Making particles that can discharge medicines into our bodies -- like slow-release fertiliser in a pot plant -- is a great idea, but it's really hard to get it to work.

Finding material that's non-toxic is one thing: keeping it from being filtered out of the bloodstream, or knocked off by the immune system, is quite another. But ANSTO materials scientist Dr Chris Barbé reckons he's cracked it.

Called MuCaps, they're tiny, porous particles of silica which have active compounds trapped in their structure that slowly diffuse out.

"We can do funky chemistry with silica, which just can't be done with other things," Chris said. "We take silicates, add water with the active ingredient dissolved in it, and as the silica network builds itself in 3-D, the active ingredient gets physically incorporated into the structure.

"When you put MuCaps back in water, or into our bodies, which are mainly water, the active ingredient slowly comes out," he explained.

Chris and his team can make specks of silica with diameters ranging from 0.1 millimetres down to 10 nanometres (which is ten thousand times smaller). They don't use fiddly grinding or milling techniques to make particles of different sizes, they simply alter the recipe of the chemical soup in which they're grown.

"The trick to controlling the size of the particles is to use an emulsion, such as vinegar in oil, and make the particle inside the droplets of vinegar," Chris said. "By controlling the size of the droplets, we control the size of the particles."

Tweaking the acidity of the mix also affects the structure of the silica lattice. An acidic solution produces small gaps; basic solutions produce large ones.

A micrograph of nano particles used for medical applications

As Chris put it, "When the pores are small, the molecules struggle to get out, like a wombat wriggling out of a narrow burrow."

So, controlling the size of the gaps in the lattice also controls the rate at which the active ingredient is released. Chris says they can make this anywhere from hours to months.

When it comes to matters medical,
the neat thing about silica is the way
it slips past our immune system. This is because at first glance, silica looks as though it belongs (chemically speaking)
so it doesn't get tagged with the
immunological equivalent of a post-it
note marking it for destruction.

But these active ingredients don't have to be medical in nature. MuCaps are what Chris refers to as a generic technology -- which means they can be used in lots of ways. So far, he's had interest from companies wanting to release enzyme in washing powder, flavours in food, oils in perfumes and biocides in paint.