Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Polymer-based Fabrication Techniques for Enclosed
Microchannels in Biomedical Applications
Annabel Krebs, Thorsten Knoll, Dominic Nussbaum, Thomas Velten
Fraunhofer Institute for Biomedical Engineering
Ensheimer Str. 48, 66386 St. Ingbert, Germany
Abstract- Investigations and analyses of body fluids like
serum or whole blood are essential tasks in biomedical
research in order to understand and diagnose diseases, to
conduct pharmacological tests or to culture cells. Therefore,
microfluidic systems provide a favorable tool for processing
fluid samples as they allow downscaling of sample volumes and
handling of single fluid components such as cells or proteins.
For this reason, we present simple fabrication techniques for
microchannel systems using polymer materials only. On the
one hand, these materials are low-priced compared to
conventional silicon or glass. On the other hand, they do not
show any interaction with biological fluids. Furthermore, their
transparency guarantees an easy observability of all processes
within the system. Depending on the channel dimensions,
different adhesion bonding techniques for closing of the
systems are applied, whereas the fluidic interfaces are
included. Summing up, we provide complete fabrication
processes for fluidic systems which are simpler and more costeffective
than conventional methods and yet cope with all
essential requirements for microfluidic applications.
I. INTRODUCTION
Microfluidic systems have become a common tool in
research fields like analytical chemistry or biomedicine as
miniaturized devices require only small material and sample
volumes. Additionally, effects can be exploited which are
only dominant in the micro range. For example,
investigations on cells or other components in blood
samples can be carried out in lab-on-chip systems as
dimensions of the cells are in the same scale as the
microchannels. In biomedicine, lab-on-chip systems have
emerged to indispensable devices for the accomplishment of
medical tests with body fluids or extractions from fluids.
Besides, they also serve for cell handling and culturing,
mixing of liquids, detection and analysis of diseases or for
measuring quantitative amounts of components like glucose
or hormones in blood [1-6].
Depending on the applications of micro systems, certain
requirements to the systems need to be met. In case of
biomedical applications, the transparency of materials is
often a vital aspect in order to be able to follow processes
within the system channels or chambers. Moreover, the
employed materials should not interact with the biological
sample and channels should hold defined dimensions.
Other general demands come along such as leak-proof
closure of the channels and implementation of fluidic
interfaces. Importantly, the whole fabrication procedure has
to be affordable at the same time.
Therefore, we present fabrication techniques for
microfluidic systems with focus on biomedical applications,
meeting the requirements named above. Based on acrylic
glass substrates and the epoxy resists SU-8 and
PerMX3020, reasonable cost of the materials is assured.
These polymer materials are pellucid and do not show
interactions with whole blood or blood components. As
biocompatibility tests with SU-8 have not given cause for
concern [7, 8], SU-8 is currently used in divers biological
research fields [9, 10], although further biocompatibility
studies might be advisable [8]. In Ref. [5], we introduced a
manufacturing technique which also bases upon these
polymer materials. Yet, the here presented, modified
processes enable a wider choice of material combinations as
well as enhanced fabrication reliability and yield.
Additionally, we achieved to double the feasible aspect
ratio.
Hence, a simple fabrication technique for microchannels
is presented which rests upon photolithography and polymer
adhesion bonding. In doing so, very small channels with
aspect ratios higher than 10:1 can be created. In contrast to
conventional hybrid techniques for sealing of channels, we
use different full wafer bonding methods depending on the
channel dimensions. Unlike other working groups that have
already presented high aspect ratios and full wafer adhesion
bonding using silicon or glass substrates [11-13], we
accomplish these processes on polymer substrates. Very
cost-effective and simple structuring techniques can be
applied to these substrates, e.g. fluidic interfaces can be
implemented by mechanical drilling. More complicated,
costly procedures like laser drilling, sand blasting, glass
etching and substrate removals can be obviated. Altogether,
we obtain a complete manufacturing procedure preferable
for biomedical applications which outplays common silicon
or glass techniques in terms of material and total costs. In
comparison with other polymers like polydimethylsiloxane
(PDMS), the presented techniques are adaptive for smaller
channels and higher aspect ratios, thus they qualify for a
wider range of applications.
II.
MATERIALS AND METHODS
A. Materials
1 mm thick 10 cm x 10 cm acrylic glass (polymethyl
methaacrylate, PMMA) plates were used as substrate
materials. Two different epoxy-based photoresists, SU-8
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