Release and co-release of model hydrophobic and hydrophilic actives from 3D printed kappa-carrageenan emulsion gels

This study formulated and compared 3D printed (3DP) and cast kappa-carrageenan (кC) emulsion gels for the co-release of model lipophilic (cinnamaldehyde) and hydrophilic (erioglaucine disodium salt (EDS)) molecules. Tween 20 (T20) or whey protein isolate (WPI) were used as the emulsifier. Both 3DP and cast emulsion gels maintained their oil droplet size over 8 weeks owing to the set gel matrix. Penetration texture analysis revealed 3DP and cast 5% oil emulsion gels, required more force to break compared to 40% oil gels (3 N against 0.4–0.5 N). This was because the oil droplets, disrupted the gel matrix; thereby weakening it. 3DP gels required less force to break than cast gels, owing to failure between the printed layers. Release tests in various media showed no significant difference in the final % cinnamaldehyde released between 3DP gels and cast gels. Release tests in carried out 0.1M hydrochloric acid saw an increase in cinnamaldehyde release compared to other media, owing to cinnamaldehyde's increased solubility in acidic media. Addition of EDS into the gel matrix facilitated co-release studies, with EDS release having no effect on the cinnamaldehyde release, indicating EDS release was driven by liberation from the gel network and cinnamaldehyde release by its expulsion from the oil droplets. Simple modelling showed that diffusion rather than polymeric relaxation was more dominant for active release in 3DP gels compared to cast gels. This work shows that 3DP can be used to produce customisable кC-emulsion gels, with multiple actives; suitable for use as modified release vehicles.