Chain terminal group leads to distinct thermoresponsive behaviors of linear PNIPAM and polymer analogs

Interaction of Colloidal Particulates with Dynamic Microstructured Polymer Brushes: Computer Simulations

Microstructured surfaces composed of adherent domains and stimuli-responsive polymer domains (that undergo swelling-shrinking upon stimuli, e.g., temperature change around the low critical solution temperature, LCST) were proven to catch and release colloidal particulates (CP) effectively. Such structures have the advantage over just uniform stimuli-responsive surfaces because on the microstructured surface, sticky and pushing-off properties are decoupled so that the properties of each domain can be adjusted in a broad range. We consider the adsorption and desorption of particulates on the stimuli-responsive surface made of tethered poly(acrylic acid) (PAA) domains that contain the adherent functional motifs and thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) domains, both arranged into regular micropatterns. At temperatures above the PNIPAM LCST, the PNIPAM domains collapse in water, allowing the adsorption of the particulates on the PAA regions. When cooled below the LCST, PNIPAM swells and pushes particles off the surface. We develop coarse-grained models for the CP on the microstructured surfaces and use computer simulations to analyze the optimal structure of such surfaces in terms of the PAA chain length, types of the micropatterns, the ratio between surface areas of the PAA and PNIPAM domains, and micropattern graininess in relation to particle dimensions. The study is relevant and motivated by the problems of harvesting and sorting prokaryotic and eukaryotic cells on microstructured surfaces.

Nano- and meso-scale aggregation of poly(N-isopropylacrylamide) below the lower critical solution temperature: A wide-angle dynamic light scattering study

Poly-N-isopropylacrylamide (PNIPAm), a thermorresponsive polymer, highly soluble in water below its lower critical solution temperature (LCST), is widely used in biomedical applications like drug delivery. Being able to measure PNIPAm size and aggregation state in solution quickly, inexpensively, and accurately below the LCST is critical when stoichiometric particle or molecular ratios are required. Dynamic light scattering (DLS) is probably the most widely available, and inexpensive nanoparticle sizing technique, but there are limitations with respect to sample polydispersity. Here, we first investigated factors governing the ability of DLS to accurately measure PNIPAm size in solution at 25 °C as part of a quality study of five different molecular weight, commercially sourced PNIPAm. All samples were polydisperse and accurate particle size distribution (PSD) data was only obtained from distribution fitting, being consistent and accurate down to ∼ 0.1 wt%. In water at 1 wt%, Rh, extracted from distribution fitting: 12.4 ± 0.6 nm (55 kDa), 10.0 ± 0.22 nm (38 kDa), 6.2 ± 0.15 nm (28.5 kDa), and 9.7 ± 0.14 nm (20-25 kDa) were significantly higher than that expected for single PNIPAm chains in solution. Measurements in different buffers of varying pH (7.4-5.0) yielded similar sizes (Rh of 6-15 nm) and polydispersity indicating that these were stable aggregates. These aggregates could be broken down with Triton-X but not with sodium dodecyl sulphate, ultrasound, or by heating above the LCST and then cooling. We suggest that this nanoscale aggregation and increased polydispersity was caused a variety of factors including by solid-state aging during prolonged storage (>5 years) induced by water adsorption, and/or manufacturing processes. Stirring was found to produce larger, meso-scale (Rh > 150 nm), soluble aggregates and the rate of formation of these meso-particles was linear with stirring time (with a concomitant linear decrease in the faction of original nanoscale aggregates). Meso-particle formation was not correlated with MW, but was inversely correlated to polymer concentration suggesting that aggregation was driven by adsorption at air/liquid interfaces rather than solution phase collisions. In conclusion, PNIPAm particle size and distribution was highly dependent on multiple factors including source, storage conditions, and exposure to air-water interfaces. Standard wide angle DLS is however an effective and rapid method for identifying and quantifying PNIPAm aggregation.

Preparation of an antibacterial, injectable, thermosensitive, and physically cross-linked hemostatic hydrogel based on quaternized linetype poly(N-isopropylacrylamide)

Bleeding and wound infection are two significant potential risks to life and health. While antibacterial hemostatic hydrogels can meet the requirements for hemostasis and the prevention of wound infections, the inclusion of antibacterial agents inevitably complicates the regulation of interactions between components, making it difficult to synergistically control the mechanical and antibacterial properties of the hydrogels, which limits the overall hydrogel performance. In this study, we propose the use of linear poly(N-isopropylacrylamide) (L-P-(C6H15N+)) with an antibacterial quaternary ammonium end-group for preparing hydrogels, rather than conventionally adding antibacterial agents. An injectable, highly antibacterial and wet-adhesive double-network hemostatic hydrogel was constructed using L-P-(C6H15N+), gelatin (G), and hyaluronic acid (HA). The comprehensive properties of the hydrogel could be adjusted through changing the molecular weight of the L-P-(C6H15N+) and the end-group effects. The G/HA/L-P-(C6H15N+) hydrogel demonstrated a gel time of 12.2-14 s, an adhesion strength of 26.9 ± 2.0 kPa and a burst pressure of 264 ± 20 mmHg. It also exhibited strong antibacterial activity against E. coli (93 ± 2.7%) and S. aureus (97 ± 3.2%), with satisfactory biocompatibility. Additionally, the hydrogel demonstrated good blood clotting ability in vitro and achieved rapid hemostasis (<15 s) in vivo. This work offers a simple and efficient strategy to fabricate high-performance smart antibacterial hemostatic hydrogels.

Injectable Fluorescent Bottlebrush Polymers for Interventional Procedures and Biomedical Imaging

Injectable biomaterials play a vital role in modern medicine, offering tailored functionalities for diverse therapeutic and diagnostic applications. In ophthalmology, for instance, viscoelastic materials are crucial for procedures such as cataract surgery but often leave residues, increasing postoperative risks. This study introduces injectable fluorescent viscoelastics (FluoVs) synthesized via one-step controlled radical copolymerization of oligo(ethylene glycol) acrylate and fluorescein acrylate. These bottlebrush-shaped polymers exhibit enhanced fluorescence intensity for improved traceability and facile removal postsurgery. To prevent aggregation, charged terpolymers were synthesized, ensuring intra- and intermolecular electrostatic repulsion. Dynamic light scattering and energy-conserved dissipative particle dynamics simulations revealed how the fluorescein content and monomer sequence affect the hydrodynamic size of these copolymers. Biocompatibility assessments showed that FluoVs maintained cell viability comparable to commercial hydroxypropyl methylcellulose and nonfluorescent poly(oligo(ethylene glycol) acrylate) controls. The FluoVs combine high fluorescence intensity, low viscosity, and excellent biocompatibility, offering intraoperative traceability and significant advancements for ocular and bioimaging applications.

Analysis of the internal motions of thermoresponsive polymers and single chain nanoparticles

Data-driven techniques, such as proper orthogonal decomposition (POD) and uniform manifold approximation & projection (UMAP), are powerful methods for understanding polymer behavior in complex systems that extend beyond ideal conditions. They are based on the principle that low-dimensional behaviors are often embedded within the structure and dynamics of complex systems. Here, the internal motions of a thermoresponsive, LCST polymer are investigated for two cases: (1) the coil-to-globule transition that occurs as the system is heated above its critical temperature and (2) intramolecularly crosslinked, single chain nanoparticles (SCNPs) both above and below the critical temperature (TC). Our results demonstrate that POD can successfully extract the key features of the dynamics for both polymer globules and SCNPs. In the globular state, our results show that the relaxation modes are distorted relative to the coil state and relaxation times decrease upon chain collapse. After randomly crosslinking a globule to produce a SCNP, we observe a further distortion of the relaxation modes that depends strongly upon the particular set of monomers that are crosslinked. Yet, different sets of crosslinked monomers produce similar relaxation times for the SCNP. We observe that for SCNPs below the critical temperature, the relaxation times decrease with increasing crosslink density while above the critical temperature, they increase as crosslink density increases. Finally, using UMAP we categorize the local structure of SCNPs and examine the influence of the local structure on SCNP relaxation dynamics.

Thermoresponsive Property of Poly(N,N-bis(2-methoxyethyl)acrylamide) and Its Copolymers with Water-Soluble Poly(N,N-disubstituted acrylamide) Prepared Using Hydrosilylation-Promoted Group Transfer Polymerization

The group-transfer polymerization (GTP) of N,N-bis(2-methoxyethyl)acrylamide (MOEAm) initiated by Me2EtSiH in the hydrosilylation-promoted method and by silylketene acetal (SKA) in the conventional method proceeded in a controlled/living manner to provide poly(N,N-bis(2-methoxyethyl)acrylamide) (PMOEAm) and PMOEAm with the SKA residue at the α-chain end (MCIP-PMOEAm), respectively. PMOEAm-b-poly(N,N-dimethylacrylamide) (PDMAm) and PMOEAm-s-PDMAm and PMOEAm-b-poly(N,N-bis(2-ethoxyethyl)acrylamide) (PEOEAm) and PMOEAm-s-PEOEAm were synthesized by the block and random group-transfer copolymerization of MOEAm and N,N-dimethylacrylamide or N,N-bis(2-ethoxyethyl)acrylamide. The homo- and copolymer structures affected the thermoresponsive properties; the cloud point temperature (Tcp) increasing by decreasing the degree of polymerization (x). The chain-end group in PMOEAm affected the Tcp with PMOEAmx > MCIP-PMOEAmx. The Tcp of statistical copolymers was higher than that of block copolymers, with PMOEAmx-s-PDMAmy > PMOEAmx-b-PDMAmy and PMOEAmx-s-PEOEAmy > PMOEAmx-b-PEOEAmy.

Structure of Single-Chain Nanoparticles under Crowding Conditions: A Random Phase Approximation Approach

The conformation of poly(methyl methacrylate) (PMMA)-based single-chain nanoparticles (SCNPs) and their corresponding linear precursors in the presence of deuterated linear PMMA in deuterated dimethylformamide (DMF) solutions has been studied by small-angle neutron scattering (SANS). The SANS profiles were analyzed in terms of a three-component random phase approximation (RPA) model. The RPA approach described well the scattering profiles in dilute and crowded solutions. Considering all the contributions of the RPA leads to an accurate estimation of the single chain form factor parameters and the Flory-Huggins interaction parameter between PMMA and DMF. The value of the latter in the dilute regime indicates that the precursors and the SCNPs are in good solvent conditions, while in crowding conditions, the polymer becomes less soluble.

Fibrillar biocompatible colloidal gels based on cellulose nanocrystals and poly(N-isopropylacrylamide) for direct ink writing

HYPOTHESIS

Hydrogels based on cellulose nanocrystals (CNC) have attracted great interest because of their sustainability, biocompatibility, mechanical strength and fibrillar structure. Gelation of colloidal particles can be induced by the introduction of polymers. Existing examples include gels based on CNC and derivatives of cellulose or poly(vinyl alcohol), however, gel structure and their application for extrusion printing were not shown. Hence, we rationalize formation of colloidal gels based on mixture of poly(N-isopropylacrylamide) (PNIPAM) and CNC and control their structure and mechanical properties by variation of components ratio.

EXPERIMENTS

State diagram for colloidal system based on mixture of PNIPAM and CNC were established at 25 and 37 °C. Biocompatibility, fiber diameter and rheological properties of the gels were studied for different PNIPAM/CNC ratio.

FINDINGS

We show that depending on the ratio between PNIPAM and CNC, colloidal system could be in sol or gel state at 25 °C and at gel state or phase separated at 37 °C. Physically crosslinked hydrogels were thermosensitive and could reversibly change it transparency from translucent to opaque in biologically relevant temperature range. These colloidal hydrogels were biocompatible, had fibrillar structure and demonstrate shear-thinning behavior, which makes them a promising material for bioapplications related to extrusion printing.

Investigating Fundamental Principles of Nonequilibrium Assembly Using Temperature-Sensitive Copolymers

Both natural biomaterials and synthetic materials benefit from complex energy landscapes that provide the foundation for structure-function relationships and environmental sensitivity. Understanding these nonequilibrium dynamics is important for the development of design principles to harness this behavior. Using a model system of poly(ethylene glycol) methacrylate-based thermoresponsive lower critical solution temperature (LCST) copolymers, we explored the impact of composition and stimulus path on nonequilibrium thermal hysteretic behavior. Through turbidimetry analysis of nonsuperimposable heat-cool cycles, we observe that LCST copolymers show clear hysteresis that varies as a function of pendent side chain length and hydrophobicity. Hysteresis is further impacted by the temperature ramp rate, as insoluble states can be kinetically trapped under optimized temperature protocols. This systematic study brings to light fundamental principles that can enable the harnessing of out-of-equilibrium effects in synthetic soft materials.

Lipidation Alters the Structure and Hydration of Myristoylated Intrinsically Disordered Proteins

Lipidated proteins are an emerging class of hybrid biomaterials that can integrate the functional capabilities of proteins into precisely engineered nano-biomaterials with potential applications in biotechnology, nanoscience, and biomedical engineering. For instance, fatty-acid-modified elastin-like polypeptides (FAMEs) combine the hierarchical assembly of lipids with the thermoresponsive character of elastin-like polypeptides (ELPs) to form nanocarriers with emergent temperature-dependent structural (shape or size) characteristics. Here, we report the biophysical underpinnings of thermoresponsive behavior of FAMEs using computational nanoscopy, spectroscopy, scattering, and microscopy. This integrated approach revealed that temperature and molecular syntax alter the structure, contact, and hydration of lipid, lipidation site, and protein, aligning with the changes in the nanomorphology of FAMEs. These findings enable a better understanding of the biophysical consequence of lipidation in biology and the rational design of the biomaterials and therapeutics that rival the exquisite hierarchy and capabilities of biological systems.

Role of chain architecture in the solution phase assembly and thermoreversibility of aqueous PNIPAM/silyl methacrylate copolymers

Stimuli-responsive polymers functionalized with reactive inorganic groups enable creation of macromolecular structures such as hydrogels, micelles, and coatings that demonstrate smart behavior. Prior studies using poly(N-isopropyl acrylamide-co-3-(trimethoxysilyl)propyl methacrylate) (P(NIPAM-co-TMA)) have stabilized micelles and produced functional nanoscale coatings; however, such systems show limited responsiveness over multiple thermal cycles. Here, polymer architecture and TMA content are connected to the aqueous self-assembly, optical response, and thermo-reversibility of two distinct types of PNIPAM/TMA copolymers: random P(NIPAM-co-TMA), and a 'blocky-functionalized' copolymer where TMA is localized to one portion of the chain, P(NIPAM-b-NIPAM-co-TMA). Aqueous solution behavior characterized via cloud point testing (CPT), dynamic light scattering (DLS), and variable-temperature nuclear magnetic resonance spectroscopy (NMR) demonstrates that thermoresponsiveness and thermoreversibility over multiple cycles is a strong function of polymer configuration and TMA content. Despite low TMA content (≤2% mol), blocky-functionalized copolymers assemble into small, well-ordered structures above the cloud point that lead to distinct transmittance behaviors and stimuli-responsiveness over multiple cycles. Conversely, random copolymers form disordered aggregates at elevated temperatures, and only exhibit thermoreversibility at negligible TMA fractions (0.5% mol); higher TMA content leads to irreversible structure formation. This understanding of the architectural and assembly effects on the thermal cyclability of aqueous PNIPAM-co-TMA can be used to improve the scalability of responsive polymer applications requiring thermoreversible behavior, including sensing, separations, and functional coatings.

Thermoresponsive Self-Assembly of Twofold Fluorescently Labeled Block Copolymers in Aqueous Solution and Microemulsions

A nonionic double hydrophilic block copolymer with a long permanently hydrophilic and a small thermoresponsive block is synthesized by reversible addition-fragmentation chain-transfer polymerization (RAFT). By employing a specifically designed chain-transfer agent, the polymer is functionalized with complementary end groups which are suited for Förster resonance energy transfer (FRET). The end group attached to the permanently hydrophilic block of poly(N,N-dimethylacrylamide) pDMAm is designed as a permanently hydrophobic segment ("sticker") comprising a long alkyl chain and the 4-aminonaphthalimide fluorophore. The other end attached to the thermoresponsive block of poly(N-isopropylacrylamide) pNiPAm incorporates a coumarin fluorophore. The temperature-dependent self-assembly of the twofold fluorescently labeled copolymer is studied in pure aqueous solution as well as in an o/w microemulsion by several techniques including turbidimetry, dynamic light scattering (DLS), and fluorescence spectroscopy. It is compared to the behaviors of the analogous twofold-labeled pDMAm and pNiPAm homopolymer references. The findings indicate that the block copolymer behaves as a polymeric surfactant at low temperatures, with one relatively small hydrophobic end block and an extended hydrophilic chain forming "hairy micelles". At elevated temperatures above the LCST phase transition of the pNiPAm block, however, the copolymer behaves as an associative telechelic polymer with two nonsymmetrical hydrophobic end blocks, which do not mix. Thus, instead of a network of bridged "flower micelles", large dynamic aggregates are formed. These are connected alternatingly by the original micellar cores as well as by clusters of the collapsed pNiPAm blocks. This type of structure is even more favored in the o/w microemulsion than in pure aqueous solution, as the microemulsion droplets constitute an attractive anchoring point for the hydrophobic dodecyl sticker but not for the collapsed pNiPAm chains.

SILICON-CONTAINING OLIGOMERIC AZOINITIATORS IN THE SYNTHESIS OF BLOCK COPOLYMERS

A solvothermal synthetic pathway and functional polymer styabilizers was used for synthesis of fine silver structures of different architecture. Using polyvinylpyrrolidone as a stabilizer silver micronized wires with a diameter of 3,8–4,2 μm and aspect ratio of up to 30 were prepared. XRD technique was applied for qualitative determination of silver metal structures. New thermoresponse composite hydrogels with a structure of semi-IPNs were prepared from cross-linked polyvinyl alcohol, linear highly hydrophilic poly(2-ethyl-2-oxazoline) (PEtOx) and as-synthesized silver micro-sized wires. Effect of a structure and a composition of the polymer matrix, and inorganic anisotropic filler on structure arrangement of composite hydrogels were evaluated by DMA studies. A presence of linear hydrophilic PEtOx and anisotropic metal filler in PVA matrix reduces storage modulus Е’ from 275 to 222–230 MPa and increases loss modulus Е” up to 45,5 MPa at room temperature measurements that partially initiated by poor structuration ability of the composites under high solvation level of polymer matrices. Increasing temperature leads to redistribution of hydrogen bonds network and hybridization of PVA nad PEtOx macrochains and enhances energy dissipation ability of unfilled hydrogel. A filler due to conjugation with amine-functionalized PEtOx chains and its localization closed to a surface of metal supresses polymer-polymer interactions and elasticity parameters of composite matrix drops down. As a result, diffusion and permeability coefficients of composite hydrogels reaches 1,06–1,52·10–9 cm2/s and 0,83–1,09·10-9 g/(cm·s), respectively, that higher in comparison with cross-linked PVA matrices. A presence of hydrogen bonds of different energy in hydrogels provides an appearance of multiple relaxation transitions due to different macrochain mobility in a bulk of polymer matrix. Differences of temperature interval of LCTS for hydrogels were found from analysis Е”(T)/dT (62–70 °С) and Δχ(T)/dT (67–70 °С) dependencies are interrelated with kinetic pecularities of diffusion processes that are able to suppress a phase separation at the temperatures closed to LCTS. Phase inversion processes for hydrogel containing 5 % of PEtOx at LCTS are accompanied by desorption of 32–73 % of sorbate. Moreover, thermoresponsive properties of the hydrogels filled with metallic silver wires are higher than that of the unfilled semi-IPNs.

Determining population densities in bimodal micellar solutions using contrast-variation small angle neutron scattering

Self-assembly of amphiphilic polymers in water is of fundamental and practical importance. Significant amounts of free unimers and associated micellar aggregates often coexist over a wide range of phase regions. The thermodynamic and kinetic properties of the microphase separation are closely related to the relative population density of unimers and micelles. Although the scattering technique has been employed to identify the structure of micellar aggregates as well as their time-evolution, the determination of the population ratio of micelles to unimers remains a challenging problem due to their difference in scattering power. Here, using small-angle neutron scattering (SANS), we present a comprehensive structural study of amphiphilic n-dodecyl-PNIPAm polymers, which shows a bimodal size distribution in water. By adjusting the deuterium/hydrogen ratio of water, the intra-micellar polymer and water distributions are obtained from the SANS spectra. The micellar size and number density are further determined, and the population densities of micelles and unimers are calculated to quantitatively address the degree of micellization at different temperatures. Our method can be used to provide an in-depth insight into the solution properties of microphase separation, which are present in many amphiphilic systems.

The Two Phase Transitions of Hydrophobically End-Capped Poly(N-isopropylacrylamide)s in Water

High-sensitivity differential scanning calorimetry (HS-DSC) thermograms of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions present a sharp unimodal endotherm that signals the heat-induced dehydration/collapse of the PNIPAM chain. Similarly, α,ω-di-n-octadecyl-PNIPAM (C18-PN-C18) aqueous solutions exhibit a unimodal endotherm. In contrast, aqueous solutions of α,ω-hydrophobically modified PNIPAMs with polycyclic terminal groups, such as pyrenylbutyl (Py-PN-Py), adamantylethyl (Ad-PN-Ad), and azopyridine- (C12-PN-AzPy) moieties, exhibit bimodal thermograms. The origin of the two transitions was probed using microcalorimetry measurements, turbidity tests, variable temperature ¹H NMR (VT-NMR) spectroscopy, and 2-dimensional NOESY experiments with solutions of polymers of molar mass (M_n) from 5 to 20 kDa and polymer concentrations of 0.1 to 3.0 mg/mL. The analysis outcome led us to conclude that the difference of the thermograms reflects the distinct self-assembly structures of the polymers. C18-PN-C18 assembles in water in the form of flower micelles held together by a core of tightly packed n-C18 chains. In contrast, polymers end-tagged with azopyridine, pyrenylbutyl, or adamantylethyl form a loose core that allows chain ends to escape from the micelles, to reinsert in them, or to dangle in surrounding water. The predominant low temperature (T₁) endotherm, which is insensitive to polymer concentration, corresponds to the dehydration/collapse of PNIPAM chains within the micelles, while the higher temperature (T₂) endotherm is attributed to the dehydration of dangling chains and intermicellar bridges. This study of the two phase transitions of telechelic PNIPAM homopolymer highlights the rich variety of morphologies attainable via responsive hydrophobically modified aqueous polymers and may open the way to a variety of practical applications.

The Effect of Number of Arms on the Aggregation Behavior of Thermoresponsive Poly(N-isopropylacrylamide) Star Polymers

The thermoresponsive nature of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo-SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo-SALS data suggest that this is due to a fragmentation of the aggregates followed by re-aggregation at even higher temperatures. Although the 6-arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point.

Synthesis of Poly(3-vinylpyridine)-Block-Polystyrene Diblock Copolymers via Surfactant-Free RAFT Emulsion Polymerization

In this work, we present a novel synthetic route to diblock copolymers based on styrene and 3-vinylpyridine monomers. Surfactant-free water-based reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of styrene in the presence of the macroRAFT agent poly(3-vinylpyridine) (P3VP) is used to synthesize diblock copolymers with molecular weights of around 60 kDa. The proposed mechanism for the poly(3-vinylpyridine)-block-poly(styrene) (P3VP-b-PS) synthesis is the polymerization-induced self-assembly (PISA) which involves the in situ formation of well-defined micellar nanoscale objects consisting of a PS core and a stabilizing P3VP macroRAFT agent corona. The presented approach shows a well-controlled RAFT polymerization, allowing for the synthesis of diblock copolymers with high monomer conversion. The obtained diblock copolymers display microphase-separated structures according to their composition.

Polymers on nanoparticles: structure & dynamics

Grafting polymers to nanoparticle surfaces influences properties from the conformation of the polymer chains to the dispersion and assembly of nanoparticles within a polymeric material. Recently, a small body of work has begun to address the question of how grafting polymers to a nanoparticle surface impacts chain dynamics, and the resulting physical properties of a material. This Review discusses recent work that characterizes the structure and dynamics of polymers that are grafted to nanoparticles and opportunities for future research. Starting from the case of a single polymer chain attached to a nanoparticle core, this Review follows the structure of the chains as grafting density increases, and how this structure slows relaxation of polymer chains and affects macroscopic material properties.

Biomolecules Turn Self-Assembling Amphiphilic Block Co-polymer Platforms Into Biomimetic Interfaces

Biological membranes constitute an interface between cells and their surroundings and form distinct compartments within the cell. They also host a variety of biomolecules that carry out vital functions including selective transport, signal transduction and cell-cell communication. Due to the vast complexity and versatility of the different membranes, there is a critical need for simplified and specific model membrane platforms to explore the behaviors of individual biomolecules while preserving their intrinsic function. Information obtained from model membrane platforms should make invaluable contributions to current and emerging technologies in biotechnology, nanotechnology and medicine. Amphiphilic block co-polymers are ideal building blocks to create model membrane platforms with enhanced stability and robustness. They form various supramolecular assemblies, ranging from three-dimensional structures (e.g., micelles, nanoparticles, or vesicles) in aqueous solution to planar polymer membranes on solid supports (e.g., polymer cushioned/tethered membranes,) and membrane-like polymer brushes. Furthermore, polymer micelles and polymersomes can also be immobilized on solid supports to take advantage of a wide range of surface sensitive analytical tools. In this review article, we focus on self-assembled amphiphilic block copolymer platforms that are hosting biomolecules. We present different strategies for harnessing polymer platforms with biomolecules either by integrating proteins or peptides into assemblies or by attaching proteins or DNA to their surface. We will discuss how to obtain synthetic structures on solid supports and their characterization using different surface sensitive analytical tools. Finally, we highlight present and future perspectives of polymer micelles and polymersomes for biomedical applications and those of solid-supported polymer membranes for biosensing.

A new visible light and temperature responsive diblock copolymer

A visible light and temperature responsive diblock copolymer of poly[6-(2,6,2′,6′-tetramethoxy-4′-oxyazobenzene) hexyl methacrylate]-block-poly(N-isopropylacrylamide) (PmAzo-b-PNIPAM) was synthesized via RAFT polymerization by carefully tuning the polymerization conditions.

Tuning PNIPAm self-assembly and thermoresponse: roles of hydrophobic end-groups and hydrophilic comonomer

Systematic study of hydrophobic and hydrophilic modifications to poly(N-isopropylacrylamide) elucidates design rules for control over cloud point and aqueous self-assembly.