Polycarbonate Polyurethane Research Articles

Generation of cell adhesive substrates using peptide fluoralkyl surface modifiers

Previous studies reported on the delivery of vitamin E to the surface of a polycarbonate polyurethane (PCNU) to produce antioxidant surfaces, using a bioactive fluorinated surface modifer (BFSM). In the current report, a cell adhesive peptide sequence was coupled to the BFSM, and when blended into PCNU, generated a cell adhesive substrate. An NH 2-GK*GRGD-CONH 2 peptide sequence (referred to as RGD) with a dansyl label (*) on the lysine residue was coupled via the N-terminal to a BFSM precursor molecule. The resulting RGD BFSM was purified and the pmol peptide/mg BFSM value was assayed by amino acid quantification. The migration of the RGD BFSM in a PCNU blend was confirmed by X-ray photoelectron spectroscopy analysis. U937 macrophage-like cells and human monocytes were seeded onto the PCNU and blends of PCNU with non-bioactive fluorinated surface modifier or the RGD BFSM, in order to study the cell response. Both U937 cells and human monocytes adhered in greater numbers to the RGD BFSM substrate when compared to unmodified PCNU or the blend of PCNU with the non-bioactive fluorinated surface modifying macromolecule substrate. The study demonstrated a novel approach for the introduction of peptides onto the surface of polymers by modifying the surface from within the polymer as opposed to the use of cumbersome post-surface modification techniques. The generation of a peptide substrate points to the possibility of producing complex bioactive surfaces using various peptide BFSMs or pharmaceuticals simultaneously to manipulate cell functions.

Investigation of recombinant human elastin polypeptides as non-thrombogenic coatings

We investigated the use of a recombinant human elastin polypeptide as a coating on synthetic materials with a view to determining if these polypeptides could improve the blood compatibility of cardiovascular devices such as vascular conduits and arterial/venous catheters. Platelet adhesion and activation were studied in vitro using three commercially available synthetic materials: polyethylene terephthalate (Mylar™), a poly(tetrafluoroethylene/ethylene) copolymer (Tefzel™) and a polycarbonate polyurethane (Corethane™). Coated with adsorbed polypeptide, all three synthetic materials demonstrated reduced platelet activation and adhesion in platelet rich plasma in vitro. Compared to non-coated controls, there was a significant decrease ( p=0.05) in both platelet microparticle release and P-selectin expression for the polypeptide-coated surfaces. Scanning electron microscopy indicated fewer adhering platelets on coated surfaces compared to non-coated controls. In vivo, in a rabbit model, evaluations of polyurethane catheters coated with the polypeptide showed a marked increase in catheter patency and a significant decrease in fibrin accretion and embolism when compared to uncoated controls. This polypeptide shows a strong potential for use as a non-thrombogenic coating for small diameter vascular grafts. In addition, the results of this study indicate that the elastin polypeptide would be a valuable component of a tissue engineered vascular conduit.

Evaluation of the Release Behavior of the Dexamethasone Embedded in Polycarbonate Polyurethane Membranes: An In Vitro Study

Purpose: To evaluate the release behavior of dexamethasone embedded in a polycarbonate polyurethane membrane. Materials and Methods: Both water-soluble and water-insoluble dexamethasone were tested, and the release behavior of five water-insoluble dexamethasone films of different thickness (78 to 211 m) was also evaluated. The amount of Dexamethasone used was 10% of the total weight of the polyurethane film mass. Each film was placed in a centrifuge tube containing 25 ml of 0.1-M neutral phosphate buffer, and the tubes were placed in a shaking incubator to quantify the amount of drug released into the buffer, absorption spectroscopy (λmax=242 nm) was employed. Results: In the test involving water-soluble dexamethasone, 60% of the drug was released during the first two hours of the study. Films containing water-insoluble Dexamethasone, on the other hand, released 40%, 60% and 75% of the dexamethasone in one, three and seven days, respectively. Both types of film maintained low-dose drug release for 28 days. When release behavior was compared between water-insoluble films of different thickness, thicker film showed less initial burst and more sustained release. Conclusion: Dexamethasone release behavior varies according to drug solubility and membrane thickness, and may thus be conrolled.

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.

Polyurethane vascular prostheses decreases neointimal formation compared with expanded polytetrafluoroethylene

Purpose: Synthetic grafts have been increasingly used for complex vascular reconstructions in patients with limited autologous vein availability. Materials currently in use induce increased stenosis and graft thrombosis compared with autologous vein, especially in smaller vessels. We examined whether grafts constructed of a porous biodegradation-resistant polycarbonate polyurethane (PU) exert better biocompatibility in terms of faster endothelialization and decreased chronic proliferation of intimal cells compared with expanded polytetrafluoroethylene (ePTFE). Methods: PU or ePTFE interposition grafts were implanted into the abdominal aortas of male Sprague-Dawley rats (PU, n = 37; ePTFE, n = 32). Grafts were removed at days 1, 7, 14, 28, and 56 and 6 months and were evaluated by immunohistochemical, electron microscopic, and morphometric techniques. Bromodeoxyuridine (BrdU) was injected at 1 and 24 hours before death to determine cellular proliferation. Endothelial cells and smooth muscle cells were identified with antibodies to von Willebrand factor and α-actin, respectively. Results:The luminal surface of PU grafts took 4 weeks to completely endothelialize, whereas ePTFE grafts took 24 weeks ( P < .05). Neointimal cell proliferation was lower in PU grafts compared with ePTFE at 56 days (1.4 ± 0.1 versus 8.6 ± 1.5, P < .001) and at 6 months (0.15 ± 0.002 versus 3.4 ± 0.5, p < .001). Neointimal thickness at 6 months after implantation was 3.2 ± 0.8 μm for PU compared with 10.3 ± 3.1 μm for ePTFE ( P < .05). Conclusion: Polycarbonate polyurethane small vascular prostheses promoted faster luminal endothelialization, induced less chronic intimal proliferation, and produced a significantly thinner neointima than ePTFE grafts. These findings suggest that aliphatic-polycarbonate urethanes may offer advantages over standard materials such as ePTFE for vascular graft construction. (J Vasc Surg 1999;29:168-76)

Polyurethane elastomer biostability.

Polyurethanes have unique mechanical and biologic properties that make them ideal for many implantable devices. They are subject to some in vivo degradation mechanisms, however. Polyester polyurethanes are subject to hydrolytic degradation and are no longer used in long-term implanted devices. Polyether polyurethanes, while hydrolytically stable, are subject to oxidative degradation in several forms, including environmental stress cracking and metal ion oxidation. Mineralization is also known to occur. A new polycarbonate polyurethane has superior biostability in early in vivo qualification tests compared to the polyether polyurethanes, including no evidence of hydrolysis, ESC or MIO.

Gas transport properties of polycarbonate–polyurethane membrance

AbstractPolyurethanes (PU) were prepared using polymeric diols, containing polar groups, as OC(O)O(carbonate) groups, carbonate and ether (O) groups, or carbonate and ester groups [C(O)O]. PUs were prepared by the prepolymer two‐step technique using ethyl acetate (EA) as the solvent; the diol was reacted at about +80°C with TDI (ratio 1:2) to give the prepolymer terminated with NCO, which was then cross‐linked with triisopropanolamine (TIPA). The membranes were prepared using a Gardner knife and were characterized by differential thermal analysis (DSC). Most of the polymers prepared from low and medium molecular weight diols were amorphous and elastomeric at the temperature of gas transport measurement (35°C). The permeabilities (P) and the diffusion coefficients (D) of different gases (O2, N2, CO2, CH4, CO) were measured by a modified Lyssy apparatus, the solubility coefficient (S) was also calculated. The water‐vapor transport properties D and S were measured according to ASTM. Diffusivity data follow the Fujita model and the solubility coefficients the regular solution theory, as developed by Prausnitz and Shair. © 1993 John Wiley &amp; Sons, Inc.