MicCell – Microfluidics on the Microscope Stage

Casting Set for PDMS Channel Plates

The casting set mainly comprises the casting station, Polycarbonate carriers, liquid PDMS and syringes. In addition, you will need a “Master Chip” introducing your particular channel layout.

Casting set for PDMS channel plates (CP)

Injection of the liquid PDMS into the casting station

The master chip is made from Teflon coated silicon and made at GeSiM on request. Basically we accept any layout provided by a CAD drawing; a set of typical channel layouts is on the shelf. Please ask.

Foil Based Microsystems Made to Order

Alternatively GeSiM offers customized microfluidic systems made of adhesive foils that are cut by different technologies and assembled in our factory. They can be ordered in small and large quantities, thus can be used as disposable, and snugly fit in the GeSiM MicCell chamber. They are an attractive alternative to PDMS channel plates. GeSiM is currently redesigning the BSyS robot to produce them automatically.

Systems from glass are also available, please inquire.

Intricate multi-layer layouts can be achieved so that numerous applications, e.g. point-of-care diagnostics, become feasible. Interesting accessories are membranes with defined cylindrical nanopore geometries from Oxyphen AG, produced by beaming with energetic heavy ions. This has e.g. allowed the safe encapsulation of genetically engineered yeast cells in biosensors for anthropogenic pollutants in wastewater (Schirmer et al., 2018, 2019; Günther et al., 2019).

“Track-etched” membrane (Oxyphen GmbH) placed on a cut foil (darker) with round hole and channel. The speckles are the pores.

Fluidprocessor with Graphical User Interface

A macrofluidic hardware box with programmable logic controller (F-Box) is required that has replaced our old “Fluid Processor” and provides all functions, be they external (e.g. syringe pumps and other pumps, external 2/2 or selector valves, level sensors, coolers, heaters) or internal (e.g. hydrogel microvalves, temperature sensors, voltages/impedances).

F-Box Fluid Processor for an SPR sensor, featuring various valves, four syringe pumps and a Peltier cooler with temperature controller.

Forget about connecting each pump or valve to your computer with a cable and sending strange commands. With our new intuitive graphical user interface, you can quickly configure and run any microfluidic system. The GeSiM Fluidics GUI lets you also compile sequences for unsupervised 24/7 operation.

MicCell GUI. Devices in the F-Box are automatically detected. Add them to the fluid diagram via clicking and dragging (left) and manually control them (right). You can also define automatic processes including many controls, e.g. status queries, loops, counters (not shown).

MicCell GUI. Devices in the F-Box are automatically detected. Add them to the fluid diagram via clicking and dragging (top) and manually control them (bottom). You can also define automatic processes including many controls, e.g. status queries, loops, counters (not shown).

The Hydrogel Valve – Properties and Function

Hydrogel microvalve HG7

HG7 microvalve on a MicCell carrier

To add liquid, to start and stop reactions, a dead volume free microvalve (GeSiM patent) can be placed into the flow system.

The valve is made from a silicon chip but comes with different housings for convenient handling. Most popular version is called “HG-7″, based on a PEEK-housing with 1/16” fitting.

The valve chip incorporates a small but well-defined amount of a hydrogel immobilized in a liquid transparent chamber. The surrounding heater controls the temperature of the chamber in a limited range around the swelling temperature of the hydrogel.

For operation of the valve nothing but 250 mW power is required. The Fluid Processor provides full control of the device.

The sample liquid gets in contact with the enclosed hydrogel. Therefore, the valve is mainly made for aqueous solutions but tolerates <15 % methanol, acetone.

Measurement of Tiny Flows

The GeSiM flow sensors has been designed for flow rates in the range of 0…100 Microliters per minute. It is a thermocalorimetric sensor measuring the heat transfer in a very tiny chamber. The fluid sample is negligibly heated whereas the surroundig temperature distribution is monitored.

As larger the heat transport through the chamber as more precisely the measurement result will be. In other terms, as more time is allowed for a single measurement as better the accuracy.

The sensor can be used along with the MicCell Fluid Processor (See next article) but is available for standalone operation too. The sensor is cascadable, it allows to measure several independent fluid flows simultaneously. Up to four stacked sensors can be managed by a single controller. The controller connects to a PC through serial interface, a dedicated software displays the measurement result.

The versatile MicCell system: Research already done

The MicCell System gained much attention from researchers world wide. Here we present a list of possible and already done applications. Please contact us for further details.

• Micro-reaction technology, e.g., hybridization or stoppedflow chamber, using fluorescence detection
• Immobilization of biomolecules (e.g., protein or DNA) in the microchannels before assembly, e.g., by microarraying
• Generation of concentration gradients perpendicular to the microchannel cross section by a “gradient mixer”
• Semi-automatic drug screening using adherent cells or tissue slices
• Viability tests and other cell-based physiological assays
• Measurement of the interaction of cells with immobilized proteins, DNA, RNA, oligo- or polysaccharides, lipids, and other ligands
• Cell handling and sorting using optical tweezers
• Identification of cancer or stem cells using an “optical stretcher” (patent University of Leipzig)
• Electroporation in the flow
• Testing of the uniformity of microbeads and other particles, potentially with sorting
• Manipulation of elongated macromolecules (e.g., DNA or motor proteins) in hydrodynamic flow fields for the bottom-up construction of nanostructures, force measurements, etc.
• Micro-capillary electrophoresis under the microscope
• Integration of, e.g., column or filtration material for micro-purifying with or without microscope control
• Liquid processing independent of a microscope (e.g., assays using electrochemical detection)
  Chemical synthesis on the nanoscale
• Observation of opaque objects in the MicCell using the pivotable sample carrier

Below we present a few examples.

Wastewater Analysis Using Foil-Based Microfluidics

Together with Fraunhofer IKTS (Dresden) and other companies (BMBF project ANTHROPLAS), a nanoplasmonic biosensor for 24/7 detection of 10 µg/l diclofenac in wastewater was developed (Steinke et al., 2018). It features a functionalized nanostructured gold surface in a foil-based microfluidic system (Steinke et al., 2019) and a miniaturized optoelectronic unit (Wuchrer et al., 2016).

PC foil with four nanopillar arrays made by NIL

Ready-to-use chip with two 2 mm wide / 90 µm deep channels in a white laser-cut foil

Exploded view of complete sensor system

Sensor cell without PC body

Four channel sensor electronics, placed under the fluidic channels (dresden elektronik)

GeSiM’s contribution was:

• Nanopillar arrays in a UV-curable photoresist on a polymer substrate made by nanoimprint lithography with a GeSiM µCP4.1.
• Foil-based microfluidic systems, based on adhesive tape technology of Fraunhofer IKTS, with two flow channels operating in parallel.
• A casing for the microchannels with standard “chip-to-world” interface based on the GeSiM MicCell  that also integrated the optoelectronic system.
• Software for easy control of all fluidic components.

Foil based Multi-Layer Flow Cell to study gradients

Flow cells were designed in which a collagen layer with live cells is exposed to two different concentrations of an analyte to study the effect of chemical gradients on the fate, e.g. differentiation, of cells or organoids grown in extracellular matrix. A track-etched above the collagen prevents outflow of cells.

Gradient chamber principle. Two different concentrations of a substance (c1, c2) flow in two channels above this setup and diffuse through the membrane into the space underneath. Only liquids/gels and the membrane are shown.

Gradient chambers for 22×22 mm² MicCell, with collagen channels of different width, top (left) and bottom view (middle). Through holes in the top foil, the bottom channel is filled with cell-laden collagen and the two small top channels are filled with liquids to study. Five layers are needed: top cover foil, top channel foil, pore membrane, bottom channel foil, bottom cover foil. The right picture shows the PC body with six threaded holes with O-rings, and the MicCell support.

Courtesy Tilo Pompe Lab, University of Leipzig.

Detection of Biological Polutants in Waste Water

At the Kurt-Schwabe-Institute Meinsberg and the GeSiM, a foil-based microfluidic flow cell based on the MicCell System was developed for the detection of pollutants in wastewater with genetically modified yeast cells.

Left: Flow cell connected to the tubes via a polycarbonate body that is mounted on the detection unit. The sensor chambers are located underneath the polycarbonate body with the microfluidic tubes. Middle: Photo of the foil-based microfluidic flow cell. The dimensions of the flow cell are 22 x 22 mm, the height of the chambers is 100 µm. Right: Exploded drawing of the foil-based microfluidic flow cell.

The yeast cells are immobilized in the two lower cell chambers and covered by a porous membrane, which allows diffusion of nutrients and analytes from the supply chambers to the yeast cells but prevents them from leaving the cell chambers.

Courtesy of Kurt-Schwabe Institute Meinsberg

Biofilms and (Anti-)Biofouling

Primary Cell Adhesion and Biofilm Formation on Anti-(bio)fouling Surfaces

In order to exploit the potential of biofilms or minimize the risk of their formation it is important to study and characterize them. To meet these aims the biomonitoring group of the Institute of Food Technology and Bioprocess Engineering at TU Dresden has established a modular flow cell system with a parallel plate flow chamber. It is based on GeSiM’s MicCell and offers possibilities to study biofilms on opaque surfaces in continuous flows under a fluorescence microscope.

The centrepiece of the flow chamber is a microfluidic chip, consisting of a glass slide, a fluidic layer and the substrate. The fluidic layer is made from a polymer 3D printed on the glass slide and both its thick­ness and shape can be modified.

Recently an innovative sample holder was designed. It is made of stainless steel with holes to ensure liquid flow across the sample surface. The advantage of this setup is that samples with various geometries can be examined with no need for drilling before analyses. Hence the flow cell can be easily and rapidly adapted to meet different requirements.

Furthermore, due to the laminar flow inside the microfluidic channel, conditions can be tightly controlled, and we can regulate variables such as oxygen and nutrient levels simply by varying the medium supply.

We use the flow chamber to study the adhesion behaviour of microorganisms and the first stages of biofilm formation on various materials. The acquired data are used to characterize the local and time-related biofilm formation and to derive parameters like growth rate, biofilm height and biomass volume.

Technische Universität Dresden
Faculty of Mechanical Science and Engineering
Institute for Food Technology and Bioprocess Engineering
Chair of Bioprocess Engineering, Prof. Th. Bley
Biomonitoring Group, Assoc. Prof. E. Boschke, Dipl.-Ing. S. Mulansky