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.

1. Liu S, Shin YC. Additive manufacturing of Ti6Al4V alloy: A review. Materials & Design. 2019;164:107552. doi: 10.1016/j.matdes.2018.107552.

2. Posiyano K, Prasad RVS, Dzogbewu TC, et al. The potential of Ti-6Al-7Nb, and design for manufacturing considerations in mitigating failure of hip implants in service. Biomedical Engineering Advances. 2024;8:100136. doi: 10.1016/j.bea.2024.100136.

3. Gao Y, Jiang W, Zeng D, et al. Additive manufacturing of titanium alloys for biomedical applications: A systematic review. Review of Materials Research. 2025;1(1):100011. doi: 10.1016/j.revmat.2025.100011.

4. Pesode P, Barve S. A review – metastable β titanium alloy for biomedical applications. J Eng Appl Sci. 2023;70(1):25. doi: 10.1186/s44147-023-00196-7.

5. Hazwani MR, Lim LX, Lockman Z, Zuhailawati H. Fabrication of titanium-based alloys with bioactive surface oxide layer as biomedical implants: Opportunity and challenges. Transactions of Nonferrous Metals Society of China. 2022;32(1);1-44. doi: 10.1016/S1003-6326(21)65776-X.

6. Zaffe D, Bertoldi C, Consolo U. Accumulation of aluminium in lamellar bone after implantation of titanium plates, Ti-6Al-4V screws, hydroxyapatite granules. Biomaterials. 2004;25(17):3837-3844. doi: 10.1016/j.biomaterials.2003.10.020.

7. Garg D, Wagh NP, Shinde MB, et al. A comparative study between functional outcomes of proximal humerus fracture treated using closed reduction and JESS external stabilization system and open reduction and internal fixation with PHILOS plate at a tertiary health care center. Genij Ortopedii. 2025;31(5):558-566. doi: 10.18019/1028-4427-2025-315-558-566.

8. Abdulloev AM, Gvozdev NS, Tropin DV, Popkov DA. Results of limb reconstruction surgery using a telescopic titanium rod: early findings. Genij Ortopedii. 2025;31(1):51-59. doi: 10.18019/1028-4427-2025-31-1-51-59.

9. Peng Xu, Florian Pyczak, Ming Yan, Fantao Kong, Thomas Ebel. Impacts of yttrium on microstructure and tensile properties of biomedical β Ti-Nb-Zr fabricated by metal injection molding. Mater Sci Eng A. 2020;792:139816. doi: 10.1016/j.msea.2020.139816.

10. Won JW, Oh JM, Kim WC, et al. Simultaneous high tensile strength and high ductility in cast Ce-alloyed Ti. Mater Sci Eng A. 2024;918:147487. doi: 10.1016/j.msea.2024.147487.

11. Willbold E, Gu X, Albert D, et al. Effect of the addition of low rare earth elements (lanthanum, neodymium, cerium) on the biodegradation and biocompatibility of magnesium. Acta Biomater. 2015;11:554-562. doi: 10.1016/j.actbio.2014.09.041.

12. Popkov AV, Popkov DA. Biocompatible implants in orthopedics: bone tissue engineering. Genij Ortopedii. 2023;29(6):662668. doi: 10.18019/1028-4427-2023-29-6-662-668.

13. Baldin EK, de Castro VV, Santos PB, et al. Copper incorporation by low-energy ion implantation in PEO-coated additively manufactured Ti6Al4V ELI: surface microstructure, cytotoxicity and antibacterial behavior. J Alloy Compd. 2023;940:168735. doi: 10.1016/j.jallcom.2023.168735.

14. Quinn J, McFadden R, Chan CW, Carson L. Titanium for Orthopedic Applications: An Overview of Surface Modification to Improve Biocompatibility and Prevent Bacterial Biofilm Formation. iScience. 2020;23(11):101745. doi: 10.1016/j.isci.2020.101745.

15. Popkov AV, Shastov AL, Shipitsyna IV, et al. Bactericidal activity of experimental samples of titanium alloy implants with a calcium phosphate coating and an antibacterial component against gram-negative pathogens (experimental study). N.N. Priorov Journal of Traumatology and Orthopedics. 2024;31(4):517-526. (In Russ.) doi: 10.17816/vto630216.

16. Stich T, Alagboso F, Krenek T, et al. Implant-bone-interface: Reviewing the impact of titanium surface modifications on osteogenic processes in vitro and in vivo. Bioeng Transl Med. 2021;7(1):e10239. doi: 10.1002/btm2.10239.

17. Sun Y, Xu W, Jiang C, et al. Gold nanoparticle decoration potentiate the antibacterial enhancement of TiO2 nanotubes via sonodynamic therapy against peri-implant infections. Front Bioeng Biotechnol. 2022;10:1074083. doi: 10.3389/fbioe.2022.1074083.

18. Li J, Liu XM, Tan L, et al. Zinc-doped Prussian blue enhances photothermal clearance of Staphylococcus aureus and promotes tissue repair in infected wounds. Nat Commun. 2019;10(1):4490. doi: 10.1038/s41467-019-12429-6.

19. Chen YH, Guan SW, Xing M, et al. Ce-doped defective titanium oxide coating with antibacterial, antioxidant and antiinflammatory properties for potential application of peri-implantitis treatment. Rare Metals. 2025;44(1):472-488. doi: 10.1007/s12598-024-02935-y.

20. Danilova L.A. Handbook of laboratory research methods. St. Petersburg: Piter. 2003:736. (In Russ.)

21. Baltatu MS, Vizureanu P, Sandu AV, et al. Research Progress of Titanium-Based Alloys for Medical Devices. Biomedicines. 2023;11(11):2997. doi: 10.3390/biomedicines11112997.

22. Emanov AA, Kuznetsov VP, Gorbach EN, et al. Osseointegration of Titanium and Steel Additive Manufactured Implant in Rabbit Tibia under External Fixation: Comparative Study. Traumatology and Orthopedics of Russia. 2020;26(2):98-108. doi: 10.21823/2311-2905-2020-26-2-98-108.

23. Galichenko KA, Sukhov AV, Timoshkin SP, et al. Experimental study of topical application of cerium oxide nanoparticles on tissue regeneration. Medical and pharmaceutical journal "Pulse". 2023;25(5):96-100. (In Russ.) doi: 10.26787/nyd ha-2686-6838-2023-25-5-96-100.

24. Legon'kova OA, Ushakova TA, Savchenkova IP, et al. Experimental Study of the Effects of Nanodispersed Ceria on Wound Repair. Bull Exp Biol Med. 2017;162(3):395-399. doi: 10.1007/s10517-017-3624-2.

25. Schubert D, Dargusch R, Raitano J, Chan SW. Cerium and yttrium oxide nanoparticles are neuroprotective. Biochem Biophys Res Commun. 2006;342(1):86-91. doi: 10.1016/j.bbrc.2006.01.129.

26. Ren L, Shi W, Tian Y, et al. A Two-Generation Reproductive Toxicity Study of Cerium Nitrate in Sprague-Dawley Rats. Biol Trace Elem Res. 2024;202(2):597-614. doi: 10.1007/s12011-023-03692-2.

27. Radtseva GL, Minaev BD, Zdornova OV, Piskareva EI. Changes in tissues and organs under experimental exposure to lanthanum. Current problems of daily medicine: Bulletin of the Ukrainian Medical Dental Academy. 2011;11(4(36)):147149. (In Russ.)

28. Chen D, Liu Y, Chen AJ, Nie YX. Experimental study of subchronic toxicity of lanthanum nitrate on liver in rats. Nonlinearity Biol Toxicol Med. 2003;1(4):469-480. doi: 10.1080/15401420390271074.