Facile Synthesis of H2O2-Cleavable Poly(ester-amide)s by Passerini Multicomponent Polymerization

Orally available dextran-aspirin nanomedicine modulates gut inflammation and microbiota homeostasis for primary colorectal cancer therapy

Reversing the aggravated immunosuppression hence overgrowth of colorectal cancer (CRC) caused by the gut inflammation and microbiota dysbiosis is pivotal for effective CRC therapy and metastasis inhibition. However, the low delivery efficiency and severe dose-limiting off-target toxicities caused by unsatisfied drug delivery systems remain the major obstacles in precisely modulating gut inflammation and microbiota in CRC therapy. Herein, a multifunctional oral dextran-aspirin nanomedicine (P3C-Asp) was utilized for oral treatment of primary CRC, as it could release salicylic acid (SA) while scavenging reactive oxygen species (ROS) and held great potential in modulating gut microbiota with prebiotic (dextran). Oral P3C-Asp retained in CRC tissues for over 12 h and significantly increased SA accumulation in CRC tissues over free aspirin (10.8-fold at 24 h). The enhanced SA accumulation and ROS scavenging of P3C-Asp cooperatively induced more potent inflammation relief over free aspirin, characterized as lower level of cyclooxygenase-2 and immunosuppressive cytokines. Remarkably, P3C-Asp promoted the microbiota homeostasis and notably increased the relative abundance of strengthening systemic anti-cancer immune response associated microbiota, especially lactobacillus and Akkermansia to 6.66- and 103- fold over the control group. Additionally, a demonstrable reduction in pathogens associated microbiota (among 96% to 79%) including Bacteroides could be detected. In line with our findings, inflammation relief along with enhanced abundance of lactobacillus was positively correlated with CRC inhibition. In primary CRC model, P3C-Asp achieved 2.1-fold tumor suppression rate over free aspirin, with an overall tumor suppression rate of 85%. Moreover, P3C-Asp cooperated with αPD-L1 further reduced the tumor weight of each mouse and extended the median survival of mice by 29 days over αPD-L1 alone. This study unravels the synergistic effect of gut inflammation and microbiota modulation in primary CRC treatment, and unlocks an unconventional route for immune regulation in TME with oral nanomedicine.

α-Substituted ketones as reagent for Passerini modification of carboxymethyl cellulose: Toward dually functionalized derivatives and thermo-sensitive chemical hydrogels

The present works describes the Passerini modification of carboxymethyl cellulose (CMC) by using a library of nine α-substituted ketones derivatives, differing in their hydrophobicity and reactivity, conjointly with cyclohexyl isocyanide. The Passerini ligation, achieved in aqueous and mild conditions, was shown to be successful, leading to a large panel of dually functionalized CMC derivatives, in an eco-friendly manner. A particular attention was dedicated to the influence of the experimental parameters such as the stoichiometry, the nature of a co-solvent or the temperature, which allowed to tune the extent of modification. The reactivity of the ketone was proven to be governed by its i) compatibility with water, ii) sterical accessibility, and by iii) the presence of neighboring electron-withdrawing group. The resulting Passerini CMC products modified by methacrylate moieties (CMC-MA) were used as reactive macromonomer under a "grafting through" approach. The copolymerization of CMC-MA with oligoethylene glycol methacrylate (OEGMA) and diethylene glycol methacrylate (DEGMA) upon thermal radical reaction conditions enabled to generate tightly cross-linked chemical hydrogels, with a thermo-sensitive and thermo-reversible behavior, reflected by a macroscopical shrinkage/swelling response, and confirmed by SAXS analysis. Such chemical strategy paves the way toward multifunctional polysaccharide-based networks with potential utilizations as drug delivery devices, dye removals or actuators.

Nontraditional Redox Active Aliphatic Luminescent Polymer for Ratiometric pH Sensing and Sensing-Removal-Reduction of Cu(II): Strategic Optimization of Composition

Here, redox active aliphatic luminescent polymers (ALPs) are synthesized via polymerization of N,N-dimethyl-2-propenamide (DMPA) and 2-methyl-2-propenoic acid (MPA). The structures and properties of the optimum ALP3, ALP3-aggregate and Cu(I)-ALP3, ratiometric pH sensing, redox activity, aggregation enhanced emission (AEE), Stokes shift, and oxygen-donor selective coordination-reduction of Cu(II) to Cu(I) are explored via spectroscopic, microscopic, density functional theory-reduced density gradient (DFT-RDG), fluorescence quenching, adsorption isotherm-thermodynamics, and electrochemical methods. The intense blue and green fluorescence of ALP3 emerges at pH = 7.0 and 9.0, respectively, due to alteration of fluorophores from -C(═O)N(CH₃ )₂ / -C(═O)OH to -C(O^- )═N⁺ (CH₃ )₂ / -C(═O)O^- , inferred from binding energies at 401.32 eV (-C(O^- )═N⁺ (CH₃ )₂ ) and 533.08 eV (-C(═O)O^- ), significant red shifting in absorption and emission spectra, and peak at 2154 cm^-1 . The n-π* communications in ALP3-aggregate, hydrogen bondings within 2.34-2.93 Å (intramolecular) in ALP3 and within 1.66-2.89 Å (intermolecular) in ALP3-aggregate, respectively, contribute significantly in fluorescence, confirmed from NMR titration, ratiometric pH sensing, AEE, excitation dependent emission, and Stokes shift and DFT-RDG analyses. For ALP3, Stokes shift, excellent limit of detection, adsorption capacity, and redox potentials are 13561 cm^-1 /1.68 eV, 0.137 ppb, 122.93 mg g^-1 , and 0.33/-1.04 V at pH 7.0, respectively.

Recent Studies on Hydrogels Based on H2O2-Responsive Moieties: Mechanism, Preparation and Application

H₂O₂ is essential for cellular processes and plays a vital role in the regulation of cell signaling pathways, which can be viewed as a warning signal for many kinds of disease including cancer, cardiovascular disease, reproductive abnormalities, diabetes, and renal failure. A H₂O₂-responsive hydrogel (H₂O₂-Gel) is a promising candidate for biomedical applications because of its good biocompatibility, similarity to soft biological tissues, ease of preparation, and its ability to respond to H₂O₂. In this study, the H₂O₂-responsive moieties used to fabricate H₂O₂-Gels were reviewed, including thioethers, disulfide bonds, selenides, diselenium bonds, diketones, boronic, and others. Next, the preparation method of H₂O₂-Gel was divided into two major categories according to their reaction mechanisms: either self-crosslinking or mechanisms entailing the addition of difunctional crosslinkers. Last, the applications of H₂O₂-Gels were emphasized, which have been viewed as desirable candidates in the fields of drug delivery, the detection of H₂O₂, glucose-responsive systems, ROS scavengers, tissue engineering, and cell-encapsulation.

Recent Advances of Poly(ester amide)s-Based Biomaterials

Biodegradable and biocompatible biomaterials have offered much more opportunities from an engineering standpoint for treating diseases and maintaining health. Poly(ester amide)s (PEAs), as an outstanding family among such biomaterials, have risen overwhelmingly in the past decades. These synthetic polymers have easily and widely available raw materials and a diversity of synthetic approaches, which have attracted considerable attention. More importantly, combining the superiorities of polyamides and polyesters, PEAs have emerged with better functions. They could have improved biodegradability, biocompatibility, and cell-material interactions. The PEAs derived from α-amino acids even allow the introduction of pendant sites for further modification or functionalization. Meanwhile, it is gradually recognized that the chemical structures are closely related to the physiochemical and biological properties of PEAs so that their properties can be precisely controlled. PEAs therefore become significant materials in the biomedical fields. This review will attempt to summarize the recent progress in the development of PEAs with respect to the preparation materials and methods, structure-property relationships along with their latest biomedical accomplishments, especially for drug delivery and tissue engineering.

Copper(II)-β-cyclodextrin immobilized on graphitic carbon nitride nanosheets as a highly effective catalyst for tandem oxidative amidation of benzylic alcohols

In this study, an efficient catalyst based on graphitic carbon nitride nanosheets (CN) and copper(II) supported β-cyclodextrin (β-CD/Cu(II)) was synthesized and used for tandem oxidative amidation of benzylic alcohols. In this regard, CN was functionalized by β-CD/Cu(II) via 1,3-dibromopropane linker (CN-Pr-β-CD/Cu(II)). The prepared catalyst was characterized using FT-IR, XRD, FE-SEM, EDS, TGA, ICP-OES, BET, and TEM analyses. CN-Pr-β-CD/Cu(II) was subsequently applied in a direct oxidative amidation reaction and it was observed that different benzyl alcohols were converted to desire amides with good to excellent efficiency. This reaction was performed in the presence of amine hydrochloride salts, tert-butyl hydroperoxide (TBHP), and Ca₂CO₃ in acetonitrile (CH₃CN) under nitrogen atmosphere. CN-Pr-β-CD/Cu(II) can be recycled and reused five times without significant reduction in reaction efficiency.

Synthesis of multifunctional poly(carbamoyl ester)s containing dual-cleavable linkages and an AIE luminogen via Passerini-type multicomponent polymerization

We conducted Passerini multicomponent polymerizations with aldehydes, carboxylic acids, and isocyanide and afforded novel functional poly(carbamoyl ester)s with dual-cleavable linkages and an aggregation-induced emission luminogen.

Clusterization-Triggered Color-Tunable Room-Temperature Phosphorescence from 1,4-Dihydropyridine-Based Polymers

A series of poly(1,4-dihydropyridine)s (PDHPs) were successfully synthesized via one-pot metal-free multicomponent polymerization of diacetylenic esters, benzaldehyde, and aniline derivatives. These PDHPs without traditional luminescent units were endowed with tunable triplet energy levels by through-space conjugation from the formation of different cluster sizes. The large and compact clusters can effectively extend the phosphorescence wavelength. The triplet excitons can be stabilized by using benzophenone as a rigid matrix to achieve room-temperature phosphorescence. The nonconjugated polymeric clusters can show a phosphorescence emission up to 645 nm. A combination of static and dynamic laser light scattering was conducted for insight into the structural information on formed clusters in the host matrix melt. Moreover, both the fluorescence and phosphorescence emission can be easily tuned by the variation of the excitation wavelength, the concentration, and the molecular weight of the guest polymers. This work provides a unique insight for designing polymeric host-guest systems and a new strategy for the development of long wavelength phosphorescence materials.

Room-Temperature Metal-Free Multicomponent Polymerizations of Elemental Selenium toward Stable Alicyclic Poly(oxaselenolane)s with High Refractive Index

Selenium-containing polymers are a group of fascinating functional polymers with unique structures, properties, and applications, which have been developed recently but only with limited examples. The challenges of developing selenium-containing polymers with structural and functional diversity include the lack of economic and safe monomers, lack of efficient and convenient synthetic approaches, and poor stability of selenium-involving covalent bonds. In this work, room-temperature metal-free multicomponent polymerizations (MCPs) of elemental selenium, diisocyanides, and dipropargyl alcohols were developed, and polymers with a selenium-containing aliphatic heterocycle, 1,3-oxaselenolane, were synthesized through these MCPs directly from elemental selenium. The alicyclic poly(oxaselenolane)s enjoyed high yields (up to 93%), high molecular weights (up to 15 600 g/mol), high thermal and chemical stability, good solubility and processability. With the structural design of the poly(oxaselenolane)s and their high selenium contents of up to 33.7 wt %, the refractive indices of their spin-coated thin films could reach 1.8026 at 633 nm and maintain 1.7770 at 1700 nm. It is anticipated that these efficient, convenient, mild, and economic multicomponent polymerizations of elemental selenium can promote the selenium-related polymer chemistry and accelerate the exploration of diversified selenium-containing functional polymer materials.

An oxidation responsive nano-radiosensitizer increases radiotherapy efficacy by remolding tumor vasculature

As an excellent candidate material for nano-sensitizers, gold nanostructures have shown great potential in radiotherapy. Nevertheless, severe hypoxia and low accumulation of nanomedicine caused by poor perfusion at the tumor site have significantly reduced radiotherapy efficacy. Vascular normalization has gained attention owing to its ability to relieve hypoxia and increase perfusion. The synergistic therapy of tumor vascular normalization and radiotherapy has become a new option to increase anti-cancer efficacy. However, the commonly used strategy of suppressing a single growth factor to induce vascular normalization is limited by tumor compensatory effects. In this work, we developed a strategy to inhibit oxidative stress in tumors by generating chelating agents in response to hydrogen peroxide, thereby inhibiting multi-angiogenic factors simultaneously to normalize blood vessels. Concretely, sodium alginate (SA) reacted with 8-quinoline boric acid (QBA) to form SA-QBA. Then gold nanoparticles (Au NPs) were modified with SA-QBA to obtain Au@SA-QBA. The system was simple in structure and could generate 8HQ in response to H₂O₂in vitro to inhibit oxidative stress and reduce the expression of VEGF, bFGF, and Ang-2. In vivo, the perfusion unit (PU) increased by 78% after Au@SA-QBA treatment, and the coverage of pericytes increased by 32%, which in turn induced vascular normalization. In addition, blood routine and blood biochemical tests confirmed its good biocompatibility and 8HQ was not detected in the supernatant after homogenization of major organs. More importantly, after the synergistic treatment of vascular normalization and radiotherapy (4 Gy), the tumor growth inhibition rate was increased by 38.6% compared to the Au@SA-treated group with negligible side effects to normal tissues.

Reactive Oxygen Species Responsive Polymers for Drug Delivery Systems

Reactive oxygen species (ROS) play an essential role in regulating various physiological functions of living organisms; however, as the concentration of ROS increases in the area of a lesion, this may undermine cellular homeostasis, leading to a series of diseases. Using cell-product species as triggers for targeted regulation of polymer structures and activity represents a promising approach for the treatment. ROS-responsive polymer carriers allow the targeted delivery of drugs, reduce toxicity and side effects on normal cells, and control the release of drugs, which are all advantages compared with traditional small-molecule chemotherapy agents. These formulations have attracted great interest due to their potential applications in biomedicine. In this review, recent progresses on ROS responsive polymer carriers are summarized, with a focus on the chemical mechanism of ROS-responsive polymers and the design of molecular structures for targeted drug delivery and controlled drug release. Meanwhile, we discuss the challenges and future prospects of its applications.

Stimuli-Responsive Multifunctional Phenylboronic Acid Polymers Via Multicomponent Reactions: From Synthesis to Application

Stimuli-responsive polymers undergo changes under different environmental conditions. Among them, phenylboronic acid (PBA) containing polymers (PBA-polymers) are unique, because they can selectively react with diols to generate borates that are sensitive to pH, sugars, and H₂ O₂ , and can be effectively used to synthesize smart drug carriers and self-healing hydrogels. Recently, multifunctional PBA-polymers (MF-PBA-polymers) have been developed using multicomponent reactions (MCRs) to introduce PBA groups into polymer structures. These MF-PBA-polymers have features similar to those of traditional PBA-polymers; moreover, they exhibit additional properties, such as fluorescence, antimicrobial activity, and antioxidant capability, when different MCRs are used. In this mini review, the preparation of these MF-PBA-polymers are summarized and the new properties/functions that have been introduced into these polymers using different MCRs are discussed. The uses of these MF-PBA-polymers as fluorescent cell anticoagulants, drug carriers, and gelators of functional self-healing hydrogels have been discussed. Additionally, the challenges encountered during their preparation are discussed and also the future developments in this field are touched upon.

Cu-Catalyzed four-component polymerization of alkynes, sulfonyl azides, nucleophiles and electrophiles

A four-component polymerization method was reported using diynes, sulfonyl azides, diols, and a variety of electrophiles. Such a strategy facilitated the facile preparation of a series of α-functionalized poly(N-sulfonylimidates)s.

Chitosan Modified Cationic Polyacrylamide Initiated by UV-H2O2 for Sludge Flocculation and New Insight on the Floc Characteristics Study

In the present study, a novel graft modified flocculant CTS-g-PAMD was synthesized and applied to conduct sludge conditioning and dewatering. CTS-g-PAMD was copolymerized with AM, DMC and chitosan (CTS) under UV-H2O2 initiation. In addition, the effects of single factor experiments on the molecular weight (MW) CTS grafting efficiency (GE) of CTS-g-PAMD were determined and the optimal copolymerization conditions were achieved. The GE of CTS-g-PAMD reached 91.1% and the MW was 4.82 × 106 Da. As revealed from the characterized results of Fourier-transform infrared spectra (FT-IR), 1H/ NMR, X-ray diffraction (XRD), scanning electron microscopic (SEM) and X-ray photoelectron spectroscopy (XPS), the successful synthesis of CTS-g-PAMD was confirmed, which is considered to be conducive to explaining sludge dewatering performance. Under the optimal conditions (pH = 7.0, flocculant dosage = 35 mg/L), the best flocculating performance (FCMC: 73.7%; SRF: 4.7 × 1012 m·kg-1, turbidity: 9.4 NTU) and large and dense sludge flocs (floc size d50 = 379.142 µm, floc fractal dimension Df = 1.58) were formed. The DMC and CTS chain segments exhibiting cationic properties significantly improved the positive charge density and enhanced the electrical patching effect of CTS-g-PAMD. The long molecular chain of CTS-g-PAMD exhibited superior extensibility, which enhanced bridging effect on adsorption. Moreover, the sludge floc after undergoing CTS-g-PAMD conditioning exhibited robust shear resistance and regeneration ability. After the sludge floc was crushed and broken, a large and dense sludge floc was formed, helping significantly reduce the sludge specific resistance (SRF), turbidity and cake moisture content (FCMC) and enhance the sludge dewatering effect. The novel CTS-g-PAMD flocculant shows promising practical applications and high market value.

Design Strategies and Applications of ROS-Responsive Phenylborate Ester-Based Nanomedicine

Reactive oxygen species (ROS)-responsive nanomedicine has been extensively developed to improve the therapeutic effects while reducing the systemic toxicity. ROS, as important biological metabolites and signaling molecules, are known to overexpress in most of tumors and inflammations. Among various ROS-sensitive moieties, phenylborate ester (PBAE) with easy modifiable structure and excellent biocompatibility, represents one of the most ROS-sensitive structures. To harness it as a switch, the past several years had witnessed a booming of ROS-sensitive PBAE-based nanomedicine for various medical purposes. Much of the efforts were devoted to exploiting the potential in the management of antitumor and anti-inflammation. This review first summarizes the design strategies of PBAE in the construction of nanomedicine, with PBAE acting as not only the ROS-responsive unit, but also the roles of hydrophobic backbone or bridging segment in the macromolecular structures. The ROS-responsive mechanisms are then briefly discussed. Afterward, we focus on the introduction of the state-of-the-art research on ROS-responsive PBAE-based nanomedicine for antitumor and anti-inflammation applications. The conclusion and future perspectives of ROS-responsive nanomedicine are also provided.

The Hantzsch Reaction in Polymer Chemistry: From Synthetic Methods to Applications

The Hantzcsh reaction is a robust four-component reaction for the efficient generation of 1,4-dihydropyridine (1,4-DHP) derivatives. Recently, this reaction has been introduced into polymer chemistry in order to develop polymers having 1,4-DHP structures in the main and/or side chains. The 1,4-DHP groups confer new properties/functions to the polymers. This mini-review summarizes the recent studies on the development of new functional polymers by using the Hantzsch reaction. Several synthetic approaches, including polycondensation, post-polymerization modification (PPM), monomer to polymer strategy, and one-pot strategy are introduced; different applications (protein conjugation, formaldehyde detection, drug carrier, and anti-bacterial adhesion) of the resulting polymers are emphasized. Meanwhile, the future development of the Hantzsch reaction in exploring new functional polymers is also discussed.

A new soft-matter material with old chemistry: Passerini multicomponent polymerization-induced assembly of AIE-active double-helical polymers with rapid visible-light degradability

Mimicking the superstructures and functions of natural chiral materials is beneficial to understand specific biological activities in living organisms and broaden applications in the fields of chemistry and materials sciences. However, it is still a great challenge to construct water-soluble, double-helical polymers with multiple responsiveness. Herein, we report for the first time a straightforward, general strategy to address this issue by taking advantage of Passerini multicomponent polymerization-induced assembly (PMPIA). The polymerization-induced generation of supramolecular interactions in chiral α-acyloxy amides drives the assembly of polymers and improves their stability in various solvents. This double-helical polymer is sensitive to metal ions, temperature, pH, and solvents, making both the superstructure and the AIE effect reversibly adjustable. Meanwhile, the hydrogen-bonding-assisted cyclization of photolabile α-acyloxy amides accelerates the degradation of helical polymers under visible-light irradiation. It is anticipated that this novel PMPIA strategy opens new horizons to inspire the design of advanced chiral/helical polymers with multiple functions.

Polymersome-Based Modular Nanoreactors with Size-Selective Transmembrane Permeability

Polymersome nanoreactors encapsulating the enzymes or particulate catalysts attract interest because of their potential use as modular reactors to synthesize complex compounds via a cascade of chemical reactions in a single batch. To achieve these goals, a key requirement is the tunable permeability of the polymersome membrane, which allows the size-selective transportation of reagents and products while protecting the encapsulated catalysts during the chemical reaction. We report here a stimuli-responsive route for controlling the permeability of the polymersomes of the binary blend of poly(ethylene glycol)-b-polystyrene (PEG-b-PS) and poly(ethylene glycol)-b-poly(acrylbenzylborate) (PEG-b-PABB). The presence of H₂O₂ (1 mM) in the medium (0.1 M PBS, pH 7.4) triggers the oxidation of benzyl borate pendants of PABB to form poly(acrylic acid) (PAA). This transformation results in the perforation of the compartmentalizing membrane of polymersomes by the dissolution of PEG-b-PAA domains embedded in the inert PEG-b-PS matrix. By controlling the composition of the stimuli-responsive block copolymer, the polymersomes of the binary blend exhibit size-selective permeability without losing the structural integrity. Release of fluorescent guests with different sizes (fluorescein, PEG2k-Cm, PEG5k-Rho) can be controlled by tuning the composition (PEG-b-PS/PEG-b-PABB = 100/0-80/20) of blended polymersomes. Selective permeability of the membrane provides protection of the encapsulated enzymes from external proteases present in the medium, resulting in the one-pot synthesis of small molecules via cascades of chemical reactions. The nanoparticular catalysts are also encapsulated within the permeable polymersomes, serving as modular reactors for the conversion of organic compounds via a cascade of reactions.

Multicomponent Radziszewski Emulsion Polymerization toward Macroporous Poly(ionic liquid) Catalysts

Interconnected macroporous imidazolium-based monoliths are produced via the modified Radziszewski multicomponent reaction (MCR) applied to triamines under high internal phase emulsion (HIPE) conditions. This straightforward one-pot synthesis combines the efficiency and versatility of MCRs with the ease of implementation of the emulsion templating polymerization process. The characterization of the chemical structure and morphology of the resulting materials confirms the formation of the expected macroporous poly(ionic liquid)s (PILs) networks. The promising catalytic activity and recyclability of these porous PIL monoliths are illustrated for the transesterification reaction and the decarboxylation of caffeic acid. In these cases, almost complete conversion is reached while benefiting from the advantages associated with a heterogeneous catalyst.

Copolymers of ε-caprolactone and ε-caprolactam via polyesterification: towards sequence-controlled poly(ester amide)s

Alternating copolymer of ε-caprolactone and ε-caprolactam is synthesized through polyesterification. This efficient and straightforward strategy holds promising future for the synthesis of sequence-controlled poly(ester amide)s.

Self-immolative polymers in biomedicine

Biomedical use cases for self-immolative polymers.

Facile Synthesis of a H2O2-Responsive Alternating Copolymer Bearing Thioether Side Groups for Drug Delivery and Controlled Release

A novel amphiphilic alternating copolymer with thioether side groups (P(MSPA-a-EG)) was synthesized through an amine-epoxy click reaction of 3-(methylthio)propylamine (MSPA) and ethylene glycol diglycidyl ether. P(MSPA-a-EG) was characterized in detail by nuclear magnetic resonance (NMR), gel permeation chromatography, Fourier transformed infrared, differential scanning calorimeter, and thermogravimetric analysis to confirm the successful synthesis. Due to its amphiphilic structure, P(MSPA-a-EG) could self-assemble into spherical micelles with an average diameter of about 151 nm. As triggered by H2O2, theses micelles could disassemble because hydrophobic thioether groups are transformed to hydrophilic sulfoxide groups in MSPA units. The oxidant disassemble process of micelles was systemically studied by dynamic light scattering, transmission electron microscopy, and 1H NMR measurements. The MTT assay against NIH/3T3 cells indicated that P(MSPA-a-EG) micelles exhibited good biocompatibility. Furthermore, they could be used as smart drug carriers to encapsulate hydrophobic anticancer drug doxorubicin (DOX) with 4.90% drug loading content and 9.81% drug loading efficiency. In vitro evaluation results indicated that the loaded DOX could be released rapidly, triggered by H2O2. Therefore, such a novel alternating copolymer was expected to be promising candidates for controlled drug delivery and release.

Alternating Sequence Control for Poly(ester amide)s by Organocatalyzed Ring-Opening Polymerization

Sequence-controlled polymerization is the forefront of polymer chemistry. Herein, the feasibility of sequence regulation by using organocatalyzed ring-opening polymerization (ROP) is demonstrated. In particular, ring expansion strategy is employed to synthesize pre-organized monomers 1 and 2. ROP is conducted by using 1,5,7-triazabicyclo[4.4.0]dec-5-ene and benzyl alcohol as the catalyst and initiator, respectively. Poly(ester amide)s (PEAs) P1-P3 comprising glycolic acid, lactic acid, and 7-aminoheptanoic acid units are obtained in high molecular weights and good yields. NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry results verify the microstructural integrity of P1 and P2. Differential scanning calorimetry results show that PEA without methyl branches is crystalline. Moreover, thermal stability, surface wettability, and degradation profiles of P1-P3 are also investigated.

Recent Advances on Reactive Oxygen Species-Responsive Delivery and Diagnosis System

Reactive oxygen species (ROS) play crucial roles in biological metabolism and intercellular signaling. However, ROS level is dramatically elevated due to abnormal metabolism during multiple pathologies, including neurodegenerative diseases, diabetes, cancer, and premature aging. By taking advantage of the discrepancy of ROS levels between normal and diseased tissues, a variety of ROS-sensitive moieties or linkers have been developed to design ROS-responsive systems for the site-specific delivery of drugs and genes. In this review, we summarized the ROS-responsive chemical structures, mechanisms, and delivery systems, focusing on their current advances for precise drug/gene delivery. In particular, ROS-responsive nanocarriers, prodrugs, and supramolecular hydrogels are summarized in terms of their application for drug/gene delivery, and common strategies to elevate or diminish cellular ROS concentrations, as well as the recent development of ROS-related imaging probes were also discussed.

Synthesis of Stimuli-Responsive Heterofunctional Dendrimer by Passerini Multicomponent Reaction

We report the synthesis of a structurally diverse amphiphilic dendrimer with oxidation and ultraviolet light-sensitive groups incorporated in the dendrimer interior. Convergent synthesis is utilized by reacting branched repeating units with a nonbranched functional molecule by two synthetic strategies, Passerini multicomponent reaction and azide-alkyne cycloaddition reaction. The periphery of dendrimer was functionalized by methoxy poly(ethylene glycol) to obtain a dendrimer with a hydrophobic core and hydrophilic peripheral chains. The G2-PEG dendrimer characterized by NMR, GPC, and MALDI-TOF MS for structural integrity and oxidation- and photo-triggered degradations of the G2-PEG dendrimer was investigated. The self-assembled morphology of the dendrimer in the presence of organic dye was also investigated by TEM and DLS analyses, together with dissipative particle dynamics simulation. The encapsulation of dye molecules in self-assembled nanospheres of the dendrimer and their responsive releases, triggered by the efficient disassembly of a dendrimer, have been demonstrated.

Ugi Three-Component Polymerization Toward Poly(α-amino amide)s

Due to their great modularity, ease of implementation, and atom economy, multicomponent reactions (MCRs) are becoming increasingly popular macromolecular engineering tools. In this context, MCRs suitable in polymer synthesis are eagerly searched for. This work demonstrates the potential of the Ugi-three component reaction (Ugi-3CR) for the design of polymers and, in particular, of poly(α-amino amide)s. A series of polymers containing amino and amido groups within their backbone were obtained through a one-pot process by reacting aliphatic or aromatic diamines, diisocyanides, and aldehydes. The impact of temperature, concentration, catalyst loading, and substrates on polymerization efficiency is discussed. A preliminary study on the thermal properties and the solution behavior of these poly(α-amino amide)s was carried out. An aliphatic-rich derivative notably showed some pH-responsiveness in water via protonation-deprotonation of its amino groups.

The polymerization kinetics, oxidation-responsiveness, and in vitro anticancer efficacy of poly(ester-thioether)s

The oxidation-responsiveness and biomedical properties of poly(ester-thioether)s could be tuned by varying the polymer backbones.

A PEGylated alternating copolymer with oxidation-sensitive phenylboronic ester pendants for anticancer drug delivery

An oxidation sensitive PEGylated alternating copolymer was designed for doxorubicin delivery with improved anticancer efficacy and low toxicity in vivo.

Facile synthesis of ROS-responsive biodegradable main chain poly(carbonate-thioether) copolymers

The amphiphilic main chain poly(carbonate-thioether) copolymers were synthesized based on a novel macrocyclic sulfur-substituted carbonate monomer. The assembled nanostructures have rich ROS responsiveness.

Supersensitive Oxidation-Responsive Biodegradable PEG Hydrogels for Glucose-Triggered Insulin Delivery

Reactive oxygen species (ROS)-responsive polymers and hydrogels represent an emerging family of intelligent materials owing to the key functions of ROS in physiological processes or pathological diseases. Nonetheless, the weaknesses such as low sensitivity, slow response, instability, and low mechanical strength are associated with the limited ROS-responsive polymeric or supramolecular hydrogels. In this study, a novel type of oxidation-responsive degradable hydrogels was fabricated by the redox-initiated radical polymerization of a 4-arm-poly(ethylene glycol) (PEG) acrylic macromonomer that possesses a H₂O₂-cleavable phenylboronic acid linker in each of the arms. The macroscopic hydrogels have the features of good cytocompatibility, moderate mechanical strength, and fast response toward H₂O₂ of low concentration, owing to the covalently cross-linked hydrophilic PEG network and high sensitivity of the linker. They could encapsulate biomacromolecules, such as insulin and glucose oxidase (GOx), with high efficacy, affording a new glucose-responsive insulin-delivery platform on the basis of enzymatic transformation of a biochemical signal (glucose) into an oxidative stimulus (H₂O₂). Interestingly, in vitro results demonstrate that the same GOx-loaded hydrogel exhibited disparate degradation modes under different triggering molecules, that is, bulk degradation by H₂O₂ and surface erosion by glucose. Moreover, compared to the macroscopic hydrogel, the nanogel with a diameter of ∼160 nm prepared by inverse emulsion polymerization showed a much higher degradation rate even under triggering of 20 μM H₂O₂, a pathologically available concentration in vivo.

Versatile Routes to Functional RAFT Chain Transfer Agents through the Passerini Multicomponent Reaction

The widespread adoption of RAFT polymerization stems partly from the ease and utility of installing a functional chain transfer agent onto the ends of the generated polymer chains. In parallel, the Passerini multicomponent reaction offers great versatility in converting a wide range of easily accessible building blocks to functional materials. In this work, we have combined the two approaches such that a single, commonly available, RAFT agent is used in Passerini reactions to generate a variety of multifunctional RAFT chain transfer agents containing ester linkages. Reactions to generate the multifunctional RAFT agents took place under mild conditions and in good yields. The resulting Passerini-RAFT agents were able to exert control over radical polymerization to generate materials of well-defined molecular weights and dispersity. Furthermore, the presence in these polymer cores of ester and amide functionality through the Passerini chemistries, provided regions in the materials which are inherently biodegradable, facilitating any subsequent biomedical applications. The work overall thus demonstrates a versatile and facile synthetic route to multi functional RAFT chain transfer agents and biodegradable polymers.

Synthesis of a phenylboronic ester-linked PEG-lipid conjugate for ROS-responsive drug delivery

A kind of phenylboronic ester-linked PEG-lipid conjugate was designed and synthesized for ROS-responsive drug delivery.