ABSTRACT
As polymers, SMPs can be easily conformed into different complex shapes and their properties designed or adapted to specific applications and can also be integrated with other microelectromechanical sensors (“MEMS”) to produce “intelligent” bioactuators and biodevices. Compared to other shape-memory alloys used in numerous medical devices, SMPs show a far greater capability for changing their geometry during activation. They are also much cheaper to synthesise and their large scale mass production costs are reduced by using technologies such as
injection moulding or extrusion. At the same time the use of additives provides possibilities of tailoring their properties for improving and adapting their properties to final applications. All this makes them very versatile active materials with a high potential for industry, provided they overcome some of the limitations set out in the following sections. 5.2.2 Proposed DevicesShape-memory polymers can be used as active materials in medical devices for two main proposals or for solving two different kinds of medical problems: Minimally invasive surgery. Capabilities of SMPs can be employed for obtaining reduced temporary forms that make surgical tasks or implantation easier. In this way a device can be conduced, in its temporary small size, to the desired location, where activation leads to the implantable geometry. Actuation on tissues and organs. SMP-based devices can be implanted with a temporary form and, after the patient has recovered from intervention or when the related pathology has reached a limit level, activation can be promoted in order to modify the surrounding tissue geometry. Below are explained some specific proposals for developing medical devices based on the use of shape-memory polymers, most of which have undergone in vitro laboratory testing. After undergoing in vitro testing and meeting the requirements for official approval, in some cases their commercialisation is subject to their attaining the goals described at the end of this chapter. Self-expanding stents Like the one designed by Boston Scientific Corporation using the polymer from CRG Industries known as “Veriflex” under its trade-name, to treat the problems arising when the arteries become narrow or obstructed and also for removing obstructions from other “tube-shaped” body parts, like the ureter and the bronchial tubes. The stent is inserted in its temporary form (reduced) and the body’s own heat causes it to dilate and become attached to the artery. They may be used to replace stents based on shape-memory alloys such as Nitinol, once the appropriate biocompatibility studies have been carried out. Developments of self-expanding stents have
also been carried out by using injected polyurethane (Wache et al., 2003).
