A guide to the selection of switchable functional groups for CO2-switchable compounds

CO₂-responsive species in water interconvert between neutral and bicarbonate forms, but only if the species has appropriate basicity.

Switching biological functionalities of biointerfaces via dynamic covalent bonds

We construct a stimuli responsive biointerface via a dynamic covalent bond that could switch its surface biofunctionalities on demand. The switchability is achieved via reversible attaching/detaching of aldehyde end-functionalized biomacromolecules.

Solvent-Driven Formation of Worm-Like Micelles Assembled from a CO₂-Responsive Triblock Copolymer

Polymer worm-like micelles (WLMs) are difficult to target due to the narrow composition window. In this work, we report polymer WLMs self-assembled from a linear ABC triblock copolymer consisting of an intermediate fluorinated block of poly(2,2,3,4,4,4-hexafluorobutyl methacrylate) (F), a hydrophilic segment of poly(ethylene oxide) (O) and a CO2-responsive flank of poly(2-(diethylamino)ethyl methacrylate) (E). In the mixed solvent of water and ethanol, the polymer aggregates evolve from spheres to short rods, then long cylinders and finally WLMs when the volume ratio of water increases from 0 to 50%. Upon the stimulus of CO2, the E block is protonated, thus transforms from hydrophobic to hydrophilic. However, the WLMs just partially return back to spheres even the protonation degree of E block is up to 95%. The closely packed arrangement of fluorinated block caused by the increasing interfacial tension of the fluorinated blocks and solvent could account for the formation of WLMs and its shape alternation under CO2 stimulus.

Highly Sensitive CO₂-Responsive Polymeric Microgels That Respond Within Seconds

In this work, polymeric microgels with swift response to CO2 are synthesized by polymerization of tertiary-amine containing methacrylate monomers (N,N-diethylaminoethyl methacrylate, DEAEMA) and polyethylene glycol monomethyl ether acrylate (PEGMA) as stabilizers. The obtained microgels are stable but very sensitive to CO2, which can rapidly swell and further collapse within 5 s upon bubbling of CO2, or within minutes in an atmosphere of gaseous CO2. The protonation of the tertiary amine groups in the presence of CO2 induces sensitive swelling and further irreversible collapse of the microgels due to the internal charge repulsion and relatively low cross-linking density in the core area of microgels. This rapid response to CO2 may find further applications in the fields of sensitive detection or responsive loading and release upon CO2 stimulus.

Electrochemical redox responsive polymeric micelles formed from amphiphilic supramolecular brushes

The end-decorated homopolymer poly(ε-caprolactone)-ferrocene threaded onto a β-cyclodextrin-functionalized main-chain polymer can form a class of amphiphilic noncovalent graft copolymers based on the host-guest interactions of the terminal groups on the side chains. These new supramolecular polymer brushes can further self-assemble into micellar aggregates that exhibit reversible assembly and disassembly behavior under an electrochemical redox trigger, which opens up a new route to building dynamic block copolymer topologies.

Controlled decoration of the surface with macromolecules: polymerization on a self-assembled monolayer (SAM)

Polymer functionalized surfaces are important components of various sensors, solar cells and molecular electronic devices. In this context, the use of self-assembled monolayer (SAM) formation and subsequent reactions on the surface have attracted a lot of interest due to its stability, reliability and excellent control over orientation of functional groups. The chemical reactions to be employed on a SAM must ensure an effective functional group conversion while the reaction conditions must be mild enough to retain the structural integrity. This synthetic constraint has no universal solution; specific strategies such as "graft from", "graft to", "graft through" or "direct" immobilization approaches are employed depending on the nature of the substrate, polymer and its area of applications. We have reviewed current developments in the methodology of immobilization of a polymer in the first part of the article. Special emphasis has been given to the merits and demerits of certain methods. Another issue concerns the utility - demonstrated or perceived - of conjugated or non-conjugated macromolecules anchored on a functionally decorated SAM in the areas of material science and biotechnology. In the last part of the review article, we looked at the collective research efforts towards SAM-based polymer devices and identified major pointers of progress (236 references).

Gas-breathing polymer film for constructing switchable ionic diodes

A fluidic diode is constructed based on nanopore supported gas-responsive polymer film, which exhibits on/off ratio more than 10 000 under asymmetrical stimulation with pH or gas pairs.

Amphiphilic block copolymer terminated with pyrene group: from switchable CO2-temperature dual responses to tunable fluorescence

Py-PCL-b-P(NIPAM-co-DMAEMA) micelles can present switchable CO₂-temperature dual responses and tunable fluorescence properties.

Hydrophobic effects within the dynamic pH-response of polybasic tertiary amine methacrylate brushes

Monomer hydrophobicity dominates the kinetics of the pH-response of tertiary amine methacrylate brushes as determined by in situ ellipsometry and QCM-D kinetic and equilibrium measurements.

Synthesis and self-assembly of CO2-responsive dendronized triblock copolymers

Dendronized amphiphilic block copolymers POEGMA-b-P(Gn)-b-PDEAEMA were synthesized, and their self-assembly behavior could be regulated by the dendron generation, the type of common solvent, and CO₂-stimulus.

An underwater superoleophobic surface that can be activated/deactivated via external triggers

Poly[(2-dimethylamino)ethyl methacrylate] (pDMAEMA) brush surfaces were prepared using a facile aqueous Activators ReGenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET-ATRP) protocol at ambient temperature without any need to purge reaction solutions of oxygen. This produced underwater superoleophobic surfaces, which exhibited high advancing (θA, 164-166°) and receding (θR, 153-165°) contact angles (CAs) and low CA hysteresis (1-11°) with a variety of oils. Both in situ spectroscopic ellipsometry and dynamic CA measurements confirmed that pDMAEMA brush surfaces responded to three different external stimuli (pH, ionic strength, and temperature) by changing their thicknesses, degree of hydration, or their chemical composition. Increasing pH resulted in the largest decrease in hydration, followed by increasing temperature, and increasing ionic strength gave the smallest change in hydration. Coincident with these structural changes, stimulus-responsive dynamic dewetting behavior with various oils was observed. Increasing pH or ionic strength drastically reduced the θR values of oil drops and increased CA hysteresis, resulting in a sticky surface on which oil drops were pinned. No noticeable changes in dynamic oleophobicity were observed with increasing temperature. In addition, when oil drops impacted onto the brush surface instead of being gently placed, surfaces did not exhibit stimulus-responsive dewetting properties, being oleophobic under all conditions.

CO2-switchable multi-compartment micelles with segregated corona

CO2-switchable multi-compartment micelles (MCMs) with a segregated corona formed by a purpose-designed ABC triblock copolymer are reported. They can be switched "on" and "off" when sequentially treated with CO2 and N2, due to the protonation-deprotonation of the tertiary amine groups along the polymer skeleton.

Blood compatible materials: state of the art

Devices that function in contact with blood are ubiquitous in clinical medicine and biotechnology. These devices include vascular grafts, coronary stents, heart valves, catheters, hemodialysers, heart-lung bypass systems and many others. Blood contact generally leads to thrombosis (among other adverse outcomes), and no material has yet been developed which remains thrombus-free indefinitely and in all situations: extracorporeally, in the venous circulation and in the arterial circulation. In this article knowledge on blood-material interactions and "thromboresistant" materials is reviewed. Current approaches to the development of thromboresistant materials are discussed including surface passivation; incorporation and/or release of anticoagulants, antiplatelet agents and thrombolytic agents; and mimicry of the vascular endothelium.

Critical salt effects in the swelling behavior of a weak polybasic brush

The swelling behavior of poly(2-(diethylamino)ethyl methacrylate) (PDEA) brushes in response to changes in solution pH and ionic strength has been investigated. The brushes were synthesized by ARGET ATRP methodology at the silica-aqueous solution interface via two different surface-bound initiator approaches: electrostatically adsorbed cationic macroinitiator and covalently anchored silane-based ATRP initiator moieties. The pH-response of these brushes is studied as a function of the solvated brush thickness in a constant flow regime that elucidates the intrinsic behavior of polymer brushes. In situ ellipsometry equilibrium measurements show the pH-induced brush swelling and collapse transitions are hysteretic in nature. Furthermore, high temporal resolution kinetic studies demonstrate that protonation and solvent ingress during swelling occur much faster than the brush charge neutralization and solvent expulsion during collapse. This hysteresis is attributed to the formation of a dense outer region or skin during collapse that retards solvent egress. Moreover, at a constant pH below its pKa, the PDEA brush exhibited a critical conformational change in the range 0.5-1 mM electrolyte, a range much narrower than predicted by the theory of the osmotic brush regime. This behavior is attributed to the hydrophobicity of the collapsed brush. The swelling and collapse kinetics for this salt-induced transition are nearly identical. This is in contrast to the asymmetry in the rate of the pH-induced response, suggesting an alternative mechanism for the two processes dependent on the nature of the environmental trigger.

Synthesis and properties of CO2-switchable Dex-g-PAHMA copolymers

CO₂-switchable Dex-g-PAHMA copolymers were synthesized and characterized. The properties of the graft copolymers and the cytotoxicity and cellular uptake of DOX-loaded Dex-g-PAHMA copolymer micelles were investigated.

Block copolymer self-assembly controlled by the “green” gas stimulus of carbon dioxide

CO₂ can act as a “green” stimulus to precisely tune the self-assembly of block copolymers.

A CO2-responsive surface with an amidine-terminated self-assembled monolayer for stimuli-induced selective adsorption

A novel amidine-based bifunctional molecule is synthesized for fabrication of a CO₂-responsive surface. Controlling reversible transition of surface charges and wettability in response to stimuli of dissolved CO₂ in water, the selective adsorption of hydrophobic/hydrophilic molecules can be easily achieved.