Shape memory implant

In the second stage of the pharmaceutical development of SMP implants, attention will need to be paid to the specific site of application. Particularly for parenteral administration, shape-memory implants need to fulfil several regulatory requirements, e.g. sterility and absence of endotoxins to name only a few. Some of these properties depend at least partially on environmental conditions under which... 

Poly(xylitol-co-dodecanedioate)/hydroxyapatite eomposite has a good potential in clinical applications as shape memory implant for the minimally invasive surgeries." With a shape-memory ratio of almost 100%, the poly(xylitol-eo-dodeeanedioate)/ hydroxyapatite composite provides excellent shape-memory effeet" ... 

Trepanier C, Venugopalan R, Pelton AR. Corrosion resistance and biocompatibility of passivated Nitinol. In Yahia LH, editor. Shape memory implants 2000. p. 35—45. 

Degradable implants, shape-memory polymers in, 22 355 Degradable-pendant-chain hydrogels, 13 741... 

One of the most commonly used medical devices is the stent, (Fig. 21.1), small metallic structures that are expanded in blood vessels, functioning to maintain the patency (freedom from obstruction) of the vessel in which it is placed. Although the first use of stents was in vasculature (blood vessel systems), more recent applications include, for example, implantation between two vertebrae to increase the rigidity of the spine. A typical vascular stent is placed in its anatomical location and then either plastically deformed/expanded (stainless steel) or allowed to expand to a predetermined size, as a consequence of shape memory (nitinol). 

Figure 4 The design of the implantable drug delivery system based on shape memory alloy microactuation, showing the main reservoir, pressure chamber, and the printed circuit board (PCB) with electronics and valve system. The basic concept is to have a reservoir under constant pressure pushing liquid through a calibrated flow channel and valve system. Dimensions are 50 mm with a height of 15 mm. Source From Ref. 36.

Reynaerts D, Peirs J, Van Brussel H. An implantable drag-delivery system based on shape memory alloy micro-actuation. Sens Actuators 1997 A61 455-462. 

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... 

The history of these intriguing materials goes back to 1938, when A. Oleander observed the shape memory ability of An—Cd and Cu—Zn alloys (Wayman and Harrison, 1989). Later on other materials such as indium-, nickel-, titanium-, and iron-based alloys were shown to have similar behaviour (Reardon, 2011). Unlike other shape memory alloys, Ni—Ti in particular was found to be very resistant to corrosion and/or degradation and hence ideally suited to implantation in a range of applications, including the human body, albeit more expensive than its other counterparts. Hence the very first temperature-dependent shape memory alloys to be commercialised were nickel—titanium (Bogue, 2009). 

More sophisticated versions of SMPs are those based on the so-called cold hibernated elastic memory as self-deployable intelligent structures (Sendijarevic, 2003). This technology is based on polyurethane foams whereby shape memory effect is combined with elastic recovery of the foam, thus allowing them to be packed into the smallest possible form and inserted into the body via catheters. Given the foam s excellent biocompatibility, porosity, and lightness, they can potentially be used in many other forms, e.g., orthopaedic braces and splints, vascular and coronary crafts, as well as other equally vital prosthetics and implants. 

J. Rodriguez, F. Qubb, T. Wilson, M. Miller, T. Fossum, J. Hartman, E. Tuzun, P. Singhal, D. Maitland, In vivo response to an implanted shape memory polyurethane foam in a porcine aneurysm model. J. Biomed. Mater. Res. A (2013) doi 10.1002/jbm.a,34782. 

F.A. Spelman, B.M. Qopton, A. Voie, C.N. Jolly, K. Huynh, J. Boogaard, J.W. Swanson, Cochlear implant with shape memory material and method for implanting the same, US Patent 5800500 (September 1,1998). 

Ajili, S. H., Ebrahimi, N. G., and Soleimani, M. 2009. Polyurethane/polycapro-lactane blend with shape memory effect as a projxjsed material for cardiovascular implants. Acta Biomaterialia 5 1519-1530. 

There are extensive studies centering on the fabrication of nanostructured metals in order to improve their mechanical properties. Since mechanical performance of orthopedic implant is critical to its applications, liability and lifetime, superior mechanical properties are always wanted. Depending on clinical settings, the wanted properties include, but are not limited to, enhanced mechanical strengths, toughness, ductility, wear resistance, corrosion resistance, and special characteristics such as superplasticity and shape-memory effect. Due to space limitations, only the typical aspects and examples of implant mechanical properties enhanced by nanotechnology are introduced here. 

Conductive polymer nanocomposites may also be used in different electrical applications such as the electrodes of batteries or display devices. Linseed oil-based poly(urethane amide)/nanostuctured poly(l-naphthylamine) nanocomposites can be used as antistatic and anticorrosive protective coating materials. Castor oil modified polyurethane/ nanohydroxyapatite nanocomposites have the potential for use in biomedical implants and tissue engineering. Mesua ferrea and sunflower seed oil-based HBPU/silver nanocomposites have been found suitable for use as antibacterial catheters, although more thorough work remains to be done in this field. ° Sunflower oil modified HBPU/silver nanocomposites also have considerable potential as heterogeneous catalysts for the reduction of nitro-compounds to amino compounds. Castor oil-based polyurethane/ epoxy/clay nanocomposites can be used as lubricants to reduce friction and wear. HBPU of castor oil and MWCNT nanocomposites possesses good shape memory properties and therefore could be used in smart materials. ... 

Guidewires, mechanical heart-valve housings and struts, biologic heart-valve stents, vascular stents, vena cava umbrellas, artificial heart housings, pacemaker leads, leads for implantable electrical stimulators, surgical staples, supereleastic properties of some nickel-titanium formulations, shape memory properties of some Ni titanium formulation, radiopaque markers... 

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). 

Potential applications for shape memory PU exist in almost every area of daily life from self-repairing auto bodies to kitchen utensils, from switches to sensors, from intelligent packing to tools [98]. Other potential applications are drug delivery [99], biosensors, biomedical devices [100,101], microsystem components [102], and smart textiles [103]. Because PU can be made biodegradable, they can be used as shortterm implants so removal by surgery can be avoided. Some important applications are discussed next. 

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