Shape memory polymers (SMPs) are smart materials that can remember a primary shape and can return to this primary shape from a deformed secondary shape when given an appropriate stimulus. This property allows them to be delivered in a compact form via minimally invasive surgeries in humans, and deployed to achieve complex final shapes. Here we review the various biomedical applications of SMPs and the challenges they face with respect to actuation and biocompatibility. While shape memory behavior has been demonstrated with heat, light and chemical environment, here we focus our discussion on thermally stimulated SMPs.

Biomedical applications of thermally activated shape memory polymers

The heat shock proteins (hsps) are expressed in normal cells but their expression is enhanced by a number of different stresses including heat and ischaemia. They play important roles in chaperoning the folding of other proteins and in protein degradation. In the heart a number of studies have shown that prior induction of the hsps by a mild stress has a protective effect against a more severe stress. Moreover, over-expression of an individual hsp in cardiac cells in culture or in the intact heart of either transgenic animals or using virus vectors, also produces a protective effect, directly demonstrating the ability of the hsps to produce protection. These findings indicate the potential importance of developing procedures for elevating hsp expression in a safe and efficient manner in human individuals using either pharmacological or gene therapy procedures.

Heat shock proteins and cardiac protection

We demonstrate here that the nematode Caenorhabditis elegans displays broad hormetic abilities. Hormesis is the induction of beneficial effects by exposure to low doses of otherwise harmful chemical or physical agents. Heat as well as pretreatment with hyperbaric oxygen or juglone (a chemical that generates reactive oxygen species) significantly increased subsequent resistance to the same challenge. Cross-tolerance between juglone and oxygen was also observed. The same heat or oxygen pretreatment regimens that induced subsequent stress resistance also increased life expectancy and maximum life span of populations undergoing normal aging. Pretreatment with ultraviolet or ionizing radiation did not promote subsequent resistance or increased longevity. In dose-response studies, induced thermotolerance paralleled the induced increase in life expectancy, which is consistent with a common origin.

/pdf/multiple-stressors-in-caenorhabditis-elegans-induce-stress-4elcdcksxc.pdf

Multiple Stressors in Caenorhabditis elegans Induce Stress Hormesis and Extended Longevity

Biomedical Applications of Thermally Activated Shape Memory Polymers

A catheter introduction apparatus provides a radially expandable helical coil as a radiofrequency emitter. In one application the emitter is introduced percutaneously, and transseptally advanced to the ostium of a pulmonary vein. The emitter is radially expanded, which can be accomplished by inflating an anchoring balloon about which the emitter is wrapped, in order to cause the emitter to make circumferential contact with the inner wall of the pulmonary vein. The coil is energized by a radiofrequency generator, and a circumferential ablation lesion is produced in the myocardial sleeve of the pulmonary vein, which effectively blocks electrical propagation between the pulmonary vein and the left atrium.

Radio frequency pulmonary vein isolation

https://www.annalsthoracicsurgery.org/article/0003-4975(94)91940-2/pdf

Ischemic Preconditioning Improves Preservation With Crystalloid Cardioplegia

Background—Catheter ablation of postinfarction ventricular tachycardia (VT) may be limited by insufficient myocardial coagulation or excessive endocardial or epicardial damage We propose that volumetric heating restricted to intramural sites may improve the outcome and safety of this procedure, especially if delivered at rates that enhance heat conduction and forestall adverse tissue changes Methods and Results—A novel optical fiber with a diffusing tip for direct intramural, volumetric laser heating was tested via thoracotomy and percutaneously in normal dogs Low-power (20- to 45-W) diode laser light (805 nm) diffused within tissue induced large lesions but no visible surface damage, mural thrombi, or transmural perforation Mean lesion depth approximated tip length (10 mm) Mean lesion widths in the thoracotomy and percutaneous groups were 58±05 to 91±084 mm and 52±085 to 79±11 mm, respectively, depending on the light dose Mean volumes in the percutaneous group were 1006±245 to 2471±934 mm

Slow Intramural Heating With Diffused Laser Light: A Unique Method for Deep Myocardial Coagulation

https://www.annalsthoracicsurgery.org/article/S0003-4975(98)00905-9/pdf

Heat shock improves recovery and provides protection against global ischemia after hypothermic storage.

and Reperfusion Cardioprotection by Local Heating: Improved Myocardial Salvage After Ischemia

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Ischemic Preconditioning Improves Preservation With Crystalloid Cardioplegia

Slow Intramural Heating With Diffused Laser Light: A Unique Method for Deep Myocardial Coagulation

Heat shock improves recovery and provides protection against global ischemia after hypothermic storage.

and Reperfusion Cardioprotection by Local Heating: Improved Myocardial Salvage After Ischemia