Simple mixing/blending of a special class of drug-depot forming tri-block copolymers polymers, with the opportunity to cost-effectively tailor drug delivery performances of such biodegradable, injectable depots in a clinical and an industrial setting. How to visualize these depots for various imaging related purposes is described. A composition comprising (a) an active ingredient, preferably a pharmaceutically active ingredient (b) a solvent and (c) a mixture of at least two types of tri-block copolymers of formula (1) B-A-B&emsp；&emsp；(1) wherein B stands for a hydrophobic block and wherein A stands for a hydrophilic block, wherein the mixture is prepared by mixing at least two types of tri-block copolymers having a degree of modification of 100% and wherein the at least two types of B-A-B types of tri-block copolymers differ only on the type of end-group or wherein the mixture is prepared by mixing at least two types of tri-block copolymers, wherein one of the at least two tri-block copolymers has a degree of modification of 100% and one of the at least two tri-block copolymers has a degree of modification of 0% and wherein the at least two types of B-A-B types of tri-block copolymers differ only on the degree of modification of the end-groups.L'invention décrit un mélangeage/mélange simple d'une classe spéciale de polymères copolymères tri-blocs formant un site tissulaire de stockage de médicament, qui offre l'opportunité d'adapter de manière rentable des performances d'administration de médicaments de tels sites tissulaires de stockage injectables, biodégradables, dans un milieu clinique et un milieu industriel. De plus, l'invention décrit comment visualiser ces dépôts pour divers buts apparentés d'imagerie. L'invention concerne une composition comprenant (a) un principe actif, de préférence un principe pharmaceutiquement actif, (b) un solvant et (c) un mélange d'au moins deux types de copolymères tri-blocs de formule (1) B-A-B (1) dans laquelle B représente un
