Abstract: BACKGROUND: Bone is a remarkable natural material possessing piezoelectric properties. By harnessing the biomimetic piezoelectric effect, tissue engineering materials can be employed to effectively address bone tissue defects and facilitate their repair.
OBJECTIVE: Using a solid-phase force chemistry technique, a piezoelectric scaffold with inherent osteogenic properties was meticulously fabricated. This unique scaffold was then assessed for its impact on osteoblast adhesion, proliferation, and osteogenic differentiation.
METHODS: Polyvinylidene fluoride (PVDF) powders, along with commercially available NaCl (mass ratios are 60:40, 50:50, 40:60, and 30:70, respectively), were subjected to solid-phase shear milling technology, resulting in a homogenous mixture. Through a melting process, a substantial material was formed, and subsequent treatment with a pure water solution effectively eliminated the NaCl. Consequently, PVDF piezoelectric foam scaffolds with varying pore sizes were successfully prepared. These materials were categorized as PVDF-40, PVDF-50, PVDF-60, and PVDF-70, denoting the respective mass percentages of NaCl during preparation. The surface morphology, crystal phase composition, thermodynamic behavior, mechanical properties, and piezoelectric properties of each group were meticulously characterized. The four kinds of piezoelectric foam scaffolds were co-cultured with the MG63 osteoblast cell line to evaluate its biocompatibility and potential to promote bone differentiation. 
RESULTS AND CONCLUSION: (1) The scanning electron microscopy, four groups of scaffolds had multi-level pores. As the NaCl mass fraction in the mixed powder increased, the porosity of the scaffolds increased. X-ray energy dispersion spectrum, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis collectively revealed the scaffold predominantly comprised the α phase, which inherently lacked piezoelectric properties. However, the application of solid-phase force chemistry successfully stimulated the formation of the β phase, thereby enhancing the scaffold’s piezoelectric properties. Notably, the PVDF-60 group exhibited the highest proportion of the β phase among all the tested groups. The results of cyclic compression testing and piezoelectric performance assessment demonstrated that the PVDF-60 group exhibited superior compressive strength and piezoelectric performance compared to the other groups. (2) The findings from scanning electron microscopy and laser confocal microscopy exhibited that MG63 cells adhered well to the surface of the four groups of scaffolds, with good morphology, extended more pseudopods, and secreted a large amount of extracellular matrix. CCK-8 assay revealed that the proliferative absorbance of PVDF-60 cells cultured for 4 days was higher than that of the other three groups (P < 0.000 1). Alkaline phosphatase staining and alizarin red staining showed that the expression of alkaline phosphatase and the number of calcified nodules in the PVDF-60 group were higher than those in the other three groups (P < 0.01, P < 0.000 1). (3) The piezoelectric PVDF  foam-based scaffolds demonstrated favorable cytocompatibility. Notably, the PVDF-60 group showed superior mechanical properties, piezoelectric performance, and bone-inducing capabilities.

Key words: bone tissue engineering, piezoelectric material, foam scaffold material, polyvinylidene fluoride, osteogenic differentiation, solid phase force chemistry