A Ni-free ZrCuFeAlAg bulk metallic glass with potential for biomedical applications

A tantalum-containing zirconium-based metallic glass with superior endosseous implant relevant properties

Zirconium-based metallic glasses (Zr-MGs) are demonstrated to exhibit high mechanical strength, low elastic modulus and excellent biocompatibility, making them promising materials for endosseous implants. Meanwhile, tantalum (Ta) is also well known for its ideal corrosion resistance and biological effects. However, the metal has an elastic modulus as high as 186 GPa which is not comparable to the natural bone (10-30 GPa), and it also has a relative high cost. Here, to fully exploit the advantages of Ta as endosseous implants, a small amount of Ta (as low as 3 at. %) was successfully added into a Zr-MG to generate an advanced functional endosseous implant, Zr58Cu25Al14Ta3 MG, with superior comprehensive properties. Upon carefully dissecting the atomic structure and surface chemistry, the results show that amorphization of Ta enables the uniform distribution in material surface, leading to a significantly improved chemical stability and extensive material-cell contact regulation. Systematical analyses on the immunological, angiogenesis and osteogenesis capability of the material are carried out utilizing the next-generation sequencing, revealing that Zr58Cu25Al14Ta3 MG can regulate angiogenesis through VEGF signaling pathway and osteogenesis via BMP signaling pathway. Animal experiment further confirms a sound osseointegration of Zr58Cu25Al14Ta3 MG in achieving better bone-implant-contact and inducing faster peri-implant bone formation.

Biocompatibility of a Zr-Based Metallic Glass Enabled by Additive Manufacturing

The present work explored the use of the selective laser melting (SLM) technique to develop a Zr-based bulk metallic glass (BMG) and investigate the influence of the process parameters on obtaining different levels of surface roughness. Moreover, the potential of the additively manufactured BMG Zr_59.3Cu_28.8Al_10.4Nb_1.5 (trade name AMLOY-ZR01) as an implant material was studied by evaluating the osteoblastic cell response to the alloy and its stability under simulated biological environments. The materials were characterized in terms of degree of crystallinity, surface roughness, and morphology, followed by a systematic investigation of the response of the MC3T3-E1 preosteoblastic cell line to the as-printed samples. The materials supported cell proliferation and differentiation of the preosteoblastic cells, with results comparable to the reference material Ti-6Al-4V. The surface microroughness and surface morphology (porous or groove-type laser tracks) investigated in this study did not have a significant effect on modulating the cell response. Ion release experiments showed a large increase in ion release under inflammatory conditions as compared to regular physiological conditions, which could be attributed to the increased local corrosion under inflammatory conditions. The findings in this work showed that the surface roughness of the additively manufactured BMG AMLOY-ZR01 can be tailored by controlling the laser power applied during the SLM process. The favorable cell response to the as-printed AMLOY-ZR01 represents of a significant advancement of the investigation of additively manufactured BMGs for orthopedic applications, while the results of the ion release study highlights the effect that inflammatory conditions could have on the degradation of the alloy.

Review on Biocompatibility and Prospect Biomedical Applications of Novel Functional Metallic Glasses

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. This review article intends to synthesize the latest research results in the field of biocompatible metallic glasses to create a more coherent picture of these materials. It summarizes and discusses the most recent findings in the areas of mechanical properties, corrosion resistance, in vitro cellular studies, antibacterial properties, and in vivo animal studies. Results are collected mainly for the most popular metallic glasses manufactured as thin films, coatings, and in bulk form. Considered materials include alloys based on zirconium and titanium, as well as new promising ones based on magnesium, tantalum, and palladium. From the properties of the examined metallic glasses, possible areas of application and further research directions to fill existing gaps are proposed.

Recent Developments in Additive-Manufactured Intermetallic Compounds for Bio-Implant Applications

Purpose

This paper reviews the recent developments of two newly developed intermetallic compounds (IMCs) of metallic glasses (MGs) and high-entropy alloys (HEAs) as potential implantable biomaterials.

Methods

The paper commences by summarizing the fundamental properties of recently developed MGs and high-entropy alloys (HEAs). A systematic review is presented of the recent literature about the use of AM technology in fabricating MG and HEA components for biological implant applications.

Results

The high strength, low Young’s modulus, and excellent corrosion resistance make these IMCs good candidates as bio-implantable materials. Recent studies have shown that additive manufacturing (AM) techniques provide an advantageous route for the preparation of glassy metallic components due to their intrinsically rapid cooling rates and ability to fabricate parts with virtually no size or complexity constraints. A practical example is conducted by AM producing a porous gradient Ti-based MG spinal cage. The produced MG powders and the in vivo test results on an 18 M-old Lanyu pig confirm the feasibility of the AM technique for producing implantable IMC-based prosthesis.

Conclusion

The non-crystalline structure of MGs alloy and the random crystalline composition of HEAs provide unique material properties that will substantially impact the development of future implantable prostheses.

Biocompatibility of micro/nano structures on the surface of Ti6Al4V and Ti-based bulk metallic glasses induced by femtosecond laser

Femtosecond laser surface modification has been proved to be a versatile technology to create various functional materials by modifying solid surface properties. An interesting experimental phenomenon is found by exposing a Ti6Al4V alloy and Ti-based metallic glass to femtosecond laser irradiation. The research results show that the femtosecond laser induces different micro-nano structures on the surfaces of Ti6Al4V alloy and Ti-based metallic glass. Spherical structure and LIPSS (Laser-induced periodic surface structures) can be formed on the surface of Ti6Al4V alloy after femtosecond laser irradiation. On the surface of Ti-based metallic glass, LIPSS, SWPSS (Super-wavelength periodic surface structure) and neatly arranged microholes structures can be found. Under the same laser parameters, the micro-nano structures showed different evolution trends on the Ti6Al4V alloy and Ti-based metallic glass surfaces. The difference in surface structure between Ti6Al4V alloy and Ti-based metallic glass is since amorphous materials have no crystal lattice and a fixed melting temperature. In addition, there are differences in the biocompatibility of different surface structures. The size and distance of the micro-pits on the surface of different structures determine the ability of cells to adhesion, proliferate and differentiate. This conclusion has important significance for the application of Ti6Al4V alloy and Ti-based metallic glass in the field of biomedicine.

Osteogenesis and angiogenesis of a bulk metallic glass for biomedical implants

Implantation is an essential issue in orthopedic surgery. Bulk metallic glasses (BMGs), as a kind of novel materials, attract lots of attentions in biological field owing to their comprehensive excellent properties. Here, we show that a Zr61Ti2Cu25Al12 (at. %) BMG (Zr-based BMG) displays the best cytocompatibility, pronounced positive effects on cellular migration, and tube formation from in-vitro tests as compared to those of commercial-pure titanium and poly-ether-ether-ketone. The in-vivo micro-CT and histological evaluation demonstrate the Zr-based BMG can significantly promote a bone formation. Immunofluorescence tests and digital reconstructed radiographs manifest a stimulated effect on early blood vessel formation from the Zr-based BMG. Accordingly, the intimate connection and coupling effect between angiogenesis and osteogenesis must be effective during bone regeneration after implanting Zr-based BMG. Dynamic gait analysis in rats after implanting Zr-based BMG demonstrates a tendency to decrease the pain level during recovery, simultaneously, without abnormal ionic accumulation and inflammatory reactions. Considering suitable mechanical properties, we provide a realistic candidate of the Zr61Ti2Cu25Al12 BMG for biomedical applications.

Production, Mechanical Properties and Biomedical Characterization of ZrTi-Based Bulk Metallic Glasses in Comparison with 316L Stainless Steel and Ti6Al4V Alloy

Microstructure, mechanical properties, corrosion resistance, and biocompatibility were studied for rapidly cooled 3 mm rods of Zr₄₀Ti₁₅Cu₁₀Ni₁₀Be₂₅, Zr₅₀Ti₅Cu₁₀Ni₁₀Be₂₅, and Zr₄₀Ti₁₅Cu₁₀Ni₅Si₅Be₂₅ (at.%) alloys, as well as for the reference 316L stainless steel and Ti-based Ti6Al4V alloy. Microstructure investigations confirm that Zr-based bulk metallic samples exhibit a glassy structure with minor fractions of crystalline phases. The nanoindentation tests carried out for all investigated composite materials allowed us to determine the mechanical parameters of individual phases observed in the samples. The instrumental hardness and elastic to total deformation energy ratio for every single phase observed in the manufactured Zr-based materials are higher than for the reference materials (316L stainless steel and Ti6Al4V alloy). A scratch tester used to determine the wear behavior of manufactured samples and reference materials revealed the effect of microstructure on mechanical parameters such as residual depth, friction force, and coefficient of friction. Electrochemical investigations in simulated body fluid performed up to 120 h show better or comparable corrosion resistance of Zr-based bulk metallic glasses in comparison with 316L stainless steel and Ti6Al4V alloy. The fibroblasts viability studies confirm the good biocompatibility of the produced materials. All obtained results show that fabricated biocompatible Zr-based materials are promising candidates for biomedical implants that require enhanced mechanical properties.

Application of Zr and Ti-Based Bulk Metallic Glasses for Orthopaedic and Dental Device Materials

Conventional orthopaedic and dental device materials are made of metallic materials such as stainless steel (SUS316L), titanium alloy (Ti-6Al-4V), and cobalt-chrome (Co-Cr). Those materials have the disadvantage of mechanical properties and anti-corrosion behavior. Bulk metallic glasses (BMGs), which are also called amorphous alloys, are metallic materials with metastable glassy states and have a higher strength, higher elasticity, higher failure resistance, and lower Young’s modulus compared with crystalline alloys. There are several types of BMGs. Among them, Zr-based BMGs and Ti-based BMGs have excellent mechanical properties. In addition, they have good corrosion resistance and are promising for orthopaedic and dental device materials. In this review article, in vitro and in vivo studies regarding Zr and Ti-based BMGs applications as biomaterials, especially in orthopaedic and dental device materials, are reviewed.

Hierarchical surface patterning of Ni- and Be-free Ti- and Zr-based bulk metallic glasses by thermoplastic net-shaping

In order to establish a strong cell-material interaction, the surface topography of the implant material plays an important role. This contribution aims to analyze the formation kinetics of nickel and beryllium-free Ti- and Zr-based Bulk Metallic Glasses (BMGs) with potential biomedical applications. The surface patterning of the BMGs is achieved by thermoplastic net-shaping (TPN) into anisotropically etched cavities of silicon chips. The forming kinetics of the BMG alloys is assessed by thermal and mechanical measurements to determine the most suitable processing temperature and time, and load applied. Array of pyramidal micropatterns with a tip resolution down to 50nm is achievable for the Zr-BMG, where the generated hierarchical features are crucial for surface functionalization, acting as topographic cues for cell attachment. The unique processability and intrinsic properties of this new class of amorphous alloys make them competitive with the conventional biomaterials.

In Vivo Evaluation of Bulk Metallic Glasses for Osteosynthesis Devices

Bulk metallic glasses (BMGs) show higher strength and lower Young’s modulus than Ti-6Al-4V alloy and SUS 316L stainless steel. This study aimed to perform in vivo evaluations of Zr₆₅Al_7.5Ni₁₀Cu_17.5 BMGs for osteosynthesis devices. In the study for intramedullary implants, osteotomies of the femoral bones were performed in male Wistar rats and were stabilized with Zr₆₅Al_7.5Ni₁₀Cu_17.5 BMGs, Ti-6Al-4V alloy, or 316L stainless steel intramedullary nails for 12 weeks. In the study for bone surface implants, Zr₆₅Al_7.5Ni₁₀Cu_17.5 BMGs ribbons were implanted on the femur surface for 6 weeks. Local effects on the surrounding soft tissues of the implanted BMGs were assessed by histological observation. Implanted materials’ surfaces were examined using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS). In the study for intramedullary implants, bone healing after osteotomy was assessed by peripheral quantitative computed tomography (QCT) and mechanical tests. Histological observation showed no findings of the biological effects. SEM-EDS showed no noticeable change on the surface of BMGs, while Ca and P deposition was seen on the Ti-6Al-4V alloy surface, and irregularities were seen on the 316L stainless steel surface. Mechanical test and peripheral QCT showed that, although there was no significant difference, bone healing of BMGs was more than that of Ti-6Al-4V alloy. The results indicated that Zr-based BMGs can lead to bone healing equal to or greater than Ti-6Al-4V alloy. Zr-based BMGs exhibited the advantage of less bone bonding and easier implant removal compared with Ti-6Al-4V alloy. In conclusion, Zr-based BMGs are promising for osteosynthesis devices that are eventually removed.

Bulk Metallic Glasses for Implantable Medical Devices and Surgical Tools

With increasing knowledge of the materials science of bulk metallic glasses (BMGs) and improvements in their properties and processing, they have started to become candidate materials for biomedical devices. A dichotomy in the types of medical applications has also emerged, in which some families of BMGs are being developed for permanent devices whilst another family - of Mg-based alloys - is showing promise in bioabsorbable implants. The current status of these metallurgical and technological developments is summarized.

Feasibility of using bulk metallic glass for self-expandable stent applications

Self-expandable stents are widely used to restore blood flow in a diseased artery segment by keeping the artery open after angioplasty. Despite the prevalent use of conventional crystalline metallic alloys, for example, nitinol, to construct self-expandable stents, new biomaterials such as bulk metallic glasses (BMGs) are being actively pursued to improve stent performance. Here, we conducted a series of analyses including finite element analysis and molecular dynamics simulations to investigate the feasibility of using a prototypical Zr-based BMG for self-expandable stent applications. We model stent crimping of several designs for different percutaneous applications. Our results indicate that BMG-based stents with diamond-shaped crowns suffer from severe localization of plastic deformation and abrupt failure during crimping. As a possible solution, we further illustrate that such abrupt failure could be avoided in BMG-based stents without diamond shape crowns. This work would open a new horizon for a quest toward exploiting superior mechanical and functional properties of metallic glasses to design future stents. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1874-1882, 2017.

Recent advances in bulk metallic glasses for biomedical applications

With a continuously increasing aging population and the improvement of living standards, large demands of biomaterials are expected for a long time to come. Further development of novel biomaterials, that are much safer and of much higher quality, in terms of both biomedical and mechanical properties, are therefore of great interest for both the research scientists and clinical surgeons. Compared with the conventional crystalline metallic counterparts, bulk metallic glasses have unique amorphous structures, and thus exhibit higher strength, lower Young's modulus, improved wear resistance, good fatigue endurance, and excellent corrosion resistance. For this purpose, bulk metallic glasses (BMGs) have recently attracted much attention for biomedical applications. This review discusses and summarizes the recent developments and advances of bulk metallic glasses, including Ti-based, Zr-based, Fe-based, Mg-based, Zn-based, Ca-based and Sr-based alloying systems for biomedical applications. Future research directions will move towards overcoming the brittleness, increasing the glass forming ability (GFA) thus obtaining corresponding bulk metallic glasses with larger sizes, removing/reducing toxic elements, and surface modifications.

STATEMENT OF SIGNIFICANCE

Bulk metallic glasses (BMGs), also known as amorphous alloys or liquid metals, are relative newcomers in the field of biomaterials. They have gained increasing attention during the past decades, as they exhibit an excellent combination of properties and processing capabilities desired for versatile biomedical implant applications. The present work reviewed the recent developments and advances of biomedical BMGs, including Ti-based, Zr-based, Fe-based, Mg-based, Zn-based, Ca-based and Sr-based BMG alloying systems. Besides, the critical analysis and in-depth discussion on the current status, challenge and future development of biomedical BMGs are included. The possible solution to the BMG size limitation, the brittleness of BMGs has been proposed.

A Zr-based bulk metallic glass for future stent applications: Materials properties, finite element modeling, and in vitro human vascular cell response

Despite the prevalent use of crystalline alloys in current vascular stent technology, new biomaterials are being actively sought after to improve stent performance. In this study, we demonstrated the potential of a Zr-Al-Fe-Cu bulk metallic glass (BMG) to serve as a candidate stent material. The mechanical properties of the Zr-based BMG, determined under both static and cyclic loadings, were characterized by high strength, which would allow for the design of thinner stent struts to improve stent biocompatibility. Finite element analysis further complemented the experimental results and revealed that a stent made of the Zr-based BMG was more compliant with the beats of a blood vessel, compared with medical 316L stainless steel. The Zr-based BMG was found to be corrosion resistant in a simulated body environment, owing to the presence of a highly stable ZrO2-rich surface passive film. Application-specific biocompatibility studies were conducted using human aortic endothelial cells and smooth muscle cells. The Zr-Al-Fe-Cu BMG was found to support stronger adhesion and faster coverage of endothelial cells and slower growth of smooth muscle cells than 316L stainless steel. These results suggest that the Zr-based BMG could promote re-endothelialization and potentially lower the risk of restenosis, which are critical to improve vascular stent implantation integration. In general, findings in this study raised the curtain for the potential application of BMGs as future candidates for stent applications.

STATEMENT OF SIGNIFICANCE

Vascular stents are medical devices typically used to restore the lumen of narrowed or clogged blood vessel. Despite the clinical success of metallic materials in stent-assisted angioplasty, post-surgery complications persist due to the mechanical failures, corrosion, and in-stent restenosis of current stents. To overcome these hurdles, strategies including new designs and surface functionalization have been exercised. In addition, the development of new materials with higher performance and biocompatibility can intrinsically reduce stent failure rates. The present study demonstrates the advantages of a novel material, named bulk metallic glass (BMG), over the benchmarked 316L stainless steel through experimental methods and computational simulations. It raises the curtain of new research endeavors on BMGs as competitive alternatives for stent applications.

In vivo evaluation of Zr-based bulk metallic glass alloy intramedullary nails in rat femora

Zr-based bulk metallic glasses (BMG) show high corrosion resistance in vitro and higher strength and lower Young's modulus than crystalline alloys with the similar composition. This study aimed to perform an in vivo evaluation of Zr65Al7.5Ni10Cu17.5 BMG. Osteotomy of the femur was done in rats and stabilized with intramedullary nails made of Zr65Al7.5Ni10Cu17.5 BMG, Ti-6Al-4V alloy, or 316L stainless steel. Systemic and local effects of each type of nail were evaluated by measuring the levels of Cu and Ni in the blood and the surrounding soft tissue. Changes of the surface of each nail were examined by scanning electron microscopy (SEM). Healing of the osteotomy was evaluated by peripheral quantitative computed tomography and mechanical testing. No increase of Cu and Ni levels was recognized. Surface of the BMG showed no noticeable change, while Ti-6Al-4V alloy showed Ca and P deposition and 316L stainless steel showed surface irregularities and pitting by SEM observation. The stress strain index, maximum torque, torsional stiffness, and energy absorption values were larger for the BMG than those for Ti-6Al-4V alloy, although there was no significant difference. The Zr-based BMG can promote osteotomy healing as fast as Ti-6Al-4V alloy, with the possible advantage of the Zr-based BMG that bone bonding is less likely, allowing easier nail removal compared with Ti-6Al-4V alloy. The Zr-based BMG is promising for the use in osteosynthetic devices that are eventually removed.