Study On Preparation, Modification And Cytocompatibility Of Poly-L-lactic Acid (PLLA) Scaffold For Cartilage Tissue Engineering

The preparation, modification, and cytocompatibility of poly-L-lactic acid (PLLA) scaffold for cartilage tissue engineering were studied. First, hydrophilic polymers were grafted on the PLLA membranes. Biomacromolecules were then grafted and coated on the PLLA membrane. Growth factors containing PLLA membranes were also prepared. Finally, these technologies were used to modify the 3-D PLLA scaffolds, which were prepared either by paraffin sphere leaching method or thermal induced phase separation method, to provide 3-D scaffolds with good cytocompatibility for cartilage tissue engineering.The PLLA membrane was immersed in hydrogen peroxide solution under UV-light to introduce the macromolecular hydroperoxide groups on the membrane surface. lodometry method was used to measure the content of the hydroperoxide groups on the membrane surface. The content of the hydroperoxide groups on the photooxidized PLLA membrane surface increased initially and then decreased with the photooxidization time. Under a high temperature, the process of photooxidization can be accelerated.Using the macromolecular hydroperoxide groups on the photooxidized membrane surface as initiators, three kinds of hydrophilic monomers, i.e. hydroxyethyl methacrylate (HEMA), methacrylic acid (MAA) or acrylamide (AAm) were polymerized on the PLLA membranes, under induction by either UV irradiation or Fe2+ reduction. ATR-IR and XPS spectra verified the occurrence of the grafting. Water contact angle measurement of the control and the modified PLLA membranes indicated that the hydrophilicity of the membrane was improved obviously after the grafting modification. ATR-IR, XPS and colorimetric method were used to characterize the grafting density of the hydrophilic polymers on the PLLA membranes, which increased with the monomer concentration and the grafting time. SEM and SFM were used to observe the surface morphology of the membranes. After grafting modification, the surface of the PLLA membrane became rougher than the control membrane. For the membranes modified by Fe2+/OOH initiation, the grafted hydrophilic polymers on the membranes surface has a more evenly distribution and a smoother surface morphology than that of the membranes modified by UV initiation.Chondrocyte culturing was performed to evaluate the cytocompatibility of the control and the modified PLLA membranes. The results showed that the improvement of surface hydrophilicity did not improve the cell adhesion and cell proliferation effectively, but had great influence on the cell spreading properties. Only on the surfaces with moderate hydrophilicity could the cell have a polygonal shape and spread well. On the control PLLA and the grafted PLLA membranes with high density of hydrophilic polymers the cells were round shape and aggregated with each other to form cell aggregates. However, the hydrophilicity is not the only factors affecting the cell spreading properties. Other factors such as the kind of functional groups and surface charge must be considered.Using water-soluble carbodiimide as condensation agent, biomacromolecules suchas gelatin, collagen and chitosan were covalently grafted on the PLLA-g-PMAA membranes. Solution of the biomacromolecules was further coated on the above membranes to increase the surface density of the biomacromolecules. This technology was designated "grafting and coating" method. The biomacromolecular layers on the PLLA membrane surfaces had good stability and good cytocompatibiliry. Cells spread very well on the gelatin or collagen coated membranes and had obviously improved adhesion rate, proliferation rate and MTT activity. By coating the collagen solution containing bone morphogenic protein (BMP) or basic fibroblast growth factors (bFGF) on the PLLA membrane surface via the "grafting and coating" method, bioactive PLLA membranes were prepared. Both BMP and bFGF can improve the MTT activity per cell obviously, but the bFGF inhibit the proliferation of the chondrocytes.3-D PLLA scaffolds with good interconnectivity were prepared using...