Robocasting of Cu2+ & La3+ doped sol-gel glass scaffolds with greatly enhanced mechanical properties: Compressive strength up to 14 MPa

Abstract

This research details the successful fabrication of scaffolds by robocasting from high silica sol-gel glass doped with Cu²⁺ or La³⁺. The parent HSSGG composition within the system SiO₂-CaO-Na₂O-P₂O₅ [67% Si - 24% Ca - 5% Na - 4% P (mol%)] was doped with 5 wt% Cu²⁺ or La³⁺ (Cu5 and La5). The paper sheds light on the importance of copper and lanthanum in improving the mechanical properties of the 3-D printed scaffolds. 1 h wet milling was sufficient to obtain a bioglass powder ready to be used in the preparation of a 40 vol% solid loading paste suitable for printing. Moreover, Cu addition showed a small reduction in the mean particle size, while La exhibited a greater reduction, compared with the parent glass. Scaffolds with macroporosity between 300 and 500 µm were successfully printed by robocasting, and then sintered at 800 °C. A small improvement in the compressive strength (7-18%) over the parent glass accompanied the addition of La. However, a much greater improvement in the compressive strength was observed with Cu addition, up to 221% greater than the parent glass, with compressive strength values of up to ∼14 MPa. This enhancement in compressive strength, around the upper limit registered for human cancellous bones, supports the potential use of this material in biomedical applications. STATEMENT OF SIGNIFICANCE: 3D porous bioactive glass scaffolds with greatly improved compressive strength were fabricated by robocasting from a high silica sol-gel glasses doped with Cu²⁺ or La³⁺. In comparison to the parent glass, the mechanical performance of scaffolds was greatly improved by copper-doping (>220%), while a modest increase of ∼9% was registered for lanthanum-doping. Doping ions (particularly La³⁺) acted as glass modifiers leading to less extents of silica polymerisation. This favoured the milling of the glass powders and the obtaining of smaller mean particle sizes. Pastes with a high solid loading (40 vol%) and with suitable rheological properties for robocasting were prepared from all glass powders. Scaffolds with dimensions of 3 × 3 × 4 mm and macro-pore sizes between 300 and 500 µm were fabricated.

Keywords: Bioactive glass; Compressive strength; Copper ions; Lanthanum ions; Particle size distribution; Sol–gel.