SHAPE MEMORY ALLOYS possess distinct dynamic properties with particular applications in neurosurgery. Because of their unique physical characteristics, these materials are finding increasing application where resiliency, conformation, and actuation are needed. Nitinol, the most frequently manufactured shape memory alloy, responds to thermal and mechanical stimuli with remarkable mechanical properties such as shape memory effect, super-elasticity, and high damping capacity. Nitinol has found particular use in the biomedical community because of its excellent fatigue resistance and biocompatibility, with special interest in neurosurgical applications. The properties of nitinol and its diffusionless phase transformations contribute to these unique mechanical capabilities. The features of nitinol, particularly its shape memory effect, super-elasticity, damping capacity, as well as its biocompatibility and biomechanics are discussed herein. Current and future applications of nitinol and other shape memory alloys in endovascular, spinal, and minimally invasive neurosurgery are introduced. An understanding of the metallurgic properties of nitinol provides a foundation for further exploration of its use in neurosurgical implant design.

Self-expandable metallic stenting (SEMS) for malignant colorectal obstruction (MCO) as a bridge to elective surgery (BTS) is a widely used procedure. The aim of this study was to assess short-term outcomes of SEMS for MCO as BTS.This study analyzed pooled data from BTS patients who were enrolled in two multicenter prospective single-arm observational clinical studies that used different stent types. Both studies were conducted by the Japan Colonic Stent Safe Procedure Research Group (JCSSPRG). The first study evaluated the WallFlex™ colonic stent for BTS or palliative treatment (PAL) from May 2012 to October 2013 and the second evaluated the Niti-S™ colonic stent from October 2013 to May 2014. Fifty-three facilities in Japan participated in the studies. Before each study started, the procedure had been shared with the participating institutions by posting details of the standard methods of SEMS placement on the JCSSPRG website. Patients were followed until discharged after surgery.A total of 723 consecutive patients were enrolled in the two studies. After excluding nine patients, the remaining 714 patients were evaluated as a per-protocol cohort. SEMS placement was performed in 426 patients (312 WallFlex and 114 Niti-S) as BTS and in 288 as PAL. In the 426 BTS patients, the technical success rate was 98.1% (418/426). The clinical success rate was 93.8% (392/418). SEMS-related preoperative complications occurred in 8.5% of patients (36/426), perforations in 1.9% (8/426), and stent migration in 1.2% (5/426). Primary anastomosis was possible in 91.8% of patients (391/426), 3.8% of whom (15/393) had anastomosis leakage. The overall stoma creation rate was 10.6% (45/426). The postoperative complication rate was 16.9% (72/426) and mortality rate was 0.5% (2/426).SEMS placement for MCO as BTS is safe and effective with respect to peri-procedural outcomes. Further investigations are needed to confirm long-term oncological outcomes.

Endovascular stenting has matured into a commonly used treatment for peripheral arterial disease (PAD) due to its minimally invasive nature and associated reductions in short-term morbidity and mortality. The mechanical properties of the superelastic Nitinol alloy have played a major role in the explosion of peripheral artery stenting, with modern stents demonstrating reasonable resilience and durability. Yet in the superficial femoral and popliteal arteries, even the newest generation Nitinol stents continue to demonstrate clinical outcomes that leave significant room for improvement. Restenosis and progression of native arterial disease often lead to recurrence of symptoms and reinterventions that increase morbidity and health care expenditures. One of the main factors thought to be associated with stent failure in the femoropopliteal artery (FPA) is the unique and highly dynamic mechanical environment of the lower limb. Clinical and experimental data demonstrate that the FPA undergoes significant deformations with limb flexion. It is hypothesized that the inability of many existing stent designs to conform to these deformations likely plays a role in reconstruction failure, as repetitive movements of the leg and thigh combine with mechanical mismatch between the artery and the stent and result in mechanical damage to both the artery and the stent. In this review we will identify challenges and provide a mechanical perspective of FPA stenting, and then discuss current research directions with promise to provide a better understanding of Nitinol, specific features of stent design, and improved characterization of the biomechanical environment of the FPA to facilitate development of better stents for patients with PAD.

Plasma nanocoated films with trimethylsilane-oxygen monomers showed outstanding biocompatibility in our previous studies. In this study, endothelialization on biomedical nitinol alloy surfaces was systematically investigated. Our study focuses on elucidating the effects of surface micropatternings with micropores and microgrooves combined with plasma nanocoating. Plasma nanocoatings with controlled thickness between 40 and 50 nm were deposited onto micropatterned nitinol surface in a direct current plasma reactor. Bovine aortic endothelial cells were cultured in vitro on these nitinol samples for 1, 3 and 5 days. It was found that rougher surfaces could enhance cell adhesion compared with the smoother surfaces; the surfaces patterned with micropores showed much more endothelialization than microgrooved surface after a 3 days culture. The cell culture results also showed that plasma nanocoatings significantly further increased cell proliferation and cell adhesion on the micropatterned nitinol surfaces, as compared with non-plasma nanocoated surface of nitinol samples. The surface micropatternings combined with plasma nanocoatings could improve the cell adhesion and accelerate surface endothelialization after implantation of intravascular stents, which is expected to reduce in-stent restenosis.

The field of percutaneous coronary intervention has seen a plethora of advances over the past few decades, which have allowed for its development into safe and effective treatments for patients suffering from cardiovascular diseases. However, stent thrombosis and in-stent restenosis remain clinically significant problems. Herein, we describe the synthesis and characterization of fibrous polymer coatings on stent material nitinol, in the hopes of developing a more suitable stent surface to enhance re-endothelialization. Electrospinning technique was used to fabricate polyethylene glycol dimethacrylate/poly l-lactide acid (PEGDMA/PLLA) blend fiber substrate with tunable elasticity and hydrophilicity for use as coatings. Attachment of platelets and arterial smooth muscle cells (SMC) onto the coatings as well as the secretory effect of mesenchymal stem cells cultured on the coatings on the proliferation and migration of arterial endothelial cells and SMCs were assessed. It was demonstrated that electrospun PEGDMA/PLLA coating with 1:1 ratio of the components on the nitinol stent-reduced platelet and SMC attachment and increased stem cell secretory factors that enhance endothelial proliferation. We therefore postulate that the fibrous coating surface would possess enhanced biological compatibility of nitinol stents and hold the potential in preventing stent failure through restenosis and thrombosis.

The aim of this study is to systematically investigate the molecular mechanism of different effects of nickel titanium (NiTi) alloy surface and titanium nitride (TiN) coating on endothelial cell function. Release of nickel (Ni) ion from bare and TiN-coated NiTi alloys and proliferation of endothelial cells on the two materials were evaluated, and then influence of the two materials on cellular protein expression profiles was investigated by proteomic technology. Subsequently, proteomic data were analyzed with bioinformatics analyses and further validated using a series of biological experiments. Results showed that although the two materials did not affect cell proliferation, the Ni ions released from bare NiTi alloy generated inhibition on pathways associated with actin cytoskeleton, focal adhesion, energy metabolism, inflammation, and amino acid metabolism. In comparison, TiN coating not only effectively prevented release of Ni ions from NiTi alloy, but also promoted actin cytoskeleton and focal adhesion formation, increased energy metabolism, enhanced regulation of inflammation, and promoted amino acid metabolism. Furthermore, the two processes, "the initial mediation of adsorbed serum protein layer to endothelial cell adhesion and growth on the two materials" from our previous study, and "the following action of the two materials on cellular protein expression profile", were linked up and comprehensively analyzed. It was found that in stage of cell adhesion (within 4 h), release of Ni ions from bare NiTi alloy was very low, and the activation of adsorbed proteins to cell adhesion and growth related biological pathways (such as regulation of actin cytoskeleton, and focal adhesion pathways) was almost as same as TiN-coated NiTi alloy. This indicated that the released Ni ions did not affect the mediation of adsorbed proteins to endothelial cell adhesion. However, in stage of cell growth and proliferation, the release of Ni ions from bare NiTi alloy increased with time and reached a higher level, which inhibited endothelial cell function at molecular level, whereas TiN coating improved endothelial cell function. Copyright © 2014 Elsevier Ltd. All rights reserved.

Nanoporous ceramic coatings such as titania are promoted to produce drug-free cardiovascular stents with a low risk of in-stent restenosis (ISR) because of their selectivity towards vascular cell proliferation. The brittle coatings applied on stents are prone to cracking because they are subjected to plastic deformation during implantation. This study aims to overcome this problem by using a unique process without refraining from biocompatibility. Accordingly, a titanium film with 1 µm thickness was deposited on 316 LVM stainless-steel sheets using magnetron sputtering. Then, the samples were anodized to produce nanoporous oxide. The nanoporous oxide was removed by ultrasonication, leaving an approximately 500 nm metallic titanium layer with a nanopatterned surface. XPS studies revealed the presence of a 5 nm-thick TiO2 surface layer with a trace amount of fluorinated titanium on nanopatterned surfaces. Oxygen plasma treatment of the nanopatterned surface produced an additional 5 nm-thick fluoride-free oxide layer. The samples did not exhibit any cracking or spallation during plastic deformation. Cell viability studies showed that nanopatterned surfaces stimulate endothelial cell proliferation while reducing the proliferation of smooth muscle cells. Plasma treatment further accelerated the proliferation of endothelial cells. Activation of blood platelets did not occur on oxygen plasma-treated, fluoride-free nanopatterned surfaces. The presented surface treatment method can also be applied to other stent materials such as CoCr, nitinol, and orthopedic implants.

In the case of medical implants, foreign materials are preferential sites for bacterial adhesion and microbial contamination, which can lead to the development of prosthetic infections. Commercially biomedical TiNi shape memory alloys are the most commonly used materials for permanent implants in contact with bone and dental, and the prevention of infections of TiNi biomedical shape memory alloys in clinical cases is therefore a crucial challenge for orthopaedic and dental surgeons. In the present study, copper has been chosen as the alloying element for design and development novel ternary biomedical Ti-Ni-Cu shape memory alloys with antibacterial properties. The effects of copper alloying element on the microstructure, mechanical properties, corrosion behaviors, cytocompatibility and antibacterial properties of biomedical Ti-Ni-Cu shape memory alloys have been systematically investigated. The results demonstrated that Ti-Ni-Cu alloys have good mechanical properties, and remain the excellent shape memory effects after adding copper alloying element. The corrosion behaviors of Ti-Ni-Cu alloys are better than the commercial biomedical Ti-50.8Ni alloys. The Ti-Ni-Cu alloys exhibit excellent antibacterial properties while maintaining the good cytocompatibility, which would further guarantee the potential application of Ti-Ni-Cu alloys as future biomedical implants and devices without inducing bacterial infections.

Nickel-titanium orthodontic wires have various temperature-dependent phases. The purpose of this study was to investigate temperature-dependent corrosion characteristics of shape memory, superelastic, and nonsuperelastic orthodontic wires.Four orthodontic wires were investigated: 27 and 40 degrees C copper Ni-Ti (superelastic and shape memory, respectively), superelastic Ni-Ti, and nonsuperelastic Nitinol Classic. Differential scanning calorimetry (DSC) was used to confirm phase/temperature behavior of the wires. Sectioned halves of as-received archwires were assessed electrochemically in artificial saliva at 5, 24, 37, and 45 degrees C. Open circuit potential (OCP) was monitored for 2h followed by polarization resistance and cyclic polarization tests.DSC results showed Nitinol was primarily martensitic-stable whereas NiTi, 27 degrees C CuNiTi, and 40 degrees C CuNiTi possessed austenite-finish temperatures of approximately 19, 21, and 38 degrees C. The OCP of the CuNiTi wires was significantly greater than NiTi and Nitinol but no apparent trend in values was apparent with regard to temperature or phases present. Corrosion current density (i(corr)) increased with temperature for all wires, but not all were equally influenced. The two lowest austenite-finish temperature wires (27 degrees C CuNiTi and NiTi) approximately tripled in i(corr) from 37 to 45 degrees C. Greater incidence of pitting was observed in the CuNiTi wires.This study showed the corrosion rate of various nickel-titanium wires increase with temperature and different phases present may influence corrosion rate trends.

An electrochemical study aiming at the evaluation of corrosion parameters using potentiodynamic and potentiostatic techniques ("scratch" and modified ASTM F746) was conducted in 0.9% NaCl on wires from equiatomic Ni-Ti and ternary Ni44Ti51Cu5 superelastic alloys with Ti90Mo10 as a reference material. The results obtained using potentiostatic tests, that simulate better the behavior of material in service conditions than potentiodynamic ones, indicate that both Ni-Ti and Ni-Ti-Cu wires exhibit low corrosion potentials (approximately 50-150 mV versus SCE) inferior to that of Ti-Mo alloy. The latter proved to be immune to localized corrosion attacks up to 800 mV.

The in vitro anticoagulant property of a medical grade 316L stainless steel with 0.05% La addition was systematically studied. The results showed that, compared with the conventionally used medical 316L stainless steel, the La added 316L steel possesses less platelets adhesion and less activation of the platelets, and their kinetic clotting time and the plasma recalcification time become longer, which reveals that the activation extent of the latter on intrinsic coagulation factors is smaller than the former and the anticoagulant property of the latter is better. Through measurement of the contact angles of the steels, and calculations of the surface tension of the steels and the interfacial tension between the steels and the blood, the anticoagulant mechanism of the steels was analyzed from the viewpoint of surface energy.

系统研究了在医用316L不锈钢中加入0.05%La后的体外抗凝血性能. 结果表明, 与传统医用316L不锈钢相比, 含La医用316L不锈钢较少地粘附和激活血小板, 且动态凝血时间及血浆复钙时间均延长, 表明其对内源性凝血因子的激活程度下降, 抗凝血性能提高. 通过测量材料的接触角, 计算了表面张力及材料与血液之间的界面张力, 从表面能的角度分析了材料的抗凝血机理.

Drug eluting stents (DES) have been extensively applied nowadays and reduce the incidence of instent restenosis (ISR) greatly as compared with bare metal stents (BMS). However, the development of DES is hindered by the risk of late stent thrombosis (LST) due to delayed re-endothelialization, while endothelialization is an important process related to ISR and LST after implantation. 316L is a traditional stent material without bioactivity and have a high risk of ISR. Cu is recognized for angiogenesis stimulation in these years. Hence a copper bearing 316L stainless steel (316L-Cu) was prepared and evaluated about its effect on endothelialization in this paper. Compared with traditional 316L, it was proved that 316L-Cu increased the proliferation of co-cultured human umbilical vein endothelial cells (HUVECs) at first day. Moreover, HUVECs stretched better on the surface of 316L-Cu. It also improved the expression of angiogenesis related genes and tube formation ability in vitro. 316L-CuBMS, DES and 316L-BMS were implanted in swine to evaluate the re-endothelialization ability in vivo. And 316L-Cu-BMS showed the best effect on endothelialization with good biosafety. Consequently, 316L-Cu is a kind of promising BMS material for coronary field.