Hydrogels are three-dimensional, cross-linked, and supramolecular networks that can absorb significant volumes of water. Hydrogels are one of the most promising biomaterials in the biological and biomedical fields, thanks to their hydrophilic properties, biocompatibility, and wide therapeutic potential. Owing to their nontoxic nature and safe use, they are widely accepted for various biomedical applications such as wound dressing, controlled drug delivery, bone regeneration, tissue engineering, biosensors, and artificial contact lenses. Herein, this review comprises different synthetic strategies for hydrogels and their chemical/physical characteristics, and various analytical, optical, and spectroscopic tools for their characterization are discussed. A range of synthetic approaches is also covered for the synthesis and design of hydrogels. It will also cover biomedical applications such as bone regeneration, tissue engineering, and drug delivery. This review addressed the fundamental, general, and applied features of hydrogels in order to facilitate undergraduates, graduates, biomedical students, and researchers in a variety of domains.

In this work, a superabsorbent polymer, sodium polyacrylate, also known as water ball (WB), loaded with Ni, Cu, and Ag zero-valent metal nanoparticles (MNPs) was applied for environmental remediation. WBs loaded with Ni, Cu, and Ag NPs were evaluated for their catalytic performance against the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) and decolorization of methyl orange (MO), Congo red (CR), and methylene blue (MB) dyes. The apparent rate constants (K_app) for the reduction of 4-NP to 4-AP in the presence of Ni, Cu, and Ag NPs were 2.1 × 10^–1, 2.9 × 10^–1, and 4.6 × 10^–1 min^–1, respectively, indicating the strongest activity of WB loaded with Ag NPs as compared to the other two catalysts. Similarly, WB loaded with Ag NPs showed the highest K_app values compared to the other two catalysts. Among all of the bacteria studied, except Providencia stuartii and Streptococcus mutans, the zone of inhibition of Ag was higher as compared to that of the Ni and Cu NPs, however, slightly low from that of the reference standard tetracycline TE30. Furthermore, the synthesized catalysts were extensively characterized through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) analyses.

Hydrogels are natural or synthetic polymeric networks, insoluble in water, or sometimes found as colloidal gel where the dispersion medium is water. Hydrogels can absorb approximately 90% water and are regarded as superabsorbent materials; hence these resemble the natural living tissues more than any other biological- based materials. Because of their ability to absorb water, they are used to investigate the properties of swollen polymer networks and have wide applications in different fields such as contact lenses, drug delivery systems for proteins, and many others. To make them biodegradable, labile chemical bonds are introduced in the main backbone through crosslinking. These unstable bonds can then be broken down by various agents chemically, physically, or enzymatically, generally by hydrolysis or through some controlled parameters. Hydrogels are frequently used in the medical field. For instance, pH and temperature-sensitive hydrogels may be used in the targeted drug delivery which have been explained in detail in the current review. The other applications of hydrogels are also explained with regard to personal health care products, biomedical, bio-separation, wound healing, tissue engineering, and drug delivery, etc., which make them promising materials in pharmaceutics. They are also used in agriculture and environmental remediation. The purpose of this review is to expose their salient features and biomedical applications.