Formation of water-in-water emulsions and microgels in nonionic surfactant + gelatin aqueous mixtures

Hypothesis

Highlights

• Water-in-water (W/W) emulsions have been obtained in a polymer-surfactant system.
• Gelatin-Kolliphor ELP aqueous mixtures exhibits a broad region of immiscibility.
• Gelatin-in-Kolliphor and kolliphor-in-gelatin W/W emulsions have been prepared.
• Gelatin-genipin crosslinked microgels were obtained and stabilized by mucin particles.

Experiments

Findings

The addition of gelatin lowered the cloud temperature of the surfactant, resulting in the formation of two aqueous two-phases: a surfactant-rich solution and a gelatin-rich solution, which enabled the preparation of W/W emulsions. Chemically crosslinked microgels were successfully obtained by cooling down gelatin-in-surfactant emulsions, crosslinking with genipin and stabilized with mucin microparticles. To the best of our knowledge, this is the first report of W/W emulsions based on polymer-surfactant mixtures, unlike most W/W emulsions reported in the literature, which rely on immiscibility between two polymers in aqueous solutions.

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Materials

Bovine skin type B gelatin was supplied by Sigma-Aldrich (Spain), with an average molecular weight of 50–100 kDa and a gel strength of 225 g Bloom. Bovine Serum Albumin (BSA) was also provided by Sigma-Aldrich (Spain) as a lyophilized powder with ≥ 96 % purity, determined by agarose gel electrophoresis. The nonionic surfactant Kolliphor ELP, previously marketed under the name ‘Cremophor ELP’, is an ethoxylated triglyceride produced by reacting castor oil, which is mainly composed of ricinoleic (insaturated hydroxystearic) fatty acid chains, with ethylene oxide at 1/35 M ratio (polyoxyl-35 castor oil), and it was supplied by Sigma-Aldrich. Mucin, type III from porcine stomach, was also supplied by Sigma-Aldrich as a partially purified product containing 0.5–1.5 % bound sialic acid. Genipin, with 98 % purity, was obtained from Challenge Bioproducts Co. (Taiwan). The fluorescent dyes, fluorescein 5(6)-isothiocyanate (FITC) and Rhodamine B isothiocyanate (RBITC), were supplied by Sigma-Aldrich. The purity of FITC was ≥ 90 %, while RBITC consisted of a mixture of various isomers with an unspecified composition. FITC produces green fluorescence, whereas RBITC results in red fluorescence. The cationic dyes methylene blue and basic yellow 1 were purchased from Merck (unknown purity) and TCI Chemicals (>95 % purity), respectively. The anionic dyes fluorescein and acid red 27 were obtained from Sigma-Aldrich (>95 % purity) and TCI Chemicals (>90 % purity), respectively. Ultrapure H₂O with a minimum resistivity of 18 MΩ∙cm was prepared using a Milli-Q® Millipore Synergy UV System. Additionally, dimethyl sulfoxide (DMSO) was supplied by Merck with a purity of ≥ 99.9 %.

Jonathan Miras, Susana Vílchez, Cyprien Bouju, Martí Blanco-Pérez, Marc Ros-Espinal, Carlos Rodríguez-Abreu, Jordi Esquena, Formation of water-in-water emulsions and microgels in nonionic surfactant + gelatin aqueous mixtures, Journal of Colloid and Interface Science, 2025, ISSN 0021-9797, https://doi.org/10.1016/j.jcis.2024.12.240.

Read also our introduction article on Gelatin here: