Hydrogels for Biomedical Applications: Their Characteristics and the Mechanisms behind Them

Abstract

Hydrogels are hydrophilic, three-dimensional networks that are able to absorb large quantities of water or biological fluids, and thus have the potential to be used as prime candidates for biosensors, drug delivery vectors, and carriers or matrices for cells in tissue engineering. In this critical review article, advantages of the hydrogels that overcome the limitations from other types of biomaterials will be discussed. Hydrogels, depending on their chemical composition, are responsive to various stimuli including heating, pH, light, and chemicals. Two swelling mechanisms will be discussed to give a detailed understanding of how the structure parameters affect swelling properties, followed by the gelation mechanism and mesh size calculation. Hydrogels prepared from natural materials such as polysaccharides and polypeptides, along with different types of synthetic hydrogels from the recent reported literature, will be discussed in detail. Finally, attention will be given to biomedical applications of different kinds of hydrogels including cell culture, self-healing, and drug delivery.

Keywords: biomaterials; cell culture; drug delivery; hydrogels; self-healing.

Figure 1

Supramolecular inclusion complex 1 formed from deoxycholate-β-CD derivative 2 and azobenzene-branched poly(acrylic acid) copolymer 3. Reprinted from [34] with permission from the American Chemical Society (2009).

Figure 2

The response of novel hybrid hydrogels containing ssDNA as a cross-linker to ssDNA. Reprinted from [36] with permission from the American Chemical Society (2005).

Figure 3

Synthetically tractable click hydrogels for three-dimensional cell culture formed using tetrazine–norbornene chemistry. Reprinted from [71] with permission from the American Chemical Society (2013).

Figure 4

Schematic representation of high concentration cationic gels adhered using 1.6 mg of Micromica supporting a tensile load of 10 kg. Reprinted from [81] with permission from the American Chemical Society (2016).