Hyaluronic acid is a unique linear macromolecular acidic mucopolysaccharide, which is formed by repeated and alternating connections of disaccharide units of glucuronic acid and N-acetylglucosamine. It is widely present in connective tissues such as joints, vitreous body, synovial fluid, umbilical cord, Cartilage, skin, cockscomb, group A and group C hemolytic streptococcus and Wharton's gum to fulfill some important functions such as toughness, support structure and metabolic regulation of cells.

1. Application of hyaluronic acid in ophthalmic preparations

The vitreous contains a large amount of hyaluronic acid, which forms the vitreous together with collagen fibers and soluble proteins. The network structure formed by collagen acts as a solid scaffold. The macromolecular network structure of hyaluronic acid can combine a large amount of water to form a gel filling in it. The two network systems are balanced with each other, and the hyaluronic acid in the corneal stroma maintains Corneal morphology plays an important role. As the medium of ophthalmic preparations, hyaluronic acid is widely used in ophthalmic preparations and has its special properties and functions. Experiments have shown that 0.1% hyaluronic acid solution can significantly prolong tear film breakup time, reduce the number of blinks in patients with dry eye, and relieve symptoms such as dryness, astringency, itching, and pain in the eyes of patients, and the effect is significantly better than that of ordinary artificial tears. As the duration of medication increases, the frequency of medication decreases significantly, and some patients do not relapse after stopping the medication.

2. Application as a slow-release carrier of drugs

The function of hyaluronic acid to release drugs is determined by its molecular characteristics. Hyaluronic acid is a straight-chain macromolecule, and each disaccharide unit in its molecule contains a carboxyl group, which can be dissociated into negative ions, and the negative ions at equal spatial distances repel each other, making the molecule appear as a rigid coil in the solution. When the concentration reaches a certain level, hyaluronic acid molecules can intertwined with each other to form a network structure, so that drug molecules can enter the network and delay the release rate of drugs.

3. Application as a targeting carrier for antitumor drugs

The biggest disadvantage of antineoplastic drugs is their poor specificity. While attacking tumor cells, they also attack normal tissues. Only a small part of the drugs taken act on tumor cells, and the adverse reactions are serious. Targeted tumor drug therapy can greatly reduce the adverse reactions of anti-tumor drugs. There are a large number of hyaluronic acid receptors—CD44 on the surface of some solid tumors and metastatic lymphocytes, and hyaluronic acid has a strong affinity for it. As a targeting carrier for antitumor drugs, hyaluronic acid can adhere smaller drug molecules to the network structure of hyaluronic acid or graft drug molecules onto hyaluronic acid drug carriers to interact with the receptors on the surface of tumor cells. Targeted binding to the body, so that more drug molecules can enter the tumor tissue, increase the absorption and residence time of anti-tumor drugs in tumors and lymph nodes, thereby improving the efficacy of drugs and reducing side effects.

The physiological functions of hyaluronic acid as a drug carrier in the body are not limited to physical and mechanical functions such as macromolecular network structure and viscoelasticity. The discovery of hyaluronic acid receptors has made a qualitative leap in the understanding of hyaluronic acid, revealing that it plays an important role in embryonic development, tumor invasion, tissue healing, etc. by binding to receptors and regulating cell functions.