Light-responsive polyurethanes: classification of light-responsive moieties, light-responsive reactions, and their applications

Stimuli responsiveness has been an attractive feature of smart material design, wherein the chemical and physical properties of the material can be varied in response to small environmental change. Polyurethane (PU), a widely used synthetic polymer can be upgraded into a light-responsive smart polymer by introducing a light-sensitive moiety into the polymer matrix. For instance, azobenzene, spiropyran, and coumarin result in reversible light-induced reactions, while o-nitrobenzyl can result in irreversible light-induced reactions. These variations of light-stimulus properties endow PU with wide ranges of physical, mechanical, and chemical changes upon exposure to different wavelengths of light. PU responsiveness has rarely been reviewed even though it is known to be one of the most versatile polymers with diverse ranges of applications in household, automotive, electronic, construction, medical, and biomedical industries. This review focuses on the classes of light-responsive moieties used in PU systems, their synthesis, and the response mechanism of light-responsive PU-based materials, which also include dual- or multi-responsive light-responsive PU systems. The advantages and limitations of light-responsive PU are reviewed and challenges in the development of light-responsive PU are discussed.

Evaluation performance of azobenzene liquid-crystal shape memory polyurethane with photo-thermo-synergy response

This paper aimed to investigate the photo-response performance of a polymeric material using a series of azobenzene liquid-crystal shape memory polyurethane (DB-SMPn) with azobenzene-4,4'-dicarboxylic acid (ADA), N, N-bis (2-hydroxyethyl) isonicotinamine...

4D Printing Strain Self-Sensing and Temperature Self-Sensing Integrated Sensor-Actuator with Bioinspired Gradient Gaps

Integrated sensor-actuators with exciting functionalities, such as action self-sensing, position self-sensing, posture self-sensing, or active sensing, are promising for applications in biomedical device, human-machine interaction, intelligent self-protection devices, and humanoid robots. Despite recent progress, it remains challenging to achieve a macroscopical integrated sensor-actuator in a material system with microstructures. To address this critical challenge, a 4D printing bioinspired microstructure strategy is reported to design a high-performance integrated sensor-actuator capable of simultaneous actuation and sensation. Decoupled thermal stimulation and strain sensation is achieved by combining nanocarbon black/polylactic acid composites with bioinspired gradient microgap structures. As a result, printed integrated sensor-actuators can actively touch objects triggered by thermal stimulation and self-sense the touching state through the resistance change. It is anticipated that the basic design principle underlying this behavior can be used to develop integrated sensor-actuators of various shapes and functionalities to meet desirable applications.

Materials as Machines

Machines are systems that harness input power to extend or advance function. Fundamentally, machines are based on the integration of materials with mechanisms to accomplish tasks-such as generating motion or lifting an object. An emerging research paradigm is the design, synthesis, and integration of responsive materials within or as machines. Herein, a particular focus is the integration of responsive materials to enable robotic (machine) functions such as gripping, lifting, or motility (walking, crawling, swimming, and flying). Key functional considerations of responsive materials in machine implementations are response time, cyclability (frequency and ruggedness), sizing, payload capacity, amenability to mechanical programming, performance in extreme environments, and autonomy. This review summarizes the material transformation mechanisms, mechanical design, and robotic integration of responsive materials including shape memory alloys (SMAs), piezoelectrics, dielectric elastomer actuators (DEAs), ionic electroactive polymers (IEAPs), pneumatics and hydraulics systems, shape memory polymers (SMPs), hydrogels, and liquid crystalline elastomers (LCEs) and networks (LCNs). Structural and geometrical fabrication of these materials as wires, coils, films, tubes, cones, unimorphs, bimorphs, and printed elements enables differentiated mechanical responses and consistently enables and extends functional use.

Synthesis and characterization of biodegradable linear shape memory polyurethanes with high mechanical performance by incorporating novel long chain diisocyanates

Novel long chain diisocyanates were developed for synthesis of biodegradable linear shape memory polyurethanes demonstrating high mechanical performance.