Preparation And Studies On Preshaped Porous Scaffolds For Tissue Engineering

Tissue engineering is believed to revolutionize Surgery to some extent in this century. It is a native interdisciplinary research field. Three dimensional porous scaffolds play an important role in tissue engineering as an adhesive substrate for implanted cells and a physical support to form new tissues or organs. To be the temporary matrix, the scaffolds should facilitate cell adhesion, promote cell growth, and allow the retention of differentiated cell functions. It should thus be biocompatible, biodegradable, highly porous with a large surface-to-volume ratio, mechanically strong, and shapable. Some basic properties of porous scaffold such as shape, pore structure, porosity, mechanical properties and degradation rate are of great importance for realization its function. The theme of this thesis is research of tissue engineering biomaterials. Much attention was paid on improvement of fabrication technique of porous scaffolds.In this thesis, biodegradable polyesters were synthesized; and three-dimensional porous scaffolds were fabricated by particulate leaching methods. Combined with compression molding technique, novel spherical pore foams with ordered internal structure and complicated external shape were prepared. The compressive properties of such porous scaffolds were investigated. Cytotoxic and histological responses of the porous scaffolds have also been examined preliminarily.The main researches are listed as follows:1. Synthesis of biodegradable polyesters by ring opening polymerization. Biodegradable polyesters including poly(D,L-lactide) (PDLLA), poly(D,L-lactide-co-glycolide) PLGA and poly(ε-caprolactone) (PCL) have been successfully synthesized by vacuum polymerization with Sn(Oct)₂ as catalyst. The molecular weight of PDLLA homopolymer can reach 400,000. Higher polymerization temperature and high GA content result in lower molecular weight of PLGA. In vitro degradation behaviors of polyesters have also beenconfirmed.2. Prepration and calibration of large scaffolds with irregular pores after combining salt-particulate leaching technique and compressive molding technique. Classic particulate leaching technique was improved to preparing large scaffold with porous structures, after combined with compressive molding at room temperature. The results revealed that larger-volume foams with highly porous three-dimensional structure could be achieved by the modified compression molding technique.3. Novel preparation method to fabricate large scaffolds with ordered spherical pores and well-defined interconnectivity between pores. Un-sticky and monodispersed paraffin microspheres were obtained via dispersion technique. Biodegradable PLGA85/15 porous foams with interconnected global pores were successfully fabricated using room temperature compression molding & particulate leaching technique based on paraffin spheres. SEM and light microscopic observations demonstrated ordered global pore structures and good pore interconnectivity. The porosity may be adjusted among 80%-95%, which covers application ranges in tissue engineering. Porosity and the pore size of the scaffolds could be controlled by modulating the ratio and the particle size of the salt porogens.4. Verify good mechanical property of scaffolds with spherical pores. Compressive strength and modulus of pore scaffolds were measured on an Instron testing machine with cylindrical samples. Mechanical properties of porous scaffolds strongly depend on porosity, but modulus is in the order of magnitude of MPa even at high porosity. Compared with the scaffolds prepared by salt particles, the spherical pore foams possess higher compression modulus, especially at high porosity above 90%.5. Preliminary examination of biocompatibility of porous scaffolds. Due to very strict demands for biomedical materials applied in clinical applications, the new spherical porous foams should be testified by cell culture and animal implantation.