Orthopaedic implants, traditionally made from non - 5 degradable materials like titanium and cobalt -chromium alloys, are used to replace lost bone or soft -tissue from various causes, including trauma and disease. These traditional implants often necessitate a second surgery for removal. Biodegradable implants, on the other hand, offer a significant advantage by eliminating the need for 10 additional surgery, as they naturally degrade within the body ov er time. In this article , the properties, biodegradation, bone -regeneration, and the applications of biodegradable Mg-based alloys for orthopaedic implants in biomedical applications are explored. It also discusses the challenges and prospects of biodegradable Mg -based 15 alloys as orthopaedic implants . 1. Introduction Conditions such as bone deformities, nonunion or malunion fractures, massive bone loss, tumors, and far -reaching distressing injuries pose significant clinical challenges as 20 traditional su rgical pro cedures have limited efficiency in treating these disorders. Orthopedic implants are used to compensate for bone or soft tissue damages due to traumas, cancers, infections, amputations, and inflammations, either permanently or temporarily, until they recover 1. Traditional 25 orthopedic metal implants, such as titanium (Ti), cobalt - chromium (Co -Cr) alloys , and Ti alloys cannot be degraded in vivo. How ever, temporary implants are needed to be removed from the body after a certain period 2. Hence, in such conditions , biodegradable implants are helpful as they 30 eliminate the necessity of a second surgery to remove the planted implants. In recent years, there has been an increasing emphasis on the investigation of biodegradable metals, including calcium, zinc, iron, and magnesium as orth opaedic implants due to 35 their suitability as temporary implants. These metals have the capability to reduce the harmful implications related with long -lasting implant materials when used as temporary implan t materials 3. This can result in the prevention of secondary surgeries, thereby accelerating the process of tissue 40 regeneration and minimizing further trauma. One notable example is the use o f magnesium -based biomaterials, which have garnered significant interest due to their low cytotoxicity, low density, excellent biocompatibility, high bioresorbability, and proper mechanical properties 4. 45 This paper explores the properties, fabrication, biological functions, and surface modification of biodegradable Mg - based alloys for orthopaedic implants in biomedical Applications. It also discussed the challenges and prospects of biodegradable Mg -based alloys as orthopedic implants. 50 2. Properties of Magnesium & Its Alloys Mg exhibits an elastic modulus between 40 to 45 GPa, which is close to that of the human bone (15 -25 GPa). Similarly, Mg 55 alloys are exceptionally lightweight with a density between 1.7 4 and 1.84 g/cm , which is close to that of bone (1.8 –2.1 g/cm ) leading to lighter implants and opposing the stress shielding effect 5. Mg and its alloys have a natural ability to biodegrade due to their corrosion susceptibility in aqueous solutions especially if 60 these contain chlorid e ions and its degradation products are non - toxic and osteogenic 6. The most common nutritional alloying elements utilized in biodegradable Mg alloys for orthopaedic implants include calcium(Ca), zinc(Zn), manganese(Mn), strontium(Sr), tin(Sn), 65 and silv er(Ag) 7. The alloying process increases yield strength , ultimate tensi le strength , creep resistance, and strengthens the properties of Mg through grain refinement, precipitation hardening, and solid solution strengthening . Mg also exhibits excellent biocompatib ility. Mg ions (Mg2+) that are released 70 during implan tation and degradation are used in the regular metabolism and, to date, no critical toxic limits or side effects have been reported for Mg2+ ions8. 3. Biodegradation of Magnesium in Vivo Magnesium biodegradation in b iological environments 75 primarily involves electrochemical reactions. When magnesium (Mg) corrodes in aqueous solutions, such as body fluids, it follows an electrochemical degradation mechanism. This process can be summarized by the reaction in equatio n 1 9. This reaction produces magnesium hydroxide (Mg(OH)₂) and hydrogen gas. 80 The magnesium hydroxide forms a slightly effective protective layer on the magnesium surface, which helps to prevent further corrosion to some extent . Mg + 2H₂O → Mg(OH)₂ + H₂ (1) In the presence of chlorine ions, magnesium hydroxide reacts, 85 leading to a local i ncrease in pH value near the host tissue. Besides chlorine ions, b ody fluid also contains calcium and phosphate ions, which trigger the production of compounds such as calcium phosphate and/or calcium magnesium phosphate 10. These compounds form a deposition layer on the magnesium 90 surface, inhibiting further corrosion and pH increase. Additionally, body fluids contain organic components like proteins, cells, and even bacteria, which can adhere to the Mg surface, affecting its dissolution behaviour 11. However, magnesium alloys often suffer from pitting corrosion 95 in chloride solutions, including body fluids. Pits formed are common initiation sites for crack formation and stress corrosion cracking (SCC). The hydrogen released from magnesium corroding in body fluids plays a significant role in corrosion - assisted cracking, as crack initiation and propagation are 100 supported by hydro gen adsorption and diffus ion into the material . Although the degradation product of pure Mg in the body is nontoxic, and the degr adation product Mg2+ can also pro mote bone regeneration, too fast degradation of Mg implants in the body can easily lead to failure of fracture treatmen t 12. Therefore , 105 enhancing the corrosion resistance of Mg implants is vital for prolonging their fixation time in vivo. 4. Role of Magnesium in Bone Regeneration Mg and Mg and its alloys are considered excellent materials for bone defect repair due to their superior biodegradation, 5 biocompatibility, adequate elastic modulus as well as the osteoinductive activity of their degradation products 13. Mg is a crucial element in the construction of soft tissue and bone, being involved in numerous biochemical reactions. It is essential for the human body, with a recommended intake of 310 –420 mg of Mg 10 ions daily for healthy adults 14. Bone recons truction is a complex process requiring the coordination of multiple stem cells within a suitable microenvironment. Research has shown that Mg and its alloys impact various kinds of osteogenic cells, promoting their differentiation and aiding in bone regeneration 15 16. The proper 15 Mg ion content in bone tissue is critical for maintaining its mechanical properties. A decrease in Mg ion content can weaken the bone tissue, increasing fragility and the risk of fractures 17 18. Mg also plays a significant role in promoting angiogenesis during bone regeneration. Bone, being a dynamic, complex, 20 heterogeneous, and highly vascularized tissue, requires the coordination of various processes for regeneration 19. Mg aids in this process through its effect on bone tissue and vascular networks by increase the expression levels of angiogenic biomarkers 20, enhanc ing the migration and invasion capabilities 25 of human umbilical vein endothelial cell s 21. It also promot es epithelialmesenchymal transition and cytoskeletal reorganization and stimulat es proliferation and migration and sensitizes microvascular cell 22. 5. Applications 30 The integration of magnesium (Mg) -based alloys in the fabrication of Orthopaedic devices marks a notable advancement in biomedical applications . Mg-based alloys are used to manufacture a range of orthopaedic devices, including fixation plates, screws, and intramedullary ho ok pins each designed for 35 specific types of bone fractures and surgical reconstructions 23. These devices are designed to cater to a diverse set of fractures, such as those occurring in the femur, tib ia, and osteoporotic bones, as well as for ultra fractures. Fixation plates and screws, essential for stabilizing fractures especially in load -bearing bones 40 such as the femur and tibia, are crafted to align wit h bone contours, ensuring effective healing. Mg-based implants are particularly beneficial for osteoporotic fractures, common in older adults, due to their biocompatibility and bone regeneration capabilities24. These 45 properties help overcome challenges associated with reduced bone density, promoting effective healing, and minimizing the risk of recurrent fractures. They are also used to c ruciate ligament reconstruction and fix tibia and femur cavities as well as femoral and ultra fra ctures. This is because it promotes new bone tissue 50 form ation, good osseointegration , and effectively inhibit s graft degradation and improved biomechanical properties of tendon graft during the early phase of g raft healing 25. Overall, these alloys in orthopaedic device s represen t a comprehensive approach to treating bone fractures and reconstructions, thus 55 making them invaluable in modern orthopaedic surgery. 6. Challenges of Magnesium Alloy Based Implants Despite the superior biodegradability , biocompatibility and the suitable mechanical compatibility of Mg& Mg based alloys for orthopaedic applications, . However, there are some 60 challenges currently impeding its development and this is majorly due to its high corrosion rate in the complex physiological environment 26. This rapid corrosio n, especially at physiological pH values (7.4 –7.6) and high chloride concentrations, leads to the quick conversion of Mg hydroxide to soluble Mg chloride which 65 results in several problems . Firstly, the mechanical integrity of Mg alloy implants deteriorates too quickly, reaching inadequate mechanical properties before sufficient healing of the host tissue. The chloride environment and Mg ions from anodic dissolution species accelerate pitting corrosion, which can induce high 70 localized stresses and lead to cr ack formation 27. Moreover, r apid corrosion is associated with the release of hydrogen gas and these hydrogen bubbles can accumulate near the implant in gas pockets in the human body. This can delay healing and potentially lead to tissue necrosis due to the 75 separation of tissues an d tissue layers 28. Also, dissolution of Mg significantly increases the pH near the implant surface. Though the body attempts to regulate pH balance, local alkalization around a rapidly corroding Mg implant is inevitable. This can negatively impact pH -dependent physiological reactions and 80 potentially lead to alk aline poisoning if the regional in vivo pH exceeds 7.8 29. Thus, a ddressing these challenges is crucial for the successful clinical application of Mg biodegradable implants. 7. Conclusion and Future Prospects In conclusion, magnesium and magnesi um-based alloys are 85 promising for bone replacement due t o their similar Young's modulus to human bone, sufficient strength, and excellent biocompatibility and biodegradability. These properties make Mg ideal for bone regeneration. However, using Mg in physiological environments is challenging, necessitating the 90 research and development of Mg scaffolds that are mechanically stable and corrode at a controlled rate. Despite magnesium (Mg) and its alloys showing promise in clinical applicat ions, there's still a sh ortage of extensive clinical studies. Further long -term biosafety assessments are 95 needed to determine the most suitable candidates for Mg - based implant use. Additionally, developing Mg -infused polymer or ceramic scaffolds could enhance healing in significant bone defects by stimulating new bone growth with bioactive Mg ions. Investigating Mg hybrid systems could 100 broaden their clinical applications. Combining M g-based implants with inert metals could also widen their usage. Finally, i ntegrating various im plant processing technologies, like additive manufacturi ng, represents a future research avenue for Mg and Mg alloy medical implants. 105