have both hydrophobic and hydrophilic character. Peptide amphiphiles are a class of molecules consisting of either hydrophobic and hydrophilic peptide sequences, or a hydrophilic peptide with an attached hydrophobic group, which is usually an alkyl chain. The structure of a peptide amphiphiles has four key domains. Firstly there is a hydrophobic section, typically an alkyl chain. Secondly there is the peptide sequence which forms intermolecular hydrogen bonding. Thirdly there is a section of charged amino acid residues to enhance the solubility of the peptide in water. The final structural feature allows the peptide to interact with biomolecules, cells, or proteins, and this is often through epitopes (part of antigens recognised by the immune system). As with other amphiphilic molecules, above a critical aggregation concentration peptide amphiphiles associate through non-covalent interactions to form ordered assemblies of different sizes, from nanometres to microns. Molecules that contain both polar and non-polar elements minimise unfavourable interactions with the aqueous environment via aggregation, which allows the hydrophilic moieties to be exposed to the aqueous environment, and the hydrophobic moieties to be protected. When aggregation occurs, a variety of assemblies can be formed depending on many parameters such as concentration, pH, temperature and geometry. The assemblies formed range from micelles to bilayer structures, such as vesicles, as well as fibrils and gels. Micelles consist of a hydrophobic inner core surrounded by a hydrophilic outer shell that is exposed to a solvent, and their structures can be spheres, disks or wormlike assemblies. Micelles form spontaneously when the concentration is above a critical micelle concentration and temperature. Amphiphiles with an intermediate level of hydrophobicity prefer to assemble into bilayer vesicles. Vesicles are spherical, hollow, lamellar structures that surround an aqueous core. The hydrophobic moiety faces inwards and forms the inner section of the bilayer, and the hydrophilic moiety is exposed to the aqueous environment on the inner and outer surface. Micelle structures have a hydrophobic interior and hydrophilic exterior. There is normally a distinct relationship between the amphiphilic character of a peptide and its function in that the amphiphilic character determines the self-assembly properties, and in turn this is what gives the peptide its functionality. The level of amphiphilicity can vary significantly in peptides and proteins; as such they can display regions that are either hydrophobic or hydrophilic in nature. An example of this is the cylindrical structure of an α-helix, as it could contain a section of