Formation of a strain sensor prototype under the action of laser radiation in layers of biocomposite nanomaterial

Abstract

Objective. In medical practice, it is necessary to control movements of various parts of the body: limbs, joints, chest, as well as edema, swelling, deformation of muscle tissue in postoperative therapy, etc. For this purpose, traditional strain sensors based on metal and semiconductor materials are unsuitable, since they have very low relative deformation (≤0.2%) and low linear sensitivity to deformation (S~100). Also, both types of sensors are difficult to bend and, therefore, they restrict the movement of biological object. For medical applications, strain sensor must have a wide range of strain (≥10%) and bending (±60deg). In this regard, we investigated a prototype strain sensor (tensoresistor), based on bionanomaterial layers, containing bovine serum albumin (BSA - matrix) [1] and single-walled carbon nanotubes (SWCNT - filler) [1]. Materials and methods. An aqueous dispersion of 15 wt% BSA/0.1 wt% SWCNT was screen printed onto flexible polyethylene terephthalate substrates. The layers had thicknesses in the range d ~ 0.2-5 microns. After drying the layers with laser radiation (LR, wavelength ~970 nm), they were shaped like a meander with a stripe width of 2 mm, a distance between stripes of 2 mm, and a total strip length of 30 mm. Subsequently, choosing the power and laser mode (pulsed, continuous), the meander was processed by LR. This made it possible to obtain layers with different parameters and properties of deformation, which served as a prototype of the deformation sensor. A special setup made it possible to control the following layer parameters during deformation: resistance R, bending angle theta, number of cycles n, measurement time, etc. One measurement cycle corresponded to a change within the range theta = ± 150deg. Results. Depending on laser radiation treatment mode, resistance of layers could either increase or decrease relative to the control samples that were not exposed to LR. Typical dependences of resistance R on bending angle theta were similar for all layers: at = ± 30deg, the R( theta) curves were approximately linear dependences (with an error of ≤ 10%); outside this range, the dependencies become nonlinear. Using the minimum bending radius (~2 mm) and d ~ 1 μm, we have obtained an estimate of the sensitivity to linear deformation S ~ 200. The slope of the R(theta) curve, i.e. S(theta) = (1/R0)dR/dtheta is considered to be the sensitivity to deformation, where R0 is the sensor resistance at theta = 0. It was found that with an increase in the number n, the values R and S(theta) increase, and the hysteresis on R(theta) decreases. For the prototype strain sensor, the best values are obtained in the range S(theta) ~1,0÷1,5%/deg. Conclusion. In previous, as in present work, we could change the resistivity of bionanomaterial depending on the mode (pulsed, continuous) and the power of laser radiation [1]. This allows to adjust the parameters of the strain sensor to the desired values. Investigated layers of BSA/SWCNT bionanomaterial as strain sensors are of particular interest for medical practice, since they can be realized by applying an aqueous dispersion of nanomaterials to human skin. Such strain sensors will be in demand for monitoring movements (hands, blinking) and detecting signs of pathology (dysphagia, respiratory diseases, angina pectoris, etc.).

Keywords: strain sensor, tensoresistor, layers of bionanomaterials, bovine serum albumin, single walled carbon nanotubes


Acknowledgements: This study was supported by the Ministry of Science and Higher Education of the Russian Federation No. 075-03-2020-216 from 27.12.2019.


References
1. Ichkitidze L.P., Glukhova O.E., Savostyanov G.V., Yu. Gerasimenko A.Yu., Podgaetsky V.M., Selishchev S.V. Proceedings of SPIE - The International Society for Optical Engineering, 2018, 106853Q, doi: 10.1117/12.2306812

Speaker

Levan Ichkitidze
Institute of Biomedical Systems of National Research University of Electronic Technology “MIET”, Institute for Bionic Technologies and Engineering of I.M. Sechenov First Moscow State Medical University
Russia

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