Preparation Of Polysaccharide Composite Cryogels By Freezing-induced Crosslinking And Bilirubin Adsorption Application

Cryogels are a macroporous polymeric monolithic materials which produced by freezing-gelation of monomers/polymers in solvents below the freezing point.Natural polysaccharide-based monolithic cryogels have been widely used in many fields such as biotechnology and water purification ascribing to their environment-friendliness,multiple functionality,easy availability,and low cost.Compared with traditional hydrogel,they are able to address some of the limitations of traditional hydrogels,such as fragility,instability,poor reproducibility,difficulty in controlling the growth process of ice crystals,and unsatisfactory application effects.In this paper,by compounding quaternized Chitosan（QCS）,microfibrillated cellulose（MFC）,and carbon nanotubes（MWCNTs）to solve the poor stability and water resistance and low removal ability of original polysaccharide,the prepared monoliths are suitable for different application scenarios and proposed the experimental process the concept of green chemistry.This work initiated for the first time a study to fabricate polysaccharide-based cryogels using a so-called‘‘freezing-triggered’’chemical crosslinking strategy（prepare cryogels with 3D macroporous structure at-12°C）,which was inspired by the chemical cross-linking of nanocelluloses–It is documented that the chemical crosslinking of nanofibers is more arduous compared with small molecules because of the strong steric hindrance to impede close intermolecular contacts.Coincidentally,the ice crystal growth will force the nanofibers to coalesce together,which may trigger chemical crosslinking.The main contents of the study are as follows:1.This work have introduced a quaternary ammonium group into the molecule of chitosan,the newly synthesized substance is called quaternized Chitosan（QCS）.It is well-documented that quaternizedchitosan（QCS）presents high solubility in a wide p H rangecompared with CS.More importantly,the electrostatic interaction between quaternary ammonium cations of QCS and bilirubin is theoretically stronger than the primary amino groups of CS.As a result,QCS is a promising candidate for the construction of bilirubin adsorption materials with good biocompatibility and high adsorption performance.2.The aim of this work is to develop a freezing-triggered chemical crosslinking strategy to fabricate polysaccharide-based cryogels with excellent mechanical performance for bilirubin adsorption and also to investigate the mechanism of activating the chemical reaction during the freeze step.This work fabricated QCS/MFC composite cryogels using microfibrillated cellulose（MFC）as a reinforcement agent（Herein,we chose MFC as the nanofiber reinforcement to demonstrate this technique because of its good biocompatibility,high aspect ratio for entanglement,and applications in our previous works）and bis（vinylsulphonyl）methane（BVSM）as the freezing-triggered chemical crosslinking agent.The fabricated cryogels is rich in positive charge,and exhibits the three-dimensional（3D）wall perforated cellular structure under SEM.The facts of the MQCS/MFC cryogel presented the macropores with the mean size range of 10 to 40μm,which ensures non-clarified and viscous feed-streams pass smoothly.Furthermore,the QCS/MFC cryogel was subjected to 200 cycliccompressions with60%strain,the QCS/MFC cryogel could maintain 91.2%of theinitial maximum stress and recover to its original volume even after200 compression cycles,demonstrating its high compression fatigue resistance.The bilirubin adsorption properties of the QCS/MFC cryogel were evaluated under static and dynamic conditions.Due to the quaternary ammoniumfunctionalization of chitosan,the QCS/MFC showed a high adsorption capacity of 100 mg/g and ashort adsorption equilibrium time of 3 h.More importantly,the QCS/MFC still exhibited high adsorptionefficiency（over 49.7%）in the presence of 40 g/L albumin.Furthermore,the QCS/MFC could alsomaintain high dynamic adsorption efficiency in self-made hemoperfusion devices.The dynamic simulation adsorption experiment shows that the 50%breakthrough volumes for bilirubin in albumin-free and albumin-rich PBS solutions were determined to be 4500 m L/g and 340 m L/g(C_bilirubin=100 mg/L).3.In this work,poly（dopamine）was introduced into the MFC and QCS systems, poly（dopamine）was exploited to improve the dispersion of MWCNTs in water,so that they could be cross-linked on the cryogel without any stacking,and prepared QCS/MFC/p-MWCNTs cryogel.The adsorption test shows that the removalefficiency of bilirubin in the entire system is more obvious after exploited the carbon nanotubes,it may be due to the existence of more adsorption sites after carbon nanotubes coated with dopamine,this can be reflected in the experiment that the adsorption test showed that high bilirubin uptake ability could be achieved to recorded to be 134 mg/g maximumly,while the theoretical maximum adsorption capacity can be as high as 200 mg/g.At a bilirubin concentration of 200 mg/L,the dynamic simulation adsorption experiment shows that the 50%breakthrough volumes for bilirubin in albumin-free and albumin-rich PBS solutions were determined to be 4700 m L/g and 343 m L/g.4.In order to evaluate the hemocompatibility of QCS/MFC and QCS/MFC/p-MWCNTscryogels,ahemolysistest,3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide（MTT）assay,and blood clotting time assay were performed,demonstrating the excellent hemocompatibility of the QCS/MFC and QCS/MFC/p-MWCNTs1 cryogels.The above two cryogel（QCS/MFC and QCS/MFC/p-MWCNTs1）avoided the use of a large number of organic solvents in the preparation process,and the whole experiment process was more facile.At the same time,this work establishes an innovative method to fabricate robust polysaccharidebased cryogels using a freezing-triggered chemical crosslinking strategy and opens up new avenues for the manufacture of hemoperfusion materials.