Steven Dirven

Soft Actuator Mimicking Human Esophageal Peristalsis for a Swallowing Robot

Provision of modified foods and drinks is one of the approaches for dysphagia management, which is based on the assumption that food with proper texture and rheological properties will allow dysphagia patients to swallow safely and maintain adequate nutrition. However, lack of information about the in vivo swallowing process and its interaction with food flow has obstructed the effective management of dysphagia. In the esophageal swallowing stage, masticated food is transported through the esophagus to the stomach by a peristaltic mechanism, which is generated by sequential contraction and relaxation of esophageal muscles. Inspired by this behavior, a soft actuator is proposed to provide a nonrisk environment aiming to facilitate investigations of the most effective properties of food for the management of the swallowing disorders. The wave-like motion is first specified according to the in vivo measurement of human esophageal peristalsis. Finite-element analysis simulations are carried out to aid the structure design before prototype manufacture. Constructed by casting silicon rubber in a three-dimensional (3-D) printed customized mold, the novel actuator has soft structure resembling its human counterpart, which has a flexible muscular structure. Multiple layers of inflatable chambers are embedded and distributed along the axis of a food passage regularly, which locates at the center of the actuator. The actuator is capable of generating a peristaltic wave and pushing a bolus along the passage. The closure of the tube and the velocity of the propagation wave are going to be adjusted to achieve the trajectories recorded experimentally, by regulating the compressed air pressure pumped into chambers actively.

Design and Characterization of a Peristaltic Actuator Inspired by Esophageal Swallowing

The specification and design of a novel peristaltic actuator is communicated. The actuation manifests as a continuous, distributed, and compliant peristaltic actuation. The occlusive nature of force distribution on the transport conduit results in materials being transported in front of a wave which has features of geometry and wave tail seal pressure. The behavior of these aspects profoundly affects the transport process. The device, of silicone rubber construction, has no internal skeletal structure and is pneumatically actuated which allows for continuous and compliant transport. The device is characterized by the synergy of geometrical and occlusive pressure measurements in response to actuation. This is performed for the “dry swallow” case (with no bolus) for single peak, single inflection waves. Techniques typical of medical investigation were exploited. Wave geometry was captured by articulography, complemented by wave seal pressure investigation by manometry. This paper describes the inspiration, specification, and experimental techniques used to develop and characterize the behavior of the biologically inspired, peristaltic, robotic device for assertion pressures up to 71.5 kPa. It is found that the device is capable of producing wave amplitudes and seal pressures of a similar magnitude (complete occlusion with >15-kPa seal) to the human esophagus which confirms achievement of the fundamental peristaltic parameters.

Biomimetic Investigation of Intrabolus Pressure Signatures by a Peristaltic Swallowing Robot

The relationships among bolus formulation, engineering rheometric quantities, and peristaltic transport effects are examined in this paper. Investigation of a series of synthetic bolus materials and swallowing strategies is conducted using a novel peristaltic swallowing robot inspired by esophageal swallowing, which manifests as a benchtop rheological instrument. To determine the validity of biomimetic swallowing, manometry, a clinical technique for capturing swallowing pressure profiles is used to establish congruence between the robotic findings and those of a clinical nature. To determine the contribution of the bolus and swallowing strategy to the intraluminal pressure signature (ILPS), three parameters were varied: peristaltic wave velocity (20, 30, 40 mm s-1), wavefront length (40, 50, and 60 mm) and starch thickener (Nutulis, Nutricia) concentration (25, 50, 75, 100, and 150 g L-1) were investigated. Wave velocity and starch-based bolus formulation concentration were found to exhibit the most profound changes in the intrabolus pressure signatures. The highest bolus tail pressure gradient of 0.33 kPa mm-1 was achieved with a 150 g L-1 bolus formulation being transported at 40 mm s-1 with a wavefront length of 60 mm. In each dimension, the relationship between the parameters and features of the manometric pressure signature are found to be nonlinear owing to the shear-thinning, non-Newtonian nature of the model bolus fluid. The robotic ILPSs are synonymous with those of a clinical nature, suggesting that the swallowing robot has merit as a novel, biologically inspired, bolus investigation tool external to the human body.

Sinusoidal Peristaltic Waves in Soft Actuator for Mimicry of Esophageal Swallowing

In order to understand fluid transport throughout esophageal swallowing in man, a biologically inspired soft-robotic peristaltic actuator has been designed and manufactured to perform biomimetic swallowing. To achieve congruence with current mathematical modeling techniques for esophageal peristalsis, this paper examines the capability of the device (empirical) towards achieving sinusoidal transport waves with variations of clinically significant parameters such as amplitude and wavelength. The performance of the device to fit the commanded trajectory, by minimization of mean squared error, is tested over the range of wavefront length 30 ≤ λ/2 ≤ 60 mm and amplitude 6-8 mm in a two-dimensional capability analysis. It is found that the device is capable of achieving propagation of families of wave shapes with less than 5% full scale mean error, which improves for increasing wavefront length and reducing amplitude. The aim for the device in the future is to inspire a novel rheometric technique in the physical domain which characterizes fluid formulations based on intrabolus pressure signatures. This analysis expresses the trajectory generation technique and performance of the novel device to produce continuous peristaltic waves towards biomimetic swallowing.

Biologically-inspired swallowing robot for investigation of texture modified foods

Textural and rheological characteristics of foods are known to profoundly affect the swallowing process. Food technologists continue to exploit this notion in the management of symptomatic swallowing disorders (dysphagia) where novel foods are designed to elicit more reliable transport characteristics. Currently, little is understood about the relationship between food bolus formulation and its flow-induced interactions with the swallowing tract. Experimentation of a medical nature in this field is extremely challenging, and may put patients at risk. In the rheological domain the deformation fields are dissimilar to that of the biological system. In response to these limitations, quantitative assessment of bolus transport by a novel rheometric testing device is proposed. This paper describes the inspiration for a biologically-inspired robotic swallowing device to be applied to address these issues. This will allow for an improved understanding of swallowing mechanics and food design in the engineering, medical, and food technology fields.

Large-Deformation Model of a Soft-Bodied Esophageal Actuator Driven by Air Pressure

To study the effect of food flow rheology on the human esophageal swallowing process, a biologically inspired actuator prototype has been developed. The actuator is made of silicone rubber where smooth and continuous peristaltic motion is generated by inflating air chambers distributed within its body. The soft material gives the actuator intrinsic compliance and infinite degrees of freedom in motion. Thus, it is challenging to model the behavior online by current methods. In order to investigate the large-scale deformation of the soft-bodied actuator in response to the air chamber pressures, a geometrically simplified two-dimensional (2-D) model composed of separated beam-shaped elements is proposed. It considers the mechanical properties of the material, the sophisticated geometry of the actuator as it deforms, and the distributed pressure behavior. Empirical data from the actuator prototype (captured by articulography) and the simulated results are compared to investigate the accuracy of the model. The differences of deformations between the experimental results and the theoretical model are analyzed.

Medically-inspired approaches for the analysis of soft-robotic motion control

Soft-robotic structures and their materials are typically chosen according to a biological example. Medical imaging has been used to obtain 3D models of biological structures to create moulds for production of artificial, soft robotic counterparts. However, it is not enough to simply copy the geometry of these organisms; robots must be able to be modeled, and controlled, such that they can perform meaningful tasks. This involves investigating the robots capability after it has been manufactured. The similarities between the biological and artificial robotic materials allow us to use methods from medical imaging in soft robotics. This paper proposes the use of medical imaging and alternative medical investigation methods for the static and dynamic characterization of soft robots and involves two soft-robotic case studies: a peristaltic pump (swallowing robot), and a peristaltic table. Articulography and manometry are shown to be useful techniques for investigation of the peristaltic pumping robot, and visual 3D scanning is demonstrated for the peristaltic table. Alternative medical investigation methods such as magnetic resonance imaging, computed tomography, and ultrasound are considered as other possibilities that require further investigation.

A Systematic Design Strategy for Antagonistic Joints Actuated by Artificial Muscles

Characterization, modeling, and control of pneumatic artificial muscles is typically demonstrated in an antagonistic architecture. There are many conflicting design constraints when designing these systems, resulting in many different styles of testing apparatus. A novel, systematic design methodology is proposed to improve these architectural constraints and describe the envelope of possible system outputs in terms of displacement and torque/force. It is founded upon a mathematical expression of actuator-model convolution. The proposed systematic antagonistic design by convolution (SADC) method involves three steps. First, model the workspace capability of each fluidic muscle. Second, devise the physical layout of the antagonistic apparatus by convolution, which investigates the structure for output workspace dexterity. Finally, establish trajectories and control, which is left to the application engineer. This method reduces the focus on the actuator capability, and instead represents a general method to approach system-level specification and design. The new SADC methodology facilitates design for a larger symmetric force capability. It is demonstrated for two cases, a symmetric and an asymmetric antagonistic system. It contributes a new pathway to explore optimization of antagonistic workspace symmetry at a system level and aids the engineer in visualizing architectural tradeoffs. It is independent of the applications control methodology and can be modified to examine alternative cost functions that require optimization.

A Stretchable Multimodal Sensor for Soft Robotic Applications

This paper presents the design, fabrication, and characterization of a multimodal sensor with integrated stretchable meandered interconnects for uniaxial strain, pressure, and uniaxial shear stress measurements. It is designed based on a capacitive sensing principle for embedded deformable sensing applications. A photolithographic process is used along with laser machining and sheet metal forming technique to pattern sensor elements together with stretchable grid-based interconnects on a thin sheet of copper polyimide laminate as a base material in a single process. The structure is embedded in a soft stretchable Ecoflex and PDMS silicon rubber encapsulation. The strain, pressure, and shear stress sensors are characterized up to 9%, 25 kPa, and ±11 kPa of maximum loading, respectively. The strain sensor exhibits an almost linear response to stretching with an average sensitivity of −28.9 fF%−1. The pressure sensor, however, shows a nonlinear and significant hysteresis characteristic due to nonlinear and viscoelastic property of the silicon rubber encapsulation. An average best-fit straight line sensitivity of 30.9 fFkPa−1 was recorded. The sensitivity of shear stress sensor is found to be 8.1 fFkPa−1. The three sensing elements also demonstrate a good cross-sensitivity performance of 3.1% on average. This paper proves that a common flexible printed circuit board (PCB) base material could be transformed into stretchable circuits with integrated multimodal sensor using established PCB fabrication technique, laser machining, and sheet metal forming method.

Design and Fabrication of a Soft Actuator for a Swallowing Robot

Textured food is provided to dysphagia populations in clinical practice for assessment and management of swallowing disorders. A considerable amount of measurements showed that the textural properties of food can affect the performance of human swallow significantly. However, the selection of food for a specific subject is difficult, due to the complexity of the biological structures and the potential risks of in vivo testing. For the purpose of providing a safe environment for food flow study, a novel soft actuator capable of producing peristalsis movement was proposed. During the esophageal swallowing, which is the last stage of human swallow, food is transported through the muscular tube by peristalsis mechanism. The motion pattern is generated by the coordinated contractions of circular muscles of the esophagus. Inspired by human esophagus and the biological process, the actuator was designed to have a completely soft body without any hard components. Discrete chambers are embedded inside the body regularly and a cylindrical food passage locates at the center of the actuator. Finite element analysis (FEA) was used to determine the structure parameters of the actuator. The soft body was fabricated by casting silicon material in a custom mold. Preliminary experiments have been performed to characterize the actuator.