Fabrication And Biological Properties Of PDLLA/n-HAP Composite Porous Tubular Scaffolds

As a key link in the tissue engineering chain, scaffolds are crucial to the rehabilitation and regeneration of damaged tissue. The porous scaffolds provide advantageous support and facilitation for cell attachment, proliferation, differentiation and ingrowth of new tissue.In this dissertation, nano-hydroxyapatite (n-HAP) was fabricated by sol-gel method, then the n-HAP powder were added into PDLLA solution to prepare tubular n-HAP/PDLLA porous composite scaffolds by thermally induced phase separation. The proportion of PDLLA/water/dioxane and quenching time/temperature were discussed as parameters to adjust the porosity and morphology of the scaffold. A novel spin-freezing technique was used to fabricated tubular scaffold with radial gradient pore structure. The n-HAP was characterized by PCS and XRD. The advantages of adding n-HAP to the composite scaffolds were demonstrated by mechanical property test, contact angle measurement, protein adsorption experiment and in vitro degradation experiment. The morphology of the scaffolds was observed by porosity measurement and SEM.The results indicate that, the average size of n-HAP particles were 88.9nm; the aggregation of n-HAP was prevented effectively by lyophilization which makes it disperse uniformly in the polymer matrix. The scaffolds fabricated by thermally induced phase separation have high porosity and interconnected pore structure. A tubular scaffold with radial gradient pore structure was gained by spin-freezing technique under condition of 2min spinning in a speed of 2000R/min. With the adding amount of n-HAP increasing, the compression modulus, hydrophillic property and the protein adsorption ability were all increased dramatically. When the content of n-HAP was 30% the compression modulus was 8MPa, contact angle was 63.8°and the protein adsorption ability were 2.2 times than that of pure PDLLA scaffolds. The alkaline n-HAP can buffer the decrease of pH value during the PDLLA degradation, and also slow down the degradation of PDLLA. After 12 weeks cultured in vitro, the pH value was 6.2 compare with 3.8 of pure PDLLA scaffold. The mass loss was decreased from 40% to 30.5%. Finally, the Ca-P coating formed after 4 weeks culturing was characterized by XRD and FTIR. The main component of the coating is apatite, which can enhance the surface activity of the pore walls and can further reduce the degradation speed of the scaffolds.