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

The preparation, degradation, and cytocompatibility of poly-L-lactic acid (PLLA) scaffold for cartilage tissue engineering were studied in this thesis.The PLLA porous scaffold was generally fabricated through porogen-leaching technique. Gelatin particles and PLLA solution were mixed and stirred, then freeze-dried, followed by removal of the gelatin particles to yield the porous scaffolds. By this pathway, however, it is difficult to balance the interconnectivity of pores and mechanical property of the scaffold. Therefore, the gelatin particles were bound together through a previous treatment in saturated water vapor condition to form a three-dimensional assembly in a mold. Thus, the scaffold with high porosity, good interconnected pores and good mechanical property can be obtained. Asymmetric and tubular PLLA porous scaffolds can also be fabricated by prewetting gelatin particles in saturated water vapor, which is beneficial to mold the PLLA scaffold.Removal of the organic solvent was realized by freeze-drying and room temperature-dying. The microstructure, porosity, apparent density and mechanical properties were compared in these two kinds of scaffolds. Scaffolds fabricated by freeze-drying exhibit better mechanical performance than that by room temperature-dying owing to different micropore structure and high crystallinity, and it is more promising probably.Influence of polymer concentration on the microstructure, porosity, apparent density and mechanical property of the scaffold was studied as well. Along with the increase of polymer concentration, the porosity of the scaffolds decreased, while the compressive modulus increased. Furthermore, remaining gelatin can improve the compressive modulus of dry PLLA scaffold, following a position correlation. Hydrated scaffolds exhibited lower mechanical performance caused mainly by the dissolution or swelling of the adhered gelatin on the skeleton surfaces in-between the pores.Degradation of the porous PLLA scaffolds was investigated, by immersion in PBS at 37℃. Owing to that the remained gelatin in the scaffolds will be dissolved during the degradation process, the water uptake of the scaffolds first lowed down and then increased up. The scaffolds lose their apparent weight more dramatically at the beginning of degradation because of the same reason. The rate of molecular weight decrease was faster than that of weight loss in the degradation process, following a bulk degradation mechanism. The accumulated carboxyl, an acidic degradation product, in the scaffolds can produce autocatalytic effect, which yields big holes in the scaffolds. Tg and Tm of the PLLA scaffolds decreased along with the degradation time, while the relativity crystallinity increased.At last, chondrocytes were cultured in different PLLA scaffolds fabricated with gelatin or sodium chloride particles as porogen in vitro. Larger number of cells in scaffolds fabricated with porogen of gelatin particles was observed under both scanning electron microscopy and confocal laser scanning microscopy (CLSM) afterthe viable cells were stained with fluorescein diacetate. Consistent higher values of MTT absorbance and GAG secretion were also determined in the scaffolds fabricated with porogen of gelatin particles than that of sodium chloride particles. The remained gelatin here takes an important role for the better biological performance of the scaffold, since gelatin contains peptide sequences such as RGD which are known to promote cell adhesion and growth. Therefore, the scaffolds can be modified by the remained gelatin in it in-site.