Research Progress of Titanium-Based Alloys for Medical Devices

Madalina Simona Baltatu, Software , Formal analysis , Investigation , Writing – original draft , 1 Petrica Vizureanu, Conceptualization , Validation , Resources , Supervision , Project administration , Funding acquisition , 1, 2, * Andrei Victor Sandu, Conceptualization , Methodology , Formal analysis , Investigation , Data curation , 1, 3, 4, 5 Carmen Solcan, Conceptualization , Methodology , Investigation , Resources , Writing – review & editing , 6, * Luminița Diana Hritcu, 6 and Mihaela Claudia Spataru, Conceptualization , Validation , Data curation , Writing – original draft , Supervision 6

Madalina Simona Baltatu

1 Faculty of Materials Science and Engineering, “Gheorghe Asachi” Technical University of Iasi, 41 “D. Mangeron” Street, 700050 Iasi, Romania; moc.oohay@anomism.lecrec (M.S.B.); or.isaiut@vas (A.V.S.)

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Petrica Vizureanu

2 Technical Sciences Academy of Romania, Dacia Blvd 26, 030167 Bucharest, Romania

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Andrei Victor Sandu

3 Romanian Inventors Forum, Str. Sf. P. Movila 3, 700089 Iasi, Romania

4 Academy of Romanian Scientists, 54 Splaiul Independentei, 050094 Bucharest, Romania

5 National Institute for Research and Development in Environmental Protection, 294 Splaiul Independentei, 060031 Bucharest, Romania

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Carmen Solcan

6 Department of Public Health, Faculty of Veterinary Medicine, Iasi University of Life Sciences, Mihail Sadoveanu Street, No 3, 700490 Iasi, Romania; moc.oohay@hidimul (L.D.H.); moc.oohay@vmfuratapsm (M.C.S.)

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Luminița Diana Hritcu

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Mihaela Claudia Spataru

Find articles by Mihaela Claudia Spataru Viviana Di Giacomo, Academic Editor

2 Technical Sciences Academy of Romania, Dacia Blvd 26, 030167 Bucharest, Romania 3 Romanian Inventors Forum, Str. Sf. P. Movila 3, 700089 Iasi, Romania 4 Academy of Romanian Scientists, 54 Splaiul Independentei, 050094 Bucharest, Romania

5 National Institute for Research and Development in Environmental Protection, 294 Splaiul Independentei, 060031 Bucharest, Romania

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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Abstract

Biomaterials are currently a unique class of materials that are essential to improving the standard of human life and extending it. In the assent of the appearance of biomaterials that contain non-toxic elements, in this study, we examine a system of Ti25Mo7Zr15TaxSi (x = 0, 0.5, 0.75, 1 wt.%) for future medical applications. The alloys were developed in a vacuum electric arc furnace and then studied from a structural, mechanical and in vivo assessment (on rabbits) perspective. The effect of the silicon addition was clearly seen in both the structural and the mechanical characteristics, standing out as beta alloys with a dendritic structure and lowering the mechanical properties as a result of the silicon addition. In experimental rabbits, the proliferation of mesenchymal stem cells was observed in the periosteum and peri-implant area, differentiating into osteoblasts and then into osteocytes. Osteoclasts were discovered within the cartilaginous islands that provide structural support to newly formed bone, playing a primary role in bone remodeling. The newly formed spongy tissue adhered to the fibrous capsule that surrounds the alloy, ensuring good osseointegration of metallic implants. The overexpression of Osteopontin, Metalloproteinase-2 (also known as gelatinase A), and Metallopeptidase-9 (also known as gelatinase B) underscores the processes of osteogenesis, bone mineralization, and normal bone remodeling.

Keywords: titanium alloys, non-toxic elements, characterization

1. Introduction

From the perspective of protecting health, biomaterials can be defined as “materials that possess new properties that make them suitable to come into immediate contact with living tissue without causing an immune rejection or an adverse reaction” [1,2,3].

Scientists can now model the properties of materials at high levels thanks to the knowledge they have accumulated over the previous 70 years. In order to meet the numerous service requirements of today’s complex society, tens of thousands of different materials have been developed with specific properties [4,5].

In reparative medicine, a broad diversity of biomaterials are used. Currently, commercially pure titanium (C.P.-Ti), Ti6Al4V, Ti6Al7Nb, CoCr and stainless-steel alloys [6,7,8] are used to fabricate orthopedic implants. Unfortunately, these materials have demonstrated a tendency to degrade over time due to various factors. They have a higher Young’s modulus than bone, low wear and corrosion resistance, and they are not biocompatible. It’s worth noting that understanding the properties of alloying elements can provide valuable insights into their suitability for biomedical applications. In this context, Young’s modulus (or elastic modulus) represents the measure of stiffness in a material. Alloying elements, such as Tantalum (Ta), Zirconium (Zr) and Silicon (Si), have specific values for Young’s modulus that play a pivotal role in determining their mechanical behavior. For instance, Tantalum possesses Young’s modulus close to that of bone, making it an attractive option for orthopedic implants. Zirconium, likewise, exhibits a favorable Young’s modulus, and when alloyed with other elements, it can improve wear and corrosion resistance. Silicon, often added in trace amounts, can influence the mechanical properties of the resulting alloy, including its Young’s modulus [8,9,10].

The identification and testing of the effectiveness of new types of implants are the essential stages for the design and development of the medical device industry. The most commonly utilized materials in medical applications are still titanium and its alloys because of their exceptional characteristics. They are mostly utilized in the domains of orthopedics, dentistry and cardiovascular medicine for the replacement of hard tissues because of their high tensile strength, satisfactory biocompatibility and good resistance to corrosion or wear [7,8,9,10]. Some studies [8] show that C.P. Ti, Ti-Nb-Zr and Ti-Mo alloys show superior corrosion resistance. While certain in vitro studies have demonstrated the superiority of Ti-based alloys over commercially pure titanium (C.P. Ti), others have indicated that Ta-xZr alloys may enhance the adhesion, proliferation, and differentiation of osteogenic cells. In in vivo studies, alloys with a higher percentage of Ta have shown increased osteogenic activity, with titanium alloys containing Ta-30Zr emerging as a promising alternative [11]. However, Ta-Zr alloys show low elastic moduli and some biomechanical particularities, which are similar to those of human bone [12,13,14,15,16].

Tantalum is considered to be non-toxic and of medium biocompatibility [17]. In vitro studies have presented the proliferation and adhesion of osteoblasts to the surface of the porous tantalum rod showing a variety of shapes and intercellular connections [18]. In in vivo studies, researchers have described peri-implant vascular proliferation and the formation of new bone tissue and bone trabeculae directly connected to the alloy [12,19,20,21]. In a study on rats, Jugdaohsingh et al. [22] showed that silicon was found in bones as well as elastane and collagen of the connective tissues in organs such as the aorta, bone, trachea or tendon up to 50 fold compared with the non-connective viscera (liver, kidney and spleen), and even if the concentration of silicon had increased with age, the highest content was found in the connective tissue of young weanling rats.

Silicon (Si), which can be found as silicide and solid solution, is a crucial element in titanium (Ti) alloys. Some studies have demonstrated that the addition of silicon to titanium alloys can improve strength, creep resistance and oxidation resistance, as well as reduce fluidity, particularly at ambient temperature [22,23,24,25,26].

The biocompatibility of implant materials is the determining characteristic for the osseointegration process and implicitly for implant stability, reliability and durability. The concept of intrinsic biocompatibility is defined as “the ability of a material to induce an appropriate host response, in the case of a specific application”. In implantology, the concept of biocompatibility of materials must be combined with that of the bifunctionality of the implant, which implies the in vivo functional performance of the implant [27,28,29,30].

It is crucial to design materials with superior biocompatibility and high durability. Although a variety of materials are now used as biomaterials, titanium alloys are quickly replacing them as the most in-demand material for most applications [31,32,33,34,35,36,37,38,39].

This scientific study explores the microstructural and biological properties of a new Ti25Mo7Zr15TaxSi (x = 0, 0.5, 0.75, 1 wt.%) system developed for medical applications. This study includes microstructure analyses, mechanical testing, and in vivo investigation of the chemical and biological characteristics of the alloys to evaluate their performance. Figure 1 provides an overview of the contents of this study and the methods used to achieve the research objectives.