Biodegradable Mg-Zn-Ca-Based Metallic Glasses

Abstract

Biodegradable Mg-Zn-Ca-based metallic glasses (MGs) present improved strength and superior corrosion resistance, compared to crystalline Mg. In particular, in vivo and in vitro attempts reveal that biodegradable Mg-Zn-Ca-based MGs possess excellent biocompatibility, suggesting that they are ideal candidates for temporary implant materials. However, the limited size and severe brittleness prevent their widespread commercialization. In this review, we firstly summarize the microstructure characteristic and mechanical properties of Mg-Zn-Ca-based MGs. Then, we provide a comprehensive and systematic understanding of the recent progress of the biocorrosion and biocompatibility of Mg-Zn-Ca-based MGs. Last, but not least, the outlook towards the fabrication routes, composition design, structure design, and reinforcement approaches of Mg-Zn-Ca-based MGs are briefly proposed.

Keywords: Mg–Zn–Ca; biodegradable; implant; metallic glass.

Figure 1

Microstructure of Mg–Zn–Ca-based MGs. (A) SEM images of as-cast alloys (diameter: 3 mm) with different Ca ratios: (A1) Mg₇₁Zn₂₈Ca₁, (A2) Mg₇₀Zn₂₈Ca₂, (A3) Mg₆₉Zn₂₈Ca₃, and (A4) Mg₆₈Zn₂₈Ca₄ alloys. The inset presents XRD patterns for the corresponding alloy, reproduced with permission from [27]. (B) XRD patterns of the Mg₆₆Zn₃₀Ca_4−xSr_x (x = 0, 0.5, 1, and 1.5 at.%) MGs, reproduced with permission from [58]. (C) SEM images of the Mg_69−xZn₂₇Ca₄Y_x alloys: (C1) x = 1, (C2) x = 2 at.%, reproduced with permission from [59]. (D) XRD patterns of the Mg_69−xZn₂₇Ca₄Y_x (x = 0, 1, and 2 at.%) alloys [59]. (E) XRD patterns of (g1) Mg₆₇Zn₂₉Ca₄ MG and (g2) Mg–Zn–Ca MGMC, with 3 vol.% porous NiTi addition. (F) SEM images of (g2). (G) EDX mapping taken from (H) ((G1): Mg; (G2): Zn; (G3): Ni; and (G4): Ti) [60]. (H) SEM images of Mg₇₅Zn₂₀Ca₅ alloy. The inset is the XRD pattern for the alloy, reproduced with permission from [27]. (I) DSC curves of Mg₆₈Zn₂₈Ca₄ MG matrix (Sample 1) and HA/ZnO-coated MG (Sample 2), reproduced with permission from [61]. (J) SEM image of cross-section HA/ZnO coating on MG surface, reproduced with permission from [61]. (K) SEM images of (K1) Pure PCL and (K2) PCL/2%nHA composite coatings, reproduced with permission from [62].

Figure 2

Mechanical properties of Mg–Zn–Ca-based MGs. (A) Compressive curves of as-cast Mg₆₅Zn₃₀Ca₅, Mg₆₅Zn₃₀Ca₄Ag₁, and Mg₆₃Zn₃₀Ca₄Ag₃ alloy rods (2 mm in diameter) under a strain rate of 5 × 10⁻⁴ s⁻¹, reproduced with permission from [83]. (B) The plots of tensile stress versus strain curve at strain rate of 10⁻⁴ s⁻¹ for the Yb2 and Yb4 MG ribbons, reproduced with permission from [84]. (C) The optical image of bent Yb2 MG ribbon, reproduced with permission from [84]. (D) Engineering strain–stress curves of the Mg_69−xZn₂₇Ca₄Y_x alloys: (a) x = 0, (b) x = 1, and (c) x = 2 at.%, reproduced with permission from [59]. (E) The vein-like pattern and (F) the melting trace and the slip direction of the fracture surface of Mg₆₆Zn₂₉Ca₅ MGMC with 10 vol% of porous Mo particles, reproduced with permission from [74]. (G) Fitted 2 parameter Weibull statistics for the fracture strength of as-cast and PCC compression rods and their corresponding fitted shape parameters (m), reproduced with permission from [89]. (H) A micrograph of a conversion-coated sample, following failure under compression (white arrows indicated the coating spalling, cracking, and delamination along the fracture, and black arrow indicated further shear band and crack formation), reproduced with permission from [89]. (I) Stress-life curves for the compression–compression fatigue tests in air and in PBS of Mg₆₆Zn₃₀Ca₃Sr₁ MG, reproduced with permission from [95].

Figure 3

Biocorrosion of Mg–Zn–Ca-based MGs. (A) Polarization curves of Mg, Mg₆₈Zn₂₈Ca₄ MG, crystal Mg₆₈Zn₂₈Ca₄ alloy, and HA-coated MG, reproduced with permission from [61]. (B) SEM images of the surface morphologies of (B1) Mg₆₆Zn₃₀Ca₄ and (B2) Mg₇₀Zn₂₅Ca₅ MGs after immersing in CrO₃ solution for 10 min, reproduced with permission from [82]. (C) The sketch map for the evolution of corrosion process of Mg–Zn–Ca MG immersed in SBF, reproduced with permission from [82]. (D) Representative polarisation curves of Mg rich MGs in MEM at 37 °C and 5% CO₂, reproduced with permission from [102]. (E) Metallic ion concentrations of the solution after the 3-days immersion test in PBS at 310 K, reproduced with permission from [66]. (F) Polarization curves in SBF of Mg_65.2Zn_28.8Ca₆ crystalline alloy, Mg_65.2Zn_28.8Ca₆ MG, and MAO-treated Mg_65.2Zn_28.8Ca₆ MG, reproduced with permission from [76].

Figure 4

Cellar biocompatibility of Mg–Zn–Ca-based MGs. (A) Cell viability after incubation with different extracts for 1, 3, and 5 days, * p < 0.05, reproduced with permission from [54]. (B) The morphology of MG63 cells cultured on (B1) Mg₆₆Zn₃₀Ca₄ and (B2) Mg₇₀Zn₂₅Ca₅ MG samples for 5 days, reproduced with permission from [82]. (C) Live (green)/dead (red) cell staining of attached MG63 cells around amorphous Mg₆₇Zn₂₈Ca₅ alloy without coating at (C1) 40× and (C2) 50× magnification, reproduced with permission from [112]. (D) Live (green)/dead (red) cell staining of attached MG63 cells around amorphous Mg₆₇Zn₂₈Ca₅ alloy with gelatin coating/2-day crosslinking at (D1) 40× and (D2) 50× magnification. White bar = 100 μm, reproduced with permission from [112]. (E) MTT assay results for coated and uncoated Mg₇₀Zn₂₆Ca₄ MG ribbon and pure Mg (* p < 0.05, compared to pure Mg), reproduced with permission from [114]. (F) SEM images of Schwann cell morphology on the surfaces of Mg₇₀Zn₂₆Ca₄ MG ribbon. (F1) Black bar = 10 μm. (F2) Black bar = 5 μm, reproduced with permission from [114].

Figure 5

X-ray (A), μ-CT (B), and 3D reconstruction photographs (C) of Mg₆₉Zn₂₇Ca₄ MG at 2 months postoperation, reproduced with permission from [54]. Micro-CT image of the rabbit’s femur implanted with Mg₆₀Zn₃₅Ca₅ MGMC at 12 (D) and 24 (E) weeks postoperatively. (F) Intergroup comparison of bone mineral density surrounding the implanted site at 12 and 24 weeks, analyzed with CTan analyzer software (* p < 0.05, ** p < 0.01, *** p < 0.001) [116].

Figure 6

Tissue biocompatibility of Mg–Zn–Ca-based MGs. (A) VG photographs of bone defect repair for 2 months postoperation: (A1,A2) Mg₆₉Zn₂₇Ca₄ MG, (A3) β-TCP (the red parts: new bone, the purple parts: cartilage), reproduced with permission from [54]. (B) Histological images of the implanted site at 24 weeks. (B1,B4) Mg₆₀Zn₃₅Ca₅ MGMC; (B2,B5) Ti6Al4V alloy; (B3,B6) PLA. Black arrows indicate new bone formation (hematoxylin and eosin staining) [116].