Extended release of high pI proteins from alginate microspheres via a novel encapsulation technique

Alginate has potential as a matrix for controlled delivery of protein-based drugs that require site-specific long-term delivery. In the current work albumin, lysozyme and chymotrypsin were encapsulated into alginate microspheres using a novel method that involved soaking the microspheres in a protein-containing NaCl solution. This was followed by recrosslinking with calcium chloride. High pI proteins also appeared to physically crosslink the sodium alginate which resulted in more sustained release. Release was affected by the nature of the releasate solution. In TRIS buffered saline, the high pI proteins chymotrypsin and lysozyme showed sustained release lasting over 150 h. Release into 0.15% NaCl led to relatively constant release of lysozyme and chymotrypsin over more than 2000 h; reduction of the releasate volume lengthened the lysozyme release to greater than 8 months. Released lysozyme was shown to remain active for at least 16 days, in some cases with activity greater than 100% of the active control. This encapsulation technique can therefore be used to rapidly load alginate microspheres with proteins, with high isoelectric point proteins showing particular promise. Furthermore, the interactions between the high pI proteins and the alginate gel could potentially be exploited to generate new protein delivery systems.