Porous implants for bone regeneration

The regeneration of critical-size bone defects requires the implantation of porous scaffolds exchanging suitable chemical, morphological and mechanical signals with cells so as to activate new bone formation and colonization of the whole scaffold. Pore size and morphology must be designed to achieve cell penetration and the establishment of a suitable vascular network to sustain the bone metabolism. The mechanical strength of the scaffolds should be sufficient for early physical stabilization soon after implantation. Several forming techniques, such as replica, foaming, spin casting, slip casting, freeze casting, are applied to establish stable suspensions of bioactive powders (e.g.: hydroxyapatite, tricalcium phosphate, titania and their composites) to be consolidated into 3D macroporous devices. In particular, by foaming process scaffolds with very high porosity extent and good mechanical strength can be obtained; freeze casting processes allow to obtain implants with oriented porosity and anisotropic mechanical properties, similarly to what occurs in long bones. The oriented porosity also support the development of a vascular network that in turn favour the bone formation and maturation in the whole scaffold. Bioactive composites associating calcium phosphates and reinforcing phases such as titania are developed and optimized to produce bone scaffolds with high osteogenic character and increased mechanical strength that can be used for regeneration of load-bearing bone parts. Sintering processes are settled and optimized to achieve the highest extent of consolidation and to maximize the mechanical strength. Natural and bio-erodible polymers are also used in blends with the ceramic phase to enhance fracture strength and tailor elastic properties towards values typical of bones. The presence of polymers provide increased physical stability to the scaffold in the early stage after implantation and favour cell adhesion and migration.