The invention relates to a device (1) consisting an intra-gastric balloon for treating morbid obesity, or a gastric ring for treating obesity, wherein said device (1) is to be in contact, on at least a fraction of the surface thereof, with at least one bodily fluid when implanted, said device (1) being characterised in that the same comprises a first coating (4) at least partially covering said surface fraction, said first coating (4) including at least a first material containing at least a silicon oxide and/or at least a silane and/or at least a siloxane and/or at least a carbosilicate compound in order to improve the tightness of said surface fraction to said bodily fluid. The invention can be used for implantable medical devices.