Flexible Pressure Sensors for Objective Assessment of Motor Disorders

Abstract

Monitoring body motion is relevant to motor control disorders as well as assessment of fine motor skills in child development. Furthermore, motion tracking is necessary for rehabilitation monitoring and injury prevention and benefits both sick and healthy individuals. Flexible pressure sensors based on resistors, capacitors, inductors, or transistors are reviewed in the context of healthcare measurements, ranging from physiological signals to body movement characteristics such as grip and gait. To demonstrate the use of flexible pressure sensors for motor assessment, a touch sensing glove that evaluates fine motor skills in autism research is developed. The results show that autistic children perform fewer taps per minute compared to typically developing children, with larger variations in tap durations. In a second example, a force and motion sensing glove is developed to assess spasticity, a neuromuscular disorder that causes muscle stiffness/resistance and jerky movement. Analyses of force versus velocity show movement-dependent muscle resistance in a patient with spasticity. Through these flexible sensor systems, the shift from subjective scores to objective measurement will promote better diagnosis and dramatically improve the accuracy in tracking patient response to therapy.patients doing certain movements, and then clinicians rank each patient's level according to qualitative descriptions in benchmark classification scales. [12,13] The subjective scores can be inconsistent between raters and do not capture finelevel changes in a patient's progress in response to therapy. Therefore, there is a critical need to tackle the issue of imprecise assessment of motor disorders.With recent advances in flexible sensors and innovations in tactile sensing, [14][15][16][17][18][19] we have new low-cost technologies that are prime to facilitate quantitative evaluation of motor control. This progress report presents current developments in wearable sensor systems applicable to motor disorders, so that consistent, objective metrics become available to accurately track whether a treatment effectively relieves symptoms. The wearable sensors are not limited to placement on patients but can also be worn by clinicians or caregivers to assist them in taking measurements during patient interactions. [20,21] The point-of-care sensor systems will allow frequent monitoring, which is highly desirable to offer a better understanding of the patient's short and long-term response to therapies, to tailor treatment and improve outcome and quality of life for patients.Other reviews [14][15][16][17][18][19] have already extensively covered the flexible materials and devices used in tracking vital signs and electronic skin applications. In light of that, this progress report focuses on the applications in monitoring motor skills, in particular to implement pressure sensor designs for wearable systems with diverse form factors, for instance, gloves, [20,22,23] epidermal tags tags, [24,25] and shoe insoles. [26,27] We will discuss the mechanis...

Soft Electronics for the Skin: From Health Monitors to Human–Machine Interfaces

“…[109] However, they still suffer from disadvantages in nonlinear sensitivity [105,131,132] and high drift over time, and are also sensitive to the thermal effect. [133] Cheng et al developed a flexible piezoresistive pressure sensor which operated at a voltage of 1.5 V with low energy consumption (<30 mW), ultralow limit of detection of 13 Pa within a short time (<17 ms), high sensitivity (>1.14 kPa −1 ), and high stability, enabling real-time monitoring of the BP of a human radial artery under both a normal condition and after physical exercise, as shown in Figure 4c. [108] This flexible pressure sensor was composed of a layer of ultrathin AuNWs-impregnated tissue paper sandwiched by an interdigitated electrode coated on PDMS and a blank PDMS support.…”

“…, where A is the overlapping area of the two parallel plates, ε 0 is the permittivity of a vacuum, ε r is the relative permittivity of the elastomeric dielectric materials between the parallel plates, and d is the separation between the parallel plates. The advantages of the piezocapacitive pressure sensors include low insensitivity to temperature and humidity change, [133] low-power consumption, [114,141] low detection limit, [111,112] and high sensitivity. [111,113] However, piezocapacitive pressure sensors have a relatively small linear dynamic range [142,143] and can be disturbed by electromagnetic interference and parasitically coupled to the surroundings.…”

“…[111,113] However, piezocapacitive pressure sensors have a relatively small linear dynamic range [142,143] and can be disturbed by electromagnetic interference and parasitically coupled to the surroundings. [133] Structuring the dielectric materials is an effective method to improve the compressibility of the dielectric layer, thereby directly increasing sensitivity. The pressure sensors can also be integrated into FETs to achieve signal amplification.…”

Organic Thin Film Transistors in Mechanical Sensors

“…This processing power also enables more efficient human‐machine interfaces such that researchers can collect, and make sense of, data sets on the human body at large scales. [ 162 ]…”

Artifacts Mitigation in Sensors for Spasticity Assessment

“…The glove only needs to fit the physician user, so that our tool can be readily applied to different patients. The instrumented glove record the force applied to move the spastic muscle F and the maneuver velocity v through flexible force-sensitive sensors [31][32][33][34] and an inertial motion unit (IMU), respectively. These two parameters are measured to determine the power P exerted to move the spastic muscle (P ¼ F * v), as a third parameter in spasticity evaluation.…”