A miniature bio-reactor for the cultivation of cells aboard Spacelab is presented. Yeast cells are grown in a 3 milliliter reactor chamber. A supply of fresh nutrient medium is provided by a piezo-electric silicon micro-pump. In the reactor, pH, temperature, and redox potential are monitored and the pH is regulated at a constant value. The complete instrument is fitted in a standard experiment container of 63 x 63 x 85 mm. The bioreactor was used on the IML-2 mission in July 1994 and is being refurbished for a reflight in the spring of 1996

Arquint, Philippe

Bechler, Birgitt

Boillat, Marc A.

Cogoli, Augusto

deRooij, Nico F.

Gass, Volker

Ivorra, Marie-Therese

Jeanneret, Sylvain

vanderSchoot, Bart H.

Walther, Isabelle

English

NASA Technical Reports Server

DEVELOPMENT OF A SPACE BIOREACTOR USING
MICROTECHNOLOGY _ / / 6
Philippe Arquint 1, Birgitt Bechler 2, Marc A. Boillat 1, Augusto Cogoli 2, Nico F. de Rooij 1, Volker
Gass 3, Marie-Thrrrse Ivorra 3, Sylvaln Jeanneret 1, Ban H. van der Schoot 1 and Isabelle Walther 2
lInstitute of Microtechnology, University of Neuchfitel,
Rue Jaquet Droz 1, CH-2007 Neuchfitel, Switzerland
2Space Biology Group ETHZ, CH-8005 Ziirich, Switzerland
3Mecanex SA, CH- 1260 Nyon, Switzerland
Abstract
A miniature bioreactor for the cultivation of cells aboard Spacelab is presented. Yeast cells are grown
in a 3 milliliter reactor chamber. Supply of fresh nutrient medium is provided by a piezo-electric silicon
micropump. In the reactor chamber, pH, temperature and redox potential are monitored and the pH is
regulated at a constant value. The complete instrument is fitted in a standard experiment container of
63x63×85mm. The bioreactor has been used on the IML-2 mission in July 1994 and is currently being
refurbished for a reflight in the spring of 1996.
Introduction
Experiments with cells in space have shown that important cellular functions are changed in
microgravity [1]. These findings are of great interest for fundamental research as well as for possible
biotechnological applications. For the cultivation of cells aboard spacelab, a miniature bioreactor is
developed. The objective is to evaluate in a controlled bioreactor experiment (chemostat cultivation)
the effects of mixing and stirring on the growth characteristics of yeast cells. The experiment has been
selected by ESA for the IML-2 mission which took place in July 1994. The experiment was located in
Biorack, a multi-user facility developed by ESA to host biological experiments in Spacelab. The
individual experiments are mounted in standard containers of various dimensions. The Type II
container allocated for this experiment has internal dimensions of 63×63 x85mm.
The design of the Space Bioreactor includes the following features;
• Supply of fresh medium to cells in the reactor chamber (working volume 3 ml) over a period of 9
days at an adjustable rate (0.2 - 1.5 ml/h)
• Measurement of pH, temperature and redox potential of the culture
• Control of pH of the culture
• On-line data transfer to ground control
In view of the complexity of the instrument and the limited dimensions of the Type II container, the
application of silicon technology to provide both the sensors and a micromachined pump and flow
sensor are of a distinct advantage.
During its first flight on IML-2 in July 1994, the technical feasibility of the bioreactor concept has
clearly been demonstrated. Due to excessive temperatures in the laboratory where the flight
experiment had to be prepared, the experiment has not yet given all the expected biological results.
Therefore, a reflight opportunity has been granted and the bioreactor is currently being prepared for
https://ntrs.nasa.gov/search.jsp?R=19960054136 2020-06-16T03:42:35+00:00Z
the STS-76 missionin the spring of 1996. In order to makethe liquid handlingmore robust, a
controlledflow systemwill beimplemented.
Experimental Setup
Figure 1 shows the individual elements of the bioreactor and their interconnections. In the following
section, these e!ements will be briefly described. It is interesting to note that the reactor chamber, the
heart of the instrument, occupies less than 1% of the volume available in the experiment container. The
largest volume is reserved for the nutrient medium reservoir. Both the fresh and used medium reservoir
are flexible and while the first is emptied during the experiment, the second takes its place while filling
up.
gas exchange_
output valve_
used medium
pH control
reactor3 mlchamber
<_ f_OW _RSOF
stirrer
micropump
filtl_r, 0.2_
fresh medium
serial data analog data { pH, T, pH control
transfer output oxygen, flow,pressure
control
electronics
Figure 1. Principal elements of the miniature bioreactor
Pumping system
The supply of fresh medium to the reactor chamber is accomplished with a microfabricated pump [2,
3]. It is a membrane pump consisting of a structured silicon part sandwiched between two glass plates.
The silicon forms two passive one-way valves that close on the thicker of the two glass layers. The
thinner glass forms the membrane that is driven by a ceramic piezo-electric disk. When used as such,
the flow rate of the pump is depending on the output pressure that has to be provided. Unforeseen
variations in the bioreactor chamber pressure were the cause that during the first flight fluid delivery
was not sufficiently controlled. For the reflight, a flow sensor is added so that the pump can operate in
a closed loop control system and supply the required flow independent of output pressure [4].
Sensors
The sensors for the bioreactor, a pH-ISFET, a temperature sensitive diode and a thin film platinum
redox electrode have all been integrated on a single chip that measures 3.5x3.5 mm. The sensor chip is
mounted on a cartier that is inserted in the reactor chamber so that the sensor surface becomes part of
the chamber wall without creation of dead angles. The reference electrode used in connection with the
chemical sensors is a gel-filled Ag/AgCI electrode.
pH-control
For optimal growth conditions for the cells, the pH in the reactor has to be maintained at a constant
value. During normal growth, yeast cells will acidify the medium for which a compensation is required.
In view of the risk connected to the use of concentrated NaOH for this purpose, an electrochemical pH
control is developed. A titanium electrode in the reactor chamber acts as a cathode for the electrolysis
of water to produce hydroxyl ions. As a counter electrode a silver wire is used, embedded in a KCI
loaded gel. The counter electrode compartment is separated from the reactor chamber by a Nation
membrane. Electrochemical compensation of the pH can be controlled very precise and avoids the
need for an additional pump for NaOH dosage.
Electronic Circuits
The operation of the bioreactor is controlled by an Intel 87C51 microcontroller. The circuitry consists
further of amplifiers for the sensors, a high voltage driver circuit for the micropump and a current
source for pH-control. The pump operation is governed by an analog control system, the set-point of
which is controlled by the microprocessor. The current source for pH-control is galvanically isolated
from the rest of the circuit to avoid interference with the sensor signals. Relevant data are available on
one multiplexed analog output channel. For preparation of the experiment before the flight a serial data
connection is provided and the instrument can be directly interfaced to a standard personal computer.
Figure 2 shows the basic electronic connections in the instrument. The circuits are built up with surface
mounted components on two printed circuit boards
pressure
now
0-200V piezo pump j
/
oxygen _ Analog data output
_7
sensors J_ +5V
-- +10V
current source -- GND
-- Your
pl-t control stirrer motor
Biorack Interface
Figure 2. Electronic circuit of the bioreactor
Results
This project has started in 1991. After 15
months a breadboard model was presented to
show the feasibility. After that the bioreactor
has been qualified in vibration and EMC tests
and, above all, in biological performance
experiments as described in [5]. Figure 3
shows a photograph of an engineering model
of the bioreactor that has been used for a
number of the qualification tests. The first
flight of the bioreactor has been relatively
successful and currently the second flight is in
preparation.
Conclusion
The development of a miniature bioreactor
with microfabricated components for fluid
handling and silicon sensors shows a
promising outlook for their application in
micro gravity experiments. In view of the
special requirements for this kind of
application, the bioreactor is an attractive
showcase for microsystem technology.
Acknowledgment
The authors wish to thank the teams of the
PRODEX program of ESA and of the Swiss
Federal Office of Science and Education for
their support in this project.
Figure 3. Engineering model of the space
bioreactor mounted on the base of a Type I1
experiment container.
References
1 F.K. Gmander, C.-G. Nordau, A. Tschopp, B. Huber and A. Cogoli, J. Biotechnol. 7 (1988)
217-228
2 H.T.G. van Lintel, F. C. M. van der Pol and S. Bouwstra, Sensors and Actuators, 15 (1988)
153-167
3 B.H. van der Schoot, S. Jeanneret, A. van den Berg and N. F. de Rooij, Sensors and Actuators
B, 6 (1992) 57-60
4 M.A. Boillat, A. J. van der Wiel, A. C. Hoogerwerf, N. F. de Rooij, Proceedings IEEE MEMS
1995, pp 350-352, Amsterdam, the Netherlands, January 29-February 2, 1995
5 I. Walther, B. H. van der Schoot, S. Jeanneret, Ph. Arquint, N. F. de Rooij, V. Gass, B. Bechler,
G Lorenzi, A. Cogoli, J. Biotechnology 38 (1994) 21-32


Development of a Space Bioreactor using Microtechnology

Development of a Space Bioreactor using Microtechnology

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