Ed Fontes looks at the role played by computer modelling by a company which miniatures laboratory applications.
The Swedish company Gyros, situated in the heart of Sweden's amedicon valley', uses modelling for understanding and design of processes in microlaboratories for the development of new drugs. Miniaturisation makes it possible to use very small sample and reagent volumes, which decreases the price of otherwise expensive analysis.
Gyros miniaturises and integrates laboratory applications and instruments for sample and reagent preparation based on microlaboratories built on the surface of compact disks. Gyros' largest product is currently being used in the proteomics field for the characterisation and interpretation of proteins' functionality and structure (Fig. 1).
“Gyros develops the microfluidic devices that are comprised in the CD and the pharmaceutical companies deliver the chemistry needed for the sample preparation“ says Gunnar Kylberg at Gyros. Gunnar gives a concrete example of the application in diagnostics of allergies. “In our CD, you could prepare a large number of allergy samples simultaneously, using cleverly designed micro reaction columns, with only a small amount of blood“.
The Spinning Laboratory
The CD-based micro laboratory makes use of the forces created as the CD rotates, which helps to transport the sample in the microchannels without the use of microscopic pumps or electrokinetic flow. In the CD structure, there are a number of different effects in microdevices and microchannels that need to be studied closer with the help of mathematical modelling. These include fluid flow in meniscuses formed in the channels, adsorption and flow in microcolumns, evaporation of solvent and also heat transfer in the CD.
Computer Modelling for understanding and design of the microscopic processes
Modelling of the unit operations in the micro laboratory gives a qualitative understanding of the transport processes involved in the preparation of the sample and can also be used for quantitative studies in the design of the microdevices.
One example of a modelling application is the estimation of the evaporation rate from a micro test tube. Evaporation of the solvent is a very common problem in the transfer of sample in microscale. Gunnar Kylberg has studied this problem in a mathematical model by using a combination of the Navier-Stokes equations with a mass balance for steam in the gas phase. Fig. 2 shows the concentration of steam in the gas phase and the pressure field in the top part of the test tube. This simulation gives an estimate of the sample concentration as a function of space-time in the micro titer device.
The adsorption process in Gyros' microlaboratories depends on the flow rate and adsorption kinetics for the specific solution. Fig. 3 shows the flow distribution between the microspheres that comprise the adsorption column. The flow field and pressure difference across the column are important design parameters for the sample preparation process. A large velocity gives a small space-time for the sample in the adsorption column and determines the amount of proteins adsorbed.
The micro channels in the CD are used for mixing and washing of the sample and the reagents. During the injection of new reagents into the micro channels, a certain mixing is obtained with the solution already present in the channel. It is important to have an estimate of the degree of mixing and the amount of new solution that is required to flush the old one out of the channel. Gunnar has made a model for these types of estimations using equations for microfluidics found in the literature. Fig. 4 shows the results of a model where a new solution is inserted into a microchannel. The old solution, coloured in red, is flushed away by the incoming solution but mixing occurs through diffusion and convection.
During the flushing process, mixing of the two solutions occurs and the model gives an estimate of this. The model was made by Gunnar Kylberg using FEMLAB's equation-based applications. In addition to the microfluidic applications, Gyros also models heat conduction problems in the CD and the electrical field applied on the sample in the mass spectrometer.
Gyros competes in a technology-driven market, which means that even small research groups can come up with ideas and prototypes that can be taken to market. In this environment, it is important to quickly understand an idea and produce a prototype. The combination of equation-based and application-based modelling in FEMLAB gives Gunnar the adaptability required in this work.
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Ed Fontes is with Comsol AB, Stockholm, Sweden. www.femlab.com.
