Sulfation Of Sodium Carboxymethyl Cellulose And Its Surface Modification On Medical Polylactic Acid

Biomedical polymer materials are a kind of functional materials that could replace,repair and treat biological tissues.At present,the most widely used implant materials are metal materials,which are mainly used for vascular stents,teeth,bones,artificial organs,etc.However,when it is implanted into a living body,it may cause infection,cause tissue damage,induce thrombosis,and long-term implantation may even lead to metal poisoning.In recent years,the research hotspot of biomedical materials-biodegradable materials,after being implanted in the organism,will be degraded after a certain period of time.Generally,carbon dioxide and water are generated and eliminated from the body.The materials are absorbed and the normal contractility of the tissue will be restored.Polylactic acid（PLA）is one of the representative biodegradable biomaterials.It is synthesized from lactic acid produced by microbial fermentation.It has good biocompatibility and degradability and is considered the most promising biomedical material.However,it has disadvantages that cannot be ignored,such as poor surface hydrophilicity,easy to induce thrombosis,and no effective sites for cell recognition.Therefore,it is of great significance to improve its blood compatibility and cell compatibility with organisms by surface modification.In this study,carboxymethylcellulose sodium（CMC）was modified by sulfation to prepare heparin-like methylcellulose sodium sulfate（SCMCs）,and then SCMCs/Chitosin（CS）multilayer film were constructed on the surface of PLA membranes using electrostatic layer-by-layer self-assembly technology（LBL）to improve its biocompatibility.Subsequently,the antibacterial drug gentamicin sulfate（Gentamicin,GS）was loaded on the multilayer film by the immersion method,and the drug release properties of the multilayer film were evaluated.In order to further improve the stability of the multilayer film,dopamine（DA）was grafted onto SCMCs to prepare DA-g-SCMCs,and then DA-g-SCMCs/CS multilayers based on covalent bonding were constructed on the surface of the PLA film,and the biocompatibility of the multilayer film is studied.The details as follows:（1）First,CMC was sulfated by sulfur trioxide-pyridine method,and three types of sulfated sodium carboxymethyl cellulose（SCMCs）with different degrees of substitution（DS）were prepared,which were denoted as SCMC₁,SCMC₂,SCMC₃,corresponding to DS are 0.64,1.06,and 0.69respectively.The ultraviolet spectrum（UV）showed a new absorption peak at 263nm,and infrared spectrum（FTIR）showed the characteristic absorption peaks of S=O and C-O-S,the hydrogen nuclear magnetic resonance spectrum（¹H-NMR）,hydrogen proton signal of each component in the range of3.0～4.5ppm was weakened,and the above results all indicate that the sulfonic acid group is successfully grafted on the CMC.The results of in vitro activity determination showed that compared with CMC,SCMCs obtained anticoagulant activity,anti-inflammatory activity and antibacterial activity,among which SCMC₂exhibited the best anticoagulant activity.（2）LBL technology was used to construct SCMC₂/CS multilayer film on the surface of PLA film.The surface morphology,chemical composition,wettability and growth pattern of the multilayer films were characterized by scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,water contact Angle（WCA）and ultraviolet visible spectrophotometer（UV-Vis）.The wetness and the growth mode of the film were characterized.SEM showed that when 15 double layers were assembled,the surface of the film was completely covered by layered and granular materials;new absorption peaks of N and S appeared in the XPS spectrum,and the peak intensity increased with the increase of the number of layers;WCA as the number of layers increases,the hydrophilicity increased;the UV-Vis results show that the growth of the film is continuous and uniform.The blood compatibility test results showed that the modified multilayer film could effectively reduce the adsorption of bovine serum albumin（BSA）,reduce the adhesion and activation of platelets,and effectively extend the activated partial thrombin time（APTT）and thrombin time（TT）,reduce coagulation activation and hemolysis rate.The results of the cytocompatibility test showed that L929 cells could proliferate and differentiate normally on the surface of the SCMC₂/CS multilayers.At the same time,the modified PLA film also showed good anti-inflammatory and antibacterial activities.（3）The GS was used as a model drug to be loaded onto the SCMC₂/CS multilayer film by the immersion method,and the drug release behavior was studied.Tracking the drug loading of the multilayer film by UV-Vis,the maximum drug loading is 951.82μg/cm².The drug release behavior in different ionic strength,p H value and temperature of drug multilayer were studied.The release dynamics was fitted with DDSolver software,and the release model was established.The antibacterial activity test showed that the drug-loaded multilayer film has a significant growth inhibition effect on E.coli and S.aureus,and the inhibition effect on S.aureus is better than that of E.coli.（4）Dopamine is grafted onto the sulfated polysaccharide molecule,which is denoted as DA-g-SCMCs.It was characterized by UV,FTIR,¹H-NMR.UV results showed that there was a characteristic absorption peak of benzene ring at 280nm;N-H stretching vibration peak appeared in the FTIR spectrum;the absorption peak of benzene ring appeared at about 7.0ppm in ¹H-NMR;results indicated that dopamine grafted successfully.The anticoagulant activity of DA-g-SCMCs was measured,and it was found that DA-g-SCMC₂showed the best anticoagulant effect.DA-g-SCMC₂/CS modified multilayer film based on covalent bond was obtained by DA-g-SCMC₂and CS alternately deposited on the surface of PLA film.The SEM observation results showed that the surface of the modified film appeared layered stacking,and it was relatively flat and smooth;WCA decreased in a zigzag shape with the increase of the number of layers.Hemocompatibility test results showed that the modified PLA membrane could effectively reduce protein adsorption,platelet adhesion and activation,prolong APTT and TT,inhibit thrombin generation to a certain extent,and reduce hemolysis rate.The results of cytocompatibility test showed that L929 cells could proliferate and differentiate on the surface of modified PLA membrane.The modified PLA film also has certain anti-inflammatory and antibacterial activities.Compared with SCMC₂/CS multilayers,DA-g-SCMC₂/CS multilayers have better stability.