Sono‐RAFT Polymerization in Aqueous Medium

Photo-Deactivation Strategy for Switchable ATRP with the Assistance of Molecular Switches

Light irradiation is an external stimulus, rapidly developed in switchable atom transfer radical polymerization (ATRP) via photo-activation methods in recent years. Herein, a photo-deactivation strategy is introduced to regulate ATRP with the assistance of photoswitchable hexaarylbiimidozole (HABI). Under visible light irradiation and in the presence of HABI, ATRP is greatly decelerated or quenched depending on the concentration of HABI. Interestingly, with visible light off, ATRP can proceed smoothly and follow a first-order kinetics. Moreover, photo-switchable ATRP alternatively with light off and on is demonstrated. Besides, the mechanism of photo-deactivation ATRP involving radical quenching is proposed in the presence of HABI.

Sonochemical Synthesis of Natural Polyphenolic Nanoparticles for Modulating Oxidative Stress

Natural polyphenolic compounds play a vital role in nature and are widely utilized as building blocks in the fabrication of emerging functional nanomaterials. Although diverse fabrication methodologies are developed in recent years, the challenges of purification, uncontrollable reaction processes and additional additives persist. Herein, a modular and facile methodology is reported toward the fabrication of natural polyphenolic nanoparticles. By utilizing low frequency ultrasound (40 kHz), the assembly of various natural polyphenolic building blocks is successfully induced, allowing for precise control over the particle formation process. The resulting natural polyphenolic nanoparticles possessed excellent in vitro antioxidative abilities and in vivo therapeutic effects in typical oxidative stress models including wound healing and acute kidney injury. This study opens new avenues for the fabrication of functional materials from naturally occurring building blocks, offering promising prospects for future advancements in this field.

Mechanochemical Controlled Radical Polymerization: From Harsh to Mild

Mechanochemistry constitutes a burgeoning field that investigates the chemical and physicochemical alterations of substances under mechanical force. It enables the synthesis of materials which is challenging to obtain via thermal, optical or electrical activation methods. In addition, it diminishes reliance on organic solvents and provides a novel route for green chemistry. Today, as a distinct branch alongside electrochemistry, photochemistry, and thermochemistry, mechanochemistry has emerged as a frontier research domain within chemistry and material science. In recent years, the intersection of mechanochemistry with controlled radical polymerization has witnessed rapid advancements, providing new routes to polymer science. Significantly, we have experienced breakthroughs in methods relying on sonochemistry, piezoelectricity and contact electrification. These methodologies not only facilitate the synthesis of polymers with high molecular weight but also enable precise control over polymer chain length and structure. Transitioning from harsh to mild conditions in mechanochemical routes has facilitated a significant improvement in the controllability of mechanochemical polymerization. From this perspective, we introduce the progress of mechanochemistry in controlled radical polymerization in recent years, aim to clarify the historcial development of this topic.

Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light

Photoinduced polymerization techniques have gathered significant attention due to their mild conditions, spatiotemporal control, and simple setup. In addition to homogeneous media, efforts have been made to implement photopolymerization in emulsions as a practical and greener process. However, previous photoinduced reversible deactivation radical polymerization (RDRP) in heterogeneous media has relied on short-wavelength lights, which have limited penetration depth, resulting in slow polymerization and relatively poor control. In this study, we demonstrate the first example of a highly efficient photoinduced miniemulsion ATRP in the open air driven by red or near-infrared (NIR) light. This was facilitated by the utilization of a water-soluble photocatalyst, methylene blue (MB+). Irradiation by red/NIR light allowed for efficient excitation of MB+ and subsequent photoreduction of the ATRP deactivator in the presence of water-soluble electron donors to initiate and mediate the polymerization process. The NIR light-driven miniemulsion photoATRP provided a successful synthesis of polymers with low dispersity (1.09 ≤ Đ ≤ 1.29) and quantitative conversion within an hour. This study further explored the impact of light penetration on polymerization kinetics in reactors of varying sizes and a large-scale reaction (250 mL), highlighting the advantages of longer-wavelength light, particularly NIR light, for large-scale polymerization in dispersed media owing to its superior penetration. This work opens new avenues for robust emulsion photopolymerization techniques, offering a greener and more practical approach with improved control and efficiency.

BaTiO3 Catalyzed Ultrasonic-Driven Piezoelectric-Induced Reversible Addition-Fragmentation Chain-Transfer Polymerization in Aqueous Media

Compared with normal stimulus such as light and heat, ultrasonic possesses much deeper penetration into tissues and organs and has lower scattering in heterogeneous systems as a noninvasive stimulus. Reversible addition-fragmentation chain-transfer polymerization (RAFT) in aqueous media is performed in a commercial ultrasonic wash bath with 40 kHz frequency ultrasonic, in the presence of piezoelectric tetragonal BaTiO3 (BTO) nanoparticles. Owing to the electron transfer from BTO under the ultrasonic action, the water can be decomposed to produce hydroxyl radical (HO•) and initiate the RAFT polymerization (piezo-RAFT). The piezo-RAFT polymerization exhibits features of controllable and livingness, such as linear increase of molar mass and narrow molar mass distributions (Mw/Mn < 1.20). Excellent temporal control of the polymerization and the chain fidelity of polymers are illustrated by "ON and OFF" experiment and chain extension, separately. Moreover, this ultrasonic-driven piezoelectric-induced RAFT polymerization in aqueous media can be directly used for the preparation of piezoelectric hydrogel which have potential application for stress sensor.

Surface Functionalization with Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization: Synthesis, Applications, and Current Challenges

Polymer brushes have received great attention in recent years due to their distinctive properties and wide range of applications. The synthesis of polymer brushes typically employs surface-initiated atom transfer radical polymerization (SI-ATRP) techniques. To realize the control of the polymerization process in different environments, various SI-ATRP techniques triggered by different stimuli have been developed. This review focuses on the latest developments in different stimuli-triggered SI-ATRP methods, such as electrochemically mediated, photoinduced, enzyme-assisted, mechanically controlled, and organocatalyzed ATRP. Additionally, SI-ATRP technology triggered by a combination of multiple stimuli sources is also discussed. Furthermore, the applications of polymer brushes in lubrication, biological applications, antifouling, and catalysis are also systematically summarized and discussed. Despite the advancements in the synthesis of various types of 1D, 2D, and 3D polymer brushes via controlled radical polymerization, contemporary challenges remain in the quest for more efficient and straightforward synthetic protocols that allow for precise control over the composition, structure, and functionality of polymer brushes. We anticipate the readers could promote the understanding of surface functionalization based on ATRP-mediated polymer brushes and envision future directions for their application in surface coating technologies.

Engineering poly(ethylene glycol) particles for targeted drug delivery

Poly(ethylene glycol) (PEG) is considered to be the "gold standard" among the stealth polymers employed for drug delivery. Using PEG to modify or engineer particles has thus gained increasing interest because of the ability to prolong blood circulation time and reduce nonspecific biodistribution of particles in vivo, owing to the low fouling and stealth properties of PEG. In addition, endowing PEG-based particles with targeting and drug-loading properties is essential to achieve enhanced drug accumulation at target sites in vivo. In this feature article, we focus on recent work on the synthesis of PEG particles, in which PEG is the main component in the particles. We highlight different synthesis methods used to generate PEG particles, the influence of the physiochemical properties of PEG particles on their stealth and targeting properties, and the application of PEG particles in targeted drug delivery.

Shake, shear, and grind! - the evolution of mechanoredox polymerization methodology

In the last half decade, mechanoredox catalysis has enabled an entirely new genre of polymerization methodology. In this paradigm, mechanical force, such as ultrasonic cavitation bubble collapse or ball mill grinding, polarizes piezoelectric nanoparticles; the resultant piezopotential drives the redox processes necessary for free- and controlled-radical polymerizations. Since being introduced, evolution of these methods facilitates exploration of mechanistic underpinnings behind key electron-transfer events. Mechanical force has not only been identified as a "greener" alternative to more traditional reaction stimuli (e.g., heat, light) for the synthesis of commodity polymers, but also a potential technology to enable the production of novel thermoplastic and thermoset materials that are either challenging, or even impossible, to access using conventional solution-state approaches. In this Feature Article, significant contributions to such methods are highlighted within. Advances and ongoing challenges in both ultrasound and ball milling driven reactions for radical polymerization and crosslinking are identified and discussed.

Composition-Orientation Induced Mechanical Synergy in Nanoparticle Brushes with Grafted Gradient Copolymers

Gradient poly(methyl methacrylate/n-butyl acrylate) copolymers, P(MMA/BA), with various compositional ratios, were grafted from surface-modified silica nanoparticles (SiO2-g-PMMA-grad-PBA) via complete conversion surface-initiated activator regenerated by electron transfer (SI-ARGET) atom transfer radical polymerization (ATRP). Miniemulsion as the reaction medium effectively confined the interparticle brush coupling within micellar compartments, preventing macroscopic gelation and enabling complete conversion. Isolation of dispersed and gelled fractions revealed dispersed particle brushes to feature a higher Young's modulus, toughness, and ultimate strain compared with those of the "gel" counterparts. Upon purification, brush nanoparticles from the dispersed phase formed uniform microstructures. Uniaxial tension testing revealed a "mechanical synergy" for copolymers with MMA/BA = 3:2 molar ratio to concurrently exhibit higher toughness and stiffness. When compared with linear analogues of similar composition, the brush nanoparticles with gradient copolymers had better mechanical properties, attributed to the synergistic effects of the combination of composition and propagation orientation, highlighting the significance of architectural design for tethered brush layers of such hybrid materials.

Fluorescence-readout as a powerful macromolecular characterisation tool

The last few decades have witnessed significant progress in synthetic macromolecular chemistry, which can provide access to diverse macromolecules with varying structural complexities, topology and functionalities, bringing us closer to the aim of controlling soft matter material properties with molecular precision. To reach this goal, the development of advanced analytical techniques, allowing for micro-, molecular level and real-time investigation, is essential. Due to their appealing features, including high sensitivity, large contrast, fast and real-time response, as well as non-invasive characteristics, fluorescence-based techniques have emerged as a powerful tool for macromolecular characterisation to provide detailed information and give new and deep insights beyond those offered by commonly applied analytical methods. Herein, we critically examine how fluorescence phenomena, principles and techniques can be effectively exploited to characterise macromolecules and soft matter materials and to further unravel their constitution, by highlighting representative examples of recent advances across major areas of polymer and materials science, ranging from polymer molecular weight and conversion, architecture, conformation to polymer self-assembly to surfaces, gels and 3D printing. Finally, we discuss the opportunities for fluorescence-readout to further advance the development of macromolecules, leading to the design of polymers and soft matter materials with pre-determined and adaptable properties.

Temporal Regulation of PET-RAFT Controlled Radical Depolymerization

A photocatalytic RAFT-controlled radical depolymerization method is introduced for precisely conferring temporal control under visible light irradiation. By regulating the deactivation of the depropagating chains and suppressing thermal initiation, an excellent temporal control was enabled, exemplified by several consecutive "on" and "off" cycles. Minimal, if any, depolymerization could be observed during the dark periods while the polymer chain-ends could be efficiently re-activated and continue to depropagate upon re-exposure to light. Notably, favoring deactivation resulted in the gradual unzipping of polymer chains and a stepwise decrease in molecular weight over time. This synthetic approach constitutes a simple methodology to modulate temporal control during the chemical recycling of RAFT-synthesized polymers while offering invaluable mechanistic insights.

Photo Fenton RAFT Polymerization of (Meth)Acrylates in DMSO Sensitized by Methylene Blue

A novel open-to-air photo RAFT polymerization of a series of acrylate and methacrylate monomers mediated by matching chain transfer agent irradiated by far-red light in DMSO is reported. Hydroxyl radical (•OH) generated from methylene blue (MB) sensitized decomposition of H2 O2 via photo-Fenton like-reaction is used for polymerization initiation. The "living/control" characteristic is evidenced by kinetic study, in which a pseudo first order curve and linearly increases of molecular weight with the increase of monomer conversion are observed. The living end-group fidelity is characterized by MALDI-TOF-MS and 1 H NMR results, and confirmed by successful chain extension. The temporary controllability is proved by light on/off switch experiment.

Tribochemically Controlled Atom Transfer Radical Polymerization Enabled by Contact Electrification

Traditional mechanochemically controlled reversible-deactivation radical polymerization (RDRP) utilizes ultrasound or ball milling to regenerate activators, which induce side reactions because of the high-energy and high-frequency stimuli. Here, we propose a facile approach for tribochemically controlled atom transfer radical polymerization (tribo-ATRP) that relies on contact-electro-catalysis (CEC) between titanium oxide (TiO2 ) particles and CuBr2 /tris(2-pyridylmethylamine (TPMA), without any high-energy input. Under the friction induced by stirring, the TiO2 particles are electrified, continuously reducing CuBr2 /TPMA into CuBr/TPMA, thereby conversing alkyl halides into active radicals to start ATRP. In addition, the effect of friction on the reaction was elucidated by theoretical simulation. The results indicated that increasing the frequency could reduce the energy barrier for the electron transfer from TiO2 particles to CuBr2 /TPMA. In this study, the design of tribo-ATRP was successfully achieved, enabling CEC (ca. 10 Hz) access to a variety of polymers with predetermined molecular weights, low dispersity, and high chain-end fidelity.

Visible Light-Accelerated Photoiniferter Polymerization in Ionic Liquid

The effect of ionic liquids on the reversible addition-fragmentation chain transfer (RAFT) polymerization mediated by a visible-light-induced photoiniferter mechanism was investigated. N,N-Dimethyl acrylamide was polymerized by photoiniferter polymerization in 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4] ionic liquid. We observed a considerable increase in the polymerization rate constants in ionic liquids (ILs), as well as in the mixed solvent of water and the IL, compared to those observed with water alone as the solvent. To demonstrate the robustness of the process, block copolymers with varying block ratios were synthesized with precise control over their molecular weight and mass dispersity (Đ). The very high chain-end fidelity provided by the photoiniferter polymerization in IL was described by using MALDI-ToF MS analysis.

Ultrasonic Transformation of Antibiotic Molecules into a Selective Chemotherapeutic Nanodrug

Ultrasound-based engineering of carrier-free nanodrugs by supramolecular self-assembly has recently emerged as an innovative and environmentally friendly synthetic approach. By applying high-frequency sound waves (490 kHz) in aqueous solutions, the transformation of small chemotherapeutic and antibiotic drug molecules into carrier-free nanodrugs with anticancer and antimicrobial activities was recently achieved. The transformation of the antibiotic drug molecules, i.e., doxycycline, into stable nanodrugs (~130 nm) with selective anticancer activity was achieved without requiring organic solvents, chemical agents, or surfactants. The obtained nanodrug exhibited reactive oxygen species (ROS)-mediated cytotoxicity on human breast cancer (MDA-MB 231 cells) but a negligible antiproliferative effect on healthy fibroblast cells. Imaging by super-resolution microscopy (STORM) provided insights into the intracellular trafficking and endosomal escape of the nanodrugs. Overall, these findings suggest that small antibiotic drugs can be transformed into chemotherapeutic nanodrugs with high selectivity against cancer cells.

Polymerization-Induced Self-Assembly for Efficient Fabrication of Biomedical Nanoplatforms

Amphiphilic copolymers can self-assemble into nano-objects in aqueous solution. However, the self-assembly process is usually performed in a diluted solution (<1 wt%), which greatly limits scale-up production and further biomedical applications. With recent development of controlled polymerization techniques, polymerization-induced self-assembly (PISA) has emerged as an efficient approach for facile fabrication of nano-sized structures with a high concentration as high as 50 wt%. In this review, after the introduction, various polymerization method-mediated PISAs that include nitroxide-mediated polymerization-mediated PISA (NMP-PISA), reversible addition-fragmentation chain transfer polymerization-mediated PISA (RAFT-PISA), atom transfer radical polymerization-mediated PISA (ATRP-PISA), and ring-opening polymerization-mediated PISA (ROP-PISA) are discussed carefully. Afterward, recent biomedical applications of PISA are illustrated from the following aspects, i.e., bioimaging, disease treatment, biocatalysis, and antimicrobial. In the end, current achievements and future perspectives of PISA are given. It is envisioned that PISA strategy can bring great chance for future design and construction of functional nano-vehicles.

Target-Synergized Biologically Mediated RAFT Polymerization for Electrochemical Aptasensing of Femtomolar Thrombin

The assay of thrombin levels is integral to the assessment of coagulation function and clinical screening of coagulation disorder-related diseases. In this work, we illustrate the ingenious use of the target-synergized biologically mediated reversible addition-fragmentation chain transfer (RAFT) polymerization (tsBMRP) as a novel amplification strategy for the electrochemical aptamer-based biosensing of thrombin at the femtomolar levels. Briefly, the tsBMRP-based strategy relies on the boronate affinity-mediated decoration of the glycan chain(s) of the target itself with RAFT agents and the subsequent recruitment of signal labels via BMRP, mediated by the direct reduction of RAFT agents by NADH into initiating/propagating radicals. Obviously, the tsBMRP-based strategy is biologically friendly, low-cost, and simple in operation. As thrombin is a glycoconjugate, its electrochemical aptasensing involves the use of the thrombin-binding aptamer (TBA) as the recognition receptor, the site-specific decoration of RAFT agents to the glycan chain of thrombin via boronate affinity, and further the recruitment of ferrocene signal labels via the BMRP of ferrocenylmethyl methacrylate (FcMMA). As boronate affinity results in the decoration of each glycan chain with tens of RAFT agents while BMRP recruits hundreds of signal labels to each RAFT agent-decorated site, the tsBMRP-based strategy allows us to detect thrombin at a concentration of 35.3 fM. This electrochemical aptasensor is highly selective, and its applicability to thrombin detection in serum samples has been further demonstrated. The merits of high sensitivity and selectivity, low cost, good anti-interference capability, and simple operation make the tsBMRP-based electrochemical thrombin aptasensor great promise in biomedical and clinical applications.

A Perspective on the History and Current Opportunities of Aqueous RAFT Polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization has proven itself as a powerful polymerization technique affording facile control of molecular weight, molecular weight distribution, architecture, and chain end groups - while maintaining a high level of tolerance for solvent and monomer functional groups. RAFT is highly suited to water as a polymerization solvent, with aqueous RAFT now utilized for applications such as controlled synthesis of ultra-high molecular weight polymers, polymerization induced self-assembly, and biocompatible polymerizations, among others. Water as a solvent represents a non-toxic, cheap, and environmentally friendly alternative to organic solvents traditionally utilized for polymerizations. This, coupled with the benefits of RAFT polymerization, makes for a powerful combination in polymer science. This perspective provides a historical account of the initial developments of aqueous RAFT polymerization at the University of Southern Mississippi from the McCormick Research Group, details practical considerations for conducting aqueous RAFT polymerizations, and highlights some of the recent advances aqueous RAFT polymerization can provide. Finally, some of the future opportunities that this versatile polymerization technique in an aqueous environment can offer are discussed, and it is anticipated that the aqueous RAFT polymerization field will continue to realize these, and other exciting opportunities into the future.

Advances in design of polymer brush functionalized inorganic nanomaterials and their applications in biomedical arena

Grafting of polymer brush (assembly of polymer chains tethered to the substrate by one end) is emerging as one of the most viable approach to alter the surface of inorganic nanomaterials. Inorganic nanomaterials despite their intrinsic functional superiority, their applications remain restricted due to their incompatibility with organic or biological moieties vis-à-vis agglomeration issues. To overcome such a shortcoming, polymer brush modified surfaces of inorganic nanomaterials have lately proved to be of immense potential. For example, polymer brush-modified inorganic nanomaterials can act as efficient substrates/platforms in biomedical applications, ranging from drug-delivery to protein-array due to their integrated advantages such as amphiphilicity, stimuli responsiveness, enhanced biocompatibility, and so on. In this review, the current state of the art related to polymer brush-modified inorganic nanomaterials focusing, not only, on their synthetic strategies and applications in biomedical field but also the architectural influence of polymer brushes on the responsiveness properties of modified nanomaterials have comprehensively been discussed and its associated future perspective is also presented. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Microdroplet-Mediated Radical Polymerization

Micrometer-sized aqueous droplets serve as a unique reactor that drives various chemical reactions not seen in bulk solutions. However, their utilization has been limited to the synthesis of low molecular weight products at low reactant concentrations (nM to μM). Moreover, the nature of chemical reactions occurring outside the droplet remains unknown. This study demonstrated that oil-confined aqueous microdroplets continuously generated hydroxyl radicals near the interface and enabled the synthesis of polymers at high reactant concentrations (mM to M), thus successfully converting the interfacial energy into the synthesis of polymeric materials. The polymerized products maintained the properties of controlled radical polymerization, and a triblock copolymer with tapered interfaces was prepared by the sequential addition of different monomers into the aqueous microdroplets. Furthermore, a polymerization reaction in the continuous oil phase was effectively achieved by the transport of the hydroxyl radicals through the oil/water interface. This interfacial phenomenon is also successfully applied to the chain extension of a hydrophilic polymer with an oil-soluble monomer across the microdroplet interface. Our comprehensive study of radical polymerization using compartmentalization in microdroplets is expected to have important implications for the emerging field of microdroplet chemistry and polymerization in cellular biochemistry without any invasive chemical initiators.

Atom Transfer Radical Polymerization: A Mechanistic Perspective

Since its inception, atom transfer radical polymerization (ATRP) has seen continuous evolution in terms of the design of the catalyst and reaction conditions; today, it is one of the most useful techniques to prepare well-defined polymers as well as one of the most notable examples of catalysis in polymer chemistry. This Perspective highlights fundamental advances in the design of ATRP reactions and catalysts, focusing on the crucial role that mechanistic studies play in understanding, rationalizing, and predicting polymerization outcomes. A critical summary of traditional ATRP systems is provided first; we then focus on the most recent developments to improve catalyst selectivity, control polymerizations via external stimuli, and employ new photochemical or dual catalytic systems with an outlook to future research directions and open challenges.

Dimensional Optimization for ZnO-Based Mechano-ATRP with Extraordinary Activity

Various piezoelectric nanomaterials were utilized in ultrasound-mediated atom transfer radical polymerization (ATRP), owing to their outstanding piezoelectric effect. However, the relationship between the morphology of those piezocatalysts and polymerization has not been clearly established. Herein, we employed different piezoelectric zinc oxide (ZnO) nanomaterials to achieve novel mechano-induced ATRP (mechano-ATRP). Based on the synergistic effect of piezoelectric properties and specific surface area, the catalytic activity of 1D ZnO nanorods (1D-ZnO NRs) with increased aspect ratio outperformed that of 0D ZnO nanoparticles (0D-ZnO NPs). Compared to the conventional ATRP system, this system exhibited extraordinary activity toward the less activated monomer acrylonitrile (67% conversion after 6 h), with a narrow molecular weight distribution (polydispersity index ∼ 1.19). Furthermore, implications of ZnO loading, copper salt amount, degree of polymerization, monomer, and solvent were also studied for the highly efficient mechano-ATRP.

Sonosynthesis of nanobiotics with antimicrobial and antioxidant properties

Transforming small-molecule antibiotics into carrier-free nanoantibiotics represents an opportunity for developing new multifunctional therapeutic agents. In this study, we demonstrate that acoustic cavitation produced by high-frequency ultrasound transforms the antibiotic doxycycline into carrier-free nanobiotics. Upon sonication for 1 h at 10-15 W cm^-3, doxycycline molecules underwent hydroxylation and dimerization processes to ultimately self-assemble into nanoparticles of ∼100-200 nm in size. Micrometer sized particles can be also obtained by increasing the acoustic power to 20 W cm^-3. The nanodrugs exhibited antioxidant properties, along with antimicrobial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial strains. Our results highlight the feasibility of the ultrasound-based approach for engineering drug molecules into a nanosized formulation with controlled and multiple bio-functionalities.

RAFT-mediated polymerization-induced self-assembly (RAFT-PISA): current status and future directions

Polymerization-induced self-assembly (PISA) combines polymerization and self-assembly in a single step with distinct efficiency that has set it apart from the conventional solution self-assembly processes. PISA holds great promise for large-scale production, not only because of its efficient process for producing nano/micro-particles with high solid content, but also thanks to the facile control over the particle size and morphology. Since its invention, many research groups around the world have developed new and creative approaches to broaden the scope of PISA initiations, morphologies and applications, etc. The growing interest in PISA is certainly reflected in the increasing number of publications over the past few years, and in this review, we aim to summarize these recent advances in the emerging aspects of RAFT-mediated PISA. These include (1) non-thermal initiation processes, such as photo-, enzyme-, redox- and ultrasound-initiation; the achievements of (2) high-order structures, (3) hybrid materials and (4) stimuli-responsive nano-objects by design and adopting new monomers and new processes; (5) the efforts in the realization of upscale production by utilization of high throughput technologies, and finally the (6) applications of current PISA nano-objects in different fields and (7) its future directions.

Diaryliodonium salts facilitate metal-free mechanoredox free radical polymerizations

Mechanically-induced redox processes offer a promising alternative to more conventional thermal and photochemical synthetic methods. For macromolecule synthesis, current methods utilize sensitive transition metal additives and suffer from background reactivity. Alternative methodology will offer exquisite control over these stimuli-induced mechanoredox reactions to couple force with redox-driven chemical transformations. Herein, we present the iodonium-initiated free-radical polymerization of (meth)acrylate monomers under ultrasonic irradiation and ball-milling conditions. We explore the kinetic and structural consequences of these complementary mechanical inputs to access high molecular weight polymers. This methodology will undoubtedly find broad utility across stimuli-controlled polymerization reactions and adaptive material design.

Well-defined polyacrylamides with AIE properties via rapid Cu-mediated living radical polymerization in aqueous solution: thermoresponsive nanoparticles for bioimaging

There is a requirement for the development of methods for the preparation of well-controlled polymers with aggregation-induced emission (AIE) properties.

Sonochemistry-assisted photocontrolled atom transfer radical polymerization enabled by manganese carbonyl

Sonochemistry-assisted photocontrolled atom transfer radical polymerization (SAP-ATRP) is developed to circumvent the problem caused by the low penetration depth of light.

High chain-end fidelity in sono-RAFT polymerization

This study presents the preparation of well-defined multi-block copolymers and understanding of the chain-end fidelity of polymers prepared via sono-RAFT technique.

Ultrasound-assisted dopamine polymerization: rapid and oxidizing agent-free polydopamine coatings on membrane surfaces

Herein, we report a controllable pathway to accelerate the polymerization kinetics of dopamine using ultrasound as a trigger. The use of ultrasound was demonstrated to dramatically accelerate the slow liquid phase reaction kinetics and increase the deposition rate of the polydopamine coating on the surface of polymeric membranes.

Polymers Strive for Accuracy: From Sequence-Defined Polymers to mRNA Vaccines against COVID-19 and Polymers in Nucleic Acid Therapeutics

Unquestionably, polymers have influenced the world over the past 100 years. They are now more crucial than ever since the COVID-19 pandemic outbreak. The pandemic paved the way for certain polymers to be in the spotlight, namely sequence-defined polymers such as messenger ribonucleic acid (mRNA), which was the first type of vaccine to be authorized in the U.S. and Europe to protect against the SARS-CoV-2 virus. This rise of mRNA will probably influence scientific research concerning nucleic acids in general and RNA therapeutics in specific. In this Perspective, we highlight the recent trends in sequence-controlled and sequence-defined polymers. Then we discuss mRNA vaccines as an example to illustrate the need of ultimate sequence control to achieve complex functions such as specific activation of the immune system. We briefly present how mRNA vaccines are produced, the importance of modified nucleotides, the characteristic features, and the advantages and challenges associated with this class of vaccines. Finally, we discuss the chances and opportunities for polymer chemistry to provide solutions and contribute to the future progress of RNA-based therapeutics. We highlight two particular roles of polymers in this context. One represents conjugation of polymers to nucleic acids to form biohybrids. The other is concerned with advanced polymer-based carrier systems for nucleic acids. We believe that polymers can help to address present problems of RNA-based therapeutic technologies and impact the field beyond the COVID-19 pandemic.

Bioinspired Electro-RAFT Polymerization for Electrochemical Sensing of Nucleic Acids

Sensing of ultralow-abundance nucleic acids (NAs) is integral to medical diagnostics and pathogen screening. We present herein an electrochemical method for the highly selective and amplified sensing of NAs, using a peptide nucleic acid (PNA) recognition probe and a bioinspired electro-RAFT polymerization (BERP)-based amplification strategy. The presented method is based on the recognition of target NAs by end-tethered PNA probes, the labeling of thiocarbonylthio reversible addition-fragmentation chain transfer (RAFT) agents, and the BERP-assisted growth of ferrocenyl polymers. The dynamic growth of polymers is electrochemically regulated by the reduction of 1-methylnicotinamide (MNA) organic cations, the redox center of nicotinamide adenine dinucleotide (NAD⁺, coenzyme I). Specifically, electroreduction of the MNA cations causes the fragmentation of thiocarbonylthio RAFT agents into radical species, triggering the polymerization of ferrocenyl monomers, thereby recruiting plenty of ferrocene electroactive tags for amplified sensing. It is obvious that the BERP-based strategy is inexpensive and simple in operation. Benefiting from the high specificity of the PNA recognition probe and the amplified signal by the BERP-based strategy, this method is highly selective and the detection limit is as low as 0.58 fM (S/N = 3). Besides, it is applicable to the sensing of NAs in serum samples, thus showing great promise in the selective and amplified sensing of NAs.

A comparison of RAFT and ATRP methods for controlled radical polymerization

Reversible addition-fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are the two most common controlled radical polymerization methods. Both methods afford functional polymers with a predefined length, composition, dispersity and end group. Further, RAFT and ATRP tame radicals by reversibly converting active polymeric radicals into dormant chains. However, the mechanisms by which the ATRP and RAFT methods control chain growth are distinct, so each method presents unique opportunities and challenges, depending on the desired application. This Perspective compares RAFT and ATRP by identifying their mechanistic strengths and weaknesses, and their latest synthetic applications.

Sono-Fenton Chemistry Converts Phenol and Phenyl Derivatives into Polyphenols for Engineering Surface Coatings

We report a sono-Fenton strategy to mediate the supramolecular assembly of metal-phenolic networks (MPNs) as substrate-independent coatings using phenol and phenyl derivatives as building blocks. The assembly process is initiated from the generation of hydroxyl radicals (^. OH) using high-frequency ultrasound (412 kHz), while the metal ions synergistically participate in the production of additional ^. OH for hydroxylation/phenolation of phenol and phenyl derivatives via the Fenton reaction and also coordinate with the phenolic compounds for film formation. The coating strategy is applicable to various phenol and phenyl derivatives and different metal ions including Fe^II , Fe^III , Cu^II , and Co^II . In addition, the sono-Fenton strategy allows real-time control over the assembly process by turning the high-frequency ultrasound on or off. The properties of the building blocks are maintained in the formed films. This work provides an environmentally friendly and controllable method to expand the application of phenolic coatings for surface engineering.

Closed-Loop Controlled Photopolymerization of Hydrogels

Here, we present a closed-loop controlled photopolymerization process for fabrication of hydrogels with controlled storage moduli. Hydrogel crosslinking was associated with a significant change in the phase angle of a piezoelectric cantilever sensor and established the timescale of the photopolymerization process. The composition, structure, and mechanical properties of the fabricated hydrogels were characterized using Raman spectroscopy, scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA). We found that the storage moduli of photocured poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(N-isopropylacrylamide) (PNIPAm) hydrogels could be controlled using bang-bang and fuzzy logic controllers. Bang-bang controlled photopolymerization resulted in constant overshoot of the storage modulus setpoint for PEGDMA hydrogels, which was mitigated by setpoint correction and fuzzy logic control. SEM and DMA studies showed that the network structure and storage modulus of PEGDMA hydrogels were dependent on the cure time and temporal profile of UV exposure during photopolymerization. This work provides an advance in pulsed and continuous photopolymerization processes for hydrogel engineering based on closed-loop control that enables reproducible fabrication of hydrogels with controlled mechanical properties.

Reversible redox controlled acids for cationic ring-opening polymerization

Advancements in externally controlled polymerization methodologies have enabled the synthesis of novel polymeric structures and architectures, and they have been pivotal to the development of new photocontrolled lithographic and 3D printing technologies. In particular, the development of externally controlled ring-opening polymerization (ROP) methodologies is of great interest, as these methods provide access to novel biocompatible and biodegradable block polymer structures. Although ROPs mediated by photoacid generators have made significant contributions to the fields of lithography and microelectronics development, these methodologies rely upon catalysts with poor stability and thus poor temporal control. Herein, we report a class of ferrocene-derived acid catalysts whose acidity can be altered through reversible oxidation and reduction of the ferrocenyl moiety to chemically and electrochemically control the ROP of cyclic esters.

High-Throughput Routes to Biomaterials Discovery

Many existing clinical treatments are limited in their ability to completely restore decreased or lost tissue and organ function, an unenviable situation only further exacerbated by a globally aging population. As a result, the demand for new medical interventions has increased substantially over the past 20 years, with the burgeoning fields of gene therapy, tissue engineering, and regenerative medicine showing promise to offer solutions for full repair or replacement of damaged or aging tissues. Success in these fields, however, inherently relies on biomaterials that are engendered with the ability to provide the necessary biological cues mimicking native extracellular matrixes that support cell fate. Accelerating the development of such "directive" biomaterials requires a shift in current design practices toward those that enable rapid synthesis and characterization of polymeric materials and the coupling of these processes with techniques that enable similarly rapid quantification and optimization of the interactions between these new material systems and target cells and tissues. This manuscript reviews recent advances in combinatorial and high-throughput (HT) technologies applied to polymeric biomaterial synthesis, fabrication, and chemical, physical, and biological screening with targeted end-point applications in the fields of gene therapy, tissue engineering, and regenerative medicine. Limitations of, and future opportunities for, the further application of these research tools and methodologies are also discussed.

Self-assembly of protein-polymer conjugates for drug delivery

Protein-polymer conjugates are a class of molecules that combine the stability of polymers with the diversity, specificity, and functionality of biomolecules. These bioconjugates can result in hybrid materials that display properties not found in their individual components and can be particularly relevant for drug delivery applications. Engineering amphiphilicity into these bioconjugate materials can lead to phase separation and the assembly of high-order structures. The assembly, termed self-assembly, of these hierarchical structures entails multiple levels of organization: at each level, new properties emerge, which are, in turn, influenced by lower levels. Here, we provide a critical review of protein-polymer conjugate self-assembly and how these materials can be used for therapeutic applications and drug delivery. In addition, we discuss central bioconjugate design questions and propose future perspectives for the field of protein-polymer conjugate self-assembly.

Ultrasound expands the versatility of polydopamine coatings

Polydopamine (PDA) coating of surfaces is a versatile strategy to fabricate functional films on various substrates, which typically requires oxygen and alkaline pH. Overcoming such limitations may enhance the versatility of this technique. Herein, we develop a simple and green sonochemical process for PDA coatings, which overcomes the limitations of traditional coating technique and expands the versatility of PDA chemistry. The oxidizing radicals generated by high frequency ultrasound (412 kHz) are utilized to initiate and accelerate the polymerization of dopamine. The sonochemical rate of film deposition is found to be about twice faster than that of the traditional method in the presence of oxygen. Importantly, the PDA coatings can be obtained in neutral or acidic aqueous solutions and even in the absence of oxygen. The PDA coatings can be moderated by turning on or off high frequency ultrasound. This study provides an environmentally friendly and economic method for the engineering of PDA coatings independent of the solution pH and nature of dissolved gas.