Degradation of Poly Alkyl Cyanoacrylate Nanoparticles

The type of degradation (bulk or surface degradation) of polymethyl-, polyethyl-, and poly(isohexyl cyanoacrylate) nanoparticles was determined using photon correlation spectroscopic measurements.48 In the case of surface degradation, the particle size should show an immediate increase while the polydispersity index remaining constant. If bulk degradation dominates, a lag period should occur, preceding the decrease in mean size due to disintegration of the particles. This process of disintegration would lead to a more heterogeneous distribution of particle sizes and consequently to an increase in the polydispersity index. Incubation of polyethyl cyanoacrylate nanoparticles with in 10k4N NaOH led to an immediate, continuous decrease in particle size, as well as an unchanged polydispersity index indicating the predominant surface degradation. Incubation of PIHCA nanoparticles in 10k4 N NaOH led to no detectable size decrease; polydis-persity was also unchanged, indicating the degradation by surface erosion at a much slower rate than poly(ethyl cyanoacrylate) nanoparticles. Coating the particles with poloxamers did not accelerate the particle degradation. At low electrolyte concentration, the size and dispersity of PIHCA nanoparticles remained unchanged during incubation in 10K4NNaOH. At high ionic strength, the size increase of nanoparticles as a result of flocculation was larger than the size decrease due to degradation. In vitro degradation was also determined by turbidimetric measurements.55 Poly(-methyl cyanoacrylate) and poly(ethyl cyanoacrylate) nanoparticles underwent the fastest degradation. A high electrolyte concentration in the medium led to the formation of larger aggregates accompanied by an increase in absorption of dispersion. The slowly degrading polymers PIBCA and PIHCA probably release a low concentration of degradation products over a prolonged period of time, indicating their low toxicity.

The stability studies on PBCA nanoparticles reveal that an acidic medium protects the nano-particles against decomposition.56,57 Higher temperatures promoted the degradation of nanoparticles. When incubated in human serum in vitro, the nanoparticles showed no particle agglomeration, suggesting their better tolerance in vivo.

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