Polymerization of hydrogels inside self-assembled block copolymer vesicles.

Block copolymer vesicles are powerful tools for investigating cell adhesion since they display the fluid, deformable, semipermeable membrane properties of lipid vesicles while having greater chemical and mechanical stability. The aim of the present study was to fabricate block copolymer vesicles containing hydrogel interiors in order to extend achievable vesicle properties and, thereby, their range of cell-like behaviors. Block copolymer vesicles based on poly(butadiene-b-ethylene oxide) were demonstrated to compartmentalize and retain acrylamide solutions through particle dialysis and to allow for subsequent in situ hydrogel polymerization. Small molecule leakage studies of the resulting particles indicated that the cross-link density of the hydrogel interiors had minimal impact on vesicle permeability to small molecules (<430 Da) relative to vesicle membrane properties. In contrast, particle deformation analyses indicated that initial vesicle surface approach and adhesion was dominated by its membrane properties, whereas its ultimate deformation was primarily governed by the hydrogel interior. Thus, the hydrogel-containing vesicles allowed orthogonal control of particle surface and mechanical properties. Analysis of particle behavior in terms of Gibb's free energy minimization indicated that vesicle adhesion energy, membrane tension, and internal osmotic pressure dominated particle adhesion and deformation. Combined, the present work demonstrates the potential for designing compartmentalized, hierarchical polymer-based cell mimics with broadly tunable dynamic-mechanical properties and surface properties.