Embedded enzymatic biomaterial degradation: Flow conditions & relative humidity

Abstract

Enzyme-catalyzed degradation of PCL films with embedded Candida antarctica Lipase B (CALB, 1.6%-by-wt) under continuous fluid exchange (flow) conditions and in controlled humidity desiccators were determined. At 0.2 mL/min flow rate, film weight loss reached 85% in 3 d relative to bulk-no flow incubations where 70% degradation occurred in 9 days. This increase in rate under flow conditions is attributed to more efficient removal of degradation products that can act as competitive inhibitors. However, further increase in flow rate from 0.2 to 0.5 mL/min results in slower weight loss (7 days, 70%) as increased flow rate appears to negatively influence enzyme stability. Another intriguing discovery is that, by using flow in place of bulk-no flow conditions, removal of degradation products is more efficient leading to formation of a porous matrix where SEM cross sectional images show larger better defined pores. The unusual phenomenon of high porosity matrices resulting from enzyme-catalyzed hydrolysis is unique to embedded enzyme systems. Studies were also conducted where 1.6% CALB-embedded PCL films were incubated in desiccators set at 20, 75 and 95% relative humidity (RH). Water-uptake and molecular weight change at 20% RH were insignificant. However, at 75 and 95% RH, by 28 days, %-water content increased to 0.30 and 0.82, and film Mn decreased by 25% to 59,300 and 58% to 33,900, respectively. While stability under controlled low-humidity environments demonstrates options for safe storage, applications are envisioned where the unique degradation properties of enzyme-embedded bioresorbable films will be exploited for release of actives ranging from fragrances, flavors and therapeutic agents.