Surface modification of poly(ether urethane urea) with modified dehydroepiandrosterone for improvedin vivo biostability

Synthesis of polycarbonate urethane elastomers and effects of the chemical structures on their thermal, mechanical and biocompatibility properties

In this study, to obtain biomedical polyurethane elastomers with good mechanical properties and biocompatibility, a series of polycarbonate urethanes were synthesized via a two-step solution of polymerization method using the poly(1,6-hexanediol)carbonate diols (PCDL) as the soft segment, 4,4′-methylenebis(cyclohexyl isocyanate) (H₁₂MDI), 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) as the hard segment with dibutyltin dilaurate as the catalyst. In this article, we illustrated the physical behaviors were obviously influenced by synthetic routes. And their chemical and physical structures were investigated by gel permeation chromatograph (GPC), differential scanning calorimeter (DSC), fourier transform infrared spectrography (FT-IR) and mechanical properties tests. The surface wettability were studied by contact angle measurement (CA). As a kind of short-term implant biomaterial, the results of the hemolysis and platelet adhesive tests were recorded by spectrophotometer and scanning electron microscopy (SEM), indicating the materials have a great potential for developments and applications in biomedical field.

Biostability and biocompatibility of poly(ether)urethane containing gold or silver nanoparticles in a porcine model

Nanocomposites from polyether-type waterborne polyurethane (PU) incorporated with different amounts of gold nanoparticles (17.4-65 ppm) or silver nanoparticles (30.2-113 ppm) were prepared. Specifically, the nanocomposite containing 43.5 ppm of gold or 30.2 ppm of silver was previously found to possess the best thermal and mechanical properties. The enhanced biostability of the nanocomposite at the specific nanoparticle content was also observed in subcutaneous rats. The latter was probably related to the free radical scavenging ability of the nanocomposite shown in vitro. In this study, the in vivo biostability of the full series of these nanocomposites was assessed by porcine subcutaneous implantation for 19 days followed by microscopic examination and chemical characterization using attenuated total reflectance-infrared spectroscopy (ATR-IR). The nanocomposite at 43.5 ppm of gold ("PU-Au 43.5 ppm") and that at 30.2 ppm of silver ("PU-Ag 30.2 ppm") exhibited superior biostability in pigs to those at higher or lower nanoparticle contents. In particular, evidence of oxidative chain scission and crosslinking of the surface was presented by ATR-IR spectra in the explanted PU and nanocomposites other than PU-Au 43.5 ppm and PU-Ag 30.2 ppm. The extent of biodegradation and that of foreign body reactions were highly associated in these nanocomposites, both of which showing negative correlation with the free radical scavenging ability. The interdependency among antioxidation/biostability/biocompatibility of PU was demonstrated in this porcine model.

Biological stability of polyurethane modified with covalent attachment of di-tert-butyl-phenol

Polyurethane cardiovascular implants are subject to oxidation initiated surface degradation, which is mediated by monocyte-derived macrophages (MDM); this often leads to surface cracking and device failure. The present studies examined the hypothesis that covalently attaching antioxidant, di-tert-butylphenol (DBP), to the urethane nitrogens of a polyether polyurethane (PU) via bromo-alkylation reactions could prevent this problem. PU was configured with two dosages of DBP, 0.14 mM DBP/g PU of DBP (PU-DBP) and a more highly modified (HM) 0.40 mM DBP/g PU (PU-DBP-HM). THP-1 cells, a human MDM cell line, stimulated with phorbol ester and seeded on PU, PU-DBP, and PU-DBP-HM films were assessed for reactive oxygen species (ROS) production via a fluorescent based dihydrorhodamine-123 assay. Results from these studies showed a significant dose-dependent reduction of ROS levels for THP-1 cells seeded on PU-DBP versus unmodified PU. PU, PU-DBP, or PU-DBP-HM films were implanted into subdermal pouches of Sprague-Dawley rats. Films were explanted after 10 weeks and assessed for oxidative degradation via light and scanning electron microscopy (SEM) and Fourier transformation infrared spectroscopy (FTIR). Light microscopy showed extensive surface cracking, which was confirmed via SEM, on unmodified PU surfaces that was absent in both PU-DBP and PU-DBP-HM explanted films. FTIR analysis showed reduction in oxidation-induced ether crosslinking that was directly related to DBP dosages. It is concluded that modifying PU with the covalent attachment of an antioxidant confers biodegradation resistance in vivo in a dose dependent manner; this effect is likely due to quenching of the ROS generated by the adherent macrophages.

Biocompatibility of poly(ether)urethane-gold nanocomposites

We have prepared the nanocomposites of a polyether-type waterborne polyurethane (PU) incorporated with different amounts (17.4-174 ppm) of gold (Au) nanoparticles ( approximately 5 nm). The nanocomposite containing a certain amount (43.5 ppm) of gold was previously demonstrated to possess the optimal thermal and mechanical properties, as well as much reduced foreign body reactions in subcutaneous rats. In this study, the surface morphology, biocompatibility, oxidative degradation, and free radical scavenging ability of the nanocomposites were characterized in vitro. The nanocomposite at 43.5 ppm of gold ("PU-Au 43.5 ppm") exhibited different surface morphology confirmed by the atomic force microscope. PU-Au 43.5 ppm also showed enhanced cellular proliferation, reduced platelet and monocyte activation, and much less bacterial adhesion, relative to PU alone or nanocomposites at the other Au contents, in general. This better biocompatibility was associated with the surface morphological change in the presence of Au. The oxidative degradation in PU-Au 43.5 ppm was also inhibited. The increased oxidative stability corresponded to the greater free radical scavenging ability of the nanocomposites.

Host inflammatory response to NiCr, CoCr, and Ti in a soft tissue implantation model

The inflammatory response to nickel chromium (NiCr), cobalt chromium (CoCr), and titanium (Ti) implants at 7 and 28 days was investigated using real-time PCR analysis along with histological and immunohistochemical staining. Contrasting inflammatory profiles were found in response to the different metal compositions. The inflammatory profile induced by CoCr remained consistent and elevated during the 28-day period with high cell counts associated with the implants and a progressive recruitment of T lymphocytes. The response to NiCr was also elevated, but with an initially low T-lymphocyte infiltration that increased by the later time period. Ti indicated an early increased inflammatory response that had reduced by 28 days. Changes in gene expression demonstrated that Ti induced very low levels of expression of the three inflammatory cytokine genes. NiCr initiated a significant upregulation in gene expression for IL-6 and TNF-alpha. CoCr resulted in the highest upregulation of IL-2 indicative of T-lymphocyte activation to this material.