Preparation And In Vitro Degradation Of Bioresorbable Polylactide/Nano β-Tricalcium Phosphate Composites For The Fabrication Of Novel Fusion Cage With Double Layer Structure

In this work, a high molecular weight polylactide stereocopolymer were first synthesized (PLA) by ring opening polymerization of L-lactide and D,L-lactide using zinc lactate as catalyst. Results show that the copolymer has a molecular weight of180,000and the L/D lactide unit ratio in the polymer chain is92:8. Well dispersed β-tricalcium phosphate (β-TCP) nanocrystallines were obtained through high engery ball milling method. A solution blending-ultrasonic dispersion-casting into film-film crush-pelletizing batch preheating-hot pressing technology was applied for the preparation of β-TCP/PLA composites. The optical moulding conditions and basic properties of composites with different β-TCP contents were investigated in detail. It was found that160℃,12MPa,10min be perfered in the hot moulding process of β-TCP/PLA composites.Totally bioresorbable composites have been prepared from nano-sized β-tricalcium phosphate and a polylactide stereocopolymer(β-TCP/PLA), aiming at the fabrication of a fusion cage with double layer structure. The composites designed for the fabrication of the outer scaffold contain10wt%,30wt%and60wt%of β-TCP, respectively. The degradation behavior, mechanical and thermal properties of the various composites have been investigated under in vitro conditions. Results show that the molecular weight of PLA in the composites largely decreased during30weeks degradation. However, little changes of weight loss (<1.1%), pH value of the medium (>6.9) and sample shape were observed. The compression strength of composites containing10wt%and60wt%TCP was above50MPa, thus fulfilling the requirements of clinical applications of fusion cages. PLA crystallized during degradation of the composite containing10wt%TCP, in contrast to those of30wt%and60wt%TCP. This finding shows that the presence of TCP disfavors PLA crystallization.The PLA/β-TCP outer scaffold composites has the potential to combine the advantages of its two components, thus could present both good bone conduction capacity and high mechanical properties, which is very crucial for a fusion cage. Basic experiment results have proved to be quite inspiring with little pH variation and high strength retaining ability during7month degradation periods. Therefore, this work provides useful information for the fabrication of novel bioresorbable fusion cage.Biodegradable three-dimensional scaffolds play a very important role in tissue engineering, since it provides the main site for the cells growth and acts as a template for tissue regeneration. Thus, porous composites with60wt%of P-TCP were prepared for the fabrication of the internal scaffold of fusion cage, using phase separation/particle leaching methods. Porous structures with pore sizes of235-435μm and1-10μm were obtained, with the poles well interconnected and the porosity up to89%. The cell biocompatibility of the porous scaffold was studied with the method of rat bone marrow mesenchymal stem cells (BMSCs) co-culture. The BMSCs cells were observed to grow better in pores of the PLA/β-TCP scaffold and thus the porous composites could have stimulative effect for the in vitro proliferation of BMSCs. It can be foreseen that with the conduct of clinical trials, more and more desired properties of PLA/β-TCP cervical fusion cage would be exhibited and proved.