With actuation capabilities that respond to temperature or light, the potential uses for shape memory polymers (SMPs) in the biomedical arena are on the rise. This article describes current and potential future uses of SMPs for medical devices.

The NiTiHf alloy is one of the most extensively studied high-temperature shape memory alloys. This article reviews the key factors affecting the actuation fatigue performance of NiTiHf as well as the current state of research in this area, and it identifies some factors that require further study.

Both shape memory and elastocaloric effects are related to the reversible martensitic phase transformation. For the shape memory effect, thermal energy is used to drive the material through the phase transformation and recover its original shape. For the elastocaloric effect, mechanical energy is used to induce phase transformation, and the associated latent heat is used to pump heat for cooling or heating. Heat pumps based on the elastocaloric effect have a low environmental impact and are highly efficient. However, designing a prototype to harvest the full potential of the elastocaloric effect has been challenging. This article summarizes prototyping efforts undertaken by three different research groups.

Advances in additive manufacturing have enabled functional grading and multi-material deposition to produce “4D printed” parts that are net or near net shape; creating highly complex features that are difficult to produce with conventional manufacturing processes. This article addresses the fundamental challenge of how to ensure that the design, manufacturing, and functional intent for 4D printed parts can be accurately and unambiguously communicated across the design, manufacturing, inspection, and supply value chain. The use case of a generic mini-gripper sheds light on the benefits that a new standard could bring to the engineering and design of shape memory materials.

This article reports on a multifaceted testing and modeling approach to investigate the fatigue life of medical grade Nitinol to one billion cycles. The goal of a the research is to understand the mechanism of Nitinol ultra-high cycle fatigue and to eventually be able to predict when fracture will occur.

Laboratory tests conducted on shape memory alloy valve actuators show them to be a viable green alternative for oil and gas applications.

Using a physical vapor deposition process to manufacture medical device components reduces post-processing time and improves materials properties. This article addresses metallic sputter deposition technologies for Nitinol medical devices.

Novel bcc CoCr-base alloys exhibit a Young’s modulus similar to human bone combined with superelastic strain twice that of NiTi alloys.

Digital image correlation data and Bayesian inference used together facilitate rigorous quantification of the uncertainty in material input parameters for finite element simulations of superelastic deformation.

Ni-ion irradiated NiTi is nearly 50% harder, retains 85% recoverable deformation, and has reduced hysteresis. This work explores the feasibility of using ion beam modification to modulate the austenite to martensite phase transformation in NiTi, thereby achieving novel or localized properties in near-surface regions.

Novel methods for altering the mechanical properties of functionally graded orthodontic medical devices leads to new applications. This article highlights recent applications of selective vaporization to enable functional grading of shape memory alloys in medical devices for the dental industry.

Nitinol fatigue fracture surfaces generally exhibit similar features to most engineering alloys, including a flat fracture plane, ratchet marks, radial lines, beachmarks, and striations.

New FDA guidance for Nitinol used in medical devices includes clarification on the determination of safety factors, the requirements for corrosion testing, and proper labeling of potentially harmful elements.

Laser melting of elastocaloric metals can create fatigue-resistant microstructures, which enables solid-state cooling technologies.

The effects of Nitinol micropurity on the durability of superficial femoral artery stents offers a potential way to enhance durability and reduce fatigue fractures. This article describes recent work on superior grades of “microclean” Nitinol and the effects on fatigue and durability of the devices.

Shape memory alloy textiles provide complex deformation and force profiles for novel wearable applications.

With the goal of improving aircraft efficiency, Boeing in collaboration with NASA Glenn Research Center (GRC) have developed and successfully flight tested environmentally activated vortex generators that passively, repeatedly, and accurately retract during cruise and deploy during take-off and landing phases. The capability discussed in this article is based upon recent advancements in shape memory alloy rotary-actuation technology, which included improved alloy systems, design tools, best practices, published standards, and previous wind tunnel and flight test demonstrations.

Newly developed nickel-titanium (NiTi) alloys are well suited for bearings and gears in demanding applications.

Dissimilar metals, each with their own special properties, can be integrated into a single composite wire to achieve a functionally driven design. Simultaneously strong, stiff, and superelastic guidewires that provide proximal stiffness and distal flexibility for medical applications are discussed in this article.

4D printing enables fabrication of complex objects that transform over time (the fourth dimension) when subjected to external stimuli. 4D printing of metallic functional materials is of special interest due to their capacity for self-assembly and multifunctionality, with the added benefit of higher actuation capability, in comparison with polymeric materials.