Agarose is a purified linear galactan polysaccharide derived from agar, extracted from red marine algae (Rhodophyta species such as Gracilaria and Gelidium). It is widely recognized for its ability to form thermoreversible gels that are essential in molecular biology and biotechnology. 

Molecular Structure

Agarose consists of repeating agarobiose disaccharide units composed of D-galactose β-(1→4)-linked to 3,6-anhydro-L-galactopyranose α-(1→3), forming uncharged linear polymer chains of approximately 800 galactose residues, corresponding to an average molecular weight of about 120 kDa. The presence of the 3,6-anhydro bridge confers conformational rigidity to the polymer backbone, promoting the formation of double helices that further aggregate into quasi-rigid fibers with diameters of 20–30 nm through extensive hydrogen bonding.

Gelation and Physicochemical Properties

When dissolved in boiling water at concentrations typically ranging from 1 to 3% (w/v), agarose undergoes a reversible sol–gel transition upon cooling, forming a three-dimensional hydrogel network with pore sizes between 50 and 200 nm, inversely correlated with polymer concentration. Gel stabilization is mediated primarily by inter-helix hydrogen bonding. Agarose gels exhibit thermal hysteresis, melting at temperatures above 80–95 °C while solidifying at 35–45 °C. They are characterized by high optical clarity, low electroendosmosis (EEO < 0.1%), and minimal sulfate content (< 0.2%), parameters that directly influence purity and electrophoretic sieving performance. In addition, agarose is stable across a pH range of 4–9, tolerates autoclaving, and demonstrates excellent biocompatibility without detectable immunogenicity.

Biomedical Applications

Agarose hydrogels are extensively used as inert matrices for cell encapsulation in tissue engineering, as diffusion-controlled drug delivery depots, and as structural components of bioinks for three-dimensional bioprinting. Their mechanical properties can be tuned over a broad range (approximately 0.1–100 kPa), and they exhibit shear-thinning behavior favorable for extrusion-based fabrication techniques. Chemically modified derivatives, such as methacrylated agarose, enable photocrosslinking and the generation of mechanically stable scaffolds that support specialized cellular processes, including chondrogenic differentiation and neural cell culture.