Novel bigels constructed from oleogels and hydrogels with contrary thermal characteristics: Phase inversion and 3D printing applications

In this study, bigels systems with semi-solid properties were prepared by using the mixture of beeswax oleogels and hydroxypropyl methylcellulose (HPMC) hydrogels in different proportions. The observation by confocal laser scanning microscopy (CLSM) showed that bigels with varying oleogel contents presented different types of O/W (20%, 40%, and 50%), semi-bicontinuous (55%), and W/O bigels (60% and 80%), respectively. FTIR results indicated that the spectra of different types of bigels exhibited significant variations between 3600 and 3300 cm−1 (O–H stretching) and 1250-1000 cm−1 (characteristic absorption peaks of HPMC) ranges, which could be used for further determination of the type of bigels. Rheological experimental results showed that W/O bigels and O/W bigels exhibited diametrically opposed thermal properties. In terms of 3D printing capability, W/O bigels with 60% oleogel content exhibited the best printing integrity, while semi-bicontinuous bigels showed the worst extrusion capability due to the inhomogeneity of the system. By printing under different models, it was found that W/O bigels seemed to be more suitable for flat stacked models, while O/W bigels had better performance in models with small-area monolayer structures. These results guided the development of bigels systems that could be applied for food 3D printing.