“Breathing” CO 2 ‐, O 2 ‐, and Light‐Responsive Vesicles from a Triblock Copolymer for Rate‐Tunable Controlled Release

Gas-Responsive Smart Membrane Separation

Membrane separation technology is one of the most important techniques in modern separation science. To understand the self-regulation mechanisms of cell membranes and mimic their working principles, a plethora of artificial membranes with responsive abilities to external stimuli have been engineered and prepared, whose smart sieving functions continue to attract attention and are applied in various fields. Among all the known stimuli, gas as a new trigger mode exhibits certain biocompatibility and offer irreplaceable advantages compared to other stimuli, such as cleanliness, ease-of-handling, and nondestructive, which make gas-responsive membranes as one of the most promising, smart separation materials. In this review, we summarize recent breakthroughs in the development of gas-responsive membranes, outline the novel strategies on membrane fabrication, and highlight their advanced applications in controlled cargo release, size-/charge-based substance separation, oil-water separation, and self-cleaning. We also outlook the perspectives on the potential research directions and opportunities in the future.

Active responsive colloids driven by intrinsic dichotomous noise

We study the influence of intrinsic noise on the structure and dynamics of responsive colloids (RCs), which actively change their size and mutual interactions. The colloidal size is explicitly resolved in our RC model as an internal degree of freedom (DOF) in addition to the particle translation. A Hertzian pair potential between the RCs leads to repulsion and shrinking of the particles, resulting in an explicit responsiveness of the system to self-crowding. To render the colloids active, their size is internally driven by a dichotomous noise, randomly switching ("breathing") between growing and shrinking states with a predefined rate, as motivated by recent experiments on synthetic active colloids. The polydispersity of this dichotomous active responsive colloid (D-ARC) model can be tuned by the parameters of the noise. Utilizing stochastic computer simulations, we study crowding effects on the spatial distributions, relaxation times, and self-diffusion of dense suspensions of the D-ARCs. We find a substantial influence of the "built-in" intrinsic noise on the system's behavior, in particular, transitions from unimodal to bimodal size distributions for an increasing colloid density as well as intrinsic noise-modified diffusive translational dynamics. We conclude that controlling the noise of internal DOFs of a macromolecule or cell is a powerful tool for active colloidal materials to enable autonomous changes in the system's collective structure and dynamics towards the adaptation of macroscopic properties to external perturbations.

Dual Gas-responsive Fluorescent Diblock Copolymer Synthesized via RAFT Polymerization

Stimulus-responsive polymers with luminescence properties have a wide range of applications in the fields of controlled drug release, fluorescent probes, and biological stents. In this paper, carbon dioxide (CO₂)/oxygen (O₂) dual-responsive fluorescent diblock copolymers were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization method with two fluorescent monomers synthesized as its luminescence source, DEAEMA (CO₂ responsive monomer) and tFMA (O₂ responsive monomer). An experimental study demonstrated that the synthesized stimulus-responsive fluorescent polymer had a high sensitivity to CO₂; the double-responsive fluorescent diblock copolymer could form and achieve the reversal of polymer micelles in the aqueous solution when it was sequentially subjected to the introduction of CO₂ and O₂.

Asymmetric polymersomes, from the formation of asymmetric membranes to the application on drug delivery

Nano drug delivery systems have attracted researchers' growing attention and are gradually emerging into the public views. More and more nano-formulations are being approved for marketing or clinical use, representing the field's booming development. Copolymer self-assembly systems such as micelles, nanoparticles, polymersomes occupy a prominent position in the field of nano-drug delivery carriers. Among them, polymersomes, unlike micelles or nanoparticles, resemble liposomes' structure and possess large internal hollow hydrophilic reservoirs, allowing them to carry hydrophilic drugs. Nevertheless, their insufficient drug loading efficiency and unruly self-assembly morphology have somewhat constrained their applications. Especially for the delivery of biomacromolecule such as peptides, the encapsulation efficiency is always considered to be a formidable obstacle, even if the enormous hydrophilic core would render the polymersomes to have considerable potential in this regard. Reassuringly, the emergence of asymmetric polymersomes holds the prospect of solving this problem. With the development of synthetic technology and a deeper understanding of the self-assembly process, the asymmetric polymersomes which are with different inner and outer shell composition have been gradually recognized by researchers. It has made possible elevated drug loading, more controllable assembly processes and release performance. The internal hydrophilic blocks different from the outer shell could be engineered to have a more remarkable affinity to the cargos or could contain a non-watery aqueous phase to enable the thermodynamically preferred encapsulation of cargos, which would allow for a substantial improvement in drug encapsulation efficiency compared to the conventional approach. In this paper, we aim to deepen the understanding to asymmetric polymersomes and lay the foundation for the development of this field by describing four main elements: the mechanism of their preparation and asymmetric membrane formation process, the characterization of asymmetric membranes, the efficient drug loading, and the special stimulus-responsive release mechanism.

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.

Fabrication of the Polymersomes with Unique and Even Nonequilibrium Morphologies

Herein, efficient fabrication of polymersomes that have unique and nonequilibrium morphologies is reported. Starting from preparing big polymeric vesicles sized around 2 µm with a flexible but crosslinkable structure, a controllable morphological transformation process from the vesicles via prolate vesicles and the pearl-chain-like structure, which are the two intermediate structures, to vesicle-end-capped tubes is conducted. Significantly, each of the intermediates is a regular polymersome and occupies a distinct phase space in the transformation process and thus can be separately processed and prepared. By crosslinking the structures, respectively, regular polymersomes with unique but stable morphologies are fabricated. Furthermore, the 1D polymersomes contain narrow necks. These narrow necks are sensitive to ultrasound vibration and broken by gentle ultrasound treatment to form regular open-ended tubes and open-ended vesicles, which are nonequilibrium but stable morphologies and difficult to prepare by existing methods.

Polymersomes: Breaking the Glass Ceiling?

Polymer vesicles, also known as polymersomes, have garnered a lot of interest even before the first report of their fabrication in the mid-1990s. These capsules have found applications in areas such as drug delivery, diagnostics and cellular models, and are made via the self-assembly of amphiphilic block copolymers, predominantly with soft, rubbery hydrophobic segments. Comparatively, and despite their remarkable impermeability, glassy polymersomes (GPs) have been less pervasive due to their rigidity, lack of biodegradability and more restricted fabrication strategies. GPs are now becoming more prominent, thanks to their ability to undergo stable shape-change (e.g., into non-spherical morphologies) as a response to a predetermined trigger (e.g., light, solvent). The basics of block copolymer self-assembly with an emphasis on polymersomes and GPs in particular are reviewed here. The principles and advantages of shape transformation of GPs as well as their general usefulness are also discussed, together with some of the challenges and opportunities currently facing this area.

CO2-Acidolysis of iminoboronate ester based polymersomes

The iminoboronate-terminalized star-like prodrug N₃-(OEG-IBCAPE)₄ was prepared to investigate the CO₂-acidolysis of polymersomes with a tunable release feature of CAPE molecules.

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.

UV-triggered shape-controllable PP fabric

A light-driven polypropylene (PP) fabric as an actuator was fabricated in which a light-responsive polymeric film acts as an active layer and a PP fabric acts as a passive layer.