used. With the synthesis of new biostable polyurethanes, the integration of advancing technology, and better knowledge of the functional and biomechanical design requirements necessary to increase the long-term durability of the polyurethane heart valve, novel clinical solutions are now in sight. METHODS: This study describes the design characteristics, hydrodynamic and biomechanical performance of a new design of polyurethane heart valve. The function and durability characteristics of this novel design of heart valve, manufactured using a proven durable non-biostable polyurethane, was compared with that of a single AorTech porcine bioprosthetic heart valve and a single tilting disc mechanical heart valve, the Björk-Shiley Monostrut valve (BSM), of similar size. RESULTS: For equivalent sizes of valve, the new polyurethane heart valve design had significantly lower pressure gradients compared with the porcine valve at all flow rates and to the BSM valve at the higher flow rates. The effective orifice area of the polyurethane valve was greater than the other two valves studied; regurgitation and total energy loss were less. The new polyurethane valve design reached over 360 million cycles in an accelerated durability tester, without failure. CONCLUSION: This new design of polyurethane heart valve showed improved hydrodynamic function in comparison with either the porcine bioprosthetic or the BSM mechanical heart valve. The pulsatile flow results showed a lower total energy loss associated with this valve, indicating improved potential patient benefit. The durability of this new design of polyurethane heart valve was demonstrated when manufactured using a medical-grade polyurethane.

Biomechanical Phenomena↗

PubMed1993

Biodegradation of the polyurethane foam covering of breast implants.

Although it is generally accepted that polyurethane-covered breast implants have decreased the incidence of clinical capsular contracture, there remain many unanswered questions regarding the physical and chemical degradation of the polyurethane foam covering itself. We have systematically studied the fibrous capsule and polyurethane foam recovered from human breast "explants" in an effort to characterize more precisely the biodegradation of polyurethane foam in the human body. Seventy-five freshly retrieved polyurethane-covered implants and surrounding capsule from 47 patients have been analyzed. Capsular tissue from several sampling sites around the surface of the implants was digested in a collagenase solution until foam was recovered or all tissue was digested. Additional samples were fixed in 10% formalin. Scanning electron microscopy was used to look for structural changes in the recovered intact foam and to determine the foam strut widths. Fourier transform IR spectroscopy and x-ray photoelectron spectroscopy were used to analyze the chemical composition of the polyurethane. The formalin-preserved capsule samples were examined histologically for further evidence of foam degradation. Of the 75 prostheses analyzed, 36 (48 percent) were removed because of capsular contracture and 10 (13 percent) because of infection or exposure of the prosthesis. The remaining 29 (39 percent) implants were removed for various other reasons. Visibly intact foam was recovered from 36 (48 percent) prostheses after enzymatic digestion of capsule tissue. There was a progressive decline in the ability to recover intact foam as the total implantation time increased. Scanning electron microscopy revealed fractures and fissures in the foam structure and thinning of the polyurethane struts. The mean strut width of control, unimplanted foam was 49 +/- 1.5 microns (+/- SEM). Retrieved foam from implants which developed capsular contracture and the infected implants had strut widths of 30 +/- 3.1 and 32 +/- 3.1 microns, respectively. In implants removed for other reasons, the polyurethane foam strut width was 41.2 +/- 2.3 microns. Despite an inability to recover visibly intact foam from 39 specimens, standard light microscopy of 37 of these same specimens showed residual polyurethane still present in the capsule. Various degrees of scalloping and fracturing of the foam were seen in the histologic sections. There is convincing evidence by scanning electron microscopy and histology that polyurethane is degrading. It was not possible to quantitate accurately the rate of degradation, but factors such as capsular contracture, infection, and time appear to have a role in the biodegradation of polyurethane in the human body. These relationships require further study.

Biodegradation, Environmental↗

PubMed2006

[Study of FTIR spectra and thermal analysis of polyurethane].

The thermal behavior of polyester-polyurethane and polyether-polyurethane in air atmosphere was investigated by using FTIR analysis in the temperature range from 20 to 400 degrees C. The thermal degradation behaviors of polyester-polyurethane and polyether-polyurethane in different atmospheres were investigated by using thermogravimetry analysis (TG) in the temperature range from 20 to 700 degrees C. The FTIR results together with the TG investigations showed that polyester-polyurethane has two degradation steps in air, but polyether-polyurethane has only one degradation step. The thermal analysis results also showed that the onset degradation temperature of polyether-polyurethane is lower than that of polyester-polyurethane, suggesting that the thermal stability of polyester-polyurethane is higher than polyether-polyurethane, and the onset degradation temperature of polyurethane in air is lower than that in nitrogen, suggesting that the presence of oxygen affects significantly the break of the polymeric chains.

English Abstract↗

PubMed1994

Synthesis, surface, and cell-adhesion properties of polyurethanes containing covalently grafted RGD-peptides.

In an attempt to improve endothelial cell adhesion and growth on a polyurethane copolymer, cell adhesive RGD-containing peptides were grafted to the polymer backbone. Two peptide grafting reaction schemes, including one-step and two-step approaches, were developed. FTIR and amino acid analysis confirmed that coupling of the peptide to the polyurethane backbone was achieved by both the one-step and two-step methods. However, the two-step approach showed a higher peptide coupling efficiency and resulted in better control of the orientation of the grafted peptide. The two-step reaction scheme was used to prepare Gly-Arg-Gly-Asp-Ser-Tyr (GRGDSY), Gly-Arg-Gly-Asp-Val-Tyr (GRGDVY), and Gly-Arg-Gly-Glu-Ser-Tyr (GRGESY) peptide-grafted polyurethanes with two different peptide densities (100 and 250 mumol/g polymer). Dynamic contact angle measurements indicated that the surfaces of the peptide-grafted polyurethanes were more hydrophilic than the starting and carboxylated versions of the precursor polyurethane. In addition, the surface hydrophilicity of the peptide-grafted polymers increased with increasing bulk peptide density. Electron spectroscopy for chemical analysis suggested that the grafted peptide was present at the polymer-air interface, in vacuo, for the peptide-grafted polyurethanes. The surface peptide density appeared to correlate with the incorporated peptide density in the bulk. In vitro endothelial cell adhesion experiments showed that, without the presence of serum in culture medium, the GRGDSY- and GRGDVY-grafted polyurethanes dramatically enhanced cell attachment and spreading compared with the starting, carboxylated, and GRGESY-grafted polymers. Increasing the peptide density from 100 to 250 mumol/g polymer for the GRGDSY- and GRGDVY-grafted polyurethanes resulted in an increase in cell attachment. With approximately the same peptide density (100 or 250 mumol/g polymer), the GRGDVY-grafted polymers supported more adherent cells than did the GRGDSY-grafted polymers. Similar trends were observed in the in vitro endothelial cell growth studies using culture medium containing serum and endothelial cell growth supplement. The GRGDSY- and GRGDVY-grafted polyurethanes promoted more cell growth than did the starting polyurethane. However, the presence of adhesive serum proteins and growth factor diminished the differences between the cell-adhesive peptide grafted polymers and the GRGESY-grafted polymers.

Amino Acid Sequence↗

PubMed1995

Contact activation during incubation of five different polyurethanes or glass in plasma.

During blood-material interaction, the enzymes factor XII fragment (factor XIIf) and kallikrein are generated (contact activation). In this study, the enzymatic activities of factor XIIf and kallikrein were examined with an assay based on the conversion of tripeptide-p-nitroanilide substrate. With the use of aprotinin to inhibit kallikrein, the proteolytic activities of factor XIIf and kallikrein could be separately determined. In this in vitro study, two commercially available polyurethanes, Pellethane and Biomer; three custom synthesized polyurethanes; a biomerlike 2000 MW polytetramethyleneoxide containing polyurethane (PU-2000); an octadecyl extended (ODCE) biomer-like 2000 MW polytetramethyleneoxide containing polyurethane (PU-2000-ODCE); a hard-segment polyurethane (HS-PU); and glass (reference material) were incubated in 25% diluted plasma. In both series of experiments, glass caused the highest amidolytic activities by factor XIIf and kallikrein compared with any of the polyurethanes. In contrast, within the polyurethane group of materials, lower amidolytic activities by factor XIIf and kallikrein were measured on the custom-made polyurethanes than on the commercially available polyurethanes, although the differences among the polyurethanes were small. In addition, the influence of different ratios of material surface to the plasma incubation volume was studied. An increased ratio of surface area over plasma volume resulted in reduced contact activation, suggesting that plasma components are the limiting factor.

Analysis of Variance↗

PubMed2003

Prevention of polyurethane valve cusp calcification with covalently attached bisphosphonate diethylamino moieties.

OBJECTIVE: Calcification of polyurethane prosthetic valve leaflets causes a major functional impairment. Previously we showed that polyurethane heart valves modified with covalently linked bisphosphonate groups were resistant to calcification in vivo. However, we also found that the highly polar anionic bisphosphonate groups on the polyurethane surface attracted sodium counter ion adsorption, and thereby increased the elastomer's water absorption to 20% of total weight. In this study we address the increased water absorption by investigating the hypothesis that covalently attaching cationic diethylamino groups to the bisphosphonate-modified polyurethane will reduce water absorption. Thus we evaluated the mechanical and in vivo anticalcification properties of heart-valve leaflets composed of this modified polymer. METHODS: Diethylamino and bisphosphonate groups (DBP) were appended to the polyurethane Biospan's hard segment using previously published bromoalkylation methodology. Water absorption and biaxial mechanical and uniaxial failure testing were used to determine the mechanical properties of the DBP-modified polymer. Rat subdermal implants (60 days) and extended (150 days) single pulmonary leaflet replacements in juvenile sheep provided in vivo assessments of the bisphosphonate-modified polyurethane. RESULTS: The water absorption properties of the DBP-modified polymers and unmodified polyurethanes were 1.86 and 2.3 %, respectively. Biaxial mechanical tests showed the DBP-modified polymer was more compliant than the unmodified control material, but all polymeric material had similar uniaxial failure properties. In both rat subdermal and sheep circulatory implants, the DBP-modified polyurethane resisted calcification, as assessed by scanning electron microscopy, with complete calcification inhibition in prosthetic sheep valve leaflet replacements. CONCLUSION: DBP polyurethane possesses physical (water absorption) and biomechanical properties comparable to unmodified polyurethane and can resist intrinsic heart-valve leaflet calcification in blood-stream implants.

Animals↗

PubMed1996

The male polyurethane condom: a review of current knowledge.

Condoms are one of the oldest form of contraceptive and the best recognized form of protection against sexually transmitted diseases. Their use, however, is limited by both behavioral factors and device-related factors, including complaints about decreased sensitivity and sexual enjoyment. To address these limitations, a male condom made of polyurethane was developed. Polyurethane is a strong impermeable material with good heat transfer characteristics that is less susceptible to deterioration during storage than latex. Because little information is available comparing polyurethane and latex condoms in terms of consumer preferences as well as breakage and slippage, we reviewed four pre-marketing studies of polyurethane condoms, one of which included comparison to latex. No significant differences in slippage and breakage rates between latex and polyurethane condoms were reported in the study that included a latex comparator, and other studies of polyurethane condoms alone resulted in rates in the same range as published for latex condoms. Subjectively, consumers expressed significantly greater preference for the polyurethane condom over latex in regard to appearance, lack of smell, likelihood of slippage, comfort, sensitivity, natural look, natural feel, and overall. While additional testing is needed, these preliminary results suggest that the male polyurethane condom reviewed performed at least as well as latex condoms and is preferred by consumers. If preference translates to greater use, the male polyurethane condom may address important barriers that have been linked with inadequate condom use in the past. These results, however, may not be generalizable to other brands of polyurethane condom currently under development.

Condoms↗

PubMed2005

Synthesis of biocompatible segmented polyurethanes from aliphatic diisocyanates and diurea diol chain extenders.

Many polyurethane elastomers display excellent mechanical properties and adequate biocompatibility. However, many medical-grade polyurethanes are prepared from aromatic diisocyanates and can degrade in vivo to carcinogenic aromatic diamines, although the question of whether the concentrations of these harmful degradation products attain physiologically relevant levels is currently unresolved and strongly debated. It is therefore desirable to synthesize new medical-grade polyurethanes from less toxic aliphatic diisocyanates. In this paper, biocompatible segmented polyurethane elastomers were synthesized from aliphatic diisocyanates (1,4-diisocyanatobutane (BDI) and lysine methyl ester diisocyanate (LDI)), novel diurea diol chain extenders based on tyrosine and tyramine, and a model poly(ethylene glycol) (PEG) diol soft segment. The objectives were to design a hard segment similar in structure to that of MDI-based polyurethanes and also investigate the effects of systematic changes in structure on mechanical and biological properties. The non-branched, symmetric polyurethane prepared from BDI and a tyramine-based chain extender had the highest modulus at 37 degrees C. Introduction of symmetric short-chain branches (SCBs) incorporated in the tyrosine-based chain extender lowered the modulus by an order of magnitude. Polyurethanes prepared from LDI were soft polymers that had a still lower modulus due to the asymmetric SCBs that hindered hard segment packing. Polyurethanes prepared from tyramine and tyrosine chain extenders thermally degraded at temperatures ranging from 110 to 150 degrees C, which are lower than that reported previously for phenyl urethanes. All four polyurethanes supported the attachment, proliferation, and high viability of MG-63 human osteoblast-like cells in vitro. Therefore, the non-cytotoxic chemistry of these polyurethanes make them good candidates for further development as biomedical implants.

Biocompatible Materials↗

PubMed1999

Bacterial adhesion to functionalized polyurethanes.

The effect of fibrinogen and high molecular weight kininogen on bacterial adhesion to functionalized polyurethanes was studied. Glass slides were coated with different polyurethanes, including Pellethane, sulfonated Pellethane, phosphonated Pellethane, a zwitterionic phosphonated polyurethane, and quaternized amine polyurethanes. The polymer-coated glass squares were exposed to radiolabelled S. aureus. When comparing adhesion to bare polyurethanes, it was found that adhesion was lowest on the phosphonated Pellethane and the zwitterionic phosphonated polyurethane while highest on the methyl quaternized polyurethanes. Fibrinogen-mediated adhesion was studied by first exposing the polymers to increasing concentrations of canine fibrinogen before incubating them with S. aureus. All the polymers except the quaternized amine polyurethanes exhibited at least ten-fold increases in bacterial adhesion as the fibrinogen treatment concentration was increased from 0.0 to 10.0 microg ml(-1). The quaternized amine polyurethanes maintained their relatively high amount of bacterial adhesion regardless of the fibrinogen concentration. The effect of two-chain high molecular weight kininogen (TCHMWK) on fibrinogen-mediated bacterial adhesion was assessed by exposing the polymers to 1.0 microg ml(-1) fibrinogen followed by two different concentrations of TCHMWK. Decreases in bacterial adhesion were observed on all the polymers except the quaternized amine polyurethanes, which again retained their relatively high amount of bacterial adhesion.

Animals↗

PubMed1996

Small caliber vascular grafts. Part II: Polyurethanes revisited.

Polyurethanes are considered to be one of the most bio- and blood-compatible biomaterials known today. By intelligent utilization of principles governing the structure/property relationship of these polymers, one can generate systems which resemble, in principle, the physical-mechanical behavior of living tissue. Thus, it is not surprising that these materials played a major role in development of small caliber vascular grafts targeted for vascular access, peripheral and coronary artery bypass indications. Numerous technologies, often esoteric in nature, were and are utilized to generate porous, potentially multilayered conduits possessing some or many characteristics of natural blood vessels. Properties such as durability, elasticity, compliance, pulsatility, and propensity for healing became attainable via polyurethanes. Furthermore, additional surface and/or bulk modification via attachments of biologically active species such as anticoagulants, cell proliferation suppressants, anti-infective compounds or biorecognizable groups are possible due to reactive groups which are part of the polyurethane structure. These modifications are designed to control or mediate host acceptance and healing of the graft. Finally, a myriad of practical processing technologies are used to fabricate functional grafts. Among those, casting, electrostatic and wet spinning of fibers and monofilaments, extrusion, dip coating or spraying of mandrels with polymer/additive solutions are often coupled with chemical-potential-difference-driven coagulation and phase inversion leading to grafts feeling and often behaving like natural vessels. Historically, the first polyurethanes utilized were hydrolytically unstable polyester polyurethanes containing hydrolysis-prone polyester polyols as soft segments, followed by hydrolytically stable but oxidation sensitive polyether polyols based polyurethanes. Polyether-based polyurethanes and their clones containing silicone and other modifying polymeric intermediates represented significant progress. Many viable technologies were discovered and developed using polyether-based polyurethanes. Chronic in vivo instability observed on prolonged implantation became, however, a major roadblock. The path led finally to the use of hydrolytically and oxidatively stable polycarbonate polyols as the soft segment to generate biodurable materials with resistance to biodegradation adequate for vascular access or perhaps peripheral graft indications. This biodurability needs to be further increased in order to utilize the full potential of polyurethanes in development of patent small caliber graft. Modification of both the soft and hard segments needs to be considered in order to maximize biodurability of both basic building blocks of the polyurethane. This paper reviews the achievements, discusses trends, and offers the view of the future in this exciting area of material/device combination.

Anti-Infective Agents↗

PubMed1996

Calcification of polyurethanes implanted subdermally in rats is enhanced by calciphylaxis.

Calcification complicates the use of the polymer polyurethane in cardiovascular implants. To date only costly experimental circulatory animal models have been useful for investigating this disease process. In this paper we report that polyurethane calcification in rat subdermal implants is enhanced by overdosing with a vitamin-D analog. The calcification-prone state, known as calciphylaxis, was induced in 4-week old rats by oral administration of a vitamin-D analog, dihydrotachysterol. We studied two commercially available polyurethanes (Biomer and Mitrathane) and two proprietary polyurethanes (PEU-2000 and PEU-100). PEU-100 is unique because it is derivatized with ethanehydroxy-bisphosphonate (EHBP) for calcification resistance. Polyurethane calcium and phosphate levels and morphological changes due to calciphylaxis were compared with those of control rat subdermal explants in 60-day studies. Increased polyurethane mineralization was observed due to calciphylaxis with 60-day rat subdermal explants of Biomer, Mitrathane, and PEU-2000 (calcium levels, respectively, 4.13 +/- 0.56, 18.61 +/- 2.73, and 3.37 +/- 0.22 microgram/mg, mean +/- standard error) as compared to control explants (calcium levels, respectively, 1.22 +/- 0.1, 12.57 +/- 0.86, and 0.20 +/- 0.86 microgram/mg). The study also demonstrated that with 60-day implants calciphylaxis had no side effects on somatic growth and serum calcium levels. Explant surface morphology of these polyurethane explants examined by scanning electron microscopy, back scattering electron imaging coupled with energy dispersive X-ray spectroscopy, and light microscopy demonstrated the presence of predominantly surface-oriented calcification. PEU-100, derivatized with 100 n.moles/ mg of EHBP, resisted calcification with explant calcium levels 0.51 +/- 0.01 (calciphylaxis) and 0.38 +/- 0.01 (control) microgram/mg. It is concluded that calciphylaxis enhances superficial polyurethane calcification in rat subdermal implants and that an EHBP-modified polyurethane resists calcification despite calciphylaxis. Rat subdermal implants using calciphylaxis may be generally useful for evaluating the calcification potential of various biomedical polymers.

Animals↗

PubMed1993

Effect of polyol type on the surface structure of sulfonate-containing polyurethanes.

Polyurethanes based upon polytetramethylene oxide (PTMO) as the polyol and derivatized with propyl sulfonate functionality pendant from the urethane nitrogen have previously been shown to possess good blood-contacting properties. Other investigators have shown that sulfonated polyurethanes containing polyethylene oxide (PEO) as the soft segment are much more thrombogenic than those containing PTMO as the soft segment. In this article, the surface properties of sulfonated polyurethanes based upon either PTMO or PEO are compared. Dynamic contact angle measurements show a significant decrease in the receding angles of the sulfonated PTMO-containing polyurethane as compared to its nonsulfonated precursor polymer. No significant difference is seen between the receding contact angles of either the sulfonated PEO-based polyurethane or its nonsulfonated analog. Variable-angle electron spectroscopy for chemical analysis (ESCA) studies of sulfonated PTMO-based polyurethane performed at room temperature show that there is a significant decrease in sulfur content at the surface. In contrast, the sulfonated PEO-based polyurethane showed little change in sulfur content with take-off angle. Finally, ESCA studies of freeze-dried surfaces show a significant increase in sulfur near the surface of the sulfonated PTMO-based polymer as compared to vacuum-dried samples but show no such increase for the sulfonated PEO-based polyurethane. It is suggested that the ability of the sulfonate functionality to be expressed at the surface may explain the observed differences in blood compatibility between the sulfonated polyurethanes based upon polyols of varying hydrophilicity.

Absorption↗

PubMed1993

Effects of oligoethylene oxide monoalkyl(aryl) alcohol ether grafting on the surface properties and blood compatibility of a polyurethane.

A series of oligoethylene oxide monoalkyl(aryl) alcohol ethers was grafted on to the backbone of a polytetramethylene oxide (PTMO)-based polyurethane, in an attempt to improve its biocompatibility. Each polyurethane contained a different pendant chain grafted to the urethane nitrogen atoms. The grafted chains consisted of various short lengths of hydrophillic oligomeric poly(ethylene oxide) (PEO) spacer segments and alkyl/aryl hydrophobic terminal groups. By using the 1H-NMR (nuclear magnetic resonance) technique, the extent of grafting was found to range from 7 to 12 mol% substitution of the urethane hydrogen groups. The surface properties of these materials were evaluated using high-vacuum, air-equilibrated and water-equilibrated methods. X-ray photoelectron spectroscopy (XPS) and static and dynamic contact angle experiments were performed. XPS showed that all of the grafted polyurethane surfaces contained higher ratios of C1s to O1s than the base polyurethane. These C:O contents correlate with the C:O ratios of the grafted chains. Dynamic contact angle analysis showed larger contact angle hysteresis for the grafted polyurethanes. The grafted polyurethanes generally exhibit lower complement activation, measured by an in vitro assay for C3a. A canine ex vivo arteriovenous series shunt was used to monitor platelet and fibrinogen deposition on these polymers. The incorporation of short ethylene oxide spacer segments with terminal C18 linear alkyl chains resulted in an improved short-term (up to 15 min) blood compatibility compared to the underivatized polyurethane. At longer blood contact times, all the grafted polyurethanes were more thrombogenic than the base polyurethane. In addition, there was no observable correlation between the material surface properties and the blood contact response.

Absorption↗

PubMed2006

Cholesterol-modified polyurethane valve cusps demonstrate blood outgrowth endothelial cell adhesion post-seeding in vitro and in vivo.

BACKGROUND: The clinical and experimental use of polyurethane heart valve prostheses has been compromised by thrombosis and calcified thrombus. This is caused in part by the lack of an intact endothelium on these implant surfaces. We hypothesize that endothelial seeding of a polyurethane heart valve leaflet with autologous sheep blood outgrowth endothelial cells (BOECs) could be achieved with cholesterol-modified polyurethane (PU-Chol) to promote BOEC adhesion, thereby resulting in an intact, shear-resistant endothelium that would promote resistance to thrombosis. METHODS: Cholesterol-derivatized polyurethane was formulated by bromoalkylation of the urethane nitrogens followed by reactive attachment of mercaptocholesterol. In vitro shear flow studies were carried out comparing BOEC retention on control surfaces versus PU-Chol using forces comparable to those observed in vivo with cardiac valves (75 dyne/cm2). Autologous sheep BOECs were seeded onto PU-Chol before pulmonary leaflet replacement surgery under cardiopulmonary bypass. Studies were terminated at 30 and 90 days followed by retrieval analyses. RESULTS: Blood outgrowth endothelial cell seeding of PU-Chol surfaces resulted in an endothelial monolayer that was positive for von Willebrand factor. Polyurethane-cholesterol demonstrated significantly greater BOEC adhesion under 75 dyne/cm2 shear force in vitro than control polyurethane (75.3% +/- 12.3% versus 5.8% +/- 3.9%, respectively; p < 0.001). Sheep pulmonary cusp replacements demonstrated retention of seeded BOECs on PU-Chol leaflets with no significant differences in the extent of cellular density comparing unimplanted specimens with explants. Control explants (nonseeded PU-Chol and nonseeded polyurethane) demonstrated no evidence of endothelial recruitment. CONCLUSIONS: Polyurethane-cholesterol represents a polyurethane formulation with very high adhesive properties for BOECs under heart valve level shear forces both in vitro and in vivo.

Alkylation↗