Oxygen vacancy healing boosts the piezoelectricity of bone scaffolds

Although barium titanate (BaTiO₃) presented tremendous potential in achieving self-powered stimulation to accelerate bone repair, pervasive oxygen vacancies restricted the full play of its piezoelectric performance. Herein, BaTiO₃-GO nanoparticles were synthesized by the in situ growth of BaTiO₃ on graphene oxide (GO), and subsequently introduced into poly-L-lactic acid (PLLA) powders to prepare PLLA/BaTiO₃-GO scaffolds by laser additive manufacturing. During the synthesis process, CO and C-OH in GO would respectively undergo cleavage and dehydrogenation at high temperature to form negatively charged oxygen groups, which were expected to occupy positively charged oxygen vacancies in BaTiO₃ and thereby inhibit the formation of oxygen vacancies. Moreover, GO could be partially reduced to reduced graphene oxide, which could act as a conductive phase to facilitate polarization charge transfer, thus further improving the piezoelectric performance. The results showed that the oxygen peak at the specific electron binding energy in O 1s declined from 54.4% to 14.6% and the Ti³⁺ peak that was positively correlated with oxygen vacancies apparently weakened for BaTiO₃-GO, illustrating that the introduced GO significantly decreased the oxygen vacancy. As a consequence, the piezoelectric current of PLLA/BaTiO₃-GO increased from 80 to 147.3 nA compared with that of PLLA/BaTiO₃. The enhanced piezoelectric current effectively accelerated cell differentiation by upregulating alkaline phosphatase expression, calcium salt deposition and calcium influx. This work provides a novel insight for the design of self-powered stimulation scaffolds for bone regeneration.