Contrary to popular belief, modern technological materials such as shape memory alloys (SMAs) that are increasingly used in a wide range of medical devices and implants are entirely biocompatible and should not induce health problems, according to a European team of scientists. SMAs are favoured for their ability to be bent and squeezed into a target body cavity or vessel after which they then revert to their original, working shape, but concerns have been voiced about the toxicity of SMAs which often contain nickel or copper. The findings of the study were published in the International Journal of Immunological Studies. SMAs are frequently used in medical implants, guide wires for catheters, blood vessel stents, filters and actuators. Despite previous tests showing them to be entirely biocompatible, people are still concerned about whether this technology could have harmful effects on a patient's health. Researchers from the University of Maribor in Slovenia, the University of Leoben in Austria and the Military Medical Academy in Belgrade in Serbia suggest that patients can now rest easy in the knowledge that SMAs made from copper-aluminium-nickel (Cu-Al-Ni) and nickel-titanium (Ni-Ti) do not damage the body or trigger cell death. SMAs belong to a group of functional, smart materials whose unique property is to 'remember' the shape they had before undergoing pseudo-plastic deformation. 'Such an effect is based on crystallographic reversible thermo-elastic martensitic transformation,' the researchers said, adding that 'Nickel-Titanium (Ni-Ti) SMAs have been mostly explored and applied in biomedicines because of their excellent flexibility and deformation behaviour similar to that of living tissues.' 'Cu-based SMAs, especially Cu-Al-Ni and Cu-Al-Mn are commercially available too, but their biomedical application has not been thoroughly investigated,' they explained. However, the team acknowledged that the Cu-Al-Ni alloys are much cheaper than Ni-Ti alloys. Currently, they are also the only option if high transformation temperatures are needed given that 'the transformation temperatures of Ni-Ti alloys can be adjusted in the range between 200°C and 120°C, whereas the characteristic temperatures of martensitic transformation of Cu-Al-Ni alloys can lie between -200°C and 200°C, depending on the content of Al and Ni'. Rebeka Rudolf from the University of Maribor, and her colleagues, used immune system cells and human peripheral blood mononuclear cells to demonstrate the relative safety of these products. The researchers prepared samples of SMAs as thin ribbons using melt spinning and then cultured PB-MNCs from 20 donors in a solution containing a Cu-Al-Ni SMA. They found no significant changes in the production of immune system mediators, known as cytokines, in 18 of the 20 test cultures. However, for two of the donor cells there was a marked immune response that was easily seen as inflammatory cytokines were released by the cells. The team said its test could provide the medical profession with a quick and easy way to test a prospective patient for biocompatibility of a particular device. 'This is the first report showing the influence of SMA materials produced as thin ribbons by spin melting technology on human cells,' the researchers noted. 'By using a simple screening test it should possible to identify those individuals who would develop an inflammatory response in contact with a biomaterial and so predict undesirable reactions before implantation.'
Austria, Serbia, Slovenia