High speed patterning of hydrogels

Materials World magazine
1 Jun 2009

Direct laser interference lithography can speed up micropatterning of
hydrogels for biomedical applications with improved resolution, says Dr
Andrés Lasagni in Germany.

He has explored the technique, which irradiates the surface of a material (via a photoresist)with several laser beams simultaneously, to produce periodic microarrays of about four micrometres at a speed of up to several centimetres squared per second using a translation stage.

Depending on the number of laser beams applied, their intensity (nano- or femtosecond pulses) and the geometry configured, varying 2D and 3D patterns are created. Beam splitters are used to obtain the interference patterns.

Lasagni, Group Leader of the Fraunhofer Institute for Material and Beam Technology, says, ‘Interference lithography has been used to fabricate 3D photonic crystals [and] patterns on other materials According to our research, this is the first time that the technique has been used with hydrogels’.

Micropatterning of this biocompatible polymer aims to increase the materials’ surface area for use in culturing living cells for tissue engineering, biomedical sensing and active flow control in the body. In the case of pH electrodes, for example, periodic arrays ensure a shorter response time to obtain measurements.

However, existing patterning techniques have their limitations, explains Lasagni. Using conventional photolithographic methods, structures of hydrogel with resolution of ~50-100µm have been achieved. Meanwhile, although laser-scanning lithography achie-ves sequential fabrication of about five to 10µm, writing each high density pattern sequentially on a large area (mm-cm2) would take ‘several hours’.

Furthermore, laser interference lithography eliminates the need for transferring patterns using masks or moulds ‘If we want to fabricate a different structure, we just need to change the geometrical configuration of our optical system to control the intensity distribution of the interference pattern,’ says Lasagni. ‘In the case of other methods, you need to fabricate a new mask or mould, [which costs] up to several thousand euros per cm2.’

Professor Pankaj Vadgama, Director of the IRC in Biomedical Materials at Queen Mary University of London, UK, sees the potential of this research.

‘Patterned interfaces can lead to patterning of cells, [and] precise cell guidance [and] localisation of bio-active molecules and reactive and sensing surfaces. The work on laser interference has the ability to create some of these organised motifs.’

He adds, however, that ‘while it is not possible to guarantee immediate value for medicine, not least because of problems of mechanical strength and integrity of highly hydrated structures,
microscale patterning could help future rational design of implants and tissue engineering scaffolds’.

The research began by Lasagni at the Georgia Institute of Technology, USA, during his postdoctoral study in a group led by Professor Suman Das.

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