Thermoresponsive oil-continuous gels based on double-interpenetrating colloidal-particle networks

Gels composed of multicomponent building blocks offer promising opportunities for the development of novel soft materials with unique and useful structures. While interpenetrating polymer networks have been extensively studied and applied in the creation of these gels, equivalent strategies utilizing colloidal particles have received limited scientific and technological attention. This study presents a novel class of thermo-responsive apolar double gels from interpenetrating networks of attractive colloidal silica and lipid particles. These double gels are easily assembled and suitable for the fabrication of 3D-printed edible soft constructs. Emphasis is focused on the rheological properties and structure emerging on the dilute regime (ϕ ≲ 0.1). Rheological investigations demonstrate that double gels exhibit greater stiffness and resilience to yielding compared to their single lipid gel counterparts. The scaling behavior of the oscillatory linear shear moduli and the critical strain for yielding with volume fraction remain comparable between single and double gels. Creep yielding in double gels exhibits two exponential decay regimes, suggesting the presence of thicker gel strands undergoing flow. Visualization and quantification of the quiescent microstructure confirms the existence of such denser aggregates devoid of larger clusters due to steric hindrance of interpenetrating networks in double gels. This is in stark contrast to lipid single gels where aggregates grow unrestrictedly into larger clusters. Our study constitutes the first demonstration on the assembly of apolar double gel networks as a promising avenue for the design of novel soft materials and foods with tailored structure and mechanics.

Comparation of micro-viscosity of liquid oil in different colloidal fat crystal networks using molecular rotors

Micro-viscosity is an important parameter to describe the microenvironment of the fat crystal network. In this study, we evaluated the micro-viscosity of the liquid oil confined in mixtures of palm kernel stearin (PKS)/soybean oil (SO) and fully hydrogenated rapeseed oil (FHRSO)/SO using molecular rotors. The micro-viscosity was shown to increase with solid fat content (SFC), as well as with high proportion of triglycerides that crystallized and formed stronger linked networks. In addition, the thickness of nanocrystals decreased with the increase of solid fat and denser fat crystal network appeared with larger box-counting fractal dimension. Mathematic fit analysis further indicated that molecular confinement of the oil was strongly dependent on the microstructure with high-space filling colloidal fat crystal networks. Larger box-counting fractal dimension led to higher micro-viscosity. However, the critical box-counting fractal dimension was found to be 1.86 irrespective of the nature of the network.

Effects of wax concentration and carbon chain length on the structural modification of fat crystals

Natural waxes are cost-effective and potential fat crystallization modifiers; however, there is limited information about their implementation in solid triacylglycerol (TAG) oil. Herein, we investigated the effects of two natural waxes, namely, candelilla wax (CLW) and rice bran wax (RW), with different concentrations (2, 4, 6, and 8 wt%) and carbon chains on the crystal growth and structure of palm kernel stearin (PKS85). CLW significantly accelerated the PKS85 crystallization process. Both waxes could induce a new hydrocarbon chain with the lengths of 3.70 and 4.15 Å during the TAG crystallization, respectively. Particularly, X-ray diffraction (XRD) indicated that PKS85 combined with CLW showed a similar lamellar thickness (d₀₀₁) and crystal domain size (ξ) with pure PKS85, whereas that of PKS85 containing RW was 1.7-1.8 and 1.5-1.8 fold higher, respectively. This result corresponded to the carbon chain length of CLW and RW, which was double and quadruple that of PKS85, respectively. Further, these variations were reflected in the crystal microstructures of PKS85 with CLW and RW, where the former showed small homogeneous crystals, while the latter displayed large rod-like layered crystals. In addition, the firmness significantly increased when CLW and RW were added, which is possibly attributed to the fact that the waxes became the backbone of the crystal "fence". Our findings give clear insight into the interaction between TAGs and wax molecules in the crystallization process, which can help guide the utilization of natural waxes in the modification of fats.

Understanding the role of hydrogen bonding in the aggregation of fumed silica particles in triglyceride solvents

HYPOTHESIS

Fumed silica particles are thought to thicken organic solvents into gels by aggregating to form networks. Hydrogen bonding between silanol groups on different particle surfaces causes the aggregation. The gel structure and hence flow behaviour is altered by varying the proportion of silanol groups on the particle surfaces. However, characterising the gel using rheology measurements alone is not sufficient to optimise the aggregation. We have used confocal microscopy to characterise the changes in the network microstructure caused by altering the particle surface chemistry.

EXPERIMENTS

Organogels were formed by dispersing fumed silica nanoparticles in a triglyceride solvent. The particle surface chemistry was systematically varied from oleophobic to oleophilic by functionalisation with hydrocarbons. We directly visualised the particle networks using confocal scanning laser microscopy and investigated the correlations between the network structure and the shear response of the organogels.

FINDINGS

Our key finding is that the sizes of the pore spaces in the networks depend on the fraction of silanol groups available to form hydrogen bonds. The reduction in the network elasticity of gels formed by methylated particles can be accounted for by the increasing pore size and tenuous nature of the networks. This is the first report that characterises the changes in the microstructure of fumed silica particle networks in non-polar solvents caused by manipulating the particle surface chemistry.

Stabilization of a non-aqueous self-double-emulsifying delivery system of rutin by fat crystals and nonionic surfactants: preparation and bioavailability study

Literature examples of non-aqueous Pickering emulsions stabilized by fat crystals are very rare. Moreover, the applications of rutin are limited due to its low solubility in both water and oils (less than 0.10 mg g^-1 and 0.25 mg g^-1, respectively). Thus, herein, we developed an optimum formulation of a non-aqueous self-double-emulsifying delivery system (SDEDS) containing rutin and evaluated its oral bioavailability. The new formulation stabilized by fat crystals (glycerol monostearate, GMS) and nonionic surfactants was prepared via a two-step emulsification process. The presence of a mixture of GMS crystals and nonionic surfactants effectively improves the stability of the emulsions. The non-aqueous SDEDS spontaneously forms oil-in-oil-in-water (O/O/W) double emulsions in the gastrointestinal environment with the inner oil phase mainly containing the active ingredients. It is stable at both 4 °C and 25 °C for 30 days and could enhance the dissolution properties of the active ingredients. Furthermore, the protection of rutin against digestion-mediated precipitation was observed when the formulation contained a high concentration of GMS crystals. The oral absolute bioavailability of rutin obtained from SDEDS (8.62%) is 1.76-fold higher than that of the actives suspension (4.90%). Thus, the non-aqueous SDEDS is an attractive candidate for the encapsulation of water-insoluble and simultaneously oil-insoluble nutrients (such as rutin) and for use in oral delivery applications.

Exploring concentration, surface area and surface chemistry effects of colloidal aggregates on fat crystal networks

An investigation into the effects of concentration, surface area and surface chemistry of silica aggregates on a model fat-structured system.