Freeze-drying and release characteristics of polyelectrolyte nanocarriers for the mucosal delivery of ovalbumin

Polyelectrolyte complexes (PEC) consisting of an alginate core entrapping the protein ovalbumin and the chitosan coating were prepared by the self-assembly of oppositely charged polyelectrolytes. The PEC were prepared at pH 4.0 and consisted of alginate, ovalbumin and chitosan in a concentration of 0.5, 0.5 and 0.05 mg/ml, respectively, having a particle size of around 300nm, a zeta potential of -44 mV and a protein association efficiency of 80%. The release of ovalbumin from PEC was mostly dependant on the pH of release medium and the presence of strong electrolytes contributed to higher release. Approximately 90% of the ovalbumin was released in a phosphate buffer media, pH 7.4. The release was lower in media with pH 4.0, reaching the value of app. 40% and 60% of ovalbumin released in water (pH 4.0) and NaCl solution (0.9% w/v, pH 4.0), respectively. In an acidic saline solution, pH 3.0, there was only 5% of ovalbumin release, however, increasing the pH to 6.8, approximately 70% of ovalbumin immediately released from the PEC. The PEC were freeze-dried aided by various excipients. Their efficiency on the redispersibility of the freeze-dried product was evaluated according to the mean particle diameter, polydispersity, average scattering intensity (particle concentration) and visual appearance of the PEC (Tyndal effect). In the presence of trehalose and mannitol, the aggregation and integrity of the PEC were prevented, yielding properties similar to the PEC dispersion before lyophilisation. The surface hydrophobicity of the ovalbumin either free or formulated in the nanocomplexes was determined by the bis-ANS fluorescence intensity, indicating a higher surface hydrophobicity for the PEC. The mild formulation conditions, nanometre-sized particles, high protein association efficiency, pH-dependant release, and modified surface properties are promising factors towards the development of an oral delivery system for protein made by the self-assembly of oppositely charged polyelectrolytes.