Evaluation of in vitro corrosion behavior of zinc-hydroxyapatite and zinc-hydroxyapatite-iron as biodegradable composites

The Mutual Incorporation of Mg2+ and CO32- into Hydroxyapatite: A DFT Study

Hydroxyapatite (HA) with a stoichiometry composition of Ca₁₀(PO₄)₆(OH)₂ is widely applied for various biomedical issues, first of all for bone defect substitution, as a catalyst, and as an adsorbent for soil and water purification. The incorporation of foreign ions changes the acid-base relation, microstructure, porosity, and other properties of the HA materials. Here, we report the results of calculations of the density functional theory and analyze the possibility of two foreign ions, CO₃^2- and Mg²⁺, to be co-localized in the HA structure. The Na⁺ was taken into account for charge balance preservation. The analysis revealed the favorable incorporation of CO₃^2- and Mg²⁺ as a complex when they interact with each other. The energy gain over the sole ion incorporation was pronounced when CO₃^2- occupied the A position and Mg²⁺ was in the Ca(2) position and amounted to -0.31 eV. In the most energy-favorable complex, the distance between Mg²⁺ and the O atom of carbonate ion decreased compared to Mg…O distances to the surrounding phosphate or hydroxide ions, and amounted to 1.98 Å. The theoretical calculations agree well with the experimental data reported earlier. Understating the structure-properties relationship in HA materials varying in terms of composition, stoichiometry, and morphology paves the way to rational designs of efficient bio-based catalytic systems.

Biocompatibility of Zinc Matrix Biodegradable Composites Reinforced by Graphene Nanosheets

As a new type of biodegradable implant material, zinc matrix composites have excellent potential in the application of biodegradable implants because of their better corrosion resistance than magnesium matrix materials. Our previous studies have shown that graphene nanosheet reinforced zinc matrix composites (Zn-GNS) prepared by spark plasma sintering (SPS) have good mechanical properties and suitable degradation rate. However, the biocompatibility of zinc matrix composites is still a problem of concern. The cytocompatibility and blood compatibility of pure zinc and Zn-GNS composites in vitro were studied. The results showed that Zn-GNS composites had acceptable toxicity to MG-63 human osteosarcoma cells. In addition, the hemolysis rate of pure zinc and its composites were less than 3%, which has no adverse effect on adhered platelets, and has good antithrombotic and antiadhesion platelets properties. In conclusion, the addition of GNS did not adversely affect the biocompatibility of Zn-GNS composites, which indicated that Zn-GNS composites are a promising candidate for bone implantation.

Corrosion behavior and degradation mechanism of micro-extruded 3D printed ordered pore topological Fe scaffolds

The fabrication of ordered pore topological structures (OPTS) with an improved biodegradation profile offers unique attributes required for bone reconstruction. These attributes consisted of fully interconnected porous structure, bone-mimicking mechanical properties, and the possibility of fully regenerating bony defects. Most of the biomaterials based on magnesium were associated with the problem of too fast degradation rate. Here, the present aim was based on the fabrication of ordered pore topological Fe structures (OPTFS) using micro-extrusion-based 3D printing followed by pressureless microwave sintering. Two different kinds of pore features namely randomly distributed interconnected micropores and designed interconnected macropores were investigated. Static in vitro degradation results inferred that the H-2 mm pore size of hexagonal based ordered pore topological Fe structures (H-OPTFS) exhibited the highest degradation rate of 6.45 mg cm^-2  day^-1 on the 28th day. Electrochemical results revealed that the corrosion current density of the T-1 Fe sample with 44% porosity increased nearly by a multiple of three times as compared to dense Fe (from 16.79 to 44.63  μA cm - 2 ) _. Similarly, these results showed more significance in H-2 mm pores size (with highest 66% porosity) of H-OPTFS as compared to H-1.75 mm and H-1.5 mm pore size of H-OPTFS (≈2 times higher degradation rate than H-1.5 mm pore size). Moreover, the MG63 osteoblast cell line was adhered to and proliferated significantly throughout the surface and illustrated more than 80% cell viability of the prepared porous Fe scaffold. The analyzed results have shown the potential of fabricated OPTFS could be considered for biomedical applications.