Rs Roel Pieters

Cellular forces and matrix assembly coordinate fibrous tissue repair

Planar in vitro models have been invaluable tools to identify the mechanical basis of wound closure. Although these models may recapitulate closure dynamics of epithelial cell sheets, they fail to capture how a wounded fibrous tissue rebuilds its 3D architecture. Here we develop a 3D biomimetic model for soft tissue repair and demonstrate that fibroblasts ensconced in a collagen matrix rapidly close microsurgically induced defects within 24 h. Traction force microscopy and time-lapse imaging reveal that closure of gaps begins with contractility-mediated whole-tissue deformations. Subsequently, tangentially migrating fibroblasts along the wound edge tow and assemble a progressively thickening fibronectin template inside the gap that provide the substrate for cells to complete closure. Unlike previously reported mechanisms based on lamellipodial protrusions and purse-string contraction, our data reveal a mode of stromal closure in which coordination of tissue-scale deformations, matrix assembly and cell migration act together to restore 3D tissue architecture.

Magnetoelectric micromachines with wirelessly controlled navigation and functionality

The use of a single energy source for both manipulating micromachines and triggering their functionalities will result in highly integrated devices and simplify the design of the controlling platform. Here, we demonstrate this concept employing magnetoelectric Janus particle-based micromachines, which are fabricated by coating SiO2 microspheres with a CoFe2O4–BaTiO3 bilayer composite. While the inner magnetic CoFe2O4 layer enables the micromachines to be maneuvered using low magnitude rotating magnetic fields, the magnetoelectric bilayer composite provides the ability to remotely generate electric charges upon the application of a time-varying magnetic field. To demonstrate the capabilities of these micromachines, noble metals such as Au, Ag and Pt are magnetoelectrochemically reduced from their corresponding precursor salts and form nanoparticles on the surface of the micromachines. Magnetoelectric micromachines are promising devices for their use as metal scavengers, cell stimulators and electric field-assisted drug delivery agents.

RodBot: A rolling microrobot for micromanipulation

We introduce the modelling and control of a rolling microrobot. The microrobot is capable of manipulating micro-objects through the use of a magnetic visual control system. This system consists of a rod-shaped microrobot, a magnetic actuation system and a visual control system. Motion of the rolling microrobot on a supporting surface is induced by a rotating magnetic field. As the robot is submerged in a liquid this motion creates a rising flow in front, a sinking flow behind, and a vortex above the robot, thus enabling non-contact transportation of micro-objects. Besides this fluid-vortex approach, the microrobot is also able to manipulate micro-objects via a pushing strategy. We present the design and modelling of the 50×60×300 μm micro-agent, the visual control system, and an experimental analysis of the micromanipulation and control methods.

Automated capsulorhexis based on a hybrid magnetic-mechanical actuation system

This paper presents a hybrid magnetic-mechanical manipulation system for automated capsulorhexis utilizing a flexible catheter with a sharp edge magnetic tip. Vision based closed loop control is implemented to guide the tip on a circular path in the anterior eye segment. A continuous motion with high repeatability is achieved. The system shows the first catheter-based application of the electromagnetic manipulation system, OctoMag, for fast and safe ophthalmic surgery that potentially reduces the risk of complications and improves precision.

Real-Time Center Detection of an OLED Structure

The research presented in this paper focuses on real-time image processing for visual servoing, i.e. the positioning of a x-y table by using a camera only instead of encoders. A camera image stream plus real-time image processing determines the position in the next iteration of the table controller. With a frame rate of 1000 fps, a maximum processing time of only 1 millisecond is allowed for each image of 80x80 pixels. This visual servoing task is performed on an OLED (Organic Light Emitting Diode) substrate that can be found in displays, with a typical size of 100 by 200 μm. The presented algorithm detects the center of an OLED well with sub-pixel accuracy (1 pixel equals 4 μm, sub-pixel accuracy reliable up to ±1 μm) and a computation time less than 1 millisecond.

Direct motion planning for vision-based control

This paper presents direct methods for vision-based control for the application of industrial inkjet printing. In this, visual control is designed with a direct coupling between camera measurements and joint motion. Traditional visual servoing commonly has a slow visual update rate and needs an additional local joint controller to guarantee stability. By only using the product as reference and sampling with a high update rate, direct visual measurements are sufficient for controlled positioning. The proposed method is simpler and more reliable than standard motor encoders, despite the tight real-time constraints. This direct visual control method is experimentally verified with a 2D planar motion stage for micrometer positioning. To achieve accurate and fast motion, a balance is found between frame rate and image size. With a frame rate of 1600 fps and an image size of 160 × 100 pixels we show the effectiveness of the approach.

Feed forward visual servoing for object exploration

A new visual servoing method is proposed which uses position based visual servoing (PBVS) in combination with an additional image based control layer on the target pose to maintain fixation on an object. The proposed method (denoted feed forward PBVS) does not require trajectory generation but instead uses via-points to explore the object. It exploits the advantages of PBVS without the disadvantages of image based visual servoing (IBVS) as occurs in hybrid approaches. The proposed method is experimentally validated with a redundant 7-DOF manipulator. Comparison with existing visual servoing methods (PBVS and one partitioned approach) shows the effectiveness of the method.

Non-Contact Manipulation for Automated Protein Crystal Harvesting Using a Rolling Microrobot

Abstract In this work, a visual control system for magnetically-driven, automated protein crystal harvesting is proposed. The system consists of a rod-shaped microrobot, a magnetic actuation system and a visual control system. The rolling motion of the microrobot on a surface is induced by a rotating magnetic field. As the robot is submerged in a low Reynolds number liquid this motion creates a vortex above the robot which enables the non-contact transportation of protein crystals towards an extraction point. We present the micro-agent, the actuation system and the visual control system to achieve this automated procedure.

Demo: An embedded vision system for high frame rate visual servoing

The frame rate of commercial off-the-shelf industrial cameras is breaking the threshold of 1000 frames-per-second, the sample rate required in high performance motion control systems. On the one hand, it enables computer vision as a cost-effective feedback source; On the other hand, it imposes multiple challenges on the vision processing system. The authors have designed and implemented an FPGA-based embedded vision system in support of high frame rate visual servoing applications. The vision system will be demonstrated together with a mechanical system for vision based inkjet printing. This demonstration shows that, with off-the-shelf components, a robust, hard realtime, low delay embedded vision system is feasible for industrial applications. The research aspect of the experiment has been published in previous papers of the authors. This demonstration paper emphasises on the practical issues for the implementation of such system, and the lessons learned from this practice.

High performance visual servoing for controlled µm-positioning

The research presented in this paper focuses on high performance visual servoing for controlled positioning on micrometer scale. Visual servoing means that the positioning of a x-y table is performed with a camera instead of encoders and one camera image and image processing should determine the position in the next iteration. With a frame rate of 1000 [fps], a maximum processing time of 1 millisecond is allowed for each image (132 × 45 pixels). The visual servoing task is performed on an OLED substrate, which can be found in displays, with a typical size of 80 by 220 µm. The repetitive pattern of the OLED substrate itself is used as an encoder and thus closing the control loop. We present the design choices made for the image processing algorithms and the experimental setup as well as their limitations.