In vivo biological testing of titanium alloys with added rare earth elements to assess their possible use in medical products

Introduction Medical implants for treating injuries and orthopedic diseases are often made of titanium and its alloys. Their physicochemical properties, including corrosion inhibition, can be improved by adding rare earth elements. The aim of this study was to evaluate the safety of new materials based on the titanium alloy Ti6Al7Nb doped with yttrium, lanthanum, and cerium using an experimental in vivo subcutaneous implantation model. Materials and Methods Male Wistar rats were subcutaneously implanted with titanium and titanium alloy samples: VT1-00 (control, n = 10); Ti6Al7Nb0.3Y (group 1, n = 12); Ti6Al7Nb0.3La (group 2, n = 12); Ti6Al7Nb0.3Ce (group 3, n = 12). The experiment lasted 28 days. The animals' general condition and behavioral responses were assessed, and the implantation area was visually marked. Body weight, body temperature, and local temperature at the implantation site were recorded. Hematological and biochemical blood tests were performed, and internal organs and peri-implant tissue condition were anatomically assessed. Results In all groups, general condition, behavioral responses, body weight, body temperature, and peri-implant tissue temperature were normal, and skin wound healing occurred by primary intention. A positive effect of the rare earth elements studied was observed on reparative processes during skin wound healing. In the control group and group 1, organs retained normal size, color, and anatomical structure. In group 1, red blood cell counts were slightly elevated, along with increased concentrations of low- and medium-molecular-weight substances. In groups 2 and 3, changes in the anatomical characteristics of the liver, kidneys, and spleen were determined. Serum AST and LDH levels increased, C-reactive protein levels decreased, the proportion of neutrophils increased, and the lymphocyte count decreased. Glucose levels decreased in group 2, while glucose and urea levels increased in group 3. Discussion Subcutaneous implantation of yttrium (Y), lanthanum (La), and cerium (Ce) at 0.3 % wt. each in titanium alloys of Ti6Al7Nb composition for one month had no negative impact on the general condition, thermoregulation, cardiovascular system, or reproductive organs of male rats. The titanium alloy doped with yttrium (Y) had a compensatory toxic effect on the body. Titanium alloys doped with lanthanum (La) and cerium (Ce) exhibited hepatotoxic and nephrotoxic effects and impaired spleen function. The results obtained are consistent with existing literature data. Conclusion Under the conditions created, yttrium-doped materials and control samples can be considered safe. Materials doped with lanthanum and cerium raise concerns when implanted in vivo , requiring a longer-term study using histological methods.