Enhanced Adsorption Stability and Biofunction Durability with Phosphonate-Grafted, PEGylated Copolymer on Hydroxyapatite Surface.

Nonfouling surfaces are crucial in applications such as biosensors, medical implants, marine coatings, and drug delivery vehicles. However, their long-term coating stability and robust surface binding strength in physiological media remain challenging. Herein, a phosphonate-grafted, PEGylated copolymer on the hydroxyapatite (HA) surface is proposed to significantly improve the adsorption stability and thus enhance the biofunction durability accordingly. The phosphoryl (-PO3) grafted branch is employed in the functional polymer to facilitate attaching to the HA substrate. In addition, the polymer integrates the nonfouling polymer brushes of poly(ethylene glycol) (PEG) with the cell-adhesive moiety of cyclic Arg-Gly-Asp-d-Phe-Cys peptides (cRGD). A systematic study on the as-synthesized PEGylated graft copolymer indicates a synergistic binding mechanism of the NH2 and PO3 groups to HA, achieving a high surface coverage with desirable adsorption stability. The cRGD/PEGylated copolymers of optimized grafting architecture are proven to effectively adsorb to HA surfaces as a self-assembled copolymer monolayer, showing stability with minimal desorption even in a complex, physiological medium and effectively preventing nonspecific protein adsorption as examined with X-ray photoelectron spectroscopy (XPS) and a quartz crystal microbalance with dissipation (QCM-D). Direct adhesion assays further confirm that the enhanced coating stability and biofunction durability of the phosphonate-grafted, cRGD-PEGylated copolymer can considerably promote osteoblast attachment on HA surfaces, meanwhile preventing microbial adhesion. This research has resulted in a solution of self-assembly polymer structure optimization that exhibits stable nonfouling characteristics.

Plasma sprayed cerium oxide coating inhibits H2O2-induced oxidative stress and supports cell viability.

Oxidative stress is a risk factor in the pathogenesis of osteoporosis, and plays a major role in bone regeneration of osteoporotic patients. Cerium oxide (CeO2) ceramics have the unique ability to protect various types of cells from oxidative damage, making them attractive for biomedical applications. In this study, we developed a plasma sprayed CeO2 coating with a hierarchical topography where ceria nanoparticles were superimposed in the micro-rough coating surface. The protective effects of the CeO2 coating on the response of osteoblasts to H2O2-induced oxidative stress have been demonstrated in terms of cell viability, apoptosis and differentiation. The CeO2 coating reversed the reduced superoxide dismutase activity, decreased reactive oxygen species production and suppressed malondialdehyde formation in H2O2-treated osteoblasts. It indicated that the CeO2 coating can preserve the intracellular antioxidant defense system. The cytocompatibility of the CeO2 coating was further assessed in vitro by cell viability assay and scanning electron microscopy analysis. Taken together, the CeO2 coating could provide an opportunity to be utilized as a potential candidate for bone regeneration under oxidative stress.

Effects of composition and hierarchical structures of calcium phosphate coating on the corrosion resistance and osteoblast compatibility of Mg alloys.

Magnesium and its alloys have been recently used in biomedical applications such as orthopedic implants, whereas the weak corrosion resistance undermines their clinical efficacy. Herein, to address this critical challenge, the preparation of hierarchically structured hydroxyapatite-based coatings was proposed. Compact coatings were fabricated on a Mg alloy through a facile two-step method of chemical deposition of brushite precursor and subsequent hydrothermal conversion. A series of HA-based coatings were obtained with kinetic conversion process with formation mechanism revealed. The hydroxyapatite coating demonstrated the greatest corrosion resistance for Mg in electrochemical and long-term immersion tests, especially against pitting corrosion, attributable to its compact structure, alkaline degradation environment and self-induced growth capacity. The in vitro cytocompatibility and osteoinductivity were dictated. Additionally, anti-corrosion mechanisms were compared among different coating compositions and structures, along with their correlation with cellular response. Our study brings hints for a tailored surface design for resorbable biomedical device applications.

Incorporation of Cerium Oxide into Hydroxyapatite Coating Protects Bone Marrow Stromal Cells Against H2O2-Induced Inhibition of Osteogenic Differentiation.

Oxidative stress exerts a key influence in osteoporosis in part by inhibiting osteogenic differentiation of bone marrow stromal cells (BMSCs). With their unique antioxidant properties and reported biocompatibility, cerium oxide (CeO2) ceramics exhibit promising potential for the treatment of osteoporosis resulting from oxidative stress. In this study, protective effects of CeO2-incorporated hydroxyapatite coatings (HA-10Ce and HA-30Ce) on the viability and osteogenic differentiation of H2O2-treated BMSCs were examined. CeO2-incorporated HA coatings enhanced cell viability and attenuated cell apoptosis caused by H2O2. An increase in CeO2 content in HA coatings better alleviated H2O2-induced inhibition of osteogenic differentiation by increasing alkaline phosphatase (ALP) activity, calcium deposition activity, and mRNA expression levels of osteogenesis markers runt-related transcription factor 2 (Runx2), ALP, and osteocalcin (OCN) in BMSCs. Furthermore, the H2O2-induced decrease of gene and protein expressions of ß-catenin and cyclin D1 in the Wnt/ß-catenin signaling pathway was successfully rescued by the CeO2 incorporated HA coatings. Besides, the decreased expression of receptor activator of nuclear factor kappa-B ligand (RANKL) and the increased ratio of osteoprotegerin (OPG)/RANKL in BMSCs on the CeO2-modified coatings was observed, indicating the inhibition of osteoclastogenesis. The above results were mediated by the antioxidant properties of CeO2. The CeO2-incorporated HA coatings reversed the decreased superoxide dismutase (SOD) activity, reduced reactive oxygen species (ROS) generation, and suppressed the malondiadehyde (MDA) formation. The findings suggested that CeO2-modified HA coatings may be promising coating materials for osteoporotic bone regeneration.

Incorporation of cerium oxide into hydroxyapatite coating regulates osteogenic activity of mesenchymal stem cell and macrophage polarization.

Biomedical coatings for orthopedic implants should facilitate osseointegration and mitigate implant-induced inflammatory reactions. Cerium oxide (CeO2) ceramics possess anti-oxidative properties and can be used to decrease mediators of inflammation, which makes them attractive for biomedical applications. In our work, two kinds of CeO2 incorporated hydroxyapatite coatings (HA-10Ce and HA-30Ce) were prepared via plasma spraying technique and the effects of CeO2 addition on the responses of bone mesenchymal stem cells (BMSCs) and RAW264.7 macrophages were investigated. An increase in CeO2 content in the HA coatings resulted in better osteogenic behaviors of BMSCs in terms of cell proliferation, alkaline phosphatase (ALP) activity and mineralized nodule formation. RT-PCR and western blot analysis suggested that the incorporation of CeO2 may promote the osteogenic differentiation of BMSCs through the Smad-dependent BMP signaling pathway, which activated Runx2 expression and subsequently enhanced the expression of ALP and OCN. The expression profiles of macrophages cultured on the CeO2 modified coating revealed a tendency toward a M2 phenotype, because of an upregulation of M2 surface markers (CD163 and CD206), anti-inflammatory cytokines (TNF-α and IL-6) and osteoblastogenesis-related genes (BMP2 and TGF-ß1) as well as a downregulation of M1 surface markers (CCR7 and CD11c), proinflammatory cytokines (IL-10 and IL-1ra) and reactive oxygen species production. The results suggested the regulation of BMSCs behaviors and macrophage-mediated responses at the coating's surface were associated with CeO2 incorporation. The incorporation of CeO2 in HA coatings can be a valuable strategy to promote osteogenic responses and reduce inflammatory reactions.

The Effects of Cerium Valence States at Cerium Oxide Coatings on the Responses of Bone Mesenchymal Stem Cells and Macrophages.

Ideal orthopedic coatings should trigger good osteogenic response and limited inflammatory response. The cerium valence states in ceria are associated with their anti-oxidative activity and anti-inflammatory property. In the study, we prepared two kinds of plasma sprayed CeO2 coatings with different Ce4+ concentrations to investigate the effects of Ce valence states on the response of bone mesenchymal stem cells (BMSCs) and macrophage RAW264.7. Both the coatings (CeO2-A and CeO2-B) were characterized via XRD, SEM, and X-ray photoelectron spectroscopy. The CeO2 coatings enhanced osteogenic behaviors of BMSCs in terms of cellular proliferation, alkaline phosphatase (ALP) activity and calcium deposition activity in comparison with the Ti substrate. In particular, the CeO2-B coating (higher Ce4+ concentration) elicited greater effects than the CeO2-A coating (higher Ce3+ concentration). RT-PCR and western blot results suggested that the CeO2-B coating promoted BMSCs osteogenic differentiation through the SMAD-dependent BMP signaling pathway, which activated Runx2 expression and subsequently enhanced the expression of ALP and OCN. With respect to either CeO2-A coating or Ti substrate, the CeO2-B coating exerted greater effects on the macrophages, increasing the anti-inflammatory cytokines (IL-10 and IL-1ra) expression and suppressing the expression of the pro-inflammatory cytokines (TNF-α and IL-6) and ROS production. Furthermore, it also upregulated the expression of osteoinductive molecules (TGF-ß1 and BMP2) in the macrophages. The regulation of cerium valence states at plasma sprayed ceria coatings can be a valuable strategy to improve osteogenic properties and alleviate inflammatory response.

Cerium Oxide-Incorporated Calcium Silicate Coating Protects MC3T3-E1 Osteoblastic Cells from H2O2-Induced Oxidative Stress.

Oxidative stress regulates cellular functions in multiple pathological conditions, including bone formation by osteoblastic cells. In this work, the protective effects of cerium oxide (CeO2)-incorporated calcium silicate (CeO2-CS) coating on the response of osteoblasts to H2O2-induced oxidative stress and the related mechanism were examined. CeO2 incorporation significantly improved osteoblast viability and reduced cell apoptosis caused by H2O2 when compared with the control. H2O2-induced reduction of differentiation marker alkaline phosphatase (ALP) was recovered in the presence of the CeO2-CS coating. The above effects were mediated by the antioxidant effect of CeO2. The CeO2-CS coating immersed in 0.1 mM H2O2 aqueous solution was able to degrade 64 % of it in 1 week. In addition, CeO2 incorporation decreased reactive oxygen species (ROS) production and suppressed malondialdehyde (MDA) formation in H2O2-treated osteoblasts. Taken together, CeO2-CS biomedical coatings with antioxidant property would be promising for bone regeneration under oxidative stress.