Shape-memory materials devices

In this chapter, we focus on recent efforts to design and fabricate soft shape-memory materials, including both polymeric and supramolecular systems. We first classify these materials based on their micro- and nanostructure (Section 5.2.2). We then highlight how soft shape-memory materials have been applied to biomedical applications as implantables (Section 5.2.3.1), drug delivery devices (Section 5.2.3.2), and tissue engineering scaffolds (Section 5.2.3.3). In addition, we briefly discuss future trends for utilizing soft shape-memory materials for biomedical applications (Section 5.2.4). 

The latest embodiment of an SMP clot retrieval system demonstrates a hybrid shape-memory material system. The design of SMP biomedical devices should not be limited to purely polymer-based devices but rather can be combined with other smart or active materials. Novel multifunctional SMP-hybrid systems could lead to multiple unique and novel platform technologies for future development. 

The reactor has natural coolant circulation in the primary circuit under all modes of operation. Before returning to the reactor, the secondary coolant passes through a system of parallel finned tubes which form the heat exchanger to atmosphere of the PDHRS. To ensure adequate heat transfer from these tubes, they are contained in a vertical duct designed to enhance the air flow. However such heat transfer is undesirable in normal operation so the entry to and exit from the tube region of the duct are closed by a system of louvres. When the temperature in the chamber between the louvres rises to 80 - 90C, direct actioning devices (thermostatic or based on a shape-memory material ) will actuate to open the louvres and initiate the PDHRS action to cool the reactor. 

Indirli M, Castellano MG, Clemente P, Martelli A (2001) Demo-application of shape memory alloy devices, the rehabilitation of S. Giorgio Church Bell-Tower. In VI international symposium on smart structures and materials - SPIE 2001, Newport Beach... 

The design of shape-memory devices is quite different from that of conventional alloys. These materials are nonlinear, have properties that are very temperature-dependent, including an elastic modulus that not only increases with increasing temperature, but can change by a large factor over a small temperature span. This difficulty in design has been addressed as a result of the demands made in the design of compHcated smart and adaptive stmctures. Informative references on all aspects of SMAs are available (7—9). 

Safety devices -standards and specifications [MATERIALS STANDARDS AND SPECIFICATIONS] (Vol 16) -shape-memory actuators for [SITAPE-MEMORYALLOYS] (Vol 21) -use of bismuth alloys [BISMUTH AND BISMUTH ALLOYS] (Vol 4)... 

The use of shape-memory alloys as actuators depends on their use in the plastic martensitic phase that has been constrained within the structural device. Shape-memory alloys (SMAs) can be divided into three functional groups one-way SMAs, tw o-vvav SMAs, and magnetically controlled SMAs. The magnetically controlled SMAs show great potential as actuator materials for smart structures because they could provide rapid strokes with large amplitudes under precise control. The most extensively used conventional shape-memory alloys are the nickel-titanium- and copper-based alloys (see Shape-Memory Alloys). 

From the crude fabrications of the earliest surgical instruments to the highly sophisticated devices of today, materials are the fundamental component of a medical device. Modern devices are usually composed of a metal, plastic, alloy, or various combinations thereof. Improvements in technology have created lighter, stronger materials as well as shape-memory alloys such as nitinol, resulting in major innovations in device design and functionality. 

From the heterostructures that make possible the use of exotic electronic states in optoelectronic devices to the application of shape memory alloys as filters for blood clots, the inception of novel materials is a central part of modern invention. While in the nineteenth century, invention was acknowledged through the celebrity of inventors like Nikola Tesla, it has become such a constant part of everyday life that inventors have been thrust into anonymity and we are faced daily with the temptation to forget to what incredible levels of advancement man s use of materials has been taken. Part of the challenge that attends these novel and sophisticated uses of materials is that of constructing reliable insights into the origins of the properties that make them attractive. The aim of the present chapter is to examine the intellectual constructs that have been put forth to characterize material response, and to take a first look at the types of models that have been advanced to explain this response. 

Stimuli-responsive polymers have gained increasing interest and served in a vast number of medical and/or pharmaceutical applications such as implants, medical devices or controlled drug delivery systems, enzyme immobilization, immune-diagnosis, sensors, sutures, adhesives, adsorbents, coatings, contact lenses, renal dialyzers, concentration and extraction of metals, for enhanced oil recovery, and other specialized systems (Chen and Hsu 1997 Chen et al. 1997 Wu and Zhou 1997 Yuk et al. 1997 Bayhan and Tuncel 1998 Tuncel 1999 Tuncel and Ozdemir 2000 Hoffman 2002 en and Sari 2005 Fong et al. 2009). Some novel applications in the biomedical field using stimuli-responsive materials in bulk or just at the surface are shape-memory (i.e., devices that can adapt shape to facilitate the implantation and recover their conformation within the body to... 

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