Description

1.1 Introduction

Hydrogels are hydrophilic, physically or chemically crosslinked polymeric materials, which are specifically well known for their enormous water-uptake capacity. In biomedical and biotechnological applications, hydrogels are a commonly applied class of materials (Zainal et al., 2021). Their structural resemblance to the extracellular matrix found in vivo makes them an excellent substrate for cell culture applications. In addition, their high water content and biocompatibility allow the cultivation of living cells inside the polymeric network structure which can conveniently be shaped and structured into various geometries. The highly elastic nature of most hydrogels allows for easy manufacturing and adaption to environmental influences (Mantha et al., 2019).By controlling the chemical composition and crosslinking density, network structure and pore size can be tuned and customized for a given application. Chemical modification of the polymeric chains allows for the incorporation of functional motives like integrin-bindng sites promoting cellular attachment, for example. Not only the chemical properties of the hydrogel can be modified but also the physical characteristics of the hydrogel are adjustable. The mechanical properties of most hydrogels can be influenced by altering the degree of crosslinking or the incorporation of additional binding sites via physical crosslinking. Another beneficial effect is the stimulus-responsive behavior of some polymers like poly(N-isopropylacrylamide) (pNIPAAm) (Ansari et al., 2022). These stimulus-responsive properties can be used to load the polymers with drugs or growth factors which will be subsequently released upon stimulation of the appropriate physical or chemical clues. The decision regarding the use of hydrogels derived from natural sources or synthetic polymers depends on the aspired properties and applications, and it is vigorously discussed in the literature (Bashir et al., 2020).