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 before injection enhances bone regen-eration therapy results. Piezoelectric stimulation may be an effective cue to promote MSC pre-differentiation, and poly(vinylidene) fluoride (PVDF) cell culture supports, when combined with CoFe2O4 (CFO), offer a wireless in vitro stimulation strategy. Under an external magnetic field, CFO shift and magnetostriction deform the polymer matrix varying the polymer surface charge due to the piezoelectric effect. To test the effect of piezoelectric stimulation on MSCs, our approach is based on a gelatin hydrogel with embedded MSCs and PVDF-CFO electroactive mi-crospheres. Microspheres were produced by electrospray technique, favouring CFO incorpora-tion, crystallisation in -phase (85 %) and a crystallinity degree of around 55 %. The absence of cytotoxicity of the 3D construct was confirmed 24 hours after cell encapsulation. Cells were via-ble, evenly distributed in the hydrogel matrix and surrounded by microspheres, allowing local stimulation. Hydrogels were stimulated using a magnetic bioreactor, and no significant changes were observed in MSCs proliferation in short or long term. Nevertheless, piezoelectric stimula-tion upregulated RUNX2 expression after 7 days, indicating the activation of the osteogenic dif-ferentiation pathway. These results open the door for optimising a stimulation protocol allow-ing the application of the magnetically activated 3D electroactive cell culture support for MSCs pre-differentiation before transplantation.