Lithium hexamethyldisilazide initiated superfast ring opening polymerization of alpha-amino acid N-carboxyanhydrides

Water-Assisted and Protein-Initiated Fast and Controlled Ring-Opening Polymerization of Proline N-Carboxyanhydride

The production of polypeptides via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is usually conducted under stringent anhydrous conditions. The ROP of proline NCA (ProNCA) for the synthesis of poly-_L-proline (PLP) is particularly challenging due to the premature product precipitation as polyproline type I helices, leading to slow reactions for up to one week, poor control of the molar mass and laborious workup. Here, we report the unexpected water-assisted controlled ROP of ProNCA, which affords well-defined PLP as polyproline II helices in 2–5 minutes and almost-quantitative yields. Experimental and theoretical studies together suggest the as-yet-unreported role of water in facilitating proton shift, which significantly lowers the energy barrier of the chain propagation. The scope of initiators can be expanded from hydrophobic amines to encompass hydrophilic amines and thiol-bearing nucleophiles, including complex biomacromolecules such as proteins. Protein-mediated ROP of ProNCA conveniently affords various protein-PLP conjugates via a grafting-from approach. PLP modification not only preserves the biological activities of the native proteins, but also enhances their resistance to extreme conditions. Moreover, PLP modification extends the elimination half-life of asparaginase (ASNase) 18-fold and mitigates the immunogenicity of wt ASNase >250-fold (ASNase is a first-line anticancer drug for lymphoma treatment). This work provides a simple solution to a long-standing problem in PLP synthesis, and offers valuable guidance for the development of water-resistant ROP of other proline-like NCAs. The facile access to PLP can greatly boost the application potential of PLP-based functional materials for engineering industry enzymes and therapeutic proteins.

Secondary Amine Pendant β-Peptide Polymers Displaying Potent Antibacterial Activity and Promising Therapeutic Potential in Treating MRSA-Induced Wound Infections and Keratitis

Interest in developing antibacterial polymers as synthetic mimics of host defense peptides (HPDs) has accelerated in recent years to combat antibiotic-resistant bacterial infections. Positively charged moieties are critical in defining the antibacterial activity and eukaryotic toxicity of HDP mimics. Most examples have utilized primary amines or guanidines as the source of positively charged moieties, inspired by the lysine and arginine residues in HDPs. Here, we explore the impact of amine group variation (primary, secondary, or tertiary amine) on the antibacterial performance of HDP-mimicking β-peptide polymers. Our studies show that a secondary ammonium is superior to either a primary ammonium or a tertiary ammonium as the cationic moiety in antibacterial β-peptide polymers. The optimal polymer, a homopolymer bearing secondary amino groups, displays potent antibacterial activity and the highest selectivity (low hemolysis and cytotoxicity). The optimal polymer displays potent activity against antibiotic-resistant bacteria and high therapeutic efficacy in treating MRSA-induced wound infections and keratitis as well as low acute dermal toxicity and low corneal epithelial cytotoxicity. This work suggests that secondary amines may be broadly useful in the design of antibacterial polymers.

Antimicrobial Peptides and Macromolecules for Combating Microbial Infections: From Agents to Interfaces

Bacterial resistance caused by the overuse of antibiotics and the shelter of biofilms has evolved into a global health crisis, which drives researchers to continuously explore antimicrobial molecules and strategies to fight against drug-resistant bacteria and biofilm-associated infections. Cationic antimicrobial peptides (AMPs) are considered to be a category of potential alternative for antibiotics owing to their excellent bactericidal potency and lesser likelihood of inducing drug resistance through their distinctive antimicrobial mechanisms. In this review, the hitherto reported plentiful action modes of AMPs are systematically classified into 15 types and three categories (membrane destructive, nondestructive membrane disturbance, and intracellular targeting mechanisms). Besides natural AMPs, cationic polypeptides, synthetic polymers, and biopolymers enable to achieve tunable antimicrobial properties by optimizing their structures. Subsequently, the applications of these cationic antimicrobial agents at the biointerface as contact-active surface coatings and multifunctional wound dressings are also emphasized here. At last, we provide our perspectives on the development of clinically significant cationic antimicrobials and related challenges in the translation of these materials.

Preparation of antibacterial polypeptides with different topologies and their antibacterial properties

Antimicrobial peptides (AMPs) are attractive antimicrobial agents used to combat bacterial infections, and have been advanced to be one of the most promising alternatives to conventional antibiotics. They stand out for their attractive broad-spectrum activity, unmatched antibacterial mechanism that is not prone to develop drug resistance and diversified topologies, which can be fabricated with manifold amino acid blocks. In this study, using n-hexylamine and amine-terminated polyamidoamine dendrimers (Gx-PAMAM, x = 1-2) as initiators, a series of AMPs with linear and star-shaped topological structures were constructed via the controllable ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs). The antibacterial performances of the tailored linear and star-shaped AMPs were comprehensively evaluated in both solution states and surface-bonded states. The results indicated that the star-shaped AMPs exhibited enhanced bactericidal activity against Gram-negative E. coli and similar bactericidal activity against Gram-positive S. aureus when compared with the linear AMPs. It is worth mentioning that star-shaped AMPs demonstrated a significantly faster bactericidal efficiency (completely killed bacteria within 5 min at a concentration of 2 × MIC for S. aureus) than their linear analogues (took 15 min to achieve the same effect). However, when the AMPs were immobilized to the surface, they similarly exhibited superior antibacterial activity and fast bactericidal efficiency towards S. aureus and E. coli in the case of the same surface grafting amount. In addition, both the surfaces grafted with AMPs of different topologies demonstrated favorable biocompatibility in vitro.

Controlled copolymerization of α-NCAs and α-NNTAs for preparing peptide/peptoid hybrid polymers with adjustable proteolysis

The living and controlled copolymerization of α-NCAs and α-NNTAs enables the facile synthesis of peptide/peptoid hybrid polymers with an alternating-like distribution of residues and adjustable proteolysis by varying the proportion of peptoid residues.

Facile synthesis of polypeptoids bearing bulky sidechains via urea accelerated ring-opening polymerization of α-amino acid N-substituted N-carboxyanhydrides

The organocatalyst 1,3-bis[3,5-bis(trifluoromethyl)phenyl]urea (U–O) accelerates the ring-opening polymerization of α-amino acid N-substituted N-carboxyanhydrides (NNCAs) for the rapid synthesis of polypeptoids bearing bulky sidechains.

Biodegradable Peptide Polymers as Alternatives to Antibiotics Used in Aquaculture

The pressure of antimicrobial resistance has forced many countries to reduce or even prohibit the use of antibiotics in feed. Therefore, it is in urgent need to develop alternatives to...

Organobase 1,1,3,3-tetramethyl guanidine catalyzed rapid ring-opening polymerization of α-amino acid N-carboxyanhydrides adaptive to amine, alcohol and carboxyl acid initiators

For amine, hydroxyl and carboxyl terminated initiators, the organobase 1,1,3,3-tetramethylguanidine (TMG) catalyzes the rapid polymerization to afford polypeptides with controllable molecular weights and dispersities.

Superfast and Water-Insensitive Polymerization on α-Amino Acid N-Carboxyanhydrides to Prepare Polypeptides Using Tetraalkylammonium Carboxylate as the Initiator

We design the tetraalkylammonium carboxylate-initiated superfast polymerization on α-amino acid N-carboxyanhydrides (NCA) for efficient synthesis of polypeptides. Carboxylates, as a new class of initiator for NCA polymerization, can initiate the superfast NCA polymerization without the need of extra catalysts and the polymerization can be operated in open vessels at ambient condition without the use of glove box. Tetraalkylammonium carboxylate-initiated polymerization on NCA easily affords block copolymers with at least 15 blocks. Moreover, this method avoids tedious purification steps and enables direct polymerization on crude NCAs in aqueous environments to prepare polypeptides and one-pot synthesis of polypeptide nanoparticles. These advantages and the mild polymerization condition of tetraalkylammonium carboxylate-initiated NCA polymerization imply its great potential in functional exploration and application of polypeptides.

Peptide Design and Self-assembly into Targeted Nanostructure and Functional Materials

Peptides have been extensively utilized to construct nanomaterials that display targeted structure through hierarchical assembly. The self-assembly of both rationally designed peptides derived from naturally occurring domains in proteins as well as intuitively or computationally designed peptides that form β-sheets and helical secondary structures have been widely successful in constructing nanoscale morphologies with well-defined 1-d, 2-d, and 3-d architectures. In this review, we discuss these successes of peptide self-assembly, especially in the context of designing hierarchical materials. In particular, we emphasize the differences in the level of peptide design as an indicator of complexity within the targeted self-assembled materials and highlight future avenues for scientific and technological advances in this field.

Synthesis of Polypeptides with High-Fidelity Terminal Functionalities under NCA Monomer-Starved Conditions

Controlled polypeptide synthesis via α-amino acid N-carboxylic anhydride (NCA) polymerization using conventional primary amine initiators encounters two major obstacles: (i) normal amine mechanism (NAM) and activated monomer mechanism (AMM) coexist due to amine basicity and nucleophilicity and (ii) NCA is notoriously sensitive towards moisture and heat and unstable upon storage. We serendipitously discover that N-phenoxycarbonyl-functionalized α-amino acid (NPCA), a latent NCA precursor, could be polymerized solely based on NAM with high initiating efficiency by using primary amine hydrochloride as an initiator. The polymerization affords well-defined polypeptides with narrow polydispersity and high-fidelity terminal functionalities, as revealed by the clean set of MALDI-TOF MS patterns. We further demonstrate successful syntheses of random and block copolypeptides, even under open-vessel conditions. Overall, the integration of moisture-insensitive and air-tolerant NPCA precursors with stable primary amine hydrochloride initiators represents a general strategy for controlled synthesis of high-fidelity polypeptides with sophisticated functions.

Synthesis of poly-α/β-peptides with tunable sequence via the copolymerization on N-carboxyanhydride and N-thiocarboxyanhydride

The fascinating functions of proteins and peptides in biological systems have attracted intense interest to explore their mimics using polymers, including polypeptides synthesized from polymerization. The folding, structures and functions of proteins and polypeptides are largely dependent on their sequence. However, sequence-tunable polymerization for polypeptide synthesis is a long-lasting challenge. The application of polypeptides is also greatly hindered by their susceptibility to enzymatic degradation. Although poly-α/β-peptide has proven to be an effective strategy to address the stability issue, the synthesis of poly-α/β-peptide from polymerization is not available yet. Hereby, we demonstrate a living and controlled copolymerization on α-NCA and β-NTA to prepare sequence-tunable poly-α/β-peptides. This polymerization strategy shows a prominent solvent-driven characteristic, providing random-like copolymers of poly-α/β-peptides in THF and block-like copolymers of poly-α/β-peptides in a mixed solvent of CHCl₃/H₂O (95/5, v/v), and opens new avenues for sequence-tunable polymerization and enables facile synthesis of proteolysis tunable poly-α/β-peptides for diverse applications.

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Realizing controlled synthesis of poly-α/β-peptides via one-pot polymerization

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Sequence-tunable copolymerization via solvent-dependent polymerization kinetics

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Adjustable proteolytic stability and antibacterial activity of poly-α/β-peptides

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Tunable self-assembly behavior of poly-α/β-peptides via one-pot polymerization

Addressing MRSA infection and antibacterial resistance with peptoid polymers

Methicillin-Resistant Staphylococcus aureus (MRSA) induced infection calls for antibacterial agents that are not prone to antimicrobial resistance. We prepare protease-resistant peptoid polymers with variable C-terminal functional groups using a ring-opening polymerization of N-substituted N-carboxyanhydrides (NNCA), which can provide peptoid polymers easily from the one-pot synthesis. We study the optimal polymer that displays effective activity against MRSA planktonic and persister cells, effective eradication of highly antibiotic-resistant MRSA biofilms, and potent anti-infectious performance in vivo using the wound infection model, the mouse keratitis model, and the mouse peritonitis model. Peptoid polymers show insusceptibility to antimicrobial resistance, which is a prominent merit of these antimicrobial agents. The low cost, convenient synthesis and structure diversity of peptoid polymers, the superior antimicrobial performance and therapeutic potential in treating MRSA infection altogether imply great potential of peptoid polymers as promising antibacterial agents in treating MRSA infection and alleviating antibiotic resistance.

Antibiotic resistance is a major issue in medicine and new antimicrobials for treating resistant infection are needed. Here, the authors report on antibacterial peptoid polymers, prepared via NNCA ring-opening polymerization, demonstrating antibacterial function against MRSA in vitro and in in vivo infection models.

A moisture-tolerant route to unprotected α/β-amino acid N-carboxyanhydrides and facile synthesis of hyperbranched polypeptides

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups. Here we report a robust method for preparing unprotected NCA monomers in air and under moisture. The method employs epoxy compounds as ultra-fast scavengers of hydrogen chloride to allow assisted ring-closure and prevent NCA from acid-catalyzed decomposition under moist conditions. The broad scope and functional group tolerance of the method are demonstrated by the facile synthesis of over 30 different α/β-amino acid NCAs, including many otherwise inaccessible compounds with reactive functional groups, at high yield, high purity, and up to decagram scales. The utility of the method and the unprotected NCAs is demonstrated by the facile synthesis of two water-soluble polypeptides that are promising candidates for drug delivery and protein modification. Overall, our strategy holds great potential for facilitating the synthesis of NCA and expanding the industrial application of synthetic polypeptides.

An Inspection into Multifarious Ways to Synthesize Poly(Amino Acid)s

Poly(α-amino acid)s (PAAs) attract growing attention due to their essential role in the application as biomaterials. To synthesize PAAs with desired structures and properties, scientists have developed various synthetic techniques with respective advantages. Here, different approaches to preparing PAAs are inspected. Basic features and recent progresses of these methods are summarized, including polymerizations of amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), as well as other synthetic routes. NCA is the most classical monomer to prepare PAAs with high molecular weights (MWs). NTA polymerizations are promising alternative pathways to produce PAAs, which can tolerate nucleophiles including alcohols, mercaptans, carboxyl acids, and water. By various techniques including choosing appropriate solvents or using organic acids as promoters, NTAs polymerize to produce polypeptoids and polypeptides with narrow dispersities and designed MWs up to 55.0 and 57.0 kg mol^-1 , respectively. NPC polymerizations are phosgene-free ways to synthesize polypeptides and polypeptoids. For the future prospects, detail investigations into polymerization mechanisms of NTA and NPC are expected. The synthesis of PAAs with designed topologies and assembly structures is another intriguing topic. The advantages and unsettled problems in various synthetic ways are discussed for readers to choose appropriate approaches for PAAs.

Poly(α-l-lysine)-based nanomaterials for versatile biomedical applications: Current advances and perspectives

Poly(α-l-lysine) (PLL) is a class of water-soluble, cationic biopolymer composed of α-l-lysine structural units. The previous decade witnessed tremendous progress in the synthesis and biomedical applications of PLL and its composites. PLL-based polymers and copolymers, till date, have been extensively explored in the contexts such as antibacterial agents, gene/drug/protein delivery systems, bio-sensing, bio-imaging, and tissue engineering. This review aims to summarize the recent advances in PLL-based nanomaterials in these biomedical fields over the last decade. The review first describes the synthesis of PLL and its derivatives, followed by the main text of their recent biomedical applications and translational studies. Finally, the challenges and perspectives of PLL-based nanomaterials in biomedical fields are addressed.

Polypeptide-based drug delivery systems for programmed release

Recent years have seen increasing interests in the use of ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs) to prepare synthetic polypeptides, a class of biocompatible and versatile materials, for various biomedical applications. Because of their rich side-chain functionalities, diverse hydrophilicity/hydrophobicity profiles, and the capability of forming stable secondary structures, polypeptides can assemble into a variety of well-organized nano-structures that have unique advantages in drug delivery and controlled release. Herein, we review the design and use of polypeptide-based drug delivery system derived from NCA chemistry, and discuss the future perspectives of this exciting and important biomaterial area that may potentially change the landscape of next-generation therapeutics and diagnosis. Given the high significance of precise control over release for polypeptide-based systems, we specifically focus on the versatile designs of drug delivery systems capable of programmed release, through the changes in the chemical and physical properties controlled by the built-in molecular structures of polypeptides.

Effective and biocompatible antibacterial surfaces via facile synthesis and surface modification of peptide polymers

It is an urgent need to tackle drug-resistance microbial infections that are associated with implantable biomedical devices. Host defense peptide-mimicking polymers have been actively explored in recent years to fight against drug-resistant microbes. Our recent report on lithium hexamethyldisilazide-initiated superfast polymerization on amino acid N-carboxyanhydrides enables the quick synthesis of host defense peptide-mimicking peptide polymers. Here we reported a facile and cost-effective thermoplastic polyurethane (TPU) surface modification of peptide polymer (DLL: BLG = 90 : 10) using plasma surface activation and substitution reaction between thiol and bromide groups. The peptide polymer-modified TPU surfaces exhibited board-spectrum antibacterial property as well as effective contact-killing ability in vitro. Furthermore, the peptide polymer-modified TPU surfaces showed excellent biocompatibility, displaying no hemolysis and cytotoxicity. In vivo study using methicillin-resistant Staphylococcus aureus (MRSA) for subcutaneous implantation infectious model showed that peptide polymer-modified TPU surfaces revealed obvious suppression of infection and great histocompatibility, compared to bare TPU surfaces. We further explored the antimicrobial mechanism of the peptide polymer-modified TPU surfaces, which revealed a surface contact-killing mechanism by disrupting the bacterial membrane. These results demonstrated great potential of the peptide-modified TPU surfaces for practical application to combat bacterial infections that are associated with implantable materials and devices.

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A convenient surface modification of peptide polymer 90 : 10 DLL : BLG to enable material surfaces antibacterial properties.

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The modified thermoplastic polyurethane (TPU) surfaces show board-spectrum antibacterial performance and excellent biocompatibility both in vitro and in vivo.

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The contact-killing surfaces demonstrate great potential for practical application to combat bacterial infections associated with implantable materials and devices.

An alpha/beta chimeric peptide molecular brush for eradicating MRSA biofilms and persister cells to mitigate antimicrobial resistance

Infections involving methicillin-resistant Staphylococcus aureus present great challenges, especially when biofilms and persister cells are involved. In this work, an α/β chimeric polypeptide molecular brush (α/β CPMB) is reported to show excellent performance in inhibiting the formation of biofilms and eradicating established biofilms. Additionally, the polymer brush efficiently killed metabolically inactive persister cells that are antibiotic-insensitive. Antimicrobial mechanism studies showed that α/β CPMB causes membrane disturbance and a substantial increase in reactive oxygen species (ROS) levels to kill bacteria, and mesosome-like structure formation was also observed. Furthermore, the polymer brush was able to kill clinically isolated multidrug resistant Gram-positive bacteria with no risk of antimicrobial resistance. The α/β CPMB has demonstrated great potential in addressing the great challenge of eradicating multidrug resistant Gram-positive bacterial infections.

α-Amino acid N-carboxyanhydride (NCA)-derived synthetic polypeptides for nucleic acids delivery

In recent years, gene therapy has come into the spotlight for the prevention and treatment of a wide range of diseases. Polypeptides have been widely used in mediating nucleic acid delivery, due to their versatilities in chemical structures, desired biodegradability, and low cytotoxicity. Chemistry plays an essential role in the development of innovative polypeptides to address the challenges of producing efficient and safe gene vectors. In this Review, we mainly focused on the latest chemical advances in the design and preparation of polypeptide-based nucleic acid delivery vehicles. We first discussed the synthetic approach of polypeptides via ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs), and introduced the various types of polypeptide-based gene delivery systems. The extracellular and intracellular barriers against nucleic acid delivery were then outlined, followed by detailed review on the recent advances in polypeptide-based delivery systems that can overcome these barriers to enable in vitro and in vivo gene transfection. Finally, we concluded this review with perspectives in this field.

Automation and data-driven design of polymer therapeutics

Polymers are uniquely suited for drug delivery and biomaterial applications due to tunable structural parameters such as length, composition, architecture, and valency. To facilitate designs, researchers may explore combinatorial libraries in a high throughput fashion to correlate structure to function. However, traditional polymerization reactions including controlled living radical polymerization (CLRP) and ring-opening polymerization (ROP) require inert reaction conditions and extensive expertise to implement. With the advent of air-tolerance and automation, several polymerization techniques are now compatible with well plates and can be carried out at the benchtop, making high throughput synthesis and high throughput screening (HTS) possible. To avoid HTS pitfalls often described as "fishing expeditions," it is crucial to employ intelligent and big data approaches to maximize experimental efficiency. This is where the disruptive technologies of machine learning (ML) and artificial intelligence (AI) will likely play a role. In fact, ML and AI are already impacting small molecule drug discovery and showing signs of emerging in drug delivery. In this review, we present state-of-the-art research in drug delivery, gene delivery, antimicrobial polymers, and bioactive polymers alongside data-driven developments in drug design and organic synthesis. From this insight, important lessons are revealed for the polymer therapeutics community including the value of a closed loop design-build-test-learn workflow. This is an exciting time as researchers will gain the ability to fully explore the polymer structural landscape and establish quantitative structure-property relationships (QSPRs) with biological significance.

Biological applications of water-soluble polypeptides with ordered secondary structures

Water-soluble polypeptides are a class of synthetic polymers with peptide bond frameworks imitating natural proteins and have broad prospects in biological applications. The regulation and dynamic transition of the secondary structures of water-soluble polypeptides have a great impact on their physio-chemical properties and biological functions. In this review article, we briefly introduce the current strategies to synthesize polypeptides and modulate their secondary structures. We then discuss the factors affecting the conformational stability/transition of polypeptides and the potential impact of side-chain functionalization on the ordered secondary structures, such as α-helix and β-sheet. We then summarize the biological applications of water-soluble polypeptides such as cell penetration, gene delivery, and antimicrobial treatment, highlighting the important roles of ordered secondary structures therein.

Density Functional Theory Studies on the Synthesis of Poly(α-Amino Acid)s Via the Amine-Mediated Ring Opening Polymerizations of N-Carboxyanhydrides and N-Thiocarboxyanhydrides

To synthesize well-defined poly (α-amino acid)s (PAAs), ring opening polymerizations (ROP) of cyclic monomers of α-amino acid N-carboxyanhydrides (NCAs) and N-thiocarboxyanhydrides (NTAs) are most widely used. In this mini-review, we summarize the mechanism details of the monomer preparation and ROP. The present study used density functional theory calculations to reveal the mechanisms together with experimental phenomena in the past decades. Detailed discussion includes normal amine mechanism and the selectivity of the initiators bearing various nucleophilic groups.

Cyclic Poly(α-peptoid)s by Lithium bis(trimethylsilyl)amide (LiHMDS)-Mediated Ring-Expansion Polymerization: Simple Access to Bioactive Backbones

Cyclic polymers display unique physicochemical and biological properties. However, their development is often limited by their challenging preparation. In this work, we present a simple route to cyclic poly(α-peptoids) from N-alkylated-N-carboxyanhydrides (NNCA) using LiHMDS promoted ring-expansion polymerization (REP) in DMF. This new method allows the unprecedented use of lysine-like monomers in REP to design bioactive macrocycles bearing pharmaceutical potential against Clostridioides difficile, a bacterium responsible for nosocomial infections.

Enzymatically Cross-linked Hydrogels Based on Synthetic Poly(α-amino acid)s Functionalized with RGD Peptide for 3D Mesenchymal Stem Cell Culture

Injectable hydrogel scaffolds combined with stem cell therapy represent a promising approach for minimally invasive surgical tissue repair. In this study, we developed and characterized a fully synthetic, biodegradable poly(N⁵-(2-hydroxyethyl)-l-glutamine)-based injectable hydrogel modified with integrin-binding arginine-glycine-aspartic acid (RGD) peptide (PHEG-Tyr-RGD). The biodegradable hydroxyphenyl polymer precursor derivative of PHEG-Tyr was enzymatically cross-linked to obtain injectable hydrogels with different physicochemical properties. The gelation time, gel yield, swelling behavior, and storage modulus of the PHEG-Tyr hydrogels were tuned by varying the concentrations of the PHEG-Tyr precursors and horseradish peroxidase as well as the n_H2O2/n_Tyr ratio. The mechanical properties and gelation time of the PHEG-Tyr hydrogel were optimized for the encapsulation of rat mesenchymal stem cells (rMSCs). We focused on the 2D and 3D spreading and viability of rMSCs within the PHEG-Tyr-RGD hydrogels with different physicochemical microenvironments in vitro. Encapsulation of rMSCs shows long-term survival and exhibits cell-matrix and cell-cell interactions reflective of both the RGD concentration and hydrogel stiffness. The presented biomaterial represents a suitable biological microenvironment to guide 3D spreading and may act as a promising 3D artificial extracellular matrix for stem cell therapy.

Recent advances in design of antimicrobial peptides and polypeptides toward clinical translation

The recent outbreaks of infectious diseases caused by multidrug-resistant pathogens have sounded a piercing alarm for the need of new effective antimicrobial agents to guard public health. Among different types of candidates, antimicrobial peptides (AMPs) and the synthetic mimics of AMPs (SMAMPs) have attracted significant enthusiasm in the past thirty years, due to their unique membrane-active antimicrobial mechanism and broad-spectrum antimicrobial activity. The extensive research has brought many drug candidates into clinical and pre-clinical development. Despite tremendous progresses have been made, several major challenges inherent to current design strategies have slowed down the clinical translational development of AMPs and SMAMPs. However, these challenges also triggered many efforts to redesign and repurpose AMPs. In this review, we will first give an overview on AMPs and their synthetic mimics, and then discuss the current status of their clinical translation. Finally, the recent advances in redesign and repurposing AMPs and SMAMPs are highlighted.

Accelerated polymerization of N-carboxyanhydrides catalyzed by crown ether

The recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) enriched the toolbox to prepare well-defined polypeptide materials. Herein we report the use of crown ether (CE) to catalyze the polymerization of NCA initiated by conventional primary amine initiators in solvents with low polarity and low hydrogen-bonding ability. The cyclic structure of the CE played a crucial role in the catalysis, with 18-crown-6 enabling the fastest polymerization kinetics. The fast polymerization kinetics outpaced common side reactions, enabling the preparation of well-defined polypeptides using an α-helical macroinitiator. Experimental results as well as the simulation methods suggested that CE changed the binding geometry between NCA and propagating amino chain-end, which promoted the molecular interactions and lowered the activation energy for ring-opening reactions of NCAs. This work not only provides an efficient strategy to prepare well-defined polypeptides with functionalized C-termini, but also guides the design of catalysts for NCA polymerization.

Hidden complexity in membrane permeabilization behavior of antimicrobial polycations

There are diverse membrane permeabilization behaviors of antimicrobial polycations in zwitterionic or charged vesicles; different mechanisms may occur over time.

Ring opening polymerization of ε-caprolactone through water

Ring opening polymerization (ROP) through water is used to synthesize biodegradable polymers such as polycaprolactone (PCL).

The membrane-targeting mechanism of host defense peptides inspiring the design of polypeptide-conjugated gold nanoparticles exhibiting effective antibacterial activity against methicillin-resistant Staphylococcus aureus

Multidrug-resistant bacterial infections are a grand challenge to global medical and health systems. Therefore, it is urgent to develop versatile antibacterial strategies that can combat bacterial resistance without displaying toxicity. Here, we synthesize antibacterial polypeptide-conjugated gold nanoparticles that exhibit potent antibacterial activities against clinically isolated multiple drug resistance Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus, and excellent in vitro and in vivo biocompatibility. The antibacterial mechanism study indicates that over-production of reactive oxygen species results in the killing of bacteria. The overall antibacterial performance of these polypeptide-conjugated gold nanoparticles and the convenient synthesis of these polypeptides via lithium hexamethyldisilazide-initiated fast ring-opening polymerization on α-amino acid N-carboxyanhydride imply the potential application of this strategy in treating bacterial infections.

The Mechanisms and the Applications of Antibacterial Polymers in Surface Modification on Medical Devices

Medical device contamination caused by microbial pathogens such as bacteria and fungi has posed a severe threat to the patients' health in hospitals. Due to the increasing resistance of pathogens to antibiotics, the efficacy of traditional antibiotics treatment is gradually decreasing for the infection treatment. Therefore, it is urgent to develop new antibacterial drugs to meet clinical or civilian needs. Antibacterial polymers have attracted the interests of researchers due to their unique bactericidal mechanism and excellent antibacterial effect. This article reviews the mechanism and advantages of antimicrobial polymers and the consideration for their translation. Their applications and advances in medical device surface coating were also reviewed. The information will provide a valuable reference to design and develop antibacterial devices that are resistant to pathogenic infections.

Robust and smart polypeptide-based nanomedicines for targeted tumor therapy

Nanomedicines based on synthetic polypeptides are among the most versatile and advanced platforms for tumor therapy. Notably, several polypeptide-based nanodrugs are currently under human clinical assessments. The previous (pre)clinical studies clearly show that dynamic stability (i.e. stable in circulation while destabilized in tumor) of nanomedicines plays a vital role in their anti-tumor performance. Various strategies have recently been developed to design dynamically stabilized polypeptide-based nanomedicines by e.g. crosslinking the nanovehicles with acid, reactive oxygen species (ROS), glutathione (GSH), or photo-sensitive linkers, inter-crosslinking between vehicles and drugs, introducing π-π stacking or lipid-lipid interactions in the nanovehicles, chemically conjugating drugs to vehicles, and forming unimolecular micelles. Interestingly, these robust and smart nanodrugs have demonstrated improved tumor targetability, anti-tumor efficacy, as well as safety profiles in different tumor models. In this review, representative strategies to robust and smart polypeptide-based nanomedicines for targeted treatment of varying malignancies are highlighted. The exciting development of dynamic nanomedicines will foresee further increasing clinical translation in the future.

Peptide-Mimicking Poly(2-oxazoline)s Displaying Potent Antimicrobial Properties

Poly(2-oxazoline)s have excellent biocompatibility and have been used as FDA-approved indirect food additives. The inert property of the hydrophilic poly(2-oxazoline)s suggests them as promising substitutes for poly(ethylene glycol) (PEG) in various applications such as anti-biofouling agents. It was recently reported that poly(2-oxazoline)s themselves have antimicrobial properties as synthetic mimics of host defense peptides. These studies revealed the bioactive properties of poly(2-oxazoline)s as a new class of functional peptide mimics, by mimicking host defense peptides to display potent and selective antimicrobial activities against methicillin-resistant Staphylococcus aureus both in vitro and in vivo, without concerns about antimicrobial resistance. The high structural diversity, facile synthesis, and potent and tunable antimicrobial properties underscore the great potential of poly(2-oxazoline)s as a class of novel antimicrobial agents in dealing with drug-resistant microbial infections and antimicrobial resistance.

Sustainable, Site-Specific Linkage of Antimicrobial Peptides to Cotton Textiles

A new general method to covalently link a peptide to cotton via thiazolidine ring formation is developed. Three different analogues of an ultrashort antibacterial peptide are synthesized to create an antibacterial fabric. The chemical ligation approach to the heterogeneous phase made up of insoluble cellulose fibers and a peptide solution in water is adapted. The selective click reaction occurs between an N-terminal cysteine on the peptide and an aldehyde on the cotton matrix. The aldehyde is generated on the primary alcohol of glucose by means of the enzyme laccase and the cocatalyst 2,2,6,6-tetramethylpiperidine-1-oxyl. This keeps the pyranose rings intact and may bring a benefit to the mechanical properties of the fabric. The presence of the peptide on cotton is demonstrated through instant colorimetric tests, UV spectroscopy, IR spectroscopy, and X-ray photoelectron spectroscopy analysis. The antibacterial activity of the peptides is maintained even after their covalent attachment to cotton fibers.

Synthetic Polypeptide Polymers as Simplified Analogues of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are naturally occurring macromolecules made of amino acids that are potent broad-spectrum antibiotics with potential as novel therapeutic agents. This review aims to summarize the fundamental principles concerning the structure and mechanism of action of these AMPs, in order to guide the design of polymeric analogues that organic chemistry can generate. Among those simplified analogues, this review particularly focuses on those made of amino acids called polypeptide polymers: they are showing great potential by providing one of the best biomimetic and bioactive structures for further biomaterials science applications.