The TIPS Preparation And Properties Of CP/PLLA Composite Scaffolds For Bone Tissue Engineering

Poly(l-lactic acid )(PLLA) is the most typical biodegradable polymer used in bone tissue engineering. PLLA has good biocompatibility and can degrade into lactic acid which is the outcome of sugar degradation. It is good scaffold material for better mechanical properties compared to other biodegrable polymers. But PLLA is hydrophobic and not very good for cells seeding. The other disadvantage is that the degradation products reduce the local PH value, which, in turn, may accelerate the PLLA degradation rates and induce an inflammatory reaction and poor mechanical properties.Calcium phosphates(CP) have been studied extensively for cell cultures and have been found to possess good osteoconductive properties. CP can be dissolved in vivo and be absorbed or displaced by tissue. The degradation rate of CP varies in different crystalline phases, which enables to adjust the degradation rate of biomaterials. But calcium phosphate ceramic with high porosity is such brittle and low toughness that it can't fit to bone tissue engineering.In order to provide appropriate scaffolds for bone tissue engineering, calcium phosphate was combined with PLLA to prepare porous material. The addition of CP can enhance the mechanical ability of PLLA greatly and give good osteoconductive properties. The decrease in value of pH by PLLA can be stabilized by the alkalescence brought by degradable CP. Inflammatory reaction can be avoided.Thermally induced phase separation(TIPS) technique was utilized to fabricate biodegradable CP/PLLA scaffolds which are capable of applying in tissue engineering. It is a good and simple method to make 3D interconnected porous material. Ideally, bone scaffold should have high porosity and uniformly distributed pores with more than 50μm better between 100~300μm to provide adequate space for cell seeding or growth while TIPS generally produces small pores of ~20μm.In this work, Pluronic F127 was used as a progen and different biodegradation rate and surface property as amorphous calcuim phosphate, a-calcuim triphosphate,β-calcuim triphosphate and a/p-calcuim triphosphate were selected to make three-dimensional porous composites with PLLA.In the phase separation of pure PLLA or CP/PLLA composite system the PPO block of PF127 can aggregate PLLA clew to induce phase separation. This resulted big round pores of 50~300μm and uniform ladder-like structure of 400~1000μm. The porosity is 80%~93%.At the same time PF127 exist at the surface of PLLA to increase the hydrophile ability.Varying the polarity of the solvent used two kinds of pore structures as round and ladder-like were achieved. When there was water in the solvent round structure was achieved. Calcium phosphate reunited of 10~15μm and exited on the PLLA pore wall. When the solvent was pure 1,4-dioxane foams showed ladder-like structure and calcium phosphate besetted in the PLLA pore wall and has good combination. The size of conglomeration is only l~5μm.The composite foams showed a significant improvement in mechanical properties over pure polymer foams. Composite scaffolds of ladder-like structure have better mechanical ability than scaffolds of round structure. Biology experiment showed that the scaffolds prepared in this work have good bioactive ability and can degrade in vivo without inflammatory reaction.This work provides an effective way to prepare high porosity(80%~93%) and big pore size(50~300μm) CP/PLLA composite scaffold. PF127 as progen increased the pore size and enhanced the hydrophile ability of PLLA. Controlling the CP species, content, polymer concentration and solvent scaffolds of different pore structure and degradation rate were achieved. Composite foams have better properties than pure polymer foams and high bioactive ability. They are promising scaffolds for bone-tissue engineering. The experiment results have important value both in theory and applied engineering.