Traditional alloying strategies for enhancing the corrosion resistance of biodegradable Mg alloys often face challenges in achieving a balance between biocompatibility and corrosion control. This study exploited the adsorption of ZrO₂ onto the calcium phosphate (Ca-P) layer to enhance the long-term corrosion resistance of a Mg alloy. The addition of trace Zr facilitated the thickening of the Ca-P salts adsorption layer formed during degradation. The results showed that Mg-Zn-Nd-Zr alloy with diffusely distributed nano Zr-rich phase presented higher corrosion rate in the short-term immersion due to the galvanic corrosion between the Zr-rich phases and the ɑ-Mg substrate. However, enhanced long-term corrosion resistance was observed, which is attributed to the presence of Zr. Nano Zr-rich phase facilitated the adsorption and deposition of Ca-P compounds, resulting in the formation of a more homogenous protective layer. And the Ca:P (atom ratio) is 1.54, close to that of hydroxyapatite structure. This study proposed and verified a new method to enhance the long-term corrosion resistance of biomedical Mg alloys, promising for future application.

Regarding the current materials used for suture anchors for rotator cuff repair, there are still limitations in terms of degradability, mechanical properties, and bioactivities in clinical applications. Magnesium alloys have preliminarily been shown to promote tendon-bone healing with good prospects for application as anchor materials. However, the design of anchor structures for the degradation characteristics of magnesium alloy materials has not been considered, which is critical for the practical application of magnesium alloy anchors. The mechanism by which magnesium promotes tendon bone healing remains to be clarified. Here, we proposed a novel split hollowed magnesium alloy suture anchors for the repair of rabbit rotator cuff injury. We found that novel split hollowed magnesium alloy anchors structure effectively solved the problem of failure due to degradation of traditional eyelet structure, providing reliable suture fixation. The open architecture facilitates the metabolic resorption of the degradation products of and promotes the ingrowth of bone tissue. Histological staining showed that magnesium anchors have better ability to promote regeneration at the fibrocartilage interface compared to PLLA anchors. The higher expression of fibrocartilage markers (Aggrecan, COL2A1, and Sox9) at the tendon-bone interface in magnesium anchors, which promotes chondrocyte differentiation at the tendon-bone interface and matrix formation, which is more conducive to achieving regeneration and maturation of fibrocartilage enthesis. Hence, this study provides a basis for further research on the clinical application of degradable magnesium alloy suture anchors.

Traditional designs and developments of bone biomaterials mostly concentrate on the positive regulation of osteoblast lineage cells, but often ignore the importance of immune responses and the equilibrium between bone resorption mediated by osteoclasts and bone formation mediated by osteoblasts. Immune dysregulation is associated with an imbalance between pro-inflammatory and anti-inflammatory processes, which may influence the efficacy of bone therapy. Therefore, implanted biomaterials should appropriately and precisely modulate subsequent immune responses. Magnesium (Mg) has been used to fabricate various Mg alloys for bone repair because of its favorable attributes such as osteogenic potential, immune regulation characteristics, biodegradability, and biocompatibility. Various basic research and clinical trials have been already conducted in many countries to explore the physical properties of Mg-containing implants and their clinical outcomes in bone fracture and defect repair. Therefore, this review summarizes the immune response to Mg-containing implants, and further organizes the current research and development progress of Mg-containing implants. The review aims to offer an overview of the current knowledge on immunomodulation of Mg-containing implants and future challenges in their clinical application, which could provide further insight in the development of better strategies for the treatment of bone defect and fracture.

Interbody fusion is recognized as the golden standard of surgical intervention for degenerative disc disease (DDD). Interbody fusion cage made of polyetheretherketone (PEEK) is commonly used in lumbar interbody fusion surgery in the treatment of DDD worldwide. However, there are some limitations of PEEK including their bio-inert nature and impediment to host bone integration. This study aimed to evaluate the degradation profile and osteoinductive potential of biodegradable Mg-Zn-Nd-Zr cages with/without micro-arc oxidation (MAO) coatings. The Mg-Zn-Nd-Zr alloy cages, whether coated with MAO or not, demonstrated commendable biocompatibility and biomechanical properties. Immersion and electrochemical tests show better corrosion resistance of MAO coatings in vitro. mRNA sequencing, RT-qPCR and Western blotting revealed that Mg-Zn-Nd-Zr and Mg-Zn-Nd-Zr/MAO had a better effectiveness on osteoinductivity. In vivo evaluations in ovine models over 12 weeks and 24 weeks post-implantation revealed radiological and histological evidence of enhanced bone formation adjacent to the Mg-Zn-Nd-Zr alloy cages compared to PEEK counterparts. Moreover, the MAO-coated cages exhibited a reduced propensity for gas formation. The Mg-Zn-Nd-Zr alloy is as a superior osteoinductive material compared with PEEK, with the MAO coating offering an advantage in mitigating gas production. Nonetheless, further research is warranted to refine the alloy’s composition or surface treatments, particularly to address the challenges associated with rapid gas evolution during the early post-implantation period.

Biodegradable magnesium-matrix composites (BMMCs) added with bone-like compounds such as hydroxyapatite (HA) have promising orthopedic application potential, but the in vivo results of BMMCs are insufficient, and the difference between in vitro and in vivo are not clarified. In this work, Mg-Zn-Nd-Zr/(10/15/20wt%) HA (Ca₁₀(PO₄)₆OH₂) composites were prepared through friction stirring processing (FSP). It was found that corrosion rate of the composites increased with increase of the HA content, where the corrosion rate from hydrogen evolution of the Mg/10wt% HA was about 0.107 mm/y, showing better corrosion resistance compared with other BMMCs, and the agglomeration of HA powders significantly aggravated the localized corrosion. The ALP specific activity of the MC3T3-E1 cells cultured for 14 days with Mg/10wt% HA (2.12 IU/mg) was higher than that of the matrix (1.85 IU/mg), but there was no difference with the FSP group (2.13 IU/mg). In the early implantation of the rabbit femur, bone volume fraction (BV/TV) of Mg/10wt% HA was 10.69, which was higher than that of the FSP group (6.35). The histological staining showed that the Mg/10wt% HA implant was surrounded by more trabecular bone tissue, exhibiting better osteoinductive regeneration. The Mg-Zn-Nd-Zr/HA composites exhibit higher osteogenic activity in vivo differently from in vitro osteogenic expression.

Magnesium (Mg) alloys have attracted a wealth of attention in orthopedic fields for their superior mechanical properties, degradability, and excellent biocompatibility. Consistently, to resolve the issues on rapid degradation, more studies are dedicated to the researches on the composition design, preparation and processing, surface modification, the degradation modes of Mg alloys. Nevertheless, the mechanisms by which Mg alloys promote bone healing remain elusive. This review gives an account of specific mechanisms on Mg alloys promoting bone healing from four aspects, immunomodulatory, angiogenesis, osteogenesis and regulation of osteoclast function. We highlight the regulation of Mg alloys on the functional status and interactions of numerous cells that are involved in bone healing, including immune cells, osteogenic-related cells, osteoclasts, endothelial cells (ECs), nerve cells, etc., and summarize the signaling pathways involved, with the aim to provide the basis and support on future investigation on mechanisms on Mg alloys driving bone regeneration. More importantly, it provides a rationale and a general new basis for the application of Mg alloys in orthopedic fields.

Despite transosseous rotator cuff tear repair using sutures is widely accepted for tendon-bone fixation, the fibrocartilaginous enthesis regeneration is still hardly achieved with the traditional sutures. In the present work, degradable magnesium (Mg) alloy wire was applied to suture supraspinatus tendon in a rat acute rotator cuff tear model with Vicryl Plus 4–0 absorbable suture as control. The shoulder joint humerus-supraspinatus tendon complex specimens were retrieved at 4, 8, and 12 weeks after operation. The Mg alloy suture groups showed better biomechanical properties in terms of ultimate load to failure. Gross observation showed that hyperplastic response of the scar tissue at the tendon-bone interface is progressively alleviated over time in the both Mg alloy suture and Vicryl suture groups. In the histological analysis, for Mg alloy suture groups, chondrocytes appear to proliferate at 4 weeks postoperatively, and the tendon-bone interface showed an orderly structural transition zone at 8 weeks postoperatively. The collagenous fiber tended to be aligned and the tendon-bone interlocking structures apparently formed, where transitional structure from unmineralized fibrocartilage to mineralized fibrocartilage was closer to the native fibrocartilaginous enthesis. In vivo degradation of the magnesium alloy wire was completed within 12 weeks. The results indicated that Mg alloy wire was promising as degradable suture with the potential to promotes fibrocartilaginous interface regeneration in rotator cuff repair.