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Currently available synthetic grafts demonstrate moderate success at the macrovascular level, but there are still challenges at small vascular scale (inner diameter of less than 6 mm). In this paper, silk fibroin (SF)/polyurethane (PU)/SF three-layer drug carrier nanofibrous tubes were developed for blood vessel repair with several advantages over existing designs. Our design consisted of a bionic three-layer microtube that was synthesized from the drug carrier SF and oligomeric proanthocyanidin nanofibers as the inner layer, PU nanofibers as the middle layer, and SF nanofibers as the outer layer. The results suggested that these three-layer tubes are attractive biocompatible materials for use as vascular grafts.

The scaffold which provides space for cell growth, proliferation, and differentiation, is a key factor in bone tissue engineering. However, improvements in scaffold design are needed to precisely match the irregular boundaries of bone defects as well as facilitate clinical application. In this study, controllable three-dimensional (3D) porous shape memory polyurethane/nano-hydroxyapatite (SMPU/nHAP) composite scaffold was successfully fabricated for bone defect reparation. Detailed studies were performed to evaluate its structure, apparent density, porosity, and mechanical properties, emphasizing the contribution of nHAP particles on shape recovery behaviors and biological performance in vitro. The effect of nHAP particles in porous SMPU/nHAP composite scaffold was found to enhance the compression resistance by 37%, shorten the compression recovery time by 41%, reduce the tensile resistance by 78%, reach the shape recovery ratio of 99%, and promote the cell proliferation by 13% after 7 days of culture. These results revealed that the 3D structure and aperture of as-prepared scaffold were controllable. And in minimally invasive surgery and bone repair surgery, this porous composite scaffold could significantly reduce the operative time and promote the bone cell growth. Therefore, this porous SMPU/nHAP composite scaffold design has potential applications for the bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 244-254, 2018., (© 2017 Wiley Periodicals, Inc.)

Tissue engineering is a promising alternative for treating bone defects. However, improvements in scaffold design are needed to precisely match the irregular boundaries of bone defects as well as facilitate clinical application. In this study, a shape memory polyurethane scaffold was fabricated using a salt-leaching-phase inverse technique. Different sizes of salts were used to obtain scaffolds with different pore sizes. Scanning electron microscope, X-ray photoelectron spectroscopy, and X-ray micro-computed tomography analysis confirmed that three-dimensional porous polyurethane scaffolds were obtained. The mechanical properties and biocompatibility of the scaffolds were analyzed by compression testing, thermal mechanical analysis, and cell experiments with osteosarcoma MG-63 cells. The results revealed that the scaffolds had good mechanical properties and shape memory properties for bone repair, and also had the ability to promote cell proliferation. Thus, this scaffold design has good prospects for application to bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1132-1137, 2017., (© 2017 Wiley Periodicals, Inc.)

Although many kinds of flexible piezoelectric materials have been developed, there were few reports on flexible multifunctional nanofibers for energy harvesting. In this study, we prepared multifunctional nanofibers from lead zirconate titanate particles and shape memory polyurethane by electrospinning. The resulting nanofibers had both piezoelectric and shape memory effects. To improve the dispersion, lead zirconate titanate particles were modified by silane coupling agents. The lead zirconate titanate/shape memory polyurethane nanofibers were used to harvest energy from sinusoidal vibrations, and the lead zirconate titanate 80 wt% sample produced voltages of 120.3 mV (peak-to-peak). Taking advantage of the shape memory effect, the lead zirconate titanate/shape memory polyurethane nanofibers can be easily deformed into desired shapes and revealed the potential for realizing energy harvesting in complex structures. [ABSTRACT FROM AUTHOR]

Herein, we first time present our research on ultrasonic dyeing of polyurethane (PU) nanofibers. The PU nanofibers were fabricated by electrospinning process and were subsequently dyed following exhaust method using sonication. The two disperse dyes selected were a low-energy disperse dye (CI Disperse Blue 56) and a high-energy disperse dye (CI Disperse Red 167:1). The ultrasonic energy was used to achieve higher color build-up on PU nanofibers. The temperature/time (T/T) diagram of proposed dyeing process has been suggested; dyeing time and dyeing temperature were optimized. Color build-up properties (measured in terms of K/S values), dye fixation (%), and color fastness properties were studied in detail. The samples were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and mechanical strength measurements. The results show 70 °C and 40 min as optimum dyeing temperature and time, respectively. The SEM, FTIR, and XRD results did not show any significant effect of ultrasonic dyeing on morphology, chemical, and crystallographic structure of PU nanofibers. Color fastness results revealed excellent light fastness, very good washing, and hot pressing fastness of both dyes. [ABSTRACT FROM AUTHOR]

Thermoplastic polyurethanes (TPUs) are copolymers with hard and soft segments. They have excellent physical properties and good biocompatibility. In particular, their shape memory properties and compatibility with plasticizers make TPU gels suitable for use as soft actuator materials. In this work, a plasticizer, dibutyl adipate (DBA), is added to four types of TPU to form gels. All the TPUs form transparent soft gels with different DBA contents. Their dielectric and mechanical properties are significantly improved by DBA addition, and the TPUs are changed from insulators to electrical actuation materials. Polyether TPU/DBA gels show the most significant changes. The bending distance of a TPU/6DBA gel tip (dimensions 20 × 5 × 0.3 mm3) is about 15 mm when the gel is sandwiched between soft electrodes and an electric field of less than 3 V μm-1 is applied. The developed materials show large deformations at low energies, and will make a significant contribution to the field of actuation materials. It is believed that TPU/DBA gels can be used as photovoltaic, dielectric, artificial muscle, robotic, and other smart materials. [ABSTRACT FROM AUTHOR]

We fabricated an actuator that was made from polyurethane (PU) with carbon nanotubes (CNTs) as the filler. To improve the dispersion of the CNTs, a mild hydrothermal treatment was carried out. Carboxyl and hydroxyl groups were introduced to the surface of the CNTs, and they were found to be highly dispersed in polar solvents such as dimethylformamide. To evaluate these films, we mainly focused on electrical properties, such as dielectric spectroscopy, space charge measurements, and actuator behavior. We found that the PU/CNTs film bents toward the cathode when an electric field was applied, and it reverted to its original position when the electric field was removed. Upon the inclusion of the CNTs as the filler for the polymer, the electrical properties of the films improved significantly. The highly polarized films had a high relative permittivity, and this produced a higher Maxwell pressure, which assisted the actuation. A high accumulated charge density was observed from space charge measurements in some of the films, and this explains the bending direction and the actuation mechanism. [ABSTRACT FROM AUTHOR]

A nanocomposite actuator film incorporated with carbon nanotubes (CNTs) was fabricated and evaluated. The materials are polyurethane and modified CNTs as the filler. The CNTs were modified using microwave-induced polymerization modification route to improve the dispersion. The actuator performance test revealed that the films bent to the cathode side when voltage was succeeded and reverted to their original position when the voltage was removed. Moreover, the electrical properties were evaluated and the charge accumulation was observed near the anode side when voltage is applied to the films. Based on this asymmetric charge density inside the films, a model which predicts the bending direction and actuation mechanism was suggested. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs) and shape memory polyurethane (SMP) were used to prepare MWCNT/SMP composites for electromagnetic interference (EMI) shielding. The uniform distribution of MWCNTs was confirmed by field emission scanning electron microscopy (SEM). The electrical conductivity of the composites was tested by the four-probe method, and the results suggested that the conductivity of the samples was significantly increased by the presence of MWCNTs. The conductivity reached 35 S/m when the MWCNT loading was 9 wt%. Dynamic mechanical analysis (DMA) revealed that the composites exhibited higher storage moduli than pure SMP. In addition, the shielding effectiveness (SE) of composites with various MWCNT loading and thickness were measured over 4–7 and 13–16 GHz. The highest SE achieved was close to 35 dB for MWCNT/SMP composites with the thickness of 2 mm and MWCNT loading of 9 wt%. The SE increased as the thickness and conductivity of the composites increased. Moreover, the SE was enhanced as the frequency increased. [ABSTRACT FROM AUTHOR]

• Their glass transition temperature was controlled and shifted lowered from 60 °C to 37 °C. • The SMP tube compression and expansion demonstrated fast tube recovery on the diameter direction. • The cell proliferation of mouse cells demonstrates these tube actuators can use with the human body with non-toxicity. [Display omitted] In this study, a tube actuator was successfully fabricated by incorporating shape memory polyurethane (SMPU) with dibutyl adipate (DBA) plasticizer, which distinctly produces softness and glass transition temperature switching close to human body temperature. The plasticized SMPU tube was activated at 37 °C, which is faster than the pure SMPU tube. The effect of thermal triggering on tensile and viscoelastic properties was investigated. Adding DBA plasticizers to SMPU demonstrated a quicker recovery rate than pure SMPU during tube compression and expansion. In addition, according to thermomechanical analysis results, the shape recovery ratio of the DBA plasticizer-doped tube is up to 83%, and its shape recovery ratio during tensile deformation is up to 99%. Particularly, mouse cell adhesions and proliferation on SMPU-DBA gel provide biocompatibility and nontoxicity. The bio-based mechanical properties of the tube make sensing under human temperature control an appealing possibility. The developed tube actuators can be used as artificial blood vessels and in other clinical applications. [ABSTRACT FROM AUTHOR]

• Actuation of the plasticized SMP was accomplished by heating and electric. • The SMP gels could be stretched up to a high strain and then rapidly recover back to their original form. • The two-way shape deformation of contraction and expansion were investigated over 6 electric on-off cycles. The largest contraction reached 6.76 % with an electric field of 34.24 V/μm. In this work, shape memory materials were developed for use as soft actuators. Shape memory polymers (SMPs) generally demonstrate good actuation on direct thermal heating. Here, we also demonstrate SMPs with good electric actuation via the incorporation of dibutyl adipate (DBA) plasticizers with shape memory polyurethane to form an SMP gel, which is a soft dielectric material. The effect of the plasticizer on the shape memory behavior under thermal stimulus was investigated. The SMP gel had faster shape recovery than the pure SMP and almost fully recovery. A dielectric SMP actuator was prepared and its two-way shape deformation of contraction and expansion, were investigated over 6 electric on-off cycles. The largest contraction reached 6.76 % with an electric field of 34.24 V/μm. The developed dielectric elastomer actuator displayed a multifunctional response to thermal and electric stimuli. This material has potential for alternative actuation applications including biomaterials. [ABSTRACT FROM AUTHOR]

Highlights • Novel fabrication of unidirectional VGCF@PU fibrous membrane by rotation spinning. • Potential spinning approach for preparing high content of carbon composite fiber. • Anisotropic electrical conductivity and microwave shielding performance. • Oriented alignment of VGCF along the direction of PU fibre. Abstract Highly aligned nonwoven vapor grown carbon fibre (VGCF) based polyurethane (PU) fibrous membrane (VGCF@PUFM) was fabricated by rotation spinning based on DMF-H 2 O exchange for directional microwave shielding. This VGCF@PUFM showed obviously different electrical conductivity and mechanical strength in parallel and perpendicular directions. Variational microwave shielding effectiveness (SE) could be observed by changing the rotation angles of VGCF@PUFM with vibrational direction of electromagnetic (EM) wave. There was the shielding difference more than 10 dB (above 20 dB in 0°, below 8 dB in 90°). Greater shielding effectiveness could be expected by enhancing the anisotropy of electrical conductivity of the VGCF@PUFM. In addition, oriented alignment of VGCF in fibre is promising for further improvement of the electrical conductivity in fibre direction. [ABSTRACT FROM AUTHOR]

Abstract Multi-layer graphene oxide (MLGO) coated shape memory polyurethane (MLGO@SMPU) with different layers was fabricated by multiple dipping for adjustable shape memory switching devices. The MLGO, which stacked together in parallel, evenly covered the surface of the SMPU. Stress strain testing indicated that the coating of GO improved the mechanical strength of these MLGO@SMPU composites in the stretching stage below the strain of approximately 6%. Adhesive force testing suggested that the first GO layer could adhere well to the SMPU surface, but the interaction force between GO layers was weak. The angle recovery ratio and time, bending recovery force, and angle fixity ratio of these MLGO@SMPU composites were evaluated using homemade evaluation apparatus. Results indicated that with the increase of GO layers from one to five layers, the MLGO@SMPU gave an angle recovery ratio reduced to 83.2%, recovery time decreased to 7.6 s, bending recovery force increased to 18.3 mN, and angle fixity ratio decreased to 83.3%. This novel and straightforward approach of dipping graphene oxide onto shape memory substrates for adjustable recovery ratio, time and force has the potential to be applied to smart switching devices including sensors and actuators. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Highlights • For the first time, we proposed dipping coating approach of SMPU onto porous sponge. • Pure carbon interface for good electromagnetic mismatch. • Ultrahigh weight loading ratio of the sponge for carbon materials. • Compression recovery ratio at least above 90% even under ultrahigh carbon loading. • Stable microwave shielding after varying thickness or compressing repeatedly. Abstract Shape memory driving thickness adjustable graphite (G) micro-flakes@shape memory polyurethane (G@SMPU) sponge was fabricated by two-step dipping separately in G-dispersed aqueous solution and SMPU/THF solution for high-performance microwave shielding. The sponge exhibited an ultrahigh G loading ratio (G/sponge, wt/wt) up to 490 wt%. For the first time, dipping coating of SMPU onto the sponge was proposed, and the obtained G@SMPU sponge exhibited a good recovery effect at least above 90% after thorough compression. And also, the thickness could be adjusted by utilizing its shape memory property. For microwave shielding, G-9@SMPU and G-18@SMPU sponges achieved the shielding effectiveness over 20 and 30 dB, respectively. Moreover, varying thickness or compressing repeatedly even up to 100 times would not obviously decrease the shielding effect of the G@SMPU sponge. This suggests the steady distribution and adhesion of G micro-flakes inside the three-dimensional sponge substrate due to the fixing of SMPU. [ABSTRACT FROM AUTHOR]

In this paper, electrically actuated shape memory composites were prepared by compounding shape memory polyurethane (SMPU) with conductive antimony-doped tin oxide/TiO 2 (ATO/TiO 2 ) whiskers. The resultant composites, ATO/TiO 2 /SMPU, can be activated by electric voltages because of heating Joule and enhancement of heating efficiency by the conductive network resulting from the overlaps of whiskers. In addition to conductivity, ATO/TiO 2 /SMPU composites featured lighter color than most electroactive shape memory composites, which exhibit black color due to the addition of carbon materials. The composites exhibited uniform electrical resistance and rapid heat transfer performances. When the composites with 50 wt% ATO/TiO 2 whiskers were used in a switch electric circuit as the switch, the circuit can turn off within 30 s. ATO/TiO 2 whiskers improved Young's moduli by at least 390% and recovery stresses by more than 250% compared with pristine SMPU. Although the recovery rates were unsatisfactory in the first test cycle, composites with 40 wt% ATO/TiO 2 whiskers and 50 wt% ATO/TiO 2 whiskers still showed recovery rates higher than 96% and 94% in the third cycle, respectively. [ABSTRACT FROM AUTHOR]

Many gel-like soft composites were obtained by using thermoplastic polyurethane (TPU) as the matrix in this work. Different contents of plasticizer dibutyl adipate (DBA) was added to TPU to swell its molecular chains and allowed them to pass through each other easily. These samples were then sandwiched between two electrodes as actuators and their actuation abilities were investigated. The results showed that the largest deflection among those samples was up to 12.11 mm, which corresponds to 48.44% of the length of samples (at 2.86 V μm−1). The deflection increased with increasing of the electric field intensity. Besides, the actuator was able to promptly respond to the change of voltage within 0.12 s. A wide response ability in the frequency region from 0.5 Hz to 10 Hz was confirmed, and the largest amplitude over 22 mm of the actuator was observed at 5 Hz. Furthermore, a new method was proposed in this paper to estimate the tiny force generated by the actuator. The small variation (less than 3%) of the measured results indicated that the proposed method is reliable even at a small bending angle. It is believed that the rapid bending capability and large deformation of the developed actuator at low intensity of electric field will make its considerable contributions to the field of soft robotics or biomaterials. Image 1 • Plasticized gel based actuators were prepared and their properties were investigated. • The largest actuating deflection was up to 48.44% of the sample length at 2.86 V μm−1 • The actuation behaviors in an electric field is a consequence of multiple factors. • A new method was proposed to estimate the tiny actuation force. [ABSTRACT FROM AUTHOR]