Mechanical and Biological Properties of a Biodegradable Mg-Zn-Ca Porous Alloy

As promising alternative to current metallic biomaterials, the porous Mg scaffold with a 3-D open-pore framework has drawn much attention in recent years due to its suitable biodegradation, biocompatibility, and mechanical properties for human bones. This experiment's aim is to study the mechanical properties, biosafety, and osteogenesis of porous Mg-Zn alloy.

A porous Mg-2Zn-0.3Ca (wt%) alloy was successfully prepared by infiltration casting, and the size of NaCl particles was detected by a laser particle size analyzer. The microstructure of the Mg-2Zn-0.3Ca alloy was characterized by the stereoscopic microscope and Sirion Field emission scanning electron microscope. X-ray computerized tomography scanning (x-CT) was used to create the 3-D image. The degradation rate was measured using the mass loss method and the pH values were determined together. The engineering stress-strain curve, compressive modulus, and yield strength were tested next. The bone marrow stromal cells (BMSC) were cultured in vitro. The CCK-8 method was used to detect the proliferation of the BMSC. Alkaline phosphatase (ALP) and alizarin red staining were used to reflect the differentiation effects. After co-culturing, cell growth on the material's surface was observed by scanning electron microscope (SEM). The cell adhesion was tested by confocal microscopy.

The obtained results showed that by using near-spherical NaCl filling particles, the porous Mg alloy formed complete open-cell foam with a very uniform size of pores in the range of 500-600 μm. Benefitting from the small size and uniform distribution of pores, the present porous alloy exhibited a very high porosity, up to 80%, and compressive yield strength up to 6.5 MPa. The degradation test showed that both the pH and the mass loss rate had similar change tendency, with a rapid rise in the early stage for 1-2 day's immersion and subsequently remaining smooth after 3 days. In vitro cytocompatibility trials demonstrated that in comparison with Ti, the porous alloy accelerated proliferation in 1, 3, 5, and 7 days (P < 0.001), and the osteogenic differentiation test showed that the ALP activity in the experimental group was significantly higher (P = 0.017) and has more osteogenesis nodules. Cell adhesion testing showed good osteoconductivity by more BMSC adhesion around the holes. The confocal microscopy results showed that cells in porous Mg-based alloy had better cytoskeletal morphology and were larger in number than in titanium.

These results indicated that this porous Mg-based alloy fabricated by infiltration casting shows great mechanical properties and biocompatibilities, and it has potential as an ideal bone tissue engineering scaffold material for bone regeneration.