Antioxidative and antibacterial gallium (III)-phenolic coating for enhanced osseointegration of titanium implants via pro-osteogenesis and inhibiting osteoclastogenesis.

Improving the ability of implants to integrate with natural bone tissue at the initial stage of implantation remains a huge challenge because bone-to-implant interfaces are often accompanied by abnormal microenvironments with infection, reactive oxygen species (ROS) and unbalanced bone homeostasis. In this study, a multifunctional coating was fabricated on the basis of gallium (III)-phenolic networks. It is easily obtained by immersing the implants into a mixed solution of tannic acids (TAs) and gallium ions. The thickness of the coating can be precisely controlled by adjusting the number and time of immersion experiments. The resulting coating displays excellent near-infrared photothermal property. As the coating degrades, TAs and gallium ions with low concentration are released from the coating, which is more rapid in acidic and oxidative stress microenvironments. Photothermal performance as well as released TAs and gallium ions give the coating outstanding broad-spectrum antibacterial ability. Furthermore, the coating effectively reduces intracellular ROS of osteoblasts. In vitro and in vivo experiments demonstrate the capability of the coating enhancing implants' osseointegration via pro-osteogenesis and inhibiting osteoclastogenesis. The findings imply that gallium (III)-phenolic coating holds great promise to promote implant osseointegration by rescuing abnormal microenvironments of infection, oxidative stress and unbalanced bone homeostasis.

Osteogenesis regulation of mesenchymal stem cells via autophagy induced by silica-titanium composite surfaces with different mechanical moduli.

The high surface elastic modulus of the titanium (Ti) implant is one of the critical factors causing poor osteointegration between the implant surface and surrounding bone tissue. To address this challenge, spherical silica nanoparticles (SSNs) and spherical titania nanoparticles (STNs) with different sizes were synthesized and embedded into Ti surfaces via a micro-arc oxidation (MAO) technique. There were no significant changes in the surface roughness and protein adsorption behaviors before and after the embedding of spherical silica nanoparticles and titania nanoparticles into the Ti implant. However, the surface elastic modulus of Ti-SSNs decreased from 93 GPa to 6.7 GPa, while there was still no change in surface elastic modulus between Ti and Ti-STN groups. In vitro experiments showed that Ti-SSNs, especially Ti-SSN3, significantly stimulated the expression level and nuclear localization of the transcription factor YAP. YAP/TAZ could further inhibit the phosphorylation of AKT and mTOR proteins in MSCs, leading to higher LC3-II protein expression and osteogenic differentiation of MSCs. Ti-SSNs also showed a higher level of autophagosome formation, ALP activity and mineralization capability compared to the other groups. Our results showed that the surface elasticity modulus of an implant plays an important role in the regulation of MSC behaviors. Therefore, designing an implant with an optimal elastic modulus at the surface might have great clinical potential in the bone repair field.

Differentiation regulation of mesenchymal stem cells via autophagy induced by structurally-different silica based nanobiomaterials.

Autophagy is associated with the proliferation and differentiation of mesenchymal stem cells (MSCs). In this study, we investigated the biological impact of silica-based nanobiomateiral-induced autophagy on the differentiation of MSCs, in which the nanoparticulate cues include solid silica nanoparticles (SSN), mesoporous silica nanoparticles (MSN) and biodegradable mesoporous silica nanoparticles (DMSN). The treatment with SSN significantly up-regulated the LC3-II expression via ERK1/2 and AKT/mTOR signaling pathways compared to DMSN and MSN, leading to a higher autophagic activity in MSCs. The enhanced protein adsorption of DMSN and MSN could prevent the direct interaction between cells and nanoparticles, which consequently reduces the autophagic stimulation of MSCs. It should be noted that MSCs exhibited increased differentiation potential when the autophagic activity was enhanced by the treatment with different nanoparticles. In comparison, no difference in the cell differentiation potential was found when an autophagy inhibitor (chloroquine, CQ) was incorporated in all groups. The study may contribute to the development of silica-based nanobiomaterials in the future.

Remote eradication of biofilm on titanium implant via near-infrared light triggered photothermal/photodynamic therapy strategy.

Biofilm formation is a main challenge in treatment of bone-implant-associated infections, resulting in tolerance to immune system and antibiotics. However, smart non-surgical or non-invasive treatment methods of combating established biofilm on an implant have been less reported. Herein, a therapeutic system consisting of mesoporous polydopamine nanoparticles (MPDA) to combat biofilm is reported for the first time. We develop a synergistic photothermal/photodynamic therapy (PTT/PDT) strategy aiming for biofilms eradication on titanium (Ti) implant, which is integrated with MPDA loading with photosensitizer Indocyanine Green (ICG) by π-π stacking. Specifically, MPDA is functionalized with RGD peptide to endow the modified Ti sample (Ti-M/I/RGD) with good cytocompatibility. More importantly, Ti-M/I/RGD implant remarkably kills Staphylococcus aureus (S. aureus) biofilm with an efficiency of 95.4% in vivo upon near infrared (NIR). After biofilm eradication, implant still displays great performance regarding osteogenesis and osseointegration. Overall, this study provides a PTT/PDT strtategy for the development of antibacterial Ti implants for potential orthpediac application.

Biocompatible MoS2/PDA-RGD coating on titanium implant with antibacterial property via intrinsic ROS-independent oxidative stress and NIR irradiation.

To inhibit bacterial infection in situ and improve osseointegration are essentially important for long-term survival of an orthopedic implant, in particular for infection-associating revision surgery. Herein, we fabricate a functional molybdenum disulfide (MoS2)/polydopamine (PDA)-arginine-glycine-aspartic acid (RGD) coating on titanium (Ti) implant to address above concerns simultaneously. The coating not only improved the osteogenesis of mesenchymal stem cells (MSCs), but also endowed Ti substrates with effective antibacterial ability when exposing to near-infrared (NIR) irradiation. It accelerated glutathione (GSH) oxidation via photothermal energy and induced intrinsic ROS-independent oxidative stress damage deriving from MoS2 nanosheets. The results displayed that RGD-decorated MoS2 nanosheets significantly increased the cellular osteogenic behaviors of MSCs via up-regulating osteogenesis-related genes (ALP, Runx2, Col I and OCN) in vitro. Moreover, the functionalized Ti substrates demonstrated great antibacterial efficiency of over 92.6% inhibition for S. aureus and E. coli under NIR-irradiation. Hyperthermia induced by photothermal effect accelerated the GSH consumption and ROS-independent oxidative stress destroyed the integrity of bacteria membranes, which synergistically led to protein leakage and ATP decrease. Furthermore, co-culture experiment showed that S. aureus contamination was efficiently cleaned from MoS2/PDA-RGD surface after NIR photothermal treatment, while MSCs adhered and proliferated on the MoS2/PDA-RGD surface. In an S. aureus infection model in vivo, MoS2/PDA-RGD modified Ti rods killed bacteria with an efficiency of 94.6% under NIR irradiation, without causing damage to normal tissue. More importantly, the MoS2/PDA-RGD modified Ti implants accelerated new bone formation in comparison with TNT implants in vivo.

Multilayered coating of titanium implants promotes coupled osteogenesis and angiogenesis in vitro and in vivo.

We used surface-modified titanium (Ti) substrates with a multilayered structure composed of chitosan-catechol (Chi-C), gelatin (Gel) and hydroxyapatite (HA) nanofibers, which were previously shown to improve osteogenesis, as a platform to investigate the interaction of osteogenesis and angiogenesis during bone healing. Combined techniques of Transwell co-culture, wound healing assay, enzyme linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR), western blotting and immunohistochemical staining were used to evaluate adhesion, morphology and migration of adipose-derived mesenchymal stem cells (Ad-MSCs) and human umbilical vein endothelial cells (HUVECs) grown on different Ti substrates. We investigated the effect of substrates on the osteogenic differentiation of Ad-MSCs and reciprocal paracrine effects of Ad-MSCs on HUVECs or vice versa. The multilayered Ti substrates directly regulated the cellular functions of Ad-MSCs and angiogenic HUVECs and mediated communication between them by enhancing paracrine effects via cell-matrix interactions in vitro. The in vivo results showed that the change of microenvironment induced by surface-modified Ti implants promoted the adhesion, recruitment and proliferation of MSCs and facilitated coupled osteogenesis and angiogenesis in bone healing. The study proved that multilayer-film-coated Ti substrates positively mediated cellular biological function in vitro and improved bone healing in vivo. STATEMENT OF SIGNIFICANCE: Recent studies have revealed that osteogenesis and angiogenesis are coupled, and that communication between osteoblasts and endothelial cells is essential for bone healing and remodeling processes; however, these conclusions only result from in vitro studies or in vivo studies using transgenic murine models. Relatively little is known about the communication between osteoblasts and endothelial cells in peri-implants during bone healing processes. Our results revealed the cellular/molecular mechanism of how multilayered Ti substrates mediate reciprocal paracrine effects between adipose-derived mesenchymal stem cells and human umbilical vein endothelial cells; moreover, the interactions between the cell-matrix and peri-implant was proven in vivo with enhanced bone healing. This study contributes to our understanding of the fundamental mechanisms of angiogenesis and osteogenesis that affect peri-implantation, and thus, provides new insights into the design of future high-quality orthopedic implants.

Peptide LL-37 coating on micro-structured titanium implants to facilitate bone formation in vivo via mesenchymal stem cell recruitment.

Titanium (Ti) and Ti-alloys were widely used in clinic orthopedics, however, the insufficient bone formation surrounding Ti-based implants still limited their biological performances. Surface modification of Ti substrates is essential to improve their interactions with bone-forming cells and bone tissue. In this study, we modified Ti substrates by coating peptide LL-37 onto micro-structured Ti substrates and aimed to (i) induce mesenchymal stem cells (MSCs) migration both in vitro and in vivo, (ii) facilitate osteogenic differentiation of MSCs and new bone formation. The surface micro-structured Ti substrates with hydroxyapatite deposition were fabricated by a two-step method including micro-arc oxidation (MAO) and hydrothermal treatment. LL-37 was loaded on micro-structured Ti substrates with the assistance of polydopamine coating. We confirmed that surface-modified Ti substrates benefited viability, adhesion, migration and osteogenic differentiation of MSCs in vitro. In a femur-defect rat model, the surface-modified Ti implants effectively induced CD29+/CD90+ positive cells migration in one week after implantation. According to the results of H&E, Masson's trichrome staining and immunohistochemical staining of OCN, OPN and collagen I, the targeted Ti implants exhibited significant new bone formation after implantation for 4 weeks. These results indicate that the surface modification of Ti samples facilitated bone formation through MSCs recruitment. STATEMENT OF SIGNIFICANCE: The inherent surface bioinertness of titanium (Ti) and Ti-alloys still limits their biological performances in clinical applications. Recently, the strategy of mesenchymal stem cells (MSCs) recruitment has been proposed to improve the osteointegration of bone implants. Herein, we reports the surface modification of Ti implants from the point of MSCs recruitment. Peptide LL-37 was coated on micro-structured Ti substrates to (i) recruit MSCs, (ii) regulate bio-physiological performance of MSCs, and (iii) facilitate bone formation in vivo. Our results improve the understanding of the interaction between Ti implants and MSCs, and provide a promising strategy of MSCs recruitment in the design of bone repair related biomaterials.