An aqueous suspension, stable in physiological medium, of nanoparticles for delivering active principles such as insulin. The delivery particles are based on a three-block copolymer: polyethylene glycol/hydrophilic polyaminoacid/hydrophobic polyaminoacid. These three-block copolymers can be associated with an active principle without denaturing it, and perform a controlled and long-term release of the active principle in vivo, and thus provide the active principle with a very prolonged release. Also disclosed is a powder form solid from which are derived the delivery particles, the preparation of the powder-form solid, a suspension of delivery particles based on the three-block copolymer, and pharmaceutical specialties obtainable from the delivery particles filled with active principle.