Modification Of Polysaccharide And Study Of Sensitivity Of Polysaccharide Hydrogel

Natural polysaccharides are classified as neutral, acidic and alkaline generally, which are the raw materials of most biomedical materials. Acidic polysaccharide hyaluronic acid (HA), alkaline polysaccharide chitosan (CS) and neutral polysaccharide curdlan are widely researched in the field of drug control and delivery, especially as carrier of anticancer drug. HA has ability of cancer targeting because HA molecular has the binding sites of cancer cells. While CS is the only alkaline polysaccharide in natural polysaccharides and pH sensitivity can be developed. When CS used as anticancer drug carrier, it will be perform pH targeting to a certain degree. Curdlan after modification can serve as a kind of anticancer drugs, and can be used as drug carrier.This article prepared the polysaccharide hydrogels with new methods. Sensitive elements were introduced on polysaccharide molecules to prepare drug carrier with environmental sensitivity through the molecular design. Sensitive units on polysaccharides responded to different changes in the environment are researched to complete the final smart drug-loading hydrogels. Besides as drug carrier, polysaccharide through a series of molecule design can also be used as drugs on the corresponding treatment. First, acidic polysaccharide HA was used as research object.3-azidopropan-l-amine (AA) and2-propynylamine (PA) were selected to modify HA to get side chain of HA with azide or alkyne groups. FTTR and H NMR was used to characterize modified HA to confirm the reaction. Then in situ injection HA hydrogels were prepared using click chemistry with cuprous sulfate and sodium ascorbate as catalyst. Swelling ratio and crosslinking content of the hydrogels was inversely proportional. Forthemore, morphologies was observed by SEM.In this study, HA micro-hydrogel was prepared by biotin-neutravidin system (BAS) specific reversible bonding. Firstly, carboxyl groups on HA were changed into amino groups with adipic acid dihydrazide (ADH) to graft with biotin by1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC-HCl) named as HA-biotin. The results of synthesis procedure were characterized by1H-NMR and FTIR, ADH and biotin have been demonstrated to graft on HA molecule. When HA-biotin solution mixed with doxorubicin hydrochloride (DOX-HCl) was blended with neutravidin,the micro-hydrogels would be formed with DOX loading. The drug loading content and drug loading efficiency were3.8%and52.6%, respectively. HA has ability of cancer cell selectivity because two kinds of HA receptors:CD44and RHAMM are over-expressed in cancer cells. So HA is an attractive material used as anticancer drug carrier to perform cancer targeting. If excess biotin was added into the microgel, it would be disjointed and DOX will release quickly.For alkaline polysaccharide, chitosan (CS) is cationic polyelectrolyte and can react with anion or polyanionic compounds to form the hydrogel with network structure. In the thesis, β-glycerophosphate (β-GP) was used to prepare chitosan hydrogels with thermosensitivity. The solution pH, dosage of (3-GP, chitosan molecular weight and temperature were discussed to find environment influence to CS hydrogels. The results indicated that CS was difficult to form hydrogel when the temperature was below4℃and solution pH<5. While when solution pH>5, temperature influenced the ability of CS hydrogels forming and CS can’t form hydrogel under low temperature. Anticancer drug doxorubicin hydrochloride was loaded in thermosensitive CS hydrogel to investigate drug release behavior.In order to perform better thermosensitivity and water-solubility of CS hydrogels, Methoxypolyethylene glycol (mPEG) was grafted on CS firstly, and then poly(N-isopropylacrylamide)(PNIPAM) was introduced on CS-g-mPEG molecular to obtain CS-g-PNIPAM that was an idea thermosensitive raw material to get thermosensitive CS hydrogels. CS-g-mPEG was used to prepare atom transfer radical polymerization (ATRP) initiator to initiate NIPAM polymerizating to get copolymer CS-g-mPEG. Structure and properties of copolymer CS-g-mPEG were characterized by FTIR,’H NMR, DSC and TG analysis. The results indicated that the thermal decomposition temperature of CS-g-mPEG was between166-500℃. The percentage of CS-g-mPEG grafting degree was14.6%, and the molecular weight can reach to242500. The water-solubility of CS-g-mPEG was similar to CS-g-PNIPAM and both of the copolymers were better than CS. The kinetics of polymerization showed polymerization with better controllability. The LCST of CS-g-PNIPAM was at about32℃. Above the LCST, PNIPAM segment on copolymer will occur phase transition to form microhydrogel to use as drug carrier.Anthor neutral polysaccharide curdlan can also be grafted with PNIPAM to increase water-solubility and enhance thermosensitivity. In this thesis, curdlan were modified by hydroxyl activation, bromination and azide substitution to get curdlan-N3with an azido at the chain end. Then PNIPAM-≡were synthesized by ATRP using a-2chloro-isomethylacetic acid propargylester as initiator, dimethyl formamide as solvent and CuCl/tris (2-dimethyl/aminoethyl) amine as catalyst. At last,"click chemistry" was used to get copolymer Curdian-g-PNIPAM with dimethyl formamide and water as solvent and pentamethyl diethylenetriamine and CuBr as catalyst. The structure of copolymer was clear and molecular weight distribution was relatively low polydispersity (PDI<1.35). The structure and properties of copolymer Curdlan-g-PNIPAM were characterized by FT-IR, UV spectrum,1H NMR and GPC. Copolymer Curdlan-g-PNIPAM has the ability of thermosensitivity and the LCST were about33℃.