RoSE Enhancement for In Vitro Simulations of Human Swallowing
Dysphagia or trouble swallowing is a prevalent medical condition among the elderly, individuals with esophageal strictures, and persons on long-term pill medication, with patient age, different pathologies, and solid dosage product characteristics (e.g., size, shape, and composition) contributing to the cause. All the in-vitro studies aiming to improve the therapeutic interventions in dysphagia lack the technologies to associate the effects of the dynamic forces involved in the esophageal peristalsis. The RoSE (Robotic Soft Esophagus) addresses this gap by combining the fields of material sciences, actuation, and control technologies. The RoSE is an open loop, pneumatically controlled, compliant, and continuous soft robotic actuator designed to mimic peristalsis. Many attributes of the esophagus, such as conduit length, diameter, peristalsis velocity, and conduit wall activation, are replicated in RoSE. Still, it lacks embedded sensors mimicking the mechanoreceptors in an esophageal lumen. Exploring the opportunities in improving the RoSE as an analytical tool for in-vitro swallowing studies has been the focus of this research. The components of this research were the following: 1) Design and characterize soft stretchable carbon black sensors and their modeling for sensor-actuator calibration and control, 2) Developing fluid-structure interaction simulation model to learn the parameter variations in bolus transit which are unknown due to lack of sensors, 3) Develop clinically relevant protocols and conduct in-vitro swallow studies for stent migration and solid dosage medication transit analysis. Many of the existing sensors technologies suffer the drawbacks such as robot occlusion, interference, or difficulties in surface compatibility. Designing soft stretchable sensing devices compatible with the soft robot and designing robust controllers are challenging problems in and of themselves. Carbon-based nanomaterials embedded in elastomers are cost-effective choices in designing stretchable sensor arrays. Piezo-resistive sensors have more hysteresis and produce nonlinear responses but have better gauge factors and sensitivity. The 4 loop sensor with a mass fraction of 11.11 (%wt) (carbon black in the elastomer), having a gauge factor of 2.35, and hysteresis of 22% at the standard operating point in RoSE is selected. Before the final selection, three distinct concentrations for different sensor architectures are fabricated and tested for the cyclic loading, strain rate, and stretch direction tests. The single-layer flat RoSE (fRoSE) and 6- layer RoSE versions of sensor-embedded actuators were developed for calibration and control. Data sets from image processing and articulography were used to calibrate these versions of RoSE. The sensor-actuator system transfer characteristics computed from fRoSE sensor data demonstrated the sensor contribution to system nonlinearities. This study used recurrent neural network-based algorithms to predict temporal nonlinearities such as sensor drift. A feedforward compensated, gain scheduled linear controller is designed on the piecewise linearised transfer characteristics of the fRoSE. The controller responses for set-point tracking with feedforward compensation attains the desired steady-state error design constraints. This contributes a general framework for the future initiatives in developing full body closed loop deformation control of RoSE or any soft robotic actuators. The fluid pressure variations, fluid velocity variations, and stress variations for different bolus consistencies under different trajectories in RoSE are unknown due to the lack of sensors. For addressing this, a multi-physics finite element-based (FEM) simulation model was built and validated against data sets from image processing and manometry experiments. The fluid velocity, pressure, and dynamic viscosity in the bolus during propagation through the conduit are conspicuously affected by the trajectory parameters and the contracting forces. The RoSE is an in-vitro tool for food texture analysis, but it has found use in swallow studies of esophageal stenting and solid dosage form transit. In both stent migration and pill swallow studies, clinically meaningful test protocols for RoSE in the supine position are developed and implemented. In tests comparing two stents of differing stiffness, the stent with the lowest stiffness reported in-situ migration and up to a maximum of 47 mm relative displacement under different trajectories. The study discovered that the direction of stent migration is also affected by bolus viscosity. The stent migration is explained with the dynamic models developed in previous investigations. The effects of internal and environmental factors on RoSE pill transit are also investigated. The pill transit time is affected by coating, surface polish, size, and pill volume density. In RoSE, the pill transit is found to be dependent on the peristalsis trajectory velocity as well as the bolus properties such as viscosity and volume. The uncoated pills had longer transit times, whereas the encapsulated pills were faster. The pill transit variations are explained with the help of finite element-based simulation models developed in this research.
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