Elastin is a structural protein found in mammals that confers elasticity to connective tissues. Examples for the function of elastin are the elasticity of big blood vessels such as the aorta or the dimensional stability of pulmonary alveolis. Elastin is made up of two domain types: A hydrophobic domain consisting of repeats of oligopeptides rich in glycin, alanine, valine and proline alternating with a hydrophilic domain that also incorporates lysine residues.

Soluble elastin is secreted by the cells and covalently linked by its lysine residues through an enzymatic process. Thereby an elastin-network is formed that is composed of elastic fibers and is able to be reversibly stretched for some of its own magnitudes.

The artificial elastin 100xELP has high similarity to human elastin and consists of oligomeric repeats of the pentapaptide Val-Pro-Gly-Xaa-Gly (Xaa – any amino acid but proline). Hence it solely consists of units that resemble the hydrophobic domain of natural elastin. Therefore it is not able to be linked to a network. However, 100xELP exhibits a good ability to be solved in aqueous solution depending on the salt concentration and temperature. It can undergo an inverse transition, i.e. the protein is soluble in an aqueous solution below its transition temperature but insoluble above this critical value.