Layer-by-layer microcapsules for pH-controlled delivery of small molecules

Abstract

The aim of this study is to investigate the influence of pH on the encapsulation and release behavior of charged and neutral small molecules in layer-by-layer microcapsules (LbL-MC). Alternative layers of polystyrene sulfonate and polyallylamine hydrochloride polyelectrolytes were adsorbed onto calcium carbonate sacrificial templates. Six model small molecules including ascorbic acid, indomethacin, imatinib mesylate, rhodamine, 5-fluorouracil and estradiol were studied for their encapsulation in LbL-MC. Encapsulation efficiency was optimized for solute concentration, pH, incubation time and NaCl concentration. In vitro release studies were performed using dialysis membrane method at pH 4, 7.4 and 9. Optical microscopy and zetasizer results showed particles of 3.1 ± 0.2 μm diameter and 1.67 ± 0.87 mV potential. FTIR and differential scanning calorimeter studies confirmed the encapsulation of small molecules in LbL-MC. Encapsulation efficiency (%) of model molecules in LbL-MC increased with increase in solute concentration and increase in pH from 2 to 6. Interestingly, encapsulation efficiency was significantly greater for charged small molecules compared to neutral molecules. Extended release of charged molecules was achieved at pH 9. Kinetic modelling of release studies showed Fickian and non-Fickian diffusion of small molecules. In conclusion, LbL-MC can be developed as a potential carrier for small molecules depending on their physical and chemical properties.