Silica based materials have been commonly studied in the field of bone regeneration, due to their bioactivity and osteogenic properties1. However, silica materials have low degradation rates and are brittle, which can be overcome by developing hybrid materials, which include an organic part bound to the silica network2. Despite these can be processed in several shapes, there is a need to fabricate these materials in a custom made morphology to adapt better to the site of defect, producing scaffolds with a desired porosity, shape and size3. However, 3D printing of silica materials normally uses very high temperatures to obtain the final structure which limits the ability to encapsulate bioactive molecules. An alternative to produce silica based materials at low temperatures is the sol-gel method, in which a precursor forms a silica network using pH or temperature as a catalyst4. Therefore, in this study, a printable sol-gel silica-based hybrid has been developed by combining tetraethylorthosilicate (TEOS), and gelatin that were cross-linked with (3-Glycidyloxypropyl)trimethoxysilane (GPTMS).
The inks were prepared by adjusting the amount of TEOS and GPTMS in the sol and the proportion of gelatin added and mixing them at 37ºC to obtain printable inks. The developed inks were 3D printed using a Cellink BioX printer, and the different physicochemical properties were analyzed. As control, pristine printed silica was used. The analyzed properties were shape fidelity, water uptake, degradation, mechanical properties and bioactivity. Cytotoxicity and proliferation were assessed using rat mesenchymal stem cells, counting the cells with a PicoGreen assay and observing the morphology with an immunofluorescence assay. In vitro osteogenic differentiation was also assessed using rMSCs and osteogenic media, using pristine silica and PLA as controls. The differentiation was measured by ALP assay. Statistical significance was accepted at p<0.05.
Three different inks were obtained, one of them with a high amount of cross-linker (HC) and two with a lower amount (LC). All inks maintained the shape fidelity of the scaffold design. Regarding the water uptake, degradation, bioactivity and mechanical properties, all of the hybrid conditions showed an improvement when comparing with pristine silica. HC showed cytotoxic effects, but not the LC conditions, which indicates the potential toxicity of the cross-linker. Conditions with gelatin showed an improved adhesion and proliferation of the cells, comparing with the pristine silica. The differentiation showed that the hybrids have lower osteogenic properties than pristine silica, however, when comparing with PLA scaffolds, it showed that, even though the gelatin decreases the ALP activity, it still promotes osteogenic differentiation.
Three different silica-gelatin 3D printable hybrids were obtained. The hybrid inks improved all physicochemical properties when comparing to pristine silica scaffolds. Moreover, the cell adhesion and proliferation was improved by hybrid scaffolds, maintaining the osteogenic activity of these silica-gelatin hybrid scaffolds.
(1) Al-Harbi, N., et al., Pharmaceuticals 2021, 14 (2), 1–20.
(2) Jones, J. R., Acta Biomater. 2013, 9 (1), 4457–4486.
(3) Bose, S., et al., Mater. Today 2013, 16 (12), 496–504.
(4) Owens, G. J., et al., Prog. Mater. Sci. 2016, 77, 1–79."