Preparation of α-amylase-immobilized freeze-dried poly(vinyl alcohol) foam and its application to microfluidic enzymatic reactor

• α-Amylase was immobilized in a freeze-dried PVA monolith prepared in a microreactor.
• The precursor solutions in the microchannel was sufficiently freeze-dried.
• The reaction performance of the reactors were dependent on the freezing steps.
• PVA gel formation linked with freezing was key to improving reactor performance.
• The reactors demonstrated continuous reaction performance over 8 days.

Freeze-drying aqueous poly(vinyl alcohol) (PVA) solutions affords porous foam materials that show potential as an interesting entrapping matrix for enzyme immobilization. When an enzyme–PVA solution is freeze-dried, the enzymes are automatically entrapped in the architecture of the PVA matrix. The obtained PVA foams barely disperse in aqueous solution because of physically cross-linked PVA cryogel formation. This method is an in situ immobilization technique such that supporting materials can be produced in any space where the precursor solutions can be loaded. In this study, an attempt was made to prepare freeze-dried PVA foams in a microchannel to prepare an α-amylase–immobilized microreactor. Freeze-dried foams for amylase immobilization were demonstrated to be successfully prepared in microreactors with a ca. 18-μL microchannel volume, and were evaluated by conducting continuous starch hydrolysis reactions over 8 d. The macroscopic pore structures seemed to be only minimally affected by the apparent activities of the immobilized enzymes; however, the cryogel structures, affected by the freezing protocol, and the microchannel materials employed were suggested as the key to determining reaction performances.