In vitro degradation of insulin-loaded poly (n-butylcyanoacrylate) nanoparticles.

Poly (n-butyl cyanoacrylate) (PBCA) nanoparticles were prepared by a dispersion polymerisation process in water at pH 3 and using dextran as a stabilising agent. The drug insulin was introduced during the latter stages of particle synthesis and was found not to interfere with the polymer structure, molecular weight, and the particle size. Nanoparticles were exposed to the enzyme esterase in phosphate buffered saline solution at 37 degrees C for time periods up to 4h. Esterase catalyses the degradation of the PBCA through hydrolysis of the side chain on the repeat unit with the release of butanol, and this was monitored as an indicator of degradation. The release of both butanol and insulin occurred via similar biphasic processes, with an initial burst release from the surface, followed by a slower diffusionally hindered release associated with particle erosion. Hydrolysis of the nanoparticle polymer was confirmed by infrared spectroscopy. Particle size reduces with time of exposure to esterase, but is greatest in the first 30 min of exposure. Despite the hydrolysis reaction, and reduction in particle size, there was no reduction in residual polymer molecular weight suggesting a progressive loss of entire chains from the active surface. Polymer loss is thought to occur through either solvation of degradation residue or through complete depolymerisation of hydrolysed chains.