Smart materials in cardiovascular implants: Shape memory alloys and shape memory polymers

Abstract

Smart materials have intrinsic properties that change in a controlled fashion in response to external stimuli. Currently, the only smart materials with a significant clinical impact in cardiovascular implant design are shape memory alloys, particularly Nitinol. Recent prodigious progress in material science has resulted in the development of sophisticated shape memory polymers. In this article, we have reviewed the literature and outline the characteristics, advantages, and disadvantages of shape memory alloys and shape memory polymers which are relevant to clinical cardiovascular applications, and describe the potential of these smart materials for applications in coronary stents and transcatheter valves.

Cardiovascular Stents: A Review of Past, Current, and Emerging Devices

“…This effect occurs when the material undergoes a change in its crystal form and results in the material's ability to recover an original shape in response to a stimulus [154][155][156]. Specifically, in the case of shape-memory alloys (e.g., nitinol), there is a reversible transformation from the austenite phase to the martensite phase, which takes place over a specific temperature range depending on the alloy composition [157][158][159]. Similarly, polymeric smart materials that recover from a deformed state to their original shape under external stimuli have also been considered [160][161][162].…”

Additively manufactured metallic biomaterials

“…However, TiO 2 coating on nitinol structures could reduce Ni ion leaching. Constant et al [ 126 , 127 ] studied nitinol degradation in biological and physiological fluids and evaluated the corrosion resistance of nitinol along with surface morphology. Here, Ni and Ti release from the specimen was recorded over six months of incubation in synovial fluids.…”

4D Printing: Technological and Manufacturing Renaissance

“…Hydrophilic polymers materials are sensitive to water or humidity because their structure contains positive (NH 2 ) or negatively (COOH, OH) charged functional groups. [ 37,154,155 ] Particularly, in SMPs shape change occurs due to hydrophobic groups including polyhedral oligomeric silsesquioxane and hydrophilic polymeric groups such as PU block copolymer. [ 156–158 ] Printed structure changes their shape when they absorb water and recover their original shape after drying.…”

“…These alloys exhibit a wide range of potential applications due to their excellent shape‐memory effect (SME) and super‐elastic properties. [ 37 ] These alloys can easily deform upon certain stimuli and retain their memorized shape. Moreover, titanium‐based and nickel‐based SMAs exhibit tremendous perspectives in different biomedical implants including orthopedics, cardiology, and neurology.…”