Physicochemical characterization and enzymatic degradation of casein microcapsules prepared by aqueous coacervation

The use of biopolymers in sustained release systems has been studied by many research groups because of the bioavailability and biodegradability of these compounds. Casein is a natural biopolymer whose degradation results in biologically utilisable compounds. The objective of the present study was to assess the potential of casein microcapsules (CAS/MC) as sustained release systems using acetaminophen as a model drug. CAS/MC were prepared by aqueous coacervation in lactate buffer containing gelatin, hydroxypropyl cellulose (HPC) and lecithin. After preparation, the microcapsules were treated, or not, with glutaraldehyde as a cross-linking agent. CAS/MC were loaded using two distinct procedures, either by dissolving 50% of the drug (w/w), relative to casein, in the polymer dispersion or by dissolving the drug in the coacervating solution. The drug present in CAS/MC was quantified by HPLC after an enzymatic degradation assay, and the CAS/MC were analysed by scanning electron microscopy and thermal analysis (differential scanning calorimetry and thermogravimetrical analysis). Loading of the drug was approximately 8% (w/w), with high resistance to enzymatic attack. The absence of an acetaminophen melting peak indicated that there was no drug present on the surface of the cross-linked systems. In addition, loading was accompanied by a reduction of the specific heat capacity of the systems, which suggests a decrease in stability. The outer morphology of the encapsulating polymer was affected by the process of microencapsulation. The data suggest that the microencapsulation process of aqueous coacervation and cross-linking is appropriate for the preparation of microencapsulated systems for sustained drug delivery.