Fixity Ratio Research Articles

Eye movement characteristics of emotional face recognizing task in patients with mild to moderate depression

ObjectiveDepression is a complex affective disorder characterized by high prevalence and severe impact, commonly presenting with cognitive impairment. The objective diagnosis of depression lacks precise standards. This study investigates eye movement characteristics during emotional face recognition task (EFRT) in depressive patients to provide empirical support for objective diagnosis.MethodsWe recruited 43 patients with depression (Depressive patients, DP) from a psychiatric hospital and 44 healthy participants (Healthy Control, HC) online. All participants completed an EFRT comprising 120 trials. Each trial presented a gray screen for 800 ms followed by a stimulus image for judgment. Emotions were categorized as positive, neutral, or negative. Eye movement trajectories were recorded throughout the task. Latency of First Fixation (LFF), Latency of First Fixation for Eye AOI, and Latency of First Fixation for Mouth AOI were used as representative indicators of early attention, Proportion of Eye AOI, and Proportion of Mouth AOI as measures of intermediate attention, Accuracy (ACC) and Reaction Time (RT) as behavioral indicators of late-stage attention. In this study, these metrics were employed to explore the differences between patients with depression and healthy individuals.ResultsCompared to healthy participants, individuals with depression exhibit longer first fixation latencies on the eyes and mouth during the early attention stage of emotional face recognition, indicating an avoidance tendency toward key facial recognition cues. In the mid-to-late attention stages, depressive individuals show an increased fixation ratio on the eyes and a decreased fixation ratio on the mouth, along with lower accuracy and longer response times. These findings suggest that, relative to healthy individuals, individuals with depression have deficits in facial recognition.ConclusionThis study identified distinct attention patterns and cognitive deficits in emotional face recognition among individuals with depression compared to healthy individuals, providing an attention-based approach for exploring potential clinical diagnostic markers for depression.

Shape Memory Polyurethane Foams With Tunable Mechanical Properties and Radiation Tolerance for Breast Repair and Reconstruction.

This study developed a shape memory polyurethane foam (SM-PUF) with tunable mechanical properties and exceptional radiation tolerance for potentially implanting tissue defects after mastectomy. The PUFs were synthesized via an insitu foaming strategy using water as a foaming agent, incorporating 4,4'-diphenylmethane diisocyanate (MDI) as the rigid segment and both polyoxytetramethylene glycol and polycaprolactone as the soft segment. The resultant PUFs possess an open-cell structure with a pore size of 30 ~ 800 μm, which achieves a compressive stress of 0.04 MPa under 70% compression strain and a tensile elongation of 667.9%. PUFs exhibit body temperature (37°C)-responsive softening and shape memory abilities, with recovery and fixation ratios reaching 88% and 98%, respectively. It was verified that PUFs can resist 40 Gy radiotherapy without changing their mechanical properties and biocompatibility. This study introduces an innovative approach to produce customizable foam for the reconstruction of implant prostheses for the breast.

Shape Memory Polymer Foam Based on Nanofibrillar Composites of Polylactide/Polyamide.

This paper presents the novel development of a shape memory polymer foam based on polymer-polymer nanocomposites. Herein, polylactide (PLA)/biosourced polyamide (PA) foams are fabricated by in situ fibrillation of polymer blends and a subsequent supercritical CO2 foaming technique. In this system, PLA serves as a shape memory polymer to endow this foam with a shape memory effect (SME), and in situ generated PA nanofibers are employed to reinforce the PLA cell walls and provide an additional permanent phase. A concentration of PA, 5 wt.%, was chosen to form an entangled nanofibrillar network. Foams of PLA/PA nanoblends with the same content of constituents were fabricated to reveal the effect of minor phase morphology on the cell structure and shape memory behavior of polymer foams. Profiting from the reinforcing effect of PA nanofibers, the PLA/PA nanocomposite foam exhibits smaller foam cells, a narrower cell size distribution and a comparable cell concentration than the PLA/PA nanoblend foam. In addition, PA nanofibers, unlike PA nanodroplets, favor the shape fixation ratio and recovery ratio and shorten the shape recovery time.

Development and 4D printing of magneto-responsive PMMA/TPU/Fe3O4 nanocomposites with superior shape memory and toughness properties

This paper introduces 4D printing of composites of polymethyl methacrylate (PMMA) and thermoplastic polyurethane (TPU) reinforced with Fe3O4 particles for the first time. PMMA/TPU blends with 70/30 wt% are selected as matrix with the best compatibility based on dynamic mechanical thermal analysis. Fe3O4 nanoparticles are added to the blends with 10 %, 15 % and 20 % weight ratios. Their addition enables remote actuation of the materials in a high frequency alternating magnetic field. Field emission scanning microscopic images confirms a full dispersion of nanoparticles inside the polymeric matrix. Nanocomposites with 20 wt% of Fe3O4 can perfectly recover the permanent shape within 1.5 min in the magnetic field. They also reveal perfect shape memory properties in the hot water. Moreover, all samples display a perfect shape fixity ratio. The addition of TPU significantly enhances the toughness and flexibility of the PMMA matrix. It is found that Fe3O4 nanoparticles further enhance the mechanical strength by 10 % to 15 %, although they reduce the strain at break from 17 % to 14 %. Finally, a gripper is 4D printed and its excellent performance in the magnetic field is demonstrated.

3D-Printed Shape Memory and Piezoelectric Bifunctional Thermoplastic Polyurethane/Polyvinylidene Fluoride Porous Composite Scaffold for Bone Regeneration.

Physical stimulations such as mechanical and electric stimulation can continuously work on bone defect locations to maintain and enhance cell activity, and it has become a hotspot for research in the field of bone repair. Herein, bifunctional porous composite scaffolds with shape memory and piezoelectric functions were fabricated using thermoplastic polyurethane (TPU) and poly(vinylidene fluoride) through triply periodic minimal surfaces design and selective laser sintering technology. Thereinto, the shape fixity ratio and recovery ratio of the composite scaffold reached 98.6% and 81.2%, respectively, showing excellent shape memory functions. More importantly, its piezoelectric coefficient (d33 = 2.47 pC/N) is close to the piezoelectric constant of bone tissue (d33 = 0.7-2.3 pC/N), and the voltage released during the compression process can reach 0.5 V. Furthermore, cyclic compression experiments showed that the strength of composite scaffold was up to 8.3 times compared with the TPU scaffold. Besides, the composite scaffold showed excellent cytocompatibility. In conclusion, the composite scaffold is expected to continuously generate mechanical and electric stimulation due to shape memory and piezoelectric function, respectively, which provide an effective strategy for bone repair.

Shape memory and shape recovery characterization of thermoplastic urethane

ABSTRACT Polyurethane shape memory polymer, as a smart material, has been becoming more and more popular due to its greater multifunctionality in various industrial and biomedical applications. Here, the authors reported the characterization, and comprehensive methodology and acquired the results of thermoplastic urethane (SMTPU) as a shape memory polymer, with 35°C as the glass transition temperature, by examining its creep. This smart polymer exhibits excellent shape memory behaviour due to its steady, chemically cross-linked network. Such behaviour of shape memory polymer determines its usability in various functional applications. Furthermore, the activation temperature range of SMPTPU is close to body temperature and room temperature as well, so it can be employed in more demanding industrial applications. Thus, it becomes essential to investigate the shape-changing/memory behaviour of commercial SMTPU. A quantitative analysis was done to determine the effects of programming temperature, maximum uniaxial strain, and compressive strain on shape memory characteristics viz. the shape recovery ratios and shape fixity ratios. Along with the excellent shape memory effect, this material also exhibits high creep and elasticity at room temperature, indicating that it may be used for various industrial and biomedical applications.

Effect of atomic oxygen and vacuum thermal aging on graphene and glass fibre reinforced cyanate ester-based shape memory polymer composite for deployable thin wall structures

Deployable components and structures are a crucial part of space exploration. Due to fewer parts, low weight and cost, shape memory polymers (SMPs) and their composites (SMPCs) are considered ideal candidates for this. However, lower thermal stability and poor durability in the space environment have limited their applicability. This research work details the development of Graphene Nanoplatelets (GNP) filled Glass Fibre (GF) reinforced cyanate ester-based SMPC with 0/90° and ±45° sandwich fibre lay-up configuration capable of multidirectional shape programming. The SMP matrix was synthesised by mixing Cyanate Ester and Polyethylene Glycol (PEG) with added GNP. SMPC was fabricated by pouring the SMP mixture into a pre-prepared glass mould with the added GF layers. The synthesised SMPC showed shape programming and recovery at 169.01 ± 0.62 °C and stable thermomechanical properties at the temperature of 130 °C. Durability tests at extreme environmental conditions including Atomic Oxygen exposure, thermal vacuum aging, and elevated-temperature behaviour tests were conducted as these tests evaluate the durability and applicability of the SMPC for use in Earth's orbits and lunar environments. The performances of the samples before and after durability tests were measured through mechanical tests, shape memory effect tests and a series of characterisation methods such as microscopic image analysis, FTIR and dynamic mechanical analysis. According to the results, AO exposure affected the SMPCs by eroding their surface. There were no changes in the chemical structure of the SMPC yet the thermomechanical, mechanical and shape memory properties were decreased without compromising their safe operational levels such as storage onset temperatures (128.79 ± 3.08 °C), maximum tensile stress (114.99 ± 21.52 MPa), shape fixity (100 %) and recovery ratios (100 %). The erosion resistance of the GNP-filled SMPCs was improved with ∼54.35 % less erosion than the SMPC without GNP. The vacuum thermal aging slightly slowed shape recovery from 31.17 % to 8.32 % at 160 °C due to PEG crosslink degradation, however, 100 % shape recovery was achieved at the end. Further durability tests under cryogenic temperatures and effects after vacuum thermal cycles are warranted to observe the synergistic effect on the SMPC for future developments. Exploring the scalability and additive manufacturability of the developed SMPC can be advantageous in the future while mitigating challenges such as complex shape programming, long-term materials degradation, resource efficiency and compliance with safety standards.

Reading eye movements among homonymous hemianopia

Abstract Purpose: To measure the reading eye movement’s parameters and quantify the oculomotor dysfunction among subjects with homonymous hemianopia compared to age-matched controls using ReadAlyzer. Methods: This was a prospective study carried out in the neuro-optometry clinic of a tertiary eye care hospital in South India, from October 2018 to Janurary 2019. Fifty consecutive patients diagnosed with homonymous hemianopia were enrolled in the study after obtaining their written informed consent. Reading eye movements were measured using ReadAlyzer in patients with homonymous hemianopia and age-matched controls. Reading eye movement parameters were represented in median [interquartile range (IQR)]. Results: Subjects with homonymous hemianopia showed increased number of fixations/100 words- median (IQR) [175 (80–270)] compared to controls [91 (52.5–127.5)]; increased number of regressions/100 words [33 (-13–79)] compared to controls [18 (-10–46)]; and reduced reading rate [93 (46–140) words/min] compared to controls [186 (144–228) words/min] (Mann–Whitney U test, P ≤ 0.05). Similar trend was observed for grade level equivalent 2 (0–4) and regression to fixation ratio 15 (1–29) compared to controls [grade equivalent 7 (3–11) and regression to fixation ratio 11 (-2–24)] (Mann–Whitney U test, P ≤ 0.005). Conclusion: Reading eye movements assessed using ReadAlyzer are found to be significantly impaired among homonymous hemianopias compared to age-matched controls (Mann–Whitney U test, P ≤ 0.05).

Self-Healable, Transparent, Biodegradable, and Shape Memorable Polyurethanes Derived from Carbon Dioxide-Based Diols.

A series of CO2-based thermoplastic polyurethanes (TPUs) were prepared using CO2-based poly(polycarbonate) diol (PPCDL), 4,4'-methylenebis (cyclohexyl isocyanate) (HMDI), and polypropylene glycol (PPG and 1,4-butanediol (BDO) as the raw materials. The mechanical, thermal, optical, and barrier properties shape memory behaviors, while biocompatibility and degradation behaviors of the CO2-based TPUs are also systematically investigated. All the synthesized TPUs are highly transparent amorphous polymers, with one glass transition temperature at ~15-45 °C varying with hard segment content and soft segment composition. When PPG is incorporated into the soft segments, the resultant TPUs exhibit excellent self-healing and shape memory performances with the average shape fixity ratio and shape recovery ratio as high as 98.9% and 88.3%, respectively. Furthermore, the CO2-based TPUs also show superior water vapor permeability resistance, good biocompatibility, and good biodegradation properties, demonstrating their pretty competitive potential in the polyurethane industry applications.

Star poly(lactide-co-glycolide) and poly(ε-caprolactone) polyurethanes with shape memory properties for biomedical applications

Shape memory polyurethane (SMPU) have the capacity to alter and regain their form in reaction to a stimulus (eg. temperature, pH) and have been investigated in biomedical applications. In this work, the shape memory properties of poly(ester-urethane)s (PEU) are studied as a function of the functionality of the poly(lactide-co-glycolide) (PLGA) and poly(e-caprolactone) (PCL) pre-polymers. Two distinct series of PEU are synthesized by reaction between linear and star-shaped PLGA polyols initiated by pentaerythritol (4-arms PLGA) or dipentaerythritol (6-arms PLGA) with PCL di-isocyanate prepolymers. The different PEUs exhibit thermally actuated shape memory properties and tunable mechanical properties with Young’s moduli reaching up to 96 MPa and elongation at break reaching 930 %. The integration of low amounts of PLGA star within the PEU structure increases the material’s shape memory properties, enhancing both fixity (from 45 % to 96 %) and recovery ratios (from 88 % to 92 %). Further exploration into potential applications led to the formulation of porous foams via the solvent casting/particles leaching (SC/PL) process. These foams exhibited high porosity ranging from 74 % to 83 % with pore sizes spanning from 100 to 300 µm. Their mechanical properties are close to the human meniscus with Young’s modulus ranging from 0.13 MPa to 0.53 MPa. Moreover, integration of PLGA star within the PEU scaffold decreases the flexural strength that is an important parameter for potential mini-invasive surgery.

Shape memory cyclic behavior and mechanical durability of woven fabric reinforced shape memory polymer composites

The shape memory cyclic behavior and mechanical durability of the shape memory polymer (SMP) and three woven fabrics (plain, twill, and satin weaves) reinforced shape memory polymer composite (WFR-SMPCs) are characterized to investigate the effect of woven textures on the mechanical and shape memory properties of WFR-SMPCs. Shape memory cycle test, shape memory durability test, and microscopic observation for SMP and WFR-SMPCs were carried out. Experimental results show that the SMP is temperature-sensitive, and higher temperature facilitates the shape memory performance of the material. The woven fabric reinforcements can significantly enhance the mechanical properties of the SMP matrix while still maintaining good shape recovery ratios above 98 % and shape fixation ratios above 90 % even though there is a slight decrease in these values. The twill WFR-SMPC displays the best mechanical performance. The satin WFR-SMPC has the highest shape recovery ratio. The twill WFR-SMPC performs the best in load-bearing capacity and recovery stress. The microscopic observations show that the rotational misalignment and bending of the fiber tows, and damage to the matrix are the main failure modes of the WFR-SMPCs at high shear strain.

The polytannic acid‐Fe(III) functionalized graphene oxide in poly (propylene carbonate) nanocomposite enabling enhanced shape memory, UV‐resistance, and self‐healing performance

AbstractPolypropylene carbonate (PPC) is a promising candidate of substrate materials used for human wearable devices due to its excellent ductility and biocompatibility. However, PPC is prone to be deformed, thus resulting in poor shape recovery property. One effective solution is to construct composites. In this work, poly (tannic acid) with Fe3+ (FPTA) @ graphene oxide (GO) was added to fabricate FPTA@GO/PPC composites. The results show that FPTA@GO can construct a tight network of hydrogen bonds into PPC to improve shape memory and self‐healing properties. By varying the FPTA@GO content, the composites exhibit tunable shape memory property. Dynamic mechanical analysis confirms that FPTA@GO/PPC composites show better shape memory properties compared with pure PPC. 5 wt% FPTA@GO/PPC composite demonstrates superior shape fixation ratio (Rf = 99%) as well as superior shape recovery ratio (Rr = 94%) in 37°C. Moreover, 5 wt% FPTA@GO/PPC composite possesses great self‐healing efficiency of 81% and tensile strength (17.2 MPa). The UV absorption capacity of 5 wt% FPTA@GO/PPC is increased by 150% (far and mid‐UV regions) and 400% (near‐UV region) compared with pure PPC. Thus, FPTA@GO/PPC composites have potential applications in developing shape memory, self‐healing, and UV‐resistant materials for human wearable devices.

Shape memory and mechanical properties of ESO modified epoxy/polyurethane semi-interpenetrating polymer networks for smart plaster

While numerous studies have explored the potential of shape memory materials in medical applications, the current research output is not enough for significant productivity in industrial products. In this research, a type of shape memory orthopedic plaster was fabricated by using epoxy/polyurethane interpenetrating networks modified with epoxidized soybean oil (ESO) and then compared with some commercial plasters. Polymer networks that were produced could be tailored to have glass transition temperatures (Tgs) within the range of 70–90 °C by changing the percentage composition of polyurethane and soybean oil. Shape recovery and fixity ratios in all samples were above 95 and 97 %. DMA results showed that IPNs with variable amount of soybean oil had lower glass transition temperature (Tg) and cross-link densities compared to IPNs without soybean oil. Based on the tensile test results, most samples exhibited an elastic modulus in the range of 280–400MPa, a level deemed somewhat acceptable when compared to commercial samples. Light microscope images had shown that the increase of polyurethane led to the phase separation of polymers, which was improved by the addition of soybean oil.

2D material-enhanced multi-fold self-sensing and programmable deployable lattice structure

The development of intelligent and programmable smart composite structure that can remember and restore their original shape after being extensively deformed is highly sought after for a wide variety of applications, such as deployable and morphing structures, soft robots, and smart infrastructure. Despite recent advancements, there remains a plethora of unexplored possibilities in the field of deployable structures utilizing shape programmable and intelligent composite materials. The aim of this research is to manufacture a deployable structure that is intelligent enough to monitor the deployment and programmable to be deployed in specific way. Here, a smart deployable auxetic structure is reported that not only possesses thermal and piezoresistive sensing properties but also acts as a thermally activated intelligent shape memory polymer composite (iSMPC). We have fabricated an intelligent fabric and embedded it as reinforcement within a polyurethane-based shape memory polymer matrix to make an intelligent auxetic (A-iSMPC) structure. It has been demonstrated that the intelligent fabric enhances the overall mechanical properties of the auxetic structure and allows monitoring the temperature variation and strain changes during shape programming and recovery. The A-iSMPC offered a negative Poisson’s ratio of − 0.44, shape recovery ratio of 96%, shape fixity ratio of 88% and compaction ratio of 62%. With its shape memory, auxetic, thermal and piezoresistive sensing capabilities, this iSMPC has the potential to be a multifunctional and multipurpose structure for a variety of applications.

Influence of Infill Patterns on the Shape Memory Effect of Cold-Programmed Additively Manufactured PLA.

In four-dimensional additive manufacturing (4DAM), specific external stimuli are applied in conjunction with additive manufacturing technologies. This combination allows the development of tailored stimuli-responsive properties in various materials, structures, or components. For shape-changing functionalities, the programming step plays a crucial role in recovery after exposure to a stimulus. Furthermore, precise tuning of the 4DAM process parameters is essential to achieve shape-change specifications. Within this context, this study investigated how the structural arrangement of infill patterns (criss-cross and concentric) affects the shape memory effect (SME) of compression cold-programmed PLA under a thermal stimulus. The stress-strain curves reveal a higher yield stress for the criss-cross infill pattern. Interestingly, the shape recovery ratio shows a similar trend across both patterns at different displacements with shallower slopes compared to a higher shape fixity ratio. This suggests that the infill pattern primarily affects the mechanical strength (yield stress) and not the recovery. Finally, the recovery force increases proportionally with displacement. These findings suggest a consistent SME under the explored interval (15-45% compression) despite the infill pattern; however, the variations in the mechanical properties shown by the stress-strain curves appear more pronounced, particularly the yield stress.

Enhanced shape memory performance and numerical simulation of knitted‐fabric reinforced polymer composites with weft yarns

AbstractFabric‐reinforced shape memory polymeric composites (SMPC) have shown great potential in the design of intelligent deformation structures. In this work, the weft‐knitted fabric inserted with weft yarns was developed as reinforcement to fabricate the shape memory epoxy polymer (SMEP) composites. The effects of weft yarn, loop density and direction on the shape memory performance of SMPC under different bending radii were experimentally investigated. The results show that the SMPC have good shape fixity ratios and shape recovery ratios of around 98%. As compared with those of SMPCs without inserting weft yarns, the SMPCs with weft yarns have shorter shape recovery time, and the recovery force of SMPCs with weft yarns in the 0° and 90° directions shows an increase of 86.4% and 79.5%, respectively. The recovery force of SMPC improve 3.7 times compared to SMEP. The multiscale models of SMPC were established with basis of the results of micro‐computed tomography scanning of specimens and viscoelastic theory. The surface buckling behaviors of SMEP and SMPC specimens after U‐bending load were discussed. Finally, the deformation of loops and weft yarns of SMPC were analyzed to reveal the shape memory mechanism.Highlights Shape memory polymeric composites (SMPC) with weft yarns has shorter shape recovery time. Recovery force of SMPC with weft yarns was obvious enhanced. Multi‐scale viscoelastic models of SMPC were established. Surface buckling behaviors of SMPC after U‐bending load were revealed.

Biobased photothermal responsive shape memory polythioether/MXene nanocomposites with self-extinguishing performance

Thermosetting shape memory polymers (TS-SMPs) have a higher shape fixity ratio (Rf) and shape recovery (Rr) due to their structure integrity and thermal stability, and the glass transition temperature (Tg) usually influences the transition temperature (Ttrans) of TS-SMPs. Therefore, it is significant to tailor the Tg range and mechanical properties for TS-SMPs. In this work, the inherently flame-retarding bio-based MXene-reinforced polythioether nanocomposites with excellent shape memory performance, driven by photothermal response, were designed. Firstly, a photopolymerizable MXene nanomonomer (MPS-MXene) was obtained by introducing 3-(methacryloxy) propyltrimethoxysilane onto the surface of the MXene monolayer. Then, the bis(4-allyl-2-methoxyphenyl) phenyl phosphonate (BEP) was synthesized by eugenol (a lignin derivative) with phenyl phosphonic dichloride. The polythioether/MXene composites (BEP-T-xM) were synthesized through in-situ thiol-ene photopolymerization of MPS-MXene, BEP, and tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate. Surprisingly, compared with neat polythioether, the Tg of BEP-T-0.2 M composite increased from 19.6 to 34.6 °C, when only 0.2 wt% MPS-MXene was added. The photothermal conversion efficiency (η = 73.8 %) and shape memory performance with Rr (>98 %) were greatly improved. Consequently, the interesting phenomena such as “sunflowers growing towards the sunlight” and “thermal shrinkage” can be observed. Meanwhile, the tensile strength and Young’s modulus increased significantly by 141 % and 91 %, respectively, due to the good dispersion of rigid MPS-MXene nanosheets. Furthermore, all the polythioether/MXene composites showed self-extinguishing performance. This study will provide a novel strategy for designing biobased photothermal-responsive TS-SMPs.

Stretchable conductive shape-memory nanocomposites for programmable electronics via photo-mediated multiscale structural design

Conductive shape-memory nanocomposites are very promising in flexible electronics, soft robotics, wearable sensors, etc. However, achieving a balance between conductivity, shape-memory behavior, and stretchability is still challenging in this field. Here, we report stretchable conductive shape-memory nanocomposites (SCSMNCs) prepared through photo-mediated multiscale structural design (PMMSD). At a molecular level, we utilize highly efficient photo-mediated radical polymerization and hydrogen abstraction reaction to fast construct a conjoined polymeric network in one step (∼68 s). Hybrid nanofibers are, meanwhile, introduced to generate highly conductive networks. This rational design facilitates the fabrication of nanocomposites simultaneously exhibiting excellent shape-memory behavior, high conductivity, improved mechanical properties, and rapid gelation. Mechanics-guided metamaterial design can be then produced in macro-scale by additive manufacturing to further increase the stretchability of the nanocomposites without compromising other key properties. Consequently, benefitting from the PMMSD strategy, the stretching strain of SCSMNCs improves significantly by 19 times compared to the samples lacking network and structural design, with conductivity > 105 S/m, shape fixation ratio and shape recovery ratio > 95 %. Notably, the combination of the increased stretchability, high conductivity and excellent shape-memory behavior endows the SCSMNCs with adaptive electrical and mechanical properties over long ranges. Based on these advanced performances, we demonstrate the utility of the designed SCSMNCs as function-programmable electromagnetic interference shields and wearable sensors. We anticipate this study will pave a new way for the design and application of high-performance SCSMNCs.

Enhancing Tensile Modulus of Polyurethane-Based Shape Memory Polymers for Wound Closure Applications through the Addition of Palm Oil.

Thermo-responsive, biocompatible polyurethane (PU) with shape memory properties is highly desirable for biomedical applications. An innovative approach to producing wound closure strips using shape memory polymers (SMPs) is of significant interest. In this work, PU composed of polycaprolactone (PCL) and 1,4-butanediol (BDO) was synthesized using two-step polymerization. Palm oil (PO) was added to PU for enhancing the Young's modulus of the PU beyond the set criterion of 130 MPa. It was found that PU had the ability to crystallize at room temperature and the segments of individual PCL and BDO polyurethanes crystallized separately. The crystalline domains and hard segment of PU greatly affected the tensile properties. The reduction of crystalline domains by the addition of PO and deformation at the higher melting temperature of the crystalline PCL polyurethane phase improved the shape fixity and shape recovery ratios. The new irreversible phase, raised from the permanent deformation upon stretching at the between melting temperature of the crystalline PCL and BDO polyurethanes of 70 °C, resulted in a decrease in shape fixity ratio after the first thermomechanical stretching-recovering cycles. The demonstration of PU as a wound closure strip showed its efficiency and potential until the surgical wound healed.

Bending shape memory properties and multi-scale viscoelastic behaviors of knitted-fabric reinforced polymer composites

Knitted fabrics with easily deformable loop structure have the potential in the development of shape memory polymeric composites with large recovery deformations. The knitted fabric reinforced shape memory epoxy polymer composites (SMPC) were prepared in this work. The effects of loop densities, orientations and bending radii on shape memory properties of SMPC were investigated. The shape fixity ratio and shape recovery ratio of SMPC subjected to U-shaped bending radius of 5 mm are above 98 %. The shape recovery force of SMPC can reach up to 5.9 N. The thermodynamic properties of SMP were also characterized to obtain mechanical parameters and a user-defined material subroutine (UMAT) of shape memory epoxy polymer (SMEP) was written. Based on viscoelastic theory and the multi-scale geometrical structures, the macroscopic homogeneous thermodynamic model and mesoscopic thermodynamic model of knitted fabric reinforced SMPC were established to study the macro-scale stress distribution and meso-scale deformation evolution during shape memory process, respectively. The neutral surface position of SMPC during bending deformation is offset inner. The unique anisotropic loop structure of knitted fabric determines the shape memory behavior of the SMPC. Finally, micro-CT characterizations of knitted fabric reinforced SMPC were conducted to further understand the loop deformation mechanism during shape memory process. This study will provide important theoretical and technical support for large deformation structure design and deformation prediction of smart composites.