Influence of drug loading level on drug release and dynamic swelling of crosslinked gelatin microspheres

The effect of drug loading level both on dynamic swelling and drug release was evaluated using crosslinked gelatin microspheres. Owing to water penetration the microsphere diameter went first to a maximum value, which was not affected by the payload; the diameter gradually approached to an equilibrium swollen value, which was affected by drug loading level. Water absorption increases and drug diffusion decreases the microsphere diameter. Obviously, the diameter variation depends on the factor (water absorption or drug diffusion) predominating in the process. As the payload affected only the equilibrium swollen value it is reasonable to hypothesize that drug loading level has a greater effect on drug diffusion than on polymer relaxation. This rationale could explain the increase of the diffusion component of the drug release process as the payload increased.