Fabrication of Cyclic Brush Copolymers with Heterogeneous Amphiphilic Polymer Brushes for Controlled Drug Release

Various Topological Poly(tert-butyl acrylate)s and Their Impacts on Thermal and Solution Properties

This study reports the synthesis of acrylate-based polymers with diverse topologies, including cyclic and 8-shaped structures, using a combination of atom transfer radical polymerization (ATRP) and click coupling reactions. The linear and tetra-arm poly(tert-butyl acrylate) (PtBA) polymers with similar molar masses are synthesized via the activators regenerated by electron transfer atom transfer radical polymerization. These polymers are further transformed into cyclic and 8-shaped topologies, respectively, through a click reaction. All topologies possessed similar molar mass are confirmed using 1H NMR, FT-IR, SEC, and MALDI-TOF mass spectrometry. The influence of macromolecular topology on intrinsic viscosity and glass transition temperature (Tg) is systematically investigated. The findings show that within the PtBA topology series, Tg increases with structural compactness, with cyclic polymers exhibiting higher Tg than their precursors. Additionally, intrinsic viscosity decreases as compactness increases across the various topological macromolecules. These observations highlight the potential of topology as a tool for fine-tuning polymer properties, facilitating the development of advanced materials with specific behaviors in solution and bulk properties.

The Preparation of Cyclic Binary Block Polymer Using Bimolecular Homodifunctional Coupling Reaction and Characterization of Its Performance as a Drug Carrier

There is relatively little research on cyclic amphiphilic block polymers, having both hydrophilic and hydrophobic segments placed in the ring and thus resulting in a higher degree of topological restriction, as drug vehicles. Cyclic amphiphilic binary block polymer is synthesized by the click coupling reaction of bimolecular homodifunctional precursors. The results indicate that cyclization between linear polymer precursors is successful if the trace linear by-products generated are ignored, which also suggests that the small molecule bifunctional terminating agent applied in traditional bimolecular homodifunctional ring-closure process can be extended to large molecule. Moreover, the study on the self-assembly behavior of polymers shows that, compared with linear counterparts, the stability and drug loading capacity of micelles based on the resultant cyclic polymer are not significantly improved due to the influence of topological structure and linear impurities. Nevertheless, drug loaded micelles formed by the obtained cyclic polymers still exhibit superior cellular uptake ability. It can be seen that topological effects do play an irreplaceable role in the application performance of polymers. Therefore, the construction and synthesis of cyclic and its derivative polymers with moderate topological confinement and high purity may be a key direction for future exploration of polymer drug delivery carriers.

Self-assembly of rigid amphiphilic graft cyclic-brush copolymers to nanochannels using dissipative particle dynamics simulation

The synthesis of specific artificial nanochannels remains a formidable challenge in the field of nanomaterials and synthetic chemistry. In particular, the preparation of artificial nanochannels using amphiphilic graft cyclic-brush copolymers (AGCCs) as monomers has garnered substantial attention. Nevertheless, because of the constrained time and length scales inherent in traditional molecular dynamics simulations, a comprehensive theoretical understanding of the morphological regulation mechanism governing the self-assembly of AGCCs into nanochannels remains elusive. In this study, we employed the dissipative particle dynamics (DPD) method to explore the self-assembly mechanism considering factors such as the DPD interaction parameters, concentrations, and sizes of AGCCs. By calculating the phase diagrams, we predicted the emergence of four distinct nanochannel types: short independent, long independent, parallel, and disordered channels. Importantly, the formation of these nanochannels is highly contingent on specific environmental conditions. Furthermore, we extensively discussed self-assembly processes that lead to different types of nanochannels. The self-assembly of AGCCs is revealed as a multistep process primarily influenced by the interaction parameters. However, while the monomer size and concentration do not introduce novel self-assembly morphologies, they do influence the final aggregation state. The elucidation of the self-assembly mechanism presented in this study deepens our understanding of AGCC nanochannel formation. Consequently, this is a valuable guide for the preparation of copolymer materials with specific functionalities, offering insights into targeted copolymer material design.

A cyclic brush zwitterionic polymer based pH-responsive nanocarrier-mediated dual drug delivery system with lubrication maintenance for osteoarthritis treatment

Enhanced joint synergistic lubrication combined with anti-inflammatory therapy is an effective strategy to delay the progression of early osteoarthritis (OA) but has been rarely reported. The hydration lubrication of zwitterions and inherent super-lubrication properties of the cyclic brush, as well as the enhancement of the steric stability of the cyclic topology, can effectively improve the drug loading and utilization; herein we report a pH-responsive cyclic brush zwitterionic polymer (CB) with SBMA and DMAEMA as brushes and a cyclic polymer (c-P(HEMA)) as the core template, possessing a low coefficient of friction (0.017). After loading with hydrophobic curcumin and hydrophilic loxoprofen sodium it demonstrates high drug-loading efficiency. In vitro and in vivo experiments confirmed the triple function of the CB on superlubrication, sequence controlled release and anti-inflammatory effects demonstrated by Micro CT, histological analysis and qRT-PCR. Overall, the CB is a promising long-acting lubricating therapeutic agent, with potential for OA treatment or other diseases.

Bottlebrush Polymers Based on RAFT and the "C1" Polymerization Method: Controlled Synthesis and Application in Anticancer Drug Delivery

In this work, we reported a strategy to synthesize well-defined bottlebrush polymers. Diazoacetate macromonomers of polystyrene (1-PS_n) with controlled molecular weights were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. The diazo can tolerate the RAFT polymerization conditions and remained on the chain end of the yielded PS macromonomer. The terminal diazo groups of the macromonomer were polymerized by the allyl PdCl/L catalyst to afford well-defined bottlebrush polymers ((1-PS_n)_ms) carrying a side chain on each backbone atom. Meanwhile, an amphiphilic bottlebrush polymer containing brush-shaped PS and polyethylene glycol (PEG) was synthesized by polymerization of the diazoacetate macromonomer of PEG (2-PEG) using Pd(II)-terminated (1-PS_n)_m as the macroinitiator. The yielded amphiphilic (1-PS₃₀)₅₀-b-(2-PEG)₁₀₀ could self assemble into a well-defined core-shell micelle in aqueous solutions. The hydrodynamic diameter of the micelle was ca. 146 nm and had good biocompatibility. These results indicate the micelles have great potential in drug delivery.

Forces between mica and end-grafted statistical copolymers of sulfobetaine and oligoethylene glycol in aqueous electrolyte solutions

This study quantified the interfacial forces associated with end-grafted, statistical (AB) co-polymers of sulfobetaine methacrylate (SBMA) and oligoethylene glycol methacrylate (OEGMA) (poly(SBMA-co-OEGMA)). Surface force apparatus measurements compared forces between mica and end-grafted copolymers containing 0, 40, or 80 mol% SBMA. Studies compared forces measured at low grafting density (weakly overlapping chains) and at high density (brushes). At high density, the range of repulsive forces did not change significantly with increasing SBMA content. By contrast, at low density, both the range and the amplitude of the repulsion increased with the percentage of SBMA in the chains. The ionic strength dependence of the film thickness and repulsive forces increased similarly with SBMA content, reflecting the increasing influence of charged monomers and their interactions with ions in solution. The forces could be described by models of simple polymers in good solvent. However, the forces and fitted model parameters change continuously with the SBMA content. The latter behavior suggests that ethyene glycol and sulfobetaine behave as non-interacting, miscible monomers that contribute independently to the interfacial forces. The results suggest that molecular scale properties of statistical poly (SBMA-co-OEGMA) films can be readily tuned by simple variation of the monomer ratios.

Differential Drug Release Kinetics from Paclitaxel-Loaded Polydioxanone Membranes and Capsules

BACKGROUND

Drug laden implantable systems can provide drug release over several hours to years, which eventually aid in the therapy of both acute and chronic diseases. The present study focuses on a fundamental evaluation of the influence of implant properties such as morphology, architecture, porosity, surface area, and wettability in regulating the drug release kinetics from drug-loaded polymeric matrices.

METHODS

For this, Polydioxanone (PDS) was selected as the polymer and Paclitaxel (Ptx) as the model drug. Two different forms of the matrix implants, viz., reservoir type capsules developed by dip coating and matrix type membranes fabricated by phase inversion and electrospinning, were utilized for the study. Drug release from all the four different matrices prepared by simple techniques was evaluated in vitro in PBS and ex vivo in peritoneal wash fluid for ~4 weeks. The drug release profiles were thereafter correlated with the physicochemical parameters of the polymeric implants.

RESULTS

Reservoir-type capsules followed a slow and steady zero-order kinetics, while matrix-type electrospun and phase inversion membranes displayed typical biphasic kinetics.

CONCLUSION

It was inferred that the slow degradation rate of PDS polymer as well as the implant properties like porosity and wettability play an important role in controlling the drug release rates.

Facile synthesis of monocyclic, dumbbell-shaped and jellyfish-like copolymers using a telechelic multisite hexablock copolymer

A heterofunctional hexablock copolymer comprising alternating reactive and non-reactive blocks is designed to generate cyclic, dumbbell-shaped and jellyfish-like copolymers.

Multi-tunable aggregation behaviors of thermo/pH-responsive toothbrush-like and jellyfish-like copolymers

Rational design of comb-like and linear conjugates comprising PNIPAM and PDMAEMA segments allows the construction of a multi-tunable hierarchical self-assembly platform and insight into the topology effect.

Amphiphilic copolymers in biomedical applications: Synthesis routes and property control

The request of new materials, matching strict requirements to be applied in precision and patient-specific medicine, is pushing for the synthesis of more and more complex block copolymers. Amphiphilic block copolymers are emerging in the biomedical field due to their great potential in terms of stimuli responsiveness, drug loading capabilities and reversible thermal gelation. Amphiphilicity guarantees self-assembly and thermoreversibility, while grafting polymers offers the possibility of combining blocks with various properties in one single material. These features make amphiphilic block copolymers excellent candidates for fine tuning drug delivery, gene therapy and for designing injectable hydrogels for tissue engineering. This manuscript revises the main techniques developed in the last decade for the synthesis of amphiphilic block copolymers for biomedical application. Strategies for fine tuning the properties of these novel materials during synthesis are discussed. A deep knowledge of the synthesis techniques and their effect on the performance and the biocompatibility of these polymers is the first step to move them from the lab to the bench. Current results predict a bright future for these materials in paving the way towards a smarter, less invasive, while more effective, medicine.

Tumor acidic microenvironment-induced drug release of RGD peptide nanoparticles for cellular uptake and cancer therapy

Spatial accuracy is crucial in drug delivery, especially to increase the efficacy and reduce the side effects of antitumor drugs. In this study, we developed a simple and broadly applicable strategy in which a target peptide ligand was introduced to construct a pH-responsive drug-loading system to achieve targeted delivery and drug release in lesions. In addition to reaching the tumor tissue through passive targeting modalities such as the enhanced permeability and retention (EPR) effect, active targeting nanoparticles used RGD motifs coupled to nanocarriers to specifically bind certain integrins, such as ανβ3, which is expressed on the surface of tumor cells, to achieve active tumor cell targeting. Self-assembling peptides have significant advantages in their structural design. The amphiphilic peptide LKR could form a spherical and self-assembled nanoparticle, which encapsulated the fat-soluble antitumor drug doxorubicin (Dox) in neutral medium. The Dox-encapsulating peptide nanoparticles swelled and burst, rapidly releasing Dox in an acidic microenvironment. Flow cytometry and fluorescence detection showed that the self-assembled LKR nanoparticles enhanced the drug accumulation in tumor cells compared with normal mammalian cells. The Dox-encapsulating peptide nanoparticles exhibited desirable antitumor effects in vivo. In summary, the acidic microenvironment of tumors was used to induce drug release from a targeted peptide drug-loading system to enhance cellular uptake and therapeutic effects in situ, providing a promising therapeutic approach for the treatment of major diseases such as hepatoma.

Molecular Modelling Guided Modulation of Molecular Shape and Charge for Design of Smart Self-Assembled Polymeric Drug Transporters

Nanomedicine employs molecular materials for prevention and treatment of disease. Recently, smart nanoparticle (NP)-based drug delivery systems were developed for the advanced transport of drug molecules. Rationally engineered organic and inorganic NP platforms hold the promise of improving drug targeting, solubility, prolonged circulation, and tissue penetration. However, despite great progress in the synthesis of NP building blocks, more interdisciplinary research is needed to understand their self-assembly and optimize their performance as smart nanocarriers. Multi-scale modeling and simulations provide a valuable ally to experiment by mapping the potential energy landscape of self-assembly, translocation, and delivery of smart drug-loaded NPs. Here, we highlight key recent advances to illustrate the concepts, methods, and applications of smart polymer-based NP drug delivery. We summarize the key design principles emerging for advanced multifunctional polymer topologies, illustrating how the unusual architecture and chemistry of dendritic polymers, self-assembling polyelectrolytes and cyclic polymers can provide exceptional drug delivery platforms. We provide a roadmap outlining the opportunities and challenges for the effective use of predictive multiscale molecular modeling techniques to accelerate the development of smart polymer-based drug delivery systems.

Iron-Based Catalytically Active Complexes in Preparation of Functional Materials

Iron complexes are particularly interesting as catalyst systems over the other transition metals (including noble metals) due to iron’s high natural abundance and mediation in important biological processes, therefore making them non-toxic, cost-effective, and biocompatible. Both homogeneous and heterogeneous catalysis mediated by iron as a transition metal have found applications in many industries, including oxidation, C-C bond formation, hydrocarboxylation and dehydration, hydrogenation and reduction reactions of low molecular weight molecules. These processes provided substrates for industrial-scale use, e.g., switchable materials, sustainable and scalable energy storage technologies, drugs for the treatment of cancer, and high molecular weight polymer materials with a predetermined structure through controlled radical polymerization techniques. This review provides a detailed statement of the utilization of homogeneous and heterogeneous iron-based catalysts for the synthesis of both low and high molecular weight molecules with versatile use, focusing on receiving functional materials with high potential for industrial application.

Effect of side-chain length on solute encapsulation by amphiphilic heterografted brush copolymers

Anisotropic nanomaterials are non-spherical structures that possess unique shape-dependent physicochemical properties and functionalities. Inspired by the abundance of filamentous entities in nature, cylindrical nanostructures have gained significant attention due to their unique performance. Herein, we discuss the effect of side-chain length on the encapsulation properties of amphiphilic heterografted bottlebrushes. We observed that by grafting a long hydrophilic block to the double-brush, we were able to restrict solute-induced conformational changes, thus producing drug-loaded anisotropic carriers. Unimolecular encapsulation in brushes was solute-dependent as shown here for probucol and rose bengal lactone. Stabilization with an amphiphilic diblock copolymer-consisting of the same type of blocks as those comprising the heterografted brush-served to explain the solute-dependent behavior observed for brushes, suggesting that solutes with a higher propensity to nucleation could be more effectively stabilized by the anisotropic carrier in a unimolecular worm-like construct.

Synthesis of cyclic graft polymeric prodrugs with heterogeneous grafts of hydrophilic OEG and reducibly conjugated CPT for controlled release

Fabrication of cyclic graft (cg) copolymer-based polymeric prodrugs by conjugation of drug molecules to cg copolymers via a dynamic covalent bond capable of responding to biorelevant signals integrates simultaneously the merits of cg copolymers and polymeric prodrugs for enhanced stability of nanocarriers and precise modulation of drug release kinetics. To completely eliminate the compromised drug conjugation efficiency due to the steric hindrance of hydrophilic grafts, it will be useful to develop cg polymeric prodrugs with heterogeneous grafts composed of hydrophilic polymers and drug species, respectively. For this purpose, we reported in this study the synthesis of cyclic graft polymeric prodrugs with heterogeneous grafts of hydrophilic oligo (ethylene glycol) (OEG) and reducibly conjugated camptothecin (CPT), cg-poly(oligo(ethylene glycol) monomethyl ether methacrylate)-b-poly((2-hydroxyethyl methacrylate)-disulfide link-camptothecin) (cg-P(OEGMA)-b-P(HEMA-SS-CPT), cg-prodrugs), via an integrated strategy of a previously reported diblock copolymer-based template and post-polymerization intermolecular click conjugation of a reducible CPT prodrug. The micelles self-assembled from cg-prodrugs on one hand had sufficient salt stability due to the branched cg structure, and on the other hand showed a reduction-triggered cleavage of the disulfide link for a promoted CPT release. Most importantly, we uncovered two interesting phenomena of the cg-based polymeric prodrugs as delivery vehicles: (i) the dimensions of both self-assemblies formed by the cg and bottlegraft (bg) polymers depend substantially on the molecular size of the cg and bg polymers likely due to the steric hindrance of the grafted structures of the cg and bg molecules and relatively low aggregation number of the self-assembled structures, and (ii) cg-prodrug-based micelles exhibited greater in vitro cytotoxicity against cancer cells despite the lower drug loading content (DLC) than the bg-based analogues, which results primarily from the faster reduction-triggered degradation and drug release as well as the greater cellular uptake efficiency of the former micelle prodrugs. Taken together, the developed cg-prodrugs provide great potential for chemotherapy, and the aforementioned interesting results will definitely inspire more upcoming studies on the future design and development of novel cg polymers for biomedical applications.

Topological Polymer Chemistry Enters Materials Science: Expanding the Applicability of Cyclic Polymers

Polymer-topology effects can alter technologically relevant properties when cyclic macromolecules are applied within diverse materials formulations. These include coatings, polymer networks, or nanostructures for delivering therapeutics. While substituting linear building blocks with cyclic analogues in commonly studied materials is itself of fundamental interest, an even more fascinating observation has been that the introduction of physical or chemical boundaries (e.g., a grafting surface or cross-links) can amplify the topology-related effects observed when employing cyclic polymer-based precursors for assembling multidimensional objects. Hence, the application of cyclic polymers has enabled the fabrication of coatings with enhanced biorepellency and superior lubricity, broadened the tuning potential for mechanical properties of polymer networks, increased the thermodynamic stability, and altered the capability of loading and releasing drugs within polymeric micelles.

Synthesis and properties of pH-cleavable toothbrush-like copolymers comprising multi-reactive Y junctions and a linear or cyclic backbone

Y-junction-bearing toothbrush-like copolymers can exhibit unique physical properties and hierarchical (co)assembly behaviors dependent on topology, external stimuli and hydrolysis.

Facile construction of stabilized, pH-sensitive micelles based on cyclic statistical copolymers of poly(oligo(ethylene glycol)methyl ether methacrylate-st-N,N-dimethylaminoethyl methacrylate) for in vitro anticancer drug delivery

This study developed a facile approach to improve the colloidal stability of a cyclic polycation as well as presented a pH-sensitive cyclic copolymer-based nanoplatform with great potential for anticancer drug delivery.

Synthesis and Solution Self-Assembly Properties of Cyclic Rod-Coil Diblock Copolymers

Typical cyclic diblock polymers are synthesized from their linear precursors via the ring-closure strategy in dilute conditions. Here we demonstrate a pseudo-high-dilution condition strategy for the efficient synthesis of cyclic rod-coil diblock copolymer from its linear precursor in selective solvents. The critical association concentration (CAC) of linear precursor is used for the control of unimer concentration during cyclization, while high copolymer synthetic concentrations are achieved via the dynamic equilibrium between unimers and micelles. The effects of CAC and micelle concentration on cyclization yield are studied and pure cyclic rod-coil diblock copolymer was obtained after azide resin treatment. Property investigations show the cyclic rod-coil copolymer has a larger second virial coefficient than its linear counterpart and self-assembles in selective solvents to form larger but looser spherical micelles due to its constraint topological structure.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

The bibliography includes 259 references.

Micelles with Cyclic Poly(ε-caprolactone) Moieties: Greater Stability, Larger Drug Loading Capacity, and Slower Degradation Property for Controlled Drug Release

Polymer topology exerts a significant effect on its properties and performance for potential applications. Cyclic topology and its derived structures have been recently shown to outperform conventional linear analogues for drug delivery applications. However, an amphiphilic tadpole-shaped copolymer consisting of a cylic hydrophobic moiety has rarely been explored. For this purpose, a tadpole-shaped amphiphilic diblock copolymer of poly(ethylene oxide)-b-(cyclic poly(ε-caprolactone)) (mPEG-b-cPCL) was synthesized successfully via ring-opening polymerization (ROP) of ε-CL using a mPEG-based macroinitiator with both a hydroxyl and an azide termini and subsequent intrachain Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) click cyclization. A comparison study on the self-assembly behaviors, in vitro drug loading and drug release profiles, and degradation properties of the resulting mPEG-b-cPCL (C) with those of the linear counterpart (mPEG-b-PCL, L) revealed that mPEG-b-cPCL micelles are a better formulation than the micelles formed by the linear counterparts in terms of micelle stability, drug loading capacity, and the degradation property. Interestingly, compared to the single degradation of L, C exhibited a slower two-stage degradation process including the topological change from tadpole shape to linear conformation and the subsequent degradation of a linear polymer. This study therefore uncovered the topological effect of a hydrophobic moiety on the properties of the self-assembled micelles and developed a complementary alternative to enhance the micelle stability by introducing a cyclic hydrophobic segment.

Converse transitions between the micelles and the vesicles of pyrrolidone-based AIE amphiphilic copolymers in polar and apolar solvents

Herein, a new family of aggregation-induced emission (AIE) amphiphilic copolymers, named poly(N-(2-methacryloyloxyethyl)pyrrolidone)-b-poly(lauryl methacrylate-co-1-ethenyl-4-(1,2,2-triphenylethenyl)benzene), PNMP_x-b-P(LMA_y-co-TPE_z), was developed by the reversible addition–fragmentation chain transfer (RAFT) polymerization method. The polymerization degree x of the NMP segment was kept constant at 35, whereas that of the LMA segment ranged from 9 to 55 with the polymerization degree ratio y/z of the LMA and TPE segments being around 9. As a result, the PNMP_x-b-P(LMA_y-co-TPE_z) copolymer gradually transformed from being water soluble to oil soluble with an increase in the length of the P(LMA_y-co-TPE_z) segment. Moreover, these copolymers could form self-organized normal and reverse assemblies in both water and n-dodecane. Various morphologies, including spherical micelles, worm-like micelles and vesicles, were confirmed by the transmission electron microscopy (TEM) observation. Specifically, the micelle-to-vesicle transition via worm-like micelles occurred in the aqueous solution upon increasing the length of the P(LMA_y-co-TPE_z) segment, whereas the reverse transition occurred in n-dodecane. Because of the presence of the AIE-active TPE segment, both the aqueous and the n-dodecane solutions of PNMP_x-b-P(LMA_y-co-TPE_z) were highly luminescent, and their fluorescence quantum yields significantly depended on the polarity of the solvent and the morphology of the assemblies. Due to the strong luminescence properties of PNMP_x-b-P(LMA_y-co-TPE_z) assemblies, these AIE-active amphiphilic copolymers acted as excellent bioimaging probes with high efficiency.

A series of AIE-active amphiphilic copolymers, PNMP_x-b-P(LMA_y-co-TPE_z), were developed as bioimaging probes. Converse transitions from spherical micelles to vesicles via wormlike micelles of them in water and n-dodecane were happened, respectively.

Efficient Heterodifunctional Unimolecular Ring-Closure Method for Cyclic Polymers by Combining RAFT and SuFEx Click Reactions

A novel ring-closure strategy for cyclic polymers by combining reversible addition-fragmentation chain transfer polymerization (RAFT) and the sulfur(VI)-fluoride exchange (SuFEx) click reaction is presented. Herein, a new heterodifunctional trithiocarbonate RAFT agent, 2-((tert-butyldimethylsilyl)oxy)ethyl (4-(fluorosulfonyl)benzyl) carbonotrithioate (TBDMS-FSBCT), containing both tert-butyldimethylsilyl ether and sulfonyl fluoride moieties, is developed. The polymerization behavior of TBDMS-FSBCT is first demonstrated by a standard RAFT polymerization procedure for two types of vinyl monomers, N-isopropylacrylamide (NIPAAm) (conjugated vinyl monomer) and N-vinylpyrrolidone (NVP) (unconjugated vinyl monomer). The tert-butyldimethylsilyl ether and sulfonyl fluoride groups at the α and ω positions of the obtained linear polymer precursors (L-PNIPAAm and L-PVP) are verified by ¹ H, ¹³ C, and ¹⁹ F NMR spectra. Subsequent intramolecular SuFEx click cyclization of the α,ω-heterofunctionalized linear precursors in air at room temperature conveniently yields the corresponding cyclic polymers (C-PNIPAAm and C-PVP). Overall, this is the first report on the preparation of cyclic polymers based on the SuFEx reaction under ambient conditions. It is envisioned that the approach may open an avenue for the formation of cyclic polymers.

Synthesis of Thermosensitive Conjugated Triblock Copolymers by Sequential Click Couplings for Drug Delivery and Cell Imaging

The elegant integration of an excellent light-emitting segment and a biorelevant signal-responsive moiety could generate advanced polymeric delivery systems with simultaneously favorable diagnostic and therapeutic functions with respect to cancer theranostics. Although polymeric delivery systems based on fluorescent polyfluorene (PF) or thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) have been extensively developed, the preparation of a ternary polymer formulation composed of a PF block, a PNIPAAm sequence, and a hydrophilic moiety remains rarely explored likely because of the difficulty in integrating different synthesis strategies for polymer synthesis. To this end, herein we reported the design and controlled synthesis of a PF- and PNIPAAm-based amphiphilic triblock copolymer, PF₁₁-b-PNIPAAm₁₂₀-b-poly(oligo(ethylene glycol) monomethyl ether methacrylate)₁₇ (PF₁₁-b-PNIPAAm₁₂₀-b-POEGMA₁₇), with a well-defined structure by a strategy of sequential click couplings between Suzuki-coupling-generated PF and atom-transfer radical polymerization (ATRP)-produced PNIPAAm and POEGMA. The as-prepared triblock copolymers can self-assemble into micelles with a core-shell-corona (CSC) structure that is composed of an inner hydrophobic core of the PF moiety for fluorescent tracking and drug encapsulation, a thermosensitive middle shell of PNIPAAm block for thermomodulated drug loading and release, and a hydrophilic outer corona of the POEGMA segment for micelle stabilization. Interestingly, the doxorubicin (DOX)-loaded micelles prepared at 25 °C had a greater drug loading capacity than the analogues fabricated at 37 °C due to the better stability of the former formulation, leading to its higher in vitro cytotoxicity in HeLa cells. Together with the integration of a localized hyperthermia-triggered drug release profile and efficiently intracellular trafficking of the nanocarriers by monitoring the fluorescence of the PF moiety, this formulation demonstrates a great potential for cancer theranostics.

Synthesis of stimuli-responsive nanosized ring-like colloids and cyclic polymers via a dual-template approach

Ring-like particles have received considerable attention due to their unique interior cavity and properties. However, the preparation of stimuli-responsive nanosized rings with internal size smaller than 100 nm remains unexplored likely due to the challenges encountered in their synthesis. The successful fulfillment of this target will not only significantly enrich the family of ring-like nanoparticles but also build a connection that bridges ring-like nanoparticles and cyclic polymers. For this purpose, we report in this study a controlled synthesis of stimuli-responsive ring-like colloids and cyclic polymers using both star-shaped polymers and β-cyclodextrin (β-CD) as the dual templates. The first template comprising star-shaped polymers generated a ring-like structure and adoption of β-CD as the second template further restricted the ring thickness to the height of a β-CD, leading to the generation of stimuli-responsive nanosized ring-like colloids with ring thickness less than 1 nm, which shifted the ring-like structure to cyclic polymers with reversible cross-linked disulfide bridges. The reported "dual-template" approach is thus a valuable alternative to the current synthetic strategies toward stimuli-responsive ring-like colloids and cyclic polymers.

The fabrication of hybrid micelles with enhanced permeability for drug delivery via a diethoxymethylsilyl-based crosslinking strategy

A novel reducible silica monomer, DESSPMA with diethoxysilyl groups for in situ crosslinking to give a lower crosslinking density and greater permeability than the triethoxysilyl-based TESSPMA was developed to realize enhanced therapeutic efficiency.