Hydrogel Application in Urban Farming: Potentials and Limitations—A Review

Abstract

Urban agriculture plays a vital role in ensuring the self-sufficiency of a great variety of fresh vegetables and nutrients. It promotes a sustainable food system as well as reducing the dependency on imports for the growing population. Urban farming has made it possible for agriculture practices to be implemented anywhere at any time in a sophisticated way. Hydrogel has been introduced in urban agriculture in the past few decades. However, the application of hydrogel in urban agriculture is still being explored in terms of hydrogel types, structure, physical and chemical properties, change due to external factors, and its suitability for different plant species. This review discusses the potentials and limitations of hydrogel in different application conditions. We present the state of knowledge on hydrogel production and crosslinking methods, hydrogel characteristics, water absorption and release mechanisms of hydrogel, hydrogel advantages and limitations, and current and future applications in urban farming.

Preparation and Properties of Egg White Dual Cross-Linked Hydrogel with Potential Application for Bone Tissue Engineering

“…Hydrogels prepared from natural polymers should inherit the advantages of natural macromolecules, such as biocompatibility and biodegradability [ 4 ]. Thus, they are attracting attention particularly in biotechnology for uses such as drug delivery [ 5 ], biological sensing [ 6 ], wound dressing [ 7 ], and desalination [ 8 , 9 ].…”

Sodium Alginate-g-acrylamide/acrylic Acid Hydrogels Obtained by Electron Beam Irradiation for Soil Conditioning

“…Based on the source materials, hydrogels for agricultural use are classified into three types: natural, synthetic and semi-synthetic [5,6]. Synthetic hydrogels are based on monomers derived from petroleum that are attractive for the synthesis of polymeric hydrogels, due to their very controllable physical and chemical properties compared to natural polymers [7,8]. The most used synthetic polymers in the synthesis of hydrogels are poly (vinyl alcohol) (PVA), poly (ethylene glycol) (PEG), poly (ethylene oxide) (PEO), poly (2-hydroxyethyl methacrylate) (PHEMA), poly (acrylic acid) (PAA) and poly(acrylamide) (PAAm) [7].…”

“…Synthetic polymer hydrogels have high water retention capacity, longer shelf life and improved gel strength [9,10]. Natural biopolymers that form hydrogels, such as cyclodextrin, dextran, chitosan, agarose, sodium alginate, fibrin, hyaluronic acid, gelatin and collagen, are derived from natural sources, so are abundant, non-toxic, cheap and biodegradable [8,9]. On the other hand, they show poor mechanical strength [7].…”

“…Another way of classifying hydrogels, regardless of the origin source, is based on the obtaining method; the cross-linking can be physical (by temporary non-covalent bonds), chemical (by permanent covalent bonds) or combined [7]. By physical cross-linking through hydrogen bonding, ionic forces, Van der Waals interactions, stereocomplexation and hydrophobic forces [7], hydrogels with reversible properties, a short life span and with poor mechanical properties are obtained [8]. For these reasons, physical cross-linked hydrogels are not proper for agricultural use.…”

“…For these reasons, physical cross-linked hydrogels are not proper for agricultural use. Instead, chemical cross-linking leads to the formation of permanent hydrogels, with mechanical and thermal stability and controllable properties, that are ideal for reducing water and nutritional stress in soils [8]. The obtaining of chemical hydrogels, not so dependent on pH as in the case of physical hydrogels, involves chemical reactions, polymerization, homopolymerization and grafting [7,8].…”