Preparation And Applications Of Acrylamide-Hydroxyethyl Methacrylate Copolymer Cryogel Monolithic Materials

Cryogel materials boast the advantages of unique interconnected macroporous structure,low flow resistance,permeability and stability,and have been widely used in tissue engineering,cell scaffolds,bioreactors and chromatographic separations.Especially,monolithic cryogels have been attempted as a new generation of chromatographic matrices.Cryogel monolithic materials are usually composed of synthetic polymers?such as polyacrylamide,polymethacrylate,polystyrene?or natural polymers?such as agarose,cellulose?.At present,the pore size range of the cryogel materials was 10-100?m,which can process some clarified and less viscous samples,and provide a new way for designing hemoperfusion products.However,for high viscosity samples,a sufficiently large pore size was required to ensure sample pass smoothly.At the same time,the crystal nucleus size is difficult to control,so that,the preparation and research of cryogel have been limited to small volumes?about a few milliliters?,which limits the use of cryogel in large-scale engineering and biological separation technologies applications.Therefore,in this study,the acrylamide and hydroxyethyl methacrylate are copolymerized to prepare the supermacroporous cryogel monolithic material.In addition,the large-volume crystal material was also prepared by modified pre-freezing method and adding enhancer?bacterial cellulose?.The details are as follows:By mixing the monomers of acrylamide?AAm?and hydroxyethyl methacrylate?HEMA?,the monolithic copolymer cryogel with larger interconnected pores and thicker pore walls was prepared.Experiments of N₂-adsorption demonstrated that the interconnected pore of the copolymer cryogel was within the range of 10-350?m,which is far larger than that of 10-50?m for the pAAm and pHEMA cryogels.Additionally,the thicker pore walls of the copolymer cryogel lead to the increase in elastic modulus,rendering the copolymer cryogel improved mechanical strength.Tris?hydroxymethyl?aminomethane?Tris?was immobilized onto cryogels,and the affinity binding of lysozymes on Tris-cryogel was evaluated.Adsorption behaviors of lysozymes on the three Tris-cryogels could be described by Langmuir adsorption isotherms and pseudo-second-order kinetic models with similar adsorption and kinetics parameters.Compared with the Tris-pAAm and Tris-pHEMA cryogels,higher adsorption capacity and purity of lysozymes could be achieved by the copolymer Tris-cryogel as the egg white solution flew through solely driven by gravity,and the egg white only was diluted twice with phosphate buffer solution.Chromatographic media with large-volume and high mechanical strength are highly desired in biomedicine and biotechnology.However,the preparation of such materials still faces immense challenges,which limits the applications of cryogel materials.Herein,a robust strategy to develop the large-volume and nonbrittle monolithic cryogels via the modified pre-freezing method and the introduction of reinforcement materials is reported.We successfully prepared large-volumed cryogels with the volume of 500 mL?17 cm in diameter?.Compared with the traditional pre-freezing method,a large amount of ice crystals were retained in the polymer mixture to ensure a uniform pore size distribution,and avoided the problem of internal collapse due to uneven heat transfer of large-volume materials.Meanwhile,its mechanical properties were enhanced due to the introduction of bacterial cellulose?BC?,where BC and pAAm-HEMA form a semi-interpenetrating network structure?semi-IPN?,which improved the strength of large-volume cryogels.In addition,poly?ethyleneimine??PEI?was immobilized onto the cryogel matrices via the reaction with epoxy groups on the cryogels,and this material was used to adsorb bilirubin.The effects of the amount of BC on the pore morphology,mechanical properties,and adsorption properties of large-volume cryogel were explored.The results show that the pore size and bilirubin adsorption capacity of the cryogel decrease slightly with the increase of the BC content?percent of polymerized monomers?from 0.4%to 2.0%,,but the mechanical properties increases markedly.When the BC content was 1.2%,the SEM results show that the large-volume cryogel has uniformly distributed interconnected pores.The compression test results show that the deformation is as high as 90%and the crystal gel is not broken and the adsorption experiment results show that its maximum adsorption amount is as high as 76 mg/g.In addition,the adsorption properties of PEI-BAH cryogel material?1.2%BC content?for metal ions and dyes were also investigated.