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Modification of titanium and its alloys implants by low temperature surface plasma treatments for cardiovascular applications

Wierzchoń T., Witkowska J., Morgiel J., Sowińska A., Tarnowski M., Czarnowska E.

Inżynieria Materiałowa

2018

Vol. 39, nr 4

130--139

Impairment of the cardiovascular system is a major cause of mortality in humans. Cardiac implants are made mostly of titanium and its alloys and various methods have been used to improve their surface properties. Titanium nitride — TiN and titanium oxide — TiO2 surface layers are promising materials to improve biocompatibility in this respect. Modifying their surface properties in the nanoscale may impact their protein adsorption and cellular response to the implant. Nitriding and oxynitriding processes in low-temperature plasma, also involving the use of an active screen, seem to be prospective methods in the production of titanium nitride and oxide forming an diffusive outer zone of titanium nitride TiN (nanocrystalline) + Ti2N + α-Ti(N) or oxynitrided TiO2(nanocrystalline) + TiN + Ti2N + α-Ti(N) surface layers on titanium alloy. Also a hybrid method that combines oxidizing and the RFCVD process for producing a-C:N:H (amorphous carbon modified with nitrogen and hydrogen) + TiO2 (nanocrystalline titanium oxide-rutile)-type composite surface layers on NiTi shape memory alloys is noteworthy in the context of medical applications. The paper presents the characteristics of these diffusion multi-phase layers in terms of their microstructure, topography, hardness, residual stress, corrosion and wear resistance, wettability as well as biological properties such as: adsorption of proteins — fibrinogen and albumin, and platelet adhesion during interaction with blood components (human plasma and platelet-rich plasma). The results suggest that these layers, produced using the new hybrid processes, exhibit a high potential for improving cardiac implant properties. The article is based on research carried out by the authors and the interpretation of the obtained results is made on the basis of literature data regarding the surface layers of titanium oxides and titanium nitride produced by various methods.

Choroby układu krążenia są jedną z głównych przyczyn śmiertelności u ludzi. Biozgodność i inne właściwości implantów kardiologicznych, wytwarzanych z tytanu i jego stopów, można kształtować, stosując różne metody inżynierii powierzchni. W pracy przedstawiono charakterystykę wielofazowych, dyfuzyjnych warstw powierzchniowych typu TiN + Ti2N + α-Ti(N) oraz TiO2 + TiN + Ti2N + α-Ti(N) wytwarzanych w niskotemperaturowej plazmie na stopie tytanu Ti6Al4V, także z wykorzystaniem aktywnego ekranu, pod kątem ich mikrostruktury, topografii powierzchni, twardości, stanu naprężeń własnych, odporności na korozję i zużycie, zwilżalności oraz właściwości biologicznych, takich jak: adsorpcja białek — fibrynogenu i albuminy oraz adhezja płytek krwi podczas inkubacji z ludzkim osoczem i osoczem bogatopłytkowym. Przedstawiono także wyniki badań warstw typu TiO2 oraz a-CNH + TiO2 wytwarzanych na stopie z pamięcią kształtu NiTi. Artykuł prezentuje wyniki badań przeprowadzonych przez autorów, a interpretacji uzyskanych wyników dokonano w porównaniu z danymi literaturowymi dotyczącymi powierzchniowych warstw złożonych z tlenku tytanu i azotku tytanu wytwarzanych różnymi metodami.

X-ray diffraction studies of NiTi shape memory alloys

Lekston Z., Łągiewka E.

Archives of Materials Science and Engineering

2007

Vol. 28, nr 11

665-672

Purpose: The purpose of this paper is to present the results of the investigations of phase transitions of TiNiCo and Ni-rich NiTi shape memory alloys designed for medical applications. Design/methodology/approach: Temperature X-ray diffraction (TXRD), differential scanning calorimetry (DSC), electrical resistivity (ER) and the temperature shape recovery measurements in three-point bending ASTM 2082-01 tests were used. Findings: It has been found in this work that ageing after solution treatment and annealing below the recrystallization temperature after cold working in the alloys studied create separate reversible B2 ↔ R ↔ B19' transformations. During thermomechanical cycles characteristic temperatures of the reversible B2 ↔ R phase transition remain stable. It was concluded that ageing after solution treatment or recovery during annealing after cold working causes the precipitation process and the changes of the defect structure of the alloys promote transitions with the R-phase contribution. Research limitations/implications: The results of the courses of transformations and their characteristic temperatures obtained by TXRD, DSC and ER techniques have a good correlation. Future TXRD research with the use of automatic rapid recording of diffraction patterns during cooling and heating are necessary. The course of phase transitions of the studied alloys determine their applications. Practical implications: The obtained results can be applied into the practice of processing and thermomechanical treatments of NiTi alloys designed for the production of shape memory medical implants and devices which act under the influence of the human body heat. Presented are the conditions of thermomechanical treatment to obtain a wide temperature range for the R-phase existence in the investigated alloys. Originality/value: The paper presents new results of optimization of the thermal treatment of NiTi shape memory alloys to obtain the reversible B2 ↔ R transformation used to prepare new shape memory implants and medical devices which exhibit shape recovery at a narrow temperature range below the human body temperature. In this paper it was shown that the temperature X-ray diffraction method can be used for the visualization of transformation courses and obtaining characteristic temperatures of transformations.