Fabrication And Properties Of Ordered Porous Composites Based On Directional Freezing Technology

With the continuous improvement of nanotechnology,more and more nanomaterials with special properties have been successfully synthesized.The properties of materials are determined by their composition and structure.Therefore,adjusting the structure of materials to a certain extent can further broaden the application fields of nanomaterials.Three-dimensional ordered porous materials refer to porous materials with uniform pore size and orderly pore structure in three-dimensional space.Because of its orderly structure,the mechanical properties,sensing properties and adsorption properties of materials are greatly improved.In recent years,as a simple,efficient,environmentally friendly and controllable method for material structure control,directional freezing technology has been widely used in tissue engineering,environment,energy,sensing and other fields.In this paper,the directional freezing technology is used for the preparation of orderly porous composites.The properties and applications of materials with two different structures,longitudinal channel and radial porous channel,are further investigated.The research results are as follows:(1)Chitosan and graphene were assembled into nerve scaffolds with longitudinal ordered channels by directional freezing technology by using the macromolecule chitosan as raw material and graphene as additive to provide mechanical properties and electrical conductivity.The scaffold displayed excellent performances,such as adjustable macroscopic shape and size;multi-channel structure,which simulates the directional microtubule structure of normal human peripheral nerve;high porosity(82-90%);light weight(72-85 mg/cm~3);high strength(stress over100 kPa at 60%strain);high elasticity(multiple compression under 60%strain can rebound in a few seconds in dry or wet environment)with the shape basically unchanged and the Poisson’s ratio maintained at 0 during compression.In vitro cell experiments showed that it had good biocompatibility(cell survival rate was more than 90%)and biodegradability(degradation rate was about 10%a month),and could guide cell alignment,axon extension and so on.In addition,chitosan-graphene aerogel could be used as a conductive scaffold,which stimulated cells to some extent,analyzed the activity of calcium ions,and promoted the transmission of nerve signals.(2)A method for preparing three-dimensional radial ordered porous aerogels was developed by using Acrylamide as raw material.The radial growth of ice crystals was guided by directional freezing technology.After low temperature polymerization crosslinking was carried out under UV irradiation,radial porous polyacrylamide(PAAM)aerogels were obtained by freeze drying.The aerogels had unique lamination structure,with radial channels,micron holes,wrinkled inner surfaces and molecular sieves,which not only provided adequate mechanical support performance,but also had good capillary ascending properties.Various forms of water transportation such as purified water,polluted water,seawater and sandy groundwater were realized.In addition,a MWCNT coating with excellent photothermal properties was modified at the top of the radial PAAM aerogel to build a bilayer polyacrylamide aerogel.The moisture transported to the top of the material was further collected through evaporation of solar energy,which has great potential application for water resources regeneration.