Great shapes

A new technique could enable manufacturers to produce microstructured polymer surfaces at lower cost and with more flexibility. Siobhan Wagner reports


A microstructure manufacturing technique being developed by university researchers could create plastic devices for micro-fluidic systems such as mixers, separators, valves and pumps.

The technology from Heriot-Watt University, Edinburgh, uses a micro-structured conductive metal stamper called a micro-stencil and electrostatic forces to shape a polymer surface.

The principle behind the process is similar to electrostatic printing or copying, in which electrostatic forces are used to form an image in powder or ink directly on the surface to be printed.

Like electrostatic printing, Heriot-Watt’s high-resolution technology is non-contact. But instead of creating printed documents, it can be used to create both flat and 3D surfaces, including internal and external radiuses.

‘The set-up really is simple,’ said Weixing Yu, a Heriot-Watt research associate working on the development. ‘The process begins by spin coating a polymer on to a conductive surface. You then need a high-voltage power supply to apply the voltage onto the micro-stencil and the polymer coated surface.’

In some cases, he said, a hot plate is needed to melt the polymer from below while the voltage is being applied. After a few minutes the polymer will begin redistributing to form the expected microstructures. ‘You will be able to see the polymer growth during the manufacture process,’ said Yu.

The microstructures will then permanently form after cooling down or curing with ultraviolet exposure, depending on the polymeric material.

Existing microstructure manufacturing techniques such as photolithography are typically suited to flat, smooth surfaces and have trouble shaping curved internal surfaces. They also require a dedicated, often expensive, manufacturing facility in a clean room environment.

‘With our technology there is no need for a clean room environment,’ said Yu. ‘No expensive facilities like UV-light source unit are involved and there is no need for photosensitive material.’

The main cost is the high voltage power supply. Yu said the electrostatic induced lithography technique has been proven to work with both DC voltage and AC voltage at frequencies up to 1kHz.

Yu said any polymer, in principle, should be suitable for this technique. ‘It has been possible to pattern polymers beyond the thickness specified by manufacturers,’ he said. ‘The fabrication cost can thereby be greatly reduced since thick photosensitive resists can be quite expensive. Also, there is no development process needed due to the one-step pattern formation after the polymer is fully formed.’

Yu and his colleagues are seeking parties interested in buying a licence to this technology, collaborating or forming a joint venture partnership to develop the technology for a variety of applications. Yu suggested the process could be used to create micro-fluidics and micro-medical devices or possibly micro-mechanisms for drug delivery inside the body.

The group recently demonstrated how the process could be used to create micro-channels in a novolak-based polymer. The polymer was originally spin-coated to a thickness of 25 microns and the researchers were able to create micro-channels with a depth of 83 microns and a width of 100 microns using the process.

The researchers believe the process could also be used for micro-moulding waveguides in polymers to guide electromagnetic waves, light or sound waves. It could even be used to create ‘smart’ polymer surfaces that are non-stick, anti-reflection or suppress radio frequency noise.