Hyaluronic Acid

Hyaluronic acid (HA) is a naturally occurring, high‑molecular‑weight glycosaminoglycan that resides primarily in the extracellular matrix of connective tissues, synovial fluid, and the vitreous humor of the eye. Its primary purpose is to retain water (up to 1 000 times its weight), thereby providing tissue hydration, visco‑elasticity, and a scaffold for cell migration and wound repair.

Hyaluronic acid is a linear polymer of repeating disaccharide units: β‑D‑glucuronic acid linked β‑1,3 to N‑acetyl‑D‑glucosamine via β‑1,4 bonds. Its empirical formula is (C₁₄H₂₁NO₁₁)n, where “n” can range from 2 000 to >10 000 disaccharide units, giving molecular weights from 0.5 MDa to >10 MDa. The IUPAC name (for the repeating unit) is [(2‑S‑O‑[2‑[N‑acetyl‑D‑glucosaminyl]‑1‑deoxy‑β‑D‑glucopyranosyl)‑(1→4)‑β‑D‑glucopyranosyl]uronic acid; the polymer is non‑ionic, highly hydrophilic, and exhibits a high degree of visco‑elasticity and water‑binding capacity.

Commercial HA is primarily derived from bacterial fermentation (e.g., Streptococcus zooepidemicus) or from rooster combs (a natural avian source). Fermentation yields a purer, animal‑free product with consistent molecular weight, while rooster‑comb extraction can contain protein impurities and raises ethical concerns. Recent advances employ recombinant E. coli or Bacillus strains for scalable, GMP‑grade HA. Quality considerations include molecular weight distribution, endotoxin levels (<0.5 EU/mg), and absence of residual DNA or proteins. Certified “pharmaceutical‑grade” HA is required for intra‑articular or ocular applications; dietary supplements may use lower‑purity “cosmetic‑grade” material.