Alginate is a naturally occurring polysaccharide extracted primarily from brown algae, valued for its biocompatibility and gel-forming properties.
Chemical Structure
Alginate is composed of linear chains of β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues linked by 1→4 glycosidic bonds. The relative proportion and sequential distribution of M and G units—organized as homopolymeric MM blocks, GG blocks, or heteropolymeric MG regions—govern its physicochemical behavior. A high G content promotes stronger gel formation through the “egg-box” model upon crosslinking with divalent cations such as calcium.
The M/G ratio, which typically ranges from 0.3 to 3.0 depending on the algal source, significantly influences alginate solubility, viscosity, and mechanical strength, making it a tunable biomaterial for diverse applications.
Extraction and Properties
Alginate is extracted from brown macroalgae such as Laminaria and Ascophyllum species through alkaline treatment with sodium hydroxide, followed by precipitation as alginic acid or conversion to sodium alginate. This process yields a polymer with high molecular weight and favorable rheological properties.
Alginate solutions exhibit high viscosity and undergo rapid gelation in the presence of Ca²⁺ or other divalent ions. Sodium alginate hydrogels are biocompatible, biodegradable, non-toxic, and non-immunogenic in their purified form. Although gel stability decreases under acidic conditions, alginate also demonstrates antioxidant activity by inhibiting lipid peroxidation.
Biomedical Applications
Alginate hydrogels are widely used in biomedical applications, particularly as scaffolds in tissue engineering for wound healing, cartilage repair, and bone regeneration. Their porous structure supports cell adhesion, proliferation, and nutrient diffusion, while enabling controlled release of drugs and growth factors.
In drug delivery systems, alginate is employed to encapsulate therapeutic agents for sustained release, form gastroprotective rafts for reflux treatment, and immobilize cells in immunotherapy and bioprocessing. Its FDA approval and low immunogenicity have further expanded its use in injectable gels and advanced cancer therapies.
