In the field of bone tissue engineering, recently developed Zn alloy scaffolds are considered potential candidates for biodegradable implants for bone regeneration and defect reconstruction. However, the clinical success of these alloys is limited due to their insufficient surface bioactivities. Further, the higher concentration of Zn²⁺ produced during degradation promotes antibacterial activity, but deteriorates osteogenic properties. This study fabricated an Azadirachta indica (neem)-assisted brushite-hydroxyapatite (HAp) coating on the recently developed Zn-2Cu-0.5Mg alloy to tackle the above dilemma. The microstructure, degradation behavior, antibacterial activity, and hemocompatibility, along with in vitro and in vivo cytocompatibility of the coated alloys, are systematically investigated. Microstructural analysis reveals flower-like morphology with uniformly grown flakes for neem-assisted deposition. The neem-assisted deposition significantly improves the adhesion strength from 12.7 to 18.8 MPa, enhancing the mechanical integrity. The potentiodynamic polarization study shows that the neem-assisted deposition decreases the degradation rate, with the lowest degradation rate of 0.027 mm/yr for the ZHN2 sample. In addition, the biomineralization process shows the apatite formation on the deposited coating after 21 days of immersion. In vitro cytotoxicity assay exhibits the maximum cell viability of 117% for neem-assisted coated alloy in 30% extract after 5d and the improved cytocompatibility which is due to the controlled release of Zn²⁺ ions. Meanwhile, neem-assisted coated alloy increases the ZOI by 32 and 24% for Gram-positive and Gram-negative bacteria, respectively. Acceptable hemolysis (<5%) and anticoagulation parameters demonstrate a promising hemocompatibility of the coated alloy. In vivo implantation illustrates a slight inflammatory response and vascularization after 2 weeks of subcutaneous implantation, and neo-bone formation in the defect areas of the rat femur. Micro-CT and histology studies demonstrate better osseointegration with satisfactory biosafety response for the neem-assisted coated alloy as compared to that without neem-assisted deposition. Hence, this neem-assisted brushite-Hap coating strategy elucidates a new perspective on the surface modification of biodegradable implants for the treatment of bone defects.

中文翻译：

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用于生物医学应用的可生物降解锌合金上的绿色辅助磷酸钙涂层的可行性见解：体外和体内研究

在骨组织工程领域，最近开发的锌合金支架被认为是用于骨再生和缺损重建的可生物降解植入物的潜在候选者。然而，由于表面生物活性不足，这些合金的临床成功受到限制。此外，降解过程中产生的较高浓度的Zn ²⁺促进了抗菌活性，但劣化了成骨特性。本研究在最近开发的 Zn-2Cu-0.5Mg 合金上制备了印楝(neem) 辅助透钙磷石-羟基磷灰石 (HAp) 涂层，以解决上述困境。对涂层合金的微观结构、降解行为、抗菌活性和血液相容性以及体外和体内细胞相容性进行了系统研究。微观结构分析揭示了花状形态，具有均匀生长的薄片，用于印楝辅助沉积。印楝辅助沉积将粘合强度从 12.7 MPa 显着提高到 18.8 MPa，从而增强了机械完整性。动电位极化研究表明，印楝辅助沉积降低了降解速率，ZHN2 样品的最低降解速率为 0.027 毫米/年。此外，生物矿化过程显示，浸泡 21 天后，沉积涂层上形成了磷灰石。体外细胞毒性测定显示，印楝辅助涂层合金在30%提取物中5天后的最大细胞活力为117%，并且由于Zn ²⁺离子的受控释放而改善了细胞相容性。同时，印楝辅助涂层合金使革兰氏阳性菌和革兰氏阴性菌的 ZOI 分别提高了 32% 和 24%。可接受的溶血（<5%）和抗凝参数表明涂层合金具有良好的血液相容性。体内植入显示皮下植入两周后出现轻微的炎症反应和血管化，以及大鼠股骨缺损区域的新骨形成。显微 CT 和组织学研究表明，与没有印楝辅助沉积的合金相比，印楝辅助涂层合金具有更好的骨整合和令人满意的生物安全响应。因此，这种印楝辅助透钙磷石-Hap涂层策略阐明了用于治疗骨缺损的可生物降解植入物表面改性的新视角。