The present invention relates to a cellulose carbamate spinning solution, the cellulose carbamate being dissolved in an ionic liquid. The envelope is modular to form with similar su pression elements a tube, which, in operation, at least partly, envelops a tubular element. The case is fitted with a connector that connects to a dedicated harness. The biocompatible material comprises at least one of a biologic material or a biologic-synthetic composite material. The protective agent includes at least one selected from the group consisting of dipropylamine, dibutylamine, triethylamine, tripropylamine, tributylamine, butanethiol, pentanethiol, hexanethiol, heptanethiol, octanethiol, nonanethiol, decanethiol, undecanethiol and dodecanethiol.