Bioinspired osteoblast-imprinted piezoelectric PDMS/BaTiO₃ nanocomposites accelerate the osteogenic differentiation of adipose-derived stem cells under mechanical stimulation

In this study, we propose a new cell culture substrate that can accelerate the osteogenic differentiation of adipose-derived mesenchymal stem cells (ADSCs) by exploiting the synergistic effects of cellular imprinting and mechanoelectrical stimulation. These substrates were prepared by imprinting osteoblast footprints onto the surface of nanocomposites based on polydimethylsiloxane (PDMS) filled with 20 wt% tetragonal barium titanate (BaTiO₃) piezoelectric nanoparticles. In order to assess the osteoinductive potential of the substrates, <i>in vitro</i> cellular assays were carried out under dynamic mechanical stimulations. The results of cellular analysis showed that the osteoblastic imprints were highly influential in the regulation of ADSCs' functions and osteogenic differentiation. In substrates based on pristine PDMS, the surface imprints simulated the micro/nano topographies of natural bone extracellular matrix (ECM) that led to the enhancement of cell-substrate interactions and direction of cellular fate. Meanwhile, the incorporation of BaTiO₃ nanoparticles into the imprinted samples further enhanced the focal adhesion, extension, and proliferation of ADSCs due to the accumulation of electric charges and elevation of surface electric potential. Extensive Ca²⁺ ion deposition and acceleration of bone mineralization were also reported for the ADSCs cultured on the PDMS/20BaTiO₃ samples. We also applied an equiaxial tensile machine for the dynamic mechanical stimulation of the cell-loaded samples. The results revealed that the mechanical stimulation of the piezoelectric samples led to the generation of localized electrical signals that facilitated the cellular signaling and osteogenic gene expression. The rational increase in the expression level of osteogenic markers in 7 days approved the reliability of the approach in accelerating ADSC osteogenic differentiation by mimicking the topographical and mechanoelectrical features of the natural bone microenvironment.