Intense efforts to develop alternative materials for gelatine as a drug-delivery system are progressing at a high rate. Some of the materials developed are hard capsules made from alginate, carrageenan, hypromellose and cellulose. However, there are still some disadvantages that must be minimised or eliminated for future use in drug-delivery systems. This review attempts to review the preparation and potential of seaweed-based, specifically carrageenan, hard capsules, summarise their properties and highlight their potential as an optional main component of hard capsules in a drug-delivery system. The characterisation methods reviewed were dimensional analysis, water and ash content, microbial activity, viscosity analysis, mechanical analysis, scanning electron microscopy, swelling degree analysis, gel permeation chromatography, Fourier-transform infrared spectroscopy and thermal analysis. The release kinetics of the capsule is highlighted as well. This review is expected to provide insights for new researchers developing innovative products from carrageenan-based hard capsules, which will support the development goals of the industry.

Hard-shell capsules commonly consist of gelatin which is not a universal material considering it is extracted from animal parts. Moreover, the mad cow disease triggered the scrutinization of the use of gelatin in pharmaceutical products. Hence, an alternative to conventional hard-shell capsules is needed. Carrageenan- (CRG-) based hard-shell capsules were successfully prepared by cross-linking CRG with maltodextrin (MD) and plasticizing with sorbitol (SOR). These CRG-MD/SOR hard-shell capsules were produced as an alternative to conventional hard-shell capsules in the oral drug delivery system (DDS). The physical properties of CRG-MD/SOR capsules were characterized using the degree of swelling, FTIR, and SEM analyses. The disintegration and dissolution profile release of paracetamol from CRG-MD/SOR hard-shell capsules was performed in an aqueous medium with three different pH levels. The degree of swelling of CRG-MD/SOR was 529.23±128.10%. The main peaks in the FTIR spectrum of CRG-MD/SOR were at 1248, 930, 847, and 805 cm⁻¹ for ester sulfate groups, 3,6-anhydrogalactose, galactose-4-sulfate, and 3,6-anhydrogalactose-2-sulfate, respectively. The SEM analysis exhibited minuscule pores on the surface of CRG and CRG-MD/SOR at 5000 times of magnification. The CRG-MD/SOR capsules required 18.47±0.11 min on average to disintegrate. The CRG-MD/SOR dissolution was better in a weakly acidic medium (pH 4.5) than in a strongly acidic (pH 1.2) and neutral (pH 6.8) media. Based on the aforementioned results, CRG-MD/SOR capsules are the potential candidate to replace conventional hard-shell capsules.

In drug release kinetics, the drug-matrix interaction is one of the important mechanisms to be dictated. Unfortunately, there is still minimum information discussing the effect of interaction between a drug and its matrix to the release profile of the drug. Therefore, there is an urgent need to conduct research related to the study of drug-matrix interaction. This paper reports the preparation of a drug delivery system (DDS) in the form of hard-shell capsules containing salicylamide (SCA) and analyses its drug-matrix interaction via dissolution test at different pH media and various release kinetics models. The matrix of hard-shell capsules was prepared from κ-carrageenan (CRG), crosslinked with maltodextrin (MD), and plasticized by sorbitol (SOR). The chemical properties of SCA were compared with paracetamol (PCT) using computational analysis to help to depict its drug-matrix interaction. The statistical analyses showed that SCA and PCT at pH 1.2, 4.5, and 6.8 had all different release profiles. Based on the goodness of fit evaluation, the diffusion mechanism of SCA at pH 1.2 and 4.5 could be best described by the Peppas-Sahlin model while the zeroth-order model fitted the dissolution profile at pH 6.8. In summary, it was proven that a different drug-matrix interaction produced a different dissolution profile.

The mechanical behavior, formulation performance, and erythromycin release kinetics of hard-shell capsules prepared from gelatin, hydrolyzed carrageenan (HC), and hydrolyzed carrageenan–maltodextrin (HC-MD) systems were comparatively evaluated. Capsules were produced using a dip-coating method and assessed for weight variation, mechanical strength, degree of swelling, disintegration time, dissolution profile, drug release kinetics, and surface wettability via contact angle measurements. Erythromycin release at pH 1.2, 4.5, and 6.8 followed diffusion- and surface-area-controlled kinetics, consistent with zero-order, first-order, Higuchi, and Hixson–Crowell models. Both HC and HC-MD capsules exhibited faster disintegration, greater swelling, and higher drug release than gelatin capsules, particularly under neutral and basic conditions. The HC-MD formulation demonstrated superior wettability and lower contact angles, which enhanced drug diffusion across the capsule surface.