**Conflict of interest**

*Engineering Steels and High Entropy-Alloys*

2, respectively, 0.9 and 2 μg l<sup>−</sup><sup>1</sup>

2, 0.2 μg l<sup>−</sup><sup>1</sup>

**5. Conclusions**

The presence of the alloying elements, Ti and Al, is comparable for both series of implants and confirms the literature data [42–45]. Spriano et al. [42] also reported an increase of metal ion concentration after a long time exposure, for the Ti6Al7Nb alloy in a SBF solution. On the other hand, the concentration of Nb cations for

two types of prostheses. The samples of series 1 released less chromium than series

Various biomaterials have been used for orthopedic implant manufacturing. Polymeric materials, as a result of their mechanical weakness, have been considered unsuitable for the stress deformation requirements of orthopedic implant components, while ceramics have good biocompatibility but are brittle, and designs should take this into account. Alloys are known for their good mechanical properties, but poorer biocompatibility, due to the systemic release of ions [46]. An orthopedic implant is frequently made of a metallic or ceramic component articulating with a metal, ceramic, or polyethylene surface [19]. Different possible combinations are possible: metal (stainless steel or Co-Cr) on ultrahigh molecular weight polyethylene, metal on metal, ceramic on polyethylene, ceramic on ceramic, or ceramic on metal [47]. Coatings such as bioinert films, which have the main purpose of hindering corrosive processes of the underlying metal and bioactive films, which are capable of improving biological compatibility, avoiding inflammation or implantassociated infection processes, are used more and more often. The ideal coating is a system in which anticorrosion, anti-infection, and osseointegration can be obtained simultaneously [48]. Because of their favorable characteristics, Ti alloys are the first choice material in case of orthopedic implants. Even in case of Co-Cr-Mo alloys, Ti-vacuum-plasma-sprayed (VPS) coatings decrease the release of the substrate elements (Co, Cr, and Mo) considerably, but they do not suppress it completely [49]. Titanium remains the predominant material used for medical implants. Despite its high strength and good resistance to corrosion, multiple studies have demonstrated that degradation products of titanium alloys may be detected in neighboring tissues as well as in distant organs. Titanium particles are released from the implant's surfaces for many reasons, such as mechanical wear, contact with chemical agents, and bacteria embedded in adherent biofilm and inflammatory cells [16]. It is obvious that none of the orthopedic prosthetic materials are "inert". However the question regarding their toxicological behavior "Which are the long-

The near future of multicomponent alloys for biomedical applications does not only belong to high-quality Co-Cr, Ti, Ta, or Zr alloys but also to customized orthopedic prostheses, manufactured by 3D printing techniques, based on a CT or MRI scan, which fit perfectly. One can also imagine the not-so-distant future, which seems to belong to the bioprinting techniques, in this case, bone-made orthopedic

 Zr. Part of the cations released in solution (Pb and Sn) probably originates from the glass reactor or the HCl composition (according to Merck information). As Cd and Cu are considered to be accidental impurities, their presence is not related to the

. The prostheses of sample #E released 6 μg l<sup>−</sup><sup>1</sup>

, respectively). The

Cu.

Zr and series

), almost identical for the

As. The specimens from series 1

Co, 0.03 μg l<sup>−</sup><sup>1</sup>

series 2 is significantly smaller than for series 1 (60–120 μg l<sup>−</sup><sup>1</sup>

affiliation of the tested sample to one or the other series of prostheses.

most important impurity is Fe (between 30 and 50 μg l<sup>−</sup><sup>1</sup>

released less Ba than series 2. Series 1 released 0.8 μg l<sup>−</sup><sup>1</sup>

Co and respectively 0.17 μg l<sup>−</sup><sup>1</sup>

Samples #B, #E and, #F released 1.4–2.6 μg l<sup>−</sup><sup>1</sup>

term consequences for humans?" still stands.

**216**

implants.

The authors declare no conflict of interest.
