Kinetically Enhanced Fabrication of Homogeneous Biomimetic and Functional Emulsion Droplets

Abstract

Characterized by a fluid and deformable interface, ligand-functionalized emulsion droplets are used as model probes to address biophysical, biological, and developmental questions. Functionalization protocols usually rely on the use of headgroup-modified phospholipids that are dissolved in the oil phase prior to emulsification, leading to a broad range of surface densities within a given droplet population. With the aim to coat particles homogeneously with biologically relevant lipids and proteins (streptavidin, immunoglobulins, etc.), we developed a reliable surface decoration protocol based on the use of polar cosolvents to dissolve the lipids in the aqueous phase after the droplet production. We show that the surface density of the lipids at the interface has a narrow normal distribution for droplets having the same size. We performed titration isotherms for lipids and biologically relevant proteins on these drops. Then, we studied the influence of the presence of surfactants in the medium on lipid insertion and compared the results for a range of polar cosolvents of increasing polarity. To assess both the generality and the biocompatibility of the method, we show that we can produce more sophisticated, monodisperse functional magnetic emulsions with a very high surface homogeneity. Using an oil denser than the surrounding culture medium, we show that IgG-coated droplets can be used as probes for phagocytosis experiments.

Phenotyping Polarization Dynamics Of Immune Cells Using A Lipid Droplet - Cell Pairing Microfluidic Platform

“…As negative control, droplets are coated with biotinylated BSA which do not engage the BCR, in lieu of F(ab’) 2 (15). To coat the droplet interface with phospholipids, we either dissolve the lipids in the oil prior to emulsification, (bulk-functionalization (22)), or adsorb the phospholipids at the surface after fabrication of the droplets (surface-functionalization, (30)). In this latter case, phospholipids are inserted to the oil/water interface with the help of a polar co-solvent, ensuring a homogeneous and finely-controlled lipid, and ultimately protein, surface concentration at the end of the adsorption process ( Fig.…”

“…The surface-functionalization protocol ensures precise quantification of the amount of antigens displayed by droplets (30). We first titrate streptavidin attachment by measuring the adsorption isotherm onto the phospholipid-coated droplet surface (see Materials and Methods section for details).…”

“…(30). The streptavidin adsorption isotherm fits with a Langmuir isotherm with a K Strep , the streptavidin concentration producing half occupation, equal to 9.7 ± 4.7 eq −1 compatible with previous analyses ( Figure 1D )(30). For a bulk concentration of streptavidin corresponding to a maximal surface coverage (1 eq.), we measured the adsorption isotherm of antigens (F(ab’) 2 ) using fluorescent secondary antibodies and epifluorescence microscopy for the quantitative fluorescence measurements of the total amount of proteins attached to droplets.…”

Mannose-Coated Fluorescent Lipid Microparticles for Specific Cellular Targeting and Internalization via Glycoreceptor-Induced Phagocytosis

“…The droplets were functionalized by the amphiphilic ligand using a recently reported procedure that allows rapid and efficient coating of O/W emulsion. 42 While most surface coating protocols rely on the in-situ fabrication of the emulsion with the functional ligand, our protocol allows functionalizing the droplets after the emulsification. Briefly, the droplets can be fabricated in a Couette emulsifier with the desired size 43 and then functionalized by being put in the presence of the ligand in a polar cosolvent (here 4% v/v DMSO) during 30 minutes.…”

“…Briefly, the droplets can be fabricated in a Couette emulsifier with the desired size 43 and then functionalized by being put in the presence of the ligand in a polar cosolvent (here 4% v/v DMSO) during 30 minutes. 42 It is thus possible to rapidly functionalize the droplets at various concentrations in mannolipid and to perform a thorough study of the surface coating with a single batch of droplets. The droplets were put in presence of increasing concentrations of mannolipid from 20 to 400 µM in the buffer.…”