Composite Cryogels: Stationary Phase for Separation of Complex Media

Abstract: Demands for efficient, economical and fast separation and purification methods for various target molecules have led to the development of new techniques and materials for bioseparation processes. Separation can be carried out in both batch and chromatographic modes. Running the separation step in a conventional chromatographic column is more efficient than batch mode, but there are some limitations with this technique for direct capture of targets from complex media or applying it for purification of products larger than 10 nanometres. Therefore there is a need for new materials that can be used for purification of a target directly from particulate-containing fluids in a short time. On the other hand, packing different adsorbent particles in a column or handling them free in suspension might be difficult and challenging due to the high backpressure and risk of leakage, while immobilization of the particle adsorbents on a matrix can reduce these problems. Cryogels, supermacroporous hydrogels, as a class of monolithic stationary phase are a product of cryogelation technology and have interconnected channels in the micrometre range. Due to the porous structure, free passage of particles is possible and efficient mass transfer and good flow through properties are expected. These polymeric networks can be used as a robust matrix for embedding different types of particles and adsorbents in order to form composite cryogels. Immobilization of particles inside cryogels leads to the creation of greater surface area inside the matrix; thus, greater binding capacity of the gels is achieved. The combination of the porous structure of the matrix and selective adsorption by the adsorbents embedded in the gel form a unique composition that is suitable for separating a wide range of small/large target molecules. Composite cryogels can be prepared by one-step polymerization either from monomer/polymer solutions or particle suspensions under cryotropic conditions. Applying a particle suspension has advantages over a monomer solution when embedding porous adsorbents inside the network, since a polymerization solution can penetrate into the pores and affect the capacity of the adsorbent during the process, while particles are larger than the size of the pores and cannot block them. Here in this work, composite cryogels were evaluated for water/wastewater treatment and also as an affinity matrix for glycoprotein purification. Activated carbon, molecularly imprinted polymer (MIP) and ion-exchange adsorbents were synthesized to form composite cryogels for environmental applications in this study. Capturing phenol, as a small organic compound, was evaluated with a carboncomposite cryogel formed from a particle suspension due to the highly porous structure of the carbon. A molecularly imprinted polymer technique was also used for fabrication of adsorbents based on inorganic and organic templates for selective removal of bromate and propranolol from aqueous/complex media, respectively. The selectivity of these adsorbents towards the target molecules was high even in the presence of analogue molecules. The selectivity of MIP adsorbents was evaluated with ion-exchange adsorbent for studying the removal of bromate. The possibility of forming different types of chromatography columns, such as affinity columns, by introducing proper (bio)ligands or functional groups on the cryogels is another feature which makes this material adaptable for different applications. By synthesizing composite cryogels as a form of affinity matrix, the binding capacity of the network will increase due to the higher surface area. This was studied in this work by preparing composite polyvinylalcohol cryogels and immobilizing concanavalin A via epoxy groups. Horseradish peroxidase was selected as a target and its binding/elution was studied in both batch and chromatographic systems. The adsorption isotherm and kinetics of the developed materials were also evaluated in this work. Improving composite cryogel materials with porous/non-porous adsorbents for direct capture of small/large targets from complex media can be valuable for synthesizing more efficient chromatographic supports with high capacity both for academic and industrial applications.