Multiple patterns of polymer gels in microspheres due to the interplay among phase separation, wetting, and gelation

Abstract

We report the spontaneous patterning of polymer microgels by confining a polymer blend within microspheres. A poly(ethylene glycol) (PEG) and gelatin solution was confined inside water-in-oil (W/O) microdroplets coated with a layer of zwitterionic lipids: dioleoylphosphatidylethanolamine (PE) and dioleoylphosphatidylcholine (PC). The droplet confinement affected the kinetics of the phase separation, wetting, and gelation after a temperature quench, which determined the final microgel pattern. The gelatin-rich phase completely wetted to the PE membrane and formed a hollow microcapsule as a stable state in the PE droplets. Gelation during phase separation varied the relation between the droplet size and thickness of the capsule wall. In the case of the PC droplets, phase separation was completed only for the smaller droplets, wherein the microgel partially wetted the PC membrane and had a hemisphere shape. In addition, the temperature decrease below the gelation point increased the interfacial tension between the PEG/ gelatin phases and triggered a dewetting transition. Interestingly, the accompanying shape deformation to minimize the interfacial area was only observed for the smaller PC droplets. The critical size decreased as the gelatin concentration increased, indicating the role of the gel elasticity as an inhibitor of the deformation. Furthermore, variously patterned microgels with spherically asymmetric shapes, such as discs and stars, were produced as kinetically trapped states by regulating the incubation time, polymer composition, and droplet size. These findings demonstrate a way to regulate the complex shapes of microgels using the interplay among phase separation, wetting, and gelation of confined polymer blends in microdroplets. microgels | aqueous two-phase systems | sol-gel phase separation | hydrogels | emulsions T he regulation of the 3D shapes of biopolymer gels at the mesoscale has numerous applications in the biomedical, cosmetic, and food materials industries, among others (1). Recently, top-down and bottom-up approaches have been reported to control the mesoscopic patterns of polymer gels. For example, photolithography and two-photon polymerization allow the regulation of gel patterns at the mesoscale (2-4). The advanced design of the molecules enables polymerization with a self-assembly and produces nonspherical microgels: spherical particles with a cavity, capsules, and cubic particles (5-7). However, these methods require highly specialized equipment and are generally difficult to adapt for biopolymer gels.Dynamical coupling between phase separation and sol-gel transition in polymer blends has also been investigated for the spontaneous formation of spherical microgels and a porous gel (8, 9). Ma et al. (10) and Choi et al. (11) confined aqueous two-phase systems (ATPSs) in microdroplets and fabricated microgels by selective polymerization. In such a confined space, phase separation accompanies wetting of a polymer to the substrate (12-15). Although the selective polymerization of phase-se...

Increasing Elasticity through Changes in the Secondary Structure of Gelatin by Gelation in a Microsized Lipid Space

“…To investigate whether the E * value depends on the lipid affinity of gelatin, we used another species of lipids, PE, having a far higher affinity to gelatin than PC. 15 Figure 3 b shows the E value of microgels as a function of R for PE. The E values increase toward a plateau value E * ∼ 39 kPa along with a decrease in microgel size.…”

“… 17 Furthermore, physicochemical analyses have shown that microsized space and boundary conditions arising due to surrounding surfactants like lipids result in various unexpected properties of the components inside the confined space. 15 , 19 , 20 Thus, it is plausible that the preparation process determines the mechanical properties of microgels.…”

Microenvironments created by liquid-liquid phase transition control the dynamic distribution of bacterial division FtsZ protein

“…The approach we propose here allows overcoming some of the difficulties associated to these procedures, including the low yield of encapsulation, the limited amount of vesicles, the restriction to certain compositions, and the need for changes in conditions to separate the phases after encapsulation that may be incompatible when including biomolecules. Encapsulation of phases within water in oil droplets has been previously achieved using surfactants to stabilize them 54 but, to the best of our knowledge, not with lipids as the boundary material, that have been however used for single phase encapsulation in droplets 44 55 . Although our model system is not exactly the same as a living bacterial cell, it captures many of its key features as it contains crowding, compartments, microscale volume and a lipid boundary.…”

Microcapsules with a permeable hydrogel shell and an aqueous core continuously produced in a 3D microdevice by all-aqueous microfluidics

“…3 A common way to make aqueous microcapsules is to mimic nature by separating the aqueous inner and outer parts of the capsule using a lipid bilayer. [4][5][6][7][8] Another strategy, which omits the use of lipids, is to employ water-in-oil-in-water double emulsion droplets as templates, and cross-link the shell. [9][10][11][12] A major limitation of such capsules, however, is the decreased permeability of the shell to most polar solutes, including many biomolecules.…”