Method for preparing an injectable cross-linked hydrogel, hydrogel obtained; and use of the obtained hydrogel

A method for preparing an injectable hydrogel of crosslinked hyaluronic acid, or one of the salts thereof, and optionally the injectable hydrogel further comprising other biocompatible polymers, the method comprising at least the following steps:

• preparing a hydrogel by integrating at least one crosslinking step of the hyaluronic acid in an aqueous solution, wherein the at least one cross-linking step is performed in an inert atmosphere;
• leaving the formed hydrogel to swell in said aqueous solution;
• purifying the hydrogel;
• packaging the hydrogel in syringes or bottles;
• and
• sterilizing the packaged hydrogel;
• wherein the method further comprises performing mandatorily at least one extraction step of the oxygen contained in the hydrogel, the extraction step being performed after the crosslinking step of the hyaluronic acid in the inert atmosphere and purification of said hydrogel and before and/or at the time of packaging the hydrogel;
• the extraction step comprising performing at least one extraction cycle in a suitable container, the extraction cycle comprising the following successive steps:
• placing the container containing the hydrogel under a vacuum at a pressure (p) lower than atmospheric pressure for a time (t);
• and
• breaking the vacuum after time (t) by adding an adapted quantity of a gas other than oxygen, wherein variation of the elastic moduli G′ of the hydrogel is less than or equal to 10% when measured at 0.7 Hz after a storage time of 12 months at ambient temperature.