Ulrich Gengenbach

Array tomography: characterizing FAC-sorted populations of zebrafish immune cells by their 3D ultrastructure.

For 3D reconstructions of whole immune cells from zebrafish, isolated from adult animals by FAC‐sorting we employed array tomography on hundreds of serial sections deposited on silicon wafers. Image stacks were either recorded manually or automatically with the newly released ZEISS Atlas 5 Array Tomography platform on a Zeiss FEGSEM. To characterize different populations of immune cells, organelle inventories were created by segmenting individual cells. In addition, arrays were used for quantification of cell populations with respect to the various cell types they contained. The detection of immunological synapses in cocultures of cell populations from thymus or WKM with cancer cells helped to identify the cytotoxic nature of these cells. Our results demonstrate the practicality and benefit of AT for high‐throughput ultrastructural imaging of substantial volumes.

Design of freeform optics for an ophthalmological application

Optical freeform surfaces are gaining importance in different optical applications. A huge demand arises e.g. in the fields of automotive and medical engineering. Innovative systems often need high-quality and high-volume optics. Injectionmoulded polymer optics represents a cost-efficient solution. However, it has to be ensured that the tight requirements with respect to the system’s performance are met by the replicated freeform optics. To reach this goal, it is not sufficient to only characterise the manufactured optics by peak-to-valley or rms data describing a deviation from the nominal surface. Instead, optical performance of the manufactured freeform optics has to be analysed and compared with the performance of the nominal surface. This can be done by integrating the measured surface data of the manufactured freeform optics into the optical simulation model. The feedback of the measured surface data into the model allows for a simulation of the optical performance of the optical subsystem containing the real freeform optics manufactured. Hence, conclusions can be drawn as to whether the specifications with respect to e.g. imaging quality are met by the real manufactured optics. This approach will be presented using an Alvarez-Humphrey optics as an example of a tuneable optics of an ophthalmological application. The focus of this article will be on design for manufacturing the freeform optics, the integration of the measured surface data into the optical simulation model, simulation of the optical performance, and analysis in comparison to the nominal surface.

Low duty cycle inter-implant communication of the Artificial Accommodation System

The Artificial Accommodation System is an autonomous mechatronic implant aiming at restoring accommodation after cataract treatment or in the case of presbyopia. The employed sensor concept requires a continuous wireless data exchange between the two systems implanted in the left and in the right eye, respectively. In this paper, we present three strategies for establishing this inter-implant communication link and evaluate them with regard to their lowest achievable duty cycle. We also describe a two-way synchronisation method for efficient computation of the relative timer offset between both systems. The method accounts for relative clock drift, which significantly increases accuracy when using clocks with large relative drift. The proposed communication strategies are currently being implemented in the industrial, scientific and medical (ISM) band at 433 MHz using off-the-shelf transceivers and microcontrollers. First measurements of synchronisation accuracy and relative clock drift predict duty cycles in the range of 0.6%–1.0 %.

Robust Design of an Optical Micromachine for an Ophthalmic Application

This article describes an approach to the robust design of an optical micromachine consisting of a freeform optics, an amplification linkage, and an actuator. The robust design approach consists of monolithic integration principles to minimize assembly efforts and of an optimization of the functional components with respect to robustness against remaining assembly and manufacturing tolerances. The design approach presented involves the determination of the relevant tolerances arising from the domains manufacturing, assembly, and operation of the micromachine followed by a sensitivity analysis with the objective of identifying the worst offender. Subsequent to the above-described steps, an optimization of the functional design of the freeform optics with respect to a compensation of the effects of the tolerances is performed. The result leads to a robust design of the freeform optics and hence ensures a defined and optimal minimum performance of the micromachine in the presence of tolerances caused by the manufacturing processes and the operation of the micromachine. The micromachine under discussion is the tunable optics of an ophthalmic implant, an artificial accommodation system recently realized as a demonstration model at a scale of 2:1. The artificial accommodation system will be developed to replace the human crystalline lens in the case of a cataract.

Optical performance simulation of free-form optics for an eye implant based on a measurement data enhanced model

This paper describes the application of a modeling approach for precise optical performance prediction of free-form optics-based subsystems on a demonstration model of an eye implant. The simulation model is enhanced by surface data measured on the free-form lens parts. The manufacturing of the free-form lens parts is realized by two different manufacturing processes: ultraprecision diamond machining and microinjection molding. Evaluation of both processes is conducted by a simulation of the optical performance on the basis of their surface measurement comparisons with the nominal geometry. The simulation results indicate that improvements from the process optimization of microinjection molding were obtained for the best manufacturing accuracy.

Comparison of Different Algorithms for Robust Detection of Pupils in Real-Time Eye-Tracking Experiments.

This paper contains a comparative investigation on algorithms to find a pupil within an image of a video eye-tracker and to extract the parameters of an ellipse describing the perimeter of the pupil within the 2D image. In future these algorithms shall be used to investigate on the accommodation behaviour of subjects during every-day life activities and to estimate the power consumption of novel, active eye implants like the Artificial Accommodation System.

Low-Cost Head Phantom for the Evaluation and Optimization of Rf-Links in Ophthalmic Implants

An inexpensive head phantom for the evaluation and optimization of radiofrequency communication links in ophthalmic implants such as the Artificial Accommodation System is presented. The eye balls of the phantom are gela- tine-based and have a solid consistency to hold the test im- plant in its place. A thin plastic head shell serves as a con- tainer for the homogeneous head tissue-equivalent. All de- ployed tissue-simulating materials are based on a sugar-salt- solution whose properties can be adjusted to approximate the permittivity and conductivity values of the human head/eye at the used frequency band. Additionally, the head phantom comprises a glass insert that can optionally be introduced to simulate the effect of nasal cavities and sinuses on the signal propagation and antenna characteristics.

Robust Design of a Lens System of Variable Refraction Power with Respect to the Assembly Process

The aim of this paper is to show that a compensation of manufacturing tolerances by means of the functional design is reasonable. The approach is discussed exemplarily in the application of a lens system of variable refraction power considering the assembly tolerances. This approach is based on the steps sensitivity analysis, tolerance analysis, and design optimisation and will result in a robust design with respect to the assembly process.

Microgripper construction kit

A large number of microgrippers has been developed in industry and academia. Although the importance of hybrid integration techniques and hence the demand for assembly tools grows continuously a large part of these developments has not yet been used in industrial production. The first grippers developed for microassembly were basically vacuum grippers and downscaled tweezers. Due to increasingly complex assembly tasks more and more functionality such as sensing or additional functions such as adhesive dispensing has been integrated into gripper systems over the last years. Most of these gripper systems are incompatible since there exists no standard interface to the assembly machine and no standard for the internal modules and interfaces. Thus these tools are not easily interchangeable between assembly machines and not easily adaptable to assembly tasks. In order to alleviate this situation a construction kit for modular microgrippers is being developed. It is composed of modules with well defined interfaces that can be combined to build task specific grippers. An abstract model of a microgripper is proposed as a tool to structure the development of the construction kit. The modular concept is illustrated with prototypes.

On the road to large volumes in LM and SEM: New tools for Array Tomography

1 Cryo EM, Centre for Advanced Materials, Universitat Heidelberg, Heidelberg, Germany 2 HEiKA, Heidelberg Karlsruhe Research Partnership, Heidelberg, Karlsruhe, Germany 3 Institute for Applied Computer Science, Karlsruhe Institute of Technology, Karlsruhe, Germany 4 Carl Zeiss Microscopy GmbH, Oberkochen, Germany 5 RMC Boeckeler, Tucson, Arizona, USA 6 Cryo EM, CellNetworks, BioQuant, Universitatsklinikum Heidelberg, Heidelberg, Germany