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Hydrogels in Action: Self-Assembly, Responsivity and Sensing

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A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Chemistry and Physics".

Deadline for manuscript submissions: closed (15 August 2023) | Viewed by 23528

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Dr. Hans Wyss

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Department of Mechanical Engineering and Institute for Complex Molecular Systems, Eindhoven University of Technology, 5612 AZ Eindhoven, The Netherlands
Interests: colloidal suspensions; gels; microgels; microfluidics
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Dear Colleagues,

Even structurally and functionally relatively simple hydrogels and hydrogel particle systems are scientifically fascinating materials, and are of key importance in numerous applications, including drug delivery, tissue engineering, advanced oil recovery, and chromatography.

This Special Issue on “Hydrogels in Action: Self-Assembly, Responsivity and Sensing” is dedicated to recent developments in the field of hydrogels where interesting dynamical, "active" aspects of hydrogel synthesis and behavior are studied and exploited. The use of phase separation processes and molecular self-assembly in the synthesis of advanced hydrogel materials exploits the complex dynamics of these mechanisms to create hydrogels with complex morphologies, tunable by the processing conditions and the molecular building blocks. Such methods of controlling hydrogel morphology can become even more powerful when combined with droplet-based microfluidic systems, which enable precise, repeatable processing conditions during the formation of each individual hydrogel particle.

Even “simple”, homogeneously structured hydrogel particle systems can exhibit a rich behavior in terms of their response to external stimuli. In response to changes in pH, temperature, light, ionic concentration, or the concentration of other solutes such as polymers dissolved in the background liquid, these systems exhibit a complex and often surprising swelling and de-swelling behavior. Hydrogels and hydrogel particles with more complex, hierarchical morphologies enabled by phase separation or self-assembly can be created with targeted, improved responsivity, which can be exploited in sensing applications.

We welcome the submission of studies covering different aspects of this general theme, using experiments and/or theory.

Dr. Hans Wyss
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

responsive hydrogels
swelling dynamics of hydrogels
drop-based microfluidics
hydrogels from aqueous two-phase systems
solvent-induced phase separation (SIPS)
molecular self-assembly of hydrogels
hydrogel particles for sensing applications
hydrogels with hierarchical pore structures

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Related Special Issue

Hydrogels in Action: Self-Assembly, Responsivity and Sensing (2nd Edition) in Gels

Published Papers (10 papers)

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Research

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16 pages, 6967 KiB

Open AccessArticle

Novel Grafted Hydrogel for Iron and Ammonia Removal from Groundwater: A Synthesis and Computational Chemistry Study

by H. M. Abd El-Salam, Ali M. El Shafey, Abdelouahid Samadi and Mahmoud K. Abdel-Latif

Gels 2023, 9(10), 781; https://doi.org/10.3390/gels9100781 - 25 Sep 2023

Viewed by 1279

Abstract

Current research is moving towards iron and ammonia elimination from groundwater. Here, we are using a poly acrylic–poly acrylamide hydrogel that is grafted with 3-chloroaniline. This copolymer was synthesized by addition polymerization technique. The effects of agitation time, dosage and adsorbent temperature on the removal process sensitivity were investigated. The copolymer was described experientially and theoretically. Isothermal kinetic adsorption models are discussed. This hydrogel could be regenerated efficiently (98.3% removal of iron and 100% removal of ammonia). The density functional theory (DFT) method, using B3LYP/6-311G(d,p), and the LANL2DZ level of the theory were managed to investigate the stationary states of the grafted copolymer and the complexation energy of the hydrogel with the studied cations. DFT has been used to investigate the Natural Bond Orbital (NBO) properties to locate the most negative centers on the hydrogel. The calculated complexation energy showed hydrogel selectivity with regard to the studied cations. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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17 pages, 3899 KiB

Open AccessArticle

Tailoring Homogeneous Hydrogel Nanospheres by Facile Ultra-Sonication Assisted Cross-Linked Copolymerization for Rhodamine B Dye Adsorption

by Gaurav Sharma, Alberto García-Peñas, Yaksha Verma, Amit Kumar, Pooja Dhiman and Florian J. Stadler

Gels 2023, 9(10), 770; https://doi.org/10.3390/gels9100770 - 22 Sep 2023

Cited by 2 | Viewed by 1111

Abstract

The present paper describes the design of shape-oriented hydrogel nanospheres using a facile ultrasonication-supported crosslinked copolymerization technique. The effect of variable monomer concentration on the homogeneity of hydrogel nanospheres was investigated. The chitosan-cl-poly(MMA) hydrogel nanospheres were well characterized using various techniques such as FTIR, XRD, TGA, SEM, and TEM. The chitosan-cl-poly(MMA) hydrogel nanospheres were studied for their swelling behavior and could potentially be used as a novel adsorbent for rhodamine B dye remediation from aqueous media. The study found that utilizing chitosan-cl-poly(MMA) nanohydrogel spheres at the optimal pH 5 increased RhB dye adsorption capacity from 7.9 to 17.8 mg/g (pH 2 to 5), followed by a slight reduction. Furthermore, when nanohydrogel concentration increased, adsorption capacity dropped from 18.03 to 2.8 mg/g, but adsorption percentage climbed from 90.2% to 97.8%. At an initial dye concentration of 140 mg/L, rhodamine B adsorption achieved 204.3 mg/g in 60 min. The rhodamine B dye adsorption study includes adsorption kinetics, isotherm, and thermodynamics analyses. The interpretation of the adsorption study revealed that Langmuir isotherms fit best with a qmax value of 276.26 mg/g, which is in close approximation with the experimental value, whereas pseudo-second-order kinetics explains the adsorption process rate. The interaction of RhB dye with chitosan-cl-poly(MMA) hydrogel nanospheres involves multiple forces such as electrostatic interactions, hydrogen bonding, van der Waals forces, etc. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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19 pages, 6754 KiB

Open AccessArticle

Stereo-Complex and Click-Chemical Bicrosslinked Amphiphilic Network Gels with Temperature/pH Response

by Wanying Yang, Jiaqi Wang, Lingjiang Jia, Jingyi Li and Shouxin Liu

Gels 2023, 9(8), 647; https://doi.org/10.3390/gels9080647 - 11 Aug 2023

Cited by 3 | Viewed by 1299

Abstract

Stimulus-responsive hydrogels have been widely used in the field of drug delivery because of their three-dimensional pore size and the ability to change the drug release rate with the change in external environment. In this paper, the temperature-sensitive monomer 2-methyl-2-acrylate-2-(2-methoxyethoxy-ethyl) ethyl ester (MEO₂MA) and oligoethylene glycol methyl ether methacrylate (OEGMA) as well as the pH-sensitive monomer N,N-Diethylaminoethyl methacrylate (DEAEMA) were used to make the gel with temperature and pH response. Four kinds of physicochemical double-crosslinked amphiphilic co-network gels with different polymerization degrees were prepared by the one-pot method using the stereocomplex between polylactic acid as physical crosslinking and click chemistry as chemical crosslinking. By testing morphology, swelling, thermal stability and mechanical properties, the properties of the four hydrogels were compared. Finally, the drug release rate of the four gels was tested by UV–Vis spectrophotometer. It was found that the synthetic hydrogels had a good drug release rate and targeting, and had great application prospect in drug delivery. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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17 pages, 3345 KiB

Open AccessArticle

KLVFF Conjugated Curcumin Microemulsion-Based Hydrogel for Transnasal Route: Formulation Development, Optimization, Physicochemical Characterization, and Ex Vivo Evaluation

by Rungsinee Phongpradist, Jutamas Jiaranaikulwanitch, Kriangkrai Thongkorn, Suree Lekawanvijit, Sasithorn Sirilun, Chuda Chittasupho and Worrapan Poomanee

Gels 2023, 9(8), 610; https://doi.org/10.3390/gels9080610 - 28 Jul 2023

Cited by 2 | Viewed by 1859

Abstract

Curcumin is a potent natural compound used to treat Alzheimer’s disease (AD). However, the clinical usefulness of curcumin to treat AD is restricted by its low oral bioavailability and difficulty permeating the blood-brain barrier. To overcome such drawbacks, various alternative strategies have been explored, including the transnasal route. However, rapid mucociliary clearance in the nasal cavity is a major hindrance to drug delivery. Thus, designing a delivery system for curcumin to lengthen the contact period between the drug and nasal mucosa must be employed. This study describes the optimization of KLVFF conjugated curcumin microemulsion-base hydrogel (KCMEG) to formulate a prototype transnasal preparation using the response surface method to improve a mucoadhesive property. A central composite design was employed to optimize and evaluate two influencing factors: the concentration of carbopol 940 and the percentage of KLVFF conjugated curcumin microemulsion (KCME). The physicochemical properties, anti-cholinesterase activity, and anti-aggregation activities of KCME were investigated in this study. The studied factors, in terms of main and interaction effects, significantly (p < 0.05) influenced hardness and adhesiveness. The optimized KCMEG was evaluated for pH, spreadability, and mucoadhesive properties. Ex vivo nasal ciliotoxicity to optimize KCMEG was performed through the porcine nasal mucosa. KCME was transparent, with a mean globule size of 70.8 ± 3.4 nm and a pH of 5.80 ± 0.02. The optimized KCMEG containing 2% carbopol 940 showed higher in vitro mucoadhesive potential (9.67 ± 0.13 min) compared with microemulsion and was also found to be free from nasal ciliotoxicity during histopathologic evaluation of the porcine nasal mucosa. The result revealed that both the concentration of carbopol 940 and the percentage of KCME play a crucial role in mucoadhesive properties. In conclusion, incorporating a mucoadhesive agent in a microemulsion can increase the retention time of the formulation, leading to enhanced brain delivery of the drug. Findings from the investigation revealed that KCMEG has the potential to constitute a promising approach to treating AD via transnasal administration. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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23 pages, 4137 KiB

Open AccessArticle

Temperature-Responsive Hydrogel for Silver Sulfadiazine Drug Delivery: Optimized Design and In Vitro/In Vivo Evaluation

by Maha Mohammad AL-Rajabi and Yeit Haan Teow

Gels 2023, 9(4), 329; https://doi.org/10.3390/gels9040329 - 13 Apr 2023

Cited by 3 | Viewed by 2186

Abstract

Response surface methodology (RSM) was applied to optimise a temperature-responsive hydrogel formulation synthesised via the direct incorporation of biocellulose, which was extracted from oil palm empty fruit bunches (OPEFB) using the PF127 method. The optimised temperature-responsive hydrogel formulation was found to contain 3.000 w/v% biocellulose percentage and 19.047 w/v% PF127 percentage. The optimised temperature-responsive hydrogel provided excellent LCST near to the human body surface temperature, with high mechanical strength, drug release duration, and inhibition zone diameter against Staphylococcus aureus. Moreover, in vitro cytotoxicity testing against human epidermal keratinocyte (HaCaT) cells was conducted to evaluate the toxicity of the optimised formula. It was found that silver sulfadiazine (SSD)-loaded temperature-responsive hydrogel can be used as a safe replacement for the commercial SSD cream with no toxic effect on HaCaT cells. Last, but not least, in vivo (animal) dermal testing—both dermal sensitization and animal irritation—were conducted to evaluate the safety and biocompatibility of the optimised formula. No sensitization effects were detected on the skin applied with SSD-loaded temperature-responsive hydrogel indicating no irritant response for topical application. Therefore, the temperature-responsive hydrogel produced from OPEFB is ready for the next stage of commercialisation. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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14 pages, 1880 KiB

Open AccessArticle

Single Hydrogel Particle Mechanics and Dynamics Studied by Combining Capillary Micromechanics with Osmotic Compression

by Kalpit J. Bakal, Andreas M. A. O. Pollet, Jaap M. J. den Toonder and Hans M. Wyss

Gels 2023, 9(3), 194; https://doi.org/10.3390/gels9030194 - 3 Mar 2023

Cited by 1 | Viewed by 2245

Abstract

Hydrogels can exhibit a remarkably complex response to external stimuli and show rich mechanical behavior. Previous studies of the mechanics of hydrogel particles have generally focused on their static, rather than dynamic, response, as traditional methods for measuring single particle response at the microscopic scale cannot readily measure time-dependent mechanics. Here, we study both the static and the time-dependent response of a single batch of polyacrylamide (PAAm) particles by combining direct contact forces, applied by using Capillary Micromechanics, a method where particles are deformed in a tapered capillary, and osmotic forces are applied by a high molecular weight dextran solution. We found higher values of the static compressive and shear elastic moduli for particles exposed to dextran, as compared to water (

K_{Dex} \approx 63

kPa vs.

K_{water} \approx 36

kPa, and

G_{Dex} \approx 16

kPa vs.

G_{water} \approx 7

kPa), which we accounted for, theoretically, as being the result of the increased internal polymer concentration. For the dynamic response, we observed surprising behavior, not readily explained by poroelastic theories. The particles exposed to dextran solutions deformed more slowly under applied external forces than did those suspended in water (

τ_{Dex} \approx 90

s vs.

τ_{water} \approx 15

s). The theoretical expectation was the opposite. However, we could account for this behaviour by considering the diffusion of dextran molecules in the surrounding solution, which we found to dominate the compression dynamics of our hydrogel particles suspended in dextran solutions. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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13 pages, 4031 KiB

Open AccessArticle

Photo-Crosslinked Coumarin-Containing Bis-Urea Amphiphile Hydrogels

by Jie Liu, Xianwen Lou, Maaike J. G. Schotman, Patricia P. Marín San Román and Rint P. Sijbesma

Gels 2022, 8(10), 615; https://doi.org/10.3390/gels8100615 - 27 Sep 2022

Cited by 6 | Viewed by 2543

Abstract

The design of photo-responsive supramolecular hydrogels based on coumarin dimerization and de-dimerization is described. The photo-responsive coumarin unit is chemically incorporated into an oligo(ethylene glycol) (OEG) bis-urea amphiphile that is capable of co-assembling with non-functionalized OEG amphiphile, to form supramolecular fibers. UV light with two different wavelengths (365 nm and 254 nm) is employed to induce a photo-reversible dimerization and de-dimerization process of coumarin units, respectively. The co-assembled solutions could be photo-crosslinked to induce a sol-to-gel transition through dimerization of coumarin with 365 nm UV light, and de-dimerization occurs with 254 nm UV light, to provide a weaker gel. In this system, the mechanical strength of supramolecular hydrogels can be tuned using the irradiation time, providing precise control of gelation in a supramolecular hydrogelator. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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10 pages, 3431 KiB

Open AccessArticle

Fabrication of Thermo-Responsive Controllable Shape-Changing Hydrogel

by Yi Luo, Werner Pauer and Gerrit A. Luinstra

Gels 2022, 8(9), 531; https://doi.org/10.3390/gels8090531 - 25 Aug 2022

Cited by 5 | Viewed by 2426

Abstract

Temperature response double network (DN) hydrogels comprising a network formed by polymerization of methacrylic acid (MA) modified PVA, N,N’-methylene bis(acrylamide), N-isopropylacryl amide (NIPAM), and one formed from crystalline polyvinyl alcohol (PVA) are prepared in a 3D printed tailor-made mold. The (PVA-MA)-g-PNIPAAm thermoset intermediate is formed in water by a radical, photo-initiated process, and in the presence of dissolved PVA polymers. A subsequent freezing-thawing sequence induces the crystallization of the PVA network, which forms a second network inside the thermoset NIPAM polymer. The prepared hydrogel is thermoresponsive by the phase transition of PNIPAAm segments (T ≈ 32 °C) and has good mechanical properties (tensile strength 1.23 MPa, compressive strength 1.47 MPa). Thermal cycling between room temperature at 40 or 50 °C shows the product converses from a virgin-state to a steady-state, which most likely involves the reorganization of PVA crystals. The swelling-deswelling cycles remain clear at a length change of about 13%. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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Review

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18 pages, 3956 KiB

Open AccessReview

Polymeric Materials for Rare Earth Elements Recovery

by Hongtao Zhang and Yongfeng Gao

Gels 2023, 9(10), 775; https://doi.org/10.3390/gels9100775 - 24 Sep 2023

Cited by 8 | Viewed by 2717

Abstract

Rare earth elements (REEs) play indispensable roles in various advanced technologies, from electronics to renewable energy. However, the heavy global REEs supply and the environmental impact of traditional mining practices have spurred the search for sustainable REEs recovery methods. Polymeric materials have emerged as promising candidates due to their selective adsorption capabilities, versatility, scalability, and regenerability. This paper provides an extensive overview of polymeric materials for REEs recovery, including polymeric resins, polymer membranes, cross-linked polymer networks, and nanocomposite polymers. Each category is examined for its advantages, challenges, and notable developments. Furthermore, we highlight the potential of polymeric materials to contribute to eco-friendly and efficient REEs recovery, while acknowledging the need to address challenges such as selectivity, stability, and scalability. The research in this field actively seeks innovative solutions to reduce reliance on hazardous chemicals and minimize waste generation. As the demand for REEs continues to rise, the development of sustainable REEs recovery technologies remains a critical area of investigation, with the collaboration between researchers and industry experts driving progress in this evolving field. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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20 pages, 1785 KiB

Open AccessEditor’s ChoiceReview

Application of Hydrogels as Three-Dimensional Bioprinting Ink for Tissue Engineering

by Mengbo Xie, Jingjing Su, Shengxi Zhou, Jingan Li and Kun Zhang

Gels 2023, 9(2), 88; https://doi.org/10.3390/gels9020088 - 19 Jan 2023

Cited by 23 | Viewed by 4667

Abstract

The use of three-dimensional bioprinting technology combined with the principle of tissue engineering is important for the construction of tissue or organ regeneration microenvironments. As a three-dimensional bioprinting ink, hydrogels need to be highly printable and provide a stiff and cell-friendly microenvironment. At present, hydrogels are used as bioprinting inks in tissue engineering. However, there is still a lack of summary of the latest 3D printing technology and the properties of hydrogel materials. In this paper, the materials commonly used as hydrogel bioinks; the advanced technologies including inkjet bioprinting, extrusion bioprinting, laser-assisted bioprinting, stereolithography bioprinting, suspension bioprinting, and digital 3D bioprinting technologies; printing characterization including printability and fidelity; biological properties, and the application fields of bioprinting hydrogels in bone tissue engineering, skin tissue engineering, cardiovascular tissue engineering are reviewed, and the current problems and future directions are prospected. Full article

(This article belongs to the Special Issue Hydrogels in Action: Self-Assembly, Responsivity and Sensing)

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