Preparation and characterization of a multilayer biomimetic scaffold for bone tissue engineering

In scaffold based bone tissue engineering, both the pore size and the mechanical properties of the scaffold are of great importance. However, an increase in pore size is generally accompanied by a decrease in mechanical properties. In order to achieve both suitable mechanical properties and porosity, a multilayer scaffold is designed to mimic the structure of cancellous bone and cortical bone. A porous nano-hydroxyapatite-chitosan composite scaffold with a multilayer structure is fabricated and encased in a smooth compact chitosan membrane layer to prevent fibrous tissue ingrowth. The exterior tube is shown to have a small pore size (15-40 microm in diameter) for the enhancement of mechanical properties, while the core of the multilayer scaffold has a large pore size (predominantly 70-150 microm in diameter) for nutrition supply and bone formation. Compared with the uniform porous scaffold, the multilayer scaffold with the same size shows an enhanced mechanical strength and larger pore size in the center. More cells are shown to grow into the center of the multilayer scaffold in vitro than into the uniform porous scaffold under the same seeding condition. Finally, the scaffolds are implanted into a rabbit fibula defect to evaluate the osteoconductivity of the scaffold and the efficacy of the scaffold as a barrier to fibrous tissue ingrowth. At 12 weeks post operation, affluent blood vessels and bone formation are found in the center of the scaffold and little fibrous tissue is noted in the defect site.