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Shape memory alloys are mainly used in medical devices and surgical implants due to their biocompatibility. Machining these alloys into intricate patterns can be challenging due to their poor thermal conductivity which could lead to a poor surface finish. The poor surface finish causes a release of toxic elements such as Nickel, leading to contact allergies and thus deteriorating its biocompatibility. Using the right cooling technology can help improve their machinability and overcome issues related to surface integrity. The current study investigates the effect of milling parameters (cutting-speed, feed rate, and depth of cut) and different cooling strategies (flood coolant, cryogenic liquid nitrogen, and a hybrid approach) on the surface integrity of F2063 Ni55.6Ti44.4 shape memory alloy. In addition, the effect of cryogenically treating the cutting tool for further enhancement of surface finish was investigated. A considerable modification on the milled surfaces was observed when using the hybrid cooling/milling approach and cryo-treated tools in terms of morphological, chemical compositional, crystallographic, and microhardness. In addition, this modified surface had a noticeably improved bioactivity due to enhanced hydrophobicity (with contact angle 92°) and surface topography (Ra: 341.69 nm), which favoured cell adhesion and proliferation. The results indicate that the modified Ni55.6Ti44.4 alloy surface might be adequate for use in medical applications.

Purpose Blood compatibility of cardiovascular implants is still a major concern. Rapid endothelialization of these implant surfaces has emerged as a promising strategy to enhance hemocompatibility and prevent complications such as thrombus formation and restenosis. The successful endothelialization of implant surfaces mostly depends on the migration of endothelial cells (ECs), the differentiation of stem cells, and the inhibition of smooth muscle cell (SMC) proliferation. Our previous study demonstrated that nanostructured titania surfaces modified with polyelectrolyte multilayers based on tanfloc (a cationic tannin derivative) and glycosaminoglycans (heparin and hyaluronic acid) have improved antithrombogenic properties. Methods In this work, we used in vitro cell culture of ECs and SMCs to investigate the outcomes of these surface modifications on endothelialization. The cells were seeded on the surfaces, and their viability, adhesion, and proliferation were evaluated after 1, 3, and 5 days. Indirect immunofluorescent staining was used to determine the cellular expression of ECs through the presence of specific marker proteins after 7 and 10 days, and EC migration on the NT surfaces was also investigated. Results The surfaces modified with tanfloc and heparin showed enhanced EC adhesion, proliferation, and migration. However, SMC proliferation is not promoted by the surfaces. Therefore, these surfaces may promote endothelialization without stimulating SMC proliferation, which could improve the hemocompatibility without enhancing the risk of SMC proliferation leading to restenosis. Conclusions The surface modification here proposed is a promising candidate to be used in cardiovascular applications due to enhanced antithrombogenic and endothelialization properties.