Study of release kinetics of small and high molecular weight substances dispersed into spray-dried ethylcellulose microspheres.

Spray-dried ethylcellulose microspheres were used as matrices for the encapsulation of a fungal lactase and/or small paramagnetic probes (Tempol or Tempo). Their dissolution in water was studied. Kinetics fitted with the model Q = kt(n) of Korsemeyer et al. [Int. J. Pharm. 15 (1983) 25] exhibited a non-Fickian diffusion. The calculated diffusional exponent (n) values were near 0.26 whatever the encapsulated probes. The release rates (k) were only slightly different for paramagnetic probes and lactase. This result indicated that the probes' release mechanisms are not diffusion controlled. Other factors such as matrix porosity and probe solubility in the matrix and in water could influence the probes' release rate