3D printing of edible hydrogels containing thiamine and their comparison to cast gels

In this study, 3% w/v kappa-carrageenan (KC) and 2% w/v agar were assessed for their suitability for hot extrusion 3D printing (3DP) and compared to cast gels of equivalent composition. Moreover, incorporation of a model active (thiamine) at varying concentrations, was studied for both 3DP and cast microstructures. Rheology and differential scanning calorimetry showed that thiamine (via electrostatic complexation) reinforced the kappa-carrageenan gel network (up to a certain threshold concentration), whereas the agar gel was structurally unaltered by the active's presence. While the KC-thiamine formulations were printable (within a relatively narrow formulation/processing window), the agar-thiamine systems were not printable via the current set up. Texture profile analysis (TPA) showed that 3DP KC-thiamine cylinders had a hardness value of 860 g +/- 11% compared to 1650 g +/- 6% for cast cylinders. When compressed they delaminated due to failure between consecutive layers of material deposited during the printing process; light microscopy revealed distinct layering across the printed gel structure. Release tests at 20 degrees C showed printed gels expelled 64% +/- 2.2% of the total active compared to 59% +/- 0.8% from the cast gels over 6 h. At 37 degrees C these values increased to 78% +/- 2.6% and 66% +/- 3.5% respectively. This difference was believed to be due to the significant swelling exhibited by the printed systems. A simple empirical model, applied to the release data, revealed that thiamine discharge from 3DP gels was solely driven by diffusion while ejection of the active from cast systems had both diffusional and relaxation contributions.

Automated summary

This study evaluated the suitability of kappa-carrageenan and agar for hot extrusion 3D printing, as well as the impact of thiamine on gel networks and release performance. While kappa-carrageenan-thiamine formulations were printable, agar-thiamine systems were not. The printed gels exhibited higher active release compared to cast gels due to significant swelling, driven solely by diffusion.