The present invention relates to a sterile in situ cross-linkable polysaccharide compositions for augmenting, filling or replacing soft tissues in various cosmetic and therapeutic applications. The composition comprises a first polysaccharide derivative functionalized with a nucleophilic group and a second polysaccharide derivative functionalized with an electrophilic group. Said nucleophilic and electrophilic functional groups spontaneously form in situ covalent linkages following co-injection in the body of a patient, resulting in the formation of a cross-linked hydrogel at the site of co-injection.
