Abstract
INTRODUCTION
Nickel-Titanium (NiTi) with a molar composition of 50:50 or nitinol alloy exhibit special mechanical properties. These properties can be put to excellent use in various biomedical applications including: intravascular stent, orthodontic wires, prosthetic heart valves, angioplastic guides, orthopaedic implants, bone substitution materials, endoscopic instruments, implant stents and filters. Microorganism adhesion properties of nitinol may be decreased by oxidizing agents and surface heat treatment. In the present study, we investigated the microorganism adhesion and cytotoxicity of the thin film of nitinol and compared these properties with that of bulk form.
METHODS
In this analytical comparative study, small parts of thin film and bulk form of nitinol (15 mm×15 mm) were selected and sterilized in autoclave (15 lb for 20 min). Five microorganism, four bacteria (Ecoli, staphylococcus aureus, pseudomonase aerugenosa, bacillus cereus) and one mold form of fungi (candida albicans) were selected. The sample materials (thin film and bulk forms of nitinol) were treated by microorganism suspensions in 37°C for 24h in different culture flasks. Every suspension of five microorganisms was counted before and after examination. Adherence activity of these forms of nitinol was studied by optical and electron microscopy. The interaction between the microorganisms and the two forms of nitinol alloy were studied by variation in number of microorganisms counted after introduction of these living organisms to the surface of the alloy.
RESULTS
It was observed that the five separate microorganisms put in contact with the thin film in comparison with the bulk form showed lower decrease rate of cells (mean decrease rate of 39% for thin film, 62% for bulk form, sd < 0.05). On the thin film, a decrease rate of 14% for Ecoli, 44% for P. aeroginesia, 30.1%for S. aureus, 22% for B. cereus and 6.4% for C. albicans were registered. However, for cells in contact with the bulk form nitinol, decrease rate of cells were 39% for E. coli, 62% for P. aeroginosa, 61.9% for S. aureeus, 49% for B. cereus and 31% for C. albicans.
DISCUSSION & CONCLUSIONS
In this study, in every forms of nitinol alloy (thin film and bulk), microorganisms numbers were declined. Thin film nitinol exhibits lower decrease rate of cells at the end of the test. This shows that this thin film nitinol have less cytotoxicity for bacterial and fungal cells in comparison with the bulk. As it appears in electron microscopic micrographs, higher adherence activity of the thin film can be attributed to smoothness and lower amount of nickle released form this surface. This property detected in vitro study may be also appeared in vivo. These different behaviours of the two forms of nitinol alloy is probably due to the better biocompatibility of the thin film. This new form of alloy with its better qualities can be a promising process for developing medical prosthetic devices.
