Hydrogels have emerged as a promising alternative to overcome shortcomings that affect traditional biomedical treatments. They have gained increasing attention in the field of tissue engineering (TE) and drug delivery thanks to their high-water content, which provides a physiologically similar environment to the native extracellular matrix, and the capability of encapsulating and transferring their payload (e.g., drugs or biomolecules) to the surrounding tissues. Among the wide plethora of existing hydrogel platforms, hydrogels based on Schiff-base linkages possess favourable properties (e.g., high reactivity under mild conditions, stability under physiological conditions, self-healing ability, pH-responsiveness) that make them attractive to prepare injectable formulations. In this scenario, this thesis work aimed to design new in situ forming injectable hydrogels based on Schiff-base linkages exploiting the versatility of poly(urethane)s (PUs) as constituent materials for TE and drug delivery applications.