High-performance piezoelectric flexible materials enabled by hierarchically porous graphite for bone tissue regeneration

• Autor(a) principal: Rodrigues, Mariana Galhós
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/36247
• topic: Piezoelectricity; Bone regeneration; Barium titanate; Three-dimensional graphite; Chitosan; Hydroxyapatite; Hydrothermal synthesis; Scaffold

Piezoelectricity has been recognised as a crucial regulator of essential bone metabolic activities, including growth, remodelling, and defect repair. The intrinsic electrophysiological properties of bone are oftentimes overlooked when designing scaffolds to regenerate this tissue. Some metallic oxides with a perovskite structure, like barium titanate, have outstanding piezoelectric performance and can be used to stimulate bone regeneration by being implemented in a flexible polymeric composite. Nonetheless, due to the much lower dielectric constant of the polymer, in comparison to the ceramic, a conductive filler is added to the ceramic to ensure the correct polarization of the barium titanate particles. Conducive carbon nanoparticles can be used to correct the dielectric differences, although the insufficient contact between the piezoelectric component cannot be rectified. Thereby the implementation of recently designed highly porous three-dimensional graphite foams can be a viable opportunity to have electroactive bone regeneration, incorporating an innovative nanostructure composed of a three-dimensional graphite foam with barium titanate nanoparticles in a chitosan/nanohydroxyapatite supportive structure prepared by freeze-drying. Barium titanate nanoparticles with high tetragonality (~99%) were successfully synthesised through hydrothermal synthesis at mild temperatures (200 °C). The effect of the reaction time and synthesis method was characterised by X-ray diffraction, Raman spectroscopy and Scanning electron microscopy. Dispersions of these particles were done in water and evaluated with zeta potential. The impregnation of these dispersions onto the three-dimensional graphite foam was done via voltage-assistance, which improved impregnation flux, as seen in the micrographs. This method was further characterised by X-ray diffraction and Atomic Force Microscopy. The construct was then fitted into a porous chitosan structure and prepared through freeze-drying to act as a scaffold for bone regeneration. The characterization of the chitosan-based scaffolds with and without nanohydroxyapatite found good porosity (~80-90%), tuneable mechanical properties, biomineralization, degradation profile and good cell viability. Piezoresponse tests were done at local (d₃₃ = 12 pC/V) and macroscale (d₃₃ = ~5 pC/N) with piezoresponse force microscopy and a d₃₃-meter, respectively. Voltage and current were also measured at the macroscale. The new design developed for piezoelectric bone scaffolds reveals a promising perspective for the active regeneration of bone tissue.