Mucin-Inspired Thermoresponsive Synthetic Hydrogels Induce Stasis in Human Pluripotent Stem Cells and Human Embryos

Kinetically Controlled Preparation of Worm-like Micelles with Tunable Diameter/Length and Structural Stability

Anisotropic nanoparticles such as worm-like micelles have aroused much attention due to their promising applications from templates to drug delivery. The fabrication of worm-like micelles with tunable structural stability and control over their diameter and length is of great importance but still challenging. Herein, we report a kinetically controlled ring-opening metathesis polymerization-induced self-assembly (ROMPISA) for the robust preparation of kinetically trapped worm-like micelles with tunable diameter/length at enlarged experimental windows by the rational manipulation of kinetic factors, including solvent property, temperature, and π-π stacking effects. The resultant worm structures were thermodynamically metastable and capable of excellent structural stability at room temperature due to the kinetic trapping effect. At elevated temperatures, these thermodynamically metastable worms could undergo morphology evolution into vesicular structures in a controlled manner. Moreover, the structural stability of worms could also be significantly enhanced by in situ cross-linking. Overall, this kinetically controlled ROMPISA opens a new avenue for PISA chemistry that is expected to prepare "smart" polymer materials by manipulating kinetic factors.

Poly(l-proline)-Stabilized Polypeptide Nanostructures via Ring-Opening Polymerization-Induced Self-Assembly (ROPISA)

Poly(proline) II helical motifs located at the protein-water interface stabilize the three-dimensional structures of natural proteins. Reported here is the first example of synthetic biomimetic poly(proline)-stabilized polypeptide nanostructures obtained by a straightforward ring-opening polymerization-induced self-assembly (ROPISA) process through consecutive N-carboxyanhydride (NCA) polymerization. It was found that the use of multifunctional 8-arm initiators is critical for the formation of nanoparticles. Worm-like micelles as well as spherical morphologies were obtained as confirmed by dynamic light scattering (DLS), transmission electron microscopy (TEM), and small angle X-ray scattering (SAXS). The loading of the nanostructures with dyes is demonstrated. This fast and open-vessel procedure gives access to amino acids-based nanomaterials with potential for applications in nanomedicine.

Mucus-Inspired Self-Healing Hydrogels: A Protective Barrier for Cells against Viral Infection

Mucus is a dynamic biological hydrogel, composed primarily of the glycoprotein mucin, exhibits unique biophysical properties and forms a barrier protecting cells against a broad-spectrum of viruses. Here, this work develops a polyglycerol sulfate-based dendronized mucin-inspired copolymer (MICP-1) with ≈10% repeating units of activated disulfide as cross-linking sites. Cryo-electron microscopy (Cryo-EM) analysis of MICP-1 reveals an elongated single-chain fiber morphology. MICP-1 shows potential inhibitory activity against many viruses such as herpes simplex virus 1 (HSV-1) and SARS-CoV-2 (including variants such as Delta and Omicron). MICP-1 produces hydrogels with viscoelastic properties similar to healthy human sputum and with tuneable microstructures using linear and branched polyethylene glycol-thiol (PEG-thiol) as cross-linkers. Single particle tracking microrheology, electron paramagnetic resonance (EPR) and cryo-scanning electron microscopy (Cryo-SEM) are used to characterize the network structures. The synthesized hydrogels exhibit self-healing properties, along with viscoelastic properties that are tuneable through reduction. A transwell assay is used to investigate the hydrogel's protective properties against viral infection against HSV-1. Live-cell microscopy confirms that these hydrogels can protect underlying cells from infection by trapping the virus, due to both network morphology and anionic multivalent effects. Overall, this novel mucin-inspired copolymer generates mucus-mimetic hydrogels on a multi-gram scale. These hydrogels can be used as models for disulfide-rich airway mucus research, and as biomaterials.

Effect of Added Salt on the RAFT Polymerization of 2-Hydroxyethyl Methacrylate in Aqueous Media

We report the effect of added salt on the reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-hydroxyethyl methacrylate (HEMA) in aqueous media. More specifically, poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC26) was employed as a salt-tolerant water-soluble block for chain extension with HEMA targeting PHEMA DPs from 100 to 800 in the presence of NaCl. Increasing the salt concentration significantly reduces the aqueous solubility of both the HEMA monomer and the growing PHEMA chains. HEMA conversions of more than 99% could be achieved within 6 h at 70 °C regardless of the NaCl concentration when targeting PMPC26-PHEMA800 vesicles at 20% w/w solids. Significantly faster rates of polymerization were observed at higher salt concentration owing to the earlier onset of micellar nucleation. Transmission electron microscopy (TEM) was used to construct a pseudo-phase diagram for this polymerization-induced self-assembly (PISA) formulation. High-quality images required cross-linking of the PHEMA chains with glutaraldehyde prior to salt removal via dialysis. Block copolymer spheres, worms, or vesicles can be accessed at any salt concentration up to 2.5 M NaCl. However, only kinetically trapped spheres could be obtained in the presence of 3 M NaCl because the relatively low HEMA monomer solubility under such conditions leads to an aqueous emulsion polymerization rather than an aqueous dispersion polymerization. In this case, dynamic light scattering studies indicated a gradual increase in z-average diameter from 26 to 86 nm when adjusting the target PHEMA degree of polymerization from 200 to 800. When targeting PMPC26-PHEMA800 vesicles, increasing the salt content up to 2.5 M NaCl leads to a systematic reduction in the z-average diameter from 953 to 92 nm. Similarly, TEM analysis and dispersion viscosity measurements indicated a gradual reduction in worm contour length with increasing salt concentration for PMPC26-PHEMA600 worms. This new PISA formulation clearly illustrates the importance of added salt on aqueous monomer solubility and how this affects (i) the kinetics of polymerization, (ii) the morphology of the corresponding diblock copolymer nano-objects, and (iii) the mode of polymerization in aqueous media.

Arginine-Functional Methacrylic Block Copolymer Nanoparticles: Synthesis, Characterization, and Adsorption onto a Model Planar Substrate

Recently, we reported the synthesis of a hydrophilic aldehyde-functional methacrylic polymer (Angew. Chem., 2021, 60, 12032-12037). Herein we demonstrate that such polymers can be reacted with arginine in aqueous solution to produce arginine-functional methacrylic polymers without recourse to protecting group chemistry. Careful control of the solution pH is essential to ensure regioselective imine bond formation; subsequent reductive amination leads to a hydrolytically stable amide linkage. This new protocol was used to prepare a series of arginine-functionalized diblock copolymer nanoparticles of varying size via polymerization-induced self-assembly in aqueous media. Adsorption of these cationic nanoparticles onto silica was monitored using a quartz crystal microbalance. Strong electrostatic adsorption occurred at pH 7 (Γ = 14.7 mg m-2), whereas much weaker adsorption occurred at pH 3 (Γ = 1.9 mg m-2). These findings were corroborated by electron microscopy, which indicated a surface coverage of 42% at pH 7 but only 5% at pH 3.

Influence of Polymer Side Chain Size and Backbone Length on the Self-Assembly of Supramolecular Polymer Bottlebrushes

Hydrogen bonds are a versatile tool for creating fibrous, bottlebrush-like assemblies of polymeric building blocks. However, a delicate balance of forces exists between the steric repulsion of the polymer chains and these directed supramolecular forces. In this work we have systematically investigated the influence of structural parameters of the attached polymers on the assembly behaviour of benzene trisurea (BTU) and benzene tris(phenylalanine) (BTP) conjugates in water. Polymers with increasing main chain lengths and different side chain sizes were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of hydroxyethyl acrylate (HEA), tri(ethylene glycol) methyl ether acrylate (TEGA) and oligo(ethylene glycol) methyl ether acrylate (OEGA). The resulting structures were analyzed using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both BTU and BTP formed fibres with PHEA attached, but a transition to spherical morphologies was observed at degrees of polymerisation (DP) of 70 and above. Overall, the main chain length appeared to be a dominating factor in inducing morphology transitions. Increasing the side chain size generally had a similar effect but mainly impeded any aggregation as is the case of POEGA. Interestingly, BTP conjugates still formed fibres, suggesting that the stronger intermolecular interactions can compensate partially for the steric repulsion.

Multifunctional Self-Assembled Block Copolymer/Iron Oxide Nanocomposite Hydrogels Formed from Wormlike Micelles

This article reports the preparation of multifunctional magnetic nanocomposite hydrogels formed from wormlike micelles. Specifically, iron oxide nanoparticles were incorporated into a temperature responsive block copolymer, poly(glycerol monomethacrylate)-b-poly(2-hydroxypropyl methacrylate) (PGMA-b-PHPMA), and graphene oxide (GO) dispersion at a low temperature (∼2 °C) through high-speed mixing and returning the mixture to room temperature, resulting in the formation of nanocomposite gels. The optimal concentrations of iron oxide and GO enhanced the gel strength of the nanocomposite gels, which exhibited a strong magnetic response when a magnetic field was applied. These materials retained the thermoresponsiveness of the PGMA-PHPMA wormlike micelles allowing for a solid-to-liquid transition to occur when the temperature was reduced. The mechanical and rheological properties and performance of the nanocomposite gels were demonstrated to be adjustable, making them suitable for a wide range of potential applications. These nanocomposite worm gels were demonstrated to be relatively adhesive and to act as strain and temperature sensors, with the measured electrical resistance of the nanocomposite gels changing with applied strain and temperature sweeps. The nanocomposite gels were found to recover efficiently after the application of high shear with approximately 100% healing efficiency within seconds. Additionally, these nanocomposite worm gels were injectable, and the addition of GO and iron oxide nanomaterials seemed to have no significant adverse impact on the biocompatibility of the copolymer gels, making them suitable not only for 3D printing in nanocomposite engineering but also for potential utilization in various biomedical applications as an injectable magnetic responsive hydrogel.

Degradable Block Copolymer Nanoparticles Synthesized by Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) combines polymerization and in situ self-assembly of block copolymers in one system and has become a widely used method to prepare block copolymer nanoparticles at high concentrations. The persistence of polymers in the environment poses a huge threat to the ecosystem and represents a significant waste of resources. There is an urgent need to develop novel chemical approaches to synthesize degradable polymers. To meet with this demand, it is crucial to install degradability into PISA nanoparticles. Most recently, degradable PISA nanoparticles have been synthesized by introducing degradation mechanisms into either shell-forming or core-forming blocks. This Minireview summarizes the development in degradable block copolymer nanoparticles synthesized by PISA, including shell-degradable, core-degradable, and all-degradable nanoparticles. Future development will benefit from expansion of polymerization techniques with new degradation mechanisms and adaptation of high-throughput approaches for both PISA syntheses and degradation studies.

Synthesis of Thermo-Responsive Monofunctionalized Diblock Copolymer Worms

Poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) with worm-like morphology is a typical example of reversible addition-fragmentation chain transfer (RAFT) dispersion polymerized thermo-responsive copolymer via polymerization-induced self-assembly (PISA) in aqueous solution. Chain transfer agents (CTAs) are the key component in controlling RAFT, the structures of which determine the end functional groups of the polymer chain. It is therefore of interest to monofunctionalize the polymers via CTA moiety, for bioactive functionality conjugation and in the meantime maintain the precisely controlled morphology of the copolymers and the related property. In this work, a newly designed CTA 5-(2-(tert-butoxycarbonylamino) ethylamino)-2-cyano-5-oxopentan-2-yl benzodithioate (t-Boc CPDB) was synthesized and used for the RAFT polymerization of PGMA45-PHPMA120. Subsequently, PGMA45-PHPMA120 copolymers with primary amine, maleimide, and reduced L-glutathione (a tripeptide) monofunctionalized terminals were synthesized via deprotection and conjugation reactions. These monofunctionalized copolymers maintain worm-like morphology and thermo-responsive property in aqueous solution (10% w/v), as confirmed by the transmission electron microscopy (TEM) images, and the observation of the phase transition behavior in between 4 °C and room temperature (~20 °C), respectively. Summarily, a range of thermo-responsive monofunctionalized PGMA45-PHPMA120 diblock copolymer worms were successfully synthesized, which are expected to offer potential biomedical applications, such as in polymer therapeutics, drug delivery, and diagnostics.

Evaluating the Feasibility of Hydrogel-Based Neural Cell Sprays

Neurological injuries have poor prognoses with serious clinical sequelae. Stem cell transplantation enhances neural repair but is hampered by low graft survival (ca. 80%) and marker expression/proliferative potential of hydrogel-sprayed astrocytes was retained. Combining a cell spray format with polymer encapsulation technologies could form the basis of a non-invasive graft delivery method, offering potential advantages over current cell delivery approaches.

Mucosa-Mimetic Materials for the Study of Intestinal Homeostasis and Disease

Mucus is a viscoelastic hydrogel that lines and protects the epithelial surfaces of the body that houses commensal microbiota and functions in host defense against pathogen invasion. As a first-line physical and biochemical barrier, intestinal mucus is involved in immune surveillance and spatial organization of the microbiome, while dysfunction of the gut mucus barrier is implicated in several diseases. Mucus can be collected from a variety of mammalian sources for study, however, established methods are challenging in terms of scale and efficiency, as well as with regard to rheological similarity to native human mucus. Therefore, there is a need for mucus-mimetic hydrogels that more accurately reflect the physical and chemical profile of the in vivo human epithelial environment to enable the investigation of the role of mucus in human disease and interactions with the intestinal microbiome. This review will evaluate the material properties of synthetic mucus mimics to date designed to address the above need, with a focus toward an improved understanding of the biochemical and immunological functions of these biopolymers related to utility for research and therapeutic applications.

Proline pre-conditioning of Jurkat cells improves recovery after cryopreservation

Cell therapies such as allogenic CAR T-cell therapy, natural killer cell therapy and stem cell transplants must be cryopreserved for transport and storage. This is typically achieved by addition of dimethyl sulfoxide (DMSO) but the cryoprotectant does not result in 100% cell recovery. New additives or technologies to improve their cryopreservation could have major impact for these emerging therapies. l-Proline is an amino acid osmolyte produced as a cryoprotectant by several organisms such as the codling moth Cydia pomonella and the larvae of the fly Chymomyza costata, and has been found to modulate post-thaw outcomes for several cell lines but has not been studied with Jurkat cells, a T lymphocyte cell line. Here we investigate the effectiveness of l-proline compared to d-proline and l-alanine for the cryopreservation of Jurkat cells. It is shown that 24-hour pre-freezing incubation of Jurkat cells with 200 mM l-proline resulted in a modest increase in cell recovery post-thaw at high cell density, but a larger increase in recovery was observed at the lower cell densities. l-Alanine was as effective as l-proline at lower cell densities, and addition of l-proline to the cryopreservation media (without incubation) had no benefit. The pre-freeze incubation with l-proline led to significant reductions in cell proliferation supporting an intracellular, biochemical, mechanism of action which was shown to be cell-density dependent. Controls with d-proline were found to reduce post-thaw recovery attributed to osmotic stress as d-proline cannot enter the cells. Preliminary analysis of apoptosis/necrosis profiles by flow cytometry indicated that inhibition of apoptosis is not the primary mode of action. Overall, this supports the use of l-proline pre-conditioning to improve T-cell post-thaw recovery without needing any changes to cryopreservation solutions nor methods and hence is simple to implement.

Thermoresponsive Poly(N,N'-dimethylacrylamide)-Based Diblock Copolymer Worm Gels via RAFT Solution Polymerization: Synthesis, Characterization, and Cell Biology Applications

RAFT solution polymerization is used to polymerize 2-hydroxypropyl methacrylate (HPMA). The resulting PHPMA precursor is then chain-extended using N,N'-dimethylacrylamide (DMAC) to produce a series of thermoresponsive PHPMA-PDMAC diblock copolymers. Such amphiphilic copolymers can be directly dispersed in ice-cold water and self-assembled at 20 °C to form spheres, worms, or vesicles depending on their copolymer composition. Construction of a pseudo-phase diagram is required to identify the pure worm phase, which corresponds to a rather narrow range of PDMAC DPs. Such worms form soft, free-standing gels in aqueous solution at around ambient temperature. Rheology studies confirm the thermoresponsive nature of such worms, which undergo a reversible worm-to-sphere on cooling below ambient temperature. This morphological transition leads to in situ degelation, and variable temperature 1H NMR studies indicate a higher degree of (partial) hydration for the weakly hydrophobic PHPMA chains at lower temperatures. The trithiocarbonate end-group located at the end of each PDMAC chain can be removed by treatment with excess hydrazine. The resulting terminal secondary thiol group can form disulfide bonds via coupling, which produces PHPMA-PDMAC-PHPMA triblock copolymer chains. Alternatively, this reactive thiol group can be used for conjugation reactions. A PHPMA141-PDMAC36 worm gel was used to store human mesenchymal stem cells (MSCs) for up to three weeks at 37 °C. MSCs retrieved from this gel subsequently underwent proliferation and maintained their ability to differentiate into osteoblastic cells.

Polysaccharides, proteins, and synthetic polymers based multimodal hydrogels for various biomedical applications: A review

Nature-derived or biologically encouraged hydrogels have attracted considerable interest in numerous biomedical applications owing to their multidimensional utility and effectiveness. The internal architecture of a hydrogel network, the chemistry of the raw materials involved, interaction across the interface of counter ions, and the ability to mimic the extracellular matrix (ECM) govern the clinical efficacy of the designed hydrogels. This review focuses on the mechanistic viewpoint of different biologically driven/inspired biomacromolecules that encourages the architectural development of hydrogel networks. In addition, the advantage of hydrogels by mimicking the ECM and the significance of the raw material selection as an indicator of bioinertness is deeply elaborated in the review. Furthermore, the article reviews and describes the application of polysaccharides, proteins, and synthetic polymer-based multimodal hydrogels inspired by or derived from nature in different biomedical areas. The review discusses the challenges and opportunities in biomaterials along with future prospects in terms of their applications in biodevices or functional components for human health issues. This review provides information on the strategy and inspiration from nature that can be used to develop a link between multimodal hydrogels as the main frame and its utility in biomedical applications as the primary target.

Histidine-Functionalized Diblock Copolymer Nanoparticles Exhibit Enhanced Adsorption onto Planar Stainless Steel

RAFT aqueous emulsion polymerization of isopropylideneglycerol monomethacrylate (IPGMA) is used to prepare a series of PGEO5MA46 -PIPGMAy nanoparticles, where PGEO5MA is a hydrophilic methacrylic steric stabilizer block bearing pendent cis-diol groups. TEM studies confirm a spherical morphology while dynamic light scattering (DLS) analysis indicated that the z-average particle diameter can be adjusted by varying the target degree of polymerization for the core-forming PIPGMA block. Periodate oxidation is used to convert the cis-diol groups on PGEO5MA46 -PIPGMA500 and PGEO5MA46 -PIPGMA1000 nanoparticles into the analogous aldehyde-functionalized nanoparticles, which are then reacted with histidine via reductive amination. In each case, the extent of functionalization is more than 99% as determined by 1 H NMR spectroscopy. Aqueous electrophoresis studies indicate that such derivatization converts initially neutral nanoparticles into zwitterionic nanoparticles with an isoelectric point at pH 7. DLS studies confirm that such histidine-derivatized nanoparticles remain colloidally stable over a wide pH range. A quartz crystal microbalance is employed at 25°C to assess the adsorption of both the cis-diol- and histidine-functionalized nanoparticles onto planar stainless steel at pH 6. The histidine-bearing nanoparticles adsorb much more strongly than their cis-diol counterparts. For the highest adsorbed amount of 70.5 mg m-2 , SEM indicates a fractional surface coverage of 0.23 for the adsorbed nanoparticles.

Shape-Shifting Thermoresponsive Block Copolymer Nano-Objects

In this Feature Article, we review our recent progress in the design of shape-shifting thermoresponsive diblock copolymer nano-objects, which are prepared using various hydroxyl-functional (meth)acrylic monomers (e.g. 2‑hydroxypropyl methacrylate, 4‑hydroxybutyl acrylate or hydroxybutyl methacrylate) to generate the thermoresponsive block. Unlike traditional thermoresponsive polymers such as poly(N-isopropylacrylamide), there is no transition between soluble and insoluble polymer chains in aqueous solution. Instead, thermally driven transitions between a series of copolymer morphologies (e.g. spheres, worms, vesicles or lamellae) occur on adjusting the aqueous solution temperature owing to a subtle change in the partial degree of hydration of the permanently insoluble thermoresponsive block. Such remarkable self-assembly behavior is unprecedented in colloid science: no other amphiphilic diblock copolymer or surfactant system undergoes such behavior at a fixed chemical composition and concentration. Such shape-shifting nano-objects are characterized by transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering, rheology and variable temperature ¹H NMR spectroscopy. Potential applications for this fascinating new class of amphiphiles are briefly considered.

Dispersion polymerization induced self-assembly (pisa) techniques for the fabrication of polymeric nanoparticles for biomedical applications

Nanoparticles offer several advantages in drug delivery. The progress in the development of nanoparticles for biomedical applications has moved from the first generation nanoparticles to the fifth generation nanoparticles and the transitions reflect their increasing versatility in biomedical applications. Polymeric nanoparticles are prepared mainly by two methods: dispersion of preformed polymers and in situ polymerization of monomers and macromonomers. Polymerization induced self-assembly (PISA) for the fabrication of nanoparticles is believed to be a better strategy than nanoparticle fabrication from preformed polymers (ease of tethering targeting ligands to the corona of the nanoparticles and unlike PISA, creation of nanostructures via self-assembly of block copolymers is performed in low concentrations. Dispersion polymerization involves one-pot synthesis of nanoparticles. RDRP processes such as atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization and nitroxide mediated polymerization have revolutionized polymer synthesis by providing polymer chemists with powerful tools that enable control over architecture, composition and chain length distributions. The technique for the fabrication of nanoparticles by dispersion polymerization (PISA) at ambient temperature was described with examples from our laboratory involving organic redox initiated polymerization using the FDA approved biodegradable polymers. Computer optimization is useful in understanding the factors that ensure optimized properties of drug-loaded nanoparticles.

Synthesis and biomedical applications of mucin mimic materials

Mucin glycoproteins are the major component of mucus and coat epithelial cell surfaces forming the glycocalyx. The glycocalyx and mucus are involved in the transport of nutrients, drugs, gases, and pathogens toward the cell surface. Mucins are also involved in diverse diseases such as cystic fibrosis and cancer. Due to inherent heterogeneity in native mucin structure, many synthetic materials have been designed to probe mucin chemistry, biology, and physics. Such materials include various glycopolymers, low molecular weight glycopeptides, glycopolypeptides, polysaccharides, and polysaccharide-protein conjugates. This review highlights advances in the area of design and synthesis of mucin mimic materials, and their biomedical applications in glycan binding, epithelial models of infection, therapeutic delivery, vaccine formulation, and beyond.

Mucus-Inspired Dynamic Hydrogels: Synthesis and Future Perspectives

Mucus hydrogels at biointerfaces are crucial for protecting against foreign pathogens and for the biological functions of the underlying cells. Since mucus can bind to and host both viruses and bacteria, establishing a synthetic model system that can emulate the properties and functions of native mucus and can be synthesized at large scale would revolutionize the mucus-related research that is essential for understanding the pathways of many infectious diseases. The synthesis of such biofunctional hydrogels in the laboratory is highly challenging, owing to their complex chemical compositions and the specific chemical interactions that occur throughout the gel network. In this perspective, we discuss the basic chemical structures and diverse physicochemical interactions responsible for the unique properties and functions of mucus hydrogels. We scrutinize the different approaches for preparing mucus-inspired hydrogels, with specific examples. We also discuss recent research and what it reveals about the challenges that must be addressed and the opportunities to be considered to achieve desirable de novo synthetic mucus hydrogels.

Reverse Sequence Polymerization‐Induced Self‐Assembly in Aqueous Media

We report a new aqueous polymerization‐induced self‐assembly (PISA) formulation that enables the hydrophobic block to be prepared first when targeting diblock copolymer nano‐objects. This counter‐intuitive reverse sequence approach uses an ionic reversible addition–fragmentation chain transfer (RAFT) agent for the RAFT aqueous dispersion polymerization of 2‐hydroxypropyl methacrylate (HPMA) to produce charge‐stabilized latex particles. Chain extension using a water‐soluble methacrylic, acrylic or acrylamide comonomer then produces sterically stabilized diblock copolymer nanoparticles in an aqueous one‐pot formulation. In each case, the monomer diffuses into the PHPMA particles, which act as the locus for the polymerization. A remarkable change in morphology occurs as the ≈600 nm latex is converted into much smaller sterically stabilized diblock copolymer nanoparticles, which exhibit thermoresponsive behavior. Such reverse sequence PISA formulations enable the efficient synthesis of new functional diblock copolymer nanoparticles.

Chemical approaches to cryopreservation

Cryopreservation of cells and biologics underpins all biomedical research from routine sample storage to emerging cell-based therapies, as well as ensuring cell banks provide authenticated, stable and consistent cell products. This field began with the discovery and wide adoption of glycerol and dimethyl sulfoxide as cryoprotectants over 60 years ago, but these tools do not work for all cells and are not ideal for all workflows. In this Review, we highlight and critically review the approaches to discover, and apply, new chemical tools for cryopreservation. We summarize the key (and complex) damage pathways during cellular cryopreservation and how each can be addressed. Bio-inspired approaches, such as those based on extremophiles, are also discussed. We describe both small-molecule-based and macromolecular-based strategies, including ice binders, ice nucleators, ice nucleation inhibitors and emerging materials whose exact mechanism has yet to be understood. Finally, looking towards the future of the field, the application of bottom-up molecular modelling, library-based discovery approaches and materials science tools, which are set to transform cryopreservation strategies, are also included.

Aldehyde-functional thermoresponsive diblock copolymer worm gels exhibit strong mucoadhesion

A series of thermoresponsive diblock copolymer worm gels is prepared via reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate using a water-soluble methacrylic precursor bearing pendent cis-diol groups. Selective oxidation using an aqueous solution of sodium periodate affords the corresponding aldehyde-functional worm gels. The aldehyde groups are located within the steric stabilizer chains and the aldehyde content can be adjusted by varying the periodate/cis-diol molar ratio. These aldehyde-functional worm gels are evaluated in terms of their mucoadhesion performance with the aid of a fluorescence microscopy-based assay. Using porcine urinary bladder mucosa as a model substrate, we demonstrate that these worm gels offer a comparable degree of mucoadhesion to that afforded by chitosan, which is widely regarded to be a 'gold standard' positive control in this context. The optimum degree of aldehyde functionality is approximately 30%: lower degrees of functionalization lead to weaker mucoadhesion, whereas higher values compromise the desirable thermoresponsive behavior of these worm gels.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Sterically Stabilized Diblock Copolymer Nanoparticles Enable Convenient Preparation of Suspension Concentrates Comprising Various Agrochemical Actives

It is well known that sterically stabilized diblock copolymer nanoparticles can be readily prepared using polymerization-induced self-assembly. Recently, we reported that such nanoparticles can be employed as a dispersant to prepare micron-sized particles of a widely used fungicide (azoxystrobin) via ball milling. In the present study, we examine the effect of varying the nature of the steric stabilizer block, the mean nanoparticle diameter, and the glass transition temperature (Tg) of the core-forming block on the particle size and colloidal stability of such azoxystrobin microparticles. In addition, the effect of crosslinking the nanoparticle cores is also investigated. Laser diffraction studies indicated the formation of azoxystrobin microparticles of approximately 2 μm diameter after milling for between 15 and 30 min at 6000 rpm. Diblock copolymer nanoparticles comprising a non-ionic steric stabilizer, rather than a cationic or anionic steric stabilizer, were determined to be more effective dispersants. Furthermore, nanoparticles of up to 51 nm diameter enabled efficient milling and ensured overall suspension concentrate stability. Moreover, crosslinking the nanoparticle cores and adjusting the Tg of the core-forming block had little effect on the milling of azoxystrobin. Finally, we show that this versatile approach is also applicable to five other organic crystalline agrochemicals, namely pinoxaden, cyproconazole, difenoconazole, isopyrazam and tebuconazole. TEM studies confirmed the adsorption of sterically stabilized nanoparticles at the surface of such agrochemical microparticles. The nanoparticles are characterized using TEM, DLS, aqueous electrophoresis and 1H NMR spectroscopy, while the final aqueous' suspension concentrates comprising microparticles of the above six agrochemical actives are characterized using optical microscopy, laser diffraction and electron microscopy.

Reversible Addition-Fragmentation Chain Transfer Aqueous Dispersion Polymerization of 4-Hydroxybutyl Acrylate Produces Highly Thermoresponsive Diblock Copolymer Nano-Objects

The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) using a poly(glycerol monomethacrylate) (PGMA) precursor is an important prototypical example of polymerization-induced self-assembly. 4-Hydroxybutyl acrylate (HBA) is a structural isomer of HPMA, but the former monomer exhibits appreciably higher aqueous solubility. For the two corresponding homopolymers, PHBA is more weakly hydrophobic than PHPMA. Moreover, PHBA has a significantly lower glass transition temperature (T g) so it exhibits much higher chain mobility than PHPMA at around ambient temperature. In view of these striking differences, we have examined the RAFT aqueous dispersion polymerization of HBA using a PGMA precursor with the aim of producing a series of PGMA57-300-PHBA100-1580 diblock copolymer nano-objects by systematic variation of the mean degree of polymerization of each block. A pseudo-phase diagram is constructed using transmission electron microscopy to assign the copolymer morphology after employing glutaraldehyde to cross-link the PHBA chains and hence prevent film formation during grid preparation. The thermoresponsive character of the as-synthesized linear nano-objects is explored using dynamic light scattering and temperature-dependent rheological measurements. Comparison with the analogous PGMA x -PHPMA y formulation is made where appropriate. In particular, we demonstrate that replacing the structure-directing PHPMA block with PHBA leads to significantly greater thermoresponsive behavior over a much wider range of diblock copolymer compositions. Given that PGMA-PHPMA worm gels can induce stasis in human stem cells (see Canton et al., ACS Central Science, 2016, 2, 65-74), our findings are likely to have implications for the design of next-generation PGMA-PHBA worm gels for cell biology applications.

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

Thermoresponsive supramolecular assemblies have been extensively explored in diverse formats, from injectable hydrogels to nanoscale carriers, for a variety of applications including drug delivery, tissue engineering and thermo-controlled catalysis. Understanding the molecular bases behind thermal sensitivity of materials is fundamentally important for the rational design of assemblies with optimal combination of properties and predictable tunability for specific applications. In this review, we summarize the recent advances in this area with a specific focus on the parameters and factors that influence thermoresponsive properties of soft materials. We summarize and analyze the effects of structures and architectures of molecules, hydrophilic and lipophilic balance, concentration, components and external additives upon the thermoresponsiveness of the corresponding molecular assemblies.

Reverse sequence polymerization-induced self-assembly in aqueous media: a counter-intuitive approach to sterically-stabilized diblock copolymer nano-objects

A 500 nm charge-stabilized latex is converted into 40 nm sterically-stabilized nanoparticles via reverse sequence polymerization-induced self-assembly (PISA).

Aldehyde-Functional Diblock Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization

We report the rational design of aldehyde-functional sterically stabilized diblock copolymer nano-objects in aqueous solution via polymerization-induced self-assembly. More specifically, reversible addition-fragmentation chain transfer aqueous dispersion polymerization of 2-hydroxypropyl methacrylate is conducted using a water-soluble precursor block in which every methacrylic repeat unit contains a pendent oligo(ethylene glycol) side chain capped with a cis-diol unit. Systematic variation of the reaction conditions enables the construction of a pseudo-phase diagram, which ensures the reproducible targeting of pure spheres, worms, or vesicles. Selective oxidation of the pendent cis-diol groups using aqueous sodium periodate under mild conditions introduces geminal diols (i.e., the hydrated form of an aldehyde obtained in the presence of water) into the steric stabilizer chains without loss of colloidal stability. In the case of diblock copolymer vesicles, such derivatization leads to the formation of a worm population, indicating partial loss of the original morphology. However, this problem can be circumvented by cross-linking the membrane-forming block prior to periodate oxidation. Moreover, such covalently stabilized aldehyde-functionalized vesicles can be subsequently reacted with either glycine or histidine in aqueous solution, followed by reductive amination to prevent hydrolysis of the labile imine bond. ζ potential measurements confirm that this derivatization significantly affects the electrophoretic behavior of these vesicles. Similarly, the membrane-crosslinked aldehyde-functionalized vesicles can be reacted with a model globular protein, bovine serum albumin, to produce "stealthy" protein-decorated vesicles.

Shape-shifting thermoreversible diblock copolymer nano-objects via RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate

2-Hydroxypropyl methacrylate (HPMA) is a useful model monomer for understanding aqueous dispersion polymerization. 4-Hydroxybutyl acrylate (HBA) is an isomer of HPMA: it has appreciably higher aqueous solubility so its homopolymer is more weakly hydrophobic. Moreover, PHBA possesses a significantly lower glass transition temperature than PHPMA, which ensures greater chain mobility. The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HBA using a poly(ethylene glycol) (PEG113) precursor at 30 °C produces PEG113-PHBA200-700 diblock copolymer nano-objects. Using glutaraldehyde to crosslink the PHBA chains allows TEM studies, which reveal the formation of spheres, worms or vesicles under appropriate conditions. Interestingly, the partially hydrated highly mobile PHBA block enabled linear PEG113-PHBA x spheres, worms or vesicles to be reconstituted from freeze-dried powders on addition of water at 20 °C. Moreover, variable temperature 1H NMR studies indicated that the apparent degree of hydration of the PHBA block increases from 5% to 80% on heating from 0 °C to 60 °C indicating uniform plasticization. In contrast, the PHPMA x chains within PEG113-PHPMA x nano-objects become dehydrated on raising the temperature: this qualitative difference is highly counter-intuitive given that PHBA and PHPMA are isomers. The greater (partial) hydration of the PHBA block at higher temperature drives the morphological evolution of PEG113-PHBA260 spheres to form worms or vesicles, as judged by oscillatory rheology, dynamic light scattering, small-angle X-ray scattering and TEM studies. Finally, a variable temperature phase diagram is constructed for 15% w/w aqueous dispersions of eight PEG113-PHBA200-700 diblock copolymers. Notably, PEG113-PHBA350 can switch reversibly from spheres to worms to vesicles to lamellae during a thermal cycle.

Shear-induced alignment of block copolymer worms in mineral oil

Poly(stearyl methacrylate)-poly(benzyl methacrylate) [PSMA-PBzMA] diblock copolymer worms were synthesized directly in mineral oil via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization at 90 °C. Free-standing gels were obtained from this polymerization-induced self-assembly (PISA) formulation when targeting PSMA₁₃-PBzMA₆₅ dispersions at 5% w/w to 20% w/w copolymer concentration. Gel permeation chromatography (GPC) studies indicated that almost identical copolymer chains were obtained in all cases, while transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies confirmed that highly anisotropic worms were formed with mean cross-sectional diameters of 11.9-13.1 nm. These worms undergo a thermoreversible worm-to-sphere transition on heating up to 150 °C. Rheological studies were conducted to characterize the shear rate- and concentration-dependent behaviour caused by this change in copolymer morphology, where the initial shear-thinning worm gels form spheres (i.e. a Newtonian fluid) on heating up to 150 °C. Complementary shear-induced polarized light imaging (SIPLI) experiments confirmed the formation of aligned linear worms under applied shear between 80 °C and 110 °C, with high-viscosity dispersions of branched worms being obtained at 20-60 °C and low-viscosity spheres being produced at 150 °C. This study informs the use of such block copolymer worms as rheology modifiers for non-polar oils, which is of potential interest for the automotive industry.

Tuning the properties of hydrogen-bonded block copolymer worm gels prepared via polymerization-induced self-assembly

Polymerization-induced self-assembly (PISA) is exploited to design hydrogen-bonded poly(stearyl methacrylate)-poly(benzyl methacrylate) [PSMA-PBzMA] worm gels in n-dodecane. Using a carboxylic acid-based RAFT agent facilitates hydrogen bonding between neighboring worms to produce much stronger physical gels than those prepared using the analogous methyl ester-based RAFT agent. Moreover, tuning the proportion of these two types of end-groups on the PSMA chains enables the storage modulus (G') of a 20% w/w worm gel to be tuned from ∼4.5 kPa up to ∼114 kPa. This is achieved via two complementary routes: (i) an in situ approach using binary mixtures of acid- and ester-capped PSMA stabilizer chains during PISA or (ii) a post-polymerization processing strategy using a thermally-induced worm-to-sphere transition to mix acid- and ester-functionalized spheres at 110 °C that fuse to form worms on cooling to 20 °C. SAXS and rheology studies of these hydrogen-bonded worm gels provide detailed insights into their inter-worm interactions and physical behavior, respectively. In the case of the carboxylic acid-functionalized worms, SAXS provides direct evidence for additional inter-worm interactions, while rheological studies confirm both a significant reduction in critical gelation concentration (from approximately 10% w/w to 2-3% w/w) and a substantial increase in critical gelation temperature (from 41 °C to 92 °C). It is remarkable that a rather subtle change in the chemical structure results in such improvements in gel strength, gelation efficiency and gel cohesion.

Protein-, (Poly)peptide-, and Amino Acid-Based Nanostructures Prepared via Polymerization-Induced Self-Assembly

Proteins and peptides, built from precisely defined amino acid sequences, are an important class of biomolecules that play a vital role in most biological functions. Preparation of nanostructures through functionalization of natural, hydrophilic proteins/peptides with synthetic polymers or upon self-assembly of all-synthetic amphiphilic copolypept(o)ides and amino acid-containing polymers enables access to novel protein-mimicking biomaterials with superior physicochemical properties and immense biorelevant scope. In recent years, polymerization-induced self-assembly (PISA) has been established as an efficient and versatile alternative method to existing self-assembly procedures for the reproducible development of block copolymer nano-objects in situ at high concentrations and, thus, provides an ideal platform for engineering protein-inspired nanomaterials. In this review article, the different strategies employed for direct construction of protein-, (poly)peptide-, and amino acid-based nanostructures via PISA are described with particular focus on the characteristics of the developed block copolymer assemblies, as well as their utilization in various pharmaceutical and biomedical applications.

Molecular Regulation of Paused Pluripotency in Early Mammalian Embryos and Stem Cells

The energetically costly mammalian investment in gestation and lactation requires plentiful nutritional sources and thus links the environmental conditions to reproductive success. Flexibility in adjusting developmental timing enhances chances of survival in adverse conditions. Over 130 mammalian species can reversibly pause early embryonic development by switching to a near dormant state that can be sustained for months, a phenomenon called embryonic diapause. Lineage-specific cells are retained during diapause, and they proliferate and differentiate upon activation. Studying diapause thus reveals principles of pluripotency and dormancy and is not only relevant for development, but also for regeneration and cancer. In this review, we focus on the molecular regulation of diapause in early mammalian embryos and relate it to maintenance of potency in stem cells in vitro. Diapause is established and maintained by active rewiring of the embryonic metabolome, epigenome, and gene expression in communication with maternal tissues. Herein, we particularly discuss factors required at distinct stages of diapause to induce, maintain, and terminate dormancy.

Rational synthesis of novel biocompatible thermoresponsive block copolymer worm gels

It is well known that reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) enables the rational design of diblock copolymer worm gels. Moreover, such hydrogels can undergo degelation on cooling below ambient temperature as a result of a worm-to-sphere transition. However, only a subset of such block copolymer worms exhibit thermoresponsive behavior. For example, PMPC26-PHPMA280 worm gels prepared using a poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC26) precursor do not undergo degelation on cooling to 6 °C (see S. Sugihara et al., J. Am. Chem. Soc., 2011, 133, 15707-15713). Informed by our recent studies (N. J. Warren et al., Macromolecules, 2018, 51, 8357-8371), we decided to reduce the mean degrees of polymerization of both the PMPC steric stabilizer block and the structure-directing PHPMA block when targeting a pure worm morphology. This rational approach reduces the hydrophobic character of the PHPMA block and hence introduces the desired thermoresponsive character, as evidenced by the worm-to-sphere transition (and concomitant degelation) that occurs on cooling a PMPC15-PHPMA150 worm gel from 40 °C to 6 °C. Moreover, worms are reconstituted on returning to 40 °C and the original gel modulus is restored. This augurs well for potential biomedical applications, which will be examined in due course. Finally, small-angle X-ray scattering studies indicated a scaling law exponent of 0.67 (≈2/3) for the relationship between the worm core cross-sectional diameter and the PHPMA DP for a series of PHPMA-based worms prepared using a range of steric stabilizer blocks, which is consistent with the strong segregation regime for such systems.

Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition

Ice binding proteins modulate ice nucleation/growth and have huge (bio)technological potential. There are few synthetic materials that reproduce their function, and rational design is challenging due to the outstanding questions about the mechanisms of ice binding, including whether ice binding is essential to reproduce all their macroscopic properties. Here we report that nanoparticles obtained by polymerization-induced self-assembly (PISA) inhibit ice recrystallization (IRI) despite their constituent polymers having no apparent activity. Poly(ethylene glycol), poly(dimethylacrylamide), and poly(vinylpyrrolidone) coronas were all IRI-active when assembled into nanoparticles. Different core-forming blocks were also screened, revealing the core chemistry had no effect. These observations show ice binding domains are not essential for macroscopic IRI activity and suggest that the size, and crowding, of polymers may increase the IRI activity of "non-active" polymers. It was also discovered that poly(vinylpyrrolidone) particles had ice crystal shaping activity, indicating this polymer can engage ice crystal surfaces, even though on its own it does not show any appreciable ice recrystallization inhibition. Larger (vesicle) nanoparticles are shown to have higher ice recrystallization inhibition activity compared to smaller (sphere) particles, whereas ice nucleation activity was not found for any material. This shows that assembly into larger structures can increase IRI activity and that increasing the "size" of an IRI does not always lead to ice nucleation. This nanoparticle approach offers a platform toward ice-controlling soft materials and insight into how IRI activity scales with molecular size of additives.

Stereochemical Control Yields Mucin Mimetic Polymers

All animals except sponges produce mucus. Across the animal kingdom, this hydrogel mediates surface wetting, viscosity, and protection against microbes. The primary components of mucus hydrogels are mucins-high molecular weight O-glycoproteins that adopt extended linear structures. Glycosylation is integral to mucin function, but other characteristics that give rise to their advantageous biological activities are unknown. We postulated that the extended conformation of mucins is critical for their ability to block microbial virulence phenotypes. To test this hypothesis, we developed synthetic mucin mimics that recapitulate the dense display of glycans and morphology of mucin. We varied the catalyst in a ring-opening metathesis polymerization (ROMP) to generate substituted norbornene-derived glycopolymers containing either cis- or trans-alkenes. Conformational analysis of the polymers based on allylic strain suggested that cis- rather than trans-poly(norbornene) glycopolymers would adopt linear structures that mimic mucins. High-resolution atomic force micrographs of our polymers and natively purified Muc2, Muc5AC, and Muc5B mucins revealed that cis-polymers adopt extended, mucin-like structures. The cis-polymers retained this structure in solution and were more water-soluble than their trans-analogs. Consistent with mucin's linear morphology, cis-glycopolymers were more potent binders of a bacterial virulence factor, cholera toxin. Our findings highlight the importance of the polymer backbone in mucin surrogate design and underscore the significance of the extended mucin backbone for inhibiting virulence.

Encapsulation of bacterial cells in cytoprotective ZIF-90 crystals as living composites

Exploiting metal-organic frameworks (MOFs) as selectively permeable shelters for encapsulating engineered cells to form hybrid living materials has attracted increasing attention in recent years. Optimizing the synthesis process to improve encapsulation efficiency (EE) is critical for further technological development and applications. Here, using ZIF-90 and genetically engineered Escherichia coli (E. coli) as a demo, we fabricated E. coli@ZIF-90 living composites in which E. coli cells were encapsulated in ZIF-90 crystals. We illustrated that ZIF-90 could serve as a protective porous cage for cells to shield against toxic bactericides including benzaldehyde, cinnamaldehyde, and kanamycin. Notably, the E. coli cells remained alive and could self-reproduce after removing the ZIF-90 crystal cages in ethylenediaminetetraacetic acid, suggesting a feasible route for protecting and prolonging the lifespan of bacterial cells. Moreover, an aqueous multiple-step deposition approach was developed to improve EE of the E. coli@ZIF-90 composites: the EE increased to 61.9 ± 5.2%, in contrast with the efficiency of the traditional method (21.3 ± 4.4%) prepared with PBS buffer. In short, we develop a simple yet viable strategy to manufacture MOF-based living hybrid materials that promise new applications across diverse fields.

Constructing Cylindrical Nanostructures Via Directional Morphology Evolution Induced by Seeded Polymerization

Herein, spindle-shaped block copolymer (BCP) nanoparticles are used in seeded polymerization of methyl methacrylate as a novel approach to generating cylindrical nanostructures. The chain-extension of BCP seeds by an amorphous coil-type polymer within the seed core composed of semifluorinated liquid-crystalline blocks triggers the deforming, stretching, and directional growth of the seeds along the long axis, eventually leads to nanorods.

Site-Directed Differentiation of Human Adipose-Derived Mesenchymal Stem Cells to Nucleus Pulposus Cells Using an Injectable Hydroxyl-Functional Diblock Copolymer Worm Gel

Adipose-derived mesenchymal stem cells (ASCs) have been identified for their promising therapeutic potential to regenerate and repopulate the degenerate intervertebral disk (IVD), which is a major cause of lower back pain. The optimal cell delivery system remains elusive but encapsulation of cells within scaffolds is likely to offer a decisive advantage over the delivery of cells in solution by ensuring successful retention within the tissue. Herein, we evaluate the use of a fully synthetic, thermoresponsive poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer worm gel that mimics the structure of hydrophilic glycosaminoglycans. The objective was to use this gel to direct differentiation of human ASCs toward a nucleus pulposus (NP) phenotype, with or without the addition of discogenic growth factors TGFβ or GDF6. Accordingly, human ASCs were incorporated into a cold, free-flowing aqueous dispersion of the diblock copolymer, gelation induced by warming to 37 °C and cell culture was conducted for 14 days with or without such growth factors to assess the expression of characteristic NP markers compared to those produced when using collagen gels. In principle, the shear-thinning nature of the biocompatible worm gel enables encapsulated human ASCs to be injected into the IVD using a 21G needle. Moreover, we find significantly higher gene expression levels of ACAN, SOX-9, KRT8, and KR18 for ASCs encapsulated within worm gels compared to collagen scaffolds, regardless of the growth factors employed. In summary, such wholly synthetic worm gels offer considerable potential as an injectable cell delivery scaffold for the treatment of degenerate disk disease by promoting the transition of ASCs toward an NP-phenotype.

Polymerisation-induced self-assembly (PISA) as a straightforward formulation strategy for stimuli-responsive drug delivery systems and biomaterials: recent advances

Stimuli-responsive amphiphilic block copolymers have emerged as promising nanocarriers for enhancing site-specific and on-demand drug release in response to a range of stimuli such as pH, the presence of redox agents, and temperature. The formulation of amphiphilic block copolymers into polymeric drug-loaded nanoparticles is typically achieved by various methods (e.g. oil-in-water emulsion solvent evaporation, solid dispersion, microphase separation, dialysis or microfluidic separation). Despite much progress that has been made, there remain many challenges to overcome to produce reliable polymeric systems. The main drawbacks of the above methods are that they produce very low solid contents (<1 wt%) and involve multiple-step procedures, thus limiting their scope. Recently, a new self-assembly methodology, polymerisation-induced self-assembly (PISA), has shown great promise in the production of polymer-derived particles using a straightforward one-pot approach, whilst facilitating high yield, scalability, and cost-effectiveness for pharmaceutical industry protocols. We therefore focus this review primarily on the most recent studies involved in the design and preparation of PISA-generated nano-objects which are responsive to specific stimuli, thus providing insight into how PISA may become an effective formulation strategy for the preparation of precisely tailored drug delivery systems and biomaterials, while some of the current challenges and limitations are also critically discussed.

Tuning the vesicle-to-worm transition for thermoresponsive block copolymer vesicles prepared via polymerisation-induced self-assembly

Does statistical copolymerization of n-butyl methacrylate with benzyl methacrylate lower the critical temperature required for vesicle-to-worm and worm-to-sphere transitions for diblock copolymer nano-objects in mineral oil?

Non-thermally initiated RAFT polymerization-induced self-assembly

This review summarizes the recent non-thermal initiation methods in RAFT mediated polymerization-induced self-assembly (PISA), including photo-, redox/oscillatory reaction-, enzyme- and ultrasound wave-initiation.

Boron-rich, cytocompatible block copolymer nanoparticles by polymerization-induced self-assembly

A new methacrylic boronate ester is synthesized and exploited to produce biocompatible nanoparticles with a boron-rich core by PISA.

Pickering Emulsifiers Based on Block Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly

Block copolymer nanoparticles prepared via polymerization-induced self-assembly (PISA) represent an emerging class of organic Pickering emulsifiers. Such nanoparticles are readily prepared by chain-extending a soluble homopolymer precursor using a carefully selected second monomer that forms an insoluble block in the chosen solvent. As the second block grows, it undergoes phase separation that drives in situ self-assembly to form sterically stabilized nanoparticles. Conducting such PISA syntheses in aqueous solution leads to hydrophilic nanoparticles that enable the formation of oil-in-water emulsions. Alternatively, hydrophobic nanoparticles can be prepared in non-polar media (e.g., n-alkanes), which enables water-in-oil emulsions to be produced. In this review, the specific advantages of using PISA to prepare such bespoke Pickering emulsifiers are highlighted, which include fine control over particle size, copolymer morphology, and surface wettability. This has enabled various fundamental scientific questions regarding Pickering emulsions to be addressed. Moreover, block copolymer nanoparticles can be used to prepare Pickering emulsions over various length scales, with mean droplet diameters ranging from millimeters to less than 200 nm.