Piezoelectric effect stimulates the rearrangement of chondrogenic cells and alters ciliary orientation via atypical PKCζ

Advanced Piezoelectric Materials, Devices, and Systems for Orthopedic Medicine

Harnessing the robust electromechanical couplings, piezoelectric materials not only enable efficient bio-energy harvesting, physiological sensing and actuating but also open enormous opportunities for therapeutic treatments through surface polarization directly interacting with electroactive cells, tissues, and organs. Known for its highly oriented and hierarchical structure, collagen in natural bones produces local electrical signals to stimulate osteoblasts and promote bone formation, inspiring the application of piezoelectric materials in orthopedic medicine. Recent studies showed that piezoelectricity can impact microenvironments by regulating molecular sensors including ion channels, cytoskeletal elements, cell adhesion proteins, and other signaling pathways. This review thus focuses on discussing the pioneering applications of piezoelectricity in the diagnosis and treatment of orthopedic diseases, aiming to offer valuable insights for advancing next-generation medical technologies. Beginning with an introduction to the principles of piezoelectricity and various piezoelectric materials, this review paper delves into the mechanisms through which piezoelectric materials accelerated osteogenesis. A comprehensive overview of piezoelectric materials, devices, and systems enhancing bone tissue repair, alleviating inflammation at infection sites, and monitoring bone health is then provided, respectively. Finally, the major challenges faced by applications of piezoelectricity in orthopedic conditions are thoroughly discussed, along with a critical outlook on future development trends.

Ultrasound Stimulation of Piezoelectric Nanocomposite Hydrogels Boosts Chondrogenic Differentiation in Vitro, in Both a Normal and Inflammatory Milieu

The use of piezoelectric nanomaterials combined with ultrasound stimulation is emerging as a promising approach for wirelessly triggering the regeneration of different tissue types. However, it has never been explored for boosting chondrogenesis. Furthermore, the ultrasound stimulation parameters used are often not adequately controlled. In this study, we show that adipose-tissue-derived mesenchymal stromal cells embedded in a nanocomposite hydrogel containing piezoelectric barium titanate nanoparticles and graphene oxide nanoflakes and stimulated with ultrasound waves with precisely controlled parameters (1 MHz and 250 mW/cm2, for 5 min once every 2 days for 10 days) dramatically boost chondrogenic cell commitment in vitro. Moreover, fibrotic and catabolic factors are strongly down-modulated: proteomic analyses reveal that such stimulation influences biological processes involved in cytoskeleton and extracellular matrix organization, collagen fibril organization, and metabolic processes. The optimal stimulation regimen also has a considerable anti-inflammatory effect and keeps its ability to boost chondrogenesis in vitro, even in an inflammatory milieu. An analytical model to predict the voltage generated by piezoelectric nanoparticles invested by ultrasound waves is proposed, together with a computational tool that takes into consideration nanoparticle clustering within the cell vacuoles and predicts the electric field streamline distribution in the cell cytoplasm. The proposed nanocomposite hydrogel shows good injectability and adhesion to the cartilage tissue ex vivo, as well as excellent biocompatibility in vivo, according to ISO 10993. Future perspectives will involve preclinical testing of this paradigm for cartilage regeneration.