Chitosan-Based Cryogels for Esterase Immobilization

Preparing chitosan (Ch) cryogels in the form of full-interpenetrating polymer networks (IPNs) is an advantageous approach since the IPN cryogels have a more regular and tight pore distribution and durable spongy structure, including enhanced mechanical properties and more functional groups. In the present research, Ch-Ch ([Ch](cry)) and Ch-pAAm (polyacrylamide) full-IPN cryogels ([Ch-pAAm](cry)) were synthesized, characterized, and then used for the immobilization of enzyme (porcine/pig liver esterase (PLE)) using the adsorption method. The results of mechanical analysis have shown that the compression elasticity modulus (E) value of [Ch-pAAm](cry) full-IPN cryogel is 47 times that of [Ch](cry). The introduction of pAAm within full-IPN cryogels increases the compression strength; however, it decreases their ability for esterase immobilization and swelling degrees (S-e). The esterase adsorption capacity (X-L) values are 90.7 and 13.4 mg g(-1) for [Ch](cry) and [Ch-pAAm](cry), respectively. Adsorption equilibrium time of [Ch](cry) is shorter (360 min) than [Ch-pAAm](cry) (600 min). According to K-m values, the order of affinity for the 4-nitrophenyl acetate (pNPA) substrate is [Ch-pAAm](cry) (6.9 mM) > [Ch](cry) (22.1 mM) > free enzyme (60.4 mM). The porosity parameter, V-p (cm(3) pore (g dry cryogel)(-1), was calculated to be 36.18 +/- 4.77 for [Ch](cry) and 5.00 +/- 0.76 for [Ch-pAAm](cry), indicating that [Ch](cry) had larger pores than [Ch-pAAm](cry).