Chips to mimic body environment for stem cell growth
Friday, 04 April 2008
By Graeme O'Neil
Stem cells are transforming medical research, promising a clinical
revolution in which doctors will employ embryonic and adult stem
cells to repair failing hearts, create new organs and tissues,
restore brains damaged by stroke or neurodegenerative disorders, and
treat hereditary defects.
However, before stem cells can realise their promise, researchers
must develop reliable systems to maintain and multiply them in
culture and learn how to manipulate the microenvironment to direct
cells into selected developmental pathways.
In other words, they must create particular microenvironments which
imitate the real environments in which they would function in the
body and in which stem cell research can be conducted.
To this end, Professor Min Gu and Dr Daniel Day, of the Centre for
Micro-Photonics at Swinburne University of Technology, are developing
microfluidic `lab-on-a-chip' devices.
Little larger than a microscope slide, the microfluidic chips will
contain tiny bioreactors, fed by microfluidic `plumbing' that will
supply controlled quantities of nutrients and cell growth factors
from on-board reservoirs, mimicking the natural milieu in which stem
cells replicate and differentiate into other cell types in the body's
tissues and organs.
Professor Gu says the chips are being designed to culture embryonic
stem cells, which can differentiate into any of the 210-odd different
cell types in the body. They will also be used to replicate adult
haemopoietic stem cells, which give rise to the specialised cells of
the blood and immune systems.
The Swinburne component is part of a major development program for
stem cell research involving the Australian Stem Cell Centre at
Monash University, the Monash University Centre for Green Chemistry,
CSIRO Molecular and Health Technologies, and the Cooperative Research
Centre for Polymers.
Professor Gu says the aim is to create designs for microfluidic chips
that can be mass-fabricated at low cost. Programmable and almost
maintenance-
laboratory experiments to Lilliputian dimensions.
Arrays of multi-chambered microfluidic chips will allow multiple
experiments to be run in parallel. Researchers will be able to
experimentally adjust each biochemical or physical parameter in the
bioreactors, and observe how stem cells respond to different
concentrations and combinations of nutrients and cytokines, as well
as changes in temperature, pressure or oxygen levels.
Professor Gu says the chips will help researchers determine the
conditions required to maintain embryonic and adult stem cells in an
undifferentiated state, and how to control their differentiation into
other cell types.
Associate Professor David Haylock, a senior research scientist with
the Australian Stem Cell Centre, says that if the project is
successful, it will take stem cell research and its clinical
applications to the next stage.
"There's no good technology for growing stem cells and their progeny
at the scale required for research or medical use," Dr Haylock
says. "The bioreactor would allow us to grow stem cells and explore
their full potential."
Microfluidic chips will allow researchers to conduct complex
experiments under highly controlled conditions that would normally
require costly, large-scale cell-culture equipment and monitoring
devices.
Where other research groups and companies are developing microfluidic
chips made of glass, silicon or polydimethylsiloxan
photolithography processes, the Swinburne researchers have developed
a manufacturing process using femtosecond lasers (a femtosecond is a
thousand-trillionth
the chips can be produced in a variety of polymers.
The technique, called `two-photon ionisation' focuses a high-energy
femtosecond pulse laser into the target substrate material, which can
be made from metal, glass or polymers. At the point where the laser
beam is focused, the energy from the laser ionises the material,
effectively removing it from the substrate. This method enables
microscopic resolution features to be fabricated in the substrate,
which can then be used as a master mould from which multiple copies
can be replicated.
Computers programmed with digital templates for the chip's components
will steer the focus point of the laser pulses through the substrate,
progressively building up complex three-dimensional shapes and
cavities.
At lower energies, the focused beam can be used to polymerise a
photosensitive resin, so structures can be etched into the chip
surface, or constructed from the resin, creating complex 3D networks
of microchannels and other microstructures.
Micropumps incorporated into the chips will pump precise quantities
of nutrients or cell growth factors through microfluidic circuits
into the bioreactor chambers containing the stem cells.
Professor Gu says the femtosecond lasers can also etch tiny optical
gratings or 3D photonic crystals into the material that are extremely
sensitive to optical changes in the cell microenvironment, such as
changing temperatures, pH levels or other conditions in the
bioreactor – including changes in the cells themselves.
By labelling antibodies with fluorescent molecules – fluorophores –
that emit specific colours under ultraviolet light, researchers can
observe the patterns of receptors expressed on the surface of the
cells. The combinations of receptors will reveal whether the stem
cells are in an undifferentiated state, or have begun to transform
into other cell lineages – and, if the latter, what type of cell will
emerge from the process.
Both the optical gratings and photonic crystals have been developed
for another of the centre's projects: to develop optical chips for
telecommunication.
The centre has also developed laser-based techniques for manipulating
micrometre-sized objects, which can be used to trap, observe and
manipulate living cells as tiny as a red blood cell.
A tightly focused laser beam can trap cells at a focal point defined
by the difference between the refractive index of the object and the
surrounding medium. The immobilised cells can then be manipulated and
studied.
Dr Haylock says thousands of the micro-scale bioreactors linked
together would enable researchers to grow stem cells "with exquisite
control" and in large numbers, representing a wide range of human
genotypes.
"Ideally, for therapeutic applications, they will allow us to culture
the recipient's own cells," he says. This would avoid the risk of
patients rejecting grafted cells, which happens if the donor and
recipient have imperfectly matched immune-system genes – a problem
that can affect organ transplants.
Dr Haylock says it is still not clear if embryonic stem (ES) cells
will provoke rejection reactions or be universally suitable for
patients. "ES cells are the great hope, and if there are rejection
problems, perhaps we can match the immune-system type of the cell to
the recipient."
He says the number of different ES cell lines in culture presently
numbers in the "many 10s", so they represent only a small sample of
the diversity of human genotypes. The bioreactor chip would be
essential for maintaining a more comprehensive range of ES cell
genotypes.
"Few of the existing ES cell lines are well-characterised
biologically, and we are only able to grow a handful of specialised
cell types from them.
"ES cells have the potential to differentiate into any of the more
than 200 human cell types, but each will have different growth
requirements. Microbioreactors will allow those conditions to be
altered very precisely."
Dr Haylock says it is likely that rather than being grown in
suspension, in solutions, the cells will be grown on micro-textured
surfaces with nutrients and cell growth factors embedded in them.
The partners in the research consortium developing the microfluidic-
chip bioreactors are already planning to establish a company to
manufacture the chips.
At Swinburne's Centre for Micro-Photonics, Dr Daniel Day
explains: "We're still in the pre-prototype phase, assessing a number
of design aspects, but we should have a first-generation microfluidic
chip some time next year."
He says the diverse, but complementary, skills offered by members of
the consortium should create a range of commercial opportunities –
for example, microfluidic chips with which drug developers can test
experimental drugs on stem cells or differentiated cell lines.
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A story provided by Swinburne Magazine. This article is under
copyright; permission must be sought from Swinburne Magazine to
reproduce it.
http://www.sciencea
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StemCells subscribers may also be interested in these sites:
Children's Neurobiological Solutions
http://www.CNSfoundation.org/
Cord Blood Registry
http://www.CordBlood.com/at.cgi?a=150123
The CNS Healing Group
http://groups.yahoo.com/group/CNS_Healing
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