Wei Min Huang

Water-driven programmable polyurethane shape memory polymer: Demonstration and mechanism

We demonstrate the new features of a polyurethane shape memory polymer: water-driven actuation and recovery in sequence (i.e., programmable). Hydrogen bonding is identified as the reason behind these features. In addition, the absorbed water is quantitatively separated into two parts, namely, the free water and bound water. Their individual contribution on the glass transition temperature is identified.

On the selection of shape memory alloys for actuators

This paper presents a series of charts for the selection of shape memory alloys (SMAs) for actuators. It is based on performance indices with special reference to the unique features of SMA actuators. The three most popular polycrystalline SMAs are candidates of current study, namely, NiTi, CuZnAl and CuAlNi. More SMAs may be added in to give a complete picture.

Thermo-moisture responsive polyurethane shape-memory polymer and composites: a review

The polyurethane shape-memory polymer (SMP) developed by Mitsubishi Heavy Industry, Japan is not only thermo-responsive, but also moisture-responsive as recently found. The moisture-responsive ability atop the well-known thermo-responsive feature could open a new dimension for applications of this fantastic material. This paper presents a concise review of the thermo- and moisture-responsive properties and thermomechanical behaviors of this SMP and its composites, and potential applications utilizing these features, in particular in biomedical engineering.

On the effects of moisture in a polyurethane shape memory polymer

It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (Tg) of polyurethane. Accompanying the decrease of Tg, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between Tg and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 °C, which is the melting temperature of this SMP.

Thermo/chemo-responsive shape memory effect in polymers: a sketch of working mechanisms, fundamentals and optimization

Based on the working mechanisms, a systematic literature review is logically presented to reveal that the thermo- and chemo- responsive shape memory effects (SMEs) are not the special phenomena of some particular polymers, but intrinsic features of most polymers (if not all). Subsequently, referring to the most recent experimental results and their theoretical origins, we reveal the fundamentals on the optimization of the SME in polymers and the approaches to design/synthesize polymeric materials with tailored features.

Significantly reducing electrical resistivity by forming conductive Ni chains in a polyurethane shape-memory polymer/carbon-black composite

We demonstrate an approach to significantly reduce the electrical resistivity in a polyurethane shape-memory polymer (SMP) filled with randomly distributed carbon black (CB). With an additional small amount of randomly distributed Ni microparticles (0.5vol%) in the SMP/CB composite, its electrical resistivity is only reduced slightly. However, if these Ni particles are aligned into chains (by applying a low magnetic field on the SMP/CB/Ni solution before curing), the drop of the electrical resistivity is significant. This approach, although demonstrated in a SMP, is applicable to other conductive polymers.

Characterization of TiNi shape-memory alloy thin films for MEMS applications

Thin film shape-memory alloys (SMAs) have been recognized as promising and high performance materials in the field of microelectromechanical systems (MEMS) applications. In this investigation, chemical composition, microstructure and phase transformation behaviors of sputter deposited TiNi films were studied. The surface and cross-section morphology of the deposited coating was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The results from the differential scanning calorimeter (DSC) showed clearly the martensitic transformation upon heating and cooling. X-Ray diffraction analysis (XRD) also revealed the crystalline structure changing with temperature. By depositing TiNi films on the bulk micromachined Si cantilever structures, micro-beams exhibiting a good shape-memory effect were obtained. Finite element simulation results of the deformation of micro-beam (using the measured NiTi thin film parameters) agree quite well with the measured behavior.

Thin Film Shape Memory Alloys: Fundamentals and Device Applications

This book, the first dedicated to this exciting and rapidly growing field, enables readers to understand and prepare high-quality, high-performance TiNi shape memory alloys (SMAs). It covers the properties, preparation and characterization of TiNi SMAs, with particular focus on the latest technologies and applications in MEMS and biological devices. Basic techniques and theory are covered to introduce new-comers to the subject, whilst various sub-topics, such as film deposition, characterization, post treatment, and applying thin films to practical situations, appeal to more informed readers. Each chapter is written by expert authors, providing an overview of each topic and summarizing all the latest developments, making this an ideal reference for practitioners and researchers alike.

Electrical conductivity of thermoresponsive shape-memory polymer with embedded micron sized Ni powder chains

The electrical resistivity of a thermoresponsive polyurethane shape-memory polymer (SMP) filled with micron sized Ni powders is investigated in this letter. We show that, by forming conductive Ni chains under a weak static magnetic field (0.03T), the electrical conductivity of the SMP composite in the chain direction can be improved significantly, which makes it more suitable for Joule heat induced shape recovery. In addition, Ni chains reinforce the SMP significantly but their influence on the glass transition temperature is about the same as that of the randomly distributed Ni powders.

Shaping tissue with shape memory materials

After being severely and quasi-plastically deformed, shape memory materials are able to return to their original shape at the presence of the right stimulus. After a brief presentation about the fundamentals, including various shape memory effects, working mechanisms, and typical shape memory materials for biomedical applications, we summarize some major applications in shaping tissue with shape memory materials. The focus is on some most recent development. Outlook is also discussed at the end of this paper.