Research On Porous Scaffolds With Complementary Pore Structures

Critical size bone defects due to trauma or disease are very difficult to repair via the natural growth of host tissue. Therefore, there exists a nccessity to replace these defects with bridging materials. Multiple approaches have been attempted by using autografts, allografts, artificial materials and bone tissue engineering scaffolds. The major problem with autografts is the insufficient supply and significant surgical morbidity associated with donor site pain and loss of function. Moreover, patients have to suffer a second procedure. Allografts are associated with infection and inflammation. Therefore, engineered bone tissue has been developed recently. In bone tissue engineering, scaffold served as the matrices of tissue formation plays a pivotal role, and has to fulfill a few basic requirements, that is, high porosity, pore interconnection, proper pore size, required surface properties permitting cell adhesion, and proliferation, desirable mechanical integrity to maintain the predesigned tissue structure, non-cytotoxicity. Large pores in the scaffold can allow effective nutrient supply, gas diffusion and metabolic waste removal. To engineer synthetic bone tissue, cells should be seeded into an appropriate three-dimensional (3D) porous scaffold matrix, and expand the cells in vitro. Recently,3D cultures have been widely adopted for tissue engineering to obtain satisfying artificial bone grafts. Cell seeding is the first step in establishing 3D cultures and achieving the seeding of cells with a uniform distribution throughout the porous scaffold could establish a basis for homogeneous tissue generation. Hydroxyapatite (HA) has a composition and structure very close to natural bone mineral and therefore has been considered to be the ideal material to build bone tissue engineering scaffold due to its osteoconductivity and osteoinductivity.HA spheres were prepared by the method of sol-gel and water/oil emulsification technology, then accumulated in a porous tube as a porous scaffold. The porosity, macro and micro porous structures of the scaffold were characterized. Three cell seeding methods were designed to distribute osteoblasts into HA spherule scaffolds:direct load, admixture load and transferring load in vitro. The effects on biological property of osteoblasts seeded in the porous scaffold by the three cell seeding methods were investigated. Wax spheres were prepared as porogen to prepare HA porous scaffolds with the same HA slurry, and the wax spheres were treated with dimethyl benzene to improve the interconection of the HA scaffold pores. The effects of interconection on biological property of osteoblasts seeded in the porous scaffold were investigated. The two kinds of HA porous scaffolds with complementary porous structures were evaluated to reseach the influence on osteoblasts in vitro and ectopia osteoinduction in vivo of macropore structures. The main conclusions were obtained as follows:1. The macropores of HA spheres accumulated porous scaffolds were completely interconnected, the pore size could be controlled by the dimension of HA spherulites, and large number of micropores existed on and in HA spheres. No negtive effect on the biocompatibility of the HA porous scaffolds were observed by the process of preparation. A uniform distribution of osteoblasts in HA spherulites accumulating scaffolds could be obtained by the operation of stirring or transferring. By transferring loading method, more osteoblasts were seeded on HA spherulites, which were the main body of HA pourous scaffolds. There were no considerable differences of cells proliferation or differentiation seeded by the three different methods designed.2. The interpore connectivity and porosity of scaffolds could be improved significantly by treating the wax spheres using dimethyl benzene. There was no significant difference in the shrinkage for the scaffolds with different porosities. Osteoblasts could migrate deeply into the center of the scaffold through the inter-connected pores and showed normal activity. Scaffolds with better interconection pores could supply more space for cell proliferation and differentiation.3. There was no significant difference of osteoblasts adherent or prolaferation seeded in the two different porous scaffolds in vitro. The two scaffolds with complementary porous structurs can induce new ectopic bone well, and the new bone formed along the edge of the pors. The porous structures of particulate leaching scaffolds were more profitable for ectopic bone formation and vascularize.