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Microgels and Hydrogels at Interfaces

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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (30 June 2018) | Viewed by 95066

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Dr. Patrick van Rijn

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Guest Editor

Department of Biomedical Engineering-FB40, W.J. Kolff Institute for Biomedical Engineering and Materials Science-FB41, University Medical Center Groningen, A. Deusinglaan 1, 9713 AV Groningen, The Netherlands
Interests: biohybrid systems; polymeric microgels; surface chemistry; biomaterials; biointerfaces; cell biology; biomedical applications
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Dr. Felix Plamper

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Guest Editor

Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany
Interests: polymer complexation; interfacial complexation; self-assembly; soft matter electrochemistry; scattering methods; microgels

Special Issue Information

Dear Colleagues,

Everything occurs at the interface… Many interesting phenomena occur when structures meet, thereby creating an interface or altering an existing one. Controlling the behaviour or directing dynamics at interfaces has moved from being an exploratory exercise to a sophisticated approach to engineer new devices and coatings within the field of biomedical applications, electronics, sensors, coatings, and many more. Many of these applications find their origin in the use of hydrogels as these can be tailored in their chemical compositions, solvent compatibility, swelling/deswelling behaviour, and mechanical properties. Such hydrogels and hydrogel-like structures include but are not limited to polymer and molecular hydrogels, polymer brushes, and microgels. Because of the large diversity in molecular compositions, highly sophisticated and smart/responsive hydrogels can be fabricated allowing for the development of ever more complex interfaces and hence applications.

The aim of this Special Issue is to focus on new developments of hydrogel structures at interfaces from both an application and a fundamental point of view where new surface modification approaches not only facilitate new technologies being developed but also provide more fundamental insights to surface structuring, adsorption/desorption phenomena, interface dynamics, and time-dependent control. Here the particular focus is amongst others on anti-fouling phenomena, interface-bound biological structures and responsive systems in the broadest sense, including temperature, pH, and light stimulation. Additionally, electrochemical approaches for both fundamental insights and new applications will be collected.

Both review articles and original research papers are solicited. There is particular interest in papers envisioning innovative approaches or novel synthetic challenges to create functional systems.

Dr. Patrick van Rijn
Dr. Felix Plamper
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

hydrogels
microgels
interfaces (solid liquid; liquid/liquid; liquid/air)
self-assembly
responsive materials
soft matter electrochemistry
interfacial segregation and complexation

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Published Papers (11 papers)

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Research

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14 pages, 5638 KiB

Open AccessArticle

Graphene Oxide Reinforced Alginate/PVA Double Network Hydrogels for Efficient Dye Removal

by Cuiyun Liu, Hongyu Liu, Tianhui Xiong, Airong Xu, Bingli Pan and Keyong Tang

Polymers 2018, 10(8), 835; https://doi.org/10.3390/polym10080835 - 28 Jul 2018

Cited by 96 | Viewed by 11337

Abstract

Dually crosslinked graphene oxide reinforced alginate/polyvinyl alcohol (PVA) double network (DN) hydrogels were prepared via a facile freeze/thaw method followed by soaking in a Ca²⁺ solution. The morphology and structure of the hydrogels were systematically examined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The effects of pH, dosage of hydrogel, adsorption time, and temperature on the adsorptive property of DN hydrogels towards methylene blue (MB) were also studied. Results indicated that the hydrogels exhibited typical 3D porous structures and had an efficient adsorption effect towards MB due to strong interactions between DN hydrogels and MB molecules. The adsorption isotherm was found to coincide with the Langmuir model with a monolayer adsorption. The highest adsorption capacity of DN hydrogels for MB was examined as 480.76 mg·g⁻¹. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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16 pages, 5260 KiB

Open AccessArticle

Fluid Dynamics of Microgel-Covered Drops Reveal Impact on Interfacial Conditions

by Miriam Faulde, Eric Siemes, Dominik Wöll and Andreas Jupke

Polymers 2018, 10(8), 809; https://doi.org/10.3390/polym10080809 - 24 Jul 2018

Cited by 16 | Viewed by 5209

Abstract

Microgels are deformable polymer-networks with conspicuous properties. Their surface- activity associated with their switchability makes their application in liquid-liquid systems, such as extraction processes, particularly promising. For their application as switchable stabilizers at the interface, a detailed understanding of their impact on process relevant phenomena, such as the sedimentation behavior, is necessary. So far, the focus of research has been on microscopic-scale properties, whereby the propagation to macroscopic effects has rarely been quantified. In this study, single microgel-covered n-butyl acetate drops rising in a quiescent continuous water phase are investigated experimentally. The dependency of the microgel properties, in terms of size and cross-linking density, on the fluid dynamics are addressed. The impact of microgels is studied in detail by sedimentation velocity, drop deformation and the resulting drag coefficient. The deformation of drops is related to shape conserving interfacial properties such as the interfacial tension. Counter to our expectations, microgel-covered drops deform less than the drops of the pure system although microgels reduce the interfacial tension. Moreover, the sedimentation velocity is of special interest, since it reveals the mobility of the interface and friction conditions at the interface. Our results demonstrate the correlation between microgel properties at the interface on a microscopic scale and the macroscopic behavior of microgel-covered drops. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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18 pages, 2307 KiB

Open AccessArticle

Surface Functionalization by Stimuli-Sensitive Microgels for Effective Enzyme Uptake and Rational Design of Biosensor Setups

by Larisa V. Sigolaeva, Dmitry V. Pergushov, Marina Oelmann, Simona Schwarz, Monia Brugnoni, Ilya N. Kurochkin, Felix A. Plamper, Andreas Fery and Walter Richtering

Polymers 2018, 10(7), 791; https://doi.org/10.3390/polym10070791 - 19 Jul 2018

Cited by 37 | Viewed by 7243

Abstract

We highlight microgel/enzyme thin films that were deposited onto solid interfaces via two sequential steps, the adsorption of temperature- and pH-sensitive microgels, followed by their complexation with the enzyme choline oxidase, ChO. Two kinds of functional (ionic) microgels were compared in this work in regard to their adsorptive behavior and interaction with ChO, that is, poly(N-isopropylacrylamide-co-N-(3-aminopropyl)methacrylamide), P(NIPAM-co-APMA), bearing primary amino groups, and poly(N-isopropylacrylamide-co-N-[3-(dimethylamino) propyl]methacrylamide), P(NIPAM-co-DMAPMA), bearing tertiary amino groups. The stimuli-sensitive properties of the microgels in the solution were characterized by potentiometric titration, dynamic light scattering (DLS), and laser microelectrophoresis. The peculiarities of the adsorptive behavior of both the microgels and the specific character of their interaction with ChO were revealed by a combination of surface characterization techniques. The surface charge was characterized by electrokinetic analysis (EKA) for the initial graphite surface and the same one after the subsequent deposition of the microgels and the enzyme under different adsorption regimes. The masses of wet microgel and microgel/enzyme films were determined by quartz crystal microbalance with dissipation monitoring (QCM-D) upon the subsequent deposition of the components under the same adsorption conditions, on a surface of gold-coated quartz crystals. Finally, the enzymatic responses of the microgel/enzyme films deposited on graphite electrodes to choline were tested amperometrically. The presence of functional primary amino groups in the P(NIPAM-co-APMA) microgel enables a covalent enzyme-to-microgel coupling via glutar aldehyde cross-linking, thereby resulting in a considerable improvement of the biosensor operational stability. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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12 pages, 9237 KiB

Open AccessArticle

Thermoresponsive Microgel Coatings as Versatile Functional Compounds for Novel Cell Manipulation Tools

by Katja Uhlig, Thomas Wegener, Yvonne Hertle, Johannes Bookhold, Magnus Jaeger, Thomas Hellweg, Andreas Fery and Claus Duschl

Polymers 2018, 10(6), 656; https://doi.org/10.3390/polym10060656 - 12 Jun 2018

Cited by 29 | Viewed by 5033

Abstract

For the effective use of live cells in biomedicine as in vitro test systems or in biotechnology, non-invasive cell processing and characterisation are key elements. Thermoresponsive polymer coatings have been demonstrated to be highly beneficial for controlling the interaction of adherent cells through their cultivation support. However, the widespread application of these coatings is hampered by limitations in their adaptability to different cell types and because the full range of applications has not yet been fully explored. In the work presented here, we address these issues by focusing on three different aspects. With regard to the first aspect, by using well-defined laminar flow in a microchannel, a highly controllable and reproducible shear force can be applied to adherent cells. Employing this tool, we demonstrate that cells can be non-invasively detached from a support using a defined shear flow. The second aspect relates to the recent development of simple methods for patterning thermoresponsive coatings. Here, we show how such patterned coatings can be used for improving the handling and reliability of a wound-healing assay. Two pattern geometries are tested using mouse fibroblasts and CHO cells. In terms of the third aspect, the adhesiveness of cells depends on the cell type. Standard thermoresponsive coatings are not functional for all types of cells. By coadsorbing charged nanoparticles and thermoresponsive microgels, it is demonstrated that the adhesion and detachment behaviour of cells on such coatings can be modulated. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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21 pages, 33224 KiB

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On the Potential of Using Dual-Function Hydrogels for Brackish Water Desalination

by Wael Ali, Beate Gebert, Sedakat Altinpinar, Thomas Mayer-Gall, Mathias Ulbricht, Jochen S. Gutmann and Karlheinz Graf

Polymers 2018, 10(6), 567; https://doi.org/10.3390/polym10060567 - 23 May 2018

Cited by 21 | Viewed by 8181

Abstract

Although current desalination technologies are mature enough and advanced, the shortage of freshwater is still considered as one of the most pressing global issues. Therefore, there is a strong incentive to explore and investigate new potential methods with low energy consumption. We have previously reported that reversible thermally induced sorption/desorption process using polymeric hydrogels hold promise for water desalination with further development. In order to develop a more effective hydrogels architecture, polyelectrolyte moieties were introduced in this work as pendent chains and a thermally responsive polymer as network backbone using reversible addition-fragmentation chain transfer (RAFT) polymerisation. The ability of the comb-type polymeric hydrogels to desalinate water was evaluated. These hydrogels were proved to absorb water with low salinity from brine solution of 2 g L

^{- 1}

NaCl and release the absorbed water at relatively low temperature conditions of 50

^{\circ}

C. The fraction of the grafted polyacrylic acid and the comb-chain length were varied to understand their influence on the swelling/deswelling behaviour for these hydrogels. The ionic fraction in the hydrogels and the resulting hydrophilic/hydrophobic balance are crucial for the proposed desalination process. In contrast, the comb-chain length impacted the swelling behaviour of hydrogels but showed relatively little influence on the dewatering process. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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11 pages, 3268 KiB

Open AccessArticle

3D Printing of Thermoresponsive Polyisocyanide (PIC) Hydrogels as Bioink and Fugitive Material for Tissue Engineering

by Nehar Celikkin, Joan Simó Padial, Marco Costantini, Hans Hendrikse, Rebecca Cohn, Christopher J. Wilson, Alan Edward Rowan and Wojciech Święszkowski

Polymers 2018, 10(5), 555; https://doi.org/10.3390/polym10050555 - 21 May 2018

Cited by 40 | Viewed by 7978

Abstract

Despite the rapid and great developments in the field of 3D hydrogel printing, a major ongoing challenge is represented by the development of new processable materials that can be effectively used for bioink formulation. In this work, we present an approach to 3D deposit, a new class of fully-synthetic, biocompatible PolyIsoCyanide (PIC) hydrogels that exhibit a reverse gelation temperature close to physiological conditions (37 °C). Being fully-synthetic, PIC hydrogels are particularly attractive for tissue engineering, as their properties—such as hydrogel stiffness, polymer solubility, and gelation kinetics—can be precisely tailored according to process requirements. Here, for the first time, we demonstrate the feasibility of both 3D printing PIC hydrogels and of creating dual PIC-Gelatin MethAcrylate (GelMA) hydrogel systems. Furthermore, we propose the use of PIC as fugitive hydrogel to template structures within GelMA hydrogels. The presented approach represents a robust and valid alternative to other commercial thermosensitive systems—such as those based on Pluronic F127—for the fabrication of 3D hydrogels through additive manufacturing technologies to be used as advanced platforms in tissue engineering. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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14 pages, 2257 KiB

Open AccessFeature PaperArticle

The Relationship between Bulk Silicone and Benzophenone-Initiated Hydrogel Coating Properties

by Damla Keskin, Taraneh Mokabbar, Yutao Pei and Patrick Van Rijn

Polymers 2018, 10(5), 534; https://doi.org/10.3390/polym10050534 - 16 May 2018

Cited by 28 | Viewed by 14842

Abstract

Polydimethylsiloxane (PDMS) is a silicone elastomer-based material that is used in various applications, including coatings, tubing, microfluidics, and medical implants. PDMS has been modified with hydrogel coatings to prevent fouling, which can be done through UV-mediated free radical polymerization using benzophenone. However, to the best of our knowledge, the properties of hydrogel coatings and their influence on the bulk properties of PDMS under various preparation conditions, such as the type and concentration of monomers, and UV treatment time, have never been investigated. Acrylate-based monomers were used to perform free radical polymerization on PDMS surfaces under various reaction conditions. This approach provides insights into the relationship between the hydrogel coating and bulk properties of PDMS. Altering the UV polymerization time and the monomer concentration resulted in different morphologies with different roughness and thickness of the hydrogel coating, as well as differences in the bulk material stiffness. The surface morphology of the coated PDMS was characterized by AFM. The cross section and thickness of the coatings were examined using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The dependence of coating development on the monomer type and concentration used was evaluated by surface hydrophilicity, as measured by water contact angle. Elongation-until-break analysis revealed that specific reaction conditions affected the bulk properties and made the coated PDMS brittle. Therefore, boundary conditions have been identified to enable high quality hydrogel coating formation without affecting the bulk properties of the material. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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12 pages, 2261 KiB

Open AccessArticle

Influence of Polycation Composition on Electrochemical Film Formation

by Sabine Schneider, Corinna Janssen, Elisabeth Klindtworth, Olga Mergel, Martin Möller and Felix Plamper

Polymers 2018, 10(4), 429; https://doi.org/10.3390/polym10040429 - 12 Apr 2018

Cited by 8 | Viewed by 5201

Abstract

The effect of polyelectrolyte composition on the electrodeposition onto platinum is investigated using a counterion switching approach. Film formation of preformed polyelectrolytes is triggered by oxidation of hexacyanoferrates(II) (ferrocyanide), leading to polyelectrolyte complexes, which are physically crosslinked by hexacyanoferrate(III) (ferricyanide) ions due to preferential ferricyanide/polycation interactions. In this study, the electrodeposition of three different linear polyelectrolytes, namely quaternized poly[2-(dimethylamino)ethyl methacrylate] (i.e., poly{[2-(methacryloyloxy)ethyl]trimethylammonium chloride}; PMOTAC), quaternized poly[2-(dimethylamino)ethyl acrylate] (i.e., poly{[2-(acryloyloxy)ethyl]trimethylammonium chloride}; POTAC), quaternized poly[N-(3-dimethylaminopropyl)methacrylamide] (i.e., poly{[3-(methacrylamido)propyl]trimethylammonium chloride}; PMAPTAC) and different statistical copolymers of these polyelectrolytes with N-(3-aminopropyl)methacrylamide (APMA), are studied. Hydrodynamic voltammetry utilizing a rotating ring disk electrode (RRDE) shows the highest deposition efficiency DE for PMOTAC over PMAPTAC and over POTAC. Increasing incorporation of APMA weakens the preferred interaction of the quaternized units with the hexacyanoferrate(III) ions. At a sufficient APMA content, electrodeposition can thus be prevented. Additional electrochemical quartz crystal microbalance measurements reveal the formation of rigid polyelectrolyte films being highly crosslinked by the hexacyanoferrate(III) ions. Results indicate a different degree of water incorporation into these polyelectrolyte films. Hence, by adjusting the polycation composition, film properties can be tuned, while different chemistries can be incorporated into these electrodeposited thin hydrogel films. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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1980 KiB

Open AccessArticle

On the Limits of Benzophenone as Cross-Linker for Surface-Attached Polymer Hydrogels

by Esther K. Riga, Julia S. Saar, Roman Erath, Michelle Hechenbichler and Karen Lienkamp

Polymers 2017, 9(12), 686; https://doi.org/10.3390/polym9120686 - 7 Dec 2017

Cited by 33 | Viewed by 8989

Abstract

The synthesis of different photo-reactive poly(alkenyl norbornenes) and poly(oxonorbornenes) containing benzophenone (BP) via ring-opening metatheses polymerization (ROMP) is described. These polymers are UV irradiated to form well-defined surface-attached polymer networks and hydrogels. The relative propensity of the polymers to cross-link is evaluated by studying their gel content and its dependency on BP content, irradiation wavelength (254 or 365 nm) and energy dose applied (up to 11 J·cm⁻²). Analysis of the UV spectra of the polymer networks demonstrates that the poly(oxonorbornenes) show the expected BP-induced crosslinking behavior at 365 nm, although high irradiation energy doses and BP content are needed. However, these polymers undergo chain scission at 254 nm. The poly(alkenyl norbornenes), on the other hand, do not cross-link at 365 nm, whereas moderate to good cross-linking is observed at 254 nm. UV spectra demonstrate that the cross-linking at 254 nm is due to BP cross-linking combined with a [2 + 2] cylcoaddition of the alkenyl double bonds. This indicates limitations of benzophenone as a universally applicable cross-linking for polymer networks and hydrogels. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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Review

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23 pages, 2282 KiB

Open AccessReview

Nanomechanics and Nanorheology of Microgels at Interfaces

by Sebastian Backes and Regine Von Klitzing

Polymers 2018, 10(9), 978; https://doi.org/10.3390/polym10090978 - 3 Sep 2018

Cited by 38 | Viewed by 4543

Abstract

The review addresses nanomechanics and nanorheology of stimuli responsive microgels adsorbed at an interface. In order to measure the mechanical properties on a local scale, an atomic force microscope is used. The tip presents an indenter with a radius of curvature of a few 10 s of nm. Static indentation experiments and dynamic studies with an excited cantilever are presented. The effect of several internal and external parameters on the mechanical properties is reviewed. The focus is on the correlation between the swelling abilities of the gels and their mechanical properties. Several results are surprising and show that the relationship is not as simple as one might expect. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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26 pages, 44887 KiB

Open AccessReview

Stimuli-Responsive Microgels and Microgel-Based Systems: Advances in the Exploitation of Microgel Colloidal Properties and Their Interfacial Activity

by Garima Agrawal and Rahul Agrawal

Polymers 2018, 10(4), 418; https://doi.org/10.3390/polym10040418 - 9 Apr 2018

Cited by 78 | Viewed by 12569

Abstract

In this paper, recent developments in the chemical design of functional microgels are summarized. A wide range of available synthetic methods allows the incorporation of various reactive groups, charges, or biological markers inside the microgel network, thus controlling the deformation and swelling degree of the resulting smart microgels. These microgels can respond to various stimuli, such as temperature, pH, light, electric field, etc. and can show unique deformation behavior at the interface. Due to their switchability and interfacial properties, these smart microgels are being extensively explored for various applications, such as antifouling coatings, cell encapsulation, catalysis, controlled drug delivery, and tissue engineering. Full article

(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)

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