Architecture in the microcosm: biocolloids, self-assembly and pattern formation

Complex microscopic structure is a common feature in biology; the mineral shells of single–celled aquatic plants and animals such as diatoms, coccolithophores, radiolaria, the organic coatings of pollen grains and the surfaces of many seeds are all familiar examples. To the human eye, viewing this exquisite complexity, the method of construction is often far from obvious. Operating on the microscopic scale, at the size range called the colloidal dimension by synthetic chemists, is a gamut of interactions between the various components, which in many cases can lead to the formation of complex structure as an entropically favourable process. The importance of these ‘colloidal interactions’ is becoming increasingly apparent to biologists seeking the link between the genetic basis of structure and its ultimate expression. It is an emerging theme that through the evolutionary history of life, self–assembly of structure from colloidal building blocks has become integral to the process of organismal development. Colloidal interactions, however, are themselves complex. Chemists therefore tend to restrict the number and diversity of components within any system being studied in order to minimize this complexity. The interactions of spherical polystyrene particles in an aqueous or organic fluid, for example, have been well documented. The introduction of a third component into such a system clearly increases the diversity of interaction (and concomitantly, the difficulty of interpretation). Yet such a system is unrealistically simple to the biologist! The investigation of the behaviour of mixed colloidal systems is essential in the formulation of concepts regarding microscopic structural development in order to further both our understanding of biological construction, and to give rise to new developments in microscopic materials technology. Here we assess the developments in the understanding of colloidal systems in microscopic biological construction and demonstrate how these have given rise to new concepts regarding the relationships and evolution of the gene and organismal structure. We show how development of these new concepts may give rise to new materials with properties that have been tried and tested by organisms over millions of years of evolution and which, by their very nature, are more compatible with humans and their environment. We suggest how self–assembling microstructure might be used in the development of new surface coatings and drug delivery mechanisms.