Alperen Acemoglu

Effects of Geometric Parameters on Swimming of Micro Organisms with Single Helical Flagellum in Circular Channels

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.

Laser Incision Depth Control in Robot-Assisted Soft Tissue Microsurgery

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 ±100μm accuracy, which proves the feasibility of this approach. The proposed technology has the potential to facilitate the surgeon’s control over laser incisions.

Characterization and Modeling of Micro Swimmers With Helical Tails and Cylindrical Heads Inside Circular Channels

Micro swimming robots offer many advantages in biomedical applications, such as delivering potent drugs to specific locations in targeted tissues and organs with limited side effects, conducting surgical operations with minimal damage to healthy tissues, treatment of clogged arteries, and collecting biological samples for diagnostic purposes. Reliable navigation techniques for micro swimmers need to be developed to improve the localization of robots inside the human body in future biomedical applications. In order to estimate the dynamic trajectory of magnetically propelled micro swimmers in channels, that mimic blood vessels and other conduits, fluid-micro robot interaction and the effect of the channel wall must be understood well. In this study, swimming of one-link robots with helical tails is modeled with Stokes equations and solved numerically with the finite element method. Forces acting on the robot are set to zero to enforce the force-free swimming and obtain forward, lateral and angular velocities that satisfy the constraints. Effects of the number of helical waves, wave amplitude, relative size of the cylindrical head of micro swimmer and the radial position on angular and linear velocity vectors of micro swimmer are presented.Copyright

Towards a Magnetically-Actuated Laser Scanner for Endoscopic Microsurgeries

This article presents the design and assembly of a novel magnetically actuated endoscopic laser scanner device. The device is designed to perform 2D position control and high speed scanning of a fiber-based laser for operation in narrow workspaces. The device includes laser focusing optics to allow non-contact incisions and tablet-based control interface for intuitive teleoperation. The performance of the proof-of-concept device is analysed through controllability and the usability studies. The computer-controlled high-speed scanning demonstrates repeatable results with 21 um precision and a stable response up to 48 Hz. Teleoperation user trials, were performed for trajectory-following tasks with 12 subjects, show an accuracy of 39 um. The innovative design of the device can be applied to both surgical and diagnostic (imaging) applications in endoscopic systems.

Magnetic laser scanner for endoscopic microsurgery

Scanning lasers increase the quality of the laser microsurgery enabling fast tissue ablation with less thermal damage. However, the possibility to perform scanning laser microsurgery in confined workspaces is restricted by the large size of currently available actuators, which are typically located outside the patient and require direct line-of-sight to the microsurgical area. Here, a magnetic scanner tool is designed to allow endoscopic scanning laser microsurgery. The tool consists of two miniature electromagnetic coil pairs and permanent magnets attached to a flexible optical fiber. The actuation mechanism is based on the interaction between the electromagnetic field and the permanent magnets. Controlled and high-speed laser scanning is achieved by bending of the optical fiber with magnetic torque. Results demonstrate the achievement of a 3×3 mm2 scanning range within the laser spot is controlled with 35μm precision. The system is also capable of automatically executing high-speed laser scanning operations over customized trajectories with a root-mean-squared-error (RMSE) in the order of 75μm. Furthermore, it can be teleoperated in real-time using any appropriate user interface device. This new technology enables laser scanning in narrow and difficult to reach workspaces, promising to bring the benefits of scanning laser microsurgery to laparoscopic or even flexible endoscopic procedures. In addition, the same technology can be potentially used for optical fiber based imaging, enabling for example the creation of new family of scanning endoscopic OCT or hyperspectral probes.