A Flexible Bi-Stable Composite Antenna with Reconfigurable Performance and Light-Responsive Behavior.

An integrated solution providing a bi-stable antenna with reconfigurable performance and light-responsive behavior is presented in this paper for the first time. The proposed antenna includes a radiation layer with conductivity, which is integrated onto the bi-stable substrate. First, the effect of the radiation layer material and substrate layer parameters on antenna performance was studied. The experiment showed that an antenna with CNTF has a wider impedance bandwidth than one with CSP, namely 10.37% versus 3.29%, respectively. The resonance frequency increases gradually with the increase in fiber laying density and fiber linear density. Second, the influence of state change of the substrate layer on the antenna radiation pattern was studied. The measured results showed that the maximum radiation angle and gain of states I and II are at 90°, 1.21 dB and 225°, 1.53 dB, respectively. The gain non-circularities of the antenna at states I and II are 4.48 dB and 8.35 dB, respectively, which shows that the antenna has good omnidirectional radiation performance in state I. The display of the array antenna, which shows that the array antenna has good omnidirectional radiation performance in state A, with gain non-circularities of 4.20 dB, proves the feasibility of this bi-stable substrate in reconfigurable antennas. Finally, the antenna deforms from state I to state II when the illumination stimulus reaches 22 s, showing good light-responsive behavior. Moreover, the bi-stable composite antenna has the characteristics of small size, light weight, high flexibility, and excellent integration.

Green One-Step Strategy of Conductive Ink for Active Health Monitoring in Rehabilitation and Early Care.

Conductive ink deposited on flexible substrates through simple methods such as dyeing or printing is one of the most promising approaches for scalable fabrication of wearable electronics. However, excessive chemical additives or a complex preparation process has limited the practical applications of conductive inks. Herein, a highly stable and antibacterial AgNPs/CNT/rGO (SACR) conductive ink with the only assistance of sustainable silk sericin (SS) is developed through a green one-step strategy. SS functions as not only the reductant of silver ions and GO by donating electrons but also the dispersant and stabilizer of CNTs through strong noncovalent interactions. The universality of SACR ink is demonstrated by depositing on various flexible substrates through handwriting, screen-printing, and dyeing techniques; meanwhile, the mechanical reliability between SACR ink and substrates is validated by peeling, bending, and twisting measurements. In addition, the synergistic effects of the multilevel hierarchical 0D/1D/2D structure and abundant interfacial interactions in SACR ink are advantageous to enhancing sensing performance. An SACR ink-based strain sensor and hydrogen peroxide (H2O2) sensor are fabricated to detect physical and biochemical indicators, demonstrating the enormous potential of SACR ink in intelligent wearables for active health monitoring in early care.

Carboxylated Carbon Nanotube/Polyimide Films with Low Thermal Expansion Coefficient and Excellent Mechanical Properties.

Polyimide (PI) films with excellent heat resistance and outstanding mechanical properties have been widely researched in microelectronics and aerospace fields. However, most PI films can only be used under ordinary conditions due to their instability of dimension. The fabrication of multifunctional PI films for harsh conditions is still a challenge. Herein, flexible, low coefficient of thermal expansion (CTE) and improved mechanical properties films modified by carboxylated carbon nanotube (C-CNT) were fabricated. Acid treatment was adapted to adjust the surface characteristics by using a mixture of concentrated H2SO4/HNO3 solution to introduce carboxyl groups on the surface and improve the interfacial performance between the CNT and matrix. Moreover, different C-CNT concentrations of 0, 1, 3, 5, 7, and 9 wt.% were synthesized to use for the PI film fabrication. The results demonstrated that the 9 wt.% and 5 wt.% C-CNT/PI films possessed the lowest CTE value and the highest mechanical properties. In addition, the thermal stability of the C-CNT/PI films was improved, making them promising applications in precise and harsh environments.

Mechanical Behavior and Energy Dissipation of Woven and Warp-Knitted Pvc Membrane Materials under Multistage Cyclic Loading.

In order to study the mechanical behavior and energy dissipation of architectural membrane materials under multistage cyclic loading, the deformation behavior, energy dissipation, and damage characteristics of four kinds of warp-knitted and woven polyvinyl chloride (PVC) membrane materials were analyzed using multistage cyclic loading experiments. The results show that, compared with the uniaxial tensile strength, the peak values of the cyclic loading and unloading of the four material samples are lower in the warp direction but higher in the fill (weft) direction. Under multistage cyclic loading, the loading and unloading moduli of the warp knitting membrane increase with the increase in fabric density. At the same fabric density, the loading modulus and the unloading modulus are smaller than those of the warp knitting material. The total absorbed strain energy, elastic strain energy, and dissipation energy of the fill samples are higher than those of the warp samples at a low load level but lower than those at a high load level. PVC membrane materials' use strength should be controlled below a 15% stress level under long-term external force loading. In the cyclic loading process, the four PVC membrane materials are viscoelastic-plastic, so it is reasonable to define the damage variable based on the accumulation of plastic deformation.

Ti3C2Tx@nonwoven Fabric Composite: Promising MXene-Coated Fabric for Wearable Piezoresistive Pressure Sensors.

Although Ti3C2Tx MXene/fabric composites have shown promise as flexible pressure sensors, the effects of MXene composition and structure on piezoresistive properties and the effects of the textile structure on sensitivity have not been systematically studied. Herein, impregnation at room temperature was used as a cost-effective and scalable method to prepare composite materials using different fabrics [plain-woven fabric, twill-woven fabric, weft plain-knitted fabric, jersey cross-tuck fabric, and nonwoven fabric (NWF)] and MXene nanosheets (Ti3C2Tx, Ti2CTx, Ti3CNTx, Mo2CTx, Nb2CTx, and Mo2TiC2Tx). The MXene nanosheets adhered to the fabric surface through hydrogen bonding, resulting in a conductive network structure. The Ti3C2Tx@NWF composite was found to be the optimal flexible pressure sensor, demonstrating high sensitivity (6.31 kPa-1), a wide sensing range (up to 150 kPa), fast response/recovery times (300 ms/260 ms), and excellent durability (2000 cycles). Furthermore, the sensor was successfully used to monitor full-scale human motion, including pulse, and a 4 × 4 pixel flexible sensor array was shown to accurately locate pressure and recognize the pressure magnitude. These findings provide a basis for the rational design of MXene/textile composites as wearable pressure sensors for medical diagnosis, human-computer interactions, and electronic skin applications.

Stretchable Supercapacitors: From Materials and Structures to Devices.

Stretchable supercapacitors have received widespread attention due to their potential applications in wearable electronics and health monitoring. Stretchable supercapacitors not only possess advantages such as high power density, long cycle life, safety, and low cost of conventional supercapacitors but also have excellent flexibility and stretchability, which make them well integrated with other wearable systems. In this review, various strategies to fabricate stretchable supercapacitors are focused. The preparation methods for stretchable electrodes/devices in the literature are carefully classified and analyzed. Three strategies for preparing stretchable electrodes/devices are summarized in detail-the design of elastic polymer substrates, stretchable electrode structures, and composite electrodes combined with elastic polymers and stretchable structures. Meanwhile, the interface problem of electrodes/devices in the stretching process is studied in depth. The research progress of multifunctional stretchable supercapacitors is also introduced. Finally, challenges and possible solutions that still need to be addressed in the future development of stretchable supercapacitors are highlighted and prospected. This review comprehensively discusses the latest research progress in the field of stretchable supercapacitors and systematically elucidates the electrochemical and mechanical properties of these devices, hoping to improve the roadmap for scientists and engineers to develop supercapacitors with high electrochemical performance and good stretchability.

Study of Compaction Properties and Permeability Prediction of Multilayered Quadriaxial Non-Crimp Fabric in Liquid Composite Molding Process.

A systematic experimental study was performed to detect the compaction and permeability properties of multilayered biaxial and quadriaxial preforms under vacuum pressure. Compression response on ply level showed that the degree of nesting between quadriaxial NCF was more pronounced and the nesting deformation mechanism was affected by the interaction with stitch yarns. Owing to the meso-channels in the fibrous structure and the nesting between layers, the in-plane permeability of quadriaxial NCF did not follow an inverse proportion relationship with the fiber volume fraction. To predict the in-plane permeability of multilayered quadriaxial NCFs, unit cell models at a high level of geometrical details were built, including local variations in yarn cross-sections and the nesting deformation between layers. Numerical methods were implemented, and the prediction results were in very good agreement with the experimental data. Besides, the major contributing parameters to the enhancement of the in-plane permeabilities were identified by investigating the correlation between permeability and structural parameters of quadriaxial NCF. The modeling methodology and the principles established can be applied to the design of the quadriaxial NCF fabrics, where the permeability enhancement was evidenced.

New surgical meshes with patterned nanofiber mats.

Abdominal wall hernia repair is one of the most common general surgeries nowadays. Surgical meshes used in hernia repair indeed improved the outcomes, but complications like chronic pain or hernia recurrence partly caused by mechanical mismatch cannot be ignored. This work designed six warp-knitted polypropylene (PP) meshes and found the properties of surgical meshes could be improved to better mimic the performances of human abdominal wall by designing meshes with appropriate textile structures. Poly-caprolactone was electrospun onto newly designed PP meshes and formed a thin layer of patterned nanofiber mat. The pattern of nanofiber mats was affected by the structure of meshes. Diverse nanofiber morphology (straight aligned, straight random or spiral random pattern) and fiber diameters (50-70 nm ultra-thin nanofibers or from 330 nm to 700 nm nanofibers) were observed in different regions of a single patterned nanofiber scaffold. The addition of electrospinning nanofibers enhanced cell adherence and proliferation as compared with naked PP meshes. Cell actin filaments spread along the nanofibers and formed a morphology exactly similar with the patterned mats on day 7. Furthermore, cells on thin and aligned patterned nanofibers showed much more elongation and better orientation than that of the spiral random fibers, suggesting that cell morphology can be altered by changing the patterns of scaffolds. This study helps us in further understanding the properties of hernia repair meshes with their textile structures and the biological interactions of cells with different substrates in order to develop new biomedical scaffolds with desired properties.

Preparation and in Vitro Evaluation of New Composite Mesh Functionalized with Cationic Antimicrobial Peptide.

Infection caused by bacteria in hernia repair site is a severe complication, and patients have to undergo a second surgery to remove the infected prosthesis. In this study, we developed a composite biological safe mesh with antibacterial activity. The composite mesh is composed of large pore polypropylene (PP) mesh, poly-caprolactone (PCL) and antimicrobial peptide (PEP-1), which we synthesized in our lab. Fourier transformed infrared (FTIR) spectroscopy was utilized to analyze the functional groups. The surface morphology, in vitro release characters, mechanical properties, antibacterial activities, and in vitro cytotoxicity of modified mesh were evaluated. Results showed that PEP-1 was loaded in fibers successfully and could diffuse from nanofibers to inhibit bacteria (E. coli) growth. However, the modified mesh did not show inhibition to S. aureus. The mechanical properties of fabricated mesh showed no difference with two commercial surgical meshes. What is more, modified mesh was proved to be nontoxic to human dermal fibroblasts, indicating that this method to fabricate meshes with antibacterial activity is feasible and provides a new strategy for the development of surgical meshes.

Fabrication and Characterization of Composite Meshes Loaded with Antimicrobial Peptides.

Biomaterials-centered infection or implant-associated infection plays critical roles in all areas of medicine with implantable devices. The widespread over use of antibiotics has caused severe bacterial resistance and even super bugs. Therefore, the development of anti-infection implantable devices with non-antibiotic-based new antimicrobial agents is indeed a priority for all of us. In this study, antimicrobial composite meshes were fabricated with broad-spectrum antimicrobial peptides (AMPs). Macroporous polypropylene meshes with poly-caprolactone electrospun nanosheets were utilized as a substrate to load AMPs and gellan gum presented as a media to gel with AMPs. Different amounts of AMPs were loaded onto gellan gum to determine the appropriate dose. The surface morphologies, Fourier-transform infrared spectroscopy spectra, in vitro release profiles, mechanical performances, in vitro antimicrobial properties, and cytocompatibility of composite scaffolds were evaluated. Results showed that AMPs were loaded into the meshes successfully, the in vitro release of AMPs in phosphate-buffered saline was prolonged, and less than 60% peptides were released in 10 days. The mechanical properties of composite meshes were also within the scope of several commercial surgical meshes. Composite meshes with the AMP loading amount of over 3 mg/cm2 showed inhibition against both Gram-negative and Gram-positive bacteria effectively, while they presented no toxicity to mammalian cells even at a loading amount of 10 mg/cm2. These results demonstrate a new simple and practicable method to offer antimicrobial properties to medical devices for hernia repair.

Characterization and Analysis of In-Plane Shear Behavior of Glass Warp-Knitted Non-Crimp Fabrics Based on Picture Frame Method.

Glass warp-knitted fabrics have been widely used as complex structural reinforcements in composites, such as wind turbine blades, boats, vehicles, etc. Understanding the mechanical behavior and formability of these textiles is very necessary for the simulation of forming processes before manufacturing. In this paper, the shear deformation mechanics of glass warp-knitted non-crimp fabrics (WKNCF) were experimentally investigated based on a picture frame testing apparatus equipped to a universal testing machine. Three commercially available fabrics of WKNCFs were tested for four cycles by the picture frame method. The aim was to characterize and compare the shear behavior of relatively high areal density fabrics during preform processing for composites. The energy normalization theory was used to obtain the normalized shear force from the testing machine data; then, the shear stress against the shear angle was fitted by cubic polynomial regression equations. The results achieved from the equations demonstrated that the in-plane shear rigidity modulus was associated with the shear angle. The effect of the shearing cycles and stitching pattern on shear resistance was also analyzed.

Experimental Study on Bi-Axial Mechanical Properties of Warp-knitted Meshes with and without Initial Notches.

Warp-knitted meshes have been widely used for structural reinforcement of rigid, semi-rigid, and flexible composite materials. In order to meet the performance requirements of different engineering applications, four typical warp-knitted meshes (rectangular, square, circular, and diamond) were designed and developed. The mechanical behaviors of these meshes under mono-axial and multi-axial tensile loads were compared. The influence of the initial notch length and orientation on the mechanical performance was also analyzed. The results showed that the biaxial tensile behavior of warp-knitted meshes tended to be more isotropic. The anisotropy level of the diamond warp-knitted mesh was the lowest (λ = 0.099), while the rectangular one was the highest (λ = 0.502). The notch on a significantly anisotropic mesh was propagated along the direction of larger modulus, while for a not remarkably anisotropic mesh, notch propagation was probably consistent with the initial notch orientation. The breaking strength of warp-knitted meshes with the same initial notch orientation decreased with the increase in notch length in both the wale and course directions. For warp-knitted meshes with the same initial notch length, the breaking strength in the wale direction was kept stable at different notch orientations, while that in the course direction decreased remarkably with notch orientation from 0° to 90°.

High-Performance Polyimide Filaments and Composites Improved by O2 Plasma Treatment.

Interface issues urgently need to be addressed in high-performance fiber reinforced composites. In this study, different periods of O2 plasma treatment are proposed to modify twist-free polyimide (PI) filaments to improve hydrophilicity and mechanical and interfacial properties. Feeding O2 produces chemically active particles to modify the filament surface via chemical reactions and physical etching. According to the X-ray photoelectron spectroscopy (XPS) results, the PI filaments exhibit an 87.16% increase in O/C atomic ratio and a 135.71% increase in the C⁻O functional group after 180 s O2 plasma treatment. The atomic force microscope (AFM) results show that the root mean square roughness (Rq) of the treated PI filaments increases by 105.34%, from 38.41 to 78.87 nm. Owing to the increased surface oxygenic functional groups and roughness after O2 plasma treatment, the contact angle between treated PI filaments and water reduces drastically from the pristine state of 105.08° to 56.15°. The O2 plasma treated PI filaments also demonstrate better mechanical properties than the pristine PI filaments. Moreover, after O2 plasma treatment, the adhesion between PI filaments and poly(amic acid) (PAA) is enhanced, and the tensile strength of the polyimide/poly(amic acid) (PI/PAA) self-reinforced composites increases from 136 to 234 MPa, even causing the failure mode of the composite changes from adhesive failure to partly cohesive failure.

Preparation and Evaluation of a Polyimide-Coated Ultrafine Gilt Molybdenum Wire and Its Knitted Mesh Used for Electromagnetic Reflectors.

In this work, polyimide (PI) was coated onto an ultrafine gilt molybdenum wire in order to protect the gilt surface and prepare an electrically stable wire mesh material which can be widely used in space. The surface of the PI-coated gilt molybdenum wires was characterized using FTIR, SEM, and EDS. Factors such as temperature stability of the PI coating, mechanical properties of the PI-coated gilt molybdenum wires, contact resistance stability, and electromagnetic microwave reflectivity of the their knitted meshes were also investigated. The results indicate that the PI coating conformed uniformly to the surface of the gilt molybdenum wires. The prepared PI coating exhibited excellent temperature stability in the -196 to 300 °C range and could efficiently protect the gilt surface and improve the stability of contact resistance, while the reflection of its wire meshes showed only a slight decrease of 1.4% with the PI coating thickness of 3 µm for electromagnetic microwaves in the S band.

Optic nerve regeneration in polyglycolic acid-chitosan conduits coated with recombinant L1-Fc.

Autografts have been extensively studied to facilitate optic nerve (ON) regeneration in animal experiments, but the clinical application of this approach to aid autoregeneration has not yet been attempted. This study aims to explore the guided regeneration by an artificial polyglycolic acid-chitosan conduit coated with recombinant L1-Fc. Consistent with previous studies; in vitro assay showed that both chitosan, a natural biomaterial, and the neural cell adhesion molecule L1-Fc enhanced neurite outgrowth. Rat optic nerve transection was used as an in vivo model. The implanted PGA-chitosan conduit was progressively degraded and absorbed, accompanied by significant axonal regeneration as revealed by immunohistochemistry, anterograde and retrograde tracing. The polyglycolic acid-chitosan conduit coated with L1-Fc showed more effective to promote axonal regeneration and remyelination. Taken together, our observations demonstrated that the L1-Fc coated PGA-chitosan conduits provided a compatible and supportive canal to guild the injured nerve regeneration and remyelination.

Ciliary neurotrophic factor-coated polylactic-polyglycolic acid chitosan nerve conduit promotes peripheral nerve regeneration in canine tibial nerve defect repair.

A variety of nerve conduits incorporated with chemical and biological factors have been developed to further stimulate nerve regeneration. Although most of the nerve guides in studies are basically limited to bridge a short gap of nerve defect in rat models, it is vital to evaluate effects of conduits on nerve regeneration over distance greater than 20 mm, or more clinically relevant nerve gap lengths in higher mammals. In this study, a poly(lactide-co-glycolide) (PLGA) nerve conduit, treated with pulsed plasma and coated with ciliary neurotrophic factor (CNTF) as well as chitosan, was used to repair 25-mm-long canine tibial nerve defects in eighteen cross-bred dogs. The canines were randomly divided into three groups (n = 6), a 25-mm segment of the tibial nerve was removed and replaced by a PLGA/chitosan-CNTF nerve conduit, PLGA/chitosan conduit and autologous nerve grafts were performed as the control. The results were evaluated by general observation, electromyogram testing, S-100 histological immunostaining, and image analysis at 3 months after operation. The histological results demonstrated that the PLGA/chitosan-CNTF conduits and PLGA/chitosan conduits were capable of leading the damaged axons through the lesioned area. Through the comparison of the three groups, the results in PLGA/chitosan-CNTF conduits group were better than that of PLGA/chitosan conduits group, while they were similar to autologous nerve grafts group. Therefore, CNTF-coated PLGA/chitosan nerve conduits could be an alternative artificial nerve conduit for nerve regeneration.

[Tissue engineered nerve based on plasma treatment and BMSCs].

OBJECTIVE: To evaluate the effect of the plasma treated PLGA nerve conduits seeded BMSCs on repairing SD rat sciatic nerve defects. METHODS: BMSCs were acquired from 30 newborn SD rats. After amplified and passaged for 3 times, PLGA nerve conduits were prepared and some of them were treated with plasma. A 1-cm-length sciatic nerve defect was made in 30 4-week-old SD rats, then they were randomly divided into 3 groups for three different nerve defects reconstruction methods (n = 10). In the experimental group, defect was repaired by plasma treatment and PGLA nerve conduits seeded with BMSCs; in the control group, by normal PLGA nerve conduits seeded with BMSCs; and in the autologous group, by autologous nerve. At 6 weeks after the surgery, the dynamic walking pattern was recorded and the sciatic function index (SFI) was calculated; the electrophysiological test was taken; the gastrocnemius wet weight recovery rate was calculated; and the image analysis of regenerated nerve was made. RESULTS: All rats survived after the surgery and lived to the end of the experiment. At 6 weeks after the surgery, the dynamic walking pattern of the experimental group and autologous group was better than that of the control group. The SFI value of the experimental, control and autologous groups was -51.02 +/- 6.54, -58.73 +/- 7.87 and 48.73 +/- 3.95, respectively, showing statistically significant differences among the experimental group, control group and autologous group (P < 0.05). The results of the motor nerve conduction velocity and wave amplitude showed that there were statistically significant differences between the experimental group and the control group (P < 0.05), and between the control group and the autologous group (P < 0.01); but no significant difference between the experimental group and autologous group (P > 0.05); The gastrocnemius wet weight recovery rate of the experimental, control and autologous groups was 56.13% +/- 4.27%, 43.14% +/- 6.52%, 59.47% +/- 3.85%, respectively; showing statistically significant differences among experimental group, control group and autologous group (P < 0.05). The density, diameter of regenerated nerve fiber as well as neural sheath thickness of the experimental group were all higher than those of the control group (P < 0.05) and lower than those of the autologous nerve group (P < 0.05); there was significant difference between the control group and the autologous group (P < 0.01). CONCLUSION: Plasma treated PLGA nerve conduits seeded with BMSCs can effectively repair sciatic nerve defects and provide a new strategy for the development of tissue engineered nerve to repair the peripheral nerve defects.