Compressive strength of bioactive sol--gel glass foam scaffolds

Larry Hench's 45S5 Bioglass® has been used in more than a million patients as a synthetic bone graft, in the form of a particulate. Bioglass is able to stimulate more bone regeneration than other bioactive ceramics. However, it is not commercially available as a porous scaffold with amorphous glass structure because the 45S5 composition crystallizes during sintering. The sol–gel foaming process was developed in Hench's laboratory to overcome this problem. Here, we concisely review the work on scaffold development from Hench's group and report new data that show maximum compressive strengths in excess of 5 MPa can be achieved while maintaining the interconnected pore networks required for vascularized bone ingrowth. This was achieved through optimization of sintering of the sol–gel foams. Sintering of the sol–gel foams was correlated to the network connectivity and silanol content. Changes in strength after immersion in simulated body fluid were found to be small over the times investigated. Relating the dissolution results to in vivo studies indicates that the scaffolds degrade more rapidly in vivo than in vitro.