A Stretchable Array of Electronic Receptors for Esophageal Swallowing Robot for Biomimetic Simulations of Bolus Transport

This paper presents the design, fabrication, calibration, and implementation of a novel stretchable array of capacitive sensors that mimics human receptors for an esophageal swallowing robot. The array is used to measure deformation of the esophageal conduit wall and the interaction between food bolus and the esophagus in the form of pressure and shear stress, which is a novel in vitro method of food bolus transport study. It is constructed from a thin sheet of copper-polyimide laminate via a cost effective fabrication process involving photolithography, wet etching, and laser engraving technique. Calibration is conducted individually on the pressure, shear, and strain sensor elements of the array. The pressure, shear, and strain sensors response exhibit an average hysteresis of 10.17%, 11.78%, and 26.37% caused by the soft silicon rubber encapsulation. Linear regression technique is used to determine the linear sensitivity transfer function for all the three sensors. The array is embedded beneath the surface of the esophageal conduit of the swallowing robot and a series of swallowing experiments are conducted. Three types of food bolus with a viscosity of 0.18, 0.62, and 1.55 Pa · s are prepared using a commercial food thickener. The swallowing robot generates a peristaltic wave of 60-mm wavefront length and 40-mm·s
^-1
wave speed to mimic the swallowing action seen in the human esophagus. Manometer measurements are taken alongside for validation. The pressure sensor records maximum pressures of 2.24, 3.17, and 7.74 kPa, respectively, for the three types of bolus during swallowing. By comparison, the maximum pressures recorded by the manometer are 1.68, 2.82, and 8.08 kPa. The shear sensor on the other hand records maximum shear values of -0.3, -0.35, and -0.37 kPa, respectively, for the three food bolus mixtures. This works prove that the novel stretchable array of capacitive sensors can be used to mimic mechanoreceptors for the esophageal swallowing robot, which significantly extends its capability to be used by food scientists as a platform for a new novel method of bolus transport study.