Hydroxyapatite-induced bioactive and cell-imprinted polydimethylsiloxane surface to accelerate osteoblast proliferation and differentiation: an <i>in vitro</i> study on preparation and differentiating capacity

Healing bone defects remains a significant orthopedic challenge. Cell therapy and tissue engineering offer promising solutions; however, obtaining high-quality, partially or fully differentiated cells remains difficult. Therefore, developing suitable substrates to guide stem cell differentiation helps in achieving this goal. Here, an optimized polydimethylsiloxane (PDMS) substrate was created by casting the PDMS composition on isolated and fixed human osteoblasts and characterizing the biological and surface features of cell patterns. A nanolayer of hydroxyapatite (nHA) was sputtered on the cell patterns to mimic the bone extracellular matrix and enhance osteo- differentiation, providing both physical and chemical stimulations. Various physical and biological properties of patterned and non-patterned PDMS substrates with and without nHA coating were evaluated to confirm the osteo-differentiation of adipose derived mesenchymal stem cells capacity. According to the results, precise cell imprinting was successfully achieved, and nHA deposition did not adversely affect the surface topography. All substrates were biocompatible, and the combination of physical (cell imprinting)-chemical (nHA coating) stimuli significantly enhanced stem cell differentiation, as evidenced by increased alkaline phosphatase activity, upregulation of bone-specific genes, and calcium deposition. A well-designed PDMS substrate can be promising for providing osteo-differentiated stem cells in large quantities for various cell therapy and tissue engineering applications.