Research

12 pages, 2116 KiB

Open AccessFeature PaperArticle

Evaluation of Mesh Size in Model Polymer Networks Consisting of Tetra-Arm and Linear Poly(ethylene glycol)s

by Yui Tsuji, Xiang Li and Mitsuhiro Shibayama

Gels 2018, 4(2), 50; https://doi.org/10.3390/gels4020050 - 25 May 2018

Cited by 56 | Viewed by 7362

The structure and mechanical properties of model polymer networks consisting of alternating tetra-functional poly(ethylene glycol)s (PEGs) and bis-functional linear PEGs were investigated by dynamic light scattering and rheological measurements. The sizes of the correlation blob (

ξ_{c}

) and the elastic blob [...] Read more.

The structure and mechanical properties of model polymer networks consisting of alternating tetra-functional poly(ethylene glycol)s (PEGs) and bis-functional linear PEGs were investigated by dynamic light scattering and rheological measurements. The sizes of the correlation blob (

ξ_{c}

) and the elastic blob (

ξ_{e l}

) were obtained from these measurements and compared to the theoretical mesh size, the geometric blob (

ξ_{g}

), calculated by using the tree-like approximation. By fixing the concentration of tetra-PEGs and tuning the molecular weight of linear-PEGs, we systematically compared these blob sizes in two cases: complete network (Case A) and incomplete network (Case B). The correlation blob,

ξ_{c}

, obtained by dynamic light scattering (DLS) was found to obey the well-known concentration dependence for polymer solutions in semidilute regime (

ξ_{c} ~ ϕ^{- 3 / 4}

) irrespective of the Cases. On the other hand, the

G^{'}

was strongly dependent on the Cases: For Case A,

G^{'}

was weakly dependent on the molecular weight of linear-PEGs (

G^{'} ~ M_{c}^{0.69}

) while

G^{'}

for Case B was a strong increasing function of

M_{c}

(

G^{'} ~ M_{c}^{1.2}

). However, both of them are different from the geometric blob (theoretical mesh) of the gel networks. In addition, interesting relationships between

G^{'}

and

ξ_{c}

,

G^{'} ~ ξ_{c}

,

G^{'} ~ ξ_{C}^{- 2}

, were obtained for Cases A and B, respectively. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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Review

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21 pages, 7891 KiB

Open AccessReview

Multiply Interpenetrating Polymer Networks: Preparation, Mechanical Properties, and Applications

by Panayiota A. Panteli and Costas S. Patrickios

Gels 2019, 5(3), 36; https://doi.org/10.3390/gels5030036 - 08 Jul 2019

Cited by 25 | Viewed by 6393

Abstract

This review summarizes work done on triply, or higher, interpenetrating polymer network materials prepared in order to widen the properties of double polymer network hydrogels (DN), doubly interpenetrating polymer networks with enhanced mechanical properties. The review will show that introduction of a third, [...] Read more.

This review summarizes work done on triply, or higher, interpenetrating polymer network materials prepared in order to widen the properties of double polymer network hydrogels (DN), doubly interpenetrating polymer networks with enhanced mechanical properties. The review will show that introduction of a third, or fourth, polymeric component in the DNs would further enhance the mechanical properties of the resulting materials, but may also introduce other useful functionalities, including electrical conductivity, low-friction coefficients, and (bio)degradability. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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9 pages, 3140 KiB

Open AccessEditor’s ChoiceReview

Challenges for Natural Hydrogels in Tissue Engineering

by Esmaiel Jabbari

Gels 2019, 5(2), 30; https://doi.org/10.3390/gels5020030 - 29 May 2019

Cited by 29 | Viewed by 5894

Abstract

Protein-based biopolymers derived from natural tissues possess a hierarchical structure in their native state. Strongly solvating, reducing and stabilizing agents, as well as heat, pressure, and enzymes are used to isolate protein-based biopolymers from their natural tissue, solubilize them in aqueous solution and [...] Read more.

Protein-based biopolymers derived from natural tissues possess a hierarchical structure in their native state. Strongly solvating, reducing and stabilizing agents, as well as heat, pressure, and enzymes are used to isolate protein-based biopolymers from their natural tissue, solubilize them in aqueous solution and convert them into injectable or preformed hydrogels for applications in tissue engineering and regenerative medicine. This review aims to highlight the need to investigate the nano-/micro-structure of hydrogels derived from the extracellular matrix proteins of natural tissues. Future work should focus on identifying the nature of secondary, tertiary, and higher order structure formation in protein-based hydrogels derived from natural tissues, quantifying their composition, and characterizing their binding pockets with cell surface receptors. These advances promise to lead to wide-spread use of protein-based hydrogels derived from natural tissues as injectable or preformed matrices for cell delivery in tissue engineering and regenerative medicine. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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10 pages, 3719 KiB

Open AccessFeature PaperReview

Recent Progress in Photon Upconverting Gels

by Pankaj Bharmoria, Nobuhiro Yanai and Nobuo Kimizuka

Gels 2019, 5(1), 18; https://doi.org/10.3390/gels5010018 - 26 Mar 2019

Cited by 18 | Viewed by 5006

Abstract

Recent progress in the development of gels showing triplet-triplet annihilation based photon upconversion (TTA-UC) is reviewed. Among the two families of upconverting gels reported, those display TTA-UC based on molecular diffusion show performances comparable to those in solutions, and the TTA-UC therein are [...] Read more.

Recent progress in the development of gels showing triplet-triplet annihilation based photon upconversion (TTA-UC) is reviewed. Among the two families of upconverting gels reported, those display TTA-UC based on molecular diffusion show performances comparable to those in solutions, and the TTA-UC therein are affected by dissolved molecular oxygen. Meanwhile, air-stable TTA-UC is achieved in organogels and hydrogels by suitably accumulating TTA-UC chromophores which are stabilized by hydrogen bonding networks of the gelators. The unique feature of the air-stable upconverting gels is that the self-assembled nanostructures are protected from molecular oxygen dissolved in the microscopically interconnected solution phase. The presence of the bicontinuous structures formed by the upconverting fibrous nanoassemblies and the solution phase is utilized to design photochemical reaction systems induced by TTA-UC. Future challenges include in vivo applications of hydrogels showing near infrared-to-visible TTA-UC. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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9 pages, 2093 KiB

Open AccessFeature PaperReview

Hydrogels as Porogens for Nanoporous Inorganic Materials

by Christian Weinberger, Dirk Kuckling and Michael Tiemann

Gels 2018, 4(4), 83; https://doi.org/10.3390/gels4040083 - 10 Oct 2018

Cited by 4 | Viewed by 5221

Abstract

Organic polymer-hydrogels are known to be capable of directing the nucleation and growth of inorganic materials, such as silica, metal oxides, apatite or metal chalcogenides. This approach can be exploited in the synthesis of materials that exhibit defined nanoporosity. When the organic polymer-based [...] Read more.

Organic polymer-hydrogels are known to be capable of directing the nucleation and growth of inorganic materials, such as silica, metal oxides, apatite or metal chalcogenides. This approach can be exploited in the synthesis of materials that exhibit defined nanoporosity. When the organic polymer-based hydrogel is incorporated in the inorganic product, a composite is formed from which the organic component may be selectively removed, yielding nanopores in the inorganic product. Such porogenic impact resembles the concept of using soft or hard templates for porous materials. This micro-review provides a survey of select examples from the literature. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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14 pages, 18296 KiB

Open AccessReview

Hybrid Physical Gels from Polymers and Self-Assembled Systems: A Novel Path for Making Functional Materials

by Jean-Michel Guenet

Gels 2018, 4(2), 35; https://doi.org/10.3390/gels4020035 - 16 Apr 2018

Cited by 9 | Viewed by 4601

Abstract

In recent years, the synthesis of novel organic molecules that spontaneously self-assemble into a large variety of molecular architecture, particularly the formation of organogels, has yielded new opportunities in the preparation of functional materials. Here, we present an original preparation path of such [...] Read more.

In recent years, the synthesis of novel organic molecules that spontaneously self-assemble into a large variety of molecular architecture, particularly the formation of organogels, has yielded new opportunities in the preparation of functional materials. Here, we present an original preparation path of such materials through the fabrication of hybrid gels of these molecules with covalent polymers. Three types of systems are described: (i) intermingled gels where a polymer gel and an organogel pervade one another; (ii) encapsulation of self-assembled filaments in polymer fibrils, which provides a system with unusual magnetic properties; (iii) the reverse situation in which self-assembled nanotubes sheathe polymer fibrils. Two covalent polymers are considered: a neutral polymer, specifically stereoregular polystyrene (isotactic or syndiotactic), and a semi-conducting polymer, P3BT. In the latter case, semi-conducting nanowires are obtained. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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Other

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10 pages, 3876 KiB

Open AccessTechnical Note

Designing Supramolecular Gelators: Challenges, Frustrations, and Hopes

by Parthasarathi Dastidar

Gels 2019, 5(1), 15; https://doi.org/10.3390/gels5010015 - 08 Mar 2019

Cited by 45 | Viewed by 5100

Abstract

This article is a personal account of the author, who serendipitously entered the field of supramolecular gels nearly two decades ago. A supramolecular synthon approach in the context of crystal engineering was utilized to develop a working hypothesis to design supramolecular gelators derived [...] Read more.

This article is a personal account of the author, who serendipitously entered the field of supramolecular gels nearly two decades ago. A supramolecular synthon approach in the context of crystal engineering was utilized to develop a working hypothesis to design supramolecular gelators derived from simple organic salts. The activity not only provided a way to occasionally predict gelation, but also afforded clear understanding of the structural landscape of such supramolecular materials. Without waiting for an ab initio approach for designing a gel, a large number of supramolecular gelators derived from organic salts were designed following the working hypothesis thus developed. Organic salts possess a number of advantages in terms of their ease of synthesis, purification, high yield and stability and, therefore, are suitable for developing materials for various applications. Organic salt-based gel materials for containing oil spills, synthesizing inorganic nanostructures and metal nanoparticles, sensing hazardous gas and dissolved glucose, adsorbing dyes, and facilitating drug delivery in self-delivery fashion have been developed. The journey through the soft world of gelators which was started merely by serendipity turned out to be rewarding, despite the challenges and frustrations in the field. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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5 pages, 2234 KiB

Open AccessFeature PaperConcept Paper

Does Drying Affect Gel Networks?

by Dave J. Adams

Gels 2018, 4(2), 32; https://doi.org/10.3390/gels4020032 - 03 Apr 2018

Cited by 38 | Viewed by 4569

Abstract

The properties of low molecular weight gels are determined by the underlying, self-assembled network. To access information on the network, it is common for techniques to be used that require the gel to be dried, such as transmission electron microscopy or scanning electron [...] Read more.

The properties of low molecular weight gels are determined by the underlying, self-assembled network. To access information on the network, it is common for techniques to be used that require the gel to be dried, such as transmission electron microscopy or scanning electron microscopy. The implicit assumption is that this drying has no bearing on the data collected. Here, we discuss the validity of this assumption. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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9 pages, 214 KiB

Open AccessConcept Paper

Controlling Variables in Molecular Gel Science: How Can We Improve the State of the Art?

by Richard G. Weiss

Gels 2018, 4(2), 25; https://doi.org/10.3390/gels4020025 - 22 Mar 2018

Cited by 27 | Viewed by 3742

Abstract

By design, no references are included in this article. It is intended to be a series of recommendations in which the focus is on lab practices for investigating substances rather than on the substances being investigated. Thus, it discusses some specific areas of [...] Read more.

By design, no references are included in this article. It is intended to be a series of recommendations in which the focus is on lab practices for investigating substances rather than on the substances being investigated. Thus, it discusses some specific areas of concern identified by the author. Other scientists are encouraged to add to or amend the contents. This article should be read as a “living” document, like a blog in which many gel scientists work, over time, to achieve a consensus about reporting everything from acronyms and definitions to procedures and methods. For those entering the field and seeking compendia on the subject, the author suggests “Googling” the words “molecular gels” or “molecular gels books”. Full article

(This article belongs to the Special Issue Challenges for Gel Materials in the 21st Century)

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