Gas-Responsive Self-Assemblies for Mimicking the Alveoli

In human body, alveoli are the primary sites for gas exchange which are formed by the dilation and protrusion of bronchioles at the end of the lung, and the rapid gas-exchanging process in the alveoli ensures normal life activities. Based on the unique structures and functions of alveoli, it is necessary to study the regulation mechanism of its formation, respiration, and apoptosis. Herein, a class of reversible addition-fragmentation chain transfer (RAFT)-derived amphiphilic triblock copolymers, PEO-b-P(DEAEMA-co-FMA)-b-PS is designed and synthesized. Due to the amphiphilic and gas-responsive segments, these triblock copolymers can self-assemble in aqueous solution and undergo the morphological transition from nanotubes to vesicles under gas stimulation; meanwhile, in the cycles of CO₂ /O₂ stimulation, these vesicles can further realize the volume expansion and contraction, eventually rupture. The gas-driven morphological transformations of these aggregates successfully imitate the formation, respiration, and apoptosis of alveoli, and provide an essential basis for revealing the life phenomena.

Thermoresponse and self-assembly of an ABC star quarterpolymer with O2 and redox dual-responsive Y junctions

The stimuli-tunable LCST-type phase transition and self-assembly behaviors of a multi-responsive 3-miktoarm star bearing O₂/redox-sensitive and H-bond-switchable Y junctions were revealed.

CO2-Switchable Membranes Prepared by Immobilization of CO2-Breathing Microgels

Herein, we report the development of a novel CO₂-responsive membrane system through immobilization of CO₂-responsive microgels into commercially available microfiltration membranes using a method of dynamic adsorption. The microgels, prepared from soap-free emulsion polymerization of CO₂-responsive monomer 2-(diethylamino)ethyl methacrylate (DEA), can be reversibly expanded and shrunken upon CO₂/N₂ alternation. When incorporated into the membranes, this switching behavior was preserved and further led to transformation between microfiltration and ultrafiltration membranes, as indicated from the dramatic changes on water flux and BSA rejection results. This CO₂-regulated performance switching of membranes was caused by the changes of water transportation channel, as revealed from the dynamic water contact angle tests and SEM observation. This work represents a simple yet versatile strategy for making CO₂-responsive membranes.

Highly Porous Poly(high internal phase emulsion) Membranes with "Open-Cell" Structure and CO2-Switchable Wettability Used for Controlled Oil/Water Separation

Polymer membranes with switchable wettability have promising applications in smart separation. Hereby, we report highly porous poly(styrene-co-N,N-(diethylamino)ethyl methacrylate) (i.e., poly(St-co-DEA)) membranes with "open-cell" structure and CO₂-switchable wettability prepared from water-in-oil (W/O) high internal phase emulsion (HIPE) templates. The open-cell porous structure facilitates fluid penetration through the membranes. The combination of CO₂-switchable functionality and porous microstructure enable the membrane with CO₂-switchable wettability from hydrophobic or superoleophilic to hydrophilic or superoleophobic through CO₂ treatment in an aqueous system. This type of membrane can be used for gravity-driven CO₂-controlled oil/water separation, in which oil selectively penetrates through the membrane and separates from water. After being treated with CO₂ switching wettability of the membrane, a reversed separation of water and oil can be achieved. Such a wettability switch is fully reversible, and the membrane could be regenerated through simple removal of CO₂ and oil residual through drying. This facile and cost-effective approach represents the development of the first CO₂-switchable polyHIPE system, which is promising for smart separation in a large volume.

Breathable Microgel Colloidosome: Gas-Switchable Microcapsules with O2 and CO2 Tunable Shell Permeability for Hierarchical Size-Selective Control Release

Microcapsules enabling precise delivery and controlled release are highly desirable. However, it is still challenging to control the release profile by regulating the microcapsule shell permeability. In this work, gas-switchable microgel colloidosome (MGC) with oxygen (O₂) and carbon dioxide (CO₂) dual gas-tunable shell permeability has been developed and tested for control release of water-soluble cargo molecules, based on the size exclusion mechanism. The O₂ and CO₂ dual gas-switchable poly(2-(diethylamino)ethyl methacrylate-co-2,3,4,5,6-pentafluorostyrene), P(DEA-co-FS), microgels having surface modified with amino group (-NH₂) were synthesized and used to stabilize oil-in-water (O/W) Pickering emulsions. The oil-soluble poly(propylene glycol) diglycidyl ether (PPGDGE) was added as an intermicrogel cross-linker. The cross-linking between adjacent microgel particles at the water-oil interface was achieved through the amine-epoxy reaction of PPGDGE with the amine groups at the particle surface. Fluorescent-labeled dextran model cargo molecules of 10 kDa (D₁) and 2000 kDa (D₂) were uploaded under CO₂ treatment and locked inside the MGC with N₂ treatment. The O₂ and CO₂ dual-gas switchable properties offered the MGC with tunable shell permeability, which allowed the hierarchical release of D₁ and D₂ based on size exclusive mechanism. This work provides a robust method for preparation of gas-switchable microcapsules with tunable permeability and size-exclusive hierarchical release profile, promising for multiple ingredient controllable release, separation, and reaction.

Gas-Responsive Polymers

Gas-responsive polymers have inspired much interest over the past ten years. Gas triggers can interact with functionalities on polymer chains and, thus, modulate their chain structures, architectures, and aggregation states. This review summarizes the latest research progresses in the theme of developing different gas triggers for fine control over some critical properties of polymers, as well as their potential applications in various areas. We focus on the interactions/reactions between gases and gas-responsive functionalities of polymers and highlight some state-of-art developments, which provided good insight and understanding of each particular gas-responsive polymer. We also offer a perspective point of view on future research directions on gas-responsive polymers, both in fundamental studies and in potential application developments.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.