Patent Publication Number: US-2011076737-A1

Title: Carriers for immobilization and reusability of enzymes

Description:
TECHNICAL FIELD  
     Polymers (Biopolymers) and Biochemistry (Enzymes). 
     BACKGROUND ART 
     Alginates and carrageenans polymers have been used as carriers for immobilization of enzymes and cells using physical techniques such as the adsorption, entrapment and encapsulation methods. As these polymers are enjoying many advantages, for examples they are hydrophilic, environmentally friendly and porous. To increase the rigidity of alginates and carrageenans (poly anions) after containing the enzymes and cells, their surfaces were treated with cationic polymers and with a di- or poly-aldehyde. 
     However, on the industrial level, the treated alginates and carrageenans (hydrogels) by these methods are not used on the industrial level due to the following: 
     1- The drawback of the non covalent bond such as adsorption or entrapment as they are weak bonds and consequently the active entrapped or adsorbed material (e.g. enzyme) is usually leaked from the polymers after the first use. 
     2- The mechanical and thermal stability of the non treated hydrogels melt or dissolve at low temperature and moderate reaction conditions. 
    
    
     DISCLOSURE OF INVENTION 
     The alginates and carrageenans are very abundant polymers in nature; FDA approved and could be shaped in many forms such as films, disks and beads. These properties were encouraging to use them on the industrial scale after some treatment. Based on the fact that these polymers are polyanionic, they could be treated with a polycation such as chitosan and polyimines. It is known that the deacetylation of chitin to chitosan resulted into chitosan with 5-15% amide and 85-95% amine groups. Thus the 85-95% free amino groups were used to form a strong polyelectrolyte with the gel. The strength of this polyelectrolyte interaction is as strong as the covalent bone). Thus, the novelty of this work is treatment of alginates and carrageenans polymers with a cationic polymer such as chitosan or polyimines then immobilizing the enzymes to the hydrogels via covalent bonds using their free amino groups through a mediator such as di-aldehyde. As a result of this treatment: 
     1- The thermal stability of the gels was improved from 35° C. to 95° C. 
     2- New functionalities have been incorporated to the treated gel with chitosan or polyimines and the di-aldehyde such as the aldehyde group, which was proved by the Infrared spectroscopy (IR). The new aldehydic&#39;s carbonyl group, which came from the reaction of the glutaraldehyde with the chitosan or the polyimines on the gel has been proved by the Infra Red (IR) technique at a wavelength of 1720 cm −1  in case of carrageenan gel and at 1647 cm −1  for the alginate, which differs than that of the chitosan&#39;s amide group at 1668 cm −1  or that of the pure alginate at 1600 cm −1 . 
     3- Few enzymes have been successfully immobilized covalently to the gels. 
     4- As a result of the strong covalent bond between the enzymes and the gels, the enzymes do not leak and the immobilized enzymes could be reused on the industrial scale for tens of times, which reduce both the cost of the enzyme and the enzymatic products. 
     The methodology of modifying the alginates and carrageenans gels for immobilization of enzymes was as follow: 
     1- The alginates and carrageenans gels&#39; powders of 1-5% (w/v) were dissolved in distilled water for 1-5 hours at 25-80° C. till complete dissolution. The gels were prepared in form of sheets, disks or beads using the syringe or the Innotech Encapsulator. 
     2- The gels were soaked in 0.1-10% (w/v) chitosan or polyimines for 10 min to 8 hours to improve the gels&#39; thermal stability. 
     3- The poly- or di-aldehyde compound to be used as a mediator between the gel and the enzyme to bind them via a covalent bond has been chosen to be glutaraldehyde, which was used at 1-10% (v/v) and for 1-5 hours. 
     4- The treated hydrogel with the active aldehyde groups were soaked in different enzymes for 1-16 hours to immobilize them with covalent bonds.