Delivery of miRNAs Using Porous Silicon Nanoparticles Incorporated into 3D Hydrogels Enhances MSC Osteogenesis by Modulation of Fatty Acid Signaling and Silicon Degradation

Strategies incorporating mesenchymal stromal cells (MSC), hydrogels and osteoinductive signals offer promise for bone repair. Osteoinductive signals such as growth factors face challenges in clinical translation due to their high cost, low stability and immunogenicity leading to interest in microRNAs as a simple, inexpensive and powerful alternative. The selection of appropriate miRNA candidates and their efficient delivery must be optimised to make this a reality. This study evaluated pro‐osteogenic miRNAs and used porous silicon nanoparticles modified with polyamidoamine dendrimers (PAMAM‐pSiNP) to deliver these to MSC encapsulated within gelatin‐PEG hydrogels. miR‐29b‐3p, miR‐101‐3p and miR‐125b‐5p are strongly pro‐osteogenic and are shown to target FASN and ELOVL4 in the fatty acid biosynthesis pathway to modulate MSC osteogenesis. Hydrogel delivery of miRNA:PAMAM‐pSiNP complexes enhanced transfection compared to 2D. The osteogenic potential of hBMSC in hydrogels with miR125b:PAMAM‐pSiNP complexes is evaluated. Importantly, a dual‐effect on osteogenesis occurred, with miRNAs increasing expression of alkaline phosphatase (ALP) and Runt‐related transcription factor 2 (RUNX2) whilst the pSiNPs enhanced mineralisation, likely via degradation into silicic acid. Overall, this work presents insights into the role of miRNAs and fatty acid signalling in osteogenesis, providing future targets to improve bone formation and a promising system to enhance bone tissue engineering. Hydrogel delivery of miRNAs to promote mesenchymal stromal cell (MSC) osteogenesis shows great promise for tissue engineering, but challenges with the selection of appropriate miRNAs and their efficient delivery must be overcome. This study develops and characterizes a new system in which pro‐osteogenic miRNAs are complexed with porous silicon nanoparticles and encapsulated alongside MSCs in gelatin‐PEG hydrogels. Findings highlight miRNA modulation of fatty acid signaling as an important pathway in osteogenesis while the overall system enhances bone formation by two mechanisms, miRNA modulation of gene expression, and via the beneficial effects of silicon nanoparticle degradation on mineralization.