**2. Properties of pectin as a biomaterial for TE applications**

Pectin shows several remarkable properties as a biomaterial. It is biocompatible and biodegradable, and it is soluble in cytocompatible and non-toxic solvents (such as water). Pectin is a versatile biomaterial as its physical properties can be facilely tuned due to the presence of several functional groups (e.g., carboxylic groups) that can serve as binding sites for other functional groups, biomolecules and drugs [21–23]. It is a low-cost biomaterial due to its ubiquity in nature, and this can strongly reduce the costs associated with the development of engineered tissues.

Pectin can form hydrogel due to the ability of its macromolecules to absorb and retain large volumes of water. This unique property makes pectin a suitable candidate to produce a natural extracellular matrix, which naturally surrounds cells. Furthermore, due to the possibility to be processed under sterile and physiological conditions (i.e., the aqueous environment at 37°C), pectin enables to encapsulate cells within its matrix to produce cell-laden scaffolds [23, 24].

Pectin tends to dissolve under physiological conditions, therefore physicochemical approaches are required to stabilize pectin-based scaffolds. These are mainly based on the use of physicochemical crosslinking approaches which consist of the formation of a stable network of links among the pectin molecules. This network reduces the interactions of pectin molecules with water and prevents the disruption of pectin-based scaffolds. For example, the most employed approach to form waterinsoluble scaffolds of low-methoxyl pectin is based on the use of divalent cations (e.g., Ca2+) that interact with the carboxylic groups of pectin forming the so-called 'egg box' structure [21]. Notably, the crosslinking treatments should also be cytocompatible (under specific conditions/concentrations), and should not interfere with the capability of pectin to encapsulate cells [25].

One of the major drawbacks that limit the application of pectin as a biomaterial for TE applications is its low cell adhesivity due to the lack of sites for cell adhesion (such as arg-gly-asp (RGD) sequences). Therefore, pectin is often combined/ blended with other biopolymers or biomolecules to enhance its bioactivity [21, 26].
