History and Applications of Hydrogels

Abstract

Hydrogels have existed for more than half century, providing one of the earliest records of crosslinked hydroxyethyl methacrylate (HEMA) hydrogels. Today, hydrogels still fascinate material scientists and biomedical researchers and great strides have been made in terms of their formulations and applications. As a class of material, hydrogels are unique, they consist of a self-supporting, waterswollen three-dimensional (3D) viscoelastic network which permits the diffusion and attachment of molecules and cells. However, hydrogels have recently drawn great attention for use in a wide variety of biomedical applications such as cell therapeutics, wound healing, cartilage/bone regeneration and the sustained release of drugs. This is due to their biocompatibility and the similarity of their physical properties to natural tissue. This review aims to give an overview of the historic and the recent design concept of hydrogels and their several applications based on the old and the most recent publications in this field. Journal of Biomedical Sciences ISSN 2254-609XThis Article is Available in: www.jbiomeds.com 2 Hydrogels can be classified into two distinct categories, the natural and the synthetic hydrogels. Natural hydrogels include collagen, fibrin, hyaluronic acid, matrigel, and derivatives of natural materials such as chitosan, alginate and skill fibers. They remain the most physiological hydrogels as they are components of the extracellular matrix (ECM) in vivo. Two main drawbacks of natural hydrogels, however, make their final microstructures and properties difficult to control reproducibly between experiments. First, the fine details of their mechanical properties and their dependence on polymerization or gelation conditions are often poorly understood. Second, due to their natural origin (bovine fibrinogen, rat tail collagen… their composition may vary from one batch to another.In contrast, synthetic hydrogels such as poly (ethylene glycol) diacrylate, poly(acryl amide), poly(vinyl alcohol) are more reproducible, although their final structure can also depend on polymerization conditions in a subtle way, so that a rigorous control of the preparation protocol, including temperature and environment control, may be necessary. Generally speaking, synthetic hydrogels offer more flexibility for tuning chemical composition and mechanical properties; users can, for example vary the concentration or molecular weight of the precursor, or alter the percentage of crosslinkers. They can also be selected or tuned to be hydrolysable or biodegradable over variable periods of time.Hydrogels may be chemically stable or they may degrade and eventually disintegrate and dissolve. They are called «reversible» or «physical» gels when the networks are held together by molecular entanglements, and/or secondary forces including ionic, H-bonding or hydrophobic forces (Figure 2) [3]. Physical hydrogels are not homogeneous, since clusters of molecular entanglements, or hydrophobically-or ionically-associated domains, can create in h...

Importance of Alginate Bioink for 3D Bioprinting in Tissue Engineering and Regenerative Medicine

“…To repair the bone, a good initiative is to induce osteogenesis in situ. To complete this process, one method is by using stem cell differentiation to form bone tissue and then seeding them in an injectable scaffold [44,45]. As of now there are numerous investigations and studies on alginate-based injectable scaffolds for the bone regeneration.…”

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“…Agar based hydrogels are used for manufacturing contact lenses, hygiene products, tissue engineering scaffolds, drug delivery systems and wound dressings [81]. In addition, thanking to its biodegradability, agar based hydrogel blended with gelatin & collagen has also been studied for wound healing, drug delivery and tissue engineering etc [82]. More studies on agar is still going on continuously to widespread its usage as biomedical polymer.…”

Introductory Chapter: Hydrogels - From First Natural Hydrocolloids to Smart Biomaterials

“…Hydrogels are known as the first biomaterials useful for therapy in humans [12], but they are still fascinating materials and subject for developing innovative formulations and applications [13][14][15]. They have unique properties derived from its three-dimensional (3D) viscoelastic network [16], essentially permitting attachment and later diffusion of particles, molecules, in controlled drug or cell/ gene delivery [17,18], as well as serving as 3D bioprinting material [19,20], in modern medicine, for tissue engineering [21,22], as implants [23], for diagnostics [24], wound dressing [25], bone regeneration [26,27], and soft contact lens [28], to exemplify only a few.…”