Enhancing corrosion resistance of biodegradable magnesium with dicalcium phosphate dihydrate and Chlorella sp. biomass

Magnesium shows promise as a material for temporary fixation, yet its rapid corrosion poses health risks due to metal ion release. To mitigate these concerns, a biofunctionalization approach involving dicalcium phosphate dihydrate (DCPD) compounds and Chlorella sp. biomass was employed via electrodeposition, silanization, and dip-coating. Surface characterization using XRD, FTIR, and SEM confirmed successful deposition and immobilization. Corrosion behavior was assessed through electrochemical, immersion, and atomic absorption tests, revealing improved resistance and reduced Mg2+ ion release. The coatings demonstrated significant enhancement in corrosion resistance, guarding against pitting and cracks. The findings suggest the potential of Mg/DCPD and Mg/DCPD/microalgae coatings in addressing corrosion-related risks in temporary fixation applications, promising improved biocompatibility and longevity for medical implants.

HA/MgO nanocrystal-based hybrid hydrogel with high mechanical strength and osteoinductive potential for bone reconstruction in diabetic rats

Bone repair and regeneration processes are markedly impaired in diabetes mellitus (DM). Intervening approaches similar to those developed for normal healing conditions have been adopted to combat DM-associated bone regeneration. However, limited outcomes were achieved for these approaches. Hence, together with osteoconductive hydroxyapatite (HA) nanocrystals, osteoinductive magnesium oxide (MgO) nanocrystals were uniformly mounted into the network matrix of an organic hydrogel composed of cysteine-modified γ-polyglutamic acid (PGA-Cys) to construct a hybrid and rough hydrogel scaffold. It was hypothesized that the HA/MgO nanocrystal hybrid hydrogel (HA/MgO-H) scaffold can significantly promote bone repair in DM rats via the controlled release of Mg²⁺. The HA/MgO-H scaffold exhibited a sponge-like morphology with porous 3D networks inside it and displayed higher mechanical strength than a PGA-Cys scaffold. Meanwhile, the HA/MgO-H scaffold gradually formed a tough hydrogel with G' of more than 1000 Pa after hydration, and its high hydration swelling ratio was still retained. Moreover, after the chemical degradation of the dispersed MgO nanocrystals, slow release of Mg²⁺ from the hydrogel matrix was achieved for up to 8 weeks because of the chelation between Mg²⁺ and the carboxyl groups of PGA-Cys. In vitro cell studies showed that the HA/MgO-H scaffold could not only effectively promote the migration and proliferation of BMSCs but could also induce osteogenic differentiation. Moreover, in the 8th week after implanting the HA/MgO-H scaffold into femur bone defect zones of DM rats, more effective bone repair was presented by micro-CT imaging. The bone mineral density (397.22 ± 16.36 mg cm^-3), trabecular thickness (0.48 ± 0.07 mm), and bone tissue volume/total tissue volume (79.37 ± 7.96%) in the HA/MgO-H group were significantly higher than those in the other groups. Moreover, higher expression of COL-I and OCN after treatment with HA/MgO-H was also displayed. The bone repair mechanism of the HA/MgO-H scaffold was highly associated with reduced infiltration of pro-inflammatory macrophages (CD80⁺) and higher angiogenesis (CD31⁺). Collectively, the HA/MgO-H scaffold without the usage of bioactive factors may be a promising biomaterial to accelerate bone defect healing under diabetes mellitus.

In Vitro and in Vivo Degradation Behavior and Biocompatibility Evaluation of Microarc Oxidation-Fluoridated Hydroxyapatite-Coated Mg-Zn-Zr-Sr Alloy for Bone Application

Magnesium and its alloys are biodegradable materials with great potential for biomedical development; however, their high rate of degradation in biological environments limits the widespread application of these materials. In order to improve the corrosion resistance of magnesium alloy, a functional calcium phosphate coating was prepared on Mg-3Zn-0.5Zr-0.5Sr alloy by microarc oxidation (MAO) combined with chemical deposition of fluoridated hydroxyapatite (FHA). A dense calcium-phosphorus coating 6 μm thick composed of needle-shaped fluoridated hydroxyapatite formed on the surface of the MAO layer. The MAO-FHA coating exhibited good mineralization ability to induce hydroxyapatite deposition on its surface during degradation testing in simulated bodily fluids.

Regulation of osteogenesis and osteoclastogenesis by zoledronic acid loaded on biodegradable magnesium-strontium alloy

Inhibiting osteoclasts and osteoclast precursors to reduce bone resorption is an important strategy to treat osteoclast-related diseases, such as peri-prosthetic osteolysis. In this study, our objective was to study the role of zoledronic acid (ZA), as a highly potent and nitrogen-containing bisphosphonate, in promoting osteogenesis and inhibiting osteoclastogenesis properties of magnesium (Mg)-based implants. ZA was chemically associated with calcium phosphate (CaP) deposited on magnesium-strontium (Mg-Sr) alloy, which was confirmed by the morphological observation, phase composition and drug releasing via SEM, XRD spectrum and High Performance Liquid Chromatography (HPLC), respectively. The in vitro performances indicated that ZA-CaP bilayer coating Mg-Sr alloy could enhance the proliferation and the osteogenic differentiation as well as the mineralization of pre-osteoblasts, however, induce the apoptosis and inhibit the osteoclast differentiation. We further investigated the possible molecular mechanisms by using Quantitative real-time PCR (qRT-PCR) and Western Blotting, and the results showed that ZA-CaP bilayer coating Mg-Sr alloy could regulate the osteogenesis and osteoclastogenesis through the Estrogen Receptor α (ERα) and NF-κB signaling pathway. Moreover, ZA-CaP bilayer coating Mg-Sr alloy could regulate the cross talk of osteoblast-osteoclast and increase the ratio of OPG: RANKL in the co-culture system through OPG/RANKL/RANK signaling pathway, which promoting the balance of bone remodeling process. Therefore, these promising results suggest the potential clinical applications of ZA pretreated Mg-Sr alloys for bone defect repairs and periprosthetical osteolysis due to the excessive differentitation and maturation of osteoclasts.

Manipulating the degradation behavior and biocompatibility of Mg alloy through a two-step treatment combining sliding friction treatment and micro-arc oxidation

Manipulating the degradation rate of biomedical Mg alloys has always been a challenge. In this study, a two-step treatment including sliding friction treatment (SFT) and micro-arc oxidation (MAO) was adopted to acquire a unique Mg-based architecture containing three typical layers comprising a MAO coating/nanocrystalline (NC) layer/coarse-grained (CG) matrix. It was found that the modified topmost MAO coating possessed enhanced corrosion resistance, cytocompatibility and hemocompatibility. The intermediate NC layer sandwiched between the coating and CG matrix was an ideal transition layer capable of avoiding degradation rate upsurge caused by coating breakdown; meanwhile, it provided an effective reinforcing effect on the overall mechanical strength. More importantly, the corrosion resistance of these layers was ranked in the order: MAO coating > NC layer > CG matrix. This kind of gradually increasing corrosion rate of the three layers with depth renders the two-step treatment a promising approach to design Mg-based implants possessing controllable degradation rates.

Effect of High- and Low-Molecular-Weight Hyaluronic-Acid-Functionalized-AZ31 Mg and Ti Alloys on Proliferation and Differentiation of Osteoblast Cells

The quality of patient care has increased dramatically in recent years because of the development of lightweight orthopedic metal implants. The success of these orthopedic implants may be compromised by impaired cytocompatibility and osteointegration. Biomimetic surface engineering of metal implants using biomacromolecules including hyaluronic acid (HA) has been used an effective approach to provide conditions favorable for the growth of bone forming cells. To date, there have been limited studies on osteoblasts functions in response to metal substrates modified with the hyaluronic acid of different molecular weight for orthopedic applications. In this study, we evaluated the osteoblasts functions such as adhesion, proliferation, and differentiation in response to high- and low-molecular-weight HA (denoted as h-HA and l-HA, respectively) functionalized on Ti (h-HA-Ti and l-HA-Ti substrates, respectively) and corrosion-resistant silane coated-AZ31 Mg alloys (h-HA-AZ31 and l-HA-AZ31). The DNA quantification study showed that adhesion and proliferation of osteoblasts were significantly decreased by h-HA immobilized on Ti or AZ31 substrates when compared to low-molecular-weight counterpart over a period of 14 days. On the contrary, h-HA significantly increased the osteogenic differentiation of osteoblast over l-HA, as confirmed by the enhanced expression of ALP, total collagen, and mineralization of extracellular matrix. In particular, the h-HA-AZ31 substrates greatly enhanced the osteoblast differentiation among tested samples (l-HA-AZ31, l-HA-Ti, h-HA-Ti, and Ti alone), which is ascribed to the osteoinductive activity of h-HA, relatively up-regulated intracellular Ca²⁺ ([Ca²⁺]_i) and Mg²⁺ ([Mg²⁺]_i) concentrations as well as the alkalization of the cell culture medium. This study suggesting that HA of appropriate molecular weight can be successfully used to modify the surface of metal implants for orthopedic applications.

Corrosion resistance and bioactivity enhancement of MAO coated Mg alloy depending on the time of hydrothermal treatment in Ca-EDTA solution

In this study, a two-step surface treatment was developed to restrain the rapid primary degradation of a biodegradable Mg alloy and to improve their biocompatibility. Micro arc oxidation (MAO) coating was performed in alkaline electrolytes such as 1.0 M NaOH with 0.1 M glycerol and 0.1 M Na3PO4. Hydrothermal treatment was performed in 0.1 M Ca-EDTA (C10H12CaN2Na2O8) and 0.5 M NaOH solution at 90 °C for different times (6, 12, 24, and 48 h). The film morphology and chemical properties were evaluated by XRD and FE-SEM. The electrochemical and corrosion behaviors were examined in the simulated body fluid, and cytotoxicity was assessed using MC3T3-E1 cells. After MAO coating, an oxide layer containing [Formula: see text] formed on the surface. During the hydrothermal treatment in Ca-EDTA solution, calcium phosphate and Mg(OH)2 were produced via a reaction between [Formula: see text] on the surface and Ca2+ in solution. The layer with ceramics and oxides was grown on the surface with increasing hydrothermal treatment time, and improved the surface corrosion resistance. The 24 h hydrothermal-treated group showed the lowest immersion corrosion rate and high cell viability. Therefore, this treatment was the most favorable surface modification for improving the initial corrosion resistance and bioactivity of the biodegradable Mg alloy.

Sealing the Pores of PEO Coating with Mg-Al Layered Double Hydroxide: Enhanced Corrosion Resistance, Cytocompatibility and Drug Delivery Ability

In recent years, magnesium (Mg) alloys show a promising application in clinic as degradable biomaterials. Nevertheless, the poor corrosion resistance of Mg alloys is the main obstacle to their clinical application. Here we successfully seal the pores of plasma electrolytic oxidation (PEO) coating on AZ31 with Mg-Al layered double hydroxide (LDH) via hydrothermal treatment. PEO/LDH composite coating possess a two layer structure, an inner layer made up of PEO coating (~5 μm) and an outer layer of Mg-Al LDH (~2 μm). Electrochemical and hydrogen evolution tests suggest preferable corrosion resistance of the PEO/LDH coating. Cytotoxicity, cell adhesion, live/dead staining and proliferation data of rat bone marrow stem cells (rBMSCs) demonstrate that PEO/LDH coating remarkably enhance the cytocompatibility of the substrate, indicating a potential application in orthopedic surgeries. In addition, hemolysis rate (HR) test shows that the HR value of PEO/LDH coating is 1.10 ± 0.47%, fulfilling the request of clinical application. More importantly, the structure of Mg-Al LDH on the top of PEO coating shows excellent drug delivery ability.

In vivo Study on the Corrosion Behavior of Magnesium Alloy Surface Treated with Micro-arc Oxidation and Hydrothermal Deposition

OBJECTIVE

To study the corrosion behavior of magnesium alloy surface treated with micro-arc oxidation and hydrothermal deposition in living animals.

METHODS

A magnesium oxide (MgO) layer was prepared on Mg alloy using micro-arc oxidation technology, and then a composite coating composed of magnesium hydroxide, hydroxyapatite, and MgO was coated on the MgO layer using the hydrothermal deposition method for 2 h and 24 h. Male 3-month-old white New Zealand rabbits (n = 48) weighting 2200-2300 g, were divided into four groups randomly. The prepared Mg alloy samples with composite coatings were implanted into the femoral medullary cavity of rabbits. For the Mg group, bare Mg samples without any treatment were implanted; for the MgO group, bare Mg samples undergoing MAO treatment were implanted; for the HT2h group, samples of the MgO group undergoing hydrothermal treatment (HT) for 2 h were implanted; and for the HT24h group, samples of group MgO undergoing HT for 24 h were implanted. Then the in vivo corrosion behaviors of implants were evaluated by X-ray observation, micro-CT analysis and serum Mg2+ examination.

RESULTS

The X-ray showed that samples implanted in animals were decreased as time went by. The micro-CT showed that on the fourth week, the residual volume percentages (RVP) of samples of the Mg, MgO, HT2h, and HT24h groups were 72.81% ± 2.10%, 71.68% ± 1.49%, 81.14% ± 1.54%, and 82.04% ± 0.89%, respectively; on the eighth week, the RVP of four groups were 29.45% ± 1.06%, 41.82% ± 1.13%, 53.92% ± 0.37%, and 62.53% ± 2.06%, respectively; while on the 12th week, RVP were 8.45% ± 0.49%, 9.97% ± 0.75%, 37.09% ± 0.89%, 46.71% ± 1.87%. The RVP of the HT2h group and the HT24h group were higher than for the Mg group and the MgO group for all three time points (P < 0.05); the RVP for HT24h was higher than for HT2h at 8 and 12 weeks, and the differences were significant, indicating that the degradation of Mg alloy slowed down after composite coating. In addition, the composite-coated Mg alloy by 24-h hydrothermal treatment exhibited a slower degradation than that treated by 2 h. Serum Mg2+ concentration results showed that on the second week, the Mg2+ concentrations of the Mg, MgO, HT2h, and HT24h groups were 2.24 ± 0.10 mmol/L, 2.12 ± 0.07 mmol/L, 2.06 ± 0.11 mmol/L, and 2.15 ± 0.12 mmol/L, respectively. On the fourth week, these concentrations were 1.99 ± 0.33 mmol/L, 2.18 ± 0.06 mmol/L, 2.17 ± 0.09 mmol/L, and 2.13 ± 0.14 mmol/L, respectively. On the eighth week, the concentrations were 2.22 ± 0.09 mmol/L, 2.20 ± 0.17 mmol/L, 2.06 ± 0.11 mmol/L, and 2.14 ± 0.07 mmol/L, respectively. On the 12th week, the concentrations were 2.18 ± 0.04 mmol/L, 2.20 ± 0.08 mmol/L, 2.09 ± 0.02 mmol/L, and 2.16 ± 0.11 mmol/L.

CONCLUSION

The combination of micro-arc oxidation and hydrothermal deposition can greatly improve the anti-corrosion behavior of Mg alloy, and Mg alloy coated with this composite coating is a promising biomaterial with a satisfactory degradation rate.

Artificial enamel induced by phase transformation of amorphous nanoparticles

Human tooth enamel has tightly packed c-axis-oriented hydroxyapatite (HAP: Ca10(PO4)6(OH)2) nanorods with high elastic modulus. Fabrication of an enamel architecture in vitro supports the repair of teeth using HAP; however, existing methods require complex and laborious steps to form an enamel-like structure. Here we present a very simple and effective technique for forming artificial enamel in near-physiological solution using a substrate composed of amorphous calcium phosphate (ACP) nanoparticles. Without any functionalized modification of the substrate surface, faint dissolution and successive phase transformation automatically induce formation of an intermediate layer of low-crystalline HAP nanoparticles, on which highly oriented HAP nanorods grow by geometrical selection. We also show that an enamel structure forms on a substrate of amorphous calcium carbonate when the surface nanoparticles react so as to form an intermediate layer similar to that in ACP. Our results demonstrate that there is a wide range of substrate choices for nanorod array formation. Contrary to current understanding, a stable surface designed in nanoscale is not essential for the growth of arranged guest crystals. Reactive amorphous nanoparticles and their transformation efficiently induce a nanorod array structure.

In situ incorporation of heparin/bivalirudin into a phytic acid coating on biodegradable magnesium with improved anticorrosion and biocompatible properties

Drugs were incorporated into a phytic acid coating on Mg by an in situ chemical route for corrosion control and biocompatibility.