1. Biodegradable material, which is a cross-linked product: a multivalent compound A, comprising 3 or more functional groups X, selected from the group consisting of a hydroxyl group, a thiol group and an amino group； a multivalent compound B, comprising 3 or more functional groups Y selected from the group consisting of a carboxyl group, an isocyanate group and a thioisocyanate group； as well as compound C having a structure formed from hydroxycarboxylic acid, the homopolymer of which obtained by homopolymerization has a glass transition temperature of -40 ° C or lower. 2. Biodegradable material according to claim 1, where the mass fraction of the structure formed from the specified compound C, is from 18 to 70 wt.%. 3. The biodegradable material according to claim 1 or 2, wherein said multivalent compound A is one of the following compounds a) to e): a) a homopolymer or copolymer of a monomer (s) of a water-soluble polymer (s) selected from the group consisting of polyethylene glycol, polypropylene glycol polyvinyl alcohol, polyhydroxyethyl acrylate, polyhydroxyethyl ethyl methacrylate, carboxymethyl cellulose, hydroxymethyl cellulose and hydroxyethyl cellulose； b) a copolymer of the specified water-soluble polymer of the hydrophobic polymer (s) monomer (s) selected c) a copolymer of a monomer of said water-soluble polymer and hydroxycarboxylic acid (s), the homopolymer (s) of which, formed by homopolymerization, has / have a glass transition temperature of -39 ° C or higher； d) a branched polymer formed by the bonding of all hydroxyl groups n1. Биоразрушаемый материал, который представляет собой сшитый поперечными химическими связями продукт:мультивалентного соединения A, включающего 3 или более функциональные группы X, выбранные из группы, состоящей из гидроксильной группы, тиольной группы и аминогруппы；мультивалентного соединения B, включающего 3 или более функциональные группы Y, выбранные из группы, состоящей из карбоксильной группы, изоцианатной группы и тио
