Open-to-Air RAFT Polymerization in Complex Solvents: From Whisky to Fermentation Broth

Observation and Modeling of a Sharp Oxygen Threshold in Aqueous Free Radical and RAFT Polymerization

It is known that oxygen (O₂) stops radical polymerization (RP). Here, it was found that the reaction turn-off occurs abruptly at a threshold concentration of O₂, [O₂]_t, for both free RP and reversible addition-fragmentation chain-transfer polymerization (RAFT). In some reactions, there was a spontaneous re-start of conversion. Three cases were investigated: RP of (i) acrylamide (Am) and (ii) sodium styrene sulfonate (SS) and (iii) Am RAFT polymerization. A controlled flow of O₂ into the reactor was employed. An abrupt turn-off was observed in all cases, where polymerization stops sharply at [O₂]_t and remains stopped when [O₂] > [O₂]_t. In (i), Am acts as a catalytic radical-transfer agent during conversion plateau, eliminating excess [O₂], and polymerization spontaneously resumes at [O₂]_t. In no reaction, the initiator alone was capable of eliminating O₂. N₂ purge was needed to re-start reactions (ii) and (iii). For (i) and (ii), while [O₂] < [O₂]_t, O₂ acts a chain termination agent, reducing the molecular weight (M_w) and reduced viscosity (RV). O₂ acts as an inhibitor for [O₂] > [O₂]_t in all cases. The radical-transfer rates from Am* and SS* to O₂ are >10,000× higher than the initial chain propagation step rates for Am and SS, which causes [O₂]_t at very low [O₂].

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.

A dual initiator approach for oxygen tolerant RAFT polymerization

Reversible-deactivation radical polymerizations are privileged approaches for the synthesis of functional and hybrid materials. A bottleneck for conducting these processes is the need to maintain oxygen free conditions. Herein we report a broadly applicable approach to "polymerize through" oxygen using the synergistic combination of two radical initiators having different rates of homolysis. The in situ monitoring of the concentrations of oxygen and monomer simultaneously provided insight into the function of the two initiators and enabled the identification of conditions to effectively remove dissolved oxygen and control polymerization under open-to-air conditions. By understanding how the surface area to volume ratio of reaction vessels influence open-to-air polymerizations, well-defined polymers were produced using acrylate, styrenic, and methacrylate monomers, which each represent an expansion of scope for the "polymerizing through" oxygen approach. Demonstration of this method in tubular reactors using continuous flow chemistry provided a more complete structure-reactivity understanding of how reaction headspace influences PTO RAFT polymerizations.

Enzyme Catalysis for Reversible Deactivation Radical Polymerization

Enzyme catalysis has been increasingly utilized in reversible deactivation radical polymerization (Enz-RDRP) on account of its mildness, efficiency, and sustainability. In this Minireview we discuss the key roles enzymes play in RDRP, including their ATRPase, initiase, deoxygenation, and photoenzyme activities. We use selected examples to highlight applications of Enz-RDRP in surface brush fabrication, sensing, polymerization-induced self-assembly, and high-throughput synthesis. We also give our reflections on the challenges and future directions of this emerging area.

Materiomically Designed Polymeric Vehicles for Nucleic Acids: Quo Vadis?

Despite rapid advances in molecular biology, particularly in site-specific genome editing technologies, such as CRISPR/Cas9 and base editing, financial and logistical challenges hinder a broad population from accessing and benefiting from gene therapy. To improve the affordability and scalability of gene therapy, we need to deploy chemically defined, economical, and scalable materials, such as synthetic polymers. For polymers to deliver nucleic acids efficaciously to targeted cells, they must optimally combine design attributes, such as architecture, length, composition, spatial distribution of monomers, basicity, hydrophilic-hydrophobic phase balance, or protonation degree. Designing polymeric vectors for specific nucleic acid payloads is a multivariate optimization problem wherein even minuscule deviations from the optimum are poorly tolerated. To explore the multivariate polymer design space rapidly, efficiently, and fruitfully, we must integrate parallelized polymer synthesis, high-throughput biological screening, and statistical modeling. Although materiomics approaches promise to streamline polymeric vector development, several methodological ambiguities must be resolved. For instance, establishing a flexible polymer ontology that accommodates recent synthetic advances, enforcing uniform polymer characterization and data reporting standards, and implementing multiplexed in vitro and in vivo screening studies require considerable planning, coordination, and effort. This contribution will acquaint readers with the challenges associated with materiomics approaches to polymeric gene delivery and offers guidelines for overcoming these challenges. Here, we summarize recent developments in combinatorial polymer synthesis, high-throughput screening of polymeric vectors, omics-based approaches to polymer design, barcoding schemes for pooled in vitro and in vivo screening, and identify materiomics-inspired research directions that will realize the long-unfulfilled clinical potential of polymeric carriers in gene therapy.

Air-tolerant Reversible Complexation Mediated Polymerization (RCMP) Using Aldehyde as Oxygen Removera

An air-tolerant reversible complexation mediated polymerization (RCMP) technique, which can be carried out without prior deoxygenation, was developed. The system contains a monomer, an alkyl iodide initiating dormant species, air (oxygen), an aldehyde, N-hydroxyphthalimide (NHPI), and a base. Oxygen is consumed via the NHPI-catalyzed conversion of the aldehyde (RCHO) to a carboxylic acid (RCOOH). The generated RCOOH is further converted to a carboxylate anion (RCOO^- ) by the base. The RCOO^- generated in situ works as an RCMP catalyst; the polymerization proceeds with the monomer, alkyl iodide dormant species, and RCOO^- catalyst. Thus, the system is not only air-tolerant but also does not require additional RCMP catalysts, which is a notable feature of this system. (NHPI is used as an oxidation catalyst for converting RCHO to RCOOH.) This technique is amenable to methyl methacrylate, butyl methacrylate, benzyl methacrylate, 2-hydroxyethyl methacrylate, and styrene, yielding polymers with relatively low-dispersity (M_w /M_n = 1.20-1.49), where M_w and M_n are the weight- and number-average molecular weights, respectively. This article is protected by copyright. All rights reserved.

Defining the Macromolecules of Tomorrow through Synergistic Sustainable Polymer Research

Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this Chemical Reviews contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena. The Review highlights signature accomplishments across a broad research portfolio and is organized into four wide-ranging research themes that address the topic in a comprehensive manner: Feedstocks, Polymerization Processes and Techniques, Intended Use, and End of Use. We emphasize those successes that benefitted from collaborative engagements across disciplinary lines.

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.

Biocatalytic nanoparticles for the stabilization of degassed single electron transfer-living radical pickering emulsion polymerizations

Synthetic polymers are indispensable in many different applications, but there is a growing need for green processes and natural surfactants for emulsion polymerization. The use of solid particles to stabilize Pickering emulsions is a particularly attractive avenue, but oxygen sensitivity has remained a formidable challenge in controlled polymerization reactions. Here we show that lignin nanoparticles (LNPs) coated with chitosan and glucose oxidase (GOx) enable efficient stabilization of Pickering emulsion and in situ enzymatic degassing of single electron transfer-living radical polymerization (SET-LRP) without extraneous hydrogen peroxide scavengers. The resulting latex dispersions can be purified by aqueous extraction or used to obtain polymer nanocomposites containing uniformly dispersed LNPs. The polymers exhibit high chain-end fidelity that allows for production of a series of well-defined block copolymers as a viable route to more complex architectures.

Open-to-Air RAFT Polymerization on a Surface under Ambient Conditions

Oxygen (O₂)-mediated controlled radical polymerization was performed on surfaces under ambient conditions, enabling on-surface polymer brush growth under open-to-air conditions at room temperature in the absence of metal components. Polymerization of zwitterionic monomers using this O₂-mediated surface-initiated reversible addition fragmentation chain-transfer (O₂-SI-RAFT) method yielded hydrophilic surfaces that exhibited anti-biofouling effects. O₂-SI-RAFT polymerization can be performed on large surfaces under open-to-air conditions. Various monomers including (meth)acrylates and acrylamides were employed for O₂-SI-RAFT polymerization; the method is thus versatile in terms of the polymers used for coating and functionalization. A wide range of hydrophilic and hydrophobic monomers can be employed. In addition, the end-group functionality of the polymer grown by O₂-SI-RAFT polymerization allowed chain extension to form block copolymer brushes on a surface.

Progress and Perspectives Beyond Traditional RAFT Polymerization

The development of advanced materials based on well-defined polymeric architectures is proving to be a highly prosperous research direction across both industry and academia. Controlled radical polymerization techniques are receiving unprecedented attention, with reversible-deactivation chain growth procedures now routinely leveraged to prepare exquisitely precise polymer products. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a powerful protocol within this domain, where the unique chemistry of thiocarbonylthio (TCT) compounds can be harnessed to control radical chain growth of vinyl polymers. With the intense recent focus on RAFT, new strategies for initiation and external control have emerged that are paving the way for preparing well-defined polymers for demanding applications. In this work, the cutting-edge innovations in RAFT that are opening up this technique to a broader suite of materials researchers are explored. Emerging strategies for activating TCTs are surveyed, which are providing access into traditionally challenging environments for reversible-deactivation radical polymerization. The latest advances and future perspectives in applying RAFT-derived polymers are also shared, with the goal to convey the rich potential of RAFT for an ever-expanding range of high-performance applications.

100th Anniversary of Macromolecular Science Viewpoint: Polymers from Lignocellulosic Biomass. Current Challenges and Future Opportunities

Sustainable polymers from lignocellulosic biomass have the potential to reduce the environmental impact of commercial plastics while also offering significant performance and cost benefits relative to petrochemical-derived macromolecules. However, most currently available biobased polymers are hampered by insufficient thermomechanical properties, low economic feasibility (e.g., high relative cost), and reduced scalability in comparison to petroleum-based incumbents. Future biobased materials must overcome these limitations to be competitive in the marketplace. Additionally, sustainability challenges at the beginning and end of the polymer lifecycle need to be addressed using green chemistry practices and improved end-of-life waste management strategies. This viewpoint provides an overview of recent developments that can mitigate many concerns with present materials and discusses key aspects of next-generation, biobased polymers derived from lignocellulosic biomass.

Metallo-Polyelectrolytes: Correlating Macromolecular Architectures with Properties and Applications

Since the middle of the 20th century, metallopolymers have represented a standalone subfield with a beneficial combination of functionality from inorganic metal centers and processability from the organic polymeric frameworks. Metallo-polyelectrolytes are a new class of soft materials that showcase fundamentally different properties from neutral polymers due to their intrinsically ionic behaviors. This review describes recent trends in metallo-polyelectrolytes and discusses emerging properties and challenges, as well as future directions from a perspective of macromolecular architectures. The correlations between macromolecular architectures and properties are discussed from copolymer self-assembly, metallo-enzymes for biomedical applications, metallo-peptides for catalysis, crosslinked networks, and metallogels.

Enzyme-mediated reversible deactivation radical polymerization for functional materials: principles, synthesis, and applications

Enzymes provide a potential and highly efficient way to mediate the formation of various functional polymer materials with wide applications.

High-Throughput Tertiary Amine Deoxygenated Photopolymerizations for Synthesizing Polymer Libraries

The huge chemical space potential of synthetic polymers means that in many studies only a small parameter range can be realistically synthesized in a short time and hence the "best" formulations may not be optimum. Throughput is traditionally limited by the need for deoxygenation in radical polymerizations, but advances in photopolymerization now provide opportunities for "in-air" polymerizations. Here, we have developed a protocol using liquid handling robots (or multichannel pipettes) with blue light photolysis of reversible addition fragmentation chain transfer agents and tertiary amine deoxygenation to enable the synthesis of polymer libraries in industry-standard 96-well plates with no specialized infrastructure and no degassing step. The roles of solvents and amine deoxygenators are explored to optimize the polymerization, particularly to look at alternatives to dimethyl sulfoxide (DMSO) for hydrophobic monomer (co)polymerization. DMSO is shown to aid the degassing process but is not easy to remove and hence prevents isolation of pure polymers. In contrast, using dioxane in-plate evaporation or precipitation of the tertiary amine allowed isolation of polymers in-plate. This removed all reaction components yielding pure polymers, which is not easily achieved with systems using metal catalysts and secondary reductants, such as ascorbic acid. As an example of the throughput, in just under 40 h, 392 polymers were synthesized and subsequently analyzed direct from plates by a 96-well plate sampling size exclusion chromatography system to demonstrate reproducibility. Due to less efficient degassing in dioxane (compared to DMSO), the molecular weight and dispersity control were limited in some cases (with acrylates giving the lowest dispersities), but the key aim of this system is to access hundreds of polymers quickly and in a format needed to enable testing. This method enables easy exploration of chemical space and development of screening libraries to identify hits for further study using precision polymerization methods.

Enzyme-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization: Precision polymer synthesis via enzymatic catalysis

Enzyme-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization provides a sustainable strategy for efficient production of well-defined polymers under mild conditions. Horseradish peroxidase (HRP), a heme-containing metalloenzyme, catalyzes oxidation of acetylacetone (ACAC) by hydrogen peroxide (H₂O₂) to generate ACAC radicals, initiating polymerization of vinyl monomers. This HRP/H₂O₂/ACAC ternary initiating system is applied to RAFT polymerization of different types of vinyl monomers. Furthermore, to overcome the inherent limitation of necessity for oxygen-free conditions, another enzyme, glucose oxidase (GOx) or pyranose 2-oxidase (P2Ox), with excellent deoxygenation capability, is introduced to consume oxygen by catalyzing oxidation of glucose to generate H₂O₂. The generated H₂O₂ is directly supplied to HRP catalysis for radical generation. Both GOx-HRP and P2Ox-HRP cascade catalysis afford RAFT polymerization with oxygen tolerance. In this chapter, we mainly focus on detailed synthetic protocols of RAFT polymerizations initiated by HRP/H₂O₂/ACAC ternary initiating system and P2Ox-HRP cascade catalysis. The general characterization and analytical methods used in these enzyme-initiated RAFT polymerizations are also included.

SI-PET-RAFT: Surface-Initiated Photoinduced Electron Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization

In this communication, surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT) is introduced. SI-PET-RAFT affords functionalization of surfaces with spatiotemporal control and provides oxygen tolerance under ambient conditions. All hallmarks of controlled radical polymerization (CRP) are met, affording well-defined polymerization kinetics, and chain end retention to allow subsequent extension of active chain ends to form block copolymers. The modularity and versatility of SI-PET-RAFT is highlighted through significant flexibility with respect to the choice of monomer, light source and wavelength, and photoredox catalyst. The ability to obtain complex patterns in the presence of air is a significant contribution to help pave the way for CRP-based surface functionalization into commercial application.

Dual Polymerizations: Untapped Potential for Biomaterials

Block copolymers with unique architectures and those that can self-assemble into supramolecular structures are used in medicine as biomaterial scaffolds and delivery vehicles for cells, therapeutics, and imaging agents. To date, much of the work relies on controlling polymer behavior by varying the monomer side chains to add functionality and tune hydrophobicity. Although varying the side chains is an efficient strategy to control polymer behavior, changing the polymer backbone can also be a powerful approach to modulate polymer self-assembly, rigidity, reactivity, and biodegradability for biomedical applications. There are many developments in the syntheses of polymers with segmented backbones, but these developments are not widely adopted as strategies to address the unique constraints and requirements of polymers for biomedical applications. This review highlights dual polymerization strategies for the synthesis of backbone-segmented block copolymers to facilitate their adoption for biomedical applications.

Enzymatically Degassed Surface-Initiated Atom Transfer Radical Polymerization with Real-Time Monitoring

Polymer brush coatings are frequently prepared by radical polymerization, a notoriously oxygen sensitive process. Glucose oxidase (GOx) can inexpensively enable radical polymerization in solution by enzymatically consuming oxygen as it oxidizes glucose. Here, we report the growth of polymeric brushes using GOx-assisted atom transfer radical polymerization (ATRP) from a surface while open to air. Specifically, we grew a set of biomedically relevant polymer brushes, including poly(oligo(ethylene glycol) methacrylate) (POEGMA), poly(2-dimethylaminoethyl methacrylate) (PDMAEMA), poly(sulfobetaine methacrylate) (PSBMA), and poly(2-(methylsulfinyl)ethyl acrylate (PMSEA). For each of these polymers, we monitored GOx-assisted and GOx-free ATRP reaction kinetics in real time using quartz crystal microbalance (QCM) and verified findings with localized surface plasmon resonance (LSPR). We modeled brush growth kinetics considering bimolecular termination. This model fit our data well ( r² > 0.987 for all samples) and shows the addition of GOx increased effective kinetic chain lengths, propagation rates, and reproducibility. We tested the antifouling properties of the polymer brush coatings against human blood plasma and were surprised to find that coatings prepared with GOx repelled more plasma proteins in all cases than their GOx-free counterparts.

Self-deoxygenating glassware

The removal of dissolved oxygen (O2) from solution is a prerequisite for many reactions, frequently requiring specialized equipment/reagents or expertise. Herein, we introduce a range of reusable, shelf-stable enzyme-functionalized glassware, which biocatalytically removes O2 from contained aqueous solutions. The effectiveness of the activated glassware is demonstrated by facilitating several O2-intolerant RAFT polymerizations.

A cocktail of vitamins for aqueous RAFT polymerization in an open-to-air microtiter plate

We report a highly biocompatible photoinitiation strategy based on Vitamin B₂ and Vitamin C. This two-component photoinitiator enables RAFT polymerization to be conducted in high throughput in an open-to-air microtiter plate.

Enzyme-Deoxygenated Low Parts per Million Atom Transfer Radical Polymerization in Miniemulsion and Ab Initio Emulsion

The development of robust oxygen-tolerant reversible deactivation radical polymerization (RDRP) systems can dramatically simplify synthesis of well-defined polymers without redundant deoxygenation procedures. Herein, we broaden the application of oxygen-tolerant RDRP from homogeneous aqueous and organic solutions to dispersed media. The glucose oxidase (GOx) degassed atom transfer radical polymerization (ATRP) was conducted in miniemulsion and ab initio emulsion systems using various catalyst regeneration methods: ARGET, ICAR, photo, and eATRP. All of these polymerization procedures led to polymers with predetermined molecular weight, low dispersity, and high chain-end functionality. Emulsion ATRP on a larger scale with preserved control was also successful. Circular dichroism (CD) studies demonstrated that the anionic surfactant, sodium dodecyl sulfate (SDS), did not damage the secondary structure of GOx. This confirms the versatility of the GOx system for various low ppm ATRP methods. GOx-assisted oxygen removal in the synthesis of hydrophobic polymers is reported for the first time. The low cost of deoxygenation reagents and the ability to scale up the procedure suggest the potential for industrial production, especially for emulsion polymerization.

Biocatalytic "Oxygen-Fueled" Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) can be carried out in a flask completely open to air using a biocatalytic system composed of glucose oxidase (GOx) and horseradish peroxidase (HRP) with an active copper catalyst complex. Nanomolar concentrations of the enzymes and ppm amounts of Cu provided excellent control over the polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA₅₀₀ ), generating polymers with high molecular weight (M_n >70 000) and low dispersities (1.13≤Đ≤1.27) in less than an hour. The continuous oxygen supply was necessary for the generation of radicals and polymer chain growth as demonstrated by temporal control and by inducing hypoxic conditions. In addition, the enzymatic cascade polymerization triggered by oxygen was used for a protein and DNA functionalized with initiators to form protein-b-POEOMA and DNA-b-POEOMA bioconjugates, respectively.

Synthesis and Assembly of Designer Styrenic Diblock Polyelectrolytes

Harnessing molecular design principles toward functional applications of ion-containing macromolecules relies on diversifying experimental data sets of well-understood materials. Here, we report a simple, tunable framework for preparing styrenic polyelectrolytes, using aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization in a parallel synthesis approach. A series of diblock polycations and polyanions were RAFT chain-extended from poly(ethylene oxide) (PEO) using (vinylbenzyl)trimethylammonium chloride (PEO-b-PVBTMA) and sodium 4-styrenesulfonate (PEO-b-PSS), with varying neutral PEO block lengths, charged styrenic block lengths, and RAFT end-group identity. The materials characterization and kinetics study of chain growth exhibited control of the molar mass distribution for both systems. These block polyelectrolytes were also demonstrated to form polyelectrolyte complex (PEC) driven self-assemblies. We present two simple outcomes of micellization to show the importance of polymer selection from a broadened pool of polyelectrolyte candidates: (i) uniform PEC-core micelles comprising PEO-b-PVBTMA and poly(acrylic acid) and (ii) PEC nanoaggregates comprising PEO-b-PVBTMA and PEO-b-PSS. The materials characteristics of these charged assemblies were investigated with dynamic light scattering, small-angle X-ray scattering, and cryogenic-transmission electron microscopy imaging. This model synthetic platform offers a straightforward path to expand the design space of conventional polyelectrolytes into gram-scale block polymer structures, which can ultimately enable the development of more sophisticated ionic materials into technology.

Up in the air: oxygen tolerance in controlled/living radical polymerisation

The requirement for deoxygenation in controlled/living radical polymerisation (CLRP) places significant limitations on its widespread implementation by necessitating the use of large reaction volumes, sealed reaction vessels as well as requiring access to specialised equipment such as a glove box and/or inert gas source. As a result, in recent years there has been intense interest in developing strategies for overcoming the effects of oxygen inhibition in CLRP and therefore remove the necessity for deoxygenation. In this review, we highlight several strategies for achieving oxygen tolerant CLRP including: "polymerising through" oxygen, enzyme mediated deoxygenation and the continuous regeneration of a redox-active catalyst. In order to provide further clarity to the field, we also establish some basic parameters for evaluating the degree of "oxygen tolerance" that can be achieved using a given oxygen scrubbing strategy. Finally, we propose some applications that could most benefit from the implementation of oxygen tolerant CLRP and provide a perspective on the future direction of this field.