CHARACTERIZATION OF THE IN VIVO RESPONSE TO ANODIZED MAGNESIUM ALLOY AS A POTENTIAL BIODEGRADABLE IMPLANT: A 6-MONTHS STUDY

MERLO, J.L; CARRIZO S.; TANO DE LA HOZ, M.F.; SALEMME ALONSO L.; OTAZ M.A; BALLARRE J.; KATUNAR M.R.; CERE S.

Mar del Plata

Congreso; XII Latin-American Congress of Artificial Organs and Biomaterials; 2023

INTEMA

Introduction and objective: Magnesium (Mg)-based alloys are promising candidates for the development of new biodegradable materials for fracture repair [1]. However, in aqueous media, together with Mg degradation, hydrogen evolution occurs, which causes pain and local swelling. Surface treatments, such as anodizing technique, emerge as a potential solution to this limitation. The aim of this study is to understand the long-term performance of Mg-based devices with anodizing as surface treatment that exhibited good short-term (30 days) response both in vitro and in vivo. However, long-term studies are scarce in literature and are fundamental for defining new biomaterials as safe.Methodology: Commercial AZ91D alloy was anodized at 5 V, 40 min. Both male WKAH/Hok rat femurs were implanted with anodized AZ91 or PLA (control) pins. After 6 months, femurs were retrieved, fixed and cut. The sections were stained with Toluidine blue for histological examination and histomorphometric analysis of the new bone. Raman spectra were also registered to characterize maturity of new bone. The concentration of magnesium in urine and leukocyte formula in blood samples were measured. Mineralization rate was determined by injecting two fluorochromes into the rats 7 and 3 days before sacrifice and using fluorescent microscopy detection.Results and discussion: Results showed no hydrogen bubbles at the interface material-tissue. New bone formed around Mg pins was higher in volume (50.3 ± 27%) and trabecular thickness (91.2 ± 44 µm) compared with those around PLA pins (33.9 ± 18% and 71 ± 26 µm, respectively). Ratios of mineral to matrix composition and the degree of carbonate substitution (both indicative of maturation state) of the new bone were calculated based on phosphate, amides and carbonate peaks from Raman spectra. Mg concentration in urine did not differ between groups (Mg pins: 24,1 ± 1,2 mg/dl; PLA pins: 21,8 ± 4,1 mg/dl). Leukocyte formula, indicative of inflammatory processes, did not differ between groups. Mineralization rate could not be determined due to fluorochromes overlapping, and the direction of the mineralization deposition did not present a clear pattern. Conclusions: Anodizing process at low voltage is a promising superficial treatment for the development of Mg- based devices for fracture fixation. The in vivo response after a long period of implantation is better than the induced by a commercial biodegradable material (PLA) currently used for other applications. Anodized AZ91 promotes bone formation to a high extent and prevents the liberation of hydrogen bubbles without causing negative effects at the systemic level.