A biocompatible hydrogel has between 0.3% and 30% by weight of dry matter of a copolymer formed at least from acrylamide, chitosan and N,N′-methylenebisacrylamide, as well as a diffusing agent. The diffusing agent is advantageously selected from the group consisting of inert ingredients which have biomechanical properties and active ingredients. A method of manufacturing the hydrogel by copolymerizing, washing, and adding the diffusing agent is provided, as well as a mechanical visco-supplementation system adapted for external or internal use that includes the hydrogel, and an external or internal mechanical visco-supplementation kit including an acrylamide and chitosan copolymer crosslinked with N,N′-methylenebisacrylamide, and a diffusing agent in solid phase or in suspension, the copolymer and the diffusing agent having been previously mixed in the form of a hydrogel during manufacture or being adapted to be mixed extemporaneously to form a hydrogel.