Sustained-release alginate-chitosan pellets prepared by melt pelletization technique.

Current drug delivery systems often struggle to maintain consistent release profiles in varying pH environments. Prior research has shown that alginate-based formulations can rapidly release drugs, especially in acidic conditions. However, the need for sustained release in more neutral pH environments remains unmet. This gap motivated the exploration of alginate-chitosan combinations to control drug release. Existing methods like extrusion-spheronization have been limited by fast dissolution rates. No prior work had resolved how to delay drug release in pH 6.8 conditions using alginate-based systems. The study aimed to address this by developing a new formulation approach. The challenge lies in preventing premature reactions during processing while allowing them in the dissolution phase. This uncertainty drove the investigation into melt pelletization as a solvent-free alternative. The goal was to design a system where cross-linking and complexation occur only during dissolution, not during production.

The primary aim was to develop a sustained-release formulation using alginate and chitosan. The specific problem addressed was the rapid drug release observed in conventional alginate-based pellets. The motivation stemmed from the need for controlled release in gastrointestinal environments with fluctuating pH. The study focused on using melt pelletization to prevent premature interactions between materials. This approach allowed reactions to occur only during dissolution, not during processing. The researchers sought to evaluate how calcium acetate and chitosan affect drug release in different pH conditions. They also aimed to compare mechanisms of sustained release in calcium alginate and alginate-chitosan systems. The ultimate goal was to determine if combining these components could synergistically enhance drug release control.

Melt pelletization was used to prepare alginate-based pellets without solvents. The process involved mixing alginate with chitosan and/or calcium acetate. This method prevented unwanted reactions during agglomeration. Pellets were tested in pH 2.2 and 6.8 media to assess drug release profiles. The dissolution behavior was analyzed to determine how formulation components influenced release rates. Calcium acetate and chitosan were introduced separately and in combination. The study evaluated cross-linking and polyelectrolyte complexation in different pH environments. Pellet dispersion and aggregation were monitored to understand release mechanisms. The researchers used in situ coacervation to achieve sustained release characteristics.

Pellets with calcium acetate or chitosan showed delayed drug release in pH 2.2 until pH 6.8. Calcium alginate pellets demonstrated sustained release due to Ca(2+)-induced cross-linking. Alginate-chitosan pellets released drugs slowly via polyelectrolyte complexation and aggregation. Pellet dispersion was reduced in calcium alginate systems, leading to slower erosion. In contrast, chitosan-based pellets formed swollen structures that limited drug diffusion. When both calcium acetate and chitosan were present, drug release was not delayed. Chitosan shielded Ca(2+), preventing cross-linking and causing rapid dispersion. Calcium acetate solvation led to chitosan loss from the matrix. Despite different mechanisms, both calcium alginate and alginate-chitosan systems achieved sustained release.

The study demonstrated that alginate-chitosan and calcium alginate pellets can achieve sustained drug release. The mechanisms differ: calcium alginate relies on cross-linking, while chitosan depends on complexation. Pellet dispersion and aggregation were key factors in controlling release rates. The presence of both calcium acetate and chitosan in the same matrix failed to enhance sustained release. This was due to chitosan shielding Ca(2+) and rapid solvation of calcium acetate. The findings suggest that formulation design must consider interactions between components. The authors propose that complementary release patterns may not always be achievable in combined systems. These results highlight the importance of pH-dependent mechanisms in drug delivery.