The continuous development of novel materials for biomedical applications is resulting in an increasingly better prognosis for patients. The application of more advanced materials relates to fewer complications and a desirable higher percentage of successful treatments. New, innovative materials being considered for biomedical applications are metallic alloys with an amorphous internal structure called metallic glasses. They are currently in a dynamic phase of development both in terms of formulating new chemical compositions and testing their properties in terms of intended biocompatibility.
One of the widely used standard materials groups for medical implants, surgical tools, and other bio-related devices are metallic alloys, including stainless steels, pure Ti and Ti-based alloys, Co-based alloys, pure Zr and Zr-based alloys, bioresorbable Mg-based alloys, pure Ta, and other miscellaneous [1][2][3]. However, they are often afflicted with many problems including insufficient corrosion fatigue, fretting fatigue resistance, as well as possible toxicity by the release of toxic ions. For the stainless steels and Mg-based materials, corrosion resistance is also problematic. For the stainless steels and Ti-based materials, the wear resistance is a serious concern. Moreover, in the case of implants, the stress shielding effect [4]—which consists of transferring the loads through the stiffer element—is challenging. In the typical case, the load is transferred through the implant (stiffer than the bone) without stimulation of surrounding bones to maintain their properties, which causes bone resorption and implant loosening. Materials such as stainless steels, Co-based materials, pure Ta, and certain alloys from other groups—which are characterized by a Young’s modulus significantly higher than the value for the bones (5.7–18.2 GPa [5])—are particularly prone to triggering this effect. However, it was reported that materials with Young’s modulus values of about 60 GPa are already effective in eliminating the stress shielding effect [6]. Ultimately, the mentioned issues lower the applicational biocompatibility of current materials for biomedical applications. Other problems relate to the inapplicability of some materials for magnetic resonance due to the displacement possibility (e.g., for ferromagnetic materials such as ferritic and martensitic stainless steels [7]) or inducing severe artifacts (e.g., for austenitic stainless steels, Co-based alloys, and even Ti-based alloys [8]). Similarly, artifacts can be induced during X-ray imaging [9].
The majority of metallic alloys at room temperature are characterized by a crystalline structure, which ensures the optimal arrangement of atoms [10]. However, to some extent, it is possible to control the structure at the manufacturing stage by altering the thermodynamic conditions. The structures obtained in rapid cooling processes were noticed in metals as early as in the 1940s [11][12] while applying metal vapors to the cold substrate. The first confirmed formation of an amorphous structure in metals obtained by cooling them from liquid to solid state dates to 1960 [13]. It was produced at that time by the Duwez research team at Caltech through the very rapid cooling of an Au-Si alloy into the shape of thin foil. This new group of metallic materials was named metallic glasses, by similarity to well-known amorphous oxide glasses.
The confirmation of the possibility of changing the internal structure in metallic alloys initiated rapid progress and research on this material group. This significant development resulted in the discovery of many new compositions of alloys with higher Glass Forming Ability (GFA), the determination of changes in physical and mechanical properties in MGs, and the development of new production methods. Firstly, the MGs were fabricated only in the form of thin ribbons or foils due to the necessity of preserving the critical cooling rate (≥106 K/s) essential to obtain the amorphous internal structure. Later, the optimization of chemical compositions resulted in the opportunity for manufacturing MGs with lower critical cooling rates (≤103 K/s) and greater critical dimensions exceeding 1 mm, so called Bulk Metallic Glasses (BMGs) [14][15], which now can be produced with critical dimensions measured even in centimeters [16][17]. Eventually, since their discovery, many MGs and BMGs compositions based on various elements have been developed. However, the necessity to maintain the critical cooling rate still restricts the maximal, composition-dependent, achievable dimensions.
Composition (at.%) | Production Method | d (mm) | Structure | σmax (MPa) | E (GPa) | Hv (HV) | εel/εpl (%) | Ref. |
---|---|---|---|---|---|---|---|---|
Zr63.5−xTixAl9Fe4.5Cu23 (x = 0, 1.5, 3, 4.5, 6) | Arc melting/suction casting | 3–10 | Fully amorphous | 1580–1690 | – | – | –/0.9–4.7 | [37] |
Zr61Ti2Cu25Al12 | Arc melting/suction casting | 2–10 | Fully amorphous | – | 83 | – | – | [38][39] |
Zr58.6Al15.4Co18.2Cu7.8 | Arc melting/suction casting | 10 | Fully amorphous | 1950 | 84 | – | –/2.0 | [40] |
Zr55Ti3HfxCu32−xAl10 (x = 0, 1, 2, 3, 4, 5) | Arc melting/suction casting | 4–8 | Fully amorphous | 1695–1824 | 73–85 | – | 2.0–2.5/0–2.6 | [41] |
Zr40Ti15Cu10Ni10Be25 | Arc melting/suction casting | 3 | Mainly amorphous | – | – | 796 | – | [42] |
Zr50Ti5Cu10Ni10Be25 | Arc melting/suction casting | 3 | Mainly amorphous | – | – | 741 | – | [42] |
Zr40Ti15Cu10Ni5Si5Be25 | Arc melting/suction casting | 3 | Partially amorphous | – | – | 843 | – | [42] |
Zr70Ni16Cu6Al8 | Arc melting/arc tilt casting | 3 | – | 1500 * | 70 | – | 2.2/0 | [43] |
Zr65−xTixCu20Al10Fe5 (x = 0, 2, 4, 6, 8) | Arc melting/suction casting | 2 | Fully amorphous for x = 0, 2, 4, and partially amorphous for x = 6, 8 | 1405–1905 | – | – | –/0–8.6 | [44] |
Zr56Cu24Al9Ni7−xTi4Fex (x = 0, 1, 3, 5, 7) | Arc melting/suction casting | 2 | Fully amorphous for x = 0, 1, 3, and partially amorphous for x = 5, 7 | 1043–1709 | – | – | 3.9–6.3/0–5.6 | [45] |
Zr60+xTi2.5Al10Fe12.5-xCu10Ag5 (x = 0, 2.5, 5) | Arc melting/suction casting/casting | 1–2 | Fully amorphous | ~1660–1740 | 70–78 | 443–460 | 2.0–2.0/4–12 | [46] |
Zr55Co30Ti15 | Arc melting/melt spinning | 0.04 | Fully amorphous | – | – | – | – | [47] |
Zr62Cu22Al10Fe5Dy1 | Induction melting/melt spinning | 0.04 | Fully amorphous | – | 96 | 495 | – | [48] |
Zr37Co34Cu20Ti9 | Arc melting/melt spinning | – | Fully amorphous | – | 81 | 567 | – | [49] |
Zr40Ti35Ni14Nb11 | Magnetron co-sputtering | 0.0006 | Fully amorphous | – | 122 | ~658 | – | [50] |
Zr46Ti40Ag14 | Magnetron co-sputtering | 0.0003 | Fully amorphous | – | 109 | ~567 | – | [51] |
Zr46Ti43Al11 | Magnetron co-sputtering | 0.0002 | Fully amorphous | – | 127 | ~520 | – | [51] |
Zr62.5Pd37.5 | Magnetron sputtering | – | Fully amorphous | – | – | – | – | [52] |
Very recently, many Zr-based glassy alloys have also been assessed in in vitro cellular research concerning their cytotoxicity which determines the next step for the broader application of this group of materials. The research with the use of MC3T3-E1 mouse preosteoblasts cells showed an excellent cytocompatibility of particular Zr-based BMGs [46][62][38] in comparison with Ti-based alloys and even PEEK polymer. Comparably excellent results were also obtained for other BMGs in direct and indirect contact with L929 mouse fibroblasts [54][63]. Another popular type of cells used for cytotoxicity verification purposes are human osteosarcoma cells (HOS), especially from the MG-63 cell lines. Zr-based metallic glasses showed little toxicity to HOS cells [47][48][49][64].
Another kind of research is related to material-blood contact and in this field, the Zr-based glassy alloys have been successfully evaluated. The research on the Zr56Al16Co28 BMG demonstrated its very low (below 0.12%) hemolytic rates indicating its compatibility with erythrocytes [30]. Moreover, the thin films of the Zr53Cu33Al9Ta5 material proved that they do not support blood cells’ adhesion and do not cause platelet aggregation leading to thrombosis [65][66][67], which is essential for the needles or stents.
In vivo animal research represents the next step in the biomedical characterization of potential candidates for wider use, as in the in vitro test it is not possible to observe the full spectrum of mutual material-organism interactions. Zr-based metallic with varied compositions showed no adverse effects after implantation into the organisms of rabbits [54], mice [30], and rats [43][86][38]. Together with possible excellent osseointegration properties [43][38] and faster recovery [38], the research results show Zr-based metallic glasses as promising candidates for bone implants.
Moreover, recent applicational studies on the MG thin films showed that particular compositions (e.g., Zr53Cu33Al9Ta5) can be very effective for coatings of medical devices such as syringe needles [66][87]. The film improved the durability, hemocompatibility, and reduced the cells’ adhesion which resulted in a less invasive procedure (lower retraction forces) and less probability of causing thrombosis.
Composition (at.%) | Production Method | d (mm) | Structure | σmax (MPa) | E (GPa) | Hv (HV) | εel/εpl (%) | Ref. |
---|---|---|---|---|---|---|---|---|
(Ti55Zr15Be20Ni10)100−xFex (x = 0, 2, 4, 6, 8, 10) | Arc melting/suction casting | 5–10 | Fully amorphous | 1878–2355 | – | – | –/3.4–1.3 | [94] |
Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2 | Arc melting/tilt pouring | 7 | Fully amorphous | 2080 | 100 | 588 | –/2.5 | [95] |
Ti48Cu37Zr7.5Fe2.5Sn2Si1Ag2 | Arc melting/tilt pouring | 6 | Fully amorphous | 2050 | 101 | 571 | 2.0/2.8 | [96] |
Ti45Zr10Cu31Pd10Sn4 | Argon atomization/spark plasma sintering | 6 | Fully amorphous | – | 100 | – | – | [97] |
Ti47−xCu40Zr7.5Fe2.5Sn2Si1Scx (x = 0, 1, 2, 3, 4) | Arc melting/suction casting/tilt pouring | 3–6 | Fully amorphous | 1982–2169 | 93–101 | 577–590 | –/0.8–5.9 | [98] |
Ti47Cu38−xZr7.5Fe2.5Sn2Si1Ag2Nbx (x = 0, 1, 2) | Arc melting/suction casting | 3–5 | Fully amorphous | 2031–2078 | 97–100 | 588–593 | –/1.9–2.5 | [99] |
Ti40Zr10Cu36Pd14 | Arc melting/tilt pouring | 5 | Fully amorphous | 2010 | 96 | 556 | 2.0/0.7 | [100][101] |
Ti40Zr10Cu36−xPd14Gax (x = 2, 4, 8, 10) | Arc melting/suction casting | 3 | Fully amorphous for x = 2, 4, and partially amorphous for x = 8, 10 | 1935–2075 | 93–140 | – | 1.9–2.1/0.8–2.5 | [102] |
Ti47Cu40−xZr7.5Fe2.5Sn2Si1Tax (x = 1, 2, 3, 4) | Arc melting/suction casting | 3 | Fully amorphous | 2041–2191 | 98–101 | 582–595 | –/1.0–3.4 | [103] |
Ti40Zr35Cu17S8 | Induction melting/arc melting/suction casting | 3 | Fully amorphous | 3200 | 96 | 509 | – | [104] |
Ti50Zr25Cu17S8 | Induction melting/arc melting/suction casting | 2 | Fully amorphous | 3100 | 98 | 524 | – | [104] |
Ti40Zr10Cu38Pd12 | Induction melting/mold casting | 2 | Fully amorphous | 2300 | 95 | 734 | –/4.0 | [105] |
Ti40Zr10Cu34Pd14Sn2 | Arc melting/suction casting | 1.5 | Fully amorphous | >2000 | 93 | – | 2.2/– | [106] |
Ti60Zr15Cu17S8 | Induction melting/arc melting/suction casting | 1 | Fully amorphous | 2800 | 98 | 547 | – | [104] |
TiCuZrPd:Bx (x = 0, 4, 8, 14) | Pulsed laser deposition | – | Fully amorphous | – | 108–174 | 454–685 | – | [107] |
Ti42Zr35Ta3Si5Co12.5Sn2.5 | Argon atomization/hot pressing | – | Fully amorphous | 1261 | 79.7 | – | – | [93] |
Recent cytocompatibility research for the Ti-based metallic glasses was mainly conducted with the use of the MC3T3-E1 mouse preosteoblasts cell line. Varied materials outperformed even the reference Ti-6Al-4V material [99][98]. or reached a similar level of cytocompatibility [95][96]. Similarly, good results were obtained in tests of Ti-based metallic glasses with the use of Saos-2 human osteosarcoma cells [115][116][109], human gingival fibroblasts [100], MG-63 human osteosarcoma cells [101], and L929 mouse fibroblasts [117][109][54]. Materials with confirmed in vitro cytocompatibility are good candidates for further biomedical applications.
In terms of interactions with blood, the Ti-based metallic glasses also showed superior hemocompatibility. The TiNbZrSi alloy coating was found to be non-hemolytic and, unlike the uncoated Ti-6Al-4V sample, does not exhibit platelet adherence and stimulation leading to thrombus formation [109]. The same results were also obtained for the thin films based on TiCuZrPd alloy with B addition [107].
In the field of in vivo animal research performed with Ti-based metallic glasses, there are also successful applications as implants. No inflammatory reactions nor necrosis or toxicity symptoms were observed after bone implantations in rats [106][59][97] and rabbits [119] indicating the preliminary signs of safety in short-term biomedical applications. Particular Ti-based chemical compositions of metallic glasses showed also excellent osseointegration properties [106][97] and induction of new bone tissue growth [119]. These properties are especially important when considering an application for load-bearing bone implants.
This entry is adapted from the peer-reviewed paper 10.3390/jfb13040245