the invention relates to a method of obtaining micro - and nanometric polymeric particles in a controlled , reproducible manner . the aforementioned particles have a spherical shape and a very narrow , uniform size distribution . the invention comprises the use of an easy particle - forming method consisting in using hydrodynamic forces to focus a composite microjet formed by two concentric fluids and can be used in the encapsulation of fragile compounds of biological interest , from peptides and proteins to cells and micro - organisms .