Permanently hydrophilic, piezoelectric PVDF nanofibrous scaffolds promoting unaided electromechanical stimulation on osteoblasts

Biomimetic functional scaffolds for tissue engineering should fulfil specific requirements concerning structural, bio-chemical and electro-mechanical characteristics, depending on the tissue that they are designed to resemble. In bone tissue engineering, piezoelectric materials based on poly(vinylidene fluoride) (PVDF) are on the forefront, due to their inherent ability to generate surface charges under minor mechanical deformations. Nevertheless, PVDF's high hydrophobicity hinders sufficient cell attachment and expansion, which are essential in building biomimetic scaffolds. In this study, PVDF nanofibrous scaffolds were fabricated by electrospinning to achieve high piezoelectricity, which was compared with drop-cast membranes, as it was confirmed by XRD and FTIR measurements. Oxygen plasma treatment of the PVDF surface rendered it hydrophilic, and surface characterization revealed a long-term stability. XPS analysis and contact angle measurements confirmed an unparalleled two-year stability of hydrophilicity. Osteoblast cell culture on the permanently hydrophilic PVDF scaffolds demonstrated better cell spreading over the non-treated ones, as well as integration into the scaffold as indicated by SEM cross-sections. Intracellular calcium imaging confirmed a higher cell activation on the piezoelectric electrospun nanofibrous scaffolds. Combining these findings, and taking advantage of the self-stimulation of the cells due to their attachment on the piezoelectric PVDF nanofibers, a 3D tissue-like functional self-sustainable scaffold for bone tissue engineering was fabricated.