Strategies exploiting functions and self-assembly properties of bioconjugates for polymer and materials sciences

An organometallic swap strategy for bottlebrush polymer-protein conjugate synthesis

Polymer-protein bioconjugation offers a powerful strategy to alter the physical properties of proteins, and various synthetic polymer compositions and architectures have been investigated for this purpose. Nevertheless, conjugation of molecular bottlebrush polymers (BPs) to proteins remains an unsolved challenge due to the large size of BPs and a general lack of methods to transform the chain ends of BPs into functional groups suitable for bioconjugation. Here, we present a strategy to address this challenge in the context of BPs prepared by "graft-through" ring-opening metathesis polymerization (ROMP), one of the most powerful methods for BP synthesis. Quenching ROMP of PEGylated norbornene macromonomers with an activated enyne terminator facilitates the transformation of the BP Ru alkylidene chain ends into Pd oxidative addition complexes (OACs) for facile bioconjugation. This strategy is shown to be effective for the synthesis of two BP-protein conjugates (albumin and ERG), setting the stage for a new class of BP-protein conjugates for future therapeutic and imaging applications.

Sustainable formulation polymers for home, beauty and personal care: challenges and opportunities

As society moves towards a net-zero future, the need to adopt more sustainable polymers is well understood, and as well as plastics, less visible formulation polymers should also be included within this shift. As researchers, industries and consumers move towards more sustainable products there is a clear need to define what sustainability means in fast moving consumer goods and how it can be considered at the design stage. In this perspective key challenges in achieving sustainable formulation polymers are highlighted, and opportunities to overcome them are presented.

Synthesis and Properties of Polyol Copolymer with Alternating Methacrylate-Vinyl Ether Backbone

Radical polymerization of a tailored diphenylsilane-bridged bi-functional monomer consisting of methacrylate and vinyl ether moieties is conducted in diluted monomer concentration, in which both two moieties are consumed at almost the same rate despite their huge difference in monomer reactivity ratio. The vinyl ether content in the backbone is quantified as 45% by ¹ H NMR after removal of the silane bridge. Since vinyl ether alone cannot be polymerized in such radical polymerization, it should be incorporated in an alternating fashion with methacrylate into the copolymer main chain. The cleavage of silane bridge also yields a series of polyol materials composed of ethylene glycol monovinyl ether (EGVE) and hydroxyethyl methacrylate (HEMA), and the EGVE content in the backbone can be regulated from 45% to 18% by increasing the bi-functional monomer concentration. Interestingly, although containing more than 50% HEMA units, the alternating copolymer exhibits new properties totally different from poly(HEMA), but more similar to poly(EGVE), e.g., good water solubility and a markedly low glass transition temperature (T_g ) of -31 °C, which is attributed to the major HEMA-EGVE repeating unit that replaced HEMA-HEMA consecutive segments so that the properties of poly(HEMA) such as 95 °C T_g are completely altered.

Self-assembling nanowires from a linear l,d-peptide conjugated to the dextran end group

Preparation and characterization of a block-like l,d-octapeptide-dextran conjugate DEX₂₉-(l-Val-d-Val)₄ self-assembling into nanowire structures is reported. The conjugate was prepared by solid phase click-chemistry on an alkyne group N-terminus functionalized peptide with a regularly alternating enantiomeric sequence. Low molecular weight dextran (X_n = 29) with moderately low dispersity (1.30) was prepared by controlled acid hydrolysis and dialysis with selected cut-off and functionalized with an azido group on the reducing end by reductive amination. The strong hydrogen bonds and hydrophobic interactions of the (l-Val-d-Val)₄ linear peptide drive the conjugate to self-assemble into long (0.1-1 μm) nanowires. To our knowledge, this is the first example of a peptide-polysaccharide conjugate that can self-assemble into a nanowire architecture.

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.

Sequence-controlled and sequence-defined polypeptoids via the Ugi reaction: synthesis and sequence-driven properties

Ugi reaction offers opportunities to facilely access unprecedented sequence control and sequence-driven properties in polypeptoids.

Bifunctional Peptide-Polymer Conjugate-Based Fibers via a One-Pot Tandem Disulfide Reduction Coupled to a Thio-Bromo "Click" Reaction

In view of the potential applications of fibers in material sciences and biomedicine, an effective synthetic strategy is described to construct peptide-based bifunctional polymeric conjugates for supramolecular self-association in solution. A direct coupling method of an α-acyl-brominated peptide Phe-Phe-Phe-Phe (FFFF) with a disulfide-bridged polymeric scaffold of poly(ethylene glycol) (PEG) (M n,GPC = 8700 g mol-1, Đ = 2.02) is reported to readily prepare the bi-headed conjugate FFFF-PEG-FFFF (M n,GPC = 3800 g mol-1, Đ = 1.10) via a one-pot, tandem disulfide reduction (based on tris(2-carboxyethyl)phosphine hydrochloride (TCEP)) coupled to a thio-bromo "click" reaction. The conjugate was investigated via transmission electron microscopy to exploit supramolecular fibril formation and solvent-dependent structuring into macroscale fibers via fibril-fibril interactions and interfibril cross-linking-induced bundling. Circular dichroism spectroscopic analysis is further performed to investigate β-sheet motifs in such fibrous scaffolds. Overall, this synthetic approach opens an attractive approach for a simplified synthesis of PEG-containing peptide conjugates.

Peptide-Assisted Design of Peptoid Sequences: One Small Step in Structure and Distinct Leaps in Functions

Using peptide sequences for the design of functional peptoids is demonstrated for a peptide-based formulation additive that was specifically tailored to solubilize the photosensitizer meta-tetra(hydroxyphenyl)-chlorin. A set of peptoid-block-poly(ethylene glycol) solubilizers with systematic sequence variations are synthesized to reveal contributions of side-chain sequence and backbone functionalities on drug hosting and release properties. The drug payload sensitively depends on the side-chain patterns, and the best performing peptoid sequence reaches 3-times higher capacity than the corresponding peptide. The peptoid backbone not only acts as a neutral scaffold but also impacts the drug release kinetics compared to the analogues peptide, by reducing the capability to assist drug transfer to blood plasma protein models.

A guide to supramolecular polymerizations

Supramolecular polymers are non-covalent assemblies of unimeric building blocks connected by secondary interactions and hold great promises due to their dynamic nature.

Pyridyl Disulfide Reaction Chemistry: An Efficient Strategy toward Redox-Responsive Cyclic Peptide-Polymer Conjugates

Cyclic peptide-polymer conjugates are capable of self-assembling into supramolecular polymeric nanotubes driven by the strong multiple hydrogen bonding interactions between the cyclic peptides. In this study, we have engineered responsive nanotubes by introducing a cleavable bond that responds to a reductant utilizing pyridyl disulfide reaction chemistry. Reactions between a cysteine containing cyclic peptide (CP-SH) and pyridyl disulfide containing polymers were initially studied, leading to the quantitative formation of cyclic peptide-polymer conjugates. An asymmetric cyclic peptide-polymer conjugate (PEG-CP-S-S-pPEGA) was then synthesized via orthogonal pyridyl disulfide reaction chemistry and NHS coupling chemistry. The disulfide linker formed by the pyridyl disulfide reaction chemistry was then selectively reduced to thiols in the presence of a reductant, enabling the transition of the conjugates from nonassembling unimers to self-assembled supramolecular polymeric nanotubes. It is anticipated that the pyridyl disulfide reaction chemistry will not only enrich the methodology toward the synthesis of cyclic peptide-polymer conjugates, but also lead to the construction of a new family of redox-responsive cyclic peptide-polymer conjugates and supramolecular polymeric nanotubes with tailored structures and functionalities.

Supramolecular switching of the self-assembly of cyclic peptide-polymer conjugates via host-guest chemistry

A supramolecular strategy of switching the self-assembly of cyclic peptide-polymer conjugates using host-guest chemistry is proposed. The formation of tubular supramolecular polymers based on cyclic peptide-polymer conjugates can be controlled by reversibly attaching cucurbit[7]uril onto the cyclic peptide via host-guest interactions.

Switchable length nanotubes from a self-assembling pH and thermosensitive linear l,d-peptide-polymer conjugate

Preparation and characterization of a pH and thermosensitive linear l,d-octapeptide-poly(dimethylamino ethyl methacrylate) ((l-Val-d-Val)₄-PDMAEMA) conjugate is reported. The hydrophobic uncharged linear (l-Val-d-Val)₄ octapeptide was designed to self-assemble in nanotubes by exploiting the tubular self-assembling properties of linear peptides with regularly alternating enantiomeric sequences. pH and thermosensitive PDMAEMA was obtained by atom transfer radical polymerization (ATRP). The conjugate was prepared by click-chemistry on the solid phase synthetized peptide. Because of the strong interactions between the peptide moieties, long single channel nanotubes (0.2-1.5 μm) are formed also at acidic pH with the fully charged polymer. At 25 °C and basic pH the size of the nanotubes did not change significantly. In basic conditions and temperature above the PDMAEMA lower critical solution temperature (LCST) a significant increase of the length of the nanotubes up to several micrometers is observed. The size is retained for several days after cooling back to room temperature. Sonication significantly reduces the nanotube length (0.2-0.5 μm) forming low polydisperse nanotubes. The elongation of the nanotubes is fully reversible by restoring acidic pH. This is the first example, to our knowledge, of thermosensitive peptide-polymer single channel nanotubes with length that can be varied from hundreds of nanometers to several micrometers.

Supramolecular assembly of functional peptide–polymer conjugates

The following review gives an overview about synthetic peptide–polymer conjugates as macromolecular building blocks and their self-assembly into a variety of supramolecular architectures, from supramolecular polymer chains, to anisotropic 1D arrays, 2D layers, and more complex 3D networks.

Controlled polymerizations using metal-organic frameworks

This short review focuses on recent developments in polymerization reactions using metal-organic frameworks (MOFs). MOFs are crystalline porous materials that are able to tune their frameworks, enabling their use as promising media for polymerization. The precise design of the MOF structure is key to controlling polymerizations, allowing for the regulation of not only primary but also higher-order structures.

Virus-mimetic polymer nanoparticles displaying hemagglutinin as an adjuvant-free influenza vaccine

The generation of virus-mimetic nanoparticles has received much attention in developing a new vaccine for overcoming the limitations of current vaccines. Thus, a method, encompassing most viral features for their size, hydrophobic domain and antigen display, would represent a meaningful direction for the vaccine development. In the present study, a polymer-templated protein nanoball with direction oriented hemagglutinin1 on its surface (H1-NB) was prepared as a new influenza vaccine, exhibiting most of the viral features. Moreover, the concentrations of antigen on the particle surface were controlled, and its effect on immunogenicity was estimated by in vivo studies. Finally, H1-NB efficiently promoted H1-specific immune activation and cross-protective activities, which consequently prevented H1N1 infections in mice.

Synthesis, Self-Assembly, and Biomedical Applications of Antimicrobial Peptide-Polymer Conjugates

Antimicrobial peptides (AMPs) have been attracting much attention due to their excellent antimicrobial efficiency and low rate in driving antimicrobial resistance (AMR), which has been increasing globally to alarming levels. Conjugation of AMPs into functional polymers not only preserves excellent antimicrobial activities but reduces the toxicity and offers more functionalities, which brings new insight toward developing multifunctional biomedical materials such as hydrogels, polymer vesicles, polymer micelles, and so forth. These nanomaterials have been exhibiting excellent antimicrobial activity against a broad spectrum of bacteria including multidrug-resistant (MDR) ones, high selectivity, and low cytotoxicity, suggesting promising potentials in wound dressing, implant coating, antibiofilm, tissue engineering, and so forth. This Perspective seeks to highlight the state-of-the-art strategy for the synthesis, self-assembly, and biomedical applications of AMP-polymer conjugates and explore the promising directions for future research ranging from synthetic strategies, multistage and stimuli-responsive antibacterial activities, antifungi applications, and potentials in elimination of inflammation during medical treatment. It also will provide perspectives on how to stem the remaining challenges and unresolved problems in combating bacteria, including MDR ones.

Precision compatibilizers for composites: in-between self-aggregation, surfaces recognition and interface stabilization

Peptide-polymer conjugates are applied as interface stabilizers that are precisely tuned to recognize the surfaces of inorganic constituents in composites. A set of peptide sequences is usually selected through phage-display and a strategy is presented for the identification of the most effective sequences through the evaluation of secondary interactions, including not only surface binding but also solubility and self-aggregation tendency.

Folding induced supramolecular assembly into pH-responsive nanorods with a protein repellent shell

ABA′ triblock peptide–polysarcosine–peptide conjugates fold into antiparallel β-sheets, which promotes the self-assembly into polysarcosine-shielded core–shell nanorods with protein repellent properties.

Defining the Field of Sequence-Controlled Polymers

Over the last ten years, the development of synthetic polymers containing controlled monomer sequences has become a prominent topic in fundamental and applied polymer science. This emerging area is particularly broad and combines classical polymer chemistry tools with techniques imported from other domains such as biology, biochemistry, organic synthesis, engineering, and bioanalytics. Consequently, it also generates new structures, terminologies, and applications that are not within the traditional scope of polymer science. The term "sequence-controlled polymers" (SCPs) was recently proposed as a generic name to describe all these recent trends. However, since the field of SCPs has been growing very rapidly in recent literature, it is urgent to accurately define its scientific frontiers. In this important context, this review is an attempt to define, rationalize, and classify the field of SCPs. In particular, all synthetic approaches that have been reported for the synthesis of SCPs are discussed and categorized. In addition, the characterization tools, properties, and potential applications of these new polymers are described herein. Overall, this review serves as a reference guide for understanding the burgeoning field of SCPs.

Basic concepts and recent advances in nanogels as carriers for medical applications

Nanogels in biomedical field are promising and innovative materials as dispersions of hydrogel nanoparticles based on crosslinked polymeric networks that have been called as next generation drug delivery systems due to their relatively high drug encapsulation capacity, uniformity, tunable size, ease of preparation, minimal toxicity, stability in the presence of serum, and stimuli responsiveness. Nanogels show a great potential in chemotherapy, diagnosis, organ targeting and delivery of bioactive substances. The main subjects reviewed in this article concentrates on: (i) Nanogel assimilation in the nanomedicine domain; (ii) Features and advantages of nanogels, the main characteristics, such as: swelling capacity, stimuli sensitivity, the great surface area, functionalization, bioconjugation and encapsulation of bioactive substances, which are taken into account in designing the structures according to the application; some data on the advantages and limitations of the preparation techniques; (iii) Recent progress in nanogels as a carrier of genetic material, protein and vaccine. The majority of the scientific literature presents the multivalency potential of bioconjugated nanogels in various conditions. Today's research focuses over the overcoming of the restrictions imposed by cost, some medical requirements and technological issues, for nanogels' commercial scale production and their integration as a new platform in biomedicine.

Click and Click-Inspired Chemistry for the Design of Sequence-Controlled Polymers

During the previous decade, many popular chemical reactions used in the area of "click" chemistry and similarly efficient "click-inspired" reactions have been applied for the design of sequence-defined and, more generally, sequence-controlled structures. This combination of topics has already made quite a significant impact on scientific research to date and has enabled the synthesis of highly functionalized and complex oligomeric and polymeric structures, which offer the prospect of many exciting further developments and applications in the near future. This minireview highlights the fruitful combination of these two topics for the preparation of sequence-controlled oligomeric and macromolecular structures and showcases the vast number of publications in this field within a relatively short span of time. It is divided into three sections according to the click-(inspired) reaction that has been applied: copper-catalyzed azide-alkyne cycloaddition, thiol-X, and related thiolactone-based reactions, and finally Diels-Alder-chemistry-based routes are outlined, respectively.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

Fabrication of device with poly(N-isopropylacrylamide)-b-ssDNA copolymer brush for resistivity study

In this study, we grafted bromo-terminated poly(N-isopropylacrylamide) (PNIPAAm) brushes onto thin gold films deposited on silicon, and then reacted with NaN₃ to produce azido-terminated PNIPAAm brushes. A probe sequence of single-stranded DNA (ssDNA) with a 4-pentynoic acid succinimidyl ester unit was grafted onto the azido-terminated PNIPAAm brushes through a click reaction, resulting in the formation of block copolymer brushes. The PNIPAAm-b-ssDNA copolymer brushes formed supramolecular complexes stabilized by bio-multiple hydrogen bonds (BMHBs), which enhanced the proton transfer and thereby decreased the resistivity of the structures. In addition, the optimal operation window for DNA detection ranges from 0 to 0.2 M of NaCl concentration. Therefore, the specimens were prepared in the PBS solution at 150 mM NaCl concentration for target hybridization. The supramolecular complex state of the PNIPAAm-b-ssDNA copolymer brushes transformed into the phase-separated state after the hybridization with 0.5 ng/µL of its target DNA sequence owing to the competition between BMHBs and complementary hydrogen bonds. This phase transformation of the PNIPAAm and probe segments inhibited the proton transfer and significantly increased the resistivity at 25 °C. Moreover, there were no significant changes in the resistivity of the copolymer brushes after hybridization with the target sequence at 45 °C. These results indicated that the phase-separated state of the PNIPAAm-b-ssDNA copolymer brushes, which was generally occurred above the LCST, can be substantially generated after hybridization with its target DNA sequence. By performing the controlled experiments, in the same manner, using another sequence with lengths similar to that of the target sequence without complementarity. In addition, the sequences featuring various degrees of complementarity were exploited to verify the phase separation behavior inside the PNIPAAm-b-ssDNA copolymer thin film.

Tailoring the supramolecular structure of amphiphilic glycopolypeptide analogue toward liver targeted drug delivery systems

Amphiphilic glycopolypeptide analogues have harboured great importance in the development of targeted drug delivery systems. In this study, lactosylated pullulan-graft-arginine dendrons (LP-g-G3P) was synthesized using Huisgen azide-alkyne 1,3-dipolar cycloaddition between lactosylated pullulan and generation 3 arginine dendrons bearing Pbf and Boc groups on the periphery. Hydrophilic lactosylated pullulan was selected for amphiphilic modification, aiming at specific lectin recognition. Macromolecular structure of LP-g-G3P combined alkyl, aromatic, and peptide dendritic hydrophobic moieties and was able to self-assemble spontaneously into core-shell nanoarchitectures with small particle sizes and low polydispersity in the aqueous media, which was confirmed by CAC, DLS and TEM. Furthermore, the polyaromatic anticancer drug (doxorubicin, DOX) was selectively encapsulated in the hydrophobic core through multiple interactions with the dendrons, including π-π interactions, hydrogen bonding and hydrophobic interactions. Such multiple interactions had the merits of enhanced drug loading capacity (16.89±2.41%), good stability against dilution, and excellent sustained release property. The cell viability assay presented that LP-g-G3P nanoparticles had an excellent biocompatibility both in the normal and tumor cells. Moreover, LP-g-G3P/DOX nanoparticles could be effectively internalized into the hepatoma carcinoma cells and dramatically inhibited cell proliferation. Thus, this approach paves the way to develop amphiphilic and biofunctional glycopolypeptide-based drug delivery systems.

Nanoarmoring of Proteins by Conjugation to Block Copolymer Micelles

The creation of polymer nanoparticles with protein functionality is of great interest to many applications such as targeted drug or gene delivery, diagnostic imaging, cancer theranostics, delivery of protein therapeutics, sensing chemical and biomolecular analytes in complex environments, and design of protective clothing resembling a second skin. Many approaches to achieving this goal are being explored in the current literature. In this chapter, we describe a relatively simple and flexible approach of conjugating the protein to an amphiphilic block copolymer and creating polymer nanoparticles with protein functionality by taking advantage of the intrinsic self-assembly behavior of the amphiphilic block copolymer. The commercially available and biocompatible polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is used as the polymer building block. For demonstrative purposes, bovine serum albumin was chosen as the protein. We determine the molecular weight of the protein-polymer conjugate and thereby the degree of conjugation using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry measurements. Retention of protein secondary structure in the conjugate was determined by circular dichroism spectroscopy, and the biological activity of the protein in the conjugated state has been evaluated by kinetic assay involving hydrolysis of an organophosphate compound. Dynamic light scattering and zeta potential measurements were used to characterize the size and charge of the protein-polymer conjugate micelle. Precise control of the size of the micelle and surface number density of the proteins on the micelle surface by coassembling with a second block copolymer have been demonstrated. These studies document a rational approach to armor the protein by conjugation with a block copolymer micelle, as a general approach.

Nonequilibrium Self-Assembly of π-Conjugated Oligopeptides in Solution

Supramolecular assembly is a powerful method that can be used to generate materials with well-defined structures across multiple length scales. Supramolecular assemblies consisting of biopolymer-synthetic polymer subunits are specifically known to exhibit exceptional structural and functional diversity as well as programmable control of noncovalent interactions through hydrogen bonding in biopolymer subunits. Despite recent progress, there is a need to control and quantitatively understand assembly under nonequilibrium conditions. In this work, we study the nonequilibrium self-assembly of π-conjugated synthetic oligopeptides using a combination of experiments and analytical modeling. By isolating an aqueous peptide solution droplet within an immiscible organic layer, the rate of peptide assembly in the aqueous solution can be controlled by tuning the transport rate of acid that is used to trigger assembly. Using this approach, peptides are guided to assemble under reaction-dominated and diffusion-dominated conditions, with results showing a transition from a diffusion-limited reaction front to spatially homogeneous assembly as the transport rate of acid decreases. Interestingly, our results show that the morphology of self-assembled peptide fibers is controlled by the assembly kinetics such that increasingly homogeneous structures of self-assembled synthetic oligopeptides were generally obtained using slower rates of assembly. We further developed an analytical reaction-diffusion model to describe oligopeptide assembly, and experimental results are compared to the reaction-diffusion model across a range of parameters. Overall, this work highlights the importance of molecular self-assembly under nonequilibrium conditions, specifically showing that oligopeptide assembly is governed by a delicate balance between reaction kinetics and transport processes.

Sequence-coded ATRP macroinitiators

Sequence-defined oligourethanes were transformed into ATRP initiators and used for the synthesis of precision macromolecular architectures.

Study of (Cyclic Peptide)-Polymer Conjugate Assemblies by Small-Angle Neutron Scattering

We present a fundamental study into the self-assembly of (cyclic peptide)-polymer conjugates as a versatile supramolecular motif to engineer nanotubes with defined structure and dimensions, as characterised in solution using small-angle neutron scattering (SANS). This work demonstrates the ability of the grafted polymer to stabilise and/or promote the formation of unaggregated nanotubes by the direct comparison to the unconjugated cyclic peptide precursor. This ideal case permitted a further study into the growth mechanism of self-assembling cyclic peptides, allowing an estimation of the cooperativity. Furthermore, we show the dependency of the nanostructure on the polymer and peptide chemical functionality in solvent mixtures that vary in the ability to compete with the intermolecular associations between cyclic peptides and ability to solvate the polymer shell.