Finite element analysis of a self-propelled capsule robot moving in the small intestine

Dynamics of the vibro-impact capsule robot with a von Mises truss

Functionalised nonlinear structures employing structural instabilities for rapid response shape-shifting are emerging technologies with a wide range of potential applications. The von Mises truss is a widely employed model for such functionalised nonlinear structures; however, few studies have delved into its functionality when integrated with a complex dynamical system. This paper investigates its efficacy on enhancing the progression speed of a vibration-driven robot, known as the vibro-impact capsule robot, which is a piecewise-smooth dynamical system having abundant coexisting attractors. Bifurcation analysis of the capsule robot integrated with a von Mises truss is conducted for this purpose. Our numerical studies focus on the influence of the frequency and amplitude of the robot's driving force on its progression. Specifically, we compare the periodic responses of both the capsule robots with and without the von Mises truss, utilising the numerical continuation techniques for piecewise-smooth dynamical systems. Our studies confirm the advantage of using the von Mises truss when the driving force of the robot is significantly small. Additionally, we identify an optimal operational regime on the amplitude-frequency control plane, where the maximum robot speed is achieved for a given amount of power consumption. The numerical studies presented in this work provide a promising indication of the advantages offered by the von Mises truss for vibration-driven robots. This research underscores the significant potential of functionalised nonlinear structures to enhance the efficiency of small-scale robots operating under power limitations.

Resistance model of an active capsule endoscope in a peristaltic intestine

In the past studies, the resistance of magnetically controlled capsules running through the small intestine has been modeled assuming that the small intestine was a circular tube with a constant diameter. Peristalsis is an important character of the human gastrointestinal system, and it would result in some changes in the diameter of the intestine, meaning that the existing resistance models would no longer be applicable. In this paper, based on the assumption that intestinal peristalsis is actually a sinusoidal wave, a resistance model of the capsule running in the peristaltic intestine is established, and then it is validated experimentally. The model provides a realistic foundation for the optimization and control of the magnetically controlled endoscopy.

The motion of micro-swimmers over a cavity in a micro-channel

This article combines the lattice Boltzmann method (LBM) with the squirmer model to investigate the motion of micro-swimmers in a channel-cavity system. The study analyses various influential factors, including the value of the squirmer-type factor (β), the swimming Reynolds number (Rep), the size of the cavity, initial position and particle size on the movement of micro-swimmers within the channel-cavity system. We simultaneously studied three types of squirmer models, Puller (β > 0), Pusher (β < 0), and Neutral (β = 0) swimmers. The findings reveal that the motion of micro-swimmers is determined by the value of β and Rep, which can be classified into six distinct motion modes. For Puller and Pusher, when the β value is constant, an increase in Rep will lead to transition in the motion mode. Moreover, the appropriate depth of cavity within the channel-cavity system plays a crucial role in capturing and separating Neutral swimmers. This study, for the first time, explores the effect of complex channel-cavity systems on the behaviour of micro-swimmers and highlights their separation and capture ability. These findings offer novel insights for the design and enhancement of micro-channel structures in achieving efficient separation and capture of micro-swimmers.