Thermoresponsive Polymer Brush Research Articles

Modeling Swelling Behavior of Thermoresponsive Polymer Brush with Lattice Density Functional Theory

A key problem in designing thermoresponsive polymer brushes on a solid surface is to find a relation between the targeted thermoresponsive properties and controllable conditions. Usually, a temperature-thickness curve showing the heating-induced swelling behavior of polymer brushes is chosen as the relation by either experimental or theoretical investigation. In this work, a lattice density functional theory (LDFT) developed previously is employed to investigate the temperature-thickness curves for five different types of polymer brushes, where the density profiles of polymer brushes calculated by LDFT are compared directly with simulation. It is found that the thermoresponsive behavior of a polymer brush can be characterized by the bulk phase behaviors of its corresponding polymer solution, including UCST, LCST, both UCST and LCST, closed LOOP and hourglass-shaped, which implies that the bulk phase diagram of polymer solutions can help us to find an appropriate polymer brush for a targeted thermoresponsive behavior. As an example, we show that the swelling behavior of a thermoresponsive polymer brush found in the experiment could be predicted by our LDFT results with the bulk phase diagram of real polymer solution only.

Particles Decorated by an Ionizable Thermoresponsive Polymer Brush in Water: Experiments and Self-Consistent Field Modeling

We have synthesized anionic multistimuli responsive core-shell polymer nanoparticles with low size dispersity composed of glassy poly(methyl methacrylate) (PMMA) cores of ca. 40 nm radius and poly(N-isopropylacrylamide) (PNIPAM) anionic brush-like shells with methacrylic acid comonomers. Using dynamic light scattering, we observed a volume phase transition upon an increase in temperature and this response was pH and ionic strength dependent. Already at room temperature we observed a pronounced polyelectrolyte effect, that is, a shift of the apparent pKa extracted from the degree of dissociation of the acids as a function of the pH. The multiresponsive behavior of the hydrophobic polyelectrolyte brush has been modeled using the Scheutjens-Fleer self-consistent field (SF-SCF) approach. Using a phenomenological relation between the Flory-Huggins χ parameter and the temperature, we confront the predicted change in the brush height with the observed change of the hydrodynamic radius and degree of dissociation and obtain estimates for the average chain lengths (number of Kuhn segments) of the corona chains, the grafting density and charge density distributions. The theory reveals a rich internal structure of the hydrophobic polyelectrolyte brush, especially near the collapse transition, where we find a microphase segregated structure. Considering this complexity, it is fair to state that the theoretical predictions follow the experimental data semiquantitatively, and it is attractive to attribute the observed disparity between theory and experiments to the unknown polydispersity of the chains, the unknown distribution of the charges, or other experimental complications. More likely, however, the deviations point to significant problems of the mean field theory, which focuses solely on the radial distributions and ignores the possibility of the formation of lateral (local) inhomogeneities in partially collapsed polyelectrolyte brushes. We argue that the PNIPAM brush at room temperature is already behaving nonideally.

Morphology tuning in the formation of vaterite crystal thin films with thermoresponsive poly(N-isopropylacrylamide) brush matrices

The use of a thermoresponsive polymer brush matrix resulted in the formation and morphology tuning of CaCO3 crystal thin films. Poly(N-isopropylacrylamide) (PNIPAm) brushes with thickness of approximately 500 nm were synthesized and employed as crystallization templates for CaCO3. The PNIPAm brush matrix induced the formation of vaterite thin films in the presence of poly(acrylic acid). Moreover, crystallization of CaCO3 at temperatures above and below the lower critical solution temperature of the PNIPAm brush matrices led to the preparation of vaterite films with distinctly different crystallographic orientations. The approach of using a stimuli-responsive polymer brush matrix may provide a novel way for the development of hybrid coating materials.

Loading and Distribution of a Model Small Molecule Drug in Poly(N-isopropylacrylamide) Brushes: a Neutron Reflectometry and AFM Study

The structure of a hydrated poly(N-isopropylacrylamide) brush loaded with 5 vol % Isoniazid is studied as a function of temperature using neutron reflectometry (NR) and atomic force microscopy (AFM). NR measurements show that Isoniazid increases the thickness of the brush before, during and after the polymer collapse, and it is retained inside the brush at all measured temperatures. The Isoniazid concentration in the expanded brush is ~14% higher than in the bulk solution, and the concentration nearly doubles in the collapsed polymer, suggesting stronger binding between Isoniazid and the polymer compared to water, even at temperatures below the lower critical solution temperature (LCST) where the polymer is hydrophilic. Typically, additives that bind strongly to the polymer backbone and increase the hydrophilicity of the polymer will delay the onset of the LCST, which is suggested by AFM and NR measurements. The extent of small-molecule loading and distribution throughout a thermo-responsive polymer brush, such as pNIPAAm, will have important consequences for applications such as drug delivery and gating.

Effect of the Hydrophobic Basal Layer of Thermoresponsive Block Co-Polymer Brushes on Thermally-Induced Cell Sheet Harvest

Thermoresponsive poly(benzyl methacrylate)-b-poly(N-isopropylacrylamide) (PBzMA-b-PIPAAm) block co-polymer brush surfaces were prepared by surface-initiated two-step reversible addition-fragmentation chain transfer radical (RAFT) polymerization. PBzMA brushes were fabricated on azoinitiator-immobilized glass substrates in the presence of dithiobenzoate (DTB) compound as a RAFT agent. The amount of grafted polymer was regulated by initial monomer concentrations. The second thermoresponsive blocks were added to the RAFT-related DTB groups located at PBzMA termini through the propagation of PIPAAm chains, resulting in formation of PBzMA-b-PIPAAm brushes. Surface characteristics of the block co-polymer brushes and its influence on thermally regulated cellular behavior were investigated using bovine carotid artery endothelial cells (BAECs), compared with PIPAAm brush surfaces. Cell adhesion/detachment behavior on thermoresponsive polymer brush surfaces significantly depended on their individual polymer architectures and chemical compositions of grafted polymers. Low-temperature treatment at 20°C, below the phase-transition temperature of PIPAAm, induced the spontaneous detachment of adhering cells from the PBzMA-b-PIPAAm brush surfaces with a higher rate than that from PIPAAm brush surfaces. In addition, the cell-repellent effect of the hydrophobic basal layer successfully accelerated for harvesting BAEC sheets from the block co-polymer brush surfaces. Unique features of thermoresponsive block co-polymer brush architectures can be applied to control cell-adhesion strength for enhancing cell adhesion or accelerating cell detachment.

Terminally Functionalized Thermoresponsive Polymer Brushes for Simultaneously Promoting Cell Adhesion and Cell Sheet Harvest

For preparing cell sheets effectively for cell sheet-based regenerative medicine, cell-adhesion strength to thermoresponsive cell culture surfaces need to be controlled precisely. To design new thermoresponsive surfaces via a terminal modification method, thermoresponsive polymer brush surfaces were fabricated through the surface-initiated reversible addition-fragmentation chain transfer (RAFT) radical polymerization of N-isopropylacrylamide (IPAAm) on glass substrates. The RAFT-mediated grafting method gave dithiobenzoate (DTB) groups to grafted PIPAAm termini, which can be converted to various functional groups. In this study, the terminal carboxylation of PIPAAm chains provided high cell adhesive property to thermoresponsive surfaces. Although cell adhesion is generally promoted by a decrease in the grafted PIPAAm amount, the decrease also decelerated thermally-induced cell detachment, whereas the influence of terminal modification was negligible on the cell detachment. Consequently, the terminally modified PIPAAm brush surfaces allowed smooth muscle cells (SMCs) to simultaneously adhere strongly and detach themselves rapidly. In this study, SMCs were unable to reach a confluent monolayer on as-prepared PIPAAm brush surfaces (grafted amount: 0.41 μg/cm(2)) without terminal carboxylation due to their insufficient cell-adhesion strength. On the other hand, though a decrease in the PIPAAm amount allowed SMCs to form a confluent cell monolayer on the PIPAAm brush surface, the SMCs were unable to be harvested as a monolithic cell sheet by low-temperature culture at 20 °C. Because of their unique property, only terminal-carboxylated PIPAAm brush surfaces achieved rapid harvesting of complete cell sheets by low-temperature culturing.

Thermoresponsive Polymer Brush on Monolithic-Silica-Rod for the High-Speed Separation of Bioactive Compounds

Poly(N-isopropylacrylamide), one of the most utilized thermoresponsive polymers, brush-grafted monolithic-silica columns were prepared through surface-initiated atom transfer radical polymerization (ATRP) for effective thermoresponsive-chromatography matrices. ATRP initiator was grafted on monolithic silica-rod surfaces by flowing a toluene solution containing ATRP initiator into monolithic silica-rod columns. N-Isopropylacrylamide (IPAAm) monomer and CuCl/CuCl(2)/Me(6)TREN, an ATRP catalytic system, were dissolved in 2-propanol, and the reaction solution was pumped into the preprepared initiator-modified columns at 25 °C for 16 h. The constructed PIPAAm-brush structure on the monolithic silica-rod surface was confirmed by XPS, elemental analysis, SEM observation, and GPC measurement of grafted PIPAAm. The prepared monolithic silica-rod columns were also characterized by chromatographic analysis. PIPAAm-brush-modified monolithic silica-rod columns were able to separate hydrophobic steroids with a short analysis time (10 min), compared to PIPAAm-brush-modified silica-beads-packed columns, because of the horizontally limited diffusion path length of monolithic supporting materials. Additionally, diluted PIPAAm-brush monolithic silica-rod column gave a further shorting analysis time (5 min). These results indicated (1) surface-initiated ATRP constructed PIPAAm-brush structures on monolithic silica-rod surfaces and (2) PIPAAm-brush grafted monolithic silica-rod column prepared by ATRP was a promising tool for analyzing hydrophobic-bioactive compounds with a short analysis time.

Micropatterned Thermoresponsive Polymer Brush Surfaces for Fabricating Cell Sheets with Well-Controlled Orientational Structures

Newly developed fabrication technique of thermoresponsive surface using RAFT-mediated block copolymerization and photolithography achieved stripe-like micropatterning of poly(N-isopropylacrylamide) (PIPAAm) brush domains and poly(N-isopropylacrylamide)-b-poly(N-acryloylmorpholine) domains. Normal human dermal fibroblasts were aligned on the physicochemically patterned surfaces simply by one-pot cell seeding. Fluorescence images showed the well-controlled orientation of actin fibers and fibronectin in the confluent cell layers with associated extracellular matrix (ECM) on the surfaces. Furthermore, the aligned cells were harvested as a tissue-like cellular monolayer, called "cell sheet" only by reducing temperature below PIPAAm's lower critical solution temperature (LCST) to 20 °C. The cell sheet harvested from the micropatterned surface possessed a different shrinking rate between vertical and parallel sides of the cell alignment (approximately 3:1 of aspect ratio). This indicates that the cell sheet maintains the alignment of cells and related ECM proteins, promising to show the mechanical and biological aspects of cell sheets harvested from the functionalized thermoresponsive surfaces.

Thermoresponsive Polymer Brush Surfaces with Hydrophobic Groups for All-Aqueous Chromatography

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionThermoresponsive Polymer Brush Surfaces with Hydrophobic Groups for All-Aqueous ChromatographyKenichi Nagase, Mio Kumazaki, Hideko Kanazawa, Jun Kobayashi, Akihiko Kikuchi, Yoshikatsu Akiyama, Masahiko Annaka, and Teruo Okano*Cite this: ACS Appl. Mater. Interfaces 2010, 2, 12, 3766Publication Date (Web):November 10, 2010Publication History Received9 October 2010Published online10 November 2010Published inissue 22 December 2010https://doi.org/10.1021/am1009716Copyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views426Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (36 KB) Get e-AlertsSUBJECTS:Chromatography,Hydrophobicity,Thermoresponsive polymers Get e-Alerts

Controlled Chain Length and Graft Density of Thermoresponsive Polymer Brushes for Optimizing Cell Sheet Harvest

Novel thermoresponsive polymer brush surfaces for harvesting cell sheet were fabricated by the surface-initiated RAFT polymerization of N-isopropylacrylamide (IPAAm) on azoinitiator-immobilized glass substrates in the presence of dithiobenzoate compound as a chain transfer agent (CTA). The chain length of the grafted PIPAAm on the surface was controlled by changing CTA concentration. Additionally, PIPAAm graft density on the surface was successfully regulated by grafting from azoinitiator-immobilized surfaces with various densities. By adjusting both the chain length and the density of grafted PIPAAm, a series of thermoresponsive polymer brush surfaces were prepared to regulate cell adhesion/detachment behavior by solely temperature change across the PIPAAm's lower critical solution temperature of 32 degrees C. PIPAAm brush surfaces were successfully optimized to recover the cell sheets of bovine carotid artery endothelial cells. Additionally, the immunostaining study revealed that the cell sheets can be recovered with their intact extracellular matrix (ECM) from PIPAAm surfaces, indicating that the cell sheets can be effectively transplanted to damaged tissues and organs.

Thermoresponsive Polymer Brush Surfaces with Hydrophobic Groups for All-Aqueous Chromatography

For developing thermoresponsive chromatographic matrices with a strong hydrophobicity, poly(N-isopropylacrylamide-co-n-butyl methacrylate) (poly(IPAAm-co-BMA)) brush grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) with a CuCl/CuCl(2)/Me(6)TREN catalytic system in 2-propanol at 25 degrees C for 16 h. The prepared beads were characterized by chromatographic analysis. Chromatograms of the benzoic-acid family and phenol as model analytes were obtained with high-resolution peaks because of their strong hydrophobic interactions to the densely grafted hydrophobized copolymers on the beads. Retention times of the analytes increased with the increase in BMA composition ratio. Dehydration of grafted copolymer with large BMA composition was performed at low temperature. These results indicated that the copolymer-brush-grafted surface prepared by ATRP was an effective tool for separating hydrophilic analytes at low temperature through modulating the strong hydrophobic interaction.

Crystallization of unidirectionally oriented fibrous calcium carbonate on thermo-responsive polymer brush matrices

We report a new approach to the formation of unidirectionally oriented fibrous calcium carbonate crystals using a surface-initiated thermo-sensitive polymer brush of poly(N-isopropylacrylamide) above the lower critical solution temperature (LCST).

Synthesis and Self-Assembly of Coil−Rod Double Hydrophilic Diblock Copolymer with Dually Responsive Asymmetric Centipede-Shaped Polymer Brush as the Rod Segment

We report on the synthesis and self-assembly of well-defined coil−rod double hydrophilic diblock copolymer with pH- and thermo-responsive asymmetric centipede-shaped polymer brush as the rod segment via a combination of atom transfer radical polymerization (ATRP) and click chemistry (Schemes 1 and 2). At first, poly(ethylene oxide)-b-poly(glycidyl methacrylate), PEO-b-PGMA, was prepared by ATRP using PEO-based macroinitiator. The ring-opening of pendent epoxide moieties in PEO-b-PGMA with NaN3 followed by esterification with 2-bromoisobutyryl bromide afforded multifunctional PEO-b-[PGMA-(N3)(Br)] bearing one azide and one bromine moieties on each monomer repeating unit of PGMA. The subsequent ATRP of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) using PEO-b-[PGMA-(N3)(Br)] as the macroinitiator yielded PEO-b-[PGMA-g-(N3)(PMEO2MA)] coil−brush diblock copolymer possessing one residual azide moiety at each grafting site. Finally, the target coil−rod diblock copolymer with asymmetric centipede-shaped polymer...

Preparation of thermoresponsive polymer brush surfaces and their interaction with cells

Poly( N-isopropylacrylamide) (PIPAAm) brush surfaces with different layer thickness on polystyrene substrates were prepared by surface-initiated atom transfer radical polymerization (ATRP). Surface characteristics of PIPAAm brushes and their influence on adhesion and detachment of bovine carotid artery endothelial cells (ECs) were controlled by PIPAAm layer thickness. Surface hydrophilicity increased with PIPAAm layer thickness at 37 °C because PIPAAm brush surfaces with higher thickness provide more extended chain conformations with relatively high chain mobility, and accompanying polymer chain hydration. These surface property alterations lead to negligible cell adhesion through minimal matrix protein adsorption and also modified surface modulus. By adjusting polymerization reaction conditions and time, polymer layers supporting confluent cultures of ECs were possible. Confluent EC monolayers spontaneously detached as contiguous cell sheets from PIPAAm brush surfaces at reduced temperatures. Thermoresponsive cell adhesion and detachment behavior were analyzed from the standpoint of surface physicochemical characteristics. Thermoresponsive surfaces prepared by surface-initiated ATRP techniques allow surface selection in preparing cell sheets from attachment-dependent cells having relatively strong adhesive property for tissue engineering applications.

Effects of Graft Densities and Chain Lengths on Separation of Bioactive Compounds by Nanolayered Thermoresponsive Polymer Brush Surfaces

We have prepared various poly(N-isopropylacrylamide) (PIPAAm)-grafted silica bead surfaces through surface-initiated atom transfer radical polymerization (ATRP) by changing graft densities and brush chain lengths. The prepared surfaces were characterized by chromatographic analysis using the modified silica beads as chromatographic stationary phases. ATRP initiator (2-(m,p-chloromethylphenyl)ethyltrichlorosilane) density on silica bead surfaces was modulated by changing the feed composition of the self-assembled monolayers (SAMs) of mixed silane coupling agents consisting of ATRP initiator and phenethyltrichlorosilane on the surfaces. IPAAm was then polymerized on SAM-modified silica bead surfaces by ATRP in 2-propanol at 25 degrees C. The chain length of the grafted PIPAAm was controlled by simply changing the ATRP reaction time at constant catalyst concentration. The thermoresponsive surface properties of the PIPAAm-grafted silica beads were investigated by temperature-dependent elution behavior of hydrophobic steroids from the surfaces using Milli-Q water as a mobile phase. On the surfaces grafted with shorter PIPAAm chains, longer retention times for steroids were observed on sparsely grafted PIPAAm surfaces compared to dense PIPAAm brushes at low temperature, because of hydrophobic interactions between the exposed phenethyl groups of SAMs on silica surfaces and steroid molecules. Retention times for steroids on dilute PIPAAm chain columns decreased with temperature similarly to conventional reverse-phase chromatographic modes on octadecyl columns. This effect was due to limited interaction of solutes with the PIPAAm-grafted surfaces. Retention times for steroids on dilute PIPAAm brush surfaces with longer PIPAAm chains became greater above the PIPAAm transition temperature. At low-temperature regions, hydrated and expanded PIPAAm at low temperatures prevented hydrophobic interactions between the phenethyl group of SAMs on the silica bead surfaces and steroid molecules. Retention times for steroids on a dense PIPAAm brush column increased with temperature since solvated polymer segments within the dense brush layer undergo dehydration over a broad range of temperatures. In conclusion, PIPAAm graft density has a crucial influence on the elution behavior of steroids because of the interaction of analytes with silica bead interfaces, and because of the characteristic dehydration of PIPAAm in dense-pack brush surfaces.

Interfacial Property Modulation of Thermoresponsive Polymer Brush Surfaces and Their Interaction with Biomolecules

Dense poly(N-isopropylacrylamide) (PIPAAm) brushes were created on silica bead surfaces by surface-initiated atom transfer radical polymerization (ATRP). Interfacial properties of PIPAAm brushes were characterized by thermoresponisve interaction with biomolecules. The grafted amounts of PIPAAm on silica bead surfaces exceeded that from previously reported polymer-hydrogel-modified silica beads prepared by conventional radical polymerization by nearly 1 order of magnitude. Temperature-dependent chromatographic interactions with soluble analytes were modulated by changing the grafted PIPAAm chain lengths. Short PIPAAm-grafted silica beads produce insufficient dehydration and chain aggregation to separate steroids using weak hydrophobic interactions. In contrast, broad unresolved peaks were observed on silica beads column grafted with long PIPAAm chains due to steroid partitioning into thick, densely grafted PIPAAm brush layers. Thus, silica beads column grafted with PIPAAm chains of proper length can demonstrate baseline separation of steroids with relatively high resolution among the tested columns. Relatively longer retention times for steroid analytes were observed on all columns compared to those previously reported for other PIPAAm-grafted silica beads. This indicates that densely PIPAAm-grafted chains enable control of strong hydrophobic interactions with steroids by changing the column temperature. Densely grafted PIPAAm columns were also successful in separating two peptides into two peaks as the column temperature was increased to 40 degrees C. This provides an effective separation alternative for peptides using substantial hydrophobicity without modification of hydrophobic surfaces and/or low mobile phase pH. In conclusion, densely PIPAAm-grafted surfaces exhibit strong, reversible temperature-modulated hydrophobic interactions, facilitating baseline separations of steroids and peptides in aqueous milieu without changes in the mobile phase pH and high ionic strength.