A microfluidic device technique called stop-flow lithography, for making custom designed polymeric particles with complex geometric shapes, has been developed by US researchers.

Patrick Doyle and colleagues from MIT are working on methods for synthesising particles with complex geometric shapes. While spherical particles are widely used in applications like optical devices, drug delivery and diagnostics, more complicated particles could enable new technologies in these areas, but they are difficult to make. Building on his team's previous work to face this challenge, with a method combining microfluidics with projection-photolithography called continuous flow lithography (CFL), Doyle devised a technique called stop-flow lithography (SFL).

SFL gives a higher particle throughput and better particle resolution than CFL. A unique feature of the new method is that the particles formed are not just spherical - it can make a wide range of shapes. SFL also allows the formation of particles in biocompatible and easily functionalised materials that are not typically amenable to photolithographic methods.

Doyle hopes to expand the range of particle morphologies and materials accessible to SFL. 'We are also looking at several potentially interesting applications for these particles in diagnostics as well as in conducting fundamental studies on colloidal assembly and rheology,' he said.

A challenge for the future is the scale-up of particle throughput to match current industrial processes. 'This is not so much of a concern for niche applications enabled by complex particles where no alternative technology exists and only small volumes of particles are desired. However, it is important when particles made using microfluidic techniques are sought to be used in more routine applications such as paints or coatings,' said Doyle.

Elinor Richards