Deformable Array of Strain and Tactile Sensors for a Biomimetic Oesophageal Swallowing Robot

Abstract

This research aims to expand the functionality of a previously developed biomimetic soft-bodied oesophageal swallowing robot by designing, fabricating, and integrating a stretchable array of pressure, shear stress and strain sensors. The built-in sensing capability provides an avenue for investigating interactions between food bolus and the wall of the oesophagus, which is not available through current clinical investigation techniques. The stretchable multimodal sensor is designed using SolidWorks 3D modelling software. Using a copper-polyimide laminate as the base material, an in-plane horseshoe meandering technique is combined with parallel plate capacitive sensor construction to produce a unique sensor design. A series of feasibility studies is conducted using finite element analysis to predict the fatigue performance of the sensor structures under strain loading. A combination of low-cost and well established fabrication techniques involving photolithography, wet etching, laser engraving, sheet metal forming, and moulding are used in manufacturing of the sensor. The sensor parts and assembly are subjected to a series of fatigue tests and characterisation procedures to validate the fatigue performance and to determine the characteristics of the sensor under different loading and environmental conditions. The pressure, shear, and strain sensors yield a best-fit straight line sensitivity of 0.087 fF.kPa−1, 1.275 fF.kPa−1, and -18.19 fF.%−1 respectively under maximum loading of 70 kPa, ± 8 kPa, and 10 % at 24 °C. The same stretchable sensor is manufactured in the form of a two dimensional array to be embedded inside the esophageal swallowing robot. Ex situ calibrations are performed on individual sensors prior to installation. Swallowing experiments are conducted using three laboratory-prepared food boluses with viscosity of 0.18, 0.62, and 1.55 Pa.s. Concurrent manometry measurements are performed alongside the embedded sensor recording for validation. Peristaltic wave of 60 mm wavefront length and 40 mm.s−1 is generated in the swallowing robot to simulate swallowing process. The embedded strain sensor records a wavefront length of 58.6 mm and wave speed of 39 mm.s−1. For each of the three bolus types, a peak pressure of 2.24, 3.17, and 7.74 kPa, and a peak shear of −0.30, −0.35, and −0.37 kPa are recorded by the embedded pressure and shear sensors.