Abstract
In this investigation, new biodegradable brush-like amphiphilic copolymers were synthesized by ring opening polymerization. Poly(L-lactide) (PLLA) was grafted onto chondroitin sulfate (CS), which is one of the physiologically significant specific glycosaminoglycans (GAGs), using a tin octanoate [Sn(Oct)2] catalyst in DMSO. The hydroxyl groups of the chondroitin sulfate were used as initiating groups. These functional groups enable specific mucoadhesion or receptor recognition. The degree of substitution (DS), the degree of polymerization (DP) and the chondroitin sulfate content (from 1.1% to 15.4%) were analyzed by 1H-NMR. The characteristics of these grafted copolymers, including the structure, the thermal properties and biodegradability etc., were examined with respect to CS content. Meanwhile, the amphiphilic core (PLLA) - corona (CS) nanoparticles, with size smaller than 200 nm, was examined by dynamic light scattering (DLS). Zeta potential analysis exhibited the value in the range -18.3 to -49.4 mV. The morphologies of the nanoparticles were observed by field-emission scanning electron microscopy (FE-SEM). The nanoparticles with lower cytotoxicity were examined by MTT assay. Furthermore, the in vitro BSA release kinetics of those CSn-PLLA nanoparticles was also determined in this study. Novel polymeric amphiphilic copolymers were synthesized using chondroitin sulfate (CS) as a hydrophilic segment and poly(L-lactide) (PLLA) as a hydrophobic segment. Micelles of those copolymers were formed in an aqueous phase and were characterized by 1H NMR spectra, fluorescence techniques, dynamic light scattering (DLS), atomic force microscopy (AFM) and confocal microscopy. Their critical aggregation concentrations (CAC) are in the range of 0.0043 to 0.0091 mg/mL at 25oC. The partition equilibrium constants, Kv, of the pyrene probe in the aqueous solution were from 3.65×105 to 1.41×106 at 25 oC. The mean diameters of the micelles were below 200 nm, and their sizes were narrowly distributed. The AFM images revealed that the self-aggregates were spherical. Additionally, the CSn-PLLA micelles can efficiently transport within the cells via endocytosis as observed from confocal microscopy. In cartilage tissue engineering, the graft copolymer was blended with poly(L-lactide) (PLLA) to form biomimic porous scaffolds. Natural CS was introduced into the polyester matrix to promote the proliferation of cells. Three-dimensional sponge-like scaffolds were fabricated by a combination of salt leaching and solvent casting methods. The morphology of the scaffolds was observed with scanning electron microscopy (SEM) with average pore size between 50~250 μm and its porosity was high (>85%). Compression analysis indicated that the mechanical properties of the scaffold were adequate to support the proliferation of cells. The hydrophilicity increased with increasing the copolymer content in the blend, as determined by measuring the contact angle. H&E, Masson and Safranin-O staining showed that cells formed a chondro-tissue gradually. Histological results revealed that abundant cartilaginous matrices surrounded spherical chondrocytes in the center of the explants. Chondrocytes cultured in this ECM-like scaffold maintained a round morphology phenotype, characterized by a significant quantity of extracellular matrix of sulfated glycosaminoglycans and collagens. Additionally, phenotypic gene expression (RT-PCR) indicated that chondrocytes expressed transcripts that encoded type II collagen and aggrecan, and generated sulfated glycosaminoglycans.