[show abstract][hide abstract] ABSTRACT: This work describes the simulation of the operation of an impedance sensor that has been developed at the authors’ institute. The sensor measures the conductivity of aqueous droplets in segmented flow and the cell content of such droplets. The sensor consists of two electrodes attached to the outside of a glass capillary. The finite element model of the impedance of the material between these electrodes shows the suitability of the sensor to measure changes in conductivity of aqueous droplets being pumped through the capillary. Until now electrical measurements of droplets in digital microfluidic systems depended only on the dielectric constant of the liquid between the electrodes, this paper shows how the conductivity can also be measured.
Chemical Engineering Transactions. 05/2011; 24:535-540.
[show abstract][hide abstract] ABSTRACT: There is an increasing trend to apply microsystems and microfluidics to solve medical and biomedical tasks. Microfluidic modules are used to modify and manipulate cells and cell clusters for therapeutic applications. Specifically, a method and technical system for encapsulation of Langerhans' islets as an option for the future treatment of diabetes mellitus is described. Type-1 diabetes patients suffer from an absolute lack of the hormone insulin caused by an autoimmune process destroying the Langerhans' islets. One way to restore glucose-dependent insulin secretion is the transplantation of human pancreatic islet cells (85% beta cells) from cadaveric donors. However, to prevent the rejection of the transplanted cells by the immune system of the host, a life long immunosuppressive medication is necessary. One possible way to prevent this rejection would be the transplantation of immunoseparated Langerhans' islets, which are encapsulated in a 3D-alginate matrix polymerized with ions like Ba2+. As has been successfully shown in animal experiments, this technique would furthermore allow the transplantation of xenograft islets and thus help to solve the problem of shortage in donor organs. We present a microfluidics-based system for encapsulation of cells in alginate.
Engineering in Life Sciences 04/2011; 11(2):165 - 173. · 1.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: Im Folgenden wird eine neue, am Heiligenstädter Institut für Bioprozess- und Analysenmesstechnik e.V (iba), entwickelte Technologieplattform vorgestellt, die eine alternative Methode zu Mikrotiterplatten-basierten Kultivierungsverfahren darstellt. Grundlage dieser Plattform ist das Prinzip des segmentierten Flusses, wobei die Flüssigkeit des Hauptstromes nicht mit einer zweiten, der zudosierenden Flüssigkeit, mischbar ist. Ein wesentlicher Vorteil dabei ist der, dass die so erzeugten Kompartimente als separate Reaktionsräume betrachtet und genutzt werden können ohne sich gegenseitig zu beeinflussen. Nachfolgend soll an drei Beispielen die vielfältige Applikationsbreite dieser Plattform kurz dargestellt werden.
[show abstract][hide abstract] ABSTRACT: Transplantation of immunoisolated endocrine tissue could improve the therapy of many diseases, especially the in industrial
countries common diabetes mellitus, without use of immunosuppressive treatment. Many efforts have been taken to choose the
proper capsule material, to make it biocompatible and to produce it in a standardized way but the capsule production process
still needs improvement. Ultra high viscosity alginate is currently the most promising capsule material because its biocompatibility
and the crosslinking conditions are biologically agreeable. Common capsule production techniques are e.g. spray-, vibration-
or jet-cutting technique but these techniques are not in a closed system and therefore open to contamination and external
influence. Here, we want to present a novel, microfluidic based encapsulation machine and first, promising results with different
[show abstract][hide abstract] ABSTRACT: The conformational transition of alpha-helix-rich cellular prion protein (PrP(C)) to an isomer with high beta-sheet content is associated with transmissible spongiform encephalopathies. With the ultimate long-term goal of using imaging techniques to study PrP aggregation, we report the results of initial experiments to determine whether PrP molecules could be visualized as single molecules, and if the observed size corresponded to the calculated size for PrP. The investigation of single molecules, and not those embedded into larger aggregates, was the key in our experimental approach. Using atomic force microscopy (AFM) as an imaging method, the immobilization of recombinant histidine (His)10-tagged PrP on mica was performed in the presence of different heavy metal ions. The addition of Cu2+ resulted in an enhanced PrP immobilization, whereas Ni2+ reduced coverage of the surface by PrP. High-resolution data from dried PrP preparations provided a first approximation to geometrical parameters of PrP precipitates, which indicated that the volume of a single PrP molecule was 30 nm3. Molecular dynamics simulations performed to complement the structural aspects of the AFM investigation yielded a calculated molecular volume of 33 nm3 for PrP. These experimentally observed and theoretically expected values provide basic knowledge for further studies on the size and composition of larger amyloidal PrP aggregates, PrP isoforms or mutants such as PrP molecules without octarepeats.
Journal of Microscopy 06/2008; 230(Pt 2):224-32. · 1.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a hydrophobization procedure for SU-8-based microfluidic chips on borofloat substrates. Different layouts of gold electrodes passivated by the polymer have been investigated. The chips are used for segmented flow in a two-fluid mode that requires a distinct hydrophobicity of the channel walls which is generated by the use of specific silane. In this paper we describe the production and silanization of the chips and demonstrate segmented flow operation.
Journal of Micromechanics and Microengineering 04/2008; 18(5):055019. · 1.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: Miniaturized biological test assays require an even distribution of the utilized cells in every single segment. For the cell dispension, two devices with a volume of about 2 milliliter were developed enabling simultaneous mixing and processing of suspensions into capillaries. These items will be used to generate homogeneous suspensions for a duration of up to one hour and distributing them with special microfluidic chips. Both devices could be easily sterilized by autoclaving and contain an agitator which is contactlessly driven with variable speed. Precise transportation of the mixed fluid in the lower microliter per minute range was realized by the use of syringe pumps. Suspensions with yeast, mammalian cells and beads were applied to investigate the efficiency of mixing and transportation as well as the effect on viability. At certain time intervals, samples were taken from the outlet, and the cell and bead content with the related viability was determined using an automated particle analyzer and counting chamber under the microscope. Yeast suspensions were handled up to two hours and hybridoma cells up to one hour without remarkable loss of viability whereby the degree of mixing was sufficient for these time periods. The results show that these modules are feasible tools for homogeneous mixing of cell suspensions, and transport through microfluidic devices allows dispensation of them into fluid segments on a microliter or nanoliter scale.
Engineering in Life Sciences 02/2008; 8(1):49 - 55. · 1.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: A newly developed Protein-Processing Platform (3P) for cell cultivation and sample handling is presented. The 3P-concept is based on a 6-well microtiter plate for cell cultivation, an autoclavable top plate as a sampling system using a new kind of microvalve and an x-y-z-plotter to manage the sample handling procedures. Furthermore, the sample can be stored in a water-cooled deep well plate and transported to a detector e.g. by addressing a dedicated protein chip based on a Black-Silicon structure. The function of microvalves is based on the swelling behavior of hydrogel depending on its temperature. The regulation system of this temperature is integrated into the 6-well microtiter top plate. In this paper, the realization of this concept is exemplarily carried out using the cultivation of hybridoma and their production of monoclonal antibodies. The cultivation conditions were not optimized. However, using different mixing methods, their influence on the antibody production was investigated. The best cell growth was observed in the dormant 6-well microtiter plate. As under these conditions, a gradient of antibody concentrations occurs, the depth of immersion of the sampling probes has to be investigated. A reproducible sampling was possible by withdrawing the sample from the middle of the cell suspension level. Procedures for sampling and washing under sterile conditions were developed using the tools of the x-y-z-plotter. The optical detection of the samples can be performed using the new protein chip based on the Black-Silicon technology in any kind of commercial reader. It is possible to integrate the single modular components of the platform into every protein expression process. Additionally, the adaptation of the sampling system to commercial microtiter plates guarantees a wide range of applications.
Engineering in Life Sciences 01/2008; 8(1):73 - 80. · 1.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: Replacing dysfunctional endocrine cells or tissues (e.g. islets, parathyroid tissue) by functional, foreign material without
using immunosuppressives could soon become reality. Immunological reactions are avoided by encapsulating cells/tissues in
hydrogel (e.g. alginate) microcapsules, preventing interaction of the enclosed material with the host’s immune system while
permitting the unhindered passage of nutrients, oxygen and secreted therapeutic factors. Detailed investigations of the physical,
physico-chemical and immunological parameters of alginate-based microcapsules have led recently to the development of a novel
class of cell-entrapping microcapsules that meet the demands of biocompatibility, long-term integrity and function. This together
with the development of ‘good medical practice’ microfluidic chip technology and of advanced cryopreservation technology for
generation and storage of immunoisolated transplants will bring cell-based therapy to clinics and the market.
Applied Physics A 11/2007; 89(4):909-922. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: Micro system technology offers convenient tools for the production of handling devices for small liquid volumes which can be used in cell cultivation. Here, a modular system for the rapid generation of cell suspension aliquots is presented. The system is used to produce and analyze high numbers of well-separated culture volumes. Selected clones may be retrieved from the system. Therefore, the principle of segmented flow is applied. Portions of aqueous culture medium containing one cell or very small cell ensembles are separated from each other by a nonmiscible liquid like dodecane, tetradecane or mineral oil. In addition, the alkane separates the culture droplets from the innerside of the walls of chip channels and capillaries. This way, compatibility problems between cell wall surfaces and the chemical character of walls are excluded. The separated culture droplets are guided by micro flow transportation in different channel and chamber topologies. The whole system has the character of a serially operating cell processing system. The aliquot generation can be sped up to frequencies of about 30 Hz in each microchannel. That means, that about 10(5) individual cultural volumes can be produced per hour or about 2 million per day. The survival and the growth of microorganisms has been shown for model organisms as well as for organisms from a natural sample (soil).
Biosensors and Bioelectronics 07/2004; 19(11):1421-8. · 5.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: Segmented fluids can easily be processed in micro reactors and micro capillaries, if several boundary conditions are fulfilled. The ability of formation of highly regular segments and segment distances in combination with the ability of controlled manipulation, splitting and fusion of carrier liquid columns and single droplets opens the way to a new class of miniaturized chemical and biological operations. The subdivision of a certain reaction or a cultivation volume in a lot of aliquotes and the individual handling of the subvolumes leads to the possibility of realizing serial processes and statistical investigations by numerous highly comparable, but well separated reactor volumes. Combination of different substances, e.g. for testing of synergetic effects in drug development or catalysts screening, can be performed to large extent. The concept of “digital” reaction technology by micro fluid segments means the introduction of a digitalization principle by use of a large number of small reaction volumes handled serially in flow channels and flow-through micro devices. For the realization a set of modules including special interconnectors, T-junctions and other injector elements, transfer units and fluid resistance elements are necessary. Flow fusion modules and segment fusion modules are needed for the reorganization and recombination of serially flowing sequences of fluid segments and for the initiation of reactions by mixing of pairs and triplets of single segments. The principle can be used for quantitative chemical analyses like titration realized by use of micro fluid segments (digital micro segment titration). Micro segments could also be applied in modular synthetic chemistry, particularly in combinatorial chemistry so far as the educts and products of the single synthesis steps are compatible with liquid/liquid two phase system. The segmented flow principle is of particular interest in microbiological experiments and screening procedures. First result show the practical advantages in the highly parallelized production of monoclonal cell cultures in culture sets of very high diversity and for the cultivation of slowly growing microbial species. In addition, the possibility of producing of separated cell cultures in high density opens a series of applications in the screening and testing of drugs.
Chemical Engineering Journal. 01/2004; 101:201-216.
[show abstract][hide abstract] ABSTRACT: Micro serial processing of continuous sample streams in microfluidic environments provides a new, powerful and scalable approach for micro scaled chemical reactions and analytical procedures. It is based on sample generation by embedding sample liquid in a continuous stream of an immiscible carrier fluid. Segmented streams are processed in capillaries with integrated microfluidic devices for chemical and analytical processing. Devices and methods were developed for generation of segmented flows and for dosing of liquid into compartments of a segmented sample stream. Segmentation is realized with predefined compartment volume and a high degree of uniformity in size and frequency. Injectors are optimized for interoperatibility with segmented flow handling in HPLC-capillary systems. For fabrication of microfluidic devices two half channels were prepared in glass by means of an isotropic etch process, followed by anodic bonding mediated by a nickel chromium metalization. Segmented streams are generated in the injector module and guided into a dosing module, where controlled infusion of liquid into the compartments of the segment stream is realized. The system was used for a neutralization reaction in compartments containing formic acid with sodium hydrogen phosphate.
[show abstract][hide abstract] ABSTRACT: The high speed production of fluid segments for the highly parallelized cultivation of monoclonal cell populations was carried out by the use of microchip segmentor modules. Aqueous fluid segments, embedded in a non-miscible carrier liquid, were produced with frequencies up to 30 s(-1) and showed a high homogeneity in size. This corresponds with the production of about 2.5 million samples per day. The segment volumes can be adapted between about 4 nl and 100 nl. The typical segment size for cultivation experiments is in the range between 40 nl and 80 nl. Nutrient medium can be applied instead of pure water. It is possible to aliquot a cell suspension in such a way that most of the aqueous fluid segments contain only one cell. In model experiments with four microbial species chip-produced aliquots of 60 nl, each containing one or a few cells, were incubated in Teflon capillary tubes. Rapid growth of the microcultures was observed. Cell densities were found to be as high as in conventional shake flask cultures.
Lab on a Chip 09/2003; 3(3):202-7. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this review we describe aspects of interactions between bioreactors and analytical systems including microsystems. Principles of bioprocess monitoring are summarized, before we focus on the miniaturization of sampling systems guaranteeing bioprocess sterility and providing analytical systems with a liquid sample. The application of negative dielectrophoresis as a new principle for cell retention in a sampling system is described followed by theoretical aspects and results. Properties of micromachined silicon membranes as filters for sampling systems and for biosensor protection are discussed.
Journal of Biotechnology 01/2002; 82(2):123-35. · 3.18 Impact Factor