| Chitosan is a natural and abundant polysaccharide which derived from chitin by N-deacetylation,and has been approved by the US Food and Drug Administration.Being biocompatible,non-toxic,biodegradable,antimicrobial and biodegradable,chitosan and its derivatives have attracted wide attentions in various biomedical applications.The biological functions of chitosan are strongly dependent on its physical and chemical properties,such as concentration,molecular weight,and the degree of deacetylation.The effect of free amino content on the biological functions of chitosan has been rarely studied.Active amino group of chitosan makes it a cationic polysaccharide and provides binding site for a variety of negatively charged molecules,such as proteoglycans,hemoglobin,glycosaminoglycans,consequently affecting various biological properties of chitosan.It is of great significance for the application of chitosan to understand the effects of cationic properties of chitosan on cell behaviors,matrix secretion and related activities in different physiological environments.To this aim,carboxymethyl chitosan hydrogels with different cationicity were prepared through crosslinking with different concentrations of genipin,and their impacts on hemostasis,osteogenesis,intraoperative operation,bone repair and wound healing were systematically studied in this paper.The main contents are as follows:1.To obtain both favorable osteogenic and hemostatic functions is desirable in surface of implant devices,we prepared carboxymethyl chitosan hydrogel coatings with different cationicity through crosslinking with different concentrations of genipin(1%,2.5%,5% and 10%).The genipin concentration strongly influenced both mesenchymal stem cells(MSCs)responses and blood coagulation activities for chitosan-hydroxyapatite samples.Increasing genipin concentration overall enhanced the osteogenic and hemostatic potentials,and an optimum window of chitosan cationicity(5% genipin in our case)led to both the best MSC response and coagulant activities.In particular,the cationicity had demonstrated a profound modulation effect on the hemostatic activities of chitosan samples,through influencing the thrombin time(TT)and prothrombin time(PT)of intrinsic coagulation pathway and activation of erythrocyte.Tuning the crosslinking degree thus provides a simple and effective approach to achieving combined osteogenic and hemostatic functions,which has great potential in surface modification of surgical implants.2.Designing and optimization of thermo-sensitive chitosan hydrogels with combined rapid gelation time and superior osteoblastic response are critical for easy intraoperative functionalization and long term osseo-integration of orthopedic implant.The chitosan hydrogels were prepared via coupled ionic and covalent crosslinking to optimize the gelation time and the cellular responses.Different amounts of carboxymethyl chitosan(CMCS,20%,60% and 100% V/V),used as a covalent crosslinking component,were mixed with the thermal-sensitive chitosan that was crosslinked by β-glycerophosphate disodium salt hydrate(CS,ionic crosslink component).The incorporation of CMCS component overall significantly improved the biocompatibility and stability of the hybrid hydrogel.The optimized CMCS/CS-0.6sample not only maintained the thermo-sensitive character with even shorter gelation time,but also exhibited well improved biological activity and chemical stability.Furthermore,a two-layer drug release platform was constructed using CMCS/CS-0.6prepared by coupled cross-linking methods and CMCS-5% prepared by chemical cross-linking.Using the active polypeptide as the drug model,it was found that the prepared multi-layer coating could achieve controlled release of the drug,effectively reduce bacteria adhesion,promote osteogenesis and inhibit inflammation.Such findings will have important implication in designing functionalized implants with potentials of both convenient intraoperative functionalization procedures and dealing with in different clinical requirements.3.The mechanical property and osteogenic activity of chitosan need to be further improved in application as bone tissue engineering scaffold.The Ca P compound can be introduced into the polymer network by mineralization,and the formed mineralized hydrogel with a uniform combination of organic and inorganic phases has improved the mechanical property and osteogenic activity.The mineralized chitosan hydrogel was prepared by enzyme-induced biomineralization,and they have improved toughness and stiffness through the formation of calcium phosphate nanostructures.The cationic degree influenced amount of mineralization compound by suppressing ion diffusion.The results suggested the enzyme-induced biomineralization is an effective approach on improving both the mechanical properties and osteogenic responses of the chitosan hydrogel in bone tissue engineering.4.It is of great clinical significance to design wound dressing materials with combined excellent wound healing property and superior capability to suppress hypertrophic scar formation.The carboxymethyl chitosan hydrogels with different genipin concentrations(2.5%,5%,10% and 15%,respectively)were prepared to examine if and how the cationicity of chitosan would affect the hypertrophic scarrelated outcomes.An optimum window of chitosan cationicity(5% in our case)demonstrated potential to mitigate hypertrophic scar in wound healing by suppressing the expression of a-smooth muscle actin(α-SMA)and promoting secretion of type I matrix metalloproteinases(MMP-1).In vivo,the CMCS-5% hydrogel showed smaller,thinner and smoother wound appearance.Moreover,the CMCS-5% sample with additional incorporation of 2%(V/V)Aloe vera gel exhibited further improved performance in scar inhibition.Overall,such findings might have important implications in chitosan-based wound dressing design for high-quality wound repair and effective scar inhibition.5.Chitosan,as a natural polymer,is used to cancer therapy.The carboxymethyl chitosan hydrogels with different genipin concentrations(1.25%,2.5%,5% and 10%,respectively)were prepared to investigate the effect of chitosan cationicity on the growth of tumor cells.Compared with MC3T3-E1,the MG-63 had more apoptotic and necrotic cells on chitosan hydrogels.Moreover,decreasing genipin concentration enhanced the number of necrotic and apoptotic cells,and a highest proportion of apoptotic and necrotic cells(64.24%)in CMCS-1.25% sample with the lowest crosslinking degree.In particular,the cantioncity had demonstrated anticancer effects through influencing two different aspects,including membrane disruption of cancer cells and apoptosis by damaging DNA and releasing cytochrome C.These findings demonstrate that possible mechanisms of chitosan as safe and effective antineoplastic agents,which sheds new light on the development of drug-free natural polymers for cancer therapy. |
PDF Full Text Request