Smart cellulose fibers coated with carbon nanotube networks

Smart multi-walled carbon nanotube (MWCNT)-coated cellulose fibers with a unique sensing ability were manufactured by a simple dip coating process. The formation of electrically-conducting MWCNT networks on cellulose mono- and multi-filament fiber surfaces was confirmed by electrical resistance measurements and visualized by scanning electron microscopy. The interaction between MWCNT networks and cellulose fiber was investigated by Raman spectroscopy. The piezoresistivity of these fibers for strain sensing was investigated. The MWCNT-coated cellulose fibers exhibited a unique linear strain-dependent electrical resistance change up to 18% strain, with good reversibility and repeatability. In addition, the sensing behavior of these fibers to volatile molecules (including vapors of methanol, ethanol, acetone, chloroform and tetrahydrofuran) was investigated. The results revealed a rapid response, high sensitivity and good reproducibility for these chemical vapors. Besides, they showed good selectivity to different vapors. It is suggested that the intrinsic physical and chemical features of cellulose fiber, well-formed MWCNT networks and favorable MWCNT-cellulose interaction caused the unique and excellent sensing ability of the MWCNT-coated cellulose fibers, which have the potential to be used as smart materials

Textile materials

In this specialised publication, the reader will find research results and real engineering developments in the field of modern technical textiles. Modern technical textile materials, ranging from ordinary reinforcing fabrics in the construction and production of modern composite materials to specialised textile materials in the composition of electronics, sensors and other intelligent devices, play an important role in many areas of human technical activity. The use of specialized textiles, for example, in medicine makes it possible to achieve important results in diagnostics, prosthetics, surgical practice and the practice of using specialized fabrics at the health recovery stage. The use of reinforcing fabrics in construction can significantly improve the mechanical properties of concrete and various plaster mixtures, which increases the reliability and durability of various structures and buildings in general. In mechanical engineering, the use of composite materials reinforced with special textiles can simultaneously reduce weight and improve the mechanical properties of machine parts. Fabric- reinforced composites occupy a significant place in the automotive industry, aerospace engineering, and shipbuilding. Here, the mechanical reliability and thermal resistance of the body material of the product, along with its low weight, are very relevant. The presented edition will be useful and interesting for engineers and researchers whose activities are related to the design, production and application of various technical textile materials

Fabrication of ultra-high working range strain sensor using carboxyl CNTs coated electrospun TPU assisted with dopamine

Fiber-based strain sensors have attracted widespread concern of researchers due to large specific surface area, good stretchability and remarkable flexibility. In this work, a stretchable strain sensor with ultra-high working range was developed by using electrospun thermal plastic polyurethane (TPU) nanofibrous membrane coated with carboxyl multi-walled carbon nanotubes (CNTs). In order to obtain an even distribution and an improved fastness of carboxyl CNTs on TPU fibers, dopamine (DA) was employed to modify the TPU nanofibrous membrane (labelled DATPU) via a fast ultrasonication-assisted deposition approach. DATPU/CNTs exhibited an ultra-high working range of about 710% with high gauge factor up to 1200. Furthermore, DATPU/CNTs were found to have stronger washing fastness than TPU/CNTs owing to the introduction of DA onto the surface of TPU nanofibers. DATPU/CNTs also maintained good electrical conductivity during 15,000 cycles of stretching-releasing test. Finally, a prototype of strain sensor based on DATPU/CNTs membrane demonstrated remarkable flexibility and sensitivity to human body motions such as elbow bending, finger bending and swallowing

Aerosol mediated localized dissolution to enhance the electrical behavior and sensitivity of piezoresistive nanofiber-based flexible sensors

This work proposes the use of solvents in the form of small size droplets to improve the connections among nanofibers (NFs) in electrospun composite nanofibers with carbon nanotube multiwalled (MWCNT) by improving the electrical and piezoresistive behavior of such electrically conductive polymer composites. The here proposed Aerosol Mediated Localized Dissolution (AMLD) process has been shown to be effective in improving the 3D microporous NF mat by inducing local dissolution that is effective in improving the connections among fibers within the mat. The AMLD process is demonstrated here for polyethylene oxide (PEO) / MWCNTs composite nanofibers, showing that the electrical conductivity is particularly improved in those samples with low content of MWCNTs, even below the original percolation threshold. The improved electrical conductivity is coupled with exceptional sensitivity of the flex sensor for low MWCNTs contents, this is particularly due to the ability of the AMLD process to preserve the high surface area of the 3D mat by inducing better fiber-to-fiber contacts in few regions only. In addition, this work demonstrates the effectiveness of applying an electrical potential difference during the AMLD process to improve the alignment of MWCNTs within the 3D microporous NF mat. The combination of voltage and AMLD allow to obtain a gauge factor as high as 571.9 with a MWCNTs loading of 1 wt%

Dynamic Facial Prosthetics for Sufferers of Facial Paralysis

BackgroundThis paper discusses the various methods and the materialsfor the fabrication of active artificial facial muscles. Theprimary use for these will be the reanimation of paralysedor atrophied muscles in sufferers of non-recoverableunilateral facial paralysis.MethodThe prosthetic solution described in this paper is based onsensing muscle motion of the contralateral healthy musclesand replicating that motion across a patient’s paralysed sideof the face, via solid state and thin film actuators. Thedevelopment of this facial prosthetic device focused onrecreating a varying intensity smile, with emphasis ontiming, displacement and the appearance of the wrinklesand folds that commonly appear around the nose and eyesduring the expression.An animatronic face was constructed with actuations beingmade to a silicone representation musculature, usingmultiple shape-memory alloy cascades. Alongside theartificial muscle physical prototype, a facial expressionrecognition software system was constructed. This formsthe basis of an automated calibration and reconfigurationsystem for the artificial muscles following implantation, soas to suit the implantee’s unique physiognomy.ResultsAn animatronic model face with silicone musculature wasdesigned and built to evaluate the performance of ShapeMemory Alloy artificial muscles, their power controlcircuitry and software control systems. A dual facial motionsensing system was designed to allow real time control overmodel – a piezoresistive flex sensor to measure physicalmotion, and a computer vision system to evaluate real toartificial muscle performance.Analysis of various facial expressions in real subjects wasmade, which give useful data upon which to base thesystems parameter limits.ConclusionThe system performed well, and the various strengths andshortcomings of the materials and methods are reviewedand considered for the next research phase, when newpolymer based artificial muscles are constructed andevaluated.Key WordsArtificial Muscles, facial prosthetics, stroke rehabilitation,facial paralysis, computer vision, automated facialrecognition

Design and Optimization of Piezoresistive PEO/PEDOT:PSS Electrospun Nanofibers for Wearable Flex Sensors

Flexible strain sensors are fundamental devices for application in human body monitoring in areas ranging from health care to soft robotics. Stretchable piezoelectric strain sensors received an ever-increasing interest to design novel, robust and low-cost sensing units for these sensors, with intrinsically conductive polymers (ICPs) as leading materials. We investigated a sensitive element based on crosslinked electrospun nanofibers (NFs) directly collected and thermal treated on a flexible and biocompatible substrate of polydimethylsiloxane (PDMS). The nanostructured active layer based on a blend of poly(ethylene oxide) (PEO) and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) as the ICP was optimized, especially in terms of the thermal treatment that promotes electrical conductivity through crosslinking of PEO and PSS, preserving the nanostructuration and optimizing the coupling between the sensitive layer and the substrate. We demonstrate that excellent properties can be obtained thanks to the nanostructured active materials. We analyzed the piezoresistive response of the sensor in both compression and traction modes, obtaining an increase in the electrical resistance up to 90%. The Gauge Factors (GFs) reflected the extraordinary piezoresistive behavior observed: 45.84 in traction and 208.55 in compression mode, which is much higher than the results presented in the literature for non-nanostructurated PEDOT

A self-sensing and self-heating planar braided composite for smart civil infrastructures reinforcement

Allocating different capabilities to structural elements simultaneously is still challenging. In this study, a field-applicable multifunctional planar braided composite with the abilities of reinforcing, self-sensing and self-heating was developed for the first time. In this route, three commercial fabrics were used, including cotton, cotton/polyamide, and polyester. The fabrics were first chemically treated and then coated with a carbon nanomaterial-based polymeric conductive paste using screen printing with different concentrations and layers. The samples were then covered and sealed with a thermoplastic polyurethane-based polymer to avoid environmental factors effects. Smart planar composites (SPC) were also used as reinforcement for cementitious specimens. The electrical conductivity and joule heating capability of the samples were also evaluated. The microstructure of the SPCs was investigated using various tests. The mechanical and self-sensing performances of the cementitious composite reinforced with different SPCs were assessed using different load patterns. The results showed a heating rate of 0.44 ˚C/s, a joule heating power of 0.7 W/˚C, and a maximum temperature of 44 ˚C which proved the proper heating capability of the cementitious composites reinforced with SPCs. The great correlation between electrical resistivity changes and strain values indicated the high potential of the composite in strain sensing for different applications. The SPCs also improved the post-crack behaviour of the specimen and its flexural strength and failure strain by approximately 50% and 118%, respectively. The outcomes of this study draw a bright horizon in multifunctional braided composite development with different applications in civil infrastructures, which is a crucial step for intelligent cities' advances.This work was partly financed by the Institute for Sustainability and Innovation in Engineering Structures (ISISE) and the R&D Unit of the Centre for Textile Science and Technology (2C2T) founded by the Portuguese Foundation for Science and technology (FCT) under the reference “UIDP/00264/2020”. The first author also acknowledges the support provided by the FCT/PhD individual fellowship with reference of “2021.07596.BD”