Ionic- and photo-crosslinked hydrogels

The extracellular matrix (ECM) plays a pivotal role in cellular functions and tissue regeneration. Thus, the development of ECM-mimetics such as the hydrogels for tissue engineering has been increasing over the years. In particular, the search for methods that do not involve the addition of harsh chemicals and allow triggering hydrogels polymerization in situ is attracting a great deal of attention. Among the numerous physical and chemical crosslinking techniques, ionic- and photo-crosslinking of hydrogels are the most appealing. Ionic-crosslinking is based on the interaction between two opposite charged molecules, where hydrogels are usually formed by addition of ions. An advantage of this method is that hydrogel polymerization occurs without requiring the addition of chemical crosslinkers, which reduces toxicity. Photo-crosslinking is based on polymerization through the formation of covalent bonds triggered by free radical formation. Hydrogel formation can be easily tuned using a light source, and achieved at a physiological temperature, being quite advantageous. The relevant reports dealing with the design strategies using ionic- and photo-crosslinking methods, their advantages and disadvantages, the materials where these polymerization methods are frequently used, and applications are overviewed herein.