Systematic Development Strategy for Smart Devices Based on Shape-Memory Polymers.

Andrés Díaz Lantada

doi:10.3390/polym9100496

Abstract

Shape-memory polymers are outstanding “smart” materials, which can perform important geometrical changes, when activated by several types of external stimuli, and which can be applied to several emerging engineering fields, from aerospace applications, to the development of biomedical devices. The fact that several shape-memory polymers can be structured in an additive way is an especially noteworthy advantage, as the development of advanced actuators with complex geometries for improved performance can be achieved, if adequate design and manufacturing considerations are taken into consideration. Present study presents a review of challenges and good practices, leading to a straightforward methodology (or integration of strategies), for the development of “smart” actuators based on shape-memory polymers. The combination of computer-aided design, computer-aided engineering and additive manufacturing technologies is analyzed and applied to the complete development of interesting shape-memory polymer-based actuators. Aspects such as geometrical design and optimization, development of the activation system, selection of the adequate materials and related manufacturing technologies, training of the shape-memory effect, final integration and testing are considered, as key processes of the methodology. Current trends, including the use of low-cost 3D and 4D printing, and main challenges, including process eco-efficiency and biocompatibility, are also discussed and their impact on the proposed methodology is considered.

Highlights

Shape-memory polymers (SMPs) are active or “smart” materials that present a mechanical response to external stimuli, normally changes in surrounding temperatures
Present study presents a review of challenges and good practices, leading to a straightforward methodology or integration of strategies, for the development of “smart” actuators based on shape-memory polymers
We combine computer-aided design and finite element modeling resources, additive manufacturing technologies for the direct fabrication of geometries using SMPs, rapid tooling techniques for casting of enhanced SMPs into rapid molds and infrared thermography for secure testing of the final devices. These materials and methods can be applied to the design and development of several smart materials and structures and are very well suited for supporting the straight-forward development of “smart” actuators based on shape-memory polymers, as the review of challenges and good practices presented in the following

Summary

Introduction

Shape-memory polymers (SMPs) are active or “smart” materials that present a mechanical response to external stimuli, normally changes in surrounding temperatures. Other types of stimuli such as light, water or chemicals, can promote shape-memory effects in polymers, we focus here on thermally activated shape-memory polymers, as they are the most common ones. When these materials are heated above their “activation” temperature (Tact ), typically corresponding to glass (Tg ) or melting transitions (Tm ), a radical stiffness change takes and the SMPs change from a rigid to an elastic state, which in some cases allows deformations of up to 400%. After being manipulated and deformed, if the material is cooled down with the imposed deformation, this structure is “frozen” and returns to a rigid but “unbalanced” state This process is usually referred to as “shape-memory training” process. Among the polymers developed with remarkable shape-memory properties, some of the most important are epoxy resins, polyurethane resins, cross-linked polyethylene, diverse styrene-butadiene copolymers, and other formulations described in previous foundational reports and studies [1,2,3,4]

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Conclusion