Abstract: The present invention relates to a novel biopolymer consisting of a three-dimensional cross-linked mixture of (a) a cross-linking agent, activated with an activating agent, dissolved in a aqueous solution, and (b) a recombinant protein, namely polyubiquitin. The novel biopolymer is based on the cross-linking of ubiquitin (monomeric and/or polymeric) with a cross-linking agent, preferably bifunctionalized polyethylene oxides or a polyethylene glycol of various molecular masses (MW 2000 to 35 000 kDa), dissolved in aqueous solution in adequate proportions. The novel biopolymer offers a wide range of formulations since the number of ubiquitin units and cross-linking agent can vary both in length and ratio. The novel hydrogel is also biodegradable by a specific protease and is resistant to a wide range of other proteases.