Designing an Optical Bendloss Sensor for Clinical ForcMeasurement

For many clinicians, their effectiveness is dependent on the force they manually apply to their patients. However, current care strategies lack quantitative feedback making it difficult to provide consistent care over time and among several clinicians. We have developed a disposable force-sensing glove that provides real-time quantitative feedback in the clinical setting. To minimally affect a clinician's function, obtain maximal signal to noise in a medical environment, and maintain patient safety, a fiber optic sensor has been developed for this application. A disposable nitrile glove with embedded fiber optic force sensor has been developed and initially tested for clinical efficacy. The sensor's design is based on the bendloss properties of optical fiber whereby the attenuation of light through a fiber is related to the bending of that fiber through a series of corrugated teeth. The sensor is fabricated in two parts, sandwiching the fiber between alternating teeth. When force is applied across the sensor, the teeth engage the fiber and bend it along an elastic, repeating profile. the specific light attenuation is dependent on the amount of bending that the fiber experiences between the teeth and can be used to measure the load applied to the sensor. Fabricated at $10×8×1$ mm, the sensor achieves an appropriate clinical thickness and minimally affects normal clinical thickness and minimally affects normal clinical function. It provides real-time force feedback up to 90 lbs with 0.1 lb resolution. The sensitivity of the sensor follows an exponential relationship with strong agreement to theoretical calculations. Because the calibration curve is non-linear, the sensor is most sensitive at low forces allowing detection of extremely delicate forces such as the pulse from the carotid artery. Each glove is fabricated with a single sensor embedded in the fingertip or palm and a magnetic connector couples the glove with a non-disposable wrist cuff. The wrist cuff houses the power supply, light source, and photodetectors. The fibers are nonpermanently coupled to their respective sources and detectors completing the optical path from source, through the fiber and sensor, to the detector. The light intensity is then transmitted to the display module which calibrates and displays the force graphically in real-time. The display module records, summarizes, and stores the data from each clinical session allowing clinicians to collaborate on treatment protocols and provide consistent care over time. Initial results from current clinical trials with physical therapists at the University of Minnesota have indicated improved recovery time after surgery. Twenty-four ACL reconstruction patients have been monitored post-operation for five weeks and the experimental group treated with the glove has demonstrated significantly faster recovery to normal range of motion than the control group. It has been suggested that the quantification of patient evaluation allowed the clinicians to recommend adjustments to at-home stretching regimens, contributing to faster healing times. Similar clinical studies are planned for chiropractic care and other physical therapy procedures. This fiberoptic force sensing glove represents a new biomedical tool which can impact patient evaluation and care by providing clinicians with a quantified sense of touch.