Interplay of surface polarization charge, dynamic electrical stimulation and compositional modification towards accelerated osteogenic response of NaxK1-xNbO3 piezo-bioceramics

RNA Coating Promotes Peri-Implant Osseointegration

In addition to transmitting and carrying genetic information, RNA plays an important abiotic role in the world of nanomaterials. RNA is a natural polyanionic biomacromolecule, and its ability to promote osteogenesis by binding with other inorganic materials as an osteogenic induction agent was discovered only recently. However, whether it can promote osseointegration on implants has not been reported. Here, we investigated the effect of the RNA-containing coating materials on peri-implant osseointegration. Total RNA extracted from rat muscle tissue was used as an osteogenic induction agent, and hyaluronic acid (HA) was used to maintain its negative charge. In simulated body fluids (SBF), in vitro studies demonstrated that the resulting material encouraged calcium salt deposition. Cytological experiments showed that the RNA-containing coating induced greater cell adhesion and osteogenic differentiation in comparison to the control. The results of animal experiments showed that the RNA-containing coating had osteoinductive and bone conduction activities, which are beneficial for bone formation and osseointegration. Therefore, the RNA-containing coatings are useful for the surface modification of titanium implants to promote osseointegration.

Accelerated Osteogenic Response of Electrodynamically Stimulated Mg1-xCaxSi1-xZrxO3 (x = 0-0.4) Bioelectrets

MgSiO3-based biodegradable ceramics demonstrated remarkable potential for treating small-scale bone defects and temporary bone replacement. In addition, the dissolution behavior of MgSiO3 bioceramics can be tuned by doping of Ca and Zr elements at Mg and Si sites, respectively. The present study reported the influence of formation of Ca- and Zr-codoped Mg1-xCaxSi1-xZrxO3 (x = 0, 0.1, 0.2, 0.3, and 0.4) bioelectrets and electrodynamic stimulation toward improving their osteogenic response. Mg1-xCaxSi1-xZrxO3 electrets were successfully synthesized by a solid-state route. A detailed X-ray photoelectron spectroscopy (XPS) analyses revealed that the electrets produced oxygen-deficient active sites. The formation of Mg1-xCaxSi1-xZrxO3 electrets significantly increased the surface hydrophilicity. Inductively coupled plasma (ICP) analyses were used to examine the leaching behavior of Ca/Zr-codoped MgSiO3 bioceramics. In vitro cell culture analyses indicated that the osteogenesis of MG-63 cells was remarkably enhanced on the electrodynamic field-treated Mg1-xCaxSi1-xZrxO3 bioelectrets as compared to hydroxyapatite (HA). Moreover, a better osteogenic response was observed for higher concentrations of Ca (0.3 and 0.4) and Zr (0.3 and 0.4) doping in the MgSiO3 bioelectrets. Further, the mechanism of enhanced cellular functionality was revealed by the measurement of intracellular Ca2+.

Electrical stimulation of piezoelectric BaTiO3 coated Ti6Al4V scaffolds promotes anti-inflammatory polarization of macrophages and bone repair via MAPK/JNK inhibition and OXPHOS activation

Bone regeneration is a highly synchronized process that requires multiple biochemical, bioelectrical, mechanical, and other physiological cues. The restoration and delivery of electrical cues locally through piezoelectric materials have been demonstrated to facilitate osteogenesis in vitro and bone repair in vivo. However, the underlying mechanism by which piezoelectric stimulation promotes osteogenesis and bone repair remains unclear yet, limiting the design and clinical application of piezoelectric materials for bone repair. Herein, a piezoelectric BaTiO3/Ti6Al4V (BT/Ti) scaffold was prepared by hydrothermal synthesis of a uniform BaTiO3 layer on three dimensionally printed Ti6Al4V scaffold. The BT/Ti scaffolds exhibited piezoelectricity and favorable biocompatibility with RAW264.7 macrophages after polarization. In vitro results demonstrated that the piezoelectric effects of the poled BT/Ti scaffolds promoted M2 polarization of macrophages and immunoregulatory osteogenesis of MC-3T3 osteoblasts. In a subcutaneous implantation model, a higher proportion of CD68⁺ CD206⁺ M2 macrophages was observed in the tissues around the poled BT/Ti scaffolds under low intensity pulsed ultrasound (LIPUS) stimulation. Improvements in macrophage M2 polarization and bone regeneration were further identified in a sheep cervical corpectomy model. RNA sequencing and mechanistic investigation revealed that the piezoelectric BT/Ti (poled) scaffolds inhibited the inflammatory MAPK/JNK signaling cascade and activated oxidative phosphorylation (OXPHOS) and ATP synthesis in macrophages. Collectively, our study provides a promising method for regulating the immune microenvironment and enhancing bone regeneration using polarized piezoelectric BT/Ti scaffolds.