No abstract

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.

Nanocomposites from a hexamethylene diisocyanate (HDI)-based polyester-type waterborne polyurethane (PU) containing different amounts (17.4-174 ppm) of gold (Au) nanoparticles (approximately 5 nm) were prepared. The microstructure and physiochemical properties of the nanocomposites were characterized. The cell attachment and proliferation, platelet activation, and bacterial adhesion on the nanocomposites were evaluated. Gold nanoparticles in small amounts induced significant changes in surface morphology and domain structures, from hard segment lamellae to soft segment micelles. These changes resembled the morphological transformation among different mesophases occurred in diblock copolymers. Better cellular proliferation, lower platelet activation, and reduced bacterial adhesion were demonstrated for the PU nanocomposite with 43.5 or 65 ppm of Au than the pure PU or the nanocomposite containing a different amount of Au. The different cellular response on PU-Au nanocomposites was attributed to the extensively modified surface morphology and phase separation in the presence of a small amount of Au nanoparticles.

A novel method to exfoliate the montmorillonite clay was developed previously to generate random nanosilicate platelets (NSP), one kind of delaminated clay. To improve their dispersion in a polymer, we modified NSPs by three types of surfactants (cationic Qa, nonionic Qb, and anionic Qc) in this study and used them to prepare nanocomposites with polyurethane (PU). The zeta potential, antimicrobial ability, and biocompatibility of these surfactant-modified NSPs (abbreviated "NSQ") were characterized. It was found that the zeta potential of Qa-modified NSP (NSQa) was positive, whereas those of NSP and the other two NSQs (NSQb and NSQc) were negative. All NSQ presented less cytotoxicity than NSP. NSQa and NSQc showed excellent antimicrobial activities against S. aureus (Gram-positive strain) and E. coli (Gram-negative strain). The nanocomposites of NSQ with PU were then characterized for surface and mechanical properties, cell attachment and proliferation, antimicrobial activity in vitro, and biocompatibility in vivo. A higher surfactant to NSP ratio was found to improve the dispersion of NSQ in PU matrix. The mechanical properties of all PU/NSQ nanocomposites were significantly enhanced. Among various NSQ, only NSQa were observed to migrate to the composite surface. The attachment and proliferation of endothelial cells and fibroblasts in vitro as well as biocompatibility in vivo were significantly better for PU/NSQa containing 1% of NSQa than other materials. The microbiostasis ratios of PU/NSQ nanocomposites containing 1% NSQa or NSQc were >90%. These results proposed the safety and potential antimicrobial applications of surfactant-modified delaminated clays and their nanocomposites with PU polymer.

Polyurethane (PU) frequently has been used to manufacture small diameter vascular grafts due to its good bicompatibility. In this study, sponge PU small diameter vascular grafts were fabricated from Pellethane 2103, as well as a self-synthesized PU, by utilization of a salt casting technique and by varying the salt/polymer ratios. Two types were made; one of them had a thin solid layer on the outer surface. The inner surface was identical and was coated with gelatin crosslinked by epoxide. Tensile properties, compliance, platelet activation, and endothelial cell attachment were evaluated in vitro. It was found that for the grafts with an outer nonporous coating, compliance could not be estimated from modulus due to anisotropy. The most compliance-matched grafts were made of self-synthesized polyurethane with a salt/polymer ratio 4 to 8 or Pellethane with a ratio 6 to 8 without the outer nonporous coating. The former had better elongation. Self-synthesized PU had lower platelet adhesion as well as more endothelial attachment than Pellethane. Porosity activated platelets strongly and reduced endothelial adhesion unless the surface was modified by the crosslinked gelatin layer. It was concluded that PU synthesized in our lab with a salt/polymer ratio of at least 4 and coated with epoxy crosslinked gelatin was a better substrate for preparation of small diameter vascular grafts.