Biodegradable invasive medical device, in particular for guided tissue regeneration, which device comprises a biodegradable polymer, composed of a thermoplastic and/or thermosetting polymer admixed to a solvent that is miscible with any aqueous and/or aqueous alcoholic and/or alcohol-group-containing solution and/or with physiological liquids, whether of a synthetic or natural type. The said water-insoluble thermoplastic and/or thermosetting polymer and the water-miscible solvent for the polymer and mixed together in such a proportion as to form an organogel or a plastigel or a xerogel, or a solid-containing pasty product of the slurry type.