J. L. Chen

Giant magnetic-field-induced strains in Heusler alloy NiMnGa with modified composition

A giant magnetic-field-induced strain (MFIS) of −3100 ppm has been obtained in Heusler alloy Ni52Mn22.2Ga25.8 single crystal in the [001] direction at a temperature from 23 to 31 °C. This MFIS reaches saturation in an applied field about 6 kOe, and exhibits the same amplitude with an opposite sign while the field is perpendicular to the samples. According to a previous model, this MFIS associates with the twin boundary motion. The martensitic self-strain has been found to be 2%, implying a preferential orientation of martensite variants. Results related to the magnetic properties are discussed.

Paclitaxel-liposome–microbubble complexes as ultrasound-triggered therapeutic drug delivery carriers

Liposome-microbubble complexes (LMC) have become a promising therapeutic carrier for ultrasound-triggered drug delivery to treat malignant tumors. However, the efficacy for ultrasound-assisted chemotherapy in vivo and the underlying mechanisms remain to be elucidated. Here, we investigated the feasibility of using paclitaxel-liposome-microbubble complexes (PLMC) as possible ultrasound (US)-triggered targeted chemotherapy against breast cancer. PTX-liposomes (PL) were conjugated to the microbubble (MB) surface through biotin-avidin linkage, increasing the drug-loading efficiency of MBs. The significant increased release of payloads from liposome-microbubble complexes was achieved upon US exposure. We used fluorescent quantum dots (QDs) as a model drug to show that released QDs were taken up by 4T1 breast cancer cells treated with QD-liposome-microbubble complexes (QLMC) and US, and uptake depended on the exposure time and intensity of insonication. We found that PLMC plus US inhibited tumor growth more effectively than PL plus US or PLMC without US, not only in vitro, but also in vivo. Histologically, the inhibition of tumor growth appeared to result from increased apoptosis and reduced angiogenesis in tumor xenografts. In addition, a significant increase of drug concentration in tumors was observed in comparison to treatment with non-conjugated PL or PLMC without US. The significant increase in an antitumor efficacy of PLMC plus US suggests their potential use as a new targeted US chemotherapeutic approach to inhibit breast cancer growth.

Stress-free two-way thermoelastic shape memory and field-enhanced strain in Ni52Mn24Ga24 single crystals

Stress-free and two-way thermoelastic shape memory, with 1.2% strain and 6 K temperature hysteresis, has been found in single crystalline Ni52Mn24Ga24. The deformation can be enhanced more than three times, up to 4.0% shrinkage with a bias field 1.2 T applied along the measurement direction, or changed to 1.5% expansion by the 1.2 T applied perpendicular to the measurement direction. For achieving a large deformation, the magnetic field exhibits a more evident contribution than an external stress on this material. These characteristics can be attributed to the low level of internal stress and the preferential orientation of the martensitic variants.

Intermartensitic transformation and magnetic-field-induced strain in Ni52Mn24.5Ga23.5 single crystals

We have found a complete thermoelastic intermartensitic transformation between modulated and unmodulated martensite in single-crystal Ni52Mn24.5Ga23.5. This intermartensitic transformation provides a much larger strain than that of the martensitic transformation. A giant switching-like strain of ±5.0% can be achieved by a small magnetic field of 0.2 T upon the intermartensitic transformation. In the modulated martensite, a large recoverable magnetic-field-induced strain of up to 1.2% has been obtained.

Precise and programmable manipulation of microbubbles by two-dimensional standing surface acoustic waves

A microfluidic device is developed to transport microbubbles (MBs) along a desired trajectory in fluid by introducing the phase-shift to a planar standing surface acoustic wave (SSAW). The radiation force of SSAW due to the acoustic pressure gradient modulated by a phase-shift can move MBs to anticipated potential wells in a programmable manner. The resolution of the transportation is approximately 2.2 µm and the estimated radiation force on the MBs is on the order of 10−9 N. This device can be used for manipulation of bioparticles, cell sorting, tissue engineering, and other biomedical applications.

Effect of low dc magnetic field on the premartensitic phase transition temperature of ferromagnetic Ni2MnGa single crystals

The temperature and field dependence of alternating-current (ac) susceptibility in a Ni50Mn25Ga25 single crystal was measured using an ac susceptometer with a dc magnetic field oriented in the [100] and [110] directions, respectively. It is found that even at very low fields the premartensitic transition temperature decreases monotonically with the increase of the applied field, and it decreases more rapidly with field applied along the [110] direction than with field along the [100] direction. In accord with a previous model, present results confirm that the magnetoelastic interaction is responsible for the premartensitic transition, and the magnitude of the magnetoelastic interaction in the [110] direction is stronger than that in the [100] direction.

Magnetic-field-induced strains and magnetic properties of Heusler alloy Ni52Mn23Ga25

Large magnetic-field-induced strain (MFIS) of −2700 ppm has been obtained from the Heusler alloy Ni52Mn23Ga25 at 300 K. The temperature for structure transformation was confirmed by three types of magnetic measurements. A burst of MFIS up to 5400 ppm could be induced by rotating a steady field of 1 T. In the martensitic phase, the material have a high saturated magnetization of 66 Am2/kg and a high anisotropy of 0.8 T. The variant reorientation mainly occurred in the region of 0.2–0.8 T. The large MFIS is sensitive to temperature, suggesting that it can only be induced when martensite and parent phase are coexisted.

Effect of internal stress and bias field on the transformation strain of the Heusler alloy Ni52Mn24.4Ga23.6

The effects of internal stress and bias field on transformation strain in the Heusler alloy Ni52Mn24.4Ga23.6 were investigated. It was found that both residual internal stress caused by the directional solidification during the growth and additional bias field with a direction consistent with the intrinsic preferential orientation would provide favourable conditions for exhibiting large transformation strain and magnetic-field-induced strain capability. These characteristics can be attributed to either nucleating favourable variants or increasing the volume fraction of favourable variants present through twin boundary motion.

Manipulation of microbubbles and targeted single cell sonoporation with by surface acoustic waves in a microfluidic device

A microfluidic device was developed to transport the aggregated microbubbles to a targeted cell at arbitrary location in liquid solution by introducing the phase-shift to a planar standing surface acoustic wave (SAW). The device consists of two perpendicular pairs of interdigital transducer (IDTs) and a polydimethyl-siloxane microchannel. By adjusting the relative phase between electric voltages applied to the independent IDTs, the microbubbles can be trapped, continuously moved or rotated due to the translation of pressure nodes. We further demonstrate that a SAW is capable of inducing microbubble cluster destruction at a desired location to achieve a single cell’s reparable sonoporation. By controlling the position of the microbubble cluster relative to the targeted cell precisely, the effective size of the collapsing microbubbles is measured to be less than 0.68 times the diameter of microbubble cluster. The sonoporation efficiency and the cell viability are 82.4%± 6.5% and 90%±8.7%, respectively, when ...