The invention relates to a method for preparing a cross-linked sterile and homogeneous hydrogel for injection, characterized in that it comprises the following steps: (a) preparing an aqueous solution containing a polymer derived from cellulose and at least one water-soluble polymer, the total polymer content ranging from 0.5 and 5 wt %, preferably from 1 to 4 wt % and more preferably from 1.5 to 3 wt %; (b) optionally adding sold particles; (c) pouring the resulting liquid mixture with the optional solid particles into a vessel and closing dais vessel using a water-tight and gas-tight system; and (d) exposing said vessel containing the liquid and the optional solid particles to a radiation dose of between 5 and 50 kGy, preferably between 20 and 30 kGy, and more preferably of about 25 kGy. The invention also relates to a hydrogel obtained according to the above method and to the use thereof in medical applications.