Preparation And Properties Of New Composite Chitosan Hydrogels For Potential Wound Dressings

Wound dressing is an important medical product for wound care.Modern wound dressings can promote wound healing by absorbing excess fluid from the wound or by holding moisture to keep the wound moist.Among them,biomedical materials derived from chitosan are widely recognized as wound-healing promoting materials,because of their excellent biocompatibility,hemostasis and antibacterial properties.The goal of this research is to prepare several crosslinking chitosan composite film/sponges and an acid-soluble carboxymethyl chitosan gels in situ,and then to characterize their chemical and physical structure by nuclear magnetic resonance(NMR),Fourier Transform infrared spectroscopy(FTIR),X-ray diffraction(XRD)and Thermogravimetric Analysis(TGA),scanning electron microscopy(SEM).The swelling rate,water vapor and oxygen transmission rate,cell toxicity,blood compatibility were also examined.The efficacy of the new composite film as a dermal wound dressing had also been investigated by using a full-thickness wound in a mice model.The main innovations of this work are as follows:(1)A cellulose derivative,succinyl hydroxypropyl methyl cellulose(HPMCS)was prepared by chemical substitute,and then the reinforced hydrogel films of HPMCS-crosslinked chitosan(HPMCS-CS)were prepared through amide bond formation using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide(EDC)and N-hydroxysuccinimide(NHS)as a catalyst.Compared to that of blend films,mechanical properties of HPMCS-CS hydrogel films were significantly enhanced both in dry and swollen state.(2)The preparation conditions of carboxymethyl konjac glucomannan(CMKGM)were studied,and the effect of carboxymethyl content on the interaction between CMKGM and chitosan was studied.(3)PEG derivative(SC-PEG-SC)was directly reacted with chitosan in solution to form gels and then dried into films without the use of any toxic crosslinking agent or initiator.The application prospect of the wound dressing was evaluated by animal experiment.(4)Acid-soluble carboxymethyl chitosan gels in situ were prepared and their sealing property and solubility in dilute acetic acid were studied.The acid solubility is provided by the synthetic PEG-ester(SC-OE-PEG-OE-SC).Mixed solution of SC-OE-PEG-OE-SC and carboxymethyl chitosan can form in situ gels.The in situ gels could be used in emergency situations,for hemostasis and closure of the wound,and could be dissolved by dilute acetic acid,which were convenient for further surgical treatment of the wound,and could avoid secondary damages to the wound.The main contents and conclusions of this thesis include the following four parts:First,hypromellose(HPMC)was grafted with succinic acid to yield hypromellose succinate(HPMCS),and then reinforced hydrogel films of HPMCS-crosslinked chitosan(HPMCS-CS)were prepared by EDC/NHS as a catalyst.The mechanical properties of the films were tested,and membrane physicochemical properties such as swelling ratio,water vapor permeability and oxygen permeability were measured.The cytotoxicity was determined by NIH3T3 cell culture and MTT method,and the haemolysis was determined by rabbit red blood cells.In vitro drug release and bactericidal properties of crosslinked films were tested by using gentamicin as a model drug.The results indicated that HPMCS-CS hydrogel films with good biocompatibility possess high swelling ratio,proper WVTR,and oxygen permeability,which might accelerate tissue regeneration.Meanwhile,gentamycin sulfate release from drug-loaded HPMCS-CS hydrogel films were sustained,which would help to protect wound from infection.Second,the hydroxyl group of KGM was replaced by carboxymethyl using isopropyl alcohol as the reaction medium under the catalysis of NaOH to yield CMKGM.Then the CMKGM/CS crosslinked sponges were prepared by crosslinking with EDC/NHS and lyophilization.FTIR,XRD,SEM,TGA were used to characterize the structure,thermal stability and other properties of cross-linked CMKGM/CS composite sponge,such as swelling ratio,porosity and water vapor transmission rate.The biocompatibility was also determined.The results showed that the CMKGM/CS composite sponges had good water absorption properties,thermal stability,good biocompatibility and could effectively reduce the evaporation of water.Third,SC-PEG-SC was synthesized by the reaction between polyethylene glycol(PEG)and N.N'-Disuccinimidyl Carbonate(DSC).The products were purified by sedimentation in ether.When SC-PEG-SC and chitosan solutions were mixed together,the active ester of SC-PEG-SC reacted with the amino-group of chitosan to form hydrogels.Crosslinked hydrogel films were then prepared by drying overnight at 37 ?.The structure and thermal stability were then characterized by NMR,FTIR,XRD and TGA.Other properties such as tensile strength,water vapor and oxygen transmission rate were also investigated.In vivo experiment was performed to test the composite hydrogel membrane as wound dressing.The results showed that the composite films were non-toxic,and had good water absorption ability and thermal stability.The tensile strength and elongation at break of crosslinked films are improved compared to those of CS membrane.The results of animal experiment showed that the composite cross-linked film promoted the healing of wound ICR mice.Last,an acid-soluble carboxymethyl chitosan hydrogels in situ were designed and prepared.The in situ hydrogels could be used as a sealant for wound closure in emergency,and could be dissolved by dilute acetate for further surgical treatment.A five-step reaction were used to synthesize PEG-Orthoester-N.N'-Disuccinimidyl Carbonate(SC-OE-PEG-OE-SC),and then SC-OE-PEG-OE-SC was quickly mixed with carboxymethyl chitosan in solution to give an in situ gel and adhesion to tissues.Acetic acid solution can be used to dissolve the gel because of the sensitivity of the ortho ester to acid.The structure of SC-OE-PEG-OE-SC was characterized by NMR.The cytotoxicity test of hydrogels and their degradation products showed that they were nontoxic.Concentrations of SC-OE-PEG-OE-SC and carboxymethyl chitosan solution were adjusted according to the gelation time.Tissue adhesion properties and acid-solubility of gels were also investigated.The results showed that the hydrogels could be firmly adhered to the tissue surface,and be dissolved completely in 5%acetic acid solution.In this work,chitosan was used as the main starting material.Four kinds of wound dressings including two transparent films,a high absorbent sponge dressing materials and an acid-soluble in situ hydrogel were prepared by chemical modification and crosslinking reaction.These wound dressings may meet the needs of different types of wound,and have practical application prospects by further optimization.