3D pattern, produced by photografting (180 µm wide). Fluorescent molecules are attached to the hydrogel, resulting in a microscopic 3D pattern. |
There
are many ways to create three dimensional objects on a micrometer
scale. But how can the chemical properties of a material be tuned at
micrometer precision? Scientists at the Vienna University of Technology
developed a method to attach molecules at exactly the right place. When
biological tissue is grown, this method can allow the positioning of
chemical signals, telling living cells where to attach. The new
technique also holds promise for sensor technology: A tiny three
dimensional “lab on a chip” could be created, in which accurately
positioned molecules react with substances from the environment.
Materials science and chemistry
“3D-photografting”
is the name of the new method. Two research teams from the Vienna
University of Technology collaborated closely to develop it: Professor
Jürgen Stampfl’s materials science team and Professor Robert Liska’s
research group for macromolecular chemistry.
Both
research groups have already attracted considerable attention in the
past, developing new kinds of 3D-printers. However, for the applications
on which the scientists are working on now, 3D-printing would not have
been useful: “Putting together a material from tiny building blocks with
different chemical properties would be extremely complicated,” says
Aleksandr Ovsianikov. “That is why we start from a three dimensional
scaffold and then attach the desired molecules at exactly the right
positions.”
Molecules in the hydrogel—locked into position by the laser
The
scientists start with a so-called hydrogel—a material made of
macromolecules, arranged in a loose meshwork. Between those molecules,
large pores remain, through which other molecules or even cells can
migrate.
3D photografting: A laser shines into the hydrogel (yellow), attaching molecules to it at specific points in space (green) |
Specially
selected molecules are introduced into the hydrogel meshwork, then
certain points are irradiated with a laser beam. At the positions where
the focused laser beam is most intense, a photochemically labile bond is
broken. That way, highly reactive intermediates are created which
locally attach to the hydrogel very quickly. The precision depends on
the laser’s lens system, at the Vienna University of Technology a
resolution of 4 µm could be obtained.
“Much
like an artist, placing colors at certain points of the canvas, we can
place molecules in the hydrogel—but in three dimensions and with high
precision,” says Aleksandr Ovsianikov.
Chemical signals for cells
This
method can be used to artificially grow biological tissue. Like a
climbing plant clinging to a rack, cells need some scaffold at which
they attach. In a natural tissue, the extracellular matrix does the
trick by using specific amino acid sequences to signal the cells, where
they are supposed to grow.
In
the lab, scientists are trying to use similar chemical signals. In
various experiments, cell attachment could be guided on two dimensional
surfaces, but in order to grow larger tissues with a specific inner
structure (such as capillaries), a truly three dimensional technique is
required.
Micro sensors detect molecules
Depending
on the application, different molecules can be used. 3D photografting
is not only useful for bio-engineering but also for other fields, such
as photovoltaics or sensor technology. In a very small space, molecules
can be positioned which attach to specific chemical substances and allow
their detection. A microscopic three-dimensional “lab on a chip”
becomes possible.
Source: Vienna University of Technology
