Smart medical stocking using memory polymer for chronic venous disorders

A Hybrid Syntactic Foam-Based Open-Cell Foam with Reversible Actuation

Herein, we report the first hybrid open-cell foam with revisable actuation. Open-cell foams with revisable actuation are favoable for many applications. However, it is challenging to fabricate such open-cell foams with very low density. This study presents a novel concept of creating hybrid two-way (2W) shape memory open-cell foams using two-way shape-memory-polymer-based syntactic foams as the matrix. Previously, a syntactic foam prepared by incorporating hollow glass microbubbles in the cross-linked semicrystalline cis-poly(1,4-butadiene) (cPBD) was proved to have enhanced strength and specific energy output compared to the neat cPBD. Here, the same syntactic foam was used as the matrix, and the open-cell structure was produced by the salt-leaching method. The hybrid foam exhibits very attractive properties, including reversible actuation strain up to 50%, density as low as 0.07 g/cm³, energy output up to 0.23 J/g, tensile strength up to 0.84 MPa, elongation at break as high as 339%, high thermal stability with peak decomposition temperature at 450 °C, and Joule heating and strain sensing capabilities. The tensile strength and stiffness are shown to follow the well-known Gibson-Ashby model for porous materials. Combining the open-cell structure with the reversible actuation and other functionalities enables numerous potential applications for the prepared hybrid foam, including adjustable filters, insulators, sealers, and smart scaffolds.

Influences of Crystallinity and Crosslinking Density on the Shape Recovery Force in Poly(ε-Caprolactone)-Based Shape-Memory Polymer Blends

Shape-memory polymers (SMPs) show great potential in various emerging applications, such as artificial muscles, soft actuators, and biomedical devices, owing to their unique shape recovery-induced contraction force. However, the factors influencing this force remain unclear. Herein, we designed a simple polymer blending system using a series of tetra-branched poly(ε-caprolactone)-based SMPs with long and short branch-chain lengths that demonstrate decreased crystallinity and increased crosslinking density gradients. The resultant polymer blends possessed mechanical properties manipulable across a wide range in accordance with the crystallinity gradient, such as stretchability (50.5-1419.5%) and toughness (0.62-130.4 MJ m-3), while maintaining excellent shape-memory properties. The experimental results show that crosslinking density affected the shape recovery force, which correlates to the SMPs' energy storage capacity. Such a polymer blending system could provide new insights on how crystallinity and crosslinking density affect macroscopic thermal and mechanical properties as well as the shape recovery force of SMP networks, improving design capability for future applications.

Smart Compression Therapy Devices for Treatment of Venous Leg Ulcers: A Review

Venous leg ulcers can have significant social and economic impacts, and are generally treated by applying compression to the lower limb, which aids in promoting blood return to the heart. Compression therapies commonly involve the use of passive bandages that suffer from issues associated with incorrect application, and although automated solutions have begun to appear; these are often bulky and hinder mobility. Emerging microtechnologies and new materials enable the development of "smart" compression therapy devices, which are defined as systems that use miniaturized and lightweight actuators and electronics to control the applied pressure. This paper reviews the state of the art in smart compression therapy research. A total of seventeen different devices has been identified, categorized as using one of three actuation mechanisms: pneumatic compression, motor-driven mechanisms, and smart materials (including shape memory alloys, shape memory polymers, and electroactive polymers). The field is still in its relative infancy and further refinements are required to create mass manufacturable compression dressing systems that meet medical, ergonomic, and economic standards. The use of miniaturized actuators has immense potential for the development of smart compression dressings, which will ultimately lead to higher compliance, increased patient comfort, enhanced mobility, and better treatment outcomes.

iWRAP: A Theranostic Wearable Device With Real-Time Vital Monitoring and Auto-Adjustable Compression Level for Venous Thromboembolism

OBJECTIVE

Venous Thromboembolism (VTE) is a commonly underdiagnosed disease with severe consequences and an exceedingly high mortality rate. Conventional compression wraps are devised for therapeutic purpose but lack diagnostic capacity. Recent advances in flexible electronics and wearable technologies offer many possibilities for chronic disease management. In particular, vital signs have been studied to show a strong correlation with the risk of VTE patients. In this study, we aim to develop an intelligent theranostic compression device, referred to as iWRAP, with the built-in capacity of real-time vital sign monitoring together with auto-adjustable compression level.

METHODS

An instantaneous pneumatic feedback control with a high-resolution pressure sensor is integrated to provide a highly stabilized compression level at the prescribed interface pressure for an improved therapeutic outcome. Meanwhile, arterial pulse waveforms extracted from the pressure readings from the smart compression device can be utilized to derive the body vital signs, including heart rate (HR), respiratory rate (RR) and blood pressure (BP).

RESULTS

A reliable delivery of the targeted compression level within ±5% accuracy in the range of 20-60 mmHg has been achieved through the feedback of the interface pressure. Both HR and RR have been measured within clinical-grade accuracies. Moreover, BP estimated using an ALA model has been achieved at low compression levels, which is also within a clinical-acceptable accuracy. The acquired vital information has been instantaneously fit into the clinically acceptable criteria for life-threatening PE risk with timely assessments.

CONCLUSION

The iWRAP has shown the potential to become the first theranostic wearable device with both continuous delivery of accurate and effective compression therapy and real-time monitoring of life-threatening conditions for VTE patients.

Thermoresponsive Shape Memory Fibers for Compression Garments

Their highly deformable properties make shape memory polymers (SMP) a promising component for the development of new compression garments. The shape memory effect (SME) can be observed when two polymers are combined. In here, polycaprolactone (PCL) and thermoplastic polyurethane (TPU) were melt spun in different arrangement types (blend, core-sheath, and island-in-sea), whereas the best SME was observed for the blend type. In order to trigger the SME, this yarn was stimulated at a temperature of 50 °C. It showed a strain fixation of 62%, a strain recovery of 99%, and a recovery stress of 2.7 MPa.

Amplifying and Leveraging Generated Force Upon Heating and Cooling in SMA Knitted Actuators

This work reexamines traditional shape memory alloy (SMA) loading paths commonly used in SMA-based actuator applications and presents a novel, superimposed condition in which SMA generates substantial forces upon heating and cooling. This atypical effect, which is investigated with a textile-based actuator, was found to be prominent at the completion of material phase transformation, at which point thermal expansion/contraction became the dominant force-generating mechanism. We demonstrate that amplification of generated forces can be accomplished by varying the applied thermal load, applied structural strain, as well as actuator architecture. Specifically, we present SMA knitted actuators as an actuator architecture that increases the effect by aggregating SMA wires within a complex strain profile-effectively providing a larger operational window for the effect to propagate. The amplification of blocking forces through this novel operational procedure suggests reconsidering traditional blocking force design paradigms and opens untapped actuator application spaces, such as the highlighted medical and aerospace wearable technologies.

Research on a physical activity tracking system based upon three-axis accelerometer for patients with leg ulcers

Venous leg ulcerations are a common problem, with high prevalence in the middle-aged and elderly population, and more attention on research of their physical activities has been paid, as they have great effects on the blood circulation of the lower limb. With enough, appropriate training, the chronic venous ulcerations in the lower limb can be avoided and alleviated, and venous hypertension can be reduced effectively. The study deals with a physical activity tracking system for the patients based on a three-axis accelerometer. The system uses a three-axis accelerometer, a microcontroller, and a wireless Bluetooth module to form a data acquisition platform to acquire accelerations of the lower limb movement, and sends it to a smart mobile phone via the wireless Bluetooth module. The system takes advantages of the smart mobile phone to guide the chronic venous leg ulcers to do prescribed rehabilitation exercises for the lower limb muscles, perform acceleration data preprocessing, wavelet transform and reconstruction, denoising and feature extraction, obtain the results of the rehabilitation exercises, and then give reasonable evaluation and judgment. It is helpful to treat underlying venous reflux, create such an environment that allows skin to grow across an ulcer, and accelerate ulcer healing process consequently.

Functionally Graded Knitted Actuators with NiTi-Based Shape Memory Alloys for Topographically Self-Fitting Wearables

Advances in actuating fabrics can enable a paradigm shift in the field of smart wearables by dynamically fitting themselves to the unique topography of the human body. Applications including soft wearable robotics, continuous health monitoring, and body-mounted haptic feedback systems are dependent upon simultaneous body proximity and garment stiffness for functionality. Passive fabrics and fitting mechanisms are unable to conform around surface concavities and require either high elasticity or a multiplicity of closure devices to achieve garment fit. The design, manufacture, and validation of the first circumferentially contractile and topographic self-fitting garments composed of NiTi-based shape memory alloy (SMA) knitted actuators that dynamically conform to the unique shape and size of the wearer's body in response to a change of the garment's temperature is introduced. Advanced materials and systems innovations 1) enable novel garment manufacturing and application strategies, 2) facilitate topographical fitting (spatial actuation) through garment architectural design, and 3) provide tunable NiTi-based SMA actuation temperatures to enable actuation on the surface of human skin. This research represents a paradigm shift for wearable applications by redefining garment fit to fully topographical conformation to the wearer through advanced materials and structures design.

Shape Memory Polyurethane-Based Smart Polymer Substrates for Physiologically Responsive, Dynamic Pressure (Re)Distribution

Shape memory polymers (SMPs) are an exciting class of stimuli-responsive smart materials that demonstrate reactive and reversible changes in mechanical property, usually by switching between different states due to external stimuli. We report on the development of a polyurethane-based SMP foam for effective pressure redistribution that demonstrates controllable changes in dynamic pressure redistribution capability at a low transition temperature (∼24 °C)-ideally suited to matching modulations in body contact pressure for dynamic pressure relief (e.g., for alleviation or pressure ulcer effects). The resultant SMP material has been extensively characterized by a series of tests including stress-strain testing, compression testing, dynamic mechanical analysis, optical microscopy, UV-visible absorbance spectroscopy, variable-temperature areal pressure distribution, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, dynamic thermogravimetric analysis, and 1H nuclear magnetic resonance spectroscopy. The foam system exhibits high responsivity when tested for plantar pressure modulation with significant potential in pressure ulcers treatment. Efficient pressure redistribution (∼80% reduction in interface pressure), high stress response (∼30% applied stress is stored in fixity and released on recovery), and excellent deformation recovery (∼100%) are demonstrated in addition to significant cycling ability without performance loss. By providing highly effective pressure redistribution and modulation when in contact with the body's surface, this SMP foam offers novel mechanisms for alleviating the risk of pressure ulcers.

Designing of advanced smart medical stocking using stress-memory polymeric filaments for pressure control and massaging

Compression treatment for the patients with chronic disorders such as venous ulcers and varicose veins needs the proper and adequate level of pressure sustainability. This has been a great challenge for health practitioners and stocking manufacturers even till today. There is an imperious need of any research, where internal compression pressure can be controlled or readjusted externally. In line with this, for the first time this study is focused mainly to design and optimize the smart stocking structure by integrating the stress-memory polymeric filament as a main load bearing element. Six different structures were employed to prepare the stocking fabric tubes. All the structures were investigated for pressure analysis and studied the effect of physical parameters such as temperature, strain, and leg radius. It is possible to control the level of massage effect by varying the stocking structures. An empirical relationship is derived, which provides the knowledge for how to control the stocking pressure with structural modifications like never done before. The effect of massage function on blood flow velocity in the popliteal vein on lower limb was objectively measured by Doppler ultrasound scanning. This study also sheds the insight of stocking structural modification for pressure control and provide the benchmark for achieving the efficient compression. This advanced stress-memory polymeric filaments based multifunctional compression stocking provides static pressure, massage effect, and easy size fitting in a more controlled manner for smart compression therapy.

Bioinspired Fabrication of Polyurethane/Regenerated Silk Fibroin Composite Fibres with Tubuliform Silk-Like Flat Stress⁻Strain Behaviour

Tubuliform silk is one of the seven different types of spider silks, which is well known for its unique tensile behaviour with Flat Tensile Stress⁻Strain (FTSS) curve. It is found that anisotropic microstructure of β-sheets is responsible for this property. In recent years, bioinspired approaches to engineer fibres supported by modern manufacturing systems have been attracting considerable interest. The present paper aims to investigate a strategy to biomimic the FTSS behaviour of tubuliform silk in synthetic polymer composite fibres by blending polyurethane (PU) and regenerated silk fibroin (RSF) at different ratios. Wet spinning of composite fibres results in the reconstruction of β-sheets in the synthetic fibre matrix. PU/RSF composite fibre at a ratio of 75/25 produce a tensile curve with FTSS characteristics. Secondary structural changes in RSF and interchain directions of β-sheets within the fibre are studied using Fourier Transform Infra-red (FTIR) spectroscopy and Transmission Electron Microscopy (TEM), respectively. Interestingly, results of TEM patterns confirm transverse anisotropic properties of RSF β-sheets. The composite fibres also display tuneable mechanical properties with respect to RSF contents.

Evaluation of Flexible Force Sensors for Pressure Monitoring in Treatment of Chronic Venous Disorders

The recent use of graduated compression therapy for treatment of chronic venous disorders such as leg ulcers and oedema has led to considerable research interest in flexible and low-cost force sensors. Properly applied low pressure during compression therapy can substantially improve the treatment of chronic venous disorders. However, achievement of the recommended low pressure levels and its accurate determination in real-life conditions is still a challenge. Several thin and flexible force sensors, which can also function as pressure sensors, are commercially available, but their real-life sensing performance has not been evaluated. Moreover, no researchers have reported information on sensor performance during static and dynamic loading within the realistic test conditions required for compression therapy. This research investigated the sensing performance of five low-cost commercial pressure sensors on a human-leg-like test apparatus and presents quantitative results on the accuracy and drift behaviour of these sensors in both static and dynamic conditions required for compression therapy. Extensive experimental work on this new human-leg-like test setup demonstrated its utility for evaluating the sensors. Results showed variation in static and dynamic sensing performance, including accuracy and drift characteristics. Only one commercially available pressure sensor was found to reliably deliver accuracy of 95% and above for all three test pressure points of 30, 50 and 70 mmHg.

Shape memory thermoplastic polyurethane (TPU)/poly(ε-caprolactone) (PCL) blends as self-knotting sutures

Thermally responsive shape memory polymers have promising applications in many fields, especially in biomedical areas. In this study, a simple method was purposed to prepare thermoplastic polyurethane (TPU)/poly(ε-caprolactone) (PCL) blends that possess shape memory attributes. TPU and PCL were melt compounded via a twin-screw extruder and injection molded at various ratios. Multiple test methods were used to characterize their shape memory properties and reveal the underling mechanism. The blends containing 25% TPU and 75% PCL possessed the best shape memory properties as indicated by a 98% shape fixing ratio and 90% shape recovery ratio. This was attributed to the hybrid crystalline and amorphous regions of PCL and TPU. We also found that PCL and TPU had good miscibility and that the PCL domain in TPU25% had higher crystallinity than neat PCL. The crystalline region in TPU25% could deform and maintain its temporary shape when stretched, which contributed to its high shape fixing attribute, while the rubbery TPU region assisted in the recovery of the sample upon heating by releasing the deformation energy stored. Moreover, the TPU25% string prepared could knot itself in a hot water bath, indicating a potential for suture applications. Lastly, the 3T3 fibroblast cells cultured on the TPU/PCL blends showed high viability and active substrate-cell interactions.

Revealing the morphological architecture of a shape memory polyurethane by simulation

The lack of specific knowledge of the network structure in shape memory polymers (SMPs) has prevented us from gaining an in-depth understanding of their mechanisms and limited the potential for materials innovation. This paper firstly reveals the unit-cell nanoscale morphological architecture of SMPs by simulation. The phase separated architecture of a segmented shape memory polyurethane (SMPU) with a 30 wt% hard segment content (HSC, 4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO)) showing good shape memory properties was investigated by dissipative particle dynamics (DPD) simulations. A linked-spherical netpoint-frame phase of MDI, a matrix-switch phase of polycaprolactone (PCL) and a connected-spider-like interphase for BDO were obtained for this SMPU. The BDO interphase can reinforce the MDI network. Based on these simulation results, a three-dimensional (3D) overall morphological architectural model of the SMPU can be established. This theoretical study has verified, enriched and integrated two existing schematic models: one being the morphological model deduced from experiments and the other the frame model for SMPs reported before. It can serve as a theoretical guide for smart polymeric materials design. This method for the simulation of polymer structure at the nanoscale can be extended to many areas such as photonic crystals where nanoscale self-assembly plays a vital role.

Animal Hairs as Water-stimulated Shape Memory Materials: Mechanism and Structural Networks in Molecular Assemblies

Animal hairs consisting of α-keratin biopolymers existing broadly in nature may be responsive to water for recovery to the innate shape from their fixed deformation, thus possess smart behavior, namely shape memory effect (SME). In this article, three typical animal hair fibers were first time investigated for their water-stimulated SME, and therefrom to identify the corresponding net-points and switches in their molecular and morphological structures. Experimentally, the SME manifested a good stability of high shape fixation ratio and reasonable recovery rate after many cycles of deformation programming under water stimulation. The effects of hydration on hair lateral size, recovery kinetics, dynamic mechanical behaviors and structural components (crystal, disulfide and hydrogen bonds) were then systematically studied. SME mechanisms were explored based on the variations of structural components in molecular assemblies of such smart fibers. A hybrid structural network model with single-switch and twin-net-points was thereafter proposed to interpret the water-stimulated shape memory mechanism of animal hairs. This original work is expected to provide inspiration for exploring other natural materials to reveal their smart functions and natural laws in animals including human as well as making more remarkable synthetic smart materials.