Yun Luo

Metal-Containing DLC: Toward a Smart Coating on Smart Materials

NiTi shape memory alloys (NiTi-SMA or Nitinol) have successful application thanksto their excellent and unique material properties. However, considering the practical applicationto human body, elution from the toxic Ni ions into human body should be taken into account.Many researchers have dealt with the issue and already proposed various surface treatmenttechniques including the surface oxidation and ion implantation.Our focus is to enhance thefunctionality of Nitinol. We have been developing the smart sensor utilizing metal-containingDiamond-like Carbon (Me-DLC) thin coating. Emphasis can be made on the unique propertiesof Me-DLC deposited on the Nitinol. Strong adhesive strength has been obtained in Me-DLCand Nitinol system. In this paper, we propose a novel Me-DLC coating with multifunctionalityof the suppression of the toxic Ni ions. The paper includes deposition technique, performanceof the coating concerning adhesive strength and suppression of the toxic Ni ions, and finallymultilayered structure aiming at multifunctionality.

Carbon-based nanostructured coatings on NiTi shape memory alloy for biomedical applications

Here, we propose carbon-based nanostructured coatings for nickel-titanium (NiTi) shape memory alloys (SMAs) for biomedical applications. NiTi SMAs are well-known biomedical materials; however, the elution of toxic Ni ions into the body has prevented SMAs from expanding their applications, particularly in the complete implantation of SMAs for human artificial muscles. One possibility for the suppression of leaching ions is to create a barrier coating, for which diamond-like carbon (DLC) may be a candidate. Due to the strong internal stress derived from the mismatch of the thermal expansion coefficient, however, the adhesive strength of DLCs is very low. In this study, we focused on the incorporation of tungsten into a DLC in order to reduce the internal stress of the coating. First, we present the definition of appropriate fabrication conditions. Uniaxial tensile tests were then performed, and we evaluated the adhesive strength of the coatings. We then determined the conditions that support the fabrication of a coating with the strongest adhesive strength. Thereafter, we deposited the coating onto the SMA with shape memory effects and conducted self-bending tests. We observed that the cracks initiated parallel to the longer direction of the specimens, most likely a result of a boundary slip between the parent phases of the SMA. The removed fraction area of the coating was estimated at less than 1% after 105 cycles, indicating the potential usage of tungsten-containing DLC coatings for biomedical applications.

BIOLOGICAL EFFECTS OF THE ARTIFICIAL ANAL SPHINCTER IN THE GOAT MODEL

Artificial anal sphincters could provide an alternative solution for severe anal incontinence when conventional surgical methods are not possible. We have created an artificial anal sphincter using a shape memory alloy (SMA) and evaluated its validity. The aim of this study was to determine the biological effects and safety after implantation of the SMA artificial anal sphincter in an animal model. The artificial anal sphincter consists of two all-round SMA plates as the main functional parts which perform two basic functions: occlusion at normal body temperature and release upon heating. The SMA artificial anal sphincter was implanted into three female goats under anesthesia. Blood was collected postoperatively from the jugular vein on days 1 and 4, at week 1, and months 1, 2, and 3, and biochemical parameters were examined. Biochemical test results were within normal limits during the 3-month study period. All biochemical measurements of organ function remained within normal range. The results demonstrated that the SMA artificial anal sphincter caused no significant failure of liver, renal, autonomic or digestive functions or damage to smooth muscle. This long-term animal experiment supported the concept and design of implantation with an SMA artificial anal sphincter, and the results demonstrate very good biocompatibility and effective system performance.