Poly(ε-caprolactone)-block-polysarcosine by Ring-Opening Polymerization of Sarcosine N-Thiocarboxyanhydride: Synthesis and Thermoresponsive Self-Assembly

The Production of Polysarcosine-Containing Nanoparticles by Ring-Opening Polymerization-Induced Self-Assembly

N-carboxyanhydride ring-opening polymerization-induced self-assembly (NCA ROPISA) offers a convenient route for generating poly(amino acid)-based nanoparticles in a single step, crucially avoiding the need for post-polymerization self-assembly. Most examples of NCA ROPISA make use of a poly(ethylene glycol) (PEG) hydrophilic stabilizing block, however this non-biodegradable, oil-derived polymer may cause an immunological response in some individuals. Alternative water-soluble polymers are therefore highly sought. This work reports the synthesis of wholly poly(amino acid)-based nanoparticles, through the chain-extension of a polysarcosine macroinitiator with L-Phenylalanine-NCA (L-Phe-NCA) and Alanine-NCA (Ala-NCA), via aqueous NCA ROPISA. The resulting polymeric structures comprise of predominantly anisotropic, rod-like nanoparticles, with morphologies primarily influenced by the secondary structure of the hydrophobic poly(amino acid) that enables their formation.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

Precision Synthesis of Polysarcosine via Controlled Ring-Opening Polymerization of N-Carboxyanhydride: Fast Kinetics, Ultrahigh Molecular Weight, and Mechanistic Insights

The rapid and controlled synthesis of high-molecular-weight (HMW) polysarcosine (pSar), a potential polyethylene glycol (PEG) alternative, via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is rare and challenging. Here, we report the well-controlled ROP of sarcosine NCA (Sar-NCA) that is catalyzed by various carboxylic acids, which accelerate the polymerization rate up to 50 times, and enables the robust synthesis of pSar with an unprecedented ultrahigh molecular weight (UHMW) up to 586 kDa (DP ∼ 8200) and exceptionally narrow dispersity (D̵) below 1.05. Mechanistic experiments and density functional theory calculations together elucidate the role of carboxylic acid as a bifunctional catalyst that significantly facilitates proton transfer processes and avoids charge separation and suggest the ring opening of NCA, rather than decarboxylation, as the rate-determining step. UHMW pSar demonstrates improved thermal and mechanical properties over the low-molecular-weight counterparts. This work provides a simple yet highly efficient approach to UHMW pSar and generates a new fundamental understanding useful not only for the ROP of Sar-NCA but also for other NCAs.

A Field Guide to Optimizing Peptoid Synthesis

N-Substituted glycines (peptoids) are a class of peptidomimetic molecules used as materials for health, environmental, and drug delivery applications. Automated solid-phase synthesis is the most widely used approach for preparing polypeptoids, with a range of published protocols and modifications for selected synthetic targets. Simultaneously, emerging solution-phase syntheses are being leveraged to overcome limitations in solid-phase synthesis and access high-molecular weight polypeptoids. This Perspective aims to outline strategies for the optimization of both solid- and solution-phase synthesis, provide technical considerations for robotic synthesizers, and offer an outlook on advances in synthetic methodologies. The solid-phase synthesis sections explore steps for protocol optimization, accessing complex side chains, and adaptation to robotic synthesizers; the sections on solution-phase synthesis cover the selection of initiators, side chain compatibility, and strategies for controlling polymerization efficiency and scale. This text acts as a "field guide" for researchers aiming to leverage the flexibility and adaptability of peptoids in their research.

Two-Dimensional Covalent Organic Frameworks as Photocatalysts for Solar Energy Utilization

In the context of energy crisis and global warming, developing clean and sustainable energy is receiving increasing attention. Photocatalytic process including water splitting, CO₂ reduction, coenzyme regeneration, etc., provides an ideal way to utilize renewable solar resources. The photocatalyst plays a central role in photocatalytic processes. Organic porous polymers have recently gained extensive attention in photocatalysis. Covalent organic frameworks (COFs), as one of the organic porous polymers, have the characteristics of high crystallinity, porosity and structural designability that make them perfect platforms for photocatalysis. In this minireview, the recent progresses of 2D COFs as photocatalysts were summarized including our recent work. The synthesis of the diversified structures of the COFs including the different linkages was first introduced. Then, the photocatalytic applications of the 2D COFs including photocatalytic hydrogen evolution, CO₂ conversion, coenzyme regeneration and other traditional organic reaction were then discussed. Finally, conclusions and prospects were provided in the last section. This article is protected by copyright. All rights reserved.

Biodegradable Polysarcosine with Inserted Alanine Residues: Synthesis and Enzymolysis

Polysarcosine (PSar), a water-soluble polypeptoid, is gifted with biodegradability via the random ring-opening copolymerization of sarcosine- and alanine-N-thiocarboxyanhydrides catalyzed by acetic acid in controlled manners. Kinetic investigation reveals the copolymerization behavior of the two monomers. The random copolymers, named PaS, with high molecular weights between 5.3 and 43.6 kg/mol and tunable Ala molar fractions varying from 6 to 43% can be degraded by porcine pancreatic elastase within 50 days under mild conditions (pH = 8.0 at 37 °C). Both the biodegradation rate and water solubility of PaS depend on the content of Ala residues. PaS with Ala fractions below 43% are soluble in water, while the one with 43% Ala self-assembles in water into nanoparticles. Moreover, PaS are noncytotoxic at the concentration of 5 mg/mL. The biodegradability and biocompatibility endow the Ala-containing PSar with the potential to replace poly(ethylene glycol) as a protective shield in drug-delivery.

Synthesis of block copolymers used in polymersome fabrication: Application in drug delivery

Amphiphilic block copolymers are common materials used for the fabrication of various nanostructures with biomedical applications including nanocapsules, nanospheres, micelles and polymeric vesicles. According to the literature, polymersomes have several advantages compared to other nanostructures used as drug delivery systems comprising better stability, facile synthesis, prolonged circulation time, and passive/active targeting capability. Various types of nanoparticles are formed by varying the ratio of the hydrophobic/hydrophilic blocks. Changing hydrophobic/hydrophilic ratio of amphiphilic block copolymers has an impact on the structural characteristics of polymers such as changing molecular weight and surface functionalization of the block copolymer. Thus, polymerization strategies are an important factor that influences polymersomes quality. In this review, different polymerization strategies for the synthesis of block copolymers applied in polymersomes formation, are described.

pH-bioresponsive poly(ε-caprolactone)-based polymersome for effective drug delivery in cancer and protein glycoxidation prevention

Artificial nanostructures using polymers to produce polymeric vesicles are inspired by the many intricate structures found in living organisms. Polymersomes are a class of self-assembled vesicles known for their great stability and application in drug delivery. They can be tuned according to their intended use by changing their components and introducing activable block copolymers that transform these polymersomes into smart nanocarriers. In this study, we propose the synthesis of a poly (ethylene oxide)-poly (ε-caprolactone)-based polymersome (PEO-PCL) loaded with GSH as a pH-responsive drug delivery molecule for cancer and protein alteration inhibition. Initially, the nanocarrier was synthesized and characterized by DLS, TEM/SEM microscopy as well as gel permeation chromatography (GPC) and ¹H NMR. Their CMC formation, encapsulation efficiency, and pH responsiveness were analyzed. In addition, empty and GSH-loaded PEO-PCL polymersomes were tested for their toxicity and therapeutic effect on normal and cancer cells via an MTT test. Subsequently, protein alteration models (aggregation, glycation, and oxidation) were performed in vitro where the polymersomes were tested. Results showed that other than being non-toxic and able to highly encapsulate and release the GSH in response to acidic conditions, the nanocomposites do not hinder its content's ameliorative effects on cancer cells and protein alterations. This infers that polymeric nanocarriers can be a base for future smart biomedicine applications and theranostics.

Polymeric micelles for the delivery of poorly soluble drugs: From nanoformulation to clinical approval

Over the last three decades, polymeric micelles have emerged as a highly promising drug delivery platform for therapeutic compounds. Particularly, poorly soluble small molecules with high potency and significant toxicity were encapsulated in polymeric micelles. Polymeric micelles have shown improved pharmacokinetic profiles in preclinical animal models and enhanced efficacy with a superior safety profile for therapeutic drugs. Several polymeric micelle formulations have reached the clinical stage and are either in clinical trials or are approved for human use. This furthers interest in this field and underscores the need for additional learning of how to best design and apply these micellar carriers to improve the clinical outcomes of many drugs. In this review, we provide detailed information on polymeric micelles for the solubilization of poorly soluble small molecules in topics such as the design of block copolymers, experimental and theoretical analysis of drug encapsulation in polymeric micelles, pharmacokinetics of drugs in polymeric micelles, regulatory approval pathways of nanomedicines, and current outcomes from micelle formulations in clinical trials. We aim to describe the latest information on advanced analytical approaches for elucidating molecular interactions within the core of polymeric micelles for effective solubilization as well as for analyzing nanomedicine's pharmacokinetic profiles. Taking into account the considerations described within, academic and industrial researchers can continue to elucidate novel interactions in polymeric micelles and capitalize on their potential as drug delivery vehicles to help improve therapeutic outcomes in systemic delivery.

Facile Mixing of Phospholipids Promotes Self-Assembly of Low-Molecular-Weight Biodegradable Block Co-Polymers into Functional Vesicular Architectures

In this work, we have used low-molecular-weight (PEG12-b-PCL6, PEG12-b-PCL9 or PEG16-b-PLA38; MW, 1.25-3.45 kDa) biodegradable block co-polymers to construct nano- and micron-scaled hybrid (polymer/lipid) vesicles, by solvent dispersion and electroformation methods, respectively. The hybrid vesicles exhibit physical properties (size, bilayer thickness and small molecule encapsulation) of a vesicular boundary, confirmed by cryogenic transmission electron microscopy, calcein leakage assay and dynamic light scattering. Importantly, we find that these low MW polymers, on their own, do not self-assemble into polymersomes at nano and micron scales. Using giant unilamellar vesicles (GUVs) model, their surface topographies are homogeneous, independent of cholesterol, suggesting more energetically favorable mixing of lipid and polymer. Despite this mixed topography with a bilayer thickness similar to that of a lipid bilayer, variation in surface topology is demonstrated using the interfacial sensitive phospholipase A2 (sPLA2). The biodegradable hybrid vesicles are less sensitive to the phospholipase digestion, reminiscent of PEGylated vesicles, and the degree of sensitivity is polymer-dependent, implying that the nano-scale surface topology can further be tuned by its chemical composition. Our results reveal and emphasize the role of phospholipids in promoting low MW polymers for spontaneous vesicular self-assembly, generating a functional hybrid lipid-polymer interface.

Thermoresponsive polysarcosine-based nanoparticles

Polysarcosine modified with limited molar amounts of (N-(2-hydroxypropyl)methacrylamide) yields a block copolymer capable of forming thermoresponsive nanoparticles that are suitable for controlled release applications.

Polymersomes with aggregation-induced emission based on amphiphilic block copolypeptoids

Fluorescent and biocompatible polymersomes based on the amphiphilic block copolypeptoid P(TPE-NAG)-b-PSar are promising for bio-imaging and drug delivery applications.

Crystallization-Driven Two-Dimensional Self-Assembly of Amphiphilic PCL-b-PEO Coated Gold Nanoparticles in Aqueous Solution

This Letter reports the first formation of free-standing plasmonic monolayer nanosheets by the self-assembly of AuNPs without assistance from a planar interface. The strategy involves the coating of poly(caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) diblock copolymers on AuNPs, followed by two-dimensional (2D) self-assembly of the resultant amphiphilic AuNPs in aqueous phase. The crystallization of the PCL blocks, affected by their grafting density and radius of gyration, drives the formation of the AuNP nanosheets, which undergoes a growth process of individual micelles to small nanosheets and eventually to large sheets. Due to the plasmonic coupling of AuNPs in close proximity, the AuNP nanosheets exhibit near-infrared (NIR) absorption with the maximum at about 700 nm. This study not only brings a new approach toward polymer-AuNP hybrid superstructures in solution, but also provides a new system for fundamental study on 2D self-assembly of AuNPs.

Physical stimuli-responsive liposomes and polymersomes as drug delivery vehicles based on phase transitions in the membrane

This paper reviews liposomes with crystalline phase and polymersomes exhibiting crystalline and thermotropic liquid crystalline phases in the membrane. Intriguing morphologies of vesicles are described, including spherical, ellipsoidal and faceted vesicles, produced by a large variety of amphiphilic molecules and polymers with nematic phase, smectic phase or crystalline phase. It is highlighted how the phase transitions and the phase grain boundaries could be used ingeniously to destabilize the vesicular structure and to achieve cargo-release under the action of external stimulation. These liposomes and polymersomes are responsive to physical stimuli, such as temperature variation, shear stress, light illumination, and magnetic and electric fields. These stimuli-responsive properties make them promising candidates as new smart drug delivery systems.

Polysarcosine brush stabilized gold nanorods for in vivo near-infrared photothermal tumor therapy

Gold nanorods (AuNRs) are suitable candidates for photothermal therapy in vivo, because of their excellent ability to transfer near-infrared (NIR) light into heat. However, appropriate surface should be generated on AuNRs before their in vivo application because of the low colloidal stability in complicate biological environment and relatively strong toxicity compared to their pristine stabilizer cetyltrimethylammonium bromide. In the current study, polysarcosine (PS), a non-ionic hydrophilic polypeptoid whose structure is similar to polypeptides, bearing repeating units of natural α-amino acid, was used to stabilize AuNRs due to its excellent hydrophilicity and biocompatibility. Polysarcosine with optimized molecular weight was synthesized and used to modify AuNRs by traditional ligand exchange. The grafting of PS on AuNRs was evidenced by fourier transform infrared (FTIR) spectroscopy and the alternation of surface zeta potential. The polysarcosine coated AuNRs (Au@PS) showed good stabilities in wide pH range and simulated physiological buffer with the ligand competition of dithiothreitol (DTT). The Au@PS NRs had neglectable cytotoxicity and showed efficient ablation of tumor cells in vitro. Moreover, Au@PS NRs had a longer circulation time in body that resulted in a higher accumulation in solid tumors after intravenous injection, compared to AuNRs capped with polyethylene glycol (PEG). Photothermal therapy in vivo demonstrated that the tumors were completely destroyed by single-time irradiation of NIR laser after one-time injection of the polysarcosine capped AuNRs. The Au@PS NRs did not cause obvious toxicity in vivo, suggesting promising potential in cancer therapy.

STATEMENT OF SIGNIFICANCE

In current study, polysarcosine (PS), a non-ionic hydrophilic polypeptoid whose structure is similar to polypeptides, bearing repeating units of natural α-amino acid, was used to stabilize AuNRs due to its excellent hydrophilicity and biocompatibility. The polysarcosine coated AuNRs (Au@PS) showed good stabilities in wide pH range and simulated physiological buffer. The Au@PS NRs had very low cytotoxicity and showed high efficacy for the ablation of cancer cells in vitro. Moreover, Au@PS NRs had a longer circulation time in blood that led to a higher accumulation in tumors after intravenous injection, compared to AuNRs capped with polyethylene glycol (PEG). In vivo photothermal therapy showed that tumors were completely cured without reoccurrence by one-time irradiation of NIR laser after a single injection of the polysarcosine modified AuNRs.

Aqueous Self-Assembly of Y-Shaped Amphiphilic Block Copolymers into Giant Vesicles

The preparation and aqueous self-assembly of newly Y-shaped amphiphilic block polyurethane (PUG) copolymers are reported here. These amphiphilic copolymers, designed to have two hydrophilic poly(ethylene oxide) (PEO) tails and one hydrophobic alkyl tail via a two-step coupling reaction, can self-assemble into giant unilamellar vesicles (GUVs) (diameter ≥ 1000 nm) with a direct dissolution method in aqueous solution, depending on their Y-shaped structures and initial concentrations. More interesting, the copolymers can self-assemble into various distinct nano-/microstructures, such as spherical micelles, small vesicles, and GUVs, with the increase of their concentrations. The traditional preparation methods of GUVs generally need conventional amphiphilic molecules and additional complicated conditions, such as alternating electrical field, buffer solution, or organic solvent. Therefore, the self-assembly of Y-shaped PUGs with a direct dissolution method in aqueous solution demonstrated in this study supplies a new clue to fabricate GUVs based on the geometric design of amphiphilic polymers.

Amphiphilic star-shaped poly(sarcosine)-block-poly(ε-caprolactone) diblock copolymers: one-pot synthesis, characterization, and solution properties

We firstly synthesized amphiphilic three-armed star-shaped poly(sarcosine)-block-poly(ε-caprolactone) diblock copolymers (s-PSar-b-PCLs), and investigated the solution properties and biocompatibility of the copolymers.

Quantification of intracellular payload release from polymersome nanoparticles

Polymersome nanoparticles (PMs) are attractive candidates for spatio-temporal controlled delivery of therapeutic agents. Although many studies have addressed cellular uptake of solid nanoparticles, there is very little data available on intracellular release of molecules encapsulated in membranous carriers, such as polymersomes. Here, we addressed this by developing a quantitative assay based on the hydrophilic dye, fluorescein. Fluorescein was encapsulated stably in PMs of mean diameter 85 nm, with minimal leakage after sustained dialysis. No fluorescence was detectable from fluorescein PMs, indicating quenching. Following incubation of L929 cells with fluorescein PMs, there was a gradual increase in intracellular fluorescence, indicating PM disruption and cytosolic release of fluorescein. By combining absorbance measurements with flow cytometry, we quantified the real-time intracellular release of a fluorescein at a single-cell resolution. We found that 173 ± 38 polymersomes released their payload per cell, with significant heterogeneity in uptake, despite controlled synchronisation of cell cycle. This novel method for quantification of the release of compounds from nanoparticles provides fundamental information on cellular uptake of nanoparticle-encapsulated compounds. It also illustrates the stochastic nature of population distribution in homogeneous cell populations, a factor that must be taken into account in clinical use of this technology.