MANMADE spores, replicas of one of nature鈥檚 most resilient creations, have been built in the lab using an ingenious technique in which the porous, hollow particles assemble themselves. Among a host of potential uses, their creators suggest they could deliver measured drug doses or make drugs inhalable.
Spores are extremely stable structures made by some lower plants, fungi and protozoans. The spores of the perennial plant Selaginella are so robust their remains have survived 50 million years. Till now it has been almost impossible to mimic their structure from scratch, but botanist Alan Hemsley and chemist Peter Griffiths at Cardiff University in the UK had a hunch that the unusual behaviour of 鈥渃olloidal鈥� particles could provide the key.
Colloids are made up of very fine particles of one substance held in another. Though they are not true solutions, the particles never separate out and cannot be filtered off. Examples of colloids include aerosols such as cigarette smoke, and emulsions such as milk. The key feature of colloids that Hemsley and Griffiths harnessed is that under different conditions the colloidal particles can self-assemble to form complex structures.
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The team created a range of colloids using chemicals chosen to mimic those that form critical structures in spores. By controlling the concentrations and rates of stirring and mixing, they made complex spore-like structures emerge.
For example, a colloid of polystyrene, sodium chloride and other ingredients, when shaken with cyclohexane, formed artificial spores in which the polystyrene built the main structure and cyclohexane took on the role of lipids in natural spores. 鈥淚t鈥檚 a one-step process because the spores build themselves,鈥� says Hemsley. 鈥淎nd we have made them using a very simple technique so they could be made in bulk,鈥� says Griffiths.
The researchers found they could control the size and shape of holes in the artificial spores (see Photograph). They suggest this could be exploited to deliver an active ingredient or drug, with the size of the hole dictating how quickly the drug is released.
鈥淪pores are wonderful because they float in the air,鈥� says colloid specialist Terence Cosgrove at the University of Bristol. That makes them ideal for delivering drugs, which could be inhaled, for example. But whether artificial spores loaded with drugs would behave the same way as natural spores is unclear, he says.
Another possible use is to improve the quality of ink-jet printing. Paper covered with artificial spores could contain the ink fired by an ink-jet, preventing it spreading after it hits the paper. Hemsley鈥檚 colleagues at Cardiff are now testing this application.