Thermo-Mechanically Coupled Thermo-Elasto-Visco-Plastic Modeling of Thermo-Induced Shape Memory Polyurethane at Finite Deformation

A series of monotonic tensile experiments of thermo-induced shape memory polyurethane （TSMPU） at different loading rates were carried out to investigate the interaction between the internal heat production and the mechanical deformation. It is shown that the tem- perature variation on the surfaces of the specimens due to the internal heat production affects the mechanical properties of TSMPU remarkably. Then, based on irreversible thermodynamics, the Helmholtz free energy was decomposed into three parts, i.e., the instantaneous elastic free energy, visco-plastic free energy and heat free energy. The total deformation gradient was decomposed into the mechanical and thermal parts, and the mechanical deformation gradient was further divided into the elastic and visco-plastic components. The Hencky＇s logarithmic strain was used in the current configuration. The heat equilibrium equation of internal heat production and heat exchange was derived in accordance with the first and second thermodynamics laws. The temperature of specimens was contributed by the internal heat production and the ambient temperature simultaneously, and a thermo-mechanically coupled thermo-elasto-visco-plastie model was established. The effect of temperature variation of specimens on the mechanical properties of the material was considered in this work. Finally, the capability of the proposed model was validated by comparing the simulated results with the corresponding experimental data of TSMPU.

3D-printed NIR-responsive shape memory polyurethane/magnesium scaffolds with tight-contact for robust bone regeneration

Patients with bone defects suffer from a high rate of disability and deformity.Poor contact of grafts with defective bones and insufficient osteogenic activities lead to increased loose risks and unsatisfied repair efficacy.Although self-expanding scaffolds were developed to enhance bone integration,the limitations on the high transition temperature and the unsatisfied bioactivity hindered greatly their clinical application.Herein,we report a near-infrared-responsive and tight-contacting scaffold that comprises of shape memory polyurethane(SMPU)as the thermal-responsive matrix and magnesium(Mg)as the photothermal and bioactive component,which fabricated by the low temperature rapid prototyping(LT-RP)3D printing technology.As designed,due to synergistic effects of the components and the fabrication approach,the composite scaffold possesses a homogeneously porous structure,significantly improved mechanical properties and stable photothermal effects.The programmed scaffold can be heated to recover under near infrared irradiation in 60s.With 4 wt%Mg,the scaffold has the balanced shape fixity ratio of 93.6%and shape recovery ratio of 95.4%.The compressed composite scaffold could lift a 100 g weight under NIR light,which was more than 1700 times of its own weight.The results of the push-out tests and the finite element analysis(FEA)confirmed the tight-contacting ability of the SMPU/4 wt%Mg scaffold,which had a signficant enhancement compared to the scaffold without shape memory effects.Furthermore,The osteopromotive function of the scaffold has been demonstrated through a series of in vitro and in vivo studies.We envision this scaffold can be a clinically effective strategy for robust bone regeneration.

Bioinspired 4D Printing Shape-Memory Polyurethane Rhinoplasty Prosthesis for Dynamic Aesthetic Adjustment

The disparity between the postoperative outcomes of rhinoplasty and the expected results frequently necessitates secondary or multiple surgeries as a compensatory measure,greatly diminishing patient satisfaction.However,there is renewed optimism for addressing these challenges through the innovative realm of Four-Dimensional(4D)printing.This groundbreaking technology enables three-dimensional objects with shape-memory properties to undergo predictable transformations under specific external stimuli.Consequently,implants crafted using 4D printing offer significant potential for dynamic adjustments.Inspired by worms in our research,we harnessed 4D printing to fabricate a Shape-Memory Polyurethane(SMPU)for use as a nasal augmentation prosthesis.The choice of SMPU was guided by its Glass Transition Temperature(Tg),which falls within the acceptable temperature range for the human body.This attribute allowed for temperature-responsive intraoperative self-deformation and postoperative remodeling.Our chosen animal model for experimentation was rabbits.Taking into account the anatomical structure of the rabbit nose,we designed and produced nasal augmentation prostheses with superior biocompatibility.These prostheses were then surgically implanted in a minimally invasive manner into the rabbit noses.Remarkably,they exhibited successful temperature-controlled in-surgery self-deformation according to the predetermined shape and non-invasive remodeling within a mere 9 days post-surgery.Subsequent histological evaluations confirmed the practical viability of these prostheses in a living organism.Our research findings posit that worm-inspired 4D-printed SMPU nasal prostheses hold significant promise for achieving dynamic aesthetic adjustments.

Investigation on Structures and Properties of Shape Memory Polyurethane/Silica Nanocomposites

In this study, high performance shape memory polyurethane （SMPU）/silica nanocomposites with different silica weight fraction including SMPU bulk, 3%, 4.5%, 6%, 7.5%, 10%, were prepared by sol-gel process initiated by the solid acid catalyst of p-toluenesulfonic acid （PTSA）. Field emission scanning electron microscopy （FE-SEM） and transmission electron microscopy （TEM） observation show that the silica nanoparticles are dispersed evenly in SMPU/silica nanocomposites. Tensile test and dynamic mechanical analysis （DMA） suggest that the mechanical properties and the glass transition temperature （Tg） of the nanocomposites were significantly influenced by silica weight fraction. Thermogravimetric analysis （TGA） was utilized to evaluate the thermal stability and determine the actual silica weight fraction. The TGA results indicate that the thermal stability can be enhanced with the hybridization of silica nanoparticles. Differential scanning calorimetry （DSC） was conducted to test the melting enthalpy （△H） and the results suggest that the AH was markedly improved for the SMPU/silica nanocomposites. Thermomechanical test was conducted to investigate the shape memory behavior and the results show that the shape fixity is improved by hybridization of silica and good shape recovery can be obtained with the increasing of cycle number for all the samples.

A shape memory scaffold for body temperature self-repairing wearable perovskite solar cells with efficiency exceeding 21%

Grain boundary cracks in flexible perovskite films can be repaired by filling with self-repairing polymers during the preparation and wearable operation.However,the self-repairing polymers are commonly active through external heating or humidification treatments,which cannot match with the human body's temperature tolerance of wearable devices.Herein,a body temperature-responsive shape memory polyurethane(SMPU)is demonstrated to achieve the real-time mechanical self-repairing of grain boundary cracks(~37°C).Furthermore,the strong intermolecular interaction between SMPU and the uncoordinated Pb2+and I−,can reduce the trap density in perovskite films.The blade-coated device achieves a power conversion efficiency(PCE)of 21.33%,which is among the best reported flexible perovskite solar cells(PSCs;0.10 cm2).Importantly,the device with SMPU can recover more than 80%of the PCE after 6000 cycles(bending radius:8 mm).Finally,the flexible PSCs are used for wearable solar power supply of a smartphone,which show great potential for self-repairing wearable electronics.