Porous and strong bioactive glass (13-93) scaffolds prepared by unidirectional freezing of camphene-based suspensions

Scaffolds of 13-93 bioactive glass (6Na(2)O, 12K(2)O, 5MgO, 20CaO, 4P(2)O(5), 53SiO(2): wt.%) with an oriented pore architecture were formed by unidirectional freezing of camphene-based suspensions, followed by thermal annealing of the frozen constructs to grow the camphene crystals. After sublimation of the camphene, the constructs were sintered (1 h at 700 degrees C) to produce a dense glass phase with oriented macropores. The objective of this work was to study how constant freezing rates (1-7 degrees C min(-1)) during the freezing step influenced the pore orientation and mechanical response of the scaffolds. When compared to scaffolds prepared by freezing the suspensions on a substrate kept at a constant temperature of 3 degrees C (time-dependent freezing rate), higher freezing rates resulted in better pore orientation, a more homogeneous microstructure and a marked improvement in the mechanical response of the scaffolds in compression. Scaffolds fabricated using a constant freezing rate of 7 degrees C min-1 (porosity = 50 +/- 4%; average pore diameter = 100 mu m), had a compressive strength of 47 +/- 5 MPa and an elastic modulus of 11 +/- 3 GPa (in the orientation direction). In comparison, scaffolds prepared by freezing on the constant-temperature substrate had strength and modulus values of 35 +/- 11 MPa and 8 +/- 3 GPa, respectively. These oriented bioactive glass scaffolds prepared by the constant freezing rate route could potentially be used for the repair of defects in load-bearing bones, such as segmental defects in the long bones. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.