Polystyrene-block-poly(2-cinnamoylethyl methacrylate) (PS-b-PCEMA) samples with n/m larger than 9.0, where n and m stand for the numbers of styrene and of CEMA units in a chain, formed essentially star micelles and those with n/m between 7 and 8.2 formed mixtures of star and long cylindrical micelles in cyclopentane with PCEMA as the core and PS as the shell. UV cross-linking of the PCEMA cores of these micelles at 50 °C yielded star polymers and nanofibers. This probably represents the first preparation of cross-linked block copolymer cylindrical micelles or nanofibers in the solution phase. While we have previously prepared star polymers using this approach, this study shows the robustness of this method in producing star polymers with as many as 4.5 × 102 arms and a molar mass of 9.9 × 107 g/mol. Detailed study showed that UV cross-linking only locked in the structure of the micelles and did not change their aggregation numbers. This allowed us to determine the molar masses of the cross-linked micelles in toluene, in which uncross-linked micelles would have disintegrated, and to equate them to those of the uncross-linked micelles in cyclopentane. The aggregation numbers of the star micelles in cyclopentane were found to follow theoretical scaling laws.

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In this work the exact data of the rate coefficients of propagation k , and termination k , , and initiator efficiencyfas well as their variations with conversion during the whole processes of the polymerization of methyl methacrylate in bulk have been measured using electron paramagnetic resonance (ESR) without any assumptions and approximations. k , was calculated directly from the synchronously measured data of the concentration of radicals and polymerization rate. k, was determined under nonsteady-state conditions by using the after-effect technique in the ESR measurement. f for the initiation with dimethyl 2,Zazoisobutyrate was evaluated from the initiation and termination rates. The ESR spectra show that the polymerization system is in a micro-heterogeneous state and there exist inactive radicals. A model of a diffusion-controlled reaction is proposed.

Biomaterial-related infections continue to represent a significant challenge to the medical community. Several approaches have been utilized to incorporate antimicrobial agents at the surface of implant devices in attempts to delay or eliminate the formation of biofilms. To date, most of these strategies have focused on drug conjugation or diffusion-limited systems for the delivery of such pharmaceutical agents. More recently, work has been presented on the feasibility of incorporating drugs into the backbone of polymers as a main-chain monomer. When sequenced into the backbone of the polymer with other monomers that are hydrolytically sensitive to enzyme-catalyzed breakdown, it is thought that drugs may be able to be selectively released. Specifically, degradable polyurethanes have been synthesized with fluoroquinolone antibiotics and have shown an ability to kill bacteria when released following degradation of the polymer chains by the macrophage-derived enzyme cholesterol esterase. However, specificity of the cleavage sites in the polymer was difficult to control. Since cholesterol esterase has specificity for hydrophobic moieties, it is desirable to alter the formulation of the polyurethanes to incorporate long hydrophobic monomers immediately adjacent to the ciprofloxacin molecule. Hence, the current study focuses on evaluating the enzyme-catalyzed degradation of a degradable polyurethane synthesized with 1,12 diisocyanatododecane as a substitute for 1,6 diisocyanatohexane, which was used in previous work. Validation of specific ciprofloxacin release and the generation of antimicrobial are shown. A preliminary cell study to assess the cytotoxicity of this biodegradable antibiotic polymer shows that the material has no observable effects on cell proliferation or cell membrane structure.

A polyetherurethane (PU) was modified using fluorinated surface-modifying macromolecules (SMMs). A double radiolabel method was used simultaneously to measure the number of adhered platelets ((51)Cr) and the quantity of adsorbed Fg ((125)I), in a cone-and-plate instrument. The objectives were to determine if adsorbed Fg levels correlated to platelet adhesion on the surfaces, and to assess if any reductions in platelet adhesion for the SMM-treated surfaces resulted from surface-induced platelet lysis, rather than changes directly related to lower platelet activation and attachment on the novel surfaces. Platelet lysis was determined from lactate dehydrogenase (LDH) and unbound (51)Cr released into plasma isolated from whole blood exposed to test materials. The corresponding Fg adsorption, evaluated under the same platelet adhesion conditions, did not account for the reduced platelet adhesion on the treated surfaces. LDH and (51)Cr platelet release were very low and indicated no statistically significant differences between the materials. It was therefore concluded that platelet lysis did not contribute to the reduction in platelet adhesion characteristic observed on the SMM-treated surfaces. More importantly, the work emphasizes that the platelet activation cannot be inferred to by assessing the quantity of fibrinogen as is commonly done in the literature. The finding suggests a much more complex mechanism of action for the SMM surface modifiers. On-going work is investigating other Fg parameters such as protein binding affinity and protein conformational state in order to establish the mechanism by which the fluorinated surface modifiers may be reducing platelet adhesion via intermediary changes in initial protein adsorption.

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