Metformin-loaded nanospheres-laden photocrosslinkable gelatin hydrogel for bone tissue engineering

The aim of this investigation was to engineer metformin (MF)-loaded mesoporous silica nanospheres (MSNs)-laden gelatin methacryloyl (GelMA) photocrosslinkable hydrogels and test their effects on the mechanical properties, swelling ratio, drug release, cytocompatibility, and osteogenic differentiation of stem cells from human exfoliated deciduous teeth (SHEDs). As-received and carboxylated MSNs (MSNs-COOH) were characterized by scanning and transmission electron microscopies (SEM and TEM), as well as Fourier-transform infrared spectroscopy (FTIR) prior to hydrogel modification. MF-MSNs-COOH were obtained by loading MF into MSNs at a 1:1 mass ratio. Upon MSNs-COOH laden-hydrogels fabrication, the mechanical properties, swelling ratio and MF release were evaluated. SHEDs were seeded on the hydrogels and cytocompatibility was examined. The effects of the MF-MSNs-COOH/GelMA on the osteogenic differentiation of SHEDs were measured by ALP activity, Alizarin Red assay, and Real-time PCR. Statistics were performed using one-way ANOVA (α = 0.05). Morphological (SEM and TEM) analyses of pristine and carboxylated MSNs revealed a mean particle size of 200 nm and 218 nm, respectively. Importantly, an intrinsic nanoporous structure was noticed. Incorporation of MSNs-COOH at 1.5 mg/mL in GelMA led to the highest compressive modulus and swelling ratio. The addition of MSNs-COOH (up to 3 mg/mL) in GelMA did not impact cell viability. The presence of MF in MSNs-COOH/GelMA significantly promoted cell proliferation. Significant upregulation of osteogenic-related genes (except OCN) were seen for modified (MSNs-COOH and MF-MSNs-COOH) hydrogels when compared to GelMA. Altogether, the engineered MF-MSNs-COOH/GelMA shows great promise in craniomaxillofacial applications as an injectable, cell-free and bioactive therapeutics for bone regeneration.