A self-assembling group of oligopeptides, which belong to a generation of hydrogels which form ionic self-complementary β-sheets, are the RADA16 peptides . These consist of periodic repeats of the RADA sequence, where positively charged arginine and negatively charged aspartic acid alternate with each other, resulting in the formation of the peptide Ac-RADARADARADARADA-NH2 (RADA16-I, commercially available as PuraMatrix TM ). Alanine, as a hydrophobic amino acid with hydrophilic residues, is believed to induce the formation of the beta-sheet . Gelation occurs spontaneously a couple of hours after dissolving this peptide in water or can be accelerated by adjusting the pH to neutral or by adding a buffer solution. It has previously been proven that it can be used as a drug release medium . Interestingly, RADA16-I has the capacity to reassemble to the same structure after sonication. Sonication presumably breaks some of the weak bonds while not affecting the β-sheet structure . As a result of this peculiarity, active compounds can easily be encapsulated into the hydrogel by incorporating them within the "dismantled" hydrogel. In this manner, the hydrogel traps active compounds when a gel is reformed and can be used for controlled drug release .