Synthesis And Characterization Of PIB-based Copolymers And Their Applications In Biomedical Materials

Polyisobutene(PIB) is a kind of sticky polymer with good properties of heat-resistant, anti-ultraviolet and oxidation resistant. According to these features, PIB was usually used as thermoplastic elastomer or self-healing materials. Meanwhile, PIB is flexible and good at biocompatibility. It has reported that, PIB can be used as a potential anti-inflammatory biomaterial after being linked to some kinds of usual polymer, like PLA, PEG, etc. This paper mainly focues on block polymers based on PIB: synthesis, characterization and their applications in drug eluting stent and hydrogel dressing.PartⅠ: Preparation of Polymeric Prodrug Paclitaxel-Poly(lactic acid)-b-Polyisobutylene and Its Application in Coatings of Drug Eluting StentTo develop a novel biodegradable and well-adhesion coating material to fabricate a paclitaxel-containing eluting stent, herein, we report two kinds of drug eluting stent materials. One of them is a prodrug, namely PTX end-capped poly(lactic acid)-b-polyisobutylene(PTX-PLA-b-PIB) copolymer, which possesses biodegradability and biocompatibility. The other is a mixture of PIB-b-PLA and PTX. The chemical structures and compositions, as well as the molecular weights and molecular weight distributions(PDIs) of these copolymers have been fully characterized by 1H NMR, FT-IR and GPC measurements. Subsequently, the surface structures, degradation temperature, glass-transition temperature(Tg) and morphologies of the bare stent and drug eluting stent were studied by atomic force microscope(AFM), thermal gravity analysis(TGA), differential scanning calorimetry(DSC) and scanning electron microscopy(SEM), respectively. PTX-PLA-b-PIB and PIB-b-PLA/PTX mixture solution were separately coated onto the metallic stents to form the drug eluting stents containing PTX. The release of PTX from these stents was carried out in a buffer medium(PBS 7.4) at 37 °C. MTT assays demonstrated that the stent coated with PTX-PLA-b-PIB displayed lower cytotoxicity than that of PIB-b-PLA/PTX mixed layer and the biocompatibility of coatings can be effectively improved by the prodrug.PartⅡ: The Synthesis and Characterization of Acetal-Functionalized Diblock Copolymer m PEG-a-PIB and Its Application in Hydrogel DressingAn acetal-functionalized copolymer polyethylene glycol-acetal-polyisobutene(m PEG-a-PIB) was synthesized via “Cu AAC” click reaction. The chemical composition and structures of the copolymers were characterized by 1H NMR and FT-IR spectroscopy, while their molecular weights and molecular weight distributions were measured by GPC. The critical aggregation concentration(CAC), size parameters and morphologies of micelles self-assembled from m PEG-a-PIB were determined by fluorescence probing, dynamic light scattering(DLS), and transmission electron microscopy(TEM), respectively. Since the acetal groups are unstable in weak acidic media, it is anticipated that this diblock copolymer micelles can be dissociated in acidic environment. This was confirmed by monitoring the size change of micelles with the increase of degradation time under acidic conditions. α-cyclodextrin(α-CD) was added into the system to interact with PEG chain via inclusion complexation, resulting in the formation of crosslinked hydrogels. XRD was carried out to analyze the inclusion complexation and rheology test was used to monitor the gelation kinetics of hydrogels. In vitro cytotoxicity tests against L929 cells by MTT assays indicated that the polymer and hydrogel displayed very low cytotoxicity. This biocompatible hydrogel provide a moist and cool environment on the wounds and can degrade in the acidic conditions due to its p H-sensitive, leading to the release of drug, which accelerate the wound healing. This hydrogel have applications in the field of dressing.