6.2.1.1　Polysaccharides

Polysaccharides have been widely used as nano-drug carrier materials because they contain lots of highly active hydrophilic groups（such as hydroxyl，carboxyl，and amino）that could be easily modified，and some of them have the function of immunoregulation，antitumor and antiviral.Currently，polysaccharides including glucan，hyaluronic acid，heparin，alginate，chitosan，and mushroom polysaccharides，etc.have been used as nanodrug carriers.Hyaluronic acid is one of the widely used carrier materials due to its tumor targeting effect.However，the strong hydrophilicity，poor stability，and short biological half-life of hyaluronic acid limit its application in nano-drug carriers.For example，the drug loading is very low and drug is leaked too fast when using hyaluronic acid to load the watersoluble drugs.Chitosan is another commonly used carrier material，because it has good biological adhesive，exhibits different inhibition to bacteria，fungi and other microorganisms，has hemostatic function，can improve human immunity，and has antitumor effect.Furthermore，it can be broken down by lysozyme in the body.Due to their strong hydrophilicity，hyaluronic acid and chitosan were usually processed into nanogels，which can serve as drug carriers.In addition，nano-gels could be modified with functional inorganic nanoparticles such as gold，quantum dots and magnetic NPs to improve their functionality.Besides，they are often used as the outer layer of the hydrophobic polymers or inorganic nano-drug carriers to improve their hydrophilicity，stability，and targeting.(https://www.daowen.com)