In vitro release modulation from crosslinked pellets for site-specific drug delivery to the gastrointestinal tract - II. Physicochemical characterization of calcium-alginate, calcium-pectinate and calcium-alginate-pectinate pellets

Pellets of calcium-alginate, calcium-pectinate and calcium-alginate-pectina te were produced via crosslinking in an aqueous medium for site-specific dr ug delivery in the gastrointestinal tract. A comparative study of their phy sicochemical characteristics by means of texture analysis, modulated temper ature differential scanning calorimetry (MTDSC), scanning electron microsco py and swelling dynamics under different pH conditions was undertaken. It w as found that the incorporation of low methoxylated pectin (i.e., degree of methoxylation approximate to 35%) together with alginate appears to influe nce the degree of crosslinking and subsequently the physical, mechanical an d resilience behavior. In general, texture analysis of various pellets indi cated that both strength and resilience profiles were in the order of calci um-alginate greater than or equal to calcium-alginatepectinate>calcium-pect inate. Calcium-alginate pellets were found to be viscoelastic, while calciu m-pectinate was highly brittle. Through the application of MTDSC, depolymer ization transitions, reversing and non-reversing heat flow were determined and interpreted for each formulation. Scanning electron microscopy and micr o-thermal analysis revealed distinct morphological differences in each case . The influence of and nature of crosslinking, and textural properties of s uch pellets on drug release rate modulation is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.