Natalia A. Demidenko

Currently, an urgent need in the field of wearable electronics is the development of flexible sensors that can be attached to the human body to monitor various physiological indicators and movements. In this work, we propose a method for forming an electrically conductive network of multi-walled carbon nanotubes (MWCNT) in a matrix of silicone elastomer to make stretchable sensors sensitive to mechanical strain. The electrical conductivity and sensitivity characteristics of the sensor were improved by using laser exposure, through the effect of forming strong carbon nanotube (CNT) networks. The initial electrical resistance of the sensors obtained using laser technology was ~3 kOhm (in the absence of deformation) at a low concentration of nanotubes of 3 wt% in composition. For comparison, in a similar manufacturing process, but without laser exposure, the active material had significantly higher values of electrical resistance, which was ~19 kOhm in this case. The laser-fabricated sensors have a high tensile sensitivity (gauge factor ~10), linearity of >0.97, a low hysteresis of 2.4%, tensile strength of 963 kPa, and a fast strain response of 1 ms. The low Young’s modulus values of ~47 kPa and the high electrical and sensitivity characteristics of the sensors made it possible to fabricate a smart gesture recognition sensor system based on them, with a recognition accuracy of ~94%. Data reading and visualization were performed using the developed electronic unit based on the ATXMEGA8E5-AU microcontroller and software. The obtained results open great prospects for the application of flexible CNT sensors in intelligent wearable devices (IWDs) for medical and industrial applications.

This article describes the manufacturing technology of biocompatible flexible strain-sensitive sensor based on Ecoflex silicone and multi-walled carbon nanotubes (MWCNT). The sensor demonstrates resistive behavior. Structural, electrical, and mechanical characteristics are compared. It is shown that laser radiation significantly reduces the resistance of the material. Through laser radiation, electrically conductive networks of MWCNT are formed in a silicone matrix. The developed sensor demonstrates highly sensitive characteristics: gauge factor at 100% elongation −4.9, gauge factor at 90° bending −0.9%/deg, stretchability up to 725%, tensile strength 0.7 MPa, modulus of elasticity at 100% 46 kPa, and the temperature coefficient of resistance in the range of 30–40 °C is −2 × 10⁻³. There is a linear sensor response (with 1 ms response time) with a low hysteresis of ≤3%. An electronic unit for reading and processing sensor signals based on the ATXMEGA8E5-AU microcontroller has been developed. The unit was set to operate the sensor in the range of electrical resistance 5–150 kOhm. The Bluetooth module made it possible to transfer the received data to a personal computer. Currently, in the field of wearable technologies and health monitoring, a vital need is the development of flexible sensors attached to the human body to track various indicators. By integrating the sensor with the joints of the human hand, effective movement sensing has been demonstrated.

Nowadays there is a great need for the development of flexible strain sensors that can register human body’s movements. In the field of wearable and smart electronics such sensors are actively being developed. Resistive-type flexible sensors are the easiest to manufacture. Their mechanism of sensitivity to deformations is based on a change in electrical resistance during deformations. In this work, we have developed the functional material for strain sensor with high tensile properties, strength and electrical conductivity. This material based on a matrix of silicone elastomer and a multi-walled carbon nanotubes (MCNTs) filler. The material showed a high elongation of 950 % with a tensile strength of 1.437 MPa. The manufacturing process included laser structuring of MCNTs to form an electrically conductive network. The linear gauge factor was 3.4, and the angular gauge factor was 0.26.

Currently, there is an interest in the development of flexible strain gauges that can be attached to human body for movements detection in postoperative period, during rehabilitation after injuries and strokes, etc. Such gauges usually consist of a polymer matrix and electrically conductive filler. In this work, manufacturing technology of strain-sensitive nanocomposite material consisting of biocompatible polymer (silicone) matrix and carbon nanotubes filler has been developed. Electrically conductive carbon nanotubes networks in non-conductive polymer matrix were obtained, high electrical conductivity of the material (~0.1 S/m) was achieved. Network architecture was built using pulsed ytterbium laser, operating at wavelength 1064 nm. Production of two types of strain gauge elements with strain gage coefficient 4-6 using technology is shown. Developed technology opens up broad prospects for production of various biomedical strain gauges.

Compared with traditional electronic materials (metals and semiconductors), electrically conductive biopolymers have improved compatibility with biological cells and human biological tissues. This allows creating new bioelectronic devices, for example, biosensors, drug delivery devices, 3D tissue-engineering matrix et al. A new laser method has been developed for the 3D manufacturing of electrically conductive nanocomposites with a given architecture. The architecture may be similar to the microelectronic component base (for example, the creation of microchannels between nanocomposite regions for designing transistors). A pulsed ytterbium fiber laser connected to a galvanometric scanner (laser wavelength - 1064 nm, pulse duration - 100 ns, frequency - 100 kHz, irradiation power up to 10 W) was used to form nanocomposites. By the galvanometric scanner, the focused laser beam moved along the trajectory (XYZ) specified in the software. As a result, the samples had the desired geometric 3D shape. Homogeneous dispersions of carbon nanotubes and biopolymers (albumin, collagen and chitosan amino sugar) were used as raw materials on a flexible substrate. The phase transition of the liquid dispersion of nanotubes into a solid was the main mechanism for the nanocomposites formation process. With focused laser irradiation, the temperature in the region of defects in carbon nanotubes increased, in contrast to other regions of nanotubes. As a result, the nanotubes were connected in an electrically conductive scaffold. Nanocomposites had high conductivity values of ~10 S/m, as well as high hardness of 300-500 MPa. The biocompatibility of nanocomposites has been proven in vitro и in vivo.

This paper presents a method for creating three-dimensional networks of carbon nanotubes by welding nanotubes under laser radiation. To carry out nanowelding, single-walled carbon nanotubes were deposited on a SiO 2 substrate, after which they were irradiated with an ytterbium laser. Structural parameters and hardness characteristics of the samples were studied. Such 3D networks can act as electrically conductive nanoframes in biomaterials.

The aim of this work is an in vivo study of the biocompatibility of samples of three-dimensional tissue-engineering structures for of muscle tissue regeneration. Three-dimensional tissue-engineering structures were formed by layer-by-layer deposition of dispersions of albumin, collagen, chitosan with carbon nanotubes using laser printing. Under the action of laser radiation, carbon nanotubes oriented into a conducting scaffold. During implantation of tissue-engineering constructions, no toxic effects were revealed to laboratory birds. Studies have shown that carbon nanotubes do not have a pathological effect on the morphology of living cells and tissues, also enhance the proliferation of fibroblasts and stimulate the growth of connective and muscle tissue.