The new technique, developed by Damien Mertz and Frank Caruso at the University of Melbourne in Australia with co-workers at the University of Strasbourg in France, involves binding isobutyramide (IBAM) grafts to proteins. The process involves inducing strong non-covalent bonds between the two structures, which results in the freestanding assembly of hollow protein capsules on the micron and sub-micron scales. The technique is straightforward and no catalysts or covalent linkers are required – as in conventional techniques – and the capsules produced are stable and strong.

“The first step in the assembly consists of modifying a silica template with IBAM groups followed by protein absorption on this template,” explained Mertz. “The protein surface can be ‘reinitiated’ with IBAM, through reactions with amine groups, and can then be coated with a second strata of protein. The protein capsules form once the template has been dissolved.”

The Australia-France team employed human serum albumin globular protein in their experiments. This protein is composed of 585 amino acids and is the most abundant protein in human blood plasma.

Designer capsules

The diameter, thickness and composition of the protein capsules can be engineered, adds Mertz, and they can be functionalized with various biological ligands. “What is more, they are not toxic to biological cells and are biodegradable. And the fact that they are simple to make also means that they could easily be fabricated in large quantities.”

Such capsules functionalized with enzymes, nucleic acids and sugars, for example, could find applications in areas such as targeted drug delivery, he told

Spurred on by these results, the Australia-France team now plans to investigate the interaction between IBAM and proteins in more detail. The researchers first reported on assemblies made from IBAM and various biomolecules, such as proteins, nucleic acids and polysaccharides, last year. They have also recently shown that similar protein capsules can be loaded with an anticancer drug that can be released under biological conditions – for example, via so-called protease degradation.

The current work is detailed in ACS Nano.