Poly Alkyl Cyanoacrylate Nanocapsules

Nanocapsules are spherical structures formed by an envelope surrounding a liquid central cavity. The technique for the preparation of PIBCA nanocapsules was first reported by Fallaouh et al.22 The nanocapsules were obtained by injecting the organic phase, consisting of oil, with the dissolved drug, isobutylcyanoacrylate, and ethanol into the aqueous phase containing Pluronic F68 (a nonionic surfactant) under magnetic stirring. The colloidal suspension was concentrated by evaporation under a vacuum and filtered to obtain nanocapsules that possessed a shell-like structure with a wall 3-nm thick. This thickness was confirmed by transmission electron microscopy (TEM) after negative staining with phosphotungstic acid. The pH of the polymerization medium played an important role in obtaining nanocapsules. Nanocapsules with uniform size and low polydispersity were obtained only between pH 4 and 10. The concentration of alcohol above 15% only led to the formation of isolated nanocapsules. The mechanism of nanocapsule formation is probably the interfacial polymerization described by Florence et al.23 for the manufacture of PACA microcapsules.

A different method was adopted by Chouinard et al.24 for the preparation of poly(isohexyl cyanoacrylate) (PIHCA) nanocapsules. The monomer was treated with sulfur dioxide and dissolved in a solution containing Miglyol 810 (caprylic/capric triglyceride) in ethanol. This solution was added slowly, in a 1:2 ratio, into an aqueous phase containing a solution of 0.5% poloxamer 407 and 10 mM phosphate buffer under stirring. The nanocapsules were then purified by centrifugation and washing with distilled water. In this method, the sulfur dioxide acts as an inhibitor, preventing the polymerization of the cyanoacrylates by the ethanol. With the addition of the oily phase to the aqueous phase, the sulfur dioxide and ethanol migrate to the external phase, resulting in the formation of a very fine emulsion. In this case, the nanocapsule size was mainly influenced by Miglyol concentration. Freeze-fracture electron microscopy studies showed that polymeric walls of different thicknesses and densities can be prepared, which could be significant for the design of nanocapsules with tailored drug-release kinetics.

Palumbo et al.25 adopted a similar technique for the preparation of polyethyl-2-cyanoacrylate nanocapsules containing idebenone (an antioxidant). In this method, the acetonic solution of Miglyol 812, idebenone, and monomer was added to 100 mL of aqueous phase (pH 7) containing Tween 80. The presence of nonionic surfactant allowed the polymerization of the ethylcyanoacry-late at the oil-water interface, thus encapsulating Miglyol 812 droplets. The immediate polymerization triggered the formation of drug-loaded nanocapsules, with the suspensions concentrated under a vacuum to remove any acetone. Tween 80 reduced the hydrodynamic size of the emulsion droplets as a function of its concentration, resulting in smaller-sized nanocapsules. These nanocapsules exhibited a negative charge that was determined by zeta-potential measurements. The freeze-fracture electron microscopy revealed the presence of internal oil droplets surrounded by the polymeric shell of the nanocapsule.

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