Multiarm Star Research Articles

Synergistic Drug-Loaded Shear-Thinning Star Polymer Hydrogel Facilitates Gastrointestinal Lesion Resection and Promotes Wound Healing.

Easy injection, long-lasting barrier, and drug loading are the critical properties of submucosal injection materials for endoscopic surgery. However, conventional injectable polymers face challenges in simultaneously attaining these properties due to the inherent conflict between injectability and in situ stability. Here, a multi-arm star polymer hydrogel (denoted as βCP hydrogel) with long-lasting submucosal barrier (exceeding 120 min), rapid hemostasis, and sustained antibacterial properties is successfully developed by grafting poly(oligo(ethylene glycol) methyl ether methacrylate)(PEGMA) side-chains from β-CD via atom transfer radical polymerization (ATRP). During the onset of shearing, βCP hydrogel experiences the unwinding of polymer side-chains between neighboring star polymers, which facilitates the process of endoscopic injectability. After submucosal injection, βCP hydrogel undergoes the winding of polymer side-chains, thereby establishing a long-lasting barrier cushion. Meanwhile, owing to its distinctive structures with a hydrophobic inner cavity and an outer layer of hydrophilic polymer side-chains, βCP hydrogel enables simultaneous loading and on-demand release of diverse categories ofdrugs. This unique performance can adapt to the diverse demands during different stages of wound healing in a porcine endoscopic surgery model. These results indicate an appealing prospect for new application of star polymers as a good submucosal injection material in endoscopic treatments.

Structural Homogeneity of Macromolecular Networks by End-to-End Click Chemistry between Discrete Tetrahedral Star Macromolecules.

Cross-linking via the end-to-end click chemistry of multiarm star polymers creates polymer networks with minimal inhomogeneities. Although it has been suggested that the mechanical and swelling properties of such networks depend on the absence of defects, the structural details of homogeneous networks created by this method have not yet been studied at the molecular level. Here, we report the synthesis of discrete tetrahedral star macromolecules (dTSMs) composed of polylactide (PLA) arms with discrete molecular weight and sequence. Polymer networks prepared by 4 × 4 cross-linking by Cu-free strain-promoted cyclooctyne-azide click chemistry (SPAAC) reaction exhibited a high degree of swelling (>40 fold by weight) in solvents without sacrificing mechanical robustness (elastic modulus >4 kPa). The structural details of the networks were investigated by network disassembly spectrometry (NDS) using MALDI-TOF mass spectrometry. By implementing a cleavable repeating unit in the discrete PLA arms of dTSM in a sequence-specific manner, the networks could be disassembled into fragments having discrete molecular weights precisely representing their connectivity in the network. This NDS analysis confirmed that end-to-end click reactions of dTSM networks resulted in the formation of a homogeneous network above the critical concentration (∼10 w/v%) of building blocks in the solution.

PH-sensitive multi-arm star polyampholytes: A novel approach for simultaneous adsorption of anionic and cationic dyes

This study introduces star-shaped polyampholyte adsorbents, comprising poly(acrylic acid) cores and poly(2-(dimethylamino)ethyl methacrylate) arms. Reversible addition fragmentation chain-transfer (RAFT) polymerization and distillation-precipitation approach were utilized to prepare star polyampholytes in different monomer/RAFT agent ratios (70, 130, and 200). Well-defined and star-like structures were validated employing proton nuclear magnetic resonance, gel permeation chromatography, and differential scanning calorimetry. pH-dependent self-assembled particle morphologies were scrutinized using field emission scanning electron microscopy and dynamic light scattering. The adsorbents exhibited substantial potential for efficient dye removal from wastewater, attaining up to 76.6% adsorption (pH = 2) for methylene orange and 48.3% (pH = 10) for methylene blue in single-dye systems using Star AA_DMAEMA_200 and Star AA_DMAEMA_130, respectively. Dual-dye systems revealed captivating synergistic interactions, showcasing intricate behaviors between dyes. The influence of molecular weight intricacies on adsorption dynamics unveiled a spectrum of diverse trends, underscoring the absorbents' versatility. These findings not only deepen our understanding of the adsorption process but also underscore the paramount potential of star-shaped polyampholyte absorbents in addressing complex environmental color removal challenges.

Multi-Stimuli Responsive Sequence Defined Multi-Arm Star Diblock Copolymers for Controlled Drug Release.

Star-shaped polymeric materials provide very high efficiency toward various engineering and biomedical applications. Due to the absence of straightforward and versatile synthetic protocols, the synthesis of sequence-defined star-shaped (co)polymers has remained a major challenge. Here, a facile approach is developed that allows synthesis of a series of unprecedented discrete, multifunctional four-, six-, and eight-arm star-shaped complex macromolecular architectures based on a well-defined triple (thermo/pH/light)-stimuli-responsive poly(N-isopropylacrylamide)-block-poly(methacrylic acid)-umbelliferone (PNIPAM-b-PMAA)n-UMB diblock copolymer, based on temperature responsive PNIPAM segment, pH-responsive PMAA segment, and photoresponsive UMB end groups. Thus, developed star-shaped copolymers self-assemble in water to form spherical nanoaggregates of diameter 90 ± 20 nm, as measured by FESEM. The star-shaped copolymer's response to external stimuli has been assessed against changes in temperature, pH, and light irradiation. The star-shaped copolymer was employed as a nanocarrier for pH responsive release of an anticancer drug, doxorubicin. This study opens up new avenues for efficient star-shaped macromolecular architecture construction for engineering and biomedical applications.

Enhancement of Epoxy Thermosets with Hyperbranched and Multiarm Star Polymers: A Review.

Hyperbranched polymers and multiarm star polymers are a type of dendritic polymers which have attracted substantial interest during the last 30 years because of their unique properties. They can be used to modify epoxy thermosets to increase their toughness and flexibility but without adversely affecting other properties such as reactivity or thermal properties. In addition, the final properties of materials can be tailored by modifying the structure, molecular weight, or type of functional end-groups of the hyperbranched and multiarm star polymers. In this review, we focus on the modification of epoxy-based thermosets with hyperbranched and multiarm star polymers in terms of the effect on the curing process of epoxy formulations, thermal, mechanical, and rheological properties, and their advantages in fire retardancy on the final thermosets.

High density star poly HEMA containing bis-indole rich dendrimer inner core for integrated anti-fouling and anti-bacterial coating applications

Multi-arm star polymers with controlled molecular architecture suitable to be used as biomaterials are rapidly developing area of research. Herein, G2 and G3 polyurethane dendrimers containing bio-active bis-indolyl building blocks were converted into corresponding multifunctional ATRP initiators via a single-step reaction and characterized thoroughly. Polymerization of 2-hydroxethyl methacrylate (HEMA) monomer for different time duration using these initiators and CuBr/2,2′-bpy ATRP system yielded star PHEMAs with molecular weight (Mn) in the range of 2.79 × 104 – 4.52 × 105 g mol−1; the poly dispersity indices were in the range of 1.16–1.49. Glass transition temperature of these star PHEMAs was found significantly low compared to the linear PHEMA. Contact angle measurements carried out on the surface of polyethylene terephthalate (PET) film coated with these polymers confirmed that these polymers are more hydrophilic compared to the un-coated PET surface. The integrated anti-fouling and anti-bacterial properties of these polymer coatings were studied with two common pathogens namely E. coli and P. aeruginosa and found that the binding of both of these bacterial cells either in live or dead form was negligibly low in the polymer coated PET surface compared to un-coated films and also found that the percentage of live cells was low compared to dead cells.

PH-responsive aggregation control of multiarm star polymers depending on the ionic segment sequence of arm polymers

pH-responsive aggregation control of multiarm star polymers depending on the ionic segment sequence of arm polymers

Star-shaped Poly(hydroxybutyrate)s from bio-based polyol cores via zinc catalyzed ring-opening polymerization of β-Butyrolactone

The ring-opening polymerization (ROP) of cyclic esters using multifunctional initiators is an efficient methodology that allows the preparation of polyesters with well-defined architectures. Here a series of star-shaped poly(β-hydroxybutyrates) (PHBs) has been synthesized by ROP of β-butyrolactone (BBL) with an amido-oxazolinate zinc catalyst. The star-shaped structure is constructed via a core-first approach, in which several bio-based multifunctional alcohols serve as the initiator for ROP. Specifically, three-, four-, and multi-armed star polymers are obtained and characterized by various techniques including NMR, GPC, TGA, and DSC, and the incorporation of the core structure in the star-shaped PHBs has been confirmed. The thermal properties can be modified by changing the arm number and arm length of PHBs, and the thermal stability decreases as the number of arms increases when they have the same arm lengths. The wetting behavior determined from AFM studies demonstrates a minimum in the macroscopic contact angle as a function of the number of arms of a star-shaped PHB.

Universal Polymeric-to-Colloidal Transition in Melts of Hairy Nanoparticles.

Two different classes of hairy self-suspended nanoparticles in the melt state, polymer-grafted nanoparticles (GNPs) and star polymers, are shown to display universal dynamic behavior across a broad range of parameter space. Linear viscoelastic measurements on well-characterized silica-poly(methyl acrylate) GNPs with a fixed core radius (Rcore) and grafting density (or number of arms f) but varying arm degree of polymerization (Narm) show two distinctly different regimes of response. The colloidal Regime I with a small Narm (large core volume fraction) is characterized by predominant low-frequency solidlike colloidal plateau and ultraslow relaxation, while the polymeric Regime II with a large Narm (small core volume fractions) has a response dominated by the starlike relaxation of partially interpenetrated arms. The transition between the two regimes is marked by a crossover where both polymeric and colloidal modes are discerned albeit without a distinct colloidal plateau. Similarly, polybutadiene multiarm stars also exhibit the colloidal response of Regime I at very large f and small Narm. The star arm retraction model and a simple scaling model of nanoparticle escape from the cage of neighbors by overcoming a hopping potential barrier due to their elastic deformation quantitatively describe the linear response of the polymeric and colloidal regimes, respectively, in all these cases. The dynamic behavior of hairy nanoparticles of different chemistry and molecular characteristics, investigated here and reported in the literature, can be mapped onto a universal dynamic diagram of f/[Rcore3/ν0)1/4] as a function of (Narmν0f)/(Rcore3), where ν0 is the monomeric volume. In this diagram, the two regimes are separated by a line where the hopping potential ΔUhop is equal to the thermal energy, kBT. ΔUhop can be expressed as a function of the overcrowding parameter x (i.e., the ratio of f to the maximum number of unperturbed chains with Narm that can fill the volume occupied by the polymeric corona); hence, this crossing is shown to occur when x = 1. For x > 1, we have colloidal Regime I with an overcrowded volume, stretched arms, and ΔUhop > kBT, while polymeric Regime II is linked to x < 1. This single-material parameter x can provide the needed design principle to tailor the dynamics of this class of soft materials across a wide range of applications from membranes for gas separation to energy storage.

Synthesis of multicyclic polymers by intramolecular cyclization via a “tail-biting” strategy and their characterization

This paper elaborates the preparation of “flower-shaped” tricyclic and hexacyclic polymers by intramolecular cyclization via a “tail-biting” strategy. Multifunctional initiators with equal amounts of alkynyl groups and 2-bromoisobutyrate groups are synthesized by catalyst-free azide-alkynyl click reaction, and then used in atom transfer radical polymerization (ATRP) of styrene to afford multiarm star polystyrenes (PS). After azidation of terminal bromines, multicyclic polymers are prepared by intramolecular cyclization via Cu-catalyzed azide-alkynyl cycloaddition (CuAAc) click reaction between terminal azide groups and interior alkynyl groups. Structures of tricyclic and hexacyclic polystyrenes are characterized by 1H NMR, GPC and FT-IR. Fluorescence emissions of initiators and polymers are observed, and the influence of topology on fluorescence intensity is discussed.

Multiarm Star-Shaped Polydimethylsiloxanes with a Dendritic Branching Center.

New multiarm stars have been synthesized based on polylithium derivatives of high-generation carbosilane dendrimers. In the synthesis of multiarm stars based on the eighth-generation dendrimer, steric hindrances were observed even during the synthesis of a polylithium initiator. Subsequently, this led to chain transfer reactions between growing arms, as well as other side effects. As a result, dense nanogel formations with a higher tendency of ordering than in classical objects of this type were isolated from the reaction mixture. The study of the rheology of multiarm stars based on sixth-generation dendrimers made it possible to determine the activation energies of viscous flow in these objects, which makes it possible to consider them as objects with a macromolecular nature and a reptation flow mechanism.

Layers of Distinct Mobility in Densely Grafted Dendrimer Arborescent Polymer Hybrids.

Melts of multiarm stars of 1,4-polybutadiene (dendrimer arborescent hybrids) with very high branching functionality (f) and small arm molar mass behave as jammed colloids and show distinct layers of segmental mobility. Three mobility layers were identified, comprising outer, intermediate, and near-core segments, all displaying a Vogel-Fulcher-Tammann temperature dependence. The respective glass temperatures increase as f^{1/2}. Our findings pave the way for further progress in this field by reconsidering previous theoretical treatments based on a single friction coefficient in hybrid nanoparticles such as densely grafted stars.

Multiarm Star Polymers. Fundamental Aspects. A Review

Multiarm Star Polymers. Fundamental Aspects. A Review

Antimicrobial Activity of Hybrid Nanomaterials Based on Star and Linear Polymers of N,N'-Dimethylaminoethyl Methacrylate with In Situ Produced Silver Nanoparticles.

Well-defined linear and multi-arm star polymer structures were used as the templates for in situ synthesis and stabilization of silver nanoparticles (AgNPs). This approach led to hybrid nanomaterials with high stability and antibacterial activity to both Gram-positive and Gram-negative bacterial strains. The ecologically friendly so called “green” synthesis of nanomaterials was performed through AgNPs preparation in the aqueous solutions of star and linear poly(N,N′-dimethylaminoethyl methacrylate)s (PDMAEMAs); the process was followed with time. The size, shape, and zeta potential of the obtained hybrids were determined. To our knowledge, this is the first time that the antibacterial activity of PDMAEMA hybrid nanomaterial against Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa was investigated and assessed by minimum inhibitory concentration (MIC) and minimum biocidal concentration (MBC). Completely quaternized with ethyl bromide, star and linear PDMAEMAs were used in comparative biological tests. The modification of the polymers with in situ-formed AgNPs increased the antibacterial properties against all studied strains of bacteria by several times in comparison to non-modified polymers and quaternized polymers. These results yield novel nanohybrid materials that can be useful for applications in medicine and biology.

Synthesis of zinc-porphyrin based multi-arm star Poly(N-isopropylacrylamide) and the effect of topology on photocatalytic performance

Zinc-porphyrin based multi-arm star polymers (ZnTHPP-(PNIPAM-Br)n) with poly(N-isopropylacrylamide) as n = 1–4 arms respectively were successfully prepared via atom transfer radical polymerization (ATRP) initiated by four zinc porphyrin initiators (ZnTHPP-nBr) with n = 1–4 initiator groups accordingly, and these structures of star-shaped polymers were characterized by FT-IR, UV–Vis, 1H NMR and GPC. They were used as photocatalyst for the degradation of Rhodamine B(RhB) under visible-light irradiation to study the effect of topology on photocatalytic activity, it was found as the number of arms increased, the photocatalytic activity and stability of the star polymer increased. The four-arm star polymer (ZnTHPP-(PNIPAM-Br)4) was shown the best photocatalytic performance and stability, could be recycled by warming.

Multiarm star polymers based on thiol–ene photoclick cyclodextrin cores

Highly efficient synthesis of multifunctional initiators based on cyclodextrin (CD) cores was achieved by a thiol–ene photoclick strategy. They were successfully employed in a “core-first” approach to prepare multiarm star polymers via ATRP.

Probing Sol–Gel Matrices and Dynamics of Star PEG Hydrogels Near Overlap Concentration

Although numerous studies have been conducted to describe the gelation of multi-arm star polymers, reports on the relationship among rheological quantities, overlap concentration (c*), and microstr...

Interaction potential between polymer grafted nanosheets in an architecturally dissimilar polymer matrix

We examine the polymer mediated interaction between two brush coated nanosheets to address the quality of dispersion of clay sheets in a polymer matrix. The distance dependent potential curve for a pair of interacting nanosheets is constructed using self-consistent field theory. We study the role of polymer chain architecture, in addition to the size and chemical dissimilarities between free and grafted chains, in controlling the nature of interaction between finite sized nanosheets. By replacing linear polymeric chains of the matrix polymer with multi-armed star polymer of same degree of polymerization, the strength of attraction is found to be weakened and is completely eliminated for high degree of branching. The compactness of star molecule overcomes entropy driven depletion between nanosheets leading to wetting of brush with purely repulsive potential, indicative of exfoliated dispersion. Thus, the quality of dispersion can be improved by altering the architecture of free and grafted polymeric chains.

Transition from Confined to Bulk Dynamics in Symmetric Star–Linear Polymer Mixtures

We report on the linear viscoelastic properties of mixtures comprising multiarm star (as model soft colloids) and long linear chain homopolymers in a good solvent. In contrast to earlier works, we investigated symmetric mixtures (with a size ratio of 1) and showed that the polymeric and colloidal responses can be decoupled. The adopted experimental protocol involved probing the linear chain dynamics in different star environments. To this end, we studied mixtures with different star mass fraction, which was kept constant while linear chains were added and their entanglement plateau modulus ($G_p$) and terminal relaxation time ($\tau_d$) were measured as functions of their concentration. Two distinct scaling regimes were observed for both $G_p$ and $\tau_d$: at low linear polymer concentrations, a weak concentration dependence was observed, that became even weaker as the fraction of stars in the mixtures increased into the star glassy regime. On the other hand, at higher linear polymer concentrations, the classical entangled polymer scaling was recovered. Simple scaling arguments show that the threshold crossover concentration between the two regimes corresponds to the maximum osmotic star compression and signals the transition from confined to bulk dynamics. These results provide the needed ingredients to complete the state diagram of soft colloid-polymer mixtures and investigate their dynamics at large polymer-colloid size ratios. They also offer an alternative way to explore aspects of the colloidal glass transition and the polymer dynamics in confinement. Finally, they provide a new avenue to tailor the rheology of soft composites.

Fast capture and multiplexed detection of short multi-arm DNA stars in solid-state nanopores.

Fast and multiplexed detection of low-abundance disease biomarkers at the point-of-need would transform medicine. Nanopores have gained attention as single-molecule counters to electrically detect a range of biological molecules in a handheld format, but challenges remain before diagnostic applications can emerge. For solid-state nanopore sensors, the specificity of the ionic current signatures and the rate of target capture required to simultaneously recognize and rapidly count a mixture of molecular targets in a complex sample are active areas of research. Herein, we study the capture and translocation characteristics of short N-arm star shaped DNA nanostructures to evaluate their potential as a family of surrogate label molecules for biomarkers of interest, designed for fast and reliable multiplexed detection based on conductance blockages. Simple hybridization of a varying number of short, easily synthesized 50 bp ssDNA strands allows the number of arms in the star shape DNA to be controlled from N = 3 to 12. By introducing more arms to the nanostructures, we show that we can controllably increase the nanopore signal-to-noise ratio for a range of pore sizes, producing conductance blockages which increase linearly with the number of arms, and we demonstrate conductance-based multiplexing through simultaneous detection of three such nanostructures. Moreover, the increased molecular signal strength facilitates detection under salt concentration asymmetries, allowing for a capture rate enhancement of two orders of magnitude without compromising the nanopore temporal and ionic signals. Together, these attributes (strong signal, multiplexing potential and increased counting rate) make the N-arm star DNA-based nanostructures promising candidates as proxy labels for the detection of multiple biomarkers of interest in future high sensitivity single-molecule solid-state nanopore-based assays.