Degradation of thin poly(lactic acid) films: Characterization by capacitance-voltage, atomic force microscopy, scanning electron microscopy and contact-angle measurements

Abstract

For the development of new biopolymers and implantable biomedical devices with predicted biodegrad-ability, simple, non-destructive, fast and inexpensive techniques capable for real-time in situ testingof the degradation kinetics of polymers are highly appreciated. In this work, a capacitive field-effectelectrolyte–insulator–semiconductor (EIS) sensor has been applied for real-time in situ monitoring ofdegradation of thin poly(d,l-lactic acid) (PDLLA) films over a long-time period of one month. Gener-ally, the polymer-modified EIS (PMEIS) sensor is capable of detecting any changes in the bulk, surfaceand interface properties of the polymer (e.g., thickness, coverage, dielectric constant, surface poten-tial) induced by degradation processes. The time-dependent capacitance–voltage (C–V) characteristicsof PMEIS structures were used as an indicator of the polymer degradation. To accelerate the PDLLAdegradation, experiments were performed in alkaline buffer solution of pH 10.6. The results of thesedegradation measurements with the EIS sensor were verified by the detection of lactic acid (product ofthe PDLLA degradation) in the degradation medium. In addition, the micro-structural and morphologicalchanges of the polymer surface induced by the polymer degradation have been systematically studied bymeans of scanning-electron microscopy, atomic-force microscopy, optical microscopy, and contact-anglemeasurements.