Quantitative in vitro assessment of Mg 65 Zn 30 Ca 5 degradation and its effect on cell viability Jake D. Cao, 1 Penny Martens, 2 Kevin J. Laws, 1 Philip Boughton, 1 * Michael Ferry 1 1 School of Materials Science and Engineering, University of New South Wales, New South Wales 2052, Australia 2 Graduate School of Biomedical Engineering, University of New South Wales, New South Wales 2052, Australia Received 4 May 2012; revised 24 July 2012; accepted 13 August 2012 Published online 21 September 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.b.32811 Abstract: A bulk metallic glass (BMG) of composition Mg 65 Zn 30 Ca 5 was cast directly from the melt and explored as a potential bioresorbable metallic material. The in vitro deg- radation behavior of the amorphous alloy and its associated effects on cellular activities were assessed against pure crys- talline magnesium. Biocorrosion tests using potentiodynamic polarization showed that the amorphous alloy corroded at a much slower rate than the crystalline Mg. Analysis of the exchanged media using inductively coupled plasma optical emission spectrometry revealed that the dissolution rate of Mg ions in the BMG was 446 lg/cm 2 /day, approximately half the rate of crystalline Mg (859 lg/cm 2 /day). A cytotoxicity study, using L929 murine fibroblasts, revealed that both the BMG and pure Mg are capable of supporting cellular activ- ities. However, direct contact with the samples created regions of minimal cell growth around both amorphous and crystalline samples, and no cell attachment was observed. V C 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Bio- mater 101B: 43–49, 2013. Key Words: MgZnCa, bioresorbable metal, bulk metallic glass, magnesium, corrosion, in vitro How to cite this article: Cao JD, Martens P, Laws KJ, Boughton P, Ferry M. 2013. Quantitative in vitro assessment of Mg 65 Zn 30 Ca 5 degradation and its effect on cell viability. J Biomed Mater Res Part B 2013:101B:43–49. INTRODUCTION In the context of metallic implants, recent years have seen significant attention focused on magnesium and its alloys for use as bioresorbable implant materials. Compared to the existing biodegradable polymers, these metals are capable of bearing much larger loads, making them suitable for or- thopedic fixation applications. However, the majority of studies have tested commercially available alloy grades that contain toxic elements and are not suitable for in vivo use. Recent research has revealed that it is now possible to syn- thesize bulk metallic glasses (BMGs) entirely from Mg, Zn, and Ca constituents, 1–4 which are pre-existing elements in the body. Bioresorbable orthopedic components made from this type of material do not need to be removed via second- ary surgery, and studies have shown that these elements can assist in the bone-healing process. 5–7 Two classes of alloy, Mg- and Ca-rich BMGs, exist within the Mg-Zn-Ca ternary system. In comparison, the Mg-based BMGs have superior corrosion resistance, 8,9 whereas the Ca- based BMGs have improved thermophysical properties, 2,10 thereby allowing them to be processed into intricate shapes by thermoplastic forming (TPF) above their glass transition temperature. Amongst the reported bioresorbable BMGs, the most notable is Mg 60 Zn 35 Ca 5 , whereby its in vivo assess- ment in domestic pigs revealed no inflammation and insig- nificant hydrogen evolution. 9 The combination of biocom- patible elements, superior corrosion resistance, and reduced hydrogen evolution indicates that Mg-based BMGs are supe- rior implant materials compared to crystalline Mg alloys. Most researchers have assumed that the alloys based on the Mg-Zn-Ca ternary system are safe for in vivo use, and indeed there is no data to suggest the contrary. Xie et al. 11 conducted an in vivo evaluation of a Ca-Mg-Zn BMG in 3- month-old C57BL/6 mice. Examination of the harvested samples, 4 weeks after first implantation, revealed no signs of inflammation, and the authors concluded that the BMG was safe to use as an implant material. Zberg et al. 9 also observed no inflammation reaction in their Mg 60 Zn 35 Ca 5 BMG when implanted in the abdomen of domestic pigs, thereby concluding that the material was biocompatible. Although these workers showed positive results at the con- clusion of each study, very little information is available about the material’s effect on the host response throughout the period of implantation. Bioresorbable metals have a different design approach compared to the traditional bioinert metals. Rather than longevity, bioresorbable metals are designed to corrode at a controlled rate. The human body has an inherent tolerance to Mg, Zn, and Ca, with the adult daily recommended allow- ance for these elements being 1000 mg/day for Ca, 12 420 *Present address: School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW, 2006, Australia. Correspondence to: J. D. Cao; e-mail: cao.jake@gmail.com Contract grant sponsor: Australian Research Council (ARC Centre of Excellence for Design in Light Metals); contract grant number: CE0561574 V C 2012 WILEY PERIODICALS, INC. 43