Xiaobing Zhao

The synergistic effect of hierarchical micro/nano-topography and bioactive ions for enhanced osseointegration

Both surface chemistry and topography have significant influence on good and fast osseointegration of biomedical implants; the main goals in orthopeadic, dental and maxillofacial surgeries. A surface modification strategy encompassing the use of bioactive trace elements together with surface micron/nano-topographical modifications was employed in this study in an attempt to enhance the osseointegration of Ti alloy (Ti-6Al-4V), a commonly used implant. Briefly, we developed strontium-substituted hardystonite (Sr-HT) ceramic coating with a hierarchical topography where the nanosized grains were superimposed in the micron-rough coating structure. Its ability to induce new bone formation was evaluated by an in vivo animal model (beagle dogs). Hardystonite (HT), classic hydroxyapatite (HAp) coated and uncoated Ti-alloy implants were parallelly investigated for comparison. In addition, we investigated the effects of surface topography and the dissolution products from the coatings on the in vitro bioactivity using canine bone marrow mesenchymal stem cells (BMMSCs) cultured on the implant surface as well as using extracts of the coated implants. Micro-CT evaluation, histological observations, biomechanical test (push-out test) and sequential fluorescent labeling and histomorphometrical analysis consistently demonstrated that our developed Sr-HT-coated Ti-alloy implants have the highest osseointegration, while the uncoated implants had the lowest. The osseointegration ability of HAp-coated Ti alloy was inferior to that seen for HT- and Sr-HT-coated Ti alloy. We demonstrated that the dissolution products, particularly strontium (Sr) from the Sr-HT-coated implants, enhanced the ALP activity and in vitro mineralization ability, while the micro/nano-topography was more related to the promotion of cell adhesion. Those results suggest that our developed Sr-HT coatings have the potential for future use as coatings for orthopedic/dental and maxillofacial devices.

UV-irradiation-induced bioactivity on TiO2 coatings with nanostructural surface

Titania (TiO2) coatings with nanostructural surface prepared using plasma spraying technology were irradiated by ultraviolet light in simulated body fluids to improve their bioactivity. The in vitro bioactivity of the coatings was evaluated by investigating the formation of apatite on their surfaces in simulated body fluids. Bone-like apatite was observed to precipitate on the UV-irradiated TiO2 coating with nanostructural surface after it was immersed in simulated body fluid for a certain period, but not on the as-sprayed and UV-irradiated TiO2 coatings without nanostructural surface. The results indicate that the nano-TiO2 surface can be activated by UV-irradiation to induce its bioactivity. The ability of apatite formation on the nano-TiO2 surface was improved with the increase of UV-irradiation time. The in vivo results reveal that the as-prepared TiO2 coating with nanostructural surface cannot induce the formation of new bones during the implantation period, but the UV-irradiated TiO2 coating with nanostructural surface could do so during an implantation time longer than 2 months. Our results indicate that the osseointegration ability of the plasma-sprayed TiO2 coating with nanostructural surface can be improved by UV irradiation.

Light-induced bioactive TiO2 surface

We have achieved bioactivity enhancement of nanostructured titania using ultraviolet (uv) light irradiation. The titania coating fabricated by nanoparticle plasma spraying consists of a nano-TiO2 coating surface composed of primarily nanosized anatase. After irradiation by ultraviolet light in air for 24 h, the as-sprayed and UV-irradiated TiO2 coatings were soaked in simulated body fluids (SBF) to investigate their bioactivity. The UV-illuminated TiO2 coating induced bonelike apatite formation on the surface whereas no apatite could be detected on the as-sprayed TiO2 coating. The formation of oxygen vacancies at the two-coordinated bridging sites by UV illumination is believed to result in the conversion of the corresponding Ti4+ sites to Ti3+ sites, which are favorable to the dissociation of water in the SBF and subsequent formation of Ti-OH and an apatite layer. Our results reveal that the surface bioactivity of titania coatings can be induced by UV illumination.

Delicate Refinement of Surface Nanotopography by Adjusting TiO2 Coating Chemical Composition for Enhanced Interfacial Biocompatibility

Surface topography and chemistry have significant influences on the biological performance of biomedical implants. Our aim is to produce an implant surface with favorable biological properties by dual modification of surface chemistry and topography in one single simple process. In this study, because of its chemical stability, excellent corrosion resistance, and biocompatibility, titanium oxide (TiO2) was chosen to coat the biomedical Ti alloy implants. Biocompatible elements (niobium (Nb) and silicon (Si)) were introduced into TiO2 matrix to change the surface chemical composition and tailor the thermophysical properties, which in turn leads to the generation of topographical features under specific thermal history of plasma spraying. Results demonstrated that introduction of Nb2O5 resulted in the formation of Ti0.95Nb0.95O4 solid solution and led to the generation of nanoplate network structures on the composite coating surface. By contrast, the addition of SiO2 resulted in a hairy nanostructure and coexistence of rutile and quartz phases in the coating. Additionally, the introduction of Nb2O5 enhanced the corrosion resistance of TiO2 coating, whereas SiO2 did not exert much effect on the corrosion behaviors. Compared to the TiO2 coating, TiO2 coating doped with Nb2O5 enhanced primary human osteoblast adhesion and promoted cell proliferation, whereas TiO2 coatings with SiO2 were inferior in their bioactivity, compared to TiO2 coatings. Our results suggest that the incorporation of Nb2O5 can enhance the biological performance of TiO2 coatings by changing the surface chemical composition and nanotopgraphy, suggesting its potential use in modification of biomedical TiO2 coatings in orthopedic applications.

Hemocompatibility and antibacterial properties of lanthanum oxide films synthesized by dual plasma deposition

Lanthanum oxide (La(2)O(3)) films with good hemocompatibility and antibacterial properties have been fabricated using dual plasma deposition. X-ray photoelectron spectroscopy (XPS) shows that La exists in the +3 oxidation state. The band gap of the materials is determined to be 3.6 eV. Activated partial thromboplastin time (APTT) and blood platelet adhesion tests were used to evaluate the blood compatibility. The bacteria, Staphylococcus aureus, were used in plate counting tests to determine the surface antibacterial properties. The APTT is a little longer than those of blood plasma and stainless steel (SS). Furthermore, the numbers of adhered, aggregated, and morphologically changed platelets are reduced compared with those on low-temperature isotropic carbon and SS. The antibacterial plate-counting test indicates that La(2)O(3) has good antibacterial activity against S. aureus. These unique hemocompatibility and antibacterial properties make La(2)O(3) useful in many biomedical applications.

Interfacial Reaction-Driven Formation of Silica Carbonate Biomorphs with Subcellular Topographical Features and Their Biological Activity.

We report the interfacial reaction-driven formation of micro/nanostructured strontium carbonate (SrCO3) biomorphs with subcellular topographical features on strontium zinc silicate (Sr2ZnSi2O7) biomedical coatings and explore their potential use in bone tissue engineering. The resulting SrCO3 crystals build a well-integrated scaffold surface that not only prevents burst release of ions from the coating but also presents nanotopographical features similar to cellular filopodia. The surface with biomorphic crystals enhances osteoblast adhesion, upregulates the alkaline phosphatase activity, and increases collagen production, highlighting the potential of the silica carbonate biomorphs for tissue regeneration.

Refining nanotopographical features on bone implant surfaces by altering surface chemical compositions

Surface nanotopographic and chemical modification are the most often used strategies to improve the performance of the currently used implants due to the well-documented effects of nanotopographic features and surface chemistry on the osseointegration of dental and orthopaedic implants. In this study, a dual-modification of surface chemistry and nanotopography was realized in one single process and a correlation between the surface chemistry and nanotopography was found. We used Nb2O5 to change the surface chemical composition of the plasma sprayed TiO2 coatings, which in turn refined the shapes and sizes of nanotopographic features due to the modulation of the rapid solidification process of plasma spraying. The refinement of nanotopographic features is dose-dependent, and the most prominent effect is found at the 50 wt% Nb2O5 doping where a solid solution with a formula of Ti0.95Nb0.95O4 was formed. The introduction of Nb2O5 into the TiO2 matrix also enhanced the corrosion resistance of TiO2 coatings and improved the bonding strength between the coating and the substrate, which are also dose-dependent. Moreover, it was found that cells on the 50 wt% Nb2O5/TiO2 coating with a nanoplate structure showed the highest viability over the culture period. This study demonstrates the potential use of TiO2 coatings doped with Nb2O5 for enhancing the bioactivity of the currently used metallic dental and orthopaedic implants.

Enhanced osteogenic activity of Ti alloy implants by modulating strontium configuration in their surface oxide layers

To guarantee the long-term stability of an orthopaedic implant, non-degradable surface coatings with the ability to selectively release bioactive drugs or ions are especially desirable. In this study, SrO–TiO2 composite coatings were deposited on the surface of Ti alloys, whose release behavior of bioactive Sr ions was modulated by the Sr configurations, either interstitial atoms in solid solution (TiySr2−2yO2) or strontium titanate (SrTiO3). A perfect linear relationship between the amount of the released Sr ions and the Sr content in the coating was observed. Among the SrO-doped TiO2 coatings, the 20% SrO–TiO2 coating where Sr existed in both forms of TiySr2−2yO2 and SrTiO3 not only promoted proliferation of bone cells but also enhanced their osteogenic differentiation, which was proved to be related to its Sr release behavior. However, overdosing with 30% SrO only resulted in one single Sr configuration (SrTiO3) and an inferior osteogenic function. This study suggests that Sr configurations of both interstitial atoms of the solid solution and SrTiO3 can realize the selective release of Sr, but they possibly have different effects on the biological functions and other properties including corrosion resistance.