Guoxia Fei

Spatial and temporal control of shape memory polymers and simultaneous drug release using high intensity focused ultrasound

In this paper, we report a new modality enabling the simultaneous control of shape memory polymers (SMPs) and release of loaded drugs. The approach uses high intensity focused ultrasound (HIFU) and explores localized heating of SMPs upon HIFU exposure. We show that the HIFU-triggered shape recovery process can be spatially and temporarily controlled, allowing the shape memory effect to manifest in selected regions on demand, endowing SMPs with the capability of adopting multiple intermediate shapes and synchronizing the release of loaded drugs in a switchable manner. To our knowledge, this is the first time that HIFU is utilized as a trigger to reveal these appealing features of SMPs.

A spatially and temporally controlled shape memory process for electrically conductive polymer–carbon nanotube composites

Crosslinked P(MMA-BA)–CNTs shape memory composites prepared by ultrasound assisted in situ polymerization, have both relatively high electrical conductivities and good shape memory properties. Electrical resistance heating was used as a trigger to realize the spatial and temporal control of the shape memory process and to obtain multiple shapes by selecting the place where the electrical voltage was applied or switching the power on/off.

Ultrasound healable shape memory dynamic polymers

The concept of using ultrasound to trigger shape memory assisted healing of covalently cross-linked dynamic polymers is demonstrated. The well-designed dynamically crosslinked poly(e-caprolactone)-based polyurethane bearing Diels–Alder bonds not only possesses high mechanical strength and toughness, but also exhibits shape memory assisted crack-closure and healing upon exposure to high-intensity focused ultrasound owing to breaking and reformation of dynamic bonds. The use of focused ultrasound allows the healing process to be activated remotely and to be controlled locally by depositing the acoustic energy only in the damaged region without detriment to the undamaged parts of the material. The healable polyurethane materials have potential applications such as long-term load-bearing engineering components and anti-fatigue medical devices.

Electro-activated surface micropattern tuning for microinjection molded electrically conductive shape memory polyurethane composites

Shape memory polymers with surface micropatterns have seen rising demand for high value applications such as adjustable adherence surfaces, dynamic micro-geometries for cell culture studies and switchable information carriers. Recently, microinjection molding has emerged as an efficient way to manufacture devices which contain surface micro-features using a wide range of polymers with high accuracy. In this study, shape memory polyurethane–carbon nanotube composites were prepared by twin-screw melt extrusion and subsequently processed using microinjection molding to obtain components with surface micropatterns. Then an electro-activated surface micropattern tuning system was developed which could recover the original micropatterned surface of the components after a thermal deformation by applying a current which heats the component using resistive heating. In order to optimize the technique, three key areas were investigated in this work: conductivity of the microinjection molded microparts, the retention of shape memory micropatterns on the surface of microparts during annealing treatment, and the macroscopic area shrinkage of microparts after thermal treatment. It has been found that the electrical conductivity of microinjection molded parts is relatively low due to the high shear rates prevalent in the process. An annealing treatment improves the electrical conductivity by several orders of magnitude, but can be detrimental to the dimensional stability of the micropatterns, which depends significantly on the micro-injection molding parameters, especially the mold temperature. Increasing the mold temperature, melt temperature, injection speed and injection pressure result in better retention of the micropattern and improved dimension stability during annealing treatment. This work demonstrates the potential of electro-activated surface micropattern control for microinjection molded electrically conductive shape memory polymer composites, which could be a promising technology for a range of application areas including electro-adjustable adherence, information storage, and anti-counterfeiting technology.

Shape recovery characteristics for shape memory polymers subjected to high intensity focused ultrasound

High intensity focused ultrasound (HIFU)-triggered shape memory has distinct features due to the unique heating mechanism based on polymer chain shearing and friction activated by ultrasonic energy. In this study we chose crosslinked poly(methyl methacrylate-co-butyl acrylate) P(MMA-BA) as a model polymer and studied in detail the HIFU induced thermal effect and shape recovery characteristics. It was found that HIFU heating for polymers is quick and spatially localized, and can be controlled by the ultrasound power, which allows for a spatiotemporally controllable shape memory process. The effects of various parameters including sample thickness, copolymer composition and crosslinker content on the HIFU-induced thermal effect and shape recovery were investigated. Under HIFU irradiation, there exists an optimum sample thickness for a maximum thermal effect and thus better shape recovery, which is different from conventional heating. Moreover, both the copolymer composition and the crosslinker content have a profound effect on the HIFU-induced temperature rise and thus the shape recovery. These effects can be related to changes in the viscoelastic parameter loss tangent (tan δ) of the copolymer around the glass transition temperature Tg that is the transition temperature for the shape recovery process.

Polydopamine Particles Reinforced Poly(vinyl alcohol) Hydrogel with NIR Light Triggered Shape Memory and Self-Healing Capability

This study focuses on developing a facile approach to prepare biocompatible poly(vinyl alcohol) (PVA) composite hydrogels containing polydopamine particles (PDAPs) with ultrafast near-infrared (NIR) light-triggered shape memory and self-healing capability. The PVA-PDAPs composite hydrogels with excellent mechanical properties can be achieved after freezing/thawing treatment, and the formation of physically cross-linked networks from the hydrogen bonding (H-bonding) between PVA and PDAPs. Due to the excellent photothermal effect of polydopamine, the composited hydrogel can achieve rapid shape recovery and efficient self-healing properties under NIR light exposure in a short time. With the excellent shape memory performance, good biocompatibility, and self-healing property, this hydrogel should have great potential in biomedical fields such as tissue engineering, arthrodial cartilage, and artificial skin.

Co-compatibilising effect of carbon nanotubes and liquid isoprene rubber on carbon black filled natural rubber/polybutadiene rubber blend

Abstract Bis-(triethoxysilylpropyl)-tetrasulfane functionalised carbon nanotubes (t-CNTs) were used as compatibiliser along with liquid isoprene rubber (LIR) in the natural rubber (NR)/polybutadiene rubber (BR) blend. Their reinforcing and compatibilising effects were evaluated by mechanical, fatigue crack growth resistance properties and blend homogeneity. Scanning electron microscope and transmission electron microscope showed enhanced interfacial adhesion between the binary rubber phases and improved dispersion of the minor phase in the rubber blend respectively with the co-existence of LIR and carbon nanotubes. The tensile strength of the carbon black (CB) filled NR/BR blend reached its optimum when 3 phr CB was replaced with an equal amount of t-CNTs in the presence of 7 phr LIR, while the fatigue crack growth resistance property achieved its maximum in the presence of 3 phr LIR. This interesting co-compatibilisation behaviour of t-CNTs and LIR suggests that t-CNTs have a better effect than CB with the assistance of LIR, which is an effective plasticiser in the NR/BR blend.

Effect of processing temperature on structure and properties of microinjection moulded thermoplastic polyurethane/multiwalled carbon nanotube composites

Abstract Thermoplastic polyurethane (TPU)/multiwalled carbon nanotubes (MWCNTs) composites were prepared through twin extrusion and microinjection moulding. The effect of processing temperature on the structure and properties of composites were studied. Scanning electron microscopy and rheological test reveal the realisation of well dispersion and network formation of carbon nanotube (CNT) in TPU. Enhanced electrical conductivity has been found with the increasing mould temperature from 25 to 150°C, post-moulding thermal treatment under 180°C for 1 h leads to a significant increase in the electrical conductivity by over three orders of magnitude for 5 wt-%MWCNT filled TPU composites. Images (SEM and TEM) characterise the morphology of CNT network under low and high temperatures and the microcontact reconstruction of CNT network is proposed to explain the enhancement of electrical conductivity. The increased crystallinity of TPU leads to the enhancement of tensile strength and Youngs modulus of composites after thermal treatment.

High-intensity focused ultrasound selective annealing induced patterned and gradient crystallization behavior of polymer

High-intensity focused ultrasound (HIFU) was developed as a spatial selective annealing method to control the crystallization behavior and performance of polymer using amorphous polyethylene terephthalate (PET) as an example for demonstration. The spatial crystallization and morphological details of HIFU induced crystallization areas at the lamellar level and spherulite scale were studied by Micro-Focus hard X-ray diffraction, small angle X-ray scattering and optical microscopy. According to the distribution of crystallinity of PET, we can indirectly detect the history of thermal distribution of the ultrasonic focal point, which is hard to obtain by other methods. The crystallinity and the area of the crystalline region of PET sample increased with ultrasound power or irradiation time. Different from common crystalline structure of polymer materials, HIFU induced crystallinity of PET has a significant gradient distribution. The gradient crystal structure leads to a better mechanical performances, which can realize the good balance between toughness and strength. Ultrasound annealing, as a complement and development of the traditional annealing technology, has the characteristics of high efficient and spatial selectivity, showing great application prospect in post processing field.

A Facile Strategy for Self-Healing Polyurethanes Containing Multiple Metal-Ligand Bonds

A metal-ligand crosslinked internal self-healing polyurethane is developed using low-cost and commercially available compounds. The mechanical, photoluminescent, and self-healing properties can be governed by incorporating multiple metal-ligand crosslinks with weak and strong coordination bonds and varying the metal ion. In-situ attenuated total reflectance Fourier transform infrared spectroscopy reveals that the metal-ligand bond is cleaved during the damage process while metal ion is still coordinated with the ligand by stronger metal-pyridyl interaction. The multiple metal-ligand coordination facilitates the crosslinks to be fully reformed during the repairing process, leading to the superior self-healing property.