Formation mechanism, degradation behavior, and cytocompatibility of a double-layered structural MAO/rGO-CaP coating on AZ31 Mg

In vitro long-term antibacterial performance and mechanism of Zn-doped micro-arc oxidation coatings

Micro-arc oxidation (MAO) coatings containing 2.86 wt%, 5.83 wt% and 8.81 wt% Zn (Zn-2.86 wt%, Zn-5.83 wt% and Zn-8.81 wt%) were separately fabricated on Ti6Al4V alloys using EDTA-ZnNa2 electrolytes. In vitro antibacterial examination exhibits that the antibacterial rates of Zn-2.86 wt%, Zn-5.83 wt% and Zn-8.81 wt% against Staphylococcus aureus (S. aureus) are 76.0 %, 100.0 % and 99.2 %, respectively. Reactive oxygen species (ROS) level of MAO samples is significantly higher than that of the untreated Ti6Al4V. Zn-containing coatings especially Zn-5.83 wt% induces the strongest oxidative stress on S. aureus due to relatively high released Zn2+ concentration. Moreover, qPCR analysis shows that MAO samples inhibit the icaADBC transcription and result in the down-regulation of PIA production, thereby mitigating biofilm formation. After immersion in simulated body fluid (SBF) for 3, 8 and 14 d, the antibacterial rate of Zn-5.83 wt% is 84.7 %, 63.2 % and 12.5 % respectively, and ROS level of MAO samples is also significantly higher than that of the untreated Ti6Al4V even after 14 d of immersion, suggesting that the antibacterial performance of MAO samples can last a relatively long immersion period and exhibit large application potential in orthopedic clinic.

Surface Modification of WE43 Magnesium Alloys with Dopamine Hydrochloride Modified GelMA Coatings

As biodegradable medical implants, magnesium alloys have attracted great concerns due to their desirable biological and mechanical performances. Nevertheless, the overfast degradation rate of magnesium alloys makes it difficult to make full use of their potential in medical sciences. Therefore, it is a hot issue to control the degradation rate and functionalize the magnesium alloys via surface modifications. Herein, methacrylate gelatin (GelMA) hydrogel was adopted as coatings on the surface of WE43 magnesium alloys to control the degradation behaviors of magnesium alloys. Inspired by mussels, dopamine (DOPA) hydrochloride was adopted to modify GelMA to further functionalize the coatings. The compositions, swelling properties, degradation behaviors, and morphologies of samples were characterized by UV-Vis spectrophotometer, nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and immersion test. It was shown that GelMA-DOPA composites could be obtained and the swelling and degradation behaviors of magnesium alloys could be controlled by adjusting the compositions of GelMA and DOPA. Furthermore, the GelMA-DOPA hydrogel coatings can be tightly bonded to the Mg alloys.

Study on Exosomes Promoting the Osteogenic Differentiation of ADSCs in Graphene Porous Titanium Alloy Scaffolds

Titanium and titanium alloys (Ti₆Al₄V and Ti) have been widely used in bone tissue engineering to repair maxillofacial bone defects caused by traumas and tumors. However, such materials are also bio-inert, which does not match the elastic modulus of bone. Therefore, different surface modifications have been proposed for clinical application. Based on the use of traditional titanium alloy in the field of bone repair defects, we prepared a compound Gr-Ti scaffold with ADSC-derived Exos. The results showed that Gr-Ti scaffolds have low toxicity and good biocompatibility, which can promote the adhesion and osteogenic differentiation of ADSCs. Exos played a role in promoting osteogenic differentiation of ADSCs: the mRNA levels of RUNX2, ALP, and Osterix in the Gr-Ti/Exos group were significantly higher than those in the Gr-Ti group, which process related to the Wnt signaling pathway. Gr-Ti scaffolds with ADSCs and ADSC-derived Exos successfully repaired rabbit mandibular defects. The bone mineral density and the bending strength of the Gr-Ti/Exos group was significantly higher than that of the Gr-Ti group. This study provides a theoretical basis for the research and development of new clinical bone repair materials.

Corrosion Resistance and Cytocompatibility of Magnesium-Calcium Alloys Modified with Zinc- or Gallium-Doped Calcium Phosphate Coatings

In orthopedic surgery, metals are preferred to support or treat damaged bones due to their high mechanical strength. However, the necessity for a second surgery for implant removal after healing creates problems. Therefore, biodegradable metals, especially magnesium (Mg), gained importance, although their extreme susceptibility to galvanic corrosion limits their applications. The focus of this study was to control the corrosion of Mg and enhance its biocompatibility. For this purpose, surfaces of magnesium-calcium (MgCa1) alloys were modified with calcium phosphate (CaP) or CaP doped with zinc (Zn) or gallium (Ga) via microarc oxidation. The effects of surface modifications on physical, chemical, and mechanical properties and corrosion resistance of the alloys were studied using surface profilometry, goniometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nanoindentation, and electrochemical impedance spectroscopy (EIS). The coating thickness was about 5-8 μm, with grain sizes of 43.1 nm for CaP coating and 28.2 and 58.1 nm for Zn- and Ga-doped coatings, respectively. According to EIS measurements, the capacitive response (Y_c) decreased from 11.29 to 8.72 and 0.15 Ω^-1 cm^-2 sⁿ upon doping with Zn and Ga, respectively. The E_corr value, which was -1933 mV for CaP-coated samples, was found significantly electropositive at -275 mV for Ga-doped ones. All samples were cytocompatible according to indirect tests. In vitro culture with Saos-2 cells led to changes in the surface compositions of the alloys. The numbers of cells attached to the Zn-doped (2.6 × 10⁴ cells/cm²) and Ga-doped (6.3 × 10⁴ cells/cm²) coatings were higher than that on the surface of the undoped coating (1.0 × 10³ cells/cm²). Decreased corrosivity and enhanced cell affinity of the modified MgCa alloys (CaP coated and Zn and Ga doped, with Ga-doped ones having the greatest positive effect) make them novel and promising candidates as biodegradable metallic implant materials for the treatment of bone damages and other orthopedic applications.

The Effects of Graphene on the Biocompatibility of a 3D-Printed Porous Titanium Alloy

3D-printed titanium (Ti) materials have attracted much attention in the field of bone tissue repair. However, the combination strength of traditional alloy materials with bone tissue is lower, and the elastic modulus is higher than that of natural bone tissue, which makes the titanium alloy susceptible to stress shielding phenomena after implantation. Therefore, it is urgent to find better surface modification technology. In this study, the physical and chemical properties, toxicity, and proliferation of adipose stem cells of composite graphene-coated titanium alloy (Gr–Ti) were investigated using 3D-printed titanium alloy as a material model. Physical and chemical property tests confirmed that 3D printing could produce porous titanium alloy materials; the compressive strength and elastic modulus of the titanium alloy scaffolds were 91 ± 3 MPa and 3.1 ± 0.4 GPa, matching the elastic modulus of normal bone tissue. The surface characterization shows that graphene can be coated on titanium alloy by a micro-arc oxidation process, which significantly improves the surface roughness of titanium alloy. The roughness factor (Ra) of the Ti stent was 4.95 ± 1.12 μm, while the Ra of the Gr–Ti stent was 6.37 ± 0.72 μm. After the adipose stem cells were co-cultured with the scaffold for 4 h and 24 h, it was found that the Gr–Ti scaffold could better promote the early cell adhesion. CCK-8 tests showed that the number of ADSCs on the G–Ti scaffold was significantly higher than that on the Ti scaffold (p < 0.01). The relative growth rate (RGR) of ADSCs in Gr–Ti was grade 0–1 (non-toxic). In the in vivo experiment of repairing a critical bone defect of a rabbit mandible, the bone volume fraction in the Gr–Ti group increased to 49.42 ± 3.28%, which was much higher than that in the Ti group (39.76 ± 3.62%) (p < 0.05). In conclusion, the porous graphene–titanium alloy promotes the proliferation and adhesion of adipose stem cells with multidirectional differentiation potential, which has great potential for the application of bone tissue engineering in repairing bone defects in the future.