self-healing properties of hydrogels based on the various types of dynamic chemistries available for their fabrication. While the main focus of the chapter is on the
chemistry of cross-linking and the conditions under which self-healing was
achieved, a brief discussion on the method utilized to ascertain the extent of selfhealing through mechanical or rheological data, as well as possible applications of
such materials, is explored.
Keywords Click reactions · Cross-linked networks · Dynamic covalent chemistry ·
Self-healing hydrogels · Stimuli-responsive
1 Introduction
Hydrogels are cross-linked polymeric materials that have gained a ubiquitous
presence as indispensable materials in various biomedical applications [1–
3]. Hydrogels can either form the bulk of the functional material, e.g., injectable
gels for therapeutic applications or tissue engineering scaffolds, or be present at the
interface of diagnostic devices for biological assays, or act as functional coatings on
implantable devices. In many of these applications, short- and long-term durability
and stability under the biological environment are crucial for their performance.
Depending on the application, hydrogels should not only be chemically stable under
the environment but also be stable to the exposed mechanical stresses. Similar to
self-healing of biological soft materials such as tissues, any damage incurred on the
hydrogels should be repairable. Thus over the past decade, hydrogels have
transformed from being static cross-linked materials to dynamic systems that upon
damage can revert to their pristine state either autonomously or through the help of
external stimuli [4–6].
Hydrogels maintain their network structure upon swelling in water through the
presence of either physical or chemical cross-links. Most physical cross-links are
dynamic in nature since they are based on crystallization, hydrophobic, electrostatic,
or hydrogen-bonding interactions, which can reform upon damage. The dynamic
nature of such physical interactions allows incorporation of energy dissipation
modes into the hydrogel which makes them more tolerant to transient stress.
Depending on the chemical composition and network structure, physically crosslinked hydrogels exhibit excellent mechanical properties suitable for many biological applications and have been of high interest in recent years [7–9]. Likewise,
chemically cross-linked hydrogels have also been explored extensively over the past
decades since their network structure, the nature of interchain linkages, and responsiveness to external stimuli can be fine-tuned through synthetic strategies [10]. Furthermore, chemically cross-linked hydrogels can possess very good mechanical
properties over a wide range of environmental conditions. In case of chemically
cross-linked hydrogels, damage results in rupture of chemical linkages that form the
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R. Kilic and A. Sanyal
chemistry of cross-linking and the conditions under which self-healing was
achieved, a brief discussion on the method utilized to ascertain the extent of selfhealing through mechanical or rheological data, as well as possible applications of
such materials, is explored.
Keywords Click reactions · Cross-linked networks · Dynamic covalent chemistry ·
Self-healing hydrogels · Stimuli-responsive
1 Introduction
Hydrogels are cross-linked polymeric materials that have gained a ubiquitous
presence as indispensable materials in various biomedical applications [1–
3]. Hydrogels can either form the bulk of the functional material, e.g., injectable
gels for therapeutic applications or tissue engineering scaffolds, or be present at the
interface of diagnostic devices for biological assays, or act as functional coatings on
implantable devices. In many of these applications, short- and long-term durability
and stability under the biological environment are crucial for their performance.
Depending on the application, hydrogels should not only be chemically stable under
the environment but also be stable to the exposed mechanical stresses. Similar to
self-healing of biological soft materials such as tissues, any damage incurred on the
hydrogels should be repairable. Thus over the past decade, hydrogels have
transformed from being static cross-linked materials to dynamic systems that upon
damage can revert to their pristine state either autonomously or through the help of
external stimuli [4–6].
Hydrogels maintain their network structure upon swelling in water through the
presence of either physical or chemical cross-links. Most physical cross-links are
dynamic in nature since they are based on crystallization, hydrophobic, electrostatic,
or hydrogen-bonding interactions, which can reform upon damage. The dynamic
nature of such physical interactions allows incorporation of energy dissipation
modes into the hydrogel which makes them more tolerant to transient stress.
Depending on the chemical composition and network structure, physically crosslinked hydrogels exhibit excellent mechanical properties suitable for many biological applications and have been of high interest in recent years [7–9]. Likewise,
chemically cross-linked hydrogels have also been explored extensively over the past
decades since their network structure, the nature of interchain linkages, and responsiveness to external stimuli can be fine-tuned through synthetic strategies [10]. Furthermore, chemically cross-linked hydrogels can possess very good mechanical
properties over a wide range of environmental conditions. In case of chemically
cross-linked hydrogels, damage results in rupture of chemical linkages that form the
244
R. Kilic and A. Sanyal