Biomimetic bone-like regeneration potentiality and strength development of Mg-Zn-Ca alloys for maxillofacial application

Abstract

BACKGROUND: This study evaluated the potential for biomimetic new bone regeneration synchronized with developing strength when the Zn proportion was increased in Mg-Zn-Ca alloys (Mg1Zn0.6Ca and Mg6Zn0.6Ca alloys). METHODS: Two types of magnesium (Mg) alloys, Mg1Zn0.6Ca and Mg6Zn0.6Ca, with a total of 100 samples (n = 50/group), were studied. The groups were divided into subgroups (n = 10/group) A; subjected to electrochemical corrosion, (B, C, and D) subgroups were biomimetic immersed in SBF for different time intervals (2,4,and 8weeks), receptively, to assess the degradation/regeneration rate. Another subgroup (n = 10/group) were used as control for initial flexural strength test. Changes in weight were recorded, and surface chemistry was analyzed through X-ray diffraction (XRD) and FTIR. Surface morphology changes were examined via environmental scanning electron microscopy (SEM) and EDXA. The formation of new bone was estimated by assessing mineral content, crystallinity, hydroxyapatite (HA) maturity, matrix amount, and the calcium/phosphorus (Ca/P) ratio. Additionally, surface roughness (Ra) and flexural strength before and after the biomimetic immersion in SBF at different intervals were measured. RESULTS: Mg1Zn0.6Ca (Group I) demonstrated controlled long-term degradation; weight loss corrosion rate reduced from 1.81 to 0.26 mm/year over 8 weeks, mature HA formation (65.5% crystallinity, 161% crystal maturity by 8 weeks), the Ca/P ratio increased from 0.29 ± 0.03 to 0.68 ± 0.03 and preserved mechanical competence (88.75 ± 0.03 MPa flexural strength). On the other hand, Mg6Zn0.6Ca (Group II) showed rapid initial passivation (Ra ∼4.87 μm at 2 weeks) but unsustainable performance because of premature embrittlement (50.87 ± 0.03 MPa), immature HA (44% maturity, 37.7% crystallinity decline), the Ca/P ratio dropped from 1.42 ± 0.03 to 0.35 ± 0.03 and persistent high degradation (~ 2 mm/year). Electrochemical corrosion revealed that group II showed a higher corrosion potential (Ecorr), Icorr, and corrosion rate value than group I. Group II (Mg6Zn0.6Ca) showed a higher biodegradation rate (about 7.37 ± 0.02 mm/year) and higher surface roughness than group I (Mg1Zn0.6Ca) over time. CONCLUSIONS: Mg1Zn0.6Ca (Group I) shows superior biomimetic synchronization for maxillofacial bone regeneration, achieving controlled long-term degradation, as it revealed a controlled degradation with stable hydroxyapatite formation that promotes osteointegration and sustained mechanical strength. It is recommended to be used in short and long-lasting load-bearing maxillofacial appliances. In contrast, Mg6Zn0.6Ca (Group II) degrades too rapidly, leading to premature strength loss and unstable mineralization. It is recommended in short loading- bearing maxillofacial appliance.1 wt% Zn is the ideal amount for biomimetic maxillofacial implants in accordance with ISO 10993-5 biomechanical thresholds.