Freeze extrusion fabrication of 13-93 bioactive glass scaffolds for bone repair.

A solid freeform fabrication technique, freeze extrusion fabrication (FEF), was investigated for the creation of three-dimensional bioactive glass (13-93) scaffolds with pre-designed porosity and pore architecture. An aqueous mixture of bioactive glass particles and polymeric additives with a paste-like consistency was extruded through a narrow nozzle, and deposited layer-by-layer in a cold environment according to a computer-aided design (CAD) file. Following sublimation of the ice in a freeze dryer, the construct was heated according to a controlled schedule to burn out the polymeric additives (below ~500°C), and to densify the glass phase at higher temperature (1 h at 700°C). The sintered scaffolds had a grid-like microstructure of interconnected pores, with a porosity of ~50%, pore width of ~300 μm, and dense glass filaments (struts) with a diameter or width of ~300 μm. The scaffolds showed an elastic response during mechanical testing in compression, with an average compressive strength of 140 MPa and an elastic modulus of 5-6 GPa, comparable to the values for human cortical bone. These bioactive glass scaffolds created by the FEF method could have potential application in the repair of load-bearing bones.