Thermoresponsive polymer brush surfaces with hydrophobic groups for all-aqueous chromatography

Bioanalytical technologies using temperature-responsive polymers

In recent decades, various bioanalytical technologies have been investigated for appropriate medical treatment and effective therapy. Temperature-responsive chromatography is a promising bioanalytical technology owing to its functional properties. Temperature-responsive chromatography uses a poly(N-isopropylacrylamide)(PNIPAAm) modified stationary phase as the column packing material. The hydrophobic interactions between PNIPAAm and the analyte could be modulated by changing the column temperature because of the temperature-responsive hydrophobicity of PNIPAAm. Thus, the chromatography system does not require organic solvents in the mobile phase, making it suitable for therapeutic drug monitoring in medical settings such as hospitals. This review summarizes recent developments in temperature-responsive chromatography systems for therapeutic drug monitoring applications. In addition, separation methods for antibody drugs using PNIPAAm are also summarized because these methods apply to the therapeutic drug monitoring of biopharmaceutics. The temperature-responsive chromatography systems can also be utilized for clinical diagnosis, as they can assess multiple medicines simultaneously. This highlights the significant potential of temperature-responsive chromatography in medicine and healthcare.

Chromatography columns packed with thermoresponsive-cationic-polymer-modified beads for therapeutic drug monitoring

Therapeutic drug monitoring, which is used to determine appropriate drug doses, is critical in pharmacological therapy. In this study, we developed thermoresponsive chromatography columns with various cationic properties for effective therapeutic drug monitoring. Thermoresponsive cationic copolymer poly(N-isopropylacrylamide-co-n-butyl methacrylate-co-N,N-dimethylaminopropyl acrylamide) (P(NIPAAm-co-BMA-co-DMAPAAm))-modified silica beads, which were used as the chromatographic stationary phase, were prepared by modifying the radical initiator of the silica beads, followed by radical polymerization. Characterization of the prepared silica beads demonstrated that thermoresponsive polymers with various cationic properties successfully modified the beads. The elution behavior of several steroids in the prepared bead-packed columns at various temperatures indicated that the optimal column operating temperature was 30 °C. Appropriate measurement conditions for 13 drugs were investigated by varying the cationic properties of the columns and the pH of the mobile phase. Drug concentrations in serum samples were determined using the developed columns and mobile phases with a suitable pH. Voriconazole concentrations in human serum samples were determined using the developed columns with all-aqueous mobile phases. We anticipate that the developed chromatography columns can be used for therapeutic drug monitoring because drug concentrations can be measured using all-aqueous mobile phases that are suitable in clinical settings.

Polystyrene magnetic nanocomposite blend: An effective, facile, and economical alternative in oil spill removal applications

Finding an efficient and economical method to remediate oil spills on water is a priority worldwide. In this article, we propose a solution to this problem using polystyrene magnetic nanocomposite blends composed of polystyrene chains grafted on the surface of silica coated on iron oxide nanoparticles and polystyrene. The hydrophobic and oleophilic magnetic polymer nanocomposite collected oil from the water surface quickly and efficiently. However, when the magnetic polymer nanocomposite was blended with polystyrene, the resulting material also absorbed oil efficiently from the water surface. The blending technique made it easier to prepare the absorbent and dramatically decreased its cost. These new absorbents absorbed oil up to 5 times their own weight in only 5 minutes. The excellent hydrophobicity, low density, and easy magnetic separation makes these new absorbents a promising alternative to recover oil from spilled in fresh and marine water.

Hydrogel Coating with Temperature Response Retention Behavior and Its Application in Selective Separation of Liquid Chromatography

We reporte the double-layer hydrogel-coated mesoporous silica material as a new stationary phase for liquid chromatography. The method of combining physical coating and chemical coating was to apply hydrogel coating on the surface of silica, and finally, a new type of liquid chromatography stationary phase with in situ coating of the functional hydrogel on silica was obtained. This hydrogel-functionalized liquid chromatography stationary phase also exhibits a certain temperature responsiveness. Experimental results show that this temperature response is mainly due to changes in the hydrogen bonding between the stationary phase and the analyte at different temperatures in the column oven, which leads to changes in retention behavior. The hydrogel-coated mesoporous silica microspheres showed excellent selectivity for many polar analytes. An excellent column efficiency was obtained (139 000 plates/m for terephthalic acid) after optimization of chromatographic conditions. In addition to rapid separation of some analytes, this new hydrogel stationary phase also has certain superiority in chromatographic performance compared with other new excellent liquid chromatography stationary phases functioned by three-dimensional cross-linking systems. The important thing is that this strategy is relatively easy to prepare a new stationary phase with different properties.

Temperature responsive chromatography for therapeutic drug monitoring with an aqueous mobile phase

Therapeutic drug monitoring is a key technology for effective pharmacological treatment. In the present study, a temperature-responsive chromatography column was developed for safe and simple therapeutic drug monitoring without the use of organic solvents. Poly(N-isopropylacrylamide) (PNIPAAm) hydrogel-modified silica beads were prepared via a condensation reaction and radical polymerization. The temperature-dependent elution behavior of the drugs was observed using a PNIPAAm-modified silica-bead packed column and an all-aqueous mobile phase. Sharp peaks with reproducible retention times were observed at temperatures of 30 °C or 40 °C because the PNIPAAm hydrogel on the silica beads shrinks at these temperatures, limiting drug diffusion into the PNIPAAm hydrogel layer. The elution behavior of the sample from the prepared column was examined using a mixture of serum and model drugs. The serum and drugs were separated on the column at 30 °C or 40 °C, and the concentration of the eluted drug was obtained using the calibration curve. The results show that the prepared chromatography column would be useful for therapeutic drug monitoring because the drug concentration in serum can be measured without using organic solvents in the mobile phase and without any need for sample preparation.

Temperature-responsive spin column for sample preparation using an all-aqueous eluent

We present a temperature-responsive spin column using an all-aqueous eluent. The method is intended as a simple sample preparation method for protein removal from serum, which is required for serum drug analysis. As packing materials for the spin column, we prepared two types of silica beads via surface-initiated radical polymerization. The large beads (diameter, 40-63 μm) were grafted with a temperature-responsive cationic copolymer, poly(N-isopropylacrylamide-co-N,N-dimethylaminopropyl acrylamide-co-n-butyl methacrylate) (P(NIPAAm-co-DMAPAAm-co-BMA)), and the small beads (diameter, 5 μm) were grafted with a temperature-responsive hydrophobic copolymer, P(NIPAAm-co-BMA). The beads were packed into the spin column as a double layer: P(NIPAAm-co-BMA) silica beads on the bottom and P(NIPAAm-co-DMAPAAm-co-BMA) silica beads on the top. The sample purification efficacy of the prepared spin column was evaluated on a model sample analyte (the antifungal drug voriconazole mixed with blood serum proteins). At 40 °C, the serum proteins and voriconazole were adsorbed on the prepared spin column via hydrophobic and electrostatic interactions. When the temperature was decreased to 4 °C, the adsorbed voriconazole was eluted from the column with the pure water eluent, while the serum proteins remained in the column. This temperature-responsive spin column realizes sample preparation simply by changing the temperature.

Thermoresponsive interfaces obtained using poly(N-isopropylacrylamide)-based copolymer for bioseparation and tissue engineering applications

Poly(N-isopropylacrylamide) (PNIPAAm) is the most well-known and widely used stimuli-responsive polymer in the biomedical field owing to its ability to undergo temperature-dependent hydration and dehydration with temperature variations, causing hydrophilic and hydrophobic alterations. This temperature-dependent property of PNIPAAm provides functionality to interfaces containing PNIPAAm. Notably, the hydrophilic and hydrophobic alterations caused by the change in the temperature-responsive property of PNIPAAm-modified interfaces induce temperature-modulated interactions with biomolecules, proteins, and cells. This intrinsic property of PNIPAAm can be effectively used in various biomedical applications, particularly in bioseparation and tissue engineering applications, owing to the functionality of PNIPAAm-modified interfaces based on the temperature modulation of the interaction between PNIPAAm-modified interfaces and biomolecules and cells. This review focuses on PNIPAAm-modified interfaces in terms of preparation method, properties, and their applications. Advances in PNIPAAm-modified interfaces for existing and developing applications are also summarized.

Effect of pore diameter on the elution behavior of analytes from thermoresponsive polymer grafted beads packed columns

Temperature-responsive chromatography using thermoresponsive polymers is innovative and can control analyte retention via column temperature. Analyte elution behavior in this type of chromatography depends on the modified thermoresponsive polymer and the structure of the base materials. In the present study, we examine the effect of the pore diameter of silica beads on analyte elution behavior in temperature-responsive chromatography. Poly(N-isopropylacrylamide-co-n-butyl methacrylate) hydrogel was applied to beads of various pore sizes: 7, 12, and 30 nm. Almost the same amount of copolymer hydrogel was applied to all beads, indicating that the efficiency of copolymer modification was independent of pore size. Analyte retention on prepared beads in a packed column was observed using steroids, benzodiazepines, and barbiturates as analytes. Analyte retention times increased with temperature on packed columns of 12- and 30-nm beads, whereas the column packed with 7-nm beads exhibited decreased retention times with increasing temperature. The difference in analyte elution behavior among the various pore sizes was attributed to analyte diffusion into the bead pores. These results demonstrate that bead pore diameter determines temperature-dependent elution behavior.

Isothermal modelling of protein adsorption to thermo-responsive polymer grafted Sepharose Fast Flow sorbents

In this study, five adsorption isotherm models, that is, the Langmuir, Freundlich, Langmuir-Freundlich, Temkin and Brunauer-Emmett-Teller isotherms, were utilized for the analysis of the experimental adsorption data for six classes of poly(N-isopropylacrylamide)-based thermo-responsive copolymer-grafted Sepharose Fast Flow sorbents of different copolymer compositions with two structurally related proteins, namely bovine holo-lactoferrin and bovine holo-transferrin at 20 and 50°C. The experimental data for bovine holo-lactoferrin could be mathematically fitted to the Freundlich and Temkin isotherms when the protein feed concentrations were in the range of 1-40 mg/mL at both 20 and 50°C. Similar analysis of the binding of the homologous protein, bovine holo-transferrin, to the same thermo-responsive copolymer-grafted sorbents revealed that the experimental data could be fitted to the Langmuir, Freundlich and Temkin isotherms with coefficients of determination value over 0.90.

Adsorption of a Humanized Monoclonal Antibody onto Thermoresponsive Copolymer-Grafted Sepharose Fast Flow Sorbents

The batch adsorption behavior of a humanized monoclonal antibody (hIgG2 mAb) with thermoresponsive polymer (TRP)-modified Sepharose Fast Flow sorbents with different compositions of grafted copolymers is described. At high protein loadings, the adsorption with negatively charged copolymer-modified sorbents exhibited S-shaped isotherms in most cases, indicative of unrestricted multilayer adsorption. The adsorption capacity of the negatively charged copolymer-modified sorbents increased with an increase in the applied environmental temperature due to increased protein-sorbent surface hydrophobic and electrostatic interactions. The affinity of the hIgG2 mAb for a positively charged copolymer-grafted sorbent was much lower than that found for the negatively charged copolymer-grafted sorbents at both 20 and 50 °C due to electrostatic repulsive effects. This study has documented that the molecular functionalities of the grafted copolymer can significantly affect the adsorption behavior of this humanized mAb at both 20 and 50 °C with the isothermal dependencies revealing subtle effects due to copolymer composition.

Antibody drug separation using thermoresponsive anionic polymer brush modified beads with optimised electrostatic and hydrophobic interactions

Antibody drugs play an important role in biopharmaceuticals, because of the specificity for target biomolecules and reduction of side effects. Thus, separation and analysis techniques for these antibody drugs have increased in importance. In the present study, we develop functional chromatography matrices for antibody drug separation and analysis. Three types of polymers, poly(N-isopropylacrylamide (NIPAAm)-co-2-acrylamido-2-methylpropanesulfonic acid (AMPS)-co-N-phenyl acrylamide (PhAAm)), P(NIPAAm-co-AMPS-co-n-butyl methacrylate (BMA)), and P(NIPAAm-co-AMPS-co-tert-butylacrylamide (tBAAm)), were modified on silica beads through atom transfer radical polymerisation. Rituximab elution profiles were observed using the prepared beads-packed column. Rituximab adsorption at high temperature and elution at low temperature from the column were observed, as a result of the temperature-modulated electrostatic and hydrophobic interactions. Using the column, rituximab purification from contaminants was performed simply by changing the temperature. Additionally, three types of antibody drugs were separated using the column through temperature-modulated hydrophobic and electrostatic interactions. These results demonstrate that the temperature-responsive column can be applied for the separation and analysis of biopharmaceuticals through a simple control of the column temperature.

Exploration of the Selectivity and Retention Behavior of Alternative Polyacrylamides in Temperature Responsive Liquid Chromatography

Temperature responsive liquid chromatography (TRLC) allows for separation of organic solutes in purely aqueous mobile phases whereby retention is controlled through temperature. The vast majority of the work has thus far been performed on poly[N-isopropylacrylamide] (PNIPAAm)-based columns, while the performance of other temperature responsive polymers has rarely been compared under identical conditions. Therefore, in this work, two novel TRLC phases based on poly[N-n-propylacrylamide] (PNNPAAm) and poly[N,N-diethylacrylamide] (PDEAAm) are reported and compared to the state of the art PNIPAAm based column. Optimal comparison is thereby obtained by the use of controlled radical polymerizations, identical molecular weights, and by maximizing carbon loads on the silica supporting material. Analysis of identical test mixtures of homologue series and pharmaceutical samples revealed that PNNPAAm performs in a similar way as PNIPAAm while offering enhanced retention and a shift of the useable temperature range toward lower temperatures. PDEAAm offers a range of novel possibilities as it depicts a different selectivity, allowing for enhanced resolution in TRLC in, for example, coupled column systems. Reduced plate heights of 3 could be obtained on the homemade columns, offering the promise for reasonable column efficiencies in TRLC despite the use of bulky polymers as stationary phases in HPLC.

Temperature-modulated cell-separation column using temperature-responsive cationic copolymer hydrogel-modified silica beads

There is strong demand for cell separation methods that do not decrease cell activity or modify cell surfaces. Here, new temperature-modulated cell-separation columns not requiring cell-surface premodification are described. The columns were packed with temperature-responsive cationic polymer hydrogel-modified silica beads. Poly(N-isopropylacrylamide-co-n-butyl methacrylate-co-N,N-dimethylaminopropyl acrylamide) hydrogels with various cationic moieties were attached to silica-bead surfaces by radical polymerization using N,N'-methylenebisacrylamide as a crosslinking agent. The beads were packed into solid-phase extraction columns, and temperature-dependent cell elution from the columns was found using HL-60 and Jurkat cells. The retention HL-60 and Jurkat cells in columns containing cationic beads at 37 °C was 95.3% to 99.6% and 95.0% to 98.8%, respectively. By contrast, beads without cationic properties exhibited low cell retention (20.6% for HL-60 and 32.5% for Jurkat cells). The cells were mainly retained through both electrostatic and hydrophobic interactions. The retained HL-60 (4.9%) and Jurkat cells (40%) were eluted at 4 °C from the column with a low composition of cationic monomer (DMAPAAm, 1 mol% in copolymer), because the temperature-responsive hydrogels on the beads became hydrophilic, decreasing the hydrophobic interactions between the cells and the beads. A higher number of Jurkat cells than HL-60 cells were eluted because of differences in their electrostatic properties (Jurkat cells: -2.53 mV; HL-60 cells: -20.7 mV). The results indicated that cell retention by the hydrogel-coated beads packed in a solid phase extraction column could be modulated simply by changing the temperature.

Effect of Polymer Phase Transition Behavior on Temperature-Responsive Polymer-Modified Liposomes for siRNA Transfection

Small interfering RNAs (siRNAs) have been attracting significant attention owing to their gene silencing properties, which can be utilized to treat intractable diseases. In this study, two temperature-responsive liposomal siRNA carriers were prepared by modifying liposomes with different polymers-poly(N-isopropylacrylamide-co-N,N-dimethylaminopropyl acrylamide) (P(NIPAAm-co-DMAPAAm)) and poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) P(NIPAAm-co-DMAAm). The phase transition of P(NIPAAm-co-DMAPAAm) was sharper than that of P(NIPAAm-co-DMAAm), which is attributed to the lower co-monomer content. The temperature dependent fixed aqueous layer thickness (FALT) of the prepared liposomes indicated that modifying liposomes with P(NIPAAm-co-DMAPAAm) led to a significant change in the thickness of the fixed aqueous monolayer between 37 °C and 42 °C; while P(NIPAAm-co-DMAAm) modification led to FALT changes over a broader temperature range. The temperature-responsive liposomes exhibited cellular uptake at 42 °C, but were not taken up by cells at 37 °C. This is likely because the thermoresponsive hydrophilic/hydrophobic changes at the liposome surface induced temperature-responsive cellular uptake. Additionally, siRNA transfection of cells for the prevention of luciferase and vascular endothelial growth factor (VEGF) expression was modulated by external temperature changes. P(NIPAAm-co-DMAPAAm) modified liposomes in particular exhibited effective siRNA transfection properties with low cytotoxicity compared with P(NIPAAm-co-DMAAm) modified analogues. These results indicated that the prepared temperature-responsive liposomes could be used as effective siRNA carriers whose transfection properties can be modulated by temperature.

Poly(N-isopropylacrylamide)-based thermoresponsive surfaces provide new types of biomedical applications

Thermoresponsive surfaces, prepared by grafting of poly(N-isopropylacrylamide) (PIPAAm) or its copolymers, have been investigated for biomedical applications. Thermoresponsive cell culture dishes that show controlled cell adhesion and detachment following external temperature changes, represent a promising application of thermoresponsive surfaces. These dishes can be used to fabricate cell sheets, which are currently used as effective therapies for patients. Thermoresponsive microcarriers for large-scale cell cultivation have also been developed by taking advantage of the thermally modulated cell adhesion and detachment properties of thermoresponsive surfaces. Furthermore, thermoresponsive bioseparation systems using thermoresponsive surfaces for separating and purifying pharmaceutical proteins and therapeutic cells have been developed, with the separation systems able to maintain their activity and biological potency throughout the procedure. These applications of thermoresponsive surfaces have been improved with progress in preparation techniques of thermoresponsive surfaces, such as polymerization methods, and surface modification techniques. In the present review, the various types of PIPAAm-based thermoresponsive surfaces are summarized by describing their preparation methods, properties, and successful biomedical applications.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Nanohybrid polymer brushes on silica for bioseparation

Surface-initiated atom transfer radical polymerization and click chemistry are used to synthesize temperature-responsive polymer brushes for glycoprotein separation.

Thermoresponsive-polymer-based materials for temperature-modulated bioanalysis and bioseparations

In this review, bioseparations using thermoresponsive polymers are summarized. Thermoresponsive chromatography for separating bioactive compounds and proteins, and cell separations using thermoresponsive polymers and their properties are reviewed.

Thermoresponsive hydrophobic copolymer brushes modified porous monolithic silica for high-resolution bioseparation

Thermoresponsive-hydrophobic copolymer brushes were prepared on porous monolithic silica rods through surface initiated ATRP. The monolithic silica can separate biomolecules with high resolution and in short analysis times.

Effects of terminal group and chain length on temperature-responsive chromatography utilizing poly(N-isopropylacrylamide) synthesized via RAFT polymerization

Even using the same homo poly(N-isopropylacrylamide) immobilized silica beads as stationary phases, terminal functional group and chain length significantly affected temperature-dependent elution behavior of steroids.

Temperature-responsive smart packing materials utilizing multi-functional polymers

Polymers that respond to small changes in environmental stimuli with large, sometimes discontinuous changes in their physical state or properties, are often called "smart" polymers. Poly(N-isopropylacrylamide), PNIPAAm, is one of the most representative smart polymer that exhibits a thermally reversible soluble-insoluble change in the vicinity of its lower critical solution temperature (LCST) at 32°C in aqueous solution. Temperature-responsive chromatography for the separation of biomolecules utilizing the poly(N-isopropylacrylamide) (PNIPAAm)-modified stationary phase is performed with an aqueous mobile phase without using an organic solvent. The surface properties and function of the stationary phase are controlled by external temperature changes without changing the mobile-phase composition. The separation of the biomolecules, such as nucleotides, was achieved by a dual temperature- and pH-responsive chromatography system. The electrostatic and hydrophobic interactions could be modulated simultaneously with the temperature in an aqueous mobile phase. Additionally, we also prepared functional copolymers composed of N-isopropylacrylamide (NIPAAm) and amino acid derivative or naphthyl alanine derivative, which have temperature-responsiveness and molecular recognition. These separation systems would have potential applications in the separation of biomolecules.

Thermoresponsive oligo(ethylene glycol)-based polymer brushes on polymer monoliths for all-aqueous chromatography

Porous polymer monoliths onto which were grafted a thermoresponsive copolymer, poly(2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA)-co-oligo(ethylene glycol) methacrylate (OEGMA)), were synthesized by the two-step atom transfer radical polymerization (ATRP) method. The copolymer-grafted monoliths were characterized by elemental analysis, scanning electron microscopy, and mercury intrusion porosimetry. They were further used as the thermoresponsive stationary phase for all-aqueous high-performance liquid chromatography (HPLC). The chromatograms of three steroids demonstrated that the chain length of the grafted copolymer, which was regulated by varying the grafting time, could affect the separation by providing different amounts of hydrophobic interaction sites with analytes. Additionally, the elution profiles of steroids on the stationary phase could also be tuned by the comonomer composition. The results showed that the porous polymer monoliths enabled separation of the test mixture in pure aqueous mobile phase under isocratic conditions. Furthermore, the proposed method provides a simple and promising tool in the design and construction of responsive surfaces for chromatography applications.

Thermally modulated cationic copolymer brush on monolithic silica rods for high-speed separation of acidic biomolecules

Poly(N-isopropylacrylamide (IPAAm)-co-2-(dimethylamino)ethylmethacrylate(DMAEMA)-co-tert-butylacrylamide (tBAAm)), a thermoresponsive-cationic-copolymer, brush-grafted monolithic-silica column was prepared through surface-initiated atom transfer radical polymerization (ATRP) for effective thermoresponsive anion-exchange chromatography matrices. ATRP-initiator was grafted on monolithic silica-rod surfaces by flowing a toluene solution containing ATRP initiator into monolithic silica-rod columns. IPAAm, DMAEMA, and tBAAm monomers and CuCl/CuCl₂/Me₆TREN, 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 copolymer-brush structure on monolithic silica-rod surface was confirmed by X-ray photoelectron spectroscopy (XPS), elemental analysis, scanning electron microscopy (SEM) observation, and gel permeation chromatography (GPC) measurement of grafted copolymer. The prepared monolithic silica-rod columns were also characterized by chromatographic analysis. The cationic copolymer brush modified monolithic silica-rod columns were able to separate adenosine nucleotides with a shorter analysis time (4 min) than thermoresponsive copolymer brush-modified silica-bead-packed columns, because of the reduced diffusion path length of monolithic supporting materials. These results indicated that thermoresponsive cationic copolymer brush grafted monolithic silica-rod column prepared by ATRP was a promising tool for analyzing acidic-bioactive compounds with a remarkably short analysis time.

New antifouling silica hydrogel

In this work, a new antifouling silica hydrogel was developed for potential biomedical applications. A zwitterionic polymer, poly(carboxybetaine methacrylate) (pCBMA), was produced via atom-transfer radical polymerization and was appended to the hydrogel network in a two-step acid-base-catalyzed sol-gel process. The pCBMA silica aerogels were obtained by drying the hydrogels under supercritical conditions using CO(2). To understand the effect of pCBMA on the gel structure, pCBMA silica aerogels with different pCBMA contents were characterized using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and the surface area from Brauner-Emmet-Teller (BET) measurements. The antifouling property of pCBMA silica hydrogel to resist protein (fibrinogen) adsorption was measured using enzyme-linked immunosorbent assay (ELISA). SEM images revealed that the particle size and porosity of the silica network decreased at low pCBMA content and increased at above 33 wt % of the polymer. The presence of pCBMA increased the surface area of the material by 91% at a polymer content of 25 wt %. NMR results confirmed that pCBMA was incorporated completely into the silica structure at a polymer content below 20 wt %. A protein adsorption test revealed a reduction in fibrinogen adsorption by 83% at 25 wt % pCBMA content in the hydrogel compared to the fibrinogen adsorption in the unmodified silica hydrogel.

High stability of thermoresponsive polymer-brush-grafted silica beads as chromatography matrices

Thermo-responsive chromatography matrices with three types of graft architecture were prepared, and their separation performance and stability for continuous use were investigated. Poly(N-isopropylacrylamide)(PIPAAm) hydrogel-modified silica beads were prepared by a radical polymerization through modified 4,4'-azobis(4-cyanovaleric acid) and N,N'-methylenebisacrylamide. Dense PIPAAm brush-grafted silica beads and dense poly(N-tert-Butylacrylamide (tBAAm)-b-IPAAm) brush-grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) using CuCl/CuCl(2)/ Tris(2-(N,N-dimethylamino)ethyl)amine (Me(6)TREN) as an ATRP catalytic system and 2-propanol as a reaction solvent. Dense PIPAAm brush-grafted silica beads exhibited the highest separation performance because of their strong hydrophobic interaction between the densely grafted well-defined PIPAAm brush on silica-bead surfaces and analytes. Using an alkaline mobile phase, dense themoresponsive polymer brushes, especially having a hydrophobic basal layer, exhibited a high stability for continuous use, because polymer brush on the silica bead surfaces prevented the access of water to silica surface, leading to the hydrolysis of silica and cleavage of grafted polymers. Thus, the precisely modulating graft configuration of thermoresponsive polymers provided chromatography matrices with a high separation efficiency and stability for continuous use, resulting in elongating the longevity of chromatographic column.

Biomimetic anchors for antifouling and antibacterial polymer brushes on stainless steel

Barnacle cement (BC) was beneficially applied on stainless steel (SS) to serve as the initiator anchor for surface-initiated polymerization. The amine and hydroxyl moieties of barnacle cement reacted with 2-bromoisobutyryl bromide to provide the alkyl halide initiator for the surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA). The hydroxyl groups of HEMA polymer (PHEMA) were then converted to carboxyl groups for coupling of chitosan (CS) to impart the SS surface with both antifouling and antibacterial properties. The surface-functionalized SS reduced bovine serum albumin adsorption, bacterial adhesion, and exhibited antibacterial efficacy against Escherichia coli (E. coli). The effectiveness of barnacle cement as an initiator anchor was compared to that of dopamine, a marine mussel inspired biomimetic anchor previously used in surface-initiated polymerization. The results indicate that the barnacle cement is a stable and effective anchor for functional surface coatings and polymer brushes.