We present a computational fluid dynamics (CFD) model for the swimming of micro organisms with a single helical flagellum in circular channels. The CFD model is developed to obtain numerical solutions of Stokes equations in three dimensions, validated with experiments reported in literature, and used to analyze the effects of geometric parameters, such as the helical radius, wavelength, radii of the channel and the tail and the tail length on forward and lateral swimming velocities, rotation rates, and the efficiency of the swimmer. Optimal shapes for the speed and the power efficiency are reported. Effects of Brownian motion and electrostatic interactions are excluded to emphasize the role of hydrodynamic forces on lateral velocities and rotations on the trajectory of swimmers. For thin flagella, as the channel radius decreases, forward velocity and the power efficiency of the swimmer decreases as well; however, for thick flagella, there is an optimal radius of the channel that maximizes the velocity and the efficiency depending on other geometric parameters. Lateral motion of the swimmer is suppressed as the channel is constricted below a critical radius, for which the magnitude of the lateral velocity reaches a maximum. Results contribute significantly to the understanding of the swimming of bacteria in micro channels and capillary tubes.

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State-of-the-art surgical laser systems achieve high quality tissue ablations with minimal thermal damage to the tissue by providing high-speed laser scanning. However, current technology is not applicable to difficult-to-reach anatomical sites for endoscopic surgery. In these cases, flexible laser fibers are used, but the resulting ablation quality is limited. Therefore, there is a need to improve flexible laser surgery systems. This paper proposes a solution to this issue based on a compact laser scanner and a focusing module designed to be placed at the distal end of a flexible endoscopic system. The device uses magnetic actuation to bend a laser fiber, thus allowing precise 2D position control and high-speed scanning of a high power surgical laser. The design, implementation and control of such a system are described in this paper, with special focus on its dynamic modeling and controller design to provide real-time control and fast automated execution of surgeon-defined trajectories. Validation experiments performed with different trajectories and scanning frequencies attest the performance of the system, which demonstrates trajectory tracing with 90 µm (1.4 mrad) accuracy for scanning frequencies up to 15 Hz. This is a significant result that promises to bring the benefits of free-beam laser scanning systems to endoscopic microsurgeries.

This paper presents the concept of a technology for the automation of laser incisions on soft tissue, especially for application in Transoral Laser Microsurgery (TLM) interventions. The technology aims at automatically controlling laser incisions based on high-level commands from the surgeon, i.e. desired incision shape, length and depth. It is based on a recently developed robotic laser microsurgery platform, which offers the controlled motion of the laser beam on the surgical site. A feed-forward controller provides (i) commands to the robotic laser aiming system and (ii) regulates the parameters of the laser source to achieve the desired results. The controller for the incision depth is extracted from experimental data. The required energy density and the number of passes are calculated to reach the targeted depth. Experimental results demonstrate that targeted depths can be achieved with [Formula: see text]m accuracy, which proves the feasibility of this approach. The proposed technology has the potential to facilitate the surgeon’s control over laser incisions.

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