These aggregates imbibe water and are responsible for the resilience of cartilage (its resistance to compression). The molecular weight (size) of hyaluronan in cartilage decreases with age, but the amount increases.A lubricating role of hyaluronan in muscular connective tissues to enhance the sliding between adjacent tissue layers has been suggested. A particular type of fibroblasts, embedded in dense fascial tissues, has been proposed as being cells specialized for the biosynthesis of the hyaluronan-rich matrix. Their related activity could be involved in regulating the sliding ability between adjacent muscular connective tissues.Hyaluronic acid is also a major component of skin, where it is involved in repairing tissue. When skin is exposed to excessive UVB rays, it becomes inflamed (sunburn), and the cells in the dermis stop producing as much hyaluronan and increase the rate of its degradation. Hyaluronan degradation products then accumulate in the skin after UV exposure.While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement, and proliferation of cells and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44 and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronans contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells. Although hyaluronan binds to receptor CD44, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4, or both TLR2 and TLR4 in macrophages and dendritic cells.
These hydrogels have properties similar to human soft tissue, but are also easily controlled and modified, making HA very suitable for tissue-engineering studies. For example, HA hydrogels are appealing for engineering vasculature from endothelial progenitor cells by using appropriate growth factors such as VEGF and Ang-1 to promote proliferation and vascular network formation. Vacuole and lumen formation have been observed in these gels, followed by branching and sprouting through degradation of the hydrogel and finally complex network formation. The ability to generate vascular networks using HA hydrogels leads to opportunities for in vivo and clinical applications. One in vivo study, where HA hydrogels with endothelial colony forming cells were implanted into mice three days after hydrogel formation, saw evidence that the host and engineered vessels joined within 2 weeks of implantation, indicating viability and functionality of the engineered vasculature.Hyaluronic acid-mediated drug delivery system was deemed useful for targeting inflammatory skin diseases condition. See also
Alguronic acid
Sodium hyaluronate

References
External links
ATC codes: D03AX05 (WHO), M09AX01 (WHO), R01AX09 (WHO), S01KA01 (WHO)
Hyaluronan at the US National Library of Medicine Medical Subject Headings (MeSH)