Key Engineering Materials Vols. 288-289

Abstract: A soluble intralumenal stent for vascular anastomosis was prepared from glucose, Dextran-40 and heparin. The solubility of the stent was tested in vitro and in vivo. Animal tests were carried out with femoral arteries of rabbits. In comparison with the literature reported surgar and poly(ethylene glycol, PEG) stents, shorter dissolving time and higher patency (or survival) rate were obtained. Cell culture experiments suggested that the heparin containing glucose and Dextran-40 stent (H-sugar) had no irritation and toxicity to the endothelia cells. No thrombosis was observed from the in vivo tests in 2 months after the anastomosis. Such a heparin containing sugar stent is a promising candidate for fast sutureless anastomosis of vessels in non-trauma surgery.

Abstract: The feasibility of using an alternating magnetic field from induction heating furnace to heat the NiTi stent and the influence of hyperthermic on smooth muscle cells (SMCs) have been studied in the present work. The electromagnetic field is capable of significantly heating NiTi stents and the heating temperature can be adjusted by changing the voltage and heating time of the furnace and the position of NiTi stents. The shape and living status of SMCs were influenced by the heat treatment procedures. There were three stages of SMCs reaction to heat: (1) when the temperature below 44°C, the living status was not changed; (2) between 44°C to 50°C, the cells shrinked and were less dyed with trypan blue, which indicated that they were still alive; (3) when the temperature was above the 50°C, all the cells died. It was found that from 44°C to 50°C, the SMCs died in apoptosis, which might allow us to heat the implanted stent to prevent restenosis.

Abstract: Now the Cardio vascular restenosis in the clinic is still an unsolved question. The fact is that, if the 316L stent is without coating, it will harm the blood vessel wall and the inflammatory reaction of eye winker. This research is about the Paclitexel-drug coating stent that can be adapted to avoid restenosis. The drug control released by different methods, and also the nano-material releasing after the coating formation are investigated.

Abstract: The biocompatibility of the NiTi alloy self-expanding stent, its dilating effect on the vascular wall, and the apoptosis of smooth muscle cells (SMCs) were studied by implantation of stent into the rabbit’s abdominal aorta for different period. All the animals lived throughout the study. There was no detectable migration or dissection of the stent, and there were no acute closures or sub-acute thromboses in the vessels. The rates of patency were 100% both at the beginning when the stent was implanted and at the end when the animal was sacrificed. It may be concluded that the vascular intima covers the whole stent at the 8-week point. The atherosclerotic process existed in the vascular intima in contact with the stent surface, while the proliferation and apoptosis of SMCs occured simultaneously. After stent implantation, the apoptosis happened in both intima and media, which indicated that the stent might not only stimulate the intima but also compress the media, leading to proliferation and apoptosis. This might contribute to vessel remodeling after stenting.

Abstract: We have first fabricated porous-coated Ti alloy dental implants with a wide range of porosity by electro-discharging-sintering of spherical Ti-6Al-4V powders. The basic physical properties of EDS implants have been evaluated. The dependence of mechanical properties of each kind of implant such as micro-hardness and compressive strength has been also analyzed. The solid core and neck sizes between powders on porous layer generally increase with both input energy and capacitance. On the other hand, the pore size decreases with both input energy and capacitance. The micro-hardness analyses at various locations such as solid core and powders on porous layer show quietly consistent values. The compressive strengths of each implant are in the range of 39 and 452 MPa which depends on the input energy. In-vivo animal experiments showed that all the implants fabricated by current method were biocompatible and support rapid and perfect osseointegration in 2 weeks.

Abstract: The effects of alloying elements such as Mo, Sn, Zr, Nb, deforming-rate, solid solution and aging treatment on mechanical property and microstructure of near βtype biomedical Ti alloys based on Ti-Nb-Zr system were studied. The Influential factors and their solution were discussed to keep matching of strength, elastic modulus, plasticity and toughness. Ti-Zr-Mo-Nb and Ti-Zr-Sn-Mo-Nb alloy systems possess excellent biocompatibility, lower elastic modulus, higher strength, finer plasticity and fracture toughness matching by means of solid solution and ageing treatment which are much more suitable for surgical implant and orthopedic materials.

Abstract: In this study, chemical methods were used to treat NiTi for the purpose of preparing bioactive NiTi implants. The surface of the bioactive NiTi alloy was investigated by XRD and ESEM. The biocompatibility and bioactivity of the bioactive NiTi samples were evaluated by in vivo implantation experiments. The results show that a Ca-P layer composed mainly of hydroxyapatite (HA) with a trace amount of other apatites and a Ca/P ratio of 1.59 covers the surface of the bioactive NiTi alloy. In vivo tests show that osteoblasts actively proliferated on the bioactive NiTi implants after 6 weeks implantation. A large amount of new bone directly in contact with the host bone was observed after 13 weeks implantation. These revealed the excellent biocompatibility and bioactivity of the prepared bioactive NiTi alloy.

Abstract: The torsion property and rotary fatigue fracture behavior of SmartÒ K file and R reamer made of nickel titanium alloy have been studied by means of Shimadzu Autograph DDS-10T universal tester and man-made cyclic system with curved copper tubes as simulated root canal. The instrument surface and the cyclic fatigue fracture surface have been investigated by optical microscope and scanning electron microscope. Comparing with ANSI/ADA specification no.28, maximum torsion values of both SmartÒ K and R endodontic instruments are satisfied in practice. Tensile stresses on the outer surface of the endodontic instruments play a dominant role in fracture initiation during cyclic fatigue fracture. The cyclic number corresponding to cyclic fatigue fracture decreases with the increase of the instrument size number/ curvature. SmartÒ K- and R endodontic instruments exhibit good ductility characteristics, therefore superior resistance to fracture.

Abstract: Under simulated human physiological solution, the fretting behaviors of flat cortical bone specimen from fresh human femur in the transverse orientation were investigated by sliding against pure titanium ball counterpart (tangential fretting technique). The friction coefficients and logs were calculated automatically. The worn surfaces of the cortical bone were analyzed by means of laser confocal scanning microscopy. The results show that the fricion coefficient of cortical bone directly relate with the magnitudes of displacement. The friction logs for cortical bone change with the magnitudes of displacement (Fn=90N) from elastic partial slip (D≤5 µm), plastoelastic partial slip (D=10 µm) to slip (D ≥20 µm) respectively. The fretting damages of cortical bone in the elastic partial slip were slight. But ploughs and delaminations were observed in the plastoelastic partial slip and gross sliding with loss of contact stiffness of cortical bone. The wear depth increased with cycles and well related to the friction coefficient of cortical bone in each fretting regime. Controlling the displacement amplitude and friction coefficients of bone-implant interface, it might be helpful to increase the anti-fretting capacities of human cortical bone.

Abstract: Porous titanium with good strength and three-dimension pore structure was fabricated by using H2O2 as vesicant foaming titanium powder. The compressive strength, bending strength and Young’s modulus of porous titanium with the porosity of 58vol% are 190.7Mpa, 159Mpa and 4.15Gpa, respectively, similar to that of the nature bone. This kind of porous titanium with good bio-mechanical compatibility may be potential to alleviate the problems caused by the mismatch of the strength and Young's modulus between implant (110 GPa for Ti) and bone. Moreover, the pores (mainly in 100-700µm) are all interconnected and there are many microspores (about 10µm) in the wall of the macrospores. This porous structure would endow the materials with better activity.