Safety

Nickel-containing alloys, such as stainless steel, have been used in human medicine for over 100 yr. Uses include surgical instruments as well as implants such as pacemaker wires, vascular clips, mechanical cardiac valves, orthopedic prostheses, Harrington rods, and inferior vena caval filters. These successful applications have demonstrated the lack of toxicity of nickel-containing metallic implants; no systemic effects were observed or reported. However, a local fibrotic reaction surrounding stainless steel implants was thought to be caused by local passivation of nickel ions into surrounding tissue despite the absence of microscopically visible corrosion. Subsequently, the US Navy developed a new nickel-containing metal, Nitinol, in the 1960s that is an alloy of nickel and titanium and displays superior corrosion resistance. This alloy still carries the name of its heritage: Nickel TItanium-Naval Ordnance Laboratory (Nitinol).

Nitinol has numerous other physical properties besides corrosion resistance that make it attractive to use in biomedical devices, such as superelasticity (pseudoelasticity), thermal shape memory, high resiliency, and fatigue resistance. Originally, thin-wire technology, the development of the "diamond-drawn" wire, provided a shape that could be used in endodontal appliances. The tendency for Nitinol to return to its nominal shape when it is deformed was especially useful in this application. This property has also made Nitinol a valuable material in the production of endoluminal devices; a Nitinol device stretched for introduction through a small delivery catheter would expand to its original shape when deployed. This new alloy has replaced many stainless steel devices, especially self-expanding stents. Fatigue resistance prevents wire fractures and makes Nitinol devices very durable. Its lack of ferromagnetic properties allows magnetic resonance imaging of implanted devices.

To date, Amplatzer devices have proven nontoxic (13). Further, devices that have been immersed in a saline bath while fatigue tested did not corrode. In addition, devices examined after 18 mo of implantation in humans and animals did not reveal surface corrosion. Importantly, nickel levels in patients before and after insertion of an Amplatzer device did not increase. The incidence of nickel allergy is estimated to be around 10% in humans. Nevertheless, with over 60,000 current implants of Amplatzer devices worldwide over the past 8 yr, no case of a reaction has been detected.

Implantation Reveal

Fig. 2. Amplatzer Ductal Occluder Device. (A) Photograph of the device with clearly visible suturing of the baffle and stuffing to the ductal plug. (B) Aortogram immediately after device placement. The aortic disk is flat against the aortic wall with the plug within the ductal lumen. There is no flow through the ductus and no obstruction of the aorta or left pulmonary artery.

Fig. 2. Amplatzer Ductal Occluder Device. (A) Photograph of the device with clearly visible suturing of the baffle and stuffing to the ductal plug. (B) Aortogram immediately after device placement. The aortic disk is flat against the aortic wall with the plug within the ductal lumen. There is no flow through the ductus and no obstruction of the aorta or left pulmonary artery.

Thermal shape memory provides great flexibility to devices constructed of Nitinol. The nominal shape is determined by heating a formed wire frame. When cooled, the device retains the memory of its configuration.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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