Characterization, <i>In Vitro</i> Dissolution, and Drug Release Kinetics in Hard Capsule Shells Made from Hydrolyzed <b>κ</b>-Carrageenan and Xanthan Gum

This study aims to enhance the mechanical properties, disintegration, and dissolution rates of cross-linked carrageenan (CRG) capsule shells by shortening the long chains of CRG through a hydrolysis reaction with citric acid (CA). The hydrolysis of CRG was carried out using varying concentrations of CA, resulting in hydrolyzed CRG (HCRG). This was followed by cross-linking with xanthan gum (XG) and the addition of sorbitol (SOR) as a plasticizer. The results indicated that the optimal swelling capacity of HCRG-XG/SOR hard-shell capsules occurred at a CA concentration of 0.5%, achieving a maximum swelling rate of 445.39% after 15 min. Additionally, the best capsule hardness was also measured at this CA concentration, reaching a hardness level of 480.157 g (F = 4.67 N). FTIR analysis demonstrated that the presence of the acid group from CA altered the composition of the CRG chains. Furthermore, SEM-EDX mapping analysis revealed that the surface morphology of the synthesized capsules exhibited a relatively smooth texture with a limited number and size of pores, resulting in good capsule stability for drug delivery. The in vitro disintegration and dissolution rates of the HCRG-XG/SOR capsules were observed to be the fastest and highest at pH 1.2, respectively. The disintegration time was recorded at 20 min and 46 s, while the dissolution test indicated a drug release of 78.08% after 5 min and 100% after 120 min. The drug delivery kinetics of HCRG-XG/SOR followed the Ritger-Peppas model, indicating a complex release mechanism that involved swelling, diffusion, erosion, and capsule disintegration.