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 .