9.2.1　Hyaluronic acid（HA）

HA is a linear non-sulfated glycosaminoglycan polymer，which is the main component of the extracellular matrix（ECM）.ECM is a key regulator that affects the metabolism of cells.The molecular weight of HA is critical to its various functions.The high molecular weight HA fragments reflect intact tissue，anti-angiogenesis，and immunosuppressive states，while smaller HA fragments，which are usually inducers of inflammation and angiogenesis，are considered as pressure signals.Due to its super capacity to retain large amounts of water，HA is responsible for the skin's moisture content.In addition，HA is involved in wound healing and aging processes.(https://www.daowen.com)