دانلود رایگان مقاله اثر پارامتر فرآیند ALD بر خواص فیزیکی و شیمیایی و سطح استنت عروق

abstract

Studies of haemocompatibility of AISI 316LVM steel point to the need for nickel elimination from the surface and replacing it with other elements showing higher biotolerance. Such layers include titanium, carbon or silicon coatings. Therefore, the authors attempted to evaluate some selected physicochemical properties of TiO2 layers, grown by atomic layer deposition (ALD) method, on the surface of 316LVM steel at variable process temperature. ALD temperature has a major role in the final quality of the surface layer grown with the use of such method, regardless of the type of the base. It was observed that the growth of temperature had an adverse influence on corrosive resistance in the artificial plasma environment and contributed to formation of a double (porous) layer showing decreased tightness. Further on, assessment of the coating adhesion to the base showed that too low process temperature T = 100 8C had an adverse effect on mechanical properties, resulting in substantially reduced critical force. On the other hand, the performed surface wettability tests showed no influence of ALD temperature in the obtained angle values.

4. Conclusions

The study evaluated the effect of temperature of TiO2 deposition with ALD method, on 316LVM steel base, used to manufacture, e.g. the vascular stents. ALD temperature has a major role in the final quality of the surface layer grown with the use of such method, regardless of the type of the base. Practically, the temperatures applied range between 100 8C and 400 8C. Therefore, the authors evaluated the electrochemical and mechanical properties of the layers grown within this temperature range, aiming for the most favourable variant of surface modification. The investigations carried out showed that the process temperature has an effect upon the ultimate quality ofthe surface layer. It was observed thatthe increase of temperature had an adverse influence on corrosive resistance in the artificial plasma and contributed to formation of a double (porous) layer showing decreased tightness, as proved by EIS tests. This is why the number of metallic ions marked after 28-day exposure was highest at the temperature of 400 8C, as proved by ICP-AES investigations. Further on, assessment of the coating adhesion to the base showed that too low process temperature T = 100 8C had an adverse effect on mechanical properties, resulting in substantially reduced critical force Lc. Moreover, it was observed that the layers grown at temperatures T = 100 8C and 400 8C showed signifi- cantly lower hardness than those grown at T = 200 8C and 300 8C. The same tendency was noted in case of adhesion. Adhesion of coatings grown over the implants' surfaces contributes remarkably to their usability, while delamination may result in a local voltaic cell, initiating therefore the corrosive process which effect in reduces haemocompatibility of a device. On the other hand, the performed surface wettability tests showed no influence of ALD temperature in the obtained angle values. It was observed however that the values were favourably increased as compared to uncoated samples. All surface layers were hydrophobic which is an advantage in case of such medical devices. To sum up, the tests carried out within the framework of this study proved explicitly that the most advantageous pattern of electrochemical and mechanical properties, in the artificial plasma environment, was shown by the TiO2 film deposited with the use of ALD method at the temperature T = 200 8C. Further blood-contact cytotoxicity and biocompatibility tests shall be designed to provide comprehensive evaluation of performance of such layers.