Dynamic polymer systems with self-regulated secretion for the control of surface properties and material healing

Abstract

Approaches for regulated fluid secretion, which typically rely on fluid encapsulation and release from a shelled compartment, do not usually allow for a fine, continuous modulation of secretion, and can be difficult to adapt for monitoring or functionintegration purposes. 1-5 Here, we report self-regulated, self-reporting secretion systems consisting of liquid-storage compartments in a supramolecular polymer-gel matrix with a thin liquid layer on top, and demonstrate that dynamic liquid exchange between the compartments, matrix and surface layer allows for repeated, responsive self-lubrication of the surface layer and for cooperative healing of the matrix. Depletion of the surface liquid or local material damage induces self-regulated secretion of the stored liquid via a dynamic feedback between polymer crosslinking, droplet shrinkage and liquid transport that can be read out through changes in the system's optical transparency. We envision diverse applications in fluid delivery, wetting and adhesion control, and material self-repair.Nearly every form of living tissue autonomously packages, transports, and secretes fluids, mediating defense, adhesion, wound healing, temperature -often several of these at once -through tightly self-regulated release systems. [6][7][8][9] Fundamental to these systems, fluid storage is itself an active, finely regulated balance. Storage droplets or vesicles continuously adjust their size, shape and contents through ongoing exchange with the surroundings, creating intrinsically responsive control mechanisms that tie secretion to a wide range of chemical and physical stimuli and feedback signals. [10][11][12][13] At the same time, collective changes in the stores are reported to the organism, alerting it that it needs to drink or eat to replenish the limited supply. Many synthetic approaches have been developed to enable triggered release from microcapsules, hydrogels, nanoparticles, vesicles, micelles, mesoporous carriers and other containers. [1][2][3][4][5][14][15][16][17] While these systems can secrete fluid in response to various stimuli, it remains a challenge to design a synthetic approach that displays finely tuned, continuous self-adjustment, integrated functionalities, and continuous liquid supply monitoring.2 Figure 1. Schematic of the self-regulated, liquid secretion system. Secretion liquid is stored as shell-less droplets inside a gel matrix composed of dynamic polymers, with ongoing liquid exchange between droplet and gel phases. If S = γ ga -(γ la + γ gl ) > 0, the matrix surface will be coated with a thin liquid overlayer. When this layer is removed, the disjoining pressure will trigger secretion of the stored liquid to restore the original film thickness, while the supramolecular gel matrix reconfigures through reversible bond disassembly and reassembly to release any buildup of mechanical stress due to shrinking droplets. With successive removal/restoring cycles, the liquid droplets will continuously shrink and the gel will become progressively transparent.Inspire...

Transparent antifouling material for improved operative field visibility in endoscopy

“…The formation of a stable lubricant overlayer on the surface creates a dynamic slippery barrier that protects the underlying substrate from direct contact with polluted media, thus drastically lowering the adsorption of various serious contaminants including bacteria (18,19) and proteins (20)(21)(22). This new, non-fouling material can be designed to perform under flow (23,24), provide enhanced damage tolerance (15,16) and selfhealing capabilities (11), or be integrated with a vascularized network that secretes the lubricant to repair the interface (25,26).…”

Antiadhesion Organogel Materials: From Liquid to Solid

“…[29] To ease the release of the liquid, Cui et al designed a supramolecular organogel with a self-regulated liquid surface layer. [15] The supramolecular polymer network was crosslinked by dynamic intermolecular hydrogen bonds, and the silicon www.advmat.de www.advancedsciencenews.com oil lubricant was stored discretely as shell-less droplets inside the polymer matrix. The thickness of the liquid surface layer was controlled to be of tens to hundreds of nanometers by the disjoining pressure of the supramolecular network.…”

“…If the liquid surface layer was disturbed or removed, a driving force created by the disjoining pressure could regulate the secretion of lubricant to retain the initial thickness. [15] In addition, the supramolecular organogel presented self-healing functionality after a knife cutting. The self-healing mechanism could be explained by the disassembly and reassembly of the hydrogen bonds within the supramolecular polymer network as schematically shown in Figure 4c.…”

“…c,d) Reproduced with permission. [15] Copyright 2015, Nature Publishing Group. Although there are some pressing issues when considering practical applications, to enhance the stability of antiadhesion organogels, unremitting efforts have been made, such as selecting high-viscosity liquids to alleviate liquid depletion, encasing vascular network as liquid reservoir, creating reversible hydrogen bonding crosslinked network to self-regulate the liquid layer, embedding fabrics in sandwich structured organogel to improve liquid retention, designing organogel in which liquid could be replenished from the vicinity, and enabling interfacial slippage of the surface materials.…”

“…designed and synthesized a copolymer of urea and poly(dimethylsiloxane) (uPDMS). [15] A homogeneous solution of uPDMS, silicone oil, and THF was coated on a substrate. With the evaporation of the solvent, uPDMS began to crosslink via forming intermolecular hydrogen bonds and the micrometer-scale silicon oil droplets began to nucleate and grow by fusing together with each other, which led to phase separation.…”