3D-photografting: the laser beam becomes a 3D 'painter'
28 August 2012
With laser beams, molecules can be fixed at exactly the right position in a three dimensional material. The method can be used to create micro sensors.
A 3D pattern produced by photografting (180µm 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 have developed a method to attach molecules in 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.
3D-photografting is the name given to the new technology. 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.
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 4µm could be obtained.
3D Photografting: a laser is shone into the hydrogel (yellow), attaching molecules to it at specific points in space (green)
“Much like an artist, placing colours at certain points on a canvas, we can place molecules in the hydrogel – but in three dimensions and with high precision”, says research team member, Aleksandr Ovsianikov.
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.
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.