Egg yolk lecithin

Perfluoro-15-crown-5-ether (PFCE) emulsion was prepared following a protocol adapted from Joseph, et al.^{15 (link)} Briefly, an aqueous dispersion of egg yolk lecithin (Sigma-Aldrich, St. Louis, MO, USA) was made in Tyrode’s solution (Sigma-Aldrich) by sonication in an ice bath. PFCE (Exfluor Research Corporation, Round Rock, TX, USA) was added, and the sample was sonicated. The resulting emulsion was filtered through a 0.8 μm membrane filter. PFCE-loaded alginate capsules (average diameter 1000 μm, Figure 1A) were prepared by mixing the PFCE at a 1:20 ratio (5%) with 2.0% low viscosity, high mannuronic acid (LVM) alginate (FMC Biopolymer, NovaMatrix, Sandvika, Norway). Using an electrostatic droplet generator (Nisco Engineering Inc., Zurich, Switzerland) with a 0.9 μm encapsulation nozzle (Nisco), the alginate/PFCE mixture was aspirated into a 50 mM strontium chloride (SrCl₂) solution containing 4.6% mannitol (Sigma-Aldrich) and 25 mM HEPES buffer (Corning Mediatech, Tewksbury, MA, USA). The PFCE capsules were washed in Hanks’ Balanced Salt Solution (HBSS) and assessed by MR using a 7 T system. A single, narrow ¹⁹F peak indicated high purity of the preparation (Figure 1B). We expected these Sr-gelled LVM alginate capsules to be highly biocompatible and durable, similar to our barium-gelled LVM alginate capsules.^{16 (link)}