The Research On The PH/GSH Responsive Hydrogels And Nanogels From Carboxymethyl Chitosan

Intelligent hydrogels and nanogels can respond to external environmentalstimulus rapidly, such as pH, temperature, ionic strength, redox potential and so on.These features make them expected as a carrier for controlled drug release system toachieve effective drug load and release. In the various environmental stimuli, pHsensitivity was widely studied. The pH values in normal cells and tumor cells aredifferent. Thereby, the lower pH of the tumor cells is often used as a trigger drugrelease of tumor cells. A reversible disulfide bond can be stable in human blood,while was split in the higher the concentration of intracellular glutathione. As far aswe know, the concentration of glutathione in tumor cells is4times as that in normalcells. Thus the design of disulfide cross-linked nanoparticles was often introducedinto the drug release within the tumor. In this paper, chitosan was chose as a substrate,and the novel pH/GSH responsive carboxymethyl chitosan hydrogel and nanogelwere prepared. Their properties were studied, and the main contents and conclusionsare as follows:(1) The novel pH/GSH responsive hydrogel was prepared from chitosan. Thestructures and associated physical and mechanical properties of hydrogel werecharacterized. There glutathione responsibility and pH sensitivity were studies.The preparation of hydrogel was under mild reaction conditions and easy tocontrol. During the reaction, the thiol group was not introduced, but a disulfide bondwas introduced directly. So the reaction could take place successfully withoutanaerobic conditions, simplifying the preparation conditions. Further,2,2’-Dithiodibenzoic acid was acylated, making it easier to grafte to thecarboxymethyl chitosan. As a result, the content of disulfide bonds in hydrogel wasincreased.(2) The swelling kinetics of pH/GSH responsive carboxymethyl chitosanhydrogel was investigated.Overshooting effect of hydrogel was appeared in pH≤5.0buffr solution. Thismay be attributed to the following two reasons. One is the hydrogen-bond interactionbetween adjacent carboxyl groups in the network structure of the gel; The other one is electrostatic attraction between unionized carboxyl group and amino group. TheOvershooting effect of hydrogel in pH≤5.0buffer solution followed the kineticsmodel proposed by Díez-Peňa and so on. When the hydrogel was in pH>5.0medium,it swelled until it reaches swelling equilibrium. However, it did not appearovershooting effect in pH≤5.0buffer solution because of the ionization of carboxylgroup, resulting in electrostatic repulsion, and the hydrogen bonds between theadjacent carboxyl disappeared. The swelling kinetics of hydrogel in pH>5.0buffersolution of follow Schott secondary swelling kinetics.(3) The pH/GSH response carboxymethyl chitosan nanogel was preparationfrom chitosan. Their morphology, particle size and distribution were characterized bytransmission electron microscopy (TEM) and dynamic light scattering instrument(DLS). Their stability, pH sensitivity and restore reduction responsibility were studiedand the formation mechanism of the core-shell nanogels was researched.TEM show that the core-shell structure nanogels had regular shape, uniformdistribution, and the average diameter was about160nm.The DLS results show the particle size and dispersion coefficients of nanogelsplaced after one month in the pH7.4buffer solution were not significantly changed,showing that the nanogel had good stability. At lower concentrations (5μM) ofglutathione, the average particle size was not change, but a significant increase wasobserved in5mM and20mM glutathione, showing reduction responsibility. Theparticle size changed with the pH value, exhibited good pH sensitivity, and thesensitivity degree was related to the thiol content in thiolated carboxymethyl chitosan.Amphiphilic macromolecules can self-assemble into nanoparticles in aqueoussolution, and crosslink in suit to obtain a core-shell nanogel. The preparation methodis simple and does not require the use of a crosslinking agent. The prepared nanogelshad pH/redux responsibility. Taking into account differences environment of tumorcells and normal cells, the nanogel could be used for controlled drug delivery totumor cells. Nanogel has a large amount of carboxyl group at its surface, which couldbe chemically modified by ligands for tumoru targeted delivery.(4) Taking methotrexate (MTX) as the model drug, the drug release behavior ofpH/GSH responsive carboxymethyl chitosan nanogel in simulated media of humanblood, normal cells and tumor cell was studied. Its in vitro cytotoxicity was evaluated.As the thiol content in thiolated carboxymethyl chitosan decreased, thecumulative release rate of MTX-loaded nanogels increased in pH7.4buffer withoutglutathione. In simulated media of human blood, normal cells and tumor cell, theMTX-loaded nanogel had a selective drug release to tumor cells, since the highconcentration of glutathione in tumor cell could split disulfide bonds. Additionally,the lower pH values favor the swell of hydrophobic shell, making internal disulfidebonds exposed completely to the external high concentration of GSH. Thus, it wouldlead to a more rapid and complete drug released.