pH-induced morphological transition of aggregates formed by miktoarm star polymers in dilute solution: a mesoscopic simulation study

The self-assembly of miktoarm star polymers μ-A i (B(D)) j C k in a neutral solution and the pH-responsive behaviors of vesicles and spherical micelles in an acidic solution have been investigated by DPD simulation. The results show that the self-assembled morphologies can be regulated by the lengths of pH-responsive arm B and hydrophilic arm C, leading to the formation of vesicles, discoidal micelles, and spherical micelles in a neutral solution. The dynamic evolution pathways of vesicles and spherical micelles are categorized into three stages: nucleation, coalescence, and growth. Subsequently, the pH-responsive behaviors of vesicles and spherical micelles have been explored by tuning the protonation degree of pH-responsive arm B. The vesicles evolves from nanodisks to nanosheets, then to nanoribbons, as the protonation degree increases, corresponding to a decrease in pH value, while the spherical micelles undergoes a transition into worm-like micelles, nanosheets, and nanoribbons. Notably, the electrostatic interaction leads the counterions to form a regular hexagonal pattern in nanosheets, while an alternative distribution of charged beads has been observed in nanoribbons. Furthermore, the role of the electrostatic interaction in the morphological transition has been elucidated through the analysis of the distribution of positive and negative charges, as well as the electrostatic potential for associates.

Brownian dynamics simulations of bottlebrush polymers in dilute solution under simple shear and uniaxial extensional flows

We study the dynamics of bottlebrush polymer molecules in dilute solutions subjected to shear and uniaxial extensional flows using Brownian dynamics simulations with hydrodynamic interaction (HI). Bottlebrush polymers are modeled using a coarse-grained representation, consisting of a set of beads interacting pairwise via a purely repulsive potential and connected by finitely extensible nonlinear springs. We present the results for molecular stretching, stress, and solution viscosity during the startup of flow as well as under steady state as a function of side chain length while keeping the backbone length fixed. In extensional flow, the backbone fractional extension and the first normal stress difference decrease with an increase in side chain length at a fixed Weissenberg number (Wi). Using simulation results both in the presence of and in the absence of HI, we show that this is primarily a consequence of steric interaction resulting from the dense grafting of side chains. In shear flow, we observe a shear-thinning behavior in all cases, although it becomes less pronounced with increasing side chain length. Furthermore, nonmonotonicity in the backbone fractional extension is observed under shear, particularly at high Wi. We contextualize our simulation results for bottlebrush polymers with respect to existing studies in the literature for linear polymers and show that the unique dynamical features characterizing bottlebrush polymers arise on account of their additional molecular thickness due to the presence of densely grafted side chains.

Discrete Miktoarm Star Block Copolymers with Tailored Molecular Architecture

Molecular architecture is a critical factor in regulating phase behaviors of the block copolymer and prompting the formation of unconventional nanostructures. This work meticulously designed a library of isomeric miktoarm star polymers with an architectural evolution from the linear-branched block copolymer to the miktoarm star block copolymer and to the star-like block copolymer (i.e., 3AB → 3(AB1)B2 → 3(AB)). All of the polymers have precise chemical composition and uniform chain length, eliminating inherent molecular uncertainties such as chain length distribution or architectural defects. The self-assembly behaviors were systematically studied and compared. Gradually increasing the relative length of the branched B1 block regulates the ratio between the bridge and loop configuration and effectively releases packing frustration in the formation of the spherical or cylindrical structures, leading to a substantial deflection of phase boundaries. Complex structures, such as Frank-Kasper phases, were captured at a surprisingly higher volume fraction. Rationally regulating the molecular architecture offers rich possibilities to tune the packing symmetry of block copolymers.

Efficient Synthesis of Cyclic Poly(ethylene glycol)s under High Concentration Conditions by the Assistance of Pseudopolyrotaxane with Cyclodextrin Derivatives

An efficient synthesis of cyclic polymers (CPs) is in high demand due to their unique properties. However, polymer cyclization generally occurs at low concentrations (0.1 g/L), and the synthesis of CPs at high concentrations remains a challenge. Herein an efficient cyclization of poly(ethylene glycol) (Mn = 2000 g/mol, 4000 g/mol) (PEG-2k, PEG-4k) in high concentration (80 g/L) is realized by the assistance of pseudopolyrotaxane (pPRx). Water-soluble pPRx with a U-like-shape inclusion motif is prepared by mixing the 2-hydroxypropyl-γ-cyclodextrin (HPγCD) and PEG with (E)-3,4,5-trimethoxycinnamate (TCA-PEG-2k, TCA-PEG-4k). Subsequent irradiation of the pPRx solution (10-80 g/L) by UV light gives cyclic polymers through the intramolecular [2 + 2] photocycloaddition of the cinnamoyl moieties. The photoreaction of TCA-PEG-2k in the pPRx system gives cyclic monomers (C-1mer) as major products with a yield of 66% at 80 g/L. Additionally, the cyclization of TCA-PEG-4k also gives C-1mer as major products with a yield of 45% at a concentration of 80 g/L.

Catalytic Living ROMP: Synthesis of Degradable Star Polymers

Star polymers have attracted considerable attention over the past few years due to their distinctive physical and chemical attributes that are different from conventional linear polymers. Here, we present a one-pot synthesis of narrowly dispersed and degradable homoarm and miktoarm star polymers exploiting the catalytic living ring-opening metathesis polymerization (ROMP) mechanism. Several complex polymeric architectures (such as A3-, A4-, A6-, A2B-, A3B-, and AB2-type star polymers) were synthesized quite straightforwardly by using appropriate vinyl ether chain transfer agents. SEC, 1H NMR, and DOSY NMR spectroscopy were employed to analyze and characterize all of the synthesized polymers. We believe that this sustainable and environmentally friendly synthesis of star polymers could become an important synthetic tool for polymer engineers working on supramolecular, industrial or biomedical applications.

Synthesis of PDMS-μ-PCL Miktoarm Star Copolymers by Combinations (Є) of Styrenics-Assisted Atom Transfer Radical Coupling and Ring-Opening Polymerization and Study of the Self-Assembled Nanostructures

Due to their diverse and unique physical properties, miktoarm star copolymers (μ-SCPs) have garnered significant attention. In our study, we employed α-monobomoisobutyryl-terminated polydimethylsiloxane (PDMS-Br) to carry out styrenics-assisted atom transfer radical coupling (SA ATRC) in the presence of 4-vinylbenzyl alcohol (VBA) at 0 °C. By achieving high coupling efficiency (χc = 0.95), we obtained mid-chain functionalized PDMS-VBAm-PDMS polymers with benzylic alcohols. Interestingly, matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis revealed the insertion of only two VBA coupling agents (m = 2). Subsequently, the PDMS-VBA2-PDMS products underwent mid-chain extensions using ε-caprolactone (ε-CL) through ring-opening polymerization (ROP) with an efficient organo-catalyst at 40 °C, resulting in the synthesis of novel (PDMS)2-μ-(PCL)2 μ-SCPs. Eventually, novel (PDMS)2-μ-(PCL)2 μ-SCPs were obtained. The obtained PDMS-μ-PCL μ-SCPs were further subjected to examination of their solid-state self-assembly through small-angle X-ray scattering (SAXS) experiments. Notably, various nanostructures, including lamellae and hexagonally packed cylinders, were observed with a periodic size of approximately 15 nm. As a result, we successfully developed a simple and effective reaction combination (Є) strategy (i.e., SA ATRC-Є-ROP) for the synthesis of well-defined PDMS-μ-PCL μ-SCPs. This approach may open up new possibilities for fabricating nanostructures from siloxane-based materials.

Design of Microstructure-Engineered Polymers for Energy and Environmental Conservation

With the ever-growing demand for sustainability, designing polymeric materials using readily accessible feedstocks provides potential solutions to address the challenges in energy and environmental conservation. Complementing the prevailing strategy of varying chemical composition, engineering microstructures of polymer chains by precisely controlling their chain length distribution, main chain regio-/stereoregularity, monomer or segment sequence, and architecture creates a powerful toolbox to rapidly access diversified material properties. In this Perspective, we lay out recent advances in utilizing appropriately designed polymers in a wide range of applications such as plastic recycling, water purification, and solar energy storage and conversion. With decoupled structural parameters, these studies have established various microstructure-function relationships. Given the progress outlined here, we envision that the microstructure-engineering strategy will accelerate the design and optimization of polymeric materials to meet sustainability criteria.

Hydrophobic Drug Carrier from Polycaprolactone-b-Poly(Ethylene Glycol) Star-Shaped Polymers Hydrogel Blend as Potential for Wound Healing Application

Blending hydrogel with an amphiphilic polymer can increase the hydrophobic drug loading and entrapment efficiency of hydrogel-based formulations. In this study, a hydrogel formulation with star-shaped polycaprolactone-b-poly(ethylene glycol) (PCL-b-PEG) as the hydrophobic drug cargo is produced. The 4-arm and 6-arm star-shaped PCL are synthesized with different molecular weights (5000, 10,000, 15,000 g/mol) via ROP and MPEG as the hydrophilic segment is attached via the Steglich esterification. FTIR and ¹H-NMR analysis showed the presence of all functional groups for homopolymers and copolymers. M_n for all synthesized polymers is close to the theoretical value while GPC spectra showed a monomodal peak with narrow molecular weight distribution (PDI:1.01-1.25). The thermal degradation temperature and crystalline melting point of synthesized polymers increase with the increase in molecular weight and number of arms. All formulations possess high drug loading and entrapment efficiency (>99%) and increase with increasing molecular weight, number of arms, and amount of polymer in the formulations. All formulations showed a sustained drug release pattern with no initial burst, which follows the Korsmeyer-Peppas kinetic model. The polymer hydrogel formulations showed antibacterial activity against E. coli and S. aureus. The hydrogel containing 4-arm PCL_15k-PEG is chosen as the best formulation due to its high drug release, good antimicrobial activity, and morphology.

Quaternized Poly(N,N'-dimethylaminoethyl methacrylate) Star Nanostructures in the Solution and on the Surface

Antibacterial polymeric materials are promising in the fight against resistant bacteria strains. Amongst them, cationic macromolecules with quaternary ammonium groups are one of intensively studied, as they interact with the bacterial membranes causing cell death. In this work, we propose to use nanostructures composed of polycations with star topology for the preparation of antibacterial materials. First, star polymers of N,N'-dimethylaminoethyl methacrylate and hydroxyl-bearing oligo(ethylene glycol) methacrylate P(DMAEMA-co-OEGMA-OH) were quaternized with various bromoalkanes and their solution behavior was studied. It was shown that in water two modes of star nanoparticles were observed, of diameters about 30 nm and up to 125 nm, independently of the quaternizing agent. Separately layers of P(DMAEMA-co-OEGMA-OH) stars were obtained. In this case, the chemical grafting of polymers to the silicon wafers modified with imidazole derivatives was applied, followed by the quaternization of the amino groups of polycations. A comparison of the quaternary reaction in solution and on the surface showed that in the solution it is influenced by the alkyl chain length of the quaternary agent, while on the surface such relationship is not observed. After physico-chemical characterization of the obtained nanolayers, their biocidal activity was tested against two strains of bacteria E. coli and B. subtilis. The best antibacterial properties exhibited layers quaternized with shorter alkyl bromide, where 100% growth inhibition of E. coli and B. subtilis after 24 h of contact was observed.

Quo Vadis Carbanionic Polymerization?

Living anionic polymerization will soon celebrate 70 years of existence. This living polymerization is considered the mother of all living and controlled/living polymerizations since it paved the way for their discovery. It provides methodologies for synthesizing polymers with absolute control of the essential parameters that affect polymer properties, including molecular weight, molecular weight distribution, composition and microstructure, chain-end/in-chain functionality, and architecture. This precise control of living anionic polymerization generated tremendous fundamental and industrial research activities, developing numerous important commodity and specialty polymers. In this Perspective, we present the high importance of living anionic polymerization of vinyl monomers by providing some examples of its significant achievements, presenting its current status, giving several insights into where it is going (Quo Vadis) and what the future holds for this powerful synthetic method. Furthermore, we attempt to explore its advantages and disadvantages compared to controlled/living radical polymerizations, the main competitors of living carbanionic polymerization.

Chain transfer agents for the catalytic ring opening metathesis polymerization of norbornenes

Here, we present a detailed study of the metathesis activity of conjugated 1,3 diene derivatives in ring opening metathesis polymerization (ROMP) using Grubbs' 3rd generation catalyst (G3). A comprehensive screening of those derivatives revealed that monosubstituted 1,3 dienes show similar reactivities towards G3-alkylidenes as norbornene derivatives. Therefore, they represent perfect candidates for chain transfer agents in a kinetically controlled catalytic ROMP. This unprecedented reactivity allowed us to catalytically synthesize mono-end-functional poly(norborneneimide)s on the gram scale. Much more complex architectures such as star-shaped polymers could also be synthesized catalytically for the very first time via ROMP. This inexpensive and greener route to produce telechelic ROMP polymers was further utilized to synthesize ROMP block copolymers using bifunctional ROMP and ATRP/NCL initiators. Finally, the regioselective reaction of G3 with 1,3 diene derivatives was also exploited in the synthesis of a ROMP-PEG diblock copolymer initiated from a PEG macroinitiator.

Self-Assembly of Miktoarm Star Polyelectrolytes in Solutions with Various Ionic Strengths

We studied the self-assembly of miktoarm star polyelectrolytes with different numbers of arms in solutions with various ionic strengths using coarse-grained molecular dynamic simulations. Spherical micelles are obtained for star polyelectrolytes with fewer arms, whereas wormlike clusters are obtained for star polyelectrolytes with more arms at a low ionic strength environment, with hydrophilic arms showing a stretched conformation. The number of clusters shows an overall decreasing tendency with increasing the number of arms in star polyelectrolytes due to strong electrostatic coupling between polycations and polyanions. The formation of wormlike clusters follows an overall stepwise pathway with an intermittent association-dissociation process for star polyelectrolytes with weak electrostatic coupling. These computational results can provide relevant physical insights to understand the self-assembly mechanism of star polyelectrolytes in solvents with various ionic strengths and to design star polyelectrolytes with functional groups that can fine-tune self-assembled structures for specific applications.

Star-Shaped ROMP Polymers Coated with Oligothiophenes That Exhibit Unique Emission

A series of oligo(thiophene)-modified "soluble" star-shaped ring-opening metathesis polymerization (ROMP) polymers were prepared by sequential living ROMP of norbornene and a cross-linking agent using a molybdenum-alkylidene catalyst, followed by Wittig-type coupling for termination with oligo(thiophene) carboxaldehydes. The resultant star-shaped ROMP polymers displayed unique emission properties affected by the core size and arm repeat units as well as the kind of oligothiophene coated. The effects of the thiophene groups on photophysical properties of star-shaped/linear polymers were studied via time-resolved fluorescence spectroscopy. Fluorescence lifetimes were determined in THF as 400, 640, 730, and 820 ps for Star 3TPh, Linear 3TPh, Star 4T, and Linear 4T, respectively. A significant enhancement of the nonradiative rate constants k _nr in the star-shaped polymers results in relatively lower fluorescence quantum yields and shorter fluorescence lifetimes compared to the corresponding linear polymers.

Polymersomes: Soft Nanoparticles from Miktoarm Stars for Applications in Drug Delivery

Self-assembly of amphiphilic macromolecules has provided an advantageous platform to address significant issues in a variety of areas, including biology. Such soft nanoparticles with a hydrophobic core and hydrophilic corona, referred to as micelles, have been extensively investigated for delivering lipophilic therapeutics by physical encapsulation. Polymeric vesicles or polymersomes with similarities in morphology to liposomes continue to play an essential role in understanding the behavior of cell membranes and, in addition, have offered opportunities in designing smart nanoformulations. With the evolution in synthetic methodologies to macromolecular precursors, the construction of such assemblies can now be modulated to tailor their properties to match desired needs. This review brings into focus the current state-of-the-art in the design of polymersomes using amphiphilic miktoarm star polymers through a detailed analysis of the synthesis of miktoarm star polymers with tuned lengths of varied polymeric arms, their self-assembly, and applications in drug delivery.

Star-shaped poly(ε-caprolactones) with well-defined architecture as potential drug carriers

The present study reported on the potential application of star-shaped poly(?-caprolactones) with different number of arms as new drug delivery matrix. Linear and star-shaped PCL ibuprofen loaded microspheres were prepared using oil-in-water (o/w) solvent evaporation technique and characterized with FTIR, DSC, XRD and SEM analysis. High yield, encapsulation efficiency and drug loadings were obtained for all microspheres. FTIR analysis revealed the existence of interactions between polymer matrix and drug, while the DSC analysis suggested that drug was encapsulated in an amorphous form. SEM analysis confirmed that regular, spherical in shape star-shaped microspheres, with diameter between 80 to 90 ?m, were obtained, while quite larger microspheres, 110 ?m, were prepared from linear PCL. The advantage of using star-shaped PCL microspheres instead of linear PCL was seen from drug release profiles which demonstrated higher amount of drug released from star-shaped polymer matrix as a consequence of their branched, flexible structure. Microspheres prepared from the polymers with the most branched structure showed the highest amount of released drug after 24 h. Finally, cytotoxicity tests, performed using normal human fibroblasts (MRC5), indicated absence of cytotoxicity at lower concentrations of microspheres proving the great potential of star-shaped PCL systems in comparison to linear ones.

Combining Hydroxyl-Yne and Thiol-Ene Click Reactions to Facilely Access Sequence-Defined Macromolecules for High-Density Data Storage

Through mimicking the synthesis of hereditary-information-containing nucleic acids, scientists are committed to synthesizing sequence-defined macromolecules. Herein, a protecting-group-free, metal-free, and atom-economical chemistry combining hydroxyl-yne and thiol-ene click reactions was developed to efficiently synthesize sequence-defined oligo(monothioacetals) (overall yield of 54% for an 11-step synthesis) from readily available starting compounds and monomers under ambient conditions. The sequences of linear oligo(monothioacetals) could be easily decoded via a tandem ESI-MS/MS technique, making them new kinds of digital macromolecules with a high data storage density (0.013 bit/Da). Moreover, star oligo(monothioacetals) could also be facilely generated through divergent and convergent strategies and their combination. An unprecedented sequence-defined miktoarm star oligo(monothioacetal) was obtained, which could serve as a new nonlinear digital macromolecule to achieve 2D information matrix encoding and hold great potential to be applied for information encryption, anticouterfeiting, secret communication, etc. Thus, this work provides a powerful stepwise iterative approach to facilely access sequence-defined linear and topological oligo(monothioacetals) for high-density data storage.

Reactive Oxygen Species-Responsive Miktoarm Amphiphile for Triggered Intracellular Release of Anti-Cancer Therapeutics

Reactive oxygen species (ROS)-responsive nanocarriers have received considerable research attention as putative cancer treatments because their tumor cell targets have high ROS levels. Here, we synthesized a miktoarm amphiphile of dithioketal-linked ditocopheryl polyethylene glycol (DTTP) by introducing ROS-cleavable thioketal groups as linkers between the hydrophilic and hydrophobic moieties. We used the product as a carrier for the controlled release of doxorubicin (DOX). DTTP has a critical micelle concentration (CMC) as low as 1.55 μg/mL (4.18 × 10⁻⁴ mM), encapsulation efficiency as high as 43.6 ± 0.23% and 14.6 nm particle size. The DTTP micelles were very responsive to ROS and released their DOX loads in a controlled manner. The tocopheryl derivates linked to DTTP generated ROS and added to the intracellular ROS in MCF-7 cancer cells but not in HEK-293 normal cells. In vitro cytotoxicity assays demonstrated that DOX-encapsulated DTTP micelles displayed strong antitumor activity but only slightly increased apoptosis in normal cells. This ROS-triggered, self-accelerating drug release device has high therapeutic efficacy and could be a practical new strategy for the clinical application of ROS-responsive drug delivery systems.

Two-Dimensional Polymers and Polymerizations

Synthetic chemists have developed robust methods to synthesize discrete molecules, linear and branched polymers, and disordered cross-linked networks. However, two-dimensional polymers (2DPs) prepared from designed monomers have been long missing from these capabilities, both as objects of chemical synthesis and in nature. Recently, new polymerization strategies and characterization methods have enabled the unambiguous realization of covalently linked macromolecular sheets. Here we review 2DPs and 2D polymerization methods. Three predominant 2D polymerization strategies have emerged to date, which produce 2DPs either as monolayers or multilayer assemblies. We discuss the fundamental understanding and scope of each of these approaches, including: the bond-forming reactions used, the synthetic diversity of 2DPs prepared, their multilayer stacking behaviors, nanoscale and mesoscale structures, and macroscale morphologies. Additionally, we describe the analytical tools currently available to characterize 2DPs in their various isolated forms. Finally, we review emergent 2DP properties and the potential applications of planar macromolecules. Throughout, we highlight achievements in 2D polymerization and identify opportunities for continued study.

Weakly Ionically Bound Thermosensitive Hyperbranched Polymers

We synthesized novel amphiphilic hyperbranched polymers (HBPs) with variable contents of weakly ionically tethered thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) macrocations in contrast to traditional covalent linking. Their assembling behavior was studied below and above the lower critical solution temperature (LCST). The HBPs underwent a morphological transition under changing temperature and ionic strength due to the LCST transition of PNIPAM and the reduction in the ionization degree of terminal ionic groups, respectively. We suggest that, in contrast to traditional branched polymers, ionically linked PNIPAM macrocations can reversibly disassociate from the sulfonate groups and form mobile coronas, endowing the dynamic micellar morphologies. In addition, assembly at the air-water interface confined PNIPAM macrocations and resulted in the formation of heterogeneous Langmuir-Blodgett (LB) monolayers with diverse surface morphologies for different peripheral compositions with circular domains formed in the condensed state. The HBPs with 25% PNIPAM showed larger and more stable circular domains that were partially preserved at high compression than those of HBPs with 50% PNIPAM. Moreover, the LB monolayers showed variable surface mechanical and surface charge distribution, which can be attributed to net dipole redistribution caused by the behavior of mobile PNIPAM macrocations and core sulfonate groups.

Nanotheranostics: A Possible Solution for Drug-Resistant Staphylococcus aureus and their Biofilms?

Staphylococcus aureus is a notorious pathogen that colonizes implants (orthopedic and breast implants) and wounds with a vicious resistance to antibiotic therapy. Methicillin-resistant S. aureus (MRSA) is a catastrophe mainly restricted to hospitals and emerged to community reservoirs, acquiring resistance and forming biofilms. Treating biofilms is problematic except via implant removal or wound debridement. Nanoparticles (NPs) and nanofibers could combat superbugs and biofilms and rapidly diagnose MRSA. Nanotheranostics combine diagnostics and therapeutics into a single agent. This comprehensive review is interpretative, utilizing mainly recent literature (since 2016) besides the older remarkable studies sourced via Google Scholar and PubMed. We unravel the molecular S. aureus resistance and complex biofilm. The diagnostic properties and detailed antibacterial and antibiofilm NP mechanisms are elucidated in exciting stories. We highlight the challenges of bacterial infections nanotheranostics. Finally, we discuss the literature and provide "three action appraisals". (i) The first appraisal consists of preventive actions (two wings), avoiding unnecessary hospital visits, hand hygiene, and legislations against over-the-counter antibiotics as the general preventive wing. Our second recommended preventive wing includes preventing the adverse side effects of the NPs from resistance and toxicity by establishing standard testing procedures. These standard procedures should provide breakpoints of bacteria's susceptibility to NPs and a thorough toxicological examination of every single batch of synthesized NPs. (ii) The second appraisal includes theranostic actions, using nanotheranostics to diagnose and treat MRSA, such as what we call "multifunctional theranostic nanofibers. (iii) The third action appraisal consists of collaborative actions.

The synthesis of thermoresponsive POSS-based eight-arm star poly(N-isopropylacrylamide): A comparison between Z-RAFT and R-RAFT strategies

Z-Type POSS-based eight-arm star poly(N-isopropylacrylamide), POSS-(PNIPAM)₈-Z, is synthesized and demonstrated to be a thermoresponsive switchable emulsifier.

Effect of Molecular Architecture on the Self-Assembly of Bottlebrush Copolymers

The characteristics of a new architecture of bottlebrush copolymers (BBCPs) self-assembly were studied using self-consistent field theory. In this molecule, a series of AB linear diblock side chains were connected at the diblock junction using a C backbone. The control over the linker length and its chemical nature created an additional constraint on the intrinsic AB diblock microphase separation. Increasing side-chain crowding by increasing the grafting density and total degree of polymerization induced improved phase separation. This was reflected in the overall reduction in the effective interaction parameter between the diblocks as well as the abrupt increase in phase density when crossing the order-disorder transition. Side-chain crowding resulted in an increase in the equilibrium domain spacing compared to a linear diblock. On the other hand, the localization of block C at the AB interface generated a diffuse domain boundary and reduction in side-chain stretching. The unique behavior of BBCPs was observed in 1D confined systems where the molecule showed the natural tendency to orient domains parallel to neutral confinement in contrast to the behavior of confined diblocks. Such behavior largely depended on the degree of incompatibility between the AB blocks and BBCP structure. A ternary phase diagram was constructed for different proportions of each block. Rich morphologies of core-shell domains and tiling patterns were observed including octagonal and pentagonal polygons. The unique architecture of this bottlebrush molecule and its improved nanoscale properties make it an attractive candidate for various applications of nanotechnology.

Thiol-Bromo Click Reaction for One-Pot Synthesis of Star-Shaped Polymers

Star-shaped polymers have unique physical properties and they are sought after materials in industry. However, the ease of synthesis is essential for translation of these materials into large-scale applications. Herein, a highly efficient synthetic method to prepare star-shaped polymers by combination of Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) and thiol-bromo click reaction is described. Well-defined linear and block polymers with a very high bromine chain end fidelity are obtained via Cu-RDRP and subsequently react with multi-functional thiol compounds. High coupling efficiencies of larger than 90% are obtained owing to the quick and efficient reaction between thiols and alkyl bromides. Moreover, the arms of the obtained star-shaped polymers are linked via thioether bonds to the core, making them susceptible for oxidative degradation.

Miktoarm Star Polymers with Environment-Selective ROS/GSH Responsive Locations: From Modular Synthesis to Tuned Drug Release through Micellar Partial Corona Shedding and/or Core Disassembly

Branched architectures with asymmetric polymeric arms provide an advantageous platform for the construction of tailored nanocarriers for therapeutic interventions. Simple and adaptable synthetic methodologies to amphiphilic miktoarm star polymers have been developed in which spatial location of reactive oxygen species (ROS) and glutathione (GSH) responsive entities is articulated to be on the corona shell surface or inside the core. The design of such architectures is facilitated through versatile building blocks and selected combinations of ring-opening polymerization, Steglich esterification, and alkyne-azide click reactions. Soft nanoparticles from aqueous self-assembly of these stimuli responsive miktoarm stars have low critical micelle concentrations and high drug loading efficiencies. Partial corona shedding upon response to ROS is accompanied by an increase in drug release, without significant changes to overall micelle morphology. The location of the GSH responsive unit at the core leads to micelle disassembly and complete drug release. Curcumin loaded soft nanoparticles show higher efficiencies in preventing ROS generation in extracellular and cellular environments, and in ROS scavenging in human glioblastoma cells. The ease in synthetic elaboration and an understanding of structure-property relationships in stimuli responsive nanoparticles offer a facile venue for well-controlled drug delivery, based on the extra- and intracellular concentrations of ROS and GSH.

Synthesis and Encapsulation of Uniform Star-Shaped Block-Macromolecules

Linear uniform oligomers synthesized via a two-step iterative cycle are postmodified with uniform octaethylene glycol monomethyl ether and finally coupled via azide-alkyne cycloaddition to yield uniform star-shaped block macromolecules with a mass ranging from 10 to 14 kDa. Each of the molecules is carefully characterized by NMR, electrospray ionization mass spectrometry (ESI-MS), and size exclusion chromatography (SEC) to underline their purity as well as their uniformity. The obtained star-shaped macromolecules are investigated in their ability to encapsulate dye molecules by carrying out qualitative solid-liquid phase transfer experiments.

Hydrolytic degradation of star-shaped poly(ε-caprolactone)s with different number of arms and their cytotoxic effects

Star-shaped polymers of biodegradable aliphatic polyester, poly( ε-caprolactone), PCL, with different number of arms (three, four, and six) were synthesized by ring-opening polymerization initiated by multifunctional alcohols used as cores. As potential biomaterials, synthesized star-shaped poly( ε-caprolactone)s, sPCL, were thoroughly characterized in terms of their degradation under different pH conditions and in respect to their cytotoxicity. The in vitro degradation was performed in phosphate buffer (pH 7.4) and hydrochloric acid solution (pH 1.0) over 5 weeks. Degradation of sPCL films was followed by the weight loss measurements, GPC, FTIR, and AFM analysis. While the most of the samples were stable against the abiotic hydrolysis at pH 7.4 after 5 weeks of degradation, degradation was significantly accelerated in the acidic medium. Degradation rate of polymer films was affected by the polymer architecture and molecular weight. The molecular weight profiles during the degradation revealed random chain scission of the ester bonds indicating bulk degradation mechanism of hydrolysis at pH 7.4, while acidic hydrolysis proceeded through the bulk degradation associated with surface erosion, confirmed by AFM. The in vitro toxicity tests, cytotoxicity applying normal human fibroblasts (MRC5) and embryotoxicity assessment (using zebra fish model, Danio rerio), suggested those polymeric materials as suitable for biomedical application.

Telodendrimers: Promising Architectural Polymers for Drug Delivery

Architectural complexity has played a key role in enhancing the efficacy of nanocarriers for a variety of applications, including those in the biomedical field. With the continued evolution in designing macromolecules-based nanoparticles for drug delivery, the combination approach of using important features of linear polymers with dendrimers has offered an advantageous and viable platform. Such nanostructures, which are commonly referred to as telodendrimers, are hybrids of linear polymers covalently linked with different dendrimer generations and backbones. There is considerable variety in selection from widely studied linear polymers and dendrimers, which can help tune the overall composition of the resulting hybrid structures. This review highlights the advances in articulating syntheses of these macromolecules, and the contributions these are making in facilitating therapeutic administration. Limited progress has been made in the design and synthesis of these hybrid macromolecules, and it is through an understanding of their physicochemical properties and aqueous self-assembly that one can expect to fully exploit their potential in drug delivery.

Miktoarm Star Polymers: Branched Architectures in Drug Delivery

Delivering active pharmaceutical agents to disease sites using soft polymeric nanoparticles continues to be a topical area of research. It is becoming increasingly evident that the composition of amphiphilic macromolecules plays a significant role in developing efficient nanoformulations. Branched architectures with asymmetric polymeric arms emanating from a central core junction have provided a pivotal venue to tailor their key parameters. The build-up of miktoarm stars offers vast polymer arm tunability, aiding in the development of macromolecules with adjustable properties, and allows facile inclusion of endogenous stimulus-responsive entities. Miktoarm star-based micelles have been demonstrated to exhibit denser coronae, very low critical micelle concentrations, high drug loading contents, and sustained drug release profiles. With significant advances in chemical methodologies, synthetic articulation of miktoarm polymer architecture, and determination of their structure-property relationships, are now becoming streamlined. This is helping advance their implementation into formulating efficient therapeutic interventions. This review brings into focus the important discoveries in the syntheses of miktoarm stars of varied compositions, their aqueous self-assembly, and contributions their formulations are making in advancing the field of drug delivery.

Preparation of Doxorubicin-Loaded Amphiphilic Poly(D,L-Lactide-Co-Glycolide)-b-Poly(N-Acryloylmorpholine) AB2 Miktoarm Star Block Copolymers for Anticancer Drug Delivery

Owing to their unique topology and physical properties, micelles based on miktoarm amphiphilic star block copolymers play an important role in the biomedical field for drug delivery. Herein, we developed a series of AB2-type poly(D,L-lactide-co-glycolide)-b-poly(N-acryloyl morpholine) (PLGA-b-PNAM2) miktoarm star block copolymers by reversible addition-fragmentation chain-transfer polymerization and ring-opening copolymerization. The resulting miktoarm star polymers were investigated by 1H NMR spectroscopy and gel permeation chromatography. The critical micellar concentration value of the micelles increases with an increase in PNAM block length. As revealed by transmission electron microscopy and dynamic light scattering, the amphiphilic miktoarm star block copolymers can self-assemble to form spherical micellar aggregates in water. The anticancer drug doxorubicin (DOX) was encapsulated by polymeric micelles; the drug-loading efficiency and drug-loading content of the DOX-loaded micelles were 81.7% and 9.1%, respectively. Acidic environments triggered the dissociation of the polymeric micelles, which led to the more release of DOX in pH 6.4 than pH 7.4. The amphiphilic PLGA-b-PNAM2 miktoarm star block copolymers may have broad application as nanocarriers for controlled drug delivery.

Soft and Condensed Nanoparticles and Nanoformulations for Cancer Drug Delivery and Repurpose

Drug repurpose or reposition is recently recognized as a high-performance strategy for developing therapeutic agents for cancer treatment. This approach can significantly reduce the risk of failure, shorten R&D time, and minimize cost and regulatory obstacles. On the other hand, nanotechnology-based delivery systems are extensively investigated in cancer therapy due to their remarkable ability to overcome drug delivery challenges, enhance tumor specific targeting, and reduce toxic side effects. With increasing knowledge accumulated over the past decades, nanoparticle formulation and delivery have opened up a new avenue for repurposing drugs and demonstrated promising results in advanced cancer therapy. In this review, recent developments in nano-delivery and formulation systems based on soft (i.e., DNA nanocages, nanogels, and dendrimers) and condensed (i.e., noble metal nanoparticles and metal-organic frameworks) nanomaterials, as well as their theranostic applications in drug repurpose against cancer are summarized.

Influence of block sequence on the colloidal self-assembly of poly(norbornene)-block-poly(ethylene oxide) amphiphilic block polymers using rapid injection processing

A facile self-assembly method, rapid injection, was used to study the self-assembly difference between AB diblock and ABA triblock copolymers.