Abstract: A composition, which upon activation, spontaneously forms a cross-linked hydrogel in aqueous liquid, includes: a) a formulation containing a hyluronan (HA-formulation) which includes a hyaluronan backbone (HA backbone) and a plurality of a reactive substituent group (reactive HA substituent) which i) is directly attached to the HA backbone, and ii) exhibits the reactive HA-group, and b) a formulation of a homo-multifunctional cross-linking reagent (CLR-formulation) exhibiting a plurality of a reactive group (reactive CLR-group). The two reactive groups are selected as a pair of counterparts that mutually and selectively react with each other to form a linkage structure. The hydrogel contains a cross-linking structure which a) is attached to the hyaluronan via two or more of the linkage structure and is defined by the reagent. The cross-linking structure exhibits a plurality of hydroxyl groups. The composition can be used in vivo or ex vivo as a support matrix.