4 July 2005: Chemists send organic particles to print

US chemists have developed a lithography process for generating organic particles of any size and shape, and produced some of the smallest ever drug delivery particles.

’Our method, for the first time, opens the world’s door to marrying organic materials to nanotechnology,’ said lead researcher Joseph DeSimone of the University of North Carolina at Chapel Hill. ’Biology, after all, is almost exclusively organic materials.’

The process, which DeSimone and his team have called Print (particle replication in nonwetting templates), is a variant of imprint lithography, in which particles are created by pressing a mould onto a thin film of some desired material. In traditional imprint lithography, this often leaves a thin connecting film between the individual particles, which is known as the ’scum layer’ and is analgous to the underlying layer formed when a mould is pressed into clay. Removing this layer requires harsh treatments, such as solvent processing, which can damage organic particles.

In Print, DeSimone and his team use moulds made of photocurable perfluoropolyether (PFPE) and place the desired material onto a highly fluorinated surface. Both the PFPE mould and the fluorinated surface are nonwetting to organic materials, which means that the mould and surface form a reversible seal that forces all the desired material into the confines of the mould. This produces individual particles with no connecting scum layer.

The chemists have used Print to create nanoparticles of many different shapes and sizes from such biocompatible organic materials as poly(d-lactic acid), polypyrrole and polyethylene glycol (PEG). They have also incorporated various bioactive agents, such as proteins and small-molecule drugs, into PEG particles under 200nm in size, by adding the agents to the PEG precursor solution prior to particle formation. DeSimone’s team also claim to have created the first synthetic viruses by incorporating DNA strands into the particles.

The organic particles are collected by gliding a fine blade across the flat surface, which DeSimone says lends itself to developing Print as a continuous manufacturing process. He has set up a new company, Liquidia Technologies, to commercialise the process. Jon Evans