The role of foaming process on shape memory behavior of polylactic acid-thermoplastic polyurethane-nano cellulose bio-nanocomposites

Design and fabrication of a novel 4D-printed customized hand orthosis to treat cerebral palsy

This research study is dedicated to additive manufacturing of the shape memory polymer hand orthosis to treat patients with cerebral palsy. The treatment process for cerebral palsy is a step-by-step process that needs different adjustments for the spastic hand to stretch it towards a normal posture, whereas meeting these requirements using conventional methods or complicated mechanisms is expensive, less flexible, time-consuming, and less practical. A comprehensive investigation was conducted to design and fabricate novel thermally actuated customized hand orthosis via digital light processing (DLP). The highly precise scanning device was used to derive the hand model, and subsequently, the Blender software was used to design the customized orthosis. The results showed that fabricated orthosis could represent a strong potential to become an alternative treatment for cerebral palsy. The shape memory actuation of the orthosis indicated that 100 % shape recovery is achievable in different actuating conditions with recovery temperatures higher than 55°C. Besides, it was found that the response time and shape recovery percentage could be tailored in the range of 5 to 40 s and 45 to 100%, respectively, by adjusting programming and actuation temperatures. Further, the repeatability of the shape memory effects in the printed orthosis was investigated as well, which proved that until 17 repetitions, 100 % shape recovery was achievable.

Shape-Memory-Recovery Characteristics of Microcellular Foamed Thermoplastic Polyurethane

We investigated the shape-recovery characteristics of thermoplastic polyurethane (TPU) with a microcellular foaming process (MCP). Additionally, we investigated the correlation between changes in the microstructure and the shape-recovery characteristics of the polymers. TPU was selected as the base material, and the shape-recovery characteristics were confirmed using a universal testing machine, by manufacturing dog-bone-type injection-molded specimens. TPUs are reticular polymers with both soft and hard segments. In this study, we investigated the shape-memory mechanism of foamed polymers by maximizing the shape-memory properties of these polymers through a physical foaming process. Toward this end, TPU specimens were prepared by varying the gas pressure, foaming temperature, and type of foaming gas in the batch MCP. The effects of internal structural changes were investigated. These experimental variables affected the microstructure and shape-recovery characteristics of the foamed polymer. The generated cell density changed, which affected the shape-recovery characteristics. In general, a higher cell density corresponded to a higher shape-recovery ratio.

Shape Memory Polyurethane-Based Smart Polymer Substrates for Physiologically Responsive, Dynamic Pressure (Re)Distribution

Shape memory polymers (SMPs) are an exciting class of stimuli-responsive smart materials that demonstrate reactive and reversible changes in mechanical property, usually by switching between different states due to external stimuli. We report on the development of a polyurethane-based SMP foam for effective pressure redistribution that demonstrates controllable changes in dynamic pressure redistribution capability at a low transition temperature (∼24 °C)-ideally suited to matching modulations in body contact pressure for dynamic pressure relief (e.g., for alleviation or pressure ulcer effects). The resultant SMP material has been extensively characterized by a series of tests including stress-strain testing, compression testing, dynamic mechanical analysis, optical microscopy, UV-visible absorbance spectroscopy, variable-temperature areal pressure distribution, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, dynamic thermogravimetric analysis, and 1H nuclear magnetic resonance spectroscopy. The foam system exhibits high responsivity when tested for plantar pressure modulation with significant potential in pressure ulcers treatment. Efficient pressure redistribution (∼80% reduction in interface pressure), high stress response (∼30% applied stress is stored in fixity and released on recovery), and excellent deformation recovery (∼100%) are demonstrated in addition to significant cycling ability without performance loss. By providing highly effective pressure redistribution and modulation when in contact with the body's surface, this SMP foam offers novel mechanisms for alleviating the risk of pressure ulcers.

Recent Trends of Foaming in Polymer Processing: A Review

Polymer foams have low density, good heat insulation, good sound insulation effects, high specific strength, and high corrosion resistance, and are widely used in civil and industrial applications. In this paper, the classification of polymer foams, principles of the foaming process, types of blowing agents, and raw materials of polymer foams are reviewed. The research progress of various foaming methods and the current problems and possible solutions are discussed in detail.