Try to stick a piece of Scotch tape underwater or on a wet surface: you will notice it won’t work. Water is one of the worst enemy for adhesives, drastically undermining their performance. However the demand for glues that can effectively function in wet environments (e.g. the human body) is pretty high: in the medical field, for example, injectable adhesives, when properly designed, could replace stitches and staples for soft tissue repair, to the delight of both surgeons and patients. In nature, many aquatic organisms have solved most of the challenges related with underwater adhesion, developing glues which set underwater because of a change in the environmental conditions (pH, exposure to oxygen..). In this thesis, we took the sandcastle worm, a seawater organism which build its own shell connecting sand-grains with a glue known as complex coacervate, as a source of inspiration to develop and optimise an injectable adhesive: this formulation which is liquid at preparation conditions, allowing injection through a syringe, turns into a tough solid when released in an aqueous environment resembling physiological conditions, enabling the formation of a strong adhesive which attaches to different types of surfaces. The liquid-to-solid transition is only ascribed to the formation of non-covalent interactions due to a change in the environmental conditions (higher temperature, lower salinity), similarly to what is observed in natural-based adhesives.