High Internal Phase Oil-in-Water Pickering Emulsions Stabilized by Chitin Nanofibrils: 3D Structuring and Solid Foam 

Abstract

Chitin nanofibrils (NCh, ∼10 nm lateral size) were produced under conditions that were less severe compared to those for other biomass-derived nanomaterials and used to formulate high internal phase Pickering emulsions (HIPPEs). Pre-emulsification followed by continuous oil feeding facilitated a “scaffold” with high elasticity, which arrested droplet mobility and coarsening, achieving edible oil-in-water emulsions with internal phase volume fraction as high as 88%. The high stabilization ability of rodlike NCh originated from the restricted coarsening, droplet breakage and coalescence upon emulsion formation. This was the result of (a) irreversible adsorption at the interface (wettability measurements by the captive bubble method) and (b) structuring in highly interconnected fibrillar networks in the continuous phase (rheology, cryo-SEM, and fluorescent microscopies). Because the surface energy of NCh can be tailored by pH (protonation of surface amino groups), emulsion formation was found to be pH-dependent. Emulsions produced at pH from 3 to 5 were most stable (at least for 3 weeks). Although at a higher pH NCh was dispersible and the three-phase contact angle indicated better interfacial wettability to the oil phase, the lower interdroplet repulsion caused coarsening at high oil loading. We further show the existence of a trade-off between NCh axial aspect and minimum NCh concentration to stabilize 88% oil-in-water HIPPEs: only 0.038 wt % (based on emulsion mass) NCh of high axial aspect was required compared to 0.064 wt % for the shorter one. The as-produced HIPPEs were easily textured by taking advantage of their elastic behavior and resilience to compositional changes. Hence, chitin-based HIPPEs were demonstrated as emulgel inks suitable for 3D printing (millimeter definition) via direct ink writing, e.g., for edible functional foods and ultralight solid foams displaying highly interconnected pores and for potential cell culturing applications.

Oil‐in‐water Pickering emulsion stabilization with oppositely charged polysaccharide particles: chitin nanocrystals/fucoidan complexes

“…Next, we used the complexes to stabilize the Pickering emulsion and further evaluated the relationship between the complexes and emulsion stability based on the particle size, zeta potential, microscopic state, flocculation, and physical and storage stability of the emulsions. The particle size of the ChN‐F‐stabilized emulsion, D 4,3 , was 1.5–8.8 μm, an order of magnitude lower than that of the emulsion stabilized by ChN alone 3, 13 . Under the same mass ratio, the D 4,3 of the emulsion stabilized by the complexes at pH levels of 3 and 4 exhibited larger particles (Fig.…”

“…Zhu et al . successfully employed chitin nanofibers to prepare a high‐internal‐phase Pickering emulsion 13 . However, the method used for obtaining nanocrystals was simpler and more controllable than that used for forming nanofibers; moreover, the nanocrystals displayed a length of less than 1 μm, whereas the nanofibers presented a length of over 1 μm 14 .…”

“…Tzoumaki et al . demonstrated that the droplet sizes of these emulsions prepared with ChN were as large as 10–100 μm, and the physical stability of these emulsions required further improvement 13, 15 . The presence of opposite charges in the self‐assembled system provided ideas for preparing new Pickering stabilizers.…”

Interfacial jamming reinforced Pickering emulgel for arbitrary architected nanocomposite with connected nanomaterial matrix

“…In addition, HIPE is hypercritical to stabilizer surface properties, thus, limiting the broader use. Thus, intensive efforts to developing Pickering emulgel with wide-ranged tailorable composition and concurrently possessing viscoelastic and interfacial stability are required 31 .…”

Colloidal systems toward 3D cell culture scaffolds

“…In one such strategy, emulsions can be further stabilized by addition of solid colloidal particles[50]. The system composed by the combination of solid beads with two immiscible phases is known as Pickering emulsion and its improved stability is explained by the irreversible adsorption of the particles at the oil/water interface, which provides enough mechanical hindrance to avoid coalescence and retain the original pore size[51,52]. A schematic representation of HIPE preparation is shown inFigure 2.…”