Photo-crosslinked PCL-PEG-PCL hydrogels as cell carrier for cartilage tissue engineering

• Main Authors: Ko, Chao Yin, 柯朝寅
• Other Authors: 朱一民
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/78060632842458065426

博士 === 國立清華大學 === 化學工程學系 === 102 === Osteoarthritis (OA) is a common type of degenerative arthritis marked by the thinning of the articular cartilage and affects sedentary or older individuals in general. Owing to the absence of blood vessels and cells, articular cartilage has very limited self-regeneration capacity following injury. Current methods to repair articular hyaline cartilage often lead to fibrocartilage formation, which is inferior for the application intended. Therefore, tissue engineering methods have been considered for cartilage repair and restoration. Injectable hydrogels are attractive candidates as cartilage engineering tissue scaffolds due to their advantages such as high water content and mechanical similarity with the cartilage. Photocrosslinked PEG-based hydrogels are one of the most widely investigated and utilized systems in tissue engineering. In this study, we fabricated PCL-PEG-PCL hydrogels via polymerization for use as cartilage reconstruction scaffolds. Chondrocytes and mesenchymal stem cells were photo-encapsulated and co-cultured. Cartilage regeneration was evaluated by biochemical assay, gene expression, histology, and in vivo tests. The study was divided into two sections, first discussing the effect of different hydrophobic/hydrophilic ratios on neocartilage regeneration, and then evaluating the different ratios of mesenchymal stem cells to chondrocytes on cartilage repair. Hydrogels have been investigated as scaffolds for cartilage tissue engineering with the properties of biocompatibility, swelling ratio, mechanical strength, and degradation behavior. First section was to design the most suitable PCL-PEG-PCL hydrogel to allow optimal proliferation and differentiation of encapsulated chondrocytes for cartilage regeneration. Poly(ethylene) glycol (PEG) was copolymerized with ε-caprolactone (PCL) and then acrylated to confer photocrosslinking capacity. Chondrocytes were encapsulated within photocrosslinked poly(ethylene glycol)-co-poly(caprolactone) hydrogels prepared with varying composition. The effects of the composition of the hydrogel on its properties and cell behavior were studied by varying the molecular weights of PEG and PCL. Hydrogels with higher PEG molecular weights (10,000) were associated with higher swelling ratios (9.6) and reduced elastic modulus (0.223 N/mm2). Biochemical analysis showed a positive correlation between swelling ratio and expression levels of glycosaminoglycans and total collagen. There was a 1.8-folds increase in glycosaminoglycan and 2.4-folds increase in total collagen content in hydrogels with the highest molecular weight (10,000) PEG compared to lowest molecular weight (2,000) PEG after 4 weeks of culture. Interestingly, histological examinations revealed more extensive type II collagen secretion and accumulation around chondrocytes when molecular weights of the hydrophobic PCL segment increased. The alternation of hydrophilic and hydrophobic segment lengths of PCL resulted in changes in hydrogel properties, which achieved maximum proliferation and production and distribution of extracellular matrix for cartilage regneration. Chondrocytes (CH) and bone marrow stem cells (BMSCs) are sources that can be used in cartilage tissue engineering. Co-culturing of CH and BMSCs is a promising strategy for promoting chondrogenic differentiation. In second section, CH and BMSCs were encapsulated in PCL-PEG-PCL photo-crosslinked hydrogels for four weeks. Various ratios of CH: BMSCs co-cultures were investigated to identify the optimal ratio for cartilage formation. The results thus obtained revealed that co-culturing CH and BMSCs in hydrogels provides an appropriate in vitro microenvironment for chondrogenic differentiation and cartilage matrix production. Co-culturing with a 1:4 CH-to-BMSCs ratio significantly increased the synthesis of GAGs and collagen. In vivo cartilage regeneration was evaluated using a co-culture system in rabbit models. The co-culture system exhibited a hyaline chondrocyte phenotype with better regeneration than achieved in spontaneous repair. This finding suggests that the co-culture of these two types of cells promotes cartilage regeneration, and the system, including the hydrogel scaffold, has potential in cartilage tissue engineering.