Ester coupling of ibuprofen in hydrogel matrix: A facile one-step strategy for controlled anti-inflammatory drug release

Ibuprofen (IBU) is a non-steroidal anti-inflammatory drug (NSAID) commonly used in the treatment of pain, fever and inflammation. However, the administration of IBU in its free carboxylic acid form is strongly dependent on its limited solubility in aqueous solution. This mandates for an increased drug concentration to reach the therapeutic window, and promotes the alternative use of IBU sodium salt, even if this latter form poses significant constraints in terms of tunable release due to its uncontrolled and rapid diffusion. A potential solution is represented by oral administration through physical encapsulation of ibuprofen in designed carriers, despite this route limits the application of this therapeutic agent. In this work, we propose the covalent tethering of ibuprofen to a hydrogel matrix via esterification reaction. Exploiting the cleavability of the ester bond under physiological conditions, we propose a controlled drug delivery system where the whole drug payload can be released, thus overcoming the questioned aspects of over-dosage and solubility-dependent administration. In particular, we tested the biological activity of cleaved ibuprofen in terms of cyclooxygenase inhibition, reporting that chemical tethering did not alter the efficiency of the NSAID. Moreover, due to the sol-gel transition of the hydrogel matrix, these ibuprofen-functionalized hydrogels could be used as injectable tools in several clinical scenarios, performing a localized drug release and opening advanced avenues for in situ treatments.