Preparation And Structural Regulation Of Porous PLLA Tissue Engineering Scaffolds

As one of the basic elements of tissue engineering, three-dimensional porous scaffolds not only provide structural support for cell adhesion, proliferation and differentiation, but also guide a special cell function and regulate interaction between cells, as well as offer reliable microenvironment for cell growth. The scaffolds play a important role in tissue engineering by involving the geometric topology structure(including pore size, porosity, connectivity, etc.). Due to the simplex structure of scaffold to date, precise structural regulation of tissue engineering scaffold has become a hot spot in the field of tissue engineering.This paper is divided into the following two parts:Part I:Ssugar spheres of different sizes were prepared by emulsion method and sugar spheres template was obtained by heat treatment. PLLA tissue engineering scaffolds were produced by combining thermal induced phase separation technique with sugar sphere template,. The diameters of spherical macropores(pore size) in the scaffolds range from 50-100?m, 100-150?m, 150-200?m, 200-250?m, 250-300?m, 300-400?m, 400-500?m, 500-600?m to 600-800?m. The effects of the size of sugar spheres, the heat treatment time of sugar template and different solvents(dioxane, tetrahydrofuran and methylene chloride) on the pore size, porosity, interconnectivity of the PLLA scaffolds have been investigated.The spatial topological structure, chemical structure, crystallization and melting behavior were characterized by scanning electron microscopy(SEM), fourier transform infrared spectroscopy(FTIR) and differential scanning calorimetry(DSC), respectively. The results showed that the porosity of all the scaffolds with different pore size is more than 90% and the pore size is fully consistent with the size of the sugar spheres. The inner connectivity of the scaffolds can be regulated precisely by controlling the degree of heat treatment of sugar template. When dioxane was used as the solvent, the pore wall in the scaffold was composed of smaller micropores with an average diameter of 10?m and of 200 nm for the thickness. The pore wall of the scaffold made from THF solution consists of short and fine microfibers, while a smooth and compact pore wall was formed when methylene chloride was used as the solvent. Cell experiments demonstrated the good biocompatibility of the PLLA scaffolds. Tissue engineering scaffolds with a micro-nano structure is favorable to the cell adhesion, growth and the cell metabolism.Part II: The polylactic acid / hydroxyapatite(PLLA / HA) composite scaffolds were prepared by soaking the PLLA scaffolds prepared above in 1.5 times simulated body fluid(SBF) with different time.The morphology, the coverage degree and crystal size of HA deposited layers were characterized by SEM. The results displayed that the weight of the composite scaffolds increases firstly and then decreases over the soaking time. Transmission electron microscopy(TEM) results revealed a lamellar structure of HA crystals. TEM-EDS measurement showed that the Ca / P atomic ratio was 1.51 which is close to the theoretical ratio of HA. The spacing of crystal lattice planes of(110) and(002) and the characteristic diffraction peak of(002) and(211) were detected by high-resolution TEM and X-ray diffraction(XRD), respectively. FTIR spectra verified that the PLLA / HA composite scaffolds have the characteristic peaks of both PLLA and HA. The contact angle test showed that the hydrophilicity of the scaffold was improved with the increasing of HA deposit layer. Cytotoxicity test(MTT) showed a good biocompatibility and high cell viability for the mouse osteoblasts(MC3T3-E1 cells) on the PLLA scaffolds and PLLA / HA scaffolds.