Synthesis of Novel Sulfobetaine Polymers with Differing Dipole Orientations in Their Side Chains, and Their Effects on the Antifouling Properties.

The impact of the orientation of zwitterionic groups, with respect to the polymer backbone, on the antifouling performance of thin hydrogel films made of polyzwitterions is explored. In an extension of the recent discussion about differences in the behavior of polymeric phosphatidylcholines and choline phosphates, a quasi-isomeric set of three poly(sulfobetaine methacrylate)s is designed for this purpose. The design is based on the established monomer 3-[N-2-(methacryloyloxy)ethyl-N,N-dimethyl]ammonio-propane-1-sulfonate and two novel sulfobetaine methacrylates, in which the positions of the cationic and the ionic groups relative to the polymerizable group, and thus also to the polymer backbone, are altered. The effect of the varied segmental dipole orientation on their water solubility, wetting behavior by water, and fouling resistance is compared. As model systems, the adsorption of the model proteins bovine serum albumin (BSA), fibrinogen, and lysozyme onto films of the various polyzwitterion surfaces is studied, as well as the settlement of a diatom (Navicula perminuta) and barnacle cyprids (Balanus improvisus) as representatives of typical marine fouling communities. The results demonstrate the important role of the zwitterionic group's orientation on the polymer behavior and fouling resistance.

Surface Modification by Polyzwitterions of the Sulfabetaine-Type, and Their Resistance to Biofouling.

Films of zwitterionic polymers are increasingly explored for conferring fouling resistance to materials. Yet, the structural diversity of polyzwitterions is rather limited so far, and clear structure-property relationships are missing. Therefore, we synthesized a series of new polyzwitterions combining ammonium and sulfate groups in their betaine moieties, so-called poly(sulfabetaine)s. Their chemical structures were varied systematically, the monomers carrying methacrylate, methacrylamide, or styrene moieties as polymerizable groups. High molar mass homopolymers were obtained by free radical polymerization. Although their solubilities in most solvents were very low, brine and lower fluorinated alcohols were effective solvents in most cases. A set of sulfabetaine copolymers containing about 1 mol % (based on the repeat units) of reactive benzophenone methacrylate was prepared, spin-coated onto solid substrates, and photo-cured. The resistance of these films against the nonspecific adsorption by two model proteins (bovine serum albumin-BSA, fibrinogen) was explored, and directly compared with a set of references. The various polyzwitterions reduced protein adsorption strongly compared to films of poly(nbutyl methacrylate) that were used as a negative control. The poly(sulfabetaine)s showed generally even somewhat higher anti-fouling activity than their poly(sulfobetaine) analogues, though detailed efficacies depended on the individual polymer-protein pairs. Best samples approach the excellent performance of a poly(oligo(ethylene oxide) methacrylate) reference.

Cationic polyacrylamide copolymers (PAMs): environmental half life determination in sludge-treated soil.

BACKGROUND: Cationic polyacrylamide copolymers (PAMs) are used for sludge dewatering in municipal waste water treatment and might enter the environment by spreading of the sludge on agricultural land. Concern has been expressed since little is known about the degradation of PAMs in soils. To obtain detailed information on the polymer's fate in the soil compartment, the degradation of 14C-radiolabelled PAM in an outdoor lysimeter was studied. RESULTS: No plant uptake and leaching of radioactivity was observed. There was practically no vertical movement of polymer and no transformation products found at the end of the study. For the top 10 cm soil layer, a mass balance was established throughout the study. About 10% of applied radioactivity was not extractable from soil even with a matrix destructive method, and this was concluded to be bound residue. Characterization of extractable radioactivity by means of GPC-analysis showed a significant decrease of the molecular weight of the PAM with time. The decrease in molecular weight indicates a breakdown of the polymer backbone (the C-C-chain), and is assumed to be primary degradation. The total radioactivity content in the 10 cm top soil layer was quantified every 6 months over a period of 3 years. The results show a significant decrease of the total radioactivity over time and this is defined as ultimate degradation following the definition of OECD and EPA. Based on the data, a half-life time of 2.0 × 103 days and a rate constant of 0.00035/day were calculated. With a χ2 of 12.0 the results of the calculation are thus valid and reliable. The rate constant indicates a mineralization of 22.5% within a period of 2 years based on the total recovered radioactivity. This half-life time is solely based on mineralization and does not take into account the degradation of the polymer backbone, hydrolysis of the side chains, incorporation into the soil matrix, and thus is a conservative approach. CONCLUSIONS: 14C-PAM degrades very slowly in soil after land-spreading as a component of sewage sludge. Even in a very conservative evaluation which only considered the loss of radioactivity, a half-life time of 5.4 years was determined.

Tuning reversible cell adhesion to methacrylate-based thermoresponsive polymers: Effects of composition on substrate hydrophobicity and cellular responses.

Thermoresponsive polymer (TRP) cell culture substrates are widely utilized for nonenzymatic, temperature-triggered release of adherent cells. Increasingly, multicomponent TRPs are being developed to facilitate refined control of cell adhesion and detachment, which requires an understanding of the relationships between composition-dependent substrate physicochemical properties and cellular responses. Here, we utilize a homologous series of poly(MEO2 MAx -co-OEGMAy ) brushes with variable copolymer ratio (x/y) to explore the effects of substrate hydrophobicity on L-929 fibroblast adhesion, morphology, and temperature-triggered cell detachment. Substrate hydrophobicity is reported in terms of the equilibrium spreading coefficient (S), and variations in copolymer ratio reveal differential hydrophobicity that is correlated to serum protein adsorption and initial cell attachment at 37°C. Furthermore, quantitative metrics of cell morphology show that cell spreading is enhanced on more hydrophobic surfaces with increased (x/y) ratio, which is further supported by gene expression analysis of biomarkers of cell spreading (e.g., RhoA, Dusp2). Temperature-dependent cell detachment is limited for pure poly(MEO2 MA); however, rapid cell rounding and detachment (<20 min) are evident for all poly(MEO2 MAx -co-OEGMAy ) substrates. These results suggest that increased MEO2 MA content in poly(MEO2 MAx -co-OEGMAy ) substrates elicits enhanced protein adsorption, cell adhesion, and cell spreading; however, integration of small amounts of the more hydrophilic OEGMA unit facilitates both cell attachment/spreading and detachment. This study demonstrates an important role for the composition-dependent control of surface hydrophobicity in the design of multicomponent TRPs for desired biological outcomes. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2416-2428, 2017.

Effects of Methacrylate-Based Thermoresponsive Polymer Brush Composition on Fibroblast Adhesion and Morphology.

Thermoresponsive polymers are being used increasingly in cell culture applications due to their temperature dependent surface properties. Poly(MEO2MA-co-OEGMA) (PMO) brushes offer tunable physical properties via variation in the copolymer ratio, but the effects of composition on cell-substrate interactions is unclear. To this end, a series of PMO brushes (0-8% OEGMA) was fabricated and L-929 fibroblast adhesion and morphology was quantified in the presence of serum (FBS) or after functionalization via the adsorption of fibronectin (FN) and vitronectin (VN). Quantification of the adsorption of model proteins, bovine serum albumin and FN, revealed that the extent of adsorption was correlated to the amount MEO2MA content, which represents the more hydrophobic component in PMO brushes. Cells exhibited delayed attachment and spreading on all PMO substrates in the presence of FBS. After 24 h, cell attachment was comparable; however, increased spreading was correlated with increased MEO2MA content. Adsorption of FN significantly increased initial cell attachment to all PMO surfaces after 2 h. This was not observed with VN; however, both FN and VN increased cell spreading/decreased cell circularity for all PMO substrates relative to FBS. Pure MEO2MA brushes with FN exhibited increased cell spreading/decreased cell circularity relative to other PMO substrates after 2 h, and elicited the highest cell density after 24 h. These results demonstrate that increased MEO2MA content in PMO substrates facilitates cell attachment and spreading, which can be further enhanced by adsorbing FN in the absence of other proteins.

Thermoresponsive Polymers and Inverse Opal Hydrogels for the Detection of Diols.

Responsive inverse opal hydrogels functionalized by boroxole moieties were synthesized and explored as sensor platforms for various low molar mass as well as polymeric diols and polyols, including saccharides, glycopolymers and catechols, by exploiting the diol induced modulation of their structural color. The underlying thermoresponsive water-soluble copolymers and hydrogels exhibit a coil-to-globule or volume phase transition, respectively, of the LCST-type. They were prepared from oligoethylene oxide methacrylate (macro)monomers and functionalized via copolymerization to bear benzoboroxole moieties. The resulting copolymers represent weak polyacids, which can bind specifically to diols within an appropriate pH window. Due to the resulting modulation of the overall hydrophilicity of the systems and the consequent shift of their phase transition temperature, the usefulness of such systems for indicating the presence of catechols, saccharides, and glycopolymers was studied, exploiting the diol/polyol induced shifts of the soluble polymers' cloud point, or the induced changes of the hydrogels' swelling. In particular, the increased acidity of benzoboroxoles compared to standard phenylboronic acids allowed performing the studies in PBS buffer (phosphate buffered saline) at the physiologically relevant pH of 7.4. The inverse opals constructed of these thermo- and analyte-responsive hydrogels enabled following the binding of specific diols by the induced shift of the optical stop band. Their highly porous structure enabled the facile and specific optical detection of not only low molar mass but also of high molar mass diol/polyol analytes such as glycopolymers. Accordingly, such thermoresponsive inverse opal systems functionalized with recognition units represent attractive and promising platforms for the facile sensing of even rather big analytes by simple optical means, or even by the bare eye.

Influence of the Near Molecular Vicinity on the Temperature Regulated Fluorescence Response of Poly(N-vinylcaprolactam).

A series of new fluorescent dye bearing monomers, including glycomonomers, based on maleamide and maleic esteramide was synthesized. The dye monomers were incorporated by radical copolymerization into thermo-responsive poly(N­vinyl-caprolactam) that displays a lower critical solution temperature (LCST) in aqueous solution. The effects of the local molecular environment on the polymers' luminescence, in particular on the fluorescence intensity and the extent of solvatochromism, were investigated below as well as above the phase transition. By attaching substituents of varying size and polarity in the close vicinity of the fluorophore, and by varying the spacer groups connecting the dyes to the polymer backbone, we explored the underlying structure⁻property relationships, in order to establish rules for successful sensor designs, e.g., for molecular thermometers. Most importantly, spacer groups of sufficient length separating the fluorophore from the polymer backbone proved to be crucial for obtaining pronounced temperature regulated fluorescence responses.

Thermoresponsive amperometric glucose biosensor.

The authors report on the fabrication of a thermoresponsive biosensor for the amperometric detection of glucose. Screen printed electrodes with heatable gold working electrodes were modified by a thermoresponsive statistical copolymer [polymer I: poly(ω-ethoxytriethylenglycol methacrylate-co-3-(N,N-dimethyl-N-2-methacryloyloxyethyl ammonio) propanesulfonate-co-ω-butoxydiethylenglycol methacrylate-co-2-(4-benzoyl-phenoxy)ethyl methacrylate)] with a lower critical solution temperature of around 28 °C in aqueous solution via electrochemically induced codeposition with a pH-responsive redox-polymer [polymer II: poly(glycidyl methacrylate-co-allyl methacrylate-co-poly(ethylene glycol)methacrylate-co-butyl acrylate-co-2-(dimethylamino)ethyl methacrylate)-[Os(bpy)2(4-(((2-(2-(2-aminoethoxy)ethoxy)ethyl)amino)methyl)-N,N-dimethylpicolinamide)](2+)] and pyrroloquinoline quinone-soluble glucose dehydrogenase acting as biological recognition element. Polymer II bears covalently bound Os-complexes that act as redox mediators for shuttling electrons between the enzyme and the electrode surface. Polymer I acts as a temperature triggered immobilization matrix. Probing the catalytic current as a function of the working electrode temperature shows that the activity of the biosensor is dramatically reduced above the phase transition temperature of polymer I. Thus, the local modulation of the temperature at the interphase between the electrode and the bioactive layer allows switching the biosensor from an on- to an off-state without heating of the surrounding analyte solution.

Responsive inverse opal hydrogels for the sensing of macromolecules.

Dual responsive inverse opal hydrogels were designed as autonomous sensor systems for (bio)macromolecules, exploiting the analyte-induced modulation of the opal's structural color. The systems that are based on oligo(ethylene glycol) macromonomers additionally incorporate comonomers with various recognition units. They combine a coil-to-globule collapse transition of the LCST type with sensitivity of the transition temperature toward molecular recognition processes. This enables the specific detection of macromolecular analytes, such as glycopolymers and proteins, by simple optical methods. While the inverse opal structure assists the effective diffusion even of large analytes into the photonic crystal, the stimulus responsiveness gives rise to strong shifts of the optical Bragg peak of more than 100 nm upon analyte binding at a given temperature. The systems' design provides a versatile platform for the development of easy-to-use, fast, and low-cost sensors for pathogens.

Engineering adhesion to thermoresponsive substrates: effect of polymer composition on liquid-liquid-solid wetting.

Adhesion control in liquid-liquid-solid systems represents a challenge for applications ranging from self-cleaning to biocompatibility of engineered materials. By using responsive polymer chemistry and molecular self-assembly, adhesion at solid/liquid interfaces can be achieved and modulated by external stimuli. Here, we utilize thermosensitive polymeric materials based on random copolymers of di(ethylene glycol) methyl ether methacrylate (x = MEO2MA) and oligo(ethylene glycol) methyl ether methacrylate (y = OEGMA), that is, P(MEO2MAx-co-OEGMAy), to investigate the role of hydrophobicity on the phenomenon of adhesion. The copolymer ratio (x/y) dictates macromolecular changes enabling control of the hydrophilic-to-lipophilic balance (HBL) of the polymer brushes through external triggers such as ionic strength and temperature. We discuss the HBL of the thermobrushes in terms of the surface energy of the substrate by measuring the contact angle at water-decane-P(MEO2MAx-co-OEGMAy) brush contact line as a function of polymer composition and temperature. Solid supported polyelectrolyte layers grafted with P(MEO2MAx-co-OEGMAy) display a transition in the wettability that is related to the lower critical solution temperature of the polymer brushes. Using experimental observation of the hydrophilic to hydrophobic transition by the contact angle, we extract the underlying energetics associated with liquid-liquid-solid adhesion as a function of the copolymer ratio. The change in cellular attachment on P(MEO2MAx-co-OEGMAy) substrates of variable (x/y) composition demonstrates the subtle role of compositional tuning on the ability to control liquid-liquid-solid adhesion in biological applications.

Flexible thermoresponsive nanomembranes at the aqueous-air interface.

A synthetic pathway is described to construct thermoresponsive freestanding nanomembranes at the aqueous-air interface of a pendant drop. Dynamic control of the reaction kinetics allows formation of viscoelastic interfaces supporting anisotropic stresses and mechanical stability, which can be tuned by external stimuli.

A water soluble fluorescent polymer as a dual colour sensor for temperature and a specific protein.

We present two thermoresponsive water soluble copolymers prepared via free radical statistical copolymerization of N-isopropylacrylamide (NIPAm) and of oligo(ethylene glycol) methacrylates (OEGMAs), respectively, with a solvatochromic 7-(diethylamino)-3-carboxy-coumarin (DEAC)-functionalized monomer. In aqueous solutions, the NIPAm-based copolymer exhibits characteristic changes in its fluorescence profile in response to a change in solution temperature as well as to the presence of a specific protein, namely an anti-DEAC antibody. This polymer emits only weakly at low temperatures, but exhibits a marked fluorescence enhancement accompanied by a change in its emission colour when heated above its cloud point. Such drastic changes in the fluorescence and absorbance spectra are observed also upon injection of the anti-DEAC antibody, attributed to the specific binding of the antibody to DEAC moieties. Importantly, protein binding occurs exclusively when the polymer is in the well hydrated state below the cloud point, enabling a temperature control on the molecular recognition event. On the other hand, heating of the polymer-antibody complexes releases a fraction of the bound antibody. In the presence of the DEAC-functionalized monomer in this mixture, the released antibody competitively binds to the monomer and the antibody-free chains of the polymer undergo a more effective collapse and inter-aggregation. In contrast, the emission properties of the OEGMA-based analogous copolymer are rather insensitive to the thermally induced phase transition or to antibody binding. These opposite behaviours underline the need for a carefully tailored molecular design of responsive polymers aimed at specific applications, such as biosensing.

Electrochemical detection of the thermally induced phase transition of a thin stimuli-responsive polymer film.

Quick and easy: An efficient approach for a direct observation of a thermally induced phase transition of a responsive polymer film on gold surfaces is described. Voltammetric measurements show that the peak current and the peak separation for a small redox couple are particularly sensitive to the conformational change of the polymer film and allow its phase transition detection.

On the influence of the architecture of poly(ethylene glycol)-based thermoresponsive polymers on cell adhesion.

Thermoresponsive polymer surface coatings are a promising tool for cell culture applications. They allow for a mild way of cell detachment that preserves the activity of membrane proteins-a prerequisite for reliable cell analysis. To enlarge the application range of these coatings to cells with different adhesion properties, we synthesized various novel poly(ethylene glycol)-based thermoresponsive polymers and describe how (i) their chemical structure and (ii) their surface density affect their efficiency. In order to quantify the influence of both factors, the time for cell spreading and rounding efficiency were observed. As a result, efficiency of cell rounding, which is closely correlated to cell detachment, is less affected by both factors than the time needed for cell spreading. This time can effectively be adjusted by the molecular architecture which includes the length of the polymer backbone and the side chains. Based on this work, recommendations are given for future optimization of functionality of thermoresponsive polymer coatings for cell culture applications.

Thermoresponsive PEG-based polymer layers: surface characterization with AFM force measurements.

Thermoresponsive polymer-coated surfaces based on poly(2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate) [P(MEO(2)MA-co-OEGMA)] allow switching between cell attachment and detachment. Here, we investigate the temperature-dependent surface interactions between the polymer coating and a colloidal probe in an aqueous medium by means of atomic force microscopy (AFM) force-distance measurements. The analysis of the adhesion forces from AFM retraction curves identifies two kinds of regimes for the copolymer at temperatures below and above the lower critical solution temperature (LCST). Whereas at 25 degrees C the surface interactions with the polymer in the swollen state are dominated by repulsive forces, at 37 degrees C the surface interactions switch to attractive forces and a stronger adhesion is detected by AFM. Running several heating/cooling cycles repeatedly shows that switching the surface properties provides reproducible adhesion force values. Time-dependent measurements give insight into the switching kinetics, demonstrating that the cell response is coupled to the polymer kinetics but probably limited by the cellular rearrangements.

Tuning the thickness of polymer brushes grafted from nonlinearly growing multilayer assemblies.

A new versatile method for tuning the thickness of surface-tethered polymer brushes is introduced. It is based on the combination of polyelectrolyte multilayer deposition and surface-initiated atom transfer radical polymerization. To control the thickness of the brushes, the nonlinear growth of certain polyelectrolyte multilayer systems is exploited. The method is demonstrated to work with different polyelectrolytes and different monomers. The relevance for applications is demonstrated by cell adhesion experiments on grafted thermoresponsive polymer layers with varying thickness.

Ordered polyelectrolyte multilayers. Rules governing layering in organic binary multilayers.

We study the growth and internal structure of polyelectrolyte multilayers obtained by combining three polyanions with nine polycations of the ionene family, of systematically varied chemical architecture. We find that, contrary to a generally held belief, ordered organic multilayers are by no way exceptional, provided one of the polyelectrolytes bears groups which induce structure in water, such as long hydrophobic segments or mesogenic groups. However, this condition is not sufficient, as order will or will not emerge in the multilayer depending on the specific pairing of the polyelectrolytes. The results support the notion that layering in the multilayer results from some degree of prestructuring of a water-swollen layer adsorbed during each step of deposition. These findings pave the way to new possible uses of polyelectrolyte multilayers, for example, for applications requiring preferential alignment or strong confinement of specific functional groups.