Andreas Schoth

Separation of blood cells and plasma in microchannel bend structures

Biological applications of micro assay devices require easy implementable on-chip microfluidics for separation of plasma or serum from blood. This is achieved by a new blood separation technique based on a microchannel bend structure developed within the collaborative Micro-Tele-BioChip (μTBC) project. Different prototype polymer chips have been manufactured with an UV-LIGA process and hot embossing technology. The separation mechanisms have been identified and the separation efficiency of these chips has been determined by experimental measurements using human blood samples. Results show different separation efficiencies for cells and plasma up to 100 % depending on microchannel geometry, hematocrit, and feed velocity. This novel technique leads to an alternative blood separation method as compared to existing micro separation technologies.

Fabrication and testing of novel blood separation devices based on microchannel bend structures

Most clinical chemistry tests are performed on cell-free serum or plasma. Therefore micro assay devices for blood tests require integrated on-chip microfluidics for separation of plasma or serum from blood. Polymers are ideally suited for these applications due to their material properties and their applicability for high volume production. These requirements are achieved by a new on-chip blood separation technique based on microchannel bend structures and a rapid processing technology for micro assay devices using injection molding or hot embossing. Different prototype polymer chips with channel dimensions down to 20 μm and aspect ratios of 4 have been fabricated by injection molding and hot embossing. The inserts for the molding tools were fabricated by an UV-LIGA technology. The separation efficiency of these chips has been tested with human blood samples. The results show different separation efficiencies up to 100 % for blood cells and plasma depending on microchannel geometry as well as cell concentration. As compared to present microfluidic devices for the separation of blood cells like filters, membranes or filtration by diffusion the microchannel bend is an integrated on-chip blood separation method. It combines the advantages of rapid separation times and a simple geometry that leads to cost-effective high volume production using injection molding.

Hybrid tooling: A review of process chains for tooling microfabrication within 4M

Abstract The current paper is based on the information gathered by the “Processing of Polymers” Division (Task 4.2 “Hybrid Tooling”) and “Processing of Metals” Division (Task 7.2 “Tooling”) within 4M Network activities. The aim of the task involves a systematic analysis of the partners’ expertise in different technologies for processing tooling inserts for further replication in polymers. Firstly, the 4M partners current capabilities in individual tooling processes is briefly presented, and also the expected capabilities for year 2010 are analysed for each of the following processes: micromilling, micro-wire electrodischarge machining (μWEDM), micro sinking electrodischarge machining (μSEDM), laser micromachining, electrochemical micromilling (μECM), and electrochemical milling with ultrashort pulses (ECF). Later the concept of ‘hybrid tooling’ as different process chains for tooling fabrication is introduced. Several examples of ‘hybrid tooling’ within 4M partners are presented. Considered materials are nickel for electroforming, stainless steel for ECF, and tool steel for the other processes. The paper results provide a global comparison between the previously mentioned processes, the current limitations of these technologies concerning feature sizes, surface finish, aspect ratios, etc. have been identified. The main conclusion drawn is the imperative requirement to combine individual processes (‘hybrid tooling’) to produce 3D free-form microshapes for tooling purposes.

Low-cost deformable mirror for laser focussing

This paper presents a new concept of low degree-of-freedom deformable mirrors. The application of the mirror is the focusing of a laser beam, featuring a variable focal length. The deformation shape, which is in this case a circular parabolic and an elliptical parabolic respectively, is achieved by a local variation of the mirrors thickness. The paper explains the analytical treating of the mirrors thickness distribution as well as an iterative approximation procedure using FEM simulation. The mirrors were fabricated using hot embossing and injection molding technology. The molds required are made from steel whereas the structuring is done by conventional milling. The fabricated mirrors were coated with a reflective gold layer. For deformation measurements a functional demonstrator consisting of the coated mirror, assembly plates and an electromagnetic actuator was produced. The deformation of the mirror was measured using a 3D coordinate measuring machine. The optical function was characterized by a CCD laser measurement setup. Deviation between the measured and the optimal deformation function was sufficiently small. The spot size of the focused laser beam was up to 470 μm whereas the focal length could be varied in a range of 250 mm to 1000 mm. Due to the use of polymeric material, the long time behavior in respect of creep was researched using FEM simulations as well as endurance tests.

Rapid processing of replication tools with high-aspect-ratio microchannels for microfluidics

Microfluidic devices are mainly used within the life sciences or chemical analysis. Polymers are ideally suited for these applications due to their physical and chemical properties. In this report, we describe a rapid low cost processing technology to fabricate mold inserts for microfluidic structures with high aspect ratio, as well as excellent surface quality and high hardness. These tools are used for hot embossing and as mold inserts for injection molding. They enable cost effective structuring of technical polymers like polycarbonate or cycloolefin copolymer. The main advantage of our approach is the availability of the geometry and the specific target material right from the start of the evaluation process of microfluidic devices. The process described enables a rapid prototyping for the development and evaluation of different microfluidic devices, and they can be used for a low-cost mass production of micro structured parts.

A new approach for focusing deformable mirrors fabricated in polymer technology

Nowadays, adaptive optics are already being used in a broad range of applications. The growing market of applications demands for low-cost adaptive optics with high optical quality. Adaptive optics like deformable mirrors, fabricated using micro structure technologies, currently cost about 60 USD. In this work, a circular adaptive mirror device for laser focussing was developed and fabricated in polymer materials. The focal length can be varied within the range from 0.1 to 1 m. Besides the cost-efficient fabrication of the mirror device this concept also features only one actuator for focussing. The driving voltage of the actuator lies in the range of 0 to 12 V, depending on the focal length of the deformable mirror

Improved and simple sealing of microfluidic structures

An innovative way for covering and sealing microfluidic devices is proposed. After giving an overview to a variety of commonly used techniques, the problem of tightness (to fluids and gases) is discussed, and a simple yet effective solution, based on a lid that has an optimized pre-curved shape, is introduced. The curvature significantly enhances uniformity of pressure distribution; evidence is presented by computer simulation as well as through fluidic measurements, showing water tightness up to nearly one bar. The method used for finding the optimized shape is briefly presented. Although the method proposed is usable with virtually any material and size, examples are given in materials and scales typical for microfluidics. The technique is fully compatible to mass production techniques for polymer materials; a water tight example for an injection molded lid and base, held together by a clamping mechanism that easily can be replaced by laser welded points, is presented.

4M Network of Excellence, Progress Report 2009

This paper gives a brief overview of the activities of the 4M Network of Excellence during the last nine months of its funded period. The 4M Divisions summarise their activity and outline their pla ...