Tissue engineering using scaffolds for bone reconstruction: a review of sol-gel silica materials for bone morphogenetic proteins (BMP) encapsulation and release

This review focused on sol-gel silica materials for surface modification of scaffolds for bone reconstruction. These silica materials can be tuned to adsorb and release specific biomolecules involved in bone reconstruction. This tuning can be possible by changing the synthesis parameters as the pH, the solvent or the presence of surfactant or by modifying its surface properties by including functional groups. It results in silica materials with very specific pore structure as hexagonal, cubic or lamellar. The grafted biomolecule studied in this review is the bone morphogenetic protein (BMP). Two methods have been highlighted in the literature for its encapsulation on silica: (i) the impregnation of already synthesized silica gels in a protein solution and (ii) the direct encapsulation of the protein during the gel formation. Both methods succeeded for adsorption and release but a good balance between these two phenomena is necessary to promote bone reconstruction. The two main parameters that will impact the protein loading and release are the texture and the surface chemistry of silica. Finally, some strategies for silica deposition on scaffolds are reviewed: the coating of the substrate with a silica film and the deposition of a dispersion of silica particles contained in another matrix. The second option seems more feasible as the deposition of a silica film requires to synthesize and process the silica gel simultaneously.