ENHANCED LOADING AND ACTIVITY RETENTION OF BIOACTIVE PROTEINS IN HYDROGEL DELIVERY SYSTEMS

A simple, general and effective technique is developed for increasing the loading of bioactive macromolecules into hydrogels using the princ iples of aqueous two-phase extraction. Model proteins, ovalbumin and a lpha-amylase, were loaded into hydrated gels by soaking the gels in a buffered solution of protein containing 12 wt% PEG-10 000 and 0.22 M s alt (KCl, KBr or KI). The PEG and salts were expected to enhance prote in sorption according to aqueous two-phase extraction heuristics. In t he absence of the solution additives, the gels absorbed little protein . But protein loading up to 270 mg ovalbumin/g polymer and 67 mg alpha -amylase/g polymer was obtained when the PEG and salt were added; load ing was not significantly dependent upon salt type. Ovalbumin release from hydrated gels was diffusion-controlled. The diffusion coefficient was 1.10(-7) cm(2)/s, consistent with protein absorption into the gel rather than adsorption onto the surface. Release kinetics of both pro teins from dried, glassy gels matched conventional behavior for releas e of absorbed drugs from glassy polymers. Finally, alpha-amylase activ ity was retained even after drying the loaded gel at 65 degrees C, con ditions which denatured the enzyme when not absorbed in the gel. (C) 1 998 Published by Elsevier Science B.V.