US chemical engineers have developed a new, cheaper approach to designing microcapsules, tiny hollow spheres, used to deliver flavour enhancers.
The scientists at Rice University say their "fundamentally new" method involves mixing a solution of polymer and salt, with tiny particles of silica that contain just a few hundred atoms apiece.
Microcapsules are typically made by depositing layers of a coating onto a template or core, which has to be removed to form the hollow centre of the structure.
The core is usually burned out with high heat processes or dissolved with harsh chemicals. Both processes can damage the tiny containers and their cargo, from flavours to perfumes and drugs.
"Our process takes place almost instantaneously, at room temperature, under normal pressure, in water, and at mild pH values," said Wong, assistant professor of chemical and biomolecular engineering, and chemistry.
The spheres naturally become hollow during the self-assembly, which is highly unusual and is an advantage over existing methods, he adds.
Wong believes the technology could be used to make micro-bioreactors that could be used in large-scale chemical or drug production.
"In comparison with the other methods of making microcapsules, the scale-up for our process is simple and inexpensive," he said.
Wong claims his approach has advantages over other microcapsule production methods that involve spraying techniques. While these techniques can be scaled up, it is difficult to adjust the material properties of the resulting microcapsules.
"We've shown that we can tailor the properties of our self-assembled microcapsules - make them smaller, larger, thicker or thinner - simply by changing the ingredients we start with or by adjusting the mixing procedure," he says.
The underlying chemistry is so easy to perform that anyone who can pour, mix, and shake can make these microcapsules in less than a minute, adds the scientist.
Wong's process involves 'self-assembly,' meaning the hollow spheres form spontaneously when the nanoparticle building blocks are mixed with polymer and salt.
Because the process takes place in water, any chemical or drug that is suspended in the water gets trapped inside the hollow sphere when it forms.
Besides encapsulating flavour compounds and other molecular cargo, Wong's team suggest the microcapsules could also be used to encapsulate enzymes, complex biomolecules that govern many cellular processes.
Because enzymes are fragile and expensive, engineers would like to protect them during chemical reactions so they can be used many times over.
Wong's group has shown they can do that to by storing enzymes inside the microcapsules. Their data show that enzymes didn't leak through the walls of the microcapsules, but smaller molecules did, meaning the enzymes could still carry out their prime function and act as a catalyst for chemical reactions.