Hydrogels: Smart Materials in Drug Delivery

*Aiswarya Sathian, Namitha Vijay, K.S. Joshy, Yogesh Bharat Dalvi and Fatima Mraiche*

### **Abstract**

The prominence of hydrogels in various fields of life sciences is due to their significant and functional three-dimensional biopolymeric networks, which tend to imbibe water due to -OH, -CONH2, -SO3H, -CONH,-COOR groups which have a hydrophilic tendency enabling them to be an excellent super absorbent and remain insoluble in water. Hydrogels can embed physiologically active molecules in their water-swollen network and are appealing materials for the controlled release of medicines. Several significant advancements in the realm of hydrogels for therapeutic delivery have resulted from recent advances in organic and polymer chemistry, bioengineering, and nanotechnology. We offer our perspective on the state-of-the-art in the field in this chapter, focusing on several intriguing issues such as current trends in hydrogel-based drug delivery, stimuli-responsive hydrogels, nanogels, and therapeutic release from 3D printed hydrogels. We also discuss the obstacles that must be solved to promote translation from academia to the clinic, as well as our predictions for the future of this quickly changing field of research.

**Keywords:** hydrogel, nanogel, drug delivery, nanocarrier

### **1. Introduction**

Recent innovations have statured hydrogels as noteworthy drug carriers which have found their eminent application in tumor drug delivery. As it has lesser side effects than the existing systemic chemotherapy and is known to be an accurate delivering agent at specific tumor sites. In addition to this, it has salient features like biocompatibility, biodegradability, and lower toxicity than nanoparticle carriers. This has paved the way for researchers to delve into and explore more on the functionality of hydrogels. Smart hydrogels can respond to stimuli in the environment (e.g., heat, pH, light, and ultrasound), enabling in situ gelations and controlled drug release, which greatly enhances the convenience and efficiency of drug delivery [1]. The repeated monomers like homopolymers or copolymers containing hydrophilic polymer chains lead to the formation of hydrogels and these monomers are arranged in different ways, as shown in **Figure 1** [3].

The (3D) network of hydrogels can intake water and remain swelled in any condition without dissolving in the medium. Hydrogel carrier is trending in drug delivery

**Figure 1.** *Chemical diversity of hydrogel polymer chains (adapted from [2]).*

due to their extended biocompatibility and tunable mechanical strength. Synthetic hydrogels are explored more because of their peculiarities like long life, higher capacity for water absorption, and high gel firmness. These can be synthesized from purely synthetic materials and these are having defined structures that can be modified to yield tailorable degradability and functionality [4].

Hydrogels are good carriers of drug delivery, and it has resulted in the elevation of therapeutic outcomes tremendously, used in clinical arenas. The delivery of cells, molecules, and macromolecular drugs in hydrogel encapsulation via spatial and temporal delivery has improved. Improving the design for the hydrogel drug delivery has overcome the limitations partially and it results in the progression of a better carrier. Current trends and different types of hydrogel drug delivery with the translation to clinical use will be discussed in this chapter [5]. There is extensive research carried out on hydrogel drug delivery. To add on, properties for drug delivery systems that were under modification, in terms of the ligands and various polymer types are researched meticulously. A wonderful disposition of a positive results was shown in the ophthalmic field i.e., from comfortable contact lenses to biodegradable drug delivery, the applications in eye care have been enormous. These possess 90% water for the drug release for a long period to deliver small or large molecules [6]. Thus, a long road of success waits for hydrogels if they are observed, studied, experimented with, and translated to clinical research.
