Strengthening Techniques for Silicate-based Glass Scaffolds

Objectives: Glass and ceramic scaffolds with high mechanical integrity and adequate interconnected porosity are needed for producing bone graft substitutes. Our goal was to investigate the effect of different pre-coating agents and coating techniques on architectural characteristics and compressive strength of potassium alumino-silicate glass scaffolds produced via the polyurethane (PU) foam replica technique.
Methods: A proprietary silicate-based glass composition was used to prepare macroporous scaffolds (n=15/group). The control group (A) was prepared by impregnation of non-coated PU foam cylinders (10x12mm) with a silicate-based glass slurry, followed by sintering under vacuum to 795ºC/2min. at 55ºC/min. Scaffolds in Groups A were coated twice and heat treated. Scaffolds in Group B received a third coat and heat treatment. Scaffolds in groups C and D were pre-coated with either gelatin (Group C) or colloidal silica (Group D) and then coated twice with glass slurry, as for group A. The rationale for pre-coating is to round the sharp angles of the PU foam struts prior to applying the glass slurry. Scaffolds architectural characteristics were investigated by SEM. Total macroporosity was determined via He-pycnometry. The mean compressive strength was measured with a Universal Testing machine. Powdered scaffolds were analyzed by XRD.
Results: XRD confirmed the absence of crystallization for groups A, B and C. A small amount of cristobalite was present for group D. All groups presented fully interconnected porosity ranging from 78±5% (D) to 84±1% (A), with a significant difference only between groups A and D (p<0.05). The compressive strength of Groups B (2.15±0.44MPa) and C (1.69±0.24MPa) was significantly higher than that of group A (1.06±0.18MPa), group D (1.38±0.33MPa) was not significantly different.
Conclusions: Application of a third coating or pre-coating with gelatin are both promising techniques for the fabrication of strong silicate-based glass scaffolds with mechanical integrity while keeping a high level of interconnected macroporosity.