Magnetically activated piezoelectric 3D platform based on poly(Vinylidene) fluoride microspheres for osteogenic differentiation of mesenchymal stem cells

Abstract

Mesenchymal stem cells (MSCs) osteogenic commitment prior to injection enhances bone 23 regeneration therapy results. Piezoelectric stimulation may be an effective cue to promote MSC pre- 24 differentiation and poly(vinylidene) fluoride (PVDF) cell culture supports, when combined with 25 CoFe2O4 (CFO), offer a wireless stimulation strategy. Under an external magnetic field, CFO shift 26 and magnetostriction deforms the polymer matrix varying the polymer surface charge due to the 27 piezoelectric effect. To test the effect of piezoelectric stimulation on MSCs, our approach is based on 28 a gelatin hydrogel with embedded MSCs and PVDF-CFO electroactive microspheres. Microspheres 29 were produced by electrospray technique, favouring CFO incorporation, crystallization in -phase 30 (85 %) and a crystallinity degree around 55 %. Absence of cytotoxicity of the 3D construct was con- 31 firmed 24 hours after cell encapsulation. Cells were viable, evenly distributed in the hydrogel matrix 32 and surrounded by microspheres, allowing local stimulation. Hydrogels were stimulated using a 33 magnetic bioreactor and no significant changes were observed on MSCs proliferation at short or 34 long term. Nevertheless, piezoelectric stimulation upregulated RUNX2 expression after 7 days, in- 35 dicating the activation of the osteogenic differentiation pathway. These results open the door for 36 the optimization of a stimulation protocol allowing the application of the magnetically activated 3D 37 electroactive cell culture support for advanced tissue engineering strategies.