A BIOLOGICAL MONITORING MODULE BASED ON A

CERAMIC MICROFLUIDIC PLATFORM

Walter Smetana

, Bruno Balluch

1,2

, Ibrahim Atassi

1,2

, Khatuna Elizbarowna Gvichiya

Erwin Gaubitzer

3,2

, Michael Edetsberger

3,2

and Gottfried Köhler

Institute of Sensor and Actuator Systems, Vienna University of Technology, Gusshausstrasse 27-29, Vienna, Austria

OnkoTec GmbH, Vestenötting 1, Waidhofen/Thaya, Austria

Max. F. Perutz Laboratories, Department of Biomolecular Structural Chemistry, University of Vienna, Vienna, Austria

Keywords: LTCC-technology, Microfluidic, FEA.

Abstract: A 3-dimensional mesofluidic biological monitoring module has been successfully designed and fabricated

using a low-temperature co-fired ceramic (LTCC) technology. This mesofluidic device consists of a

network of micro-channels, a spherical mixing cavity and measuring ports. A selection of appropriate

commercially available ceramic tapes has been chosen with regard to their biocompatibility performance.

Specific processing procedures required for the realization of such a complex structure are demonstrated.

Three dimensional numerical flow simulations have been conducted to characterize the concentration

profiles of liquids at a specific measuring port and verified by experiment.

1 INTRODUCTION

Microfluidic and mesofluidic analytical systems are

becoming increasingly popular in chemical and

biomedical applications due to the need of small

volume reagents, small wastes and short reaction

times. Microfluidic devices may be classified into

functionally limited labs-on-chip (LOC) and micro

total analysis systems (µTAS). Most LOCs are

single function and single layer devices such as

mixers, separation channels, etc. Micro total analysis

systems, on the other hand, are more complicated

and are capable of performing many functions such

as mixing, reaction, separation, etc. on a single

module. Generally these devices handle nanoliters of

reaction volumes and often accomplish their specific

tasks in milliseconds of reaction times. Most of these

systems are based on silicon, glass, poly-

methylmethacrylate (PMMA) or polydimethyl-

siloxane (PDMS) substrates (Anderson, 2000). A

range of rapid-prototyping methods using laser-

techniques for the fabrication of microfluidic

devices are reported in literature. Micro-stereo-

lithography, selective laser sintering, laser writing

method and microcladding techniques are applied

for generating complex 3-dimensional (3D)

microparts of polymer, metal and metal-matrix

composite (Kathuria, 2001, Yu, 2006).

Micropatterned ceramic components may be

fabricated in a rapid prototying process combining

stereolithography for the supply of master models

with low pressure moulding (Knitter, 2003). But true

3D microfluidic structures cannot be easily imple-

mented using these techniques due to process

limitations or material properties. The use of LTCC-

technology for microfluidic devices enables the

realization of multiple 3D microchannels, a feature

not easily attainable in other MEMS technologies

(Gongora-Rubio, 2001; Golonka, 2006). Therefore,

based on this experience LTCC technology has been

considered as an adequate approach to realize a

compact temperature controlled monitoring module

for biological reactions with low sample consump-

tion which may be considered as a µTAS device.

The process technique for making a 3D-

architecture with LTCCs is rather simple and

standardized. Device production in LTCC

technology covers the machining, punching or laser

drilling of vias and channels on individual layers.

The individual layers are stacked and laminated in a

heated platen press or in a heated isostatic press.

Subsequently the laminated stack is exposed to the

firing cycle which is a somewhat critical process

where heating rate, dwell time at burnout

Smetana W., Balluch B., Atassi I., Gvichiya K., Gaubitzer E., Edetsberger M. and Köhler G. (2009).

A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM.

In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 75-82

DOI: 10.5220/0001543400750082

 SciTePress

temperature and total firing cycle time have to be

matched to the thickness of the ceramic stack.

The field of nonlinear chemical kinetics has been

investigated about half a century. Still only a few

complex chemical reactions have been described by

means of an experimentally backed system of

coupled chemical equations. Moreover, in biological

relevant nonlinear systems most of the reactants, e.g.

proteins etc., are expensive to prepare and generally

only available in limited quantities. Therefore, it is

essential to use tiny reaction volumes for continuous

flow experiments, as realized in this reaction cell.

This hereby presented contribution outlines the

procedures of fabrication and characterization of a

reaction module designed to follow quantitatively

complex biochemical regulatory reaction networks

in vitro as a basis for advanced mathematical fitting.

This device consists of a mixing module which

provides fast mixing of reactants and four sensor

ports for simultaneous measurements. The

functionality was proved using the well known

oscillatory behaviour of the chlorite-iodide reaction

(Kügler, 2008).

2 DESIGN

Figure 1 shows the schematic of the monitoring

module also used as model for establishing finite

element analyses (FEA).

The module comprises a spherical reactor cell

where continuous mixing of the reagent fluids is

provided. Besides this mixing chamber the module

is equipped with pH-, oxygen-, temperature- and

iodide sensitive sensors for reaction monitoring as

well as with SMA-connectors for glass fibres

required for absorption or fluorescence

spectroscopic analyses (figure 2). Pumping a thermal

fluid through embedded ducts provides temperature

control. A network of micro-channels with cross

section dimensions varying from 200 µm x 200 µm

up to 2 mm x 2 mm are connecting the different

measuring sections within the ceramic module.

Special attention has to be spent on the selection of

appropriate ceramic tape material with regard to

biocompatibility and suitability to build up a

complex 3-dimensional structure which contains a

large number of cavities and channels.

Figure 1: Scheme of the monitoring module with reactor

cell and channel system.

Figure 2: Biological monitoring module (completely

assembled with sensor-, inlet-, outlet- ports and sockets for

optical fibers).

3 DEVICE FABRICATION

3.1 Biocompatibility Testing

Three different lead-free tapes have been considered

for this application like the ESL 41020, Ferro A6

and CeramTec GC-tape. The tapes should be

biocompatible but nevertheless cells should not

adhere and proliferate to a large extent on their

surfaces. The latter requirements are critical with

regard to clogging of channels by cell

agglomerations. In order to compare the

biocompatibility, proliferation, viability and

adherence of HeLa (human, cervix epithelial) cells

grown on sintered LTCC-tapes have been evaluated

using standard test procedures.

BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices

3.1.1 Proliferation Test

As a first biocompatibility testing the ability of

HeLa cells to proliferate on different LTCC tapes in

contrast to glass and standard plastic surfaces was

observed. The influence on cell proliferation was

tested with the Bromodeoxyuridine (BrdU) assay

(Gire, 1998) (Calbiochem, USA). BrdU

incorporation is detected immunochemically with

unlabelled primary antibodies and HRPO labeled

secondary antibodies.

HeLa cells were exposed in a 96 well plate (1 x

cells/well) with the different test disks (4 mm x

4 mm) for 23 hours in DMEM (Dulbecco's mod.

Eagle-Medium) containing 4.500 mg Glucose, 4.5

mM L-Glutamine, 44 mM Na-bicarbonate, 100

units/ml Penicillin, 100 µg/ml Streptomycin, 0.9

mM Na-pyruvate and 10 % fetal calf serum in a 6

volume % CO

humified atmosphere at 37 °C

(standard conditions). During the final 3 hours of

incubation BrdU is added. The BrdU concentration

is measured using a multi-plate reader (BIORAD) at

abs

= 455nm and λ

reference

= 655 nm.

Figure 3: Biocompatibility testing for HeLa cells on fired

LTCC- samples (CeramTec GC, ESL 41020, FERRO A6),

glass-cover slides (Assistent, Germany), Copper (Cu) and

standard plastic dishes (control-sample); Colour marking:

black: proliferation rates, red: percentage of viable cells,

blue: percentage of total cells compared to control group.

The results of the proliferation test are shown in

figure 3 (black bars). With exception of the

CeramTec GC-tape and the Cu- disks, the detected

proliferation-rates of all other test samples are equal

or even higher (glass support) compared to the

growing rate of the control group on plastic support

(100 ± 8.7 %). Also the deviation is comparable to

the control group. In contrast CeramTec tapes show

a 30-40 % reduction in proliferation. Nevertheless

this reduced proliferation is low in comparison with

cells incubated with Cu-disks, which under the same

conditions show a proliferation rate of 2-3 %

compared to control group.

3.1.2 Viability Testing

Next to the determination of proliferation rates it is

necessary to analyze the ability of cells to adhere to

surfaces and to determine the percentage of viable

cells. For this test series HeLa cells were incubated

in standard culture dishes with a diameter of 10 cm

(about 5 x 10

cells/dish) for 23 hours in DMEM

under standard conditions. The fired LTCC tapes to

be tested, glass cover slides and Cu-plates were

used with lateral dimensions of about 2.5 cm x 4 cm.

Cells were incubated in the presence of these

materials and on standard culture surfaces as control.

The number of cells and their viability was

evaluated with propidium-iodide (Zarnai, 2001)

using a Nucleocounter (Chemometec, Denmark).

The results of the viability tests are presented in

figure 3.

No significant reduction in number of total cells

(blue bars) has been detected for all LTTC samples

and glass as their percentage of total cells, in relation

to the control group, are comparable within the error

limits caused by inaccuracies of seeding the cells.

Only samples grown on Cu show about 40 % less

cells than the other samples.

Additionally not any significant reduction in

percentage of viable cells (red bars) was shown for

cells grown on LTCC tapes or glass support. Again,

only samples grown on Cu-plates show a diminution

of about 40 %.

3.1.3 Adhesion Testing

The side walls of channels and cavities are formed

by the laser machined edges of tapes. To observe

cell adhesion, which may rely on tape material but

also on surface finishing a test method has been

designed which enables to examine the potential

adhesion of cells on the laser machined edges of the

tapes. To evaluate the influence of the ceramic tapes

on the adhesion of cells on glass surfaces, CeramTec

and ESL ceramic tapes with laser-micro machined

tapering channels with decreasing channel width

(see figure 4-A) were mounted on standard glass

cover slides (Assistant, Germany) with a super

adhesive (Loctite). HeLa cells were seeded on the

cover slides (10

cells) and incubated over night in

DMEM medium under standard conditions. The

growth behaviour of the cells was evaluated using a

light transmission microscope.

A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM

Figure 4: A: Test sample of a ceramic tape coupon

carrying a continuous row of channel segments with

decreasing width (central circular opening is 10 mm in

diameter, the channel width is 2.122, 1.175, 0.672, 0.394,

0.228, 0.168 mm and 2.208, 1.224, 0.653, 0.396, 0.102,

0.054 mm for channels 1 to 6 of the ESL (D, F) and

CeramTec (C, E) tape, respectively. C, E: HeLa cells

grown on glass cover slides with a mounted fired

CeramTec-tape at channels 0-1 (C) and 2-3 (E). D-F:

HeLa cells grown on glass cover slides with a mounted

fired ESL-tape at channels 0-1 (D) and 3-4 (F). B: HeLa

cells grown on glass cover slides surrounded by mounting

glue (arrow). Micrographs were performed with a Zeiss

Axiovert S100TV at 10x magnification and a Digital

Camera (Nikon DMX1200).

Exemplary the results for the CeramTec and the

ESL tapes are shown in figure 4. It could be

demonstrated that the initial circular opening and

channel 1 machined in the CeramTec GC tape and

the ESL tape show only a poor influence on the

adherence of HeLa cells (figure 4-C, D; cell density

in circular opening: 250 – 300 cells/mm

, channel 1:

200 – 220 cells/mm

) but already at channels 2 and 3

(figure 4-E) with a width of about 0.6 mm a

significant decrease in adherence can be observed

for CeramTec tapes (cell density in channel 2: 45

cells/mm

, channel 3: 19 cells/mm

) as no significant

number of cells is observed at this area. In contrast

the fired ESL-tape shows quite a different cell

adherence performance. Also in channels 3-4 (figure

4-F) a rather dense cell population of cells (cell

density in channel 3 and 4: ca. 100 cells/mm

) and

even aggregation near to the edges are observed.

Only for smaller channels with width of about 0.2

mm a decrease of adherence can be observed (data

not shown). The mounting glue has not any effect on

the adherence behavior of HeLa cells to the glass

surface (figure 4-B).

3.1.4 Summary of Biocompatibility Testing

It can be concluded that all three LTCC materials

tested do not affect the viability of the cells, as the

total number of cells counted after the same period

was found identical within an error interval of ± 10

% for all LTCC-materials, standard plastic as well

as glass. An increased cell death compared to the

control group could not be found for any of the

standard materials. Only copper showed a significant

influence on viability, cell adherence and

proliferation. If only the proliferation characteristic

is considered, a distinction in tape performance can

be made. Whereas the ESL-tape shows a similar

behaviour with respect to the control assay of a

standard plastic support, FERRO-tape reacts similar

to a glass support and shows an increased

proliferation. Only the fired CeramTec-tape exhibits

a significant decrease in proliferation (figure 3).

These results are also validated by the adherence

test. When cell growth on a glass support was

restricted by sidewalls of a narrow channel

configuration, the cells reacted differently to ESL-

and CeramTec-tapes: Whereas on ESL tapes the

cells grow even in channels of very small width, it

was not the case for channels machined into

CeramTec-tapes. For these samples the area near to

the glass – ceramic interface was widely free of cells

and an efficient growth of cells was only detectable

in rather wide channels. The reasons of the

difference in cell adhesion on the channel walls are

still under investigation. It might be related to the

difference in surface energy as result of laser

machining. The quality of the cutting edges and the

surface of channel walls are defined by the

absorption of laser energy in the tape material which

may vary in dependence on the composition of the

selected LTCC- material.

The results show, that on the one hand side fired

ceramic tapes are generally biocompatible and do

not restrict the viability of cells, and on the other

hand side cells adherence can be specifically

influenced by the material selected. CeramTec GC

tape should be preferred, when adherence to the

walls of the chamber or channels should be

restricted as e.g. in microscopic observation

chambers where single cells are preferentially

observed in the center of an optical window and a

cell agglomeration along the side walls or growth

into micro fluidic flow channels should be avoided.

BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices

3.2 Processing Procedures

The CeramTec GC tape has been proved as a

suitable candidate for the realization of the

monitoring module not only with regard to the

results of the biocompatibility tests but also due to

its performance characteristic during processing.

Since the module comprises a complex network of

channels and cavities a tape material is required

which does not tend to sag during firing. Beyond the

green GC-tape with a thickness of 325 µm provides

an adequate ruggedness for handling.

The three dimensional LTCC-structure is

realized by forming a stack of adequately laser

machined (diode pumped Nd:YAG-laser (Rofin

Sinar, Germany) equipped with an acoustic optical

switch, operating power: 12 W at TEM00-mode)

single layers of tapes which are laminated and

finally exposed to a firing process. For the

realization of the complex module a single tape

shows a rather delicate structure since it is

penetrated by large-area laser machined

perforations. A standard LTCC-processing

technology cannot be easily applied for the

realization of the module since it comprises 133

ceramic layers, which deviates from the number of

tapes usually applied for conventional applications.

Figure 5: Inside view of reactor cell with various channels

and ducts (collated stack of tapes before lamination).

Special attention has to be paid on the lamination

of the ceramic tapes since the module contains a

large number of cavities and channels (e.g. the

reactor cell has a cavity volume of 1 cm

). The

finished sheets are collated in a mould (figure 5) and

aligned by registration pins providing that

successive layers are rotated by 90° to compensate

for the texture (preferential orientation) induced by

the fabrication of green tape. The lamination of the

stack of tapes has been carried out in a heated platen

press (Wabash).

A range of experimental work has been

conducted (Wang, 2008) in order to optimize

lamination parameters which should contribute to

provide the shape integrity of channel and cavity

structures. Sagging and delamination are typical for

relatively wide channels (width equal to 500 µm or

more) whilst contraction is characteristic for narrow

channels (width equal to 200 µm and less). The

application of sacrificial material for filling cavities

and channel structures is a valuable approach to

avoid sagging as well as the risk of delamination.

The selection of an appropriate sacrificial material is

absolutely essential for this complex microstructure

device. It has been found out that the main task of

the sacrificial material is to provide a uniform

pressure distribution within the LTCC-tape stack

during lamination. An additional supporting function

of cavity structures during firing is not required

since the considered LTCC material shows in all the

phases of the firing process an adequate strength and

stability. This substance should evaporate during the

burnout phase of the sintering process without

damaging the structure of the module. So the

approach was to find a material, which is

accommodated to the shrinkage performance of the

tape. An obstruction of material’s shrinkage should

be avoided. Some authors recommend carbon black

as sacrificial volume material (SVM) which may be

applied as tape or paste (Birol, 2005). This material

decomposes and exhausts at rather high temperature

when sintering of tape already starts. Different

polymer materials have been tested as potential

candidates acting as SVM since they decompose and

burn out at a temperature < 400 °C (before tape-

shrinkage is starting).

Best results have been attained with PMMA

chosen as SVM. It is also part of the organic

constituents of the considered tape and exhausts free

of residues at the burnout temperature of tape. The

organic sacrificial material has been used in powder

form. Channels and cavities are filled by a vacuum

sucking technique. It has been found out that a

uniform pressure of only 30 bar (sample

temperature: 70 °C, lamination time: 3 minutes) has

to be applied onto the ceramic layer stack which

enables to maintain the rectangular cross-section of

the buried channels while still avoiding delamination

of the ceramic batch. The applied pressure was

reasonably lower than recommended for

conventional applications.

Thermal gravimetric analyses have been

conducted to optimize the sintering profile

(especially to provide a complete and slow burn out

of the organics before sintering) in order to avoid

A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM

crack formation or delamination. The binder

decomposition process was studied by means of

Thermogravimetric Analysis (TGA) coupled with a

Mass-Spectrometer (MS) to detect simultaneously

the evolved gases (Balluch, 2008). Additionally, the

binder burnout was analyzed by Dynamic Scanning

Calorimetry (DSC). TGA revealed multistage

decomposition behaviour of the binder system. The

binder degradation is predominately governed by

exothermic reactions in the temperature range up to

400 °C and the course of the heat flow may be

correlated with the evolution of carbon dioxide. The

heat flow of GC-tape shows two exothermic peaks:

one at 250 °C and a major one at 364 °C. For the

GC-tape the first exothermic peak corresponds to the

maximum degradation rate in the TGA as can be

seen in the insert of figure 6.

Figure 6: Comparison of the heat flow signal with the ion

current for carbon dioxide for GC-tape.

The results of this study yield a useful approach

to establish the firing profile of the considered

LTCC with regard to heating rate and intermediate

dwell time for the preheat phase of firing process.

Based on the results of TGA it becomes evident that

for the burnout stage of the GC-tape firing process

an appropriate dwell time depending on the mass of

LTCC-module has to be established. It has to be

provided that the PMMA starts to pyrolyze slowly

which enables to exhaust the gaseous decomposition

products via the channels. In contrast a rapid

decomposition of the organic filler induces a sudden

intensified production of gaseous burnout products

which cannot escape adequately via the channels and

finally results in a destruction of the LTCC module.

The burnout phase of the firing schedule has to be

adapted to these requirements whereas an adequate

dwell time (depending on the mass of the LTCC

module) at the critical degradation temperature of

the filler is of great importance. Practical

experiments have shown that a dwell time at 250 °C

is ignorable if an adequate slow heat rate is selected.

A sufficient long dwell time at 350 °C for the total

binder burnout is obligatory to be provided.

Firing of the samples has been conducted in a

box furnace of Heraeus (heating rate for temperature

range 25 °C – 350 °C: 0.8 °C/min, holding time at

350 °C: 6 h, heating rate for temperature range 350

°C – 500 °C: 0.8 °C, holding time at 500 °C: 4 h,

heating rate for temperature range 500 °C – 920 °C:

1.8 °C/min, holding time at peak temperature of 920

°C: 1 h, cooling rate: 2 °C/min). Another parameter,

which has to be considered during the firing cycle,

was the temperature distribution within the sample.

A temperature gradient > 6 °C within the ceramic

module during the total firing cycle has to be

avoided with regard to potential crack formation and

fracture of the module (Kluge, 2006).

4 DEVICE CHARACTERIZATION

The influence of arrangement of inlet-channels

along the perimeter of the reactor cell and the sink

on the bottom of the cell on the flow performance of

liquids within the reactor cell has been studied for

different flow conditions by means of FEA using the

FLUENT program package. The characterization of

the device is based on time - dependent flow

simulations. The numerical model describes the flow

of dyed and pure water entering through different

inlets at varying mass flow rates and passing into the

spherical cavity of the reactor cell and the channel

system. The local distribution of fluid at the

spectroscopic port is predicted and contrasted with

the results attained by spectroscopic analyses of light

absorption at the considered port.

Exemplarily the flow characteristic for a

representative assumption has been derived by

numerical simulation and validated by experiment.

The flow condition described starts with filling the

cavity by injection of pure water at the radial inlets 1

and 2 (figure 1 and 7). The mixing initiated as a step

inflow of dyed water (0.5 % trypan blue) is imposed

on the radial inlet 2, which means that a stream of

constant mass flow–rate and dye–concentration is

applied at the respective inlet (figure 7). In the

meantime the average residence time of dye

concentration is measured at the optical port (figure

1).

The propagation of the streamlines depends

strongly on the position of the inlet along the

meridian of the spherical cavity as can be seen in

figure 7 for the corresponding inlet arrangement.

BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices

The inlet 1 (“In 1”) is placed 0.45 mm higher than

inlet 2 (“In 2”). Within a period of 2.5 s the

streamlines of the fluid entering inlet 1 are already

diffusing into the interconnecting channels while

those of the fluid starting from inlet 2 are still ending

in the mixing chamber.

Figure 7: Propagation of streamlines of fluids entering

inlet “In 1” (blue) and inlet “In 2” (red) with flow rates of

2 ml/min within a period of 2.5 s.

The model of the complete module was

constructed and meshed with the program package

GAMBIT (Fluent Inc.) Mesh elements were mainly

hexahedral and only few tetrahedral elements were

required for completely meshing the module. In all,

the model (including the recirculation tube) has a

volume of 3 cm³ and includes a total number of

292,194 mesh elements, of which 161,374 are

hexahedral, 128,737 are tetrahedral and 2,083 are

pyramidal.

The curves in figure 8 describe the increase of

the dye volume in the optical port from initially pure

water to the mixed state. For the supply of inlets

with liquids two Flodos Stepdos 03 pumps were

used and for providing the flow circulation a Flodos

NF 5 diaphragm pump was applied. The flow rates

considered in simulation and experiment are 2

ml/min at both inlets. At the optical port the

absorbance was measured using a uv-vis array-

spectrometer (EPP2000-50 µm Slit, StellarNet Inc.).

The absorbance–characteristic in a scaled

presentation is shown in figure 8. The steady state

mixed flow condition at the optical port corresponds

to a dye concentration of 47 %. It can be noticed that

the ideal and the computed curves are almost

identical. However, the experimentally derived

characteristic shows a slightly less rate of rise as

well as oscillating peaks. The oscillating peaks may

be attributed to the pulsating characteristic of the

pumps in use. Furthermore it must be noted that the

equilibrated state concentration condition is attained

also within the same period if the injection flow rate

at the inlet ports has been varied synchronously

while keeping the total sum of mass flow rates

constant. If all three inlet ports are used

simultaneously for the supply of the module

different mass flow rates have to be selected to

provide the desired mean concentration profile at the

optical port.

Figure 8: Dye concentration vs. time characteristic at the

optical port.

Besides the performed dye distribution tests, the

functionality of the microfluidic reaction module has

been demonstrated by observing the time evolution

of the iodine concentration due to the iodide-chlorite

reaction, which involves only 2 inorganic ions and is

characterized by an established set of reaction

mechanisms according to the LLKE-model, which is

named after its authors Lengyel, Li, Kustin and

Epstein (Kügler, 2008). This complex reaction

model involves an autocatalytic step and the

coupling of different reactions can cause complex

reaction patterns like oscillatory behaviour when

measured under certain conditions in continuous

flow. An intermediate of the chemical reaction leads

also to production of the starting compound, which

accelerates the reaction until the respective reaction

partner is used up, but when the reaction is

performed under continuous flow conditions

oscillatory behaviour results which can be observed

continuously. Figure 9 shows the oscillations

observed for the iodine absorption measured around

470 nm (i.e. in a range between 456 to 484 nm).

This means, that the optical density of the product is

measured as a mean value over 60 pixels of the

CCD-array (full black curve). The red curve shows

the final result when the time dependence is

additionally averaged over 20 seconds. The figure

demonstrates that such an autocatalytic reaction can

be measured in the microfluidic reaction module,

although the total reaction volume and also the

optical path of the optical detection port is very

A BIOLOGICAL MONITORING MODULE BASED ON A CERAMIC MICROFLUIDIC PLATFORM

small. Nevertheless oscillatory behaviour can also

found under such conditions. The device is sensitive

enough to record small concentration changes giving

rise to changes in the optical density below 0.001. In

future experiments the microfluidic module will be

used for measuring complex kinetics in biochemical

systems. In that case, limited amounts of reactive

compounds, e.g. of enzymes, are available and the

use of small reaction volumes is an essential

prerequisite to allow quantitative measurements.

Figure 9: Oscillations of the I

absorption observed in the

module produced by the reaction of I

and ClO

continuous flow.

5 CONCLUSIONS

The influence of different ceramic materials on the

viability and proliferation of HeLa cells has been

tested as a first basic characterization of the

biocompatibility. In respect to their use in micro

fluidic devices the growth of cells in channels of

different width has been visualized. The LTCC-

technology has been proved as a very versatile

method to build up complex three-dimensional

multilevel channel structures including even large-

volume cavities, which are suitable for biological

and diagnostic applications.

ACKNOWLEDGEMENTS

The financial support of this work by the WWTF,

project MA05 "Inverse methods in biology and

chemistry” as well as by the FFG, project N209

"Nanoflu" is greatly acknowledged by the authors.

This project is integrated within EU 4M Project

(Contract Number NMP2-CT-2004-500274). The

maintenance with ceramic tapes and many useful

advices during the course of tape processing by Dr.

C. P. Kluge (CeramTec AG) are especially

appreciated.

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