In vitro studies of the degradation kinetic of biopolymers are essential for the design and optimization of implantable biomedical devices. In the presented work, a field-effect capacitive sensor has been applied for the real-time and in situ monitoring of degradation processes of biopolymers for the first time. The polymer-covered field-effect sensor is, in principle, capable to detect any changes in bulk, surface and interface properties of the polymer induced by degradation processes. The feasibility of this approach has been experimentally proven by using the commercially available biomedical polymer poly(d,l-lactic acid) (PDLLA) as a model system. PDLLA films of different thicknesses were deposited on the Ta 2 O 5gate surface of the field-effect structure from a polymer solution by means of spin-coating method. The polymer-modified field-effect sensors have been characterized by means of capacitance-voltage and impedance-spectroscopy method. The degradation of the PDLLA was accelerated by changing the degradation medium from neutral (pH 7.2) to alkaline (pH 9) condition, resulting in drastic changes in the capacitance and impedance spectra of the polymer-modified field-effect sensor.
Conventional methods for enzyme immobilisation onto sensor surfaces often use dip-, drop-or spin-coating techniques. In this study, a nano-spotting technique has been investigated for a patterned, spatially resolved deposition of enzymes onto a capacitive field-effect electrolyte-insulator-semiconductor (EIS) sensor and compared with the drop-coating method. Therefore, four different sensor arrangements covered with immobilised penicillinase as a model enzyme have been studied: (i) The sensor surface fully drop-coated, (ii) half drop-coated, (iii) half nano-spotted and (iv) fully nano-spotted with penicillinase. The sensors have been electrochemically characterised in pH buffers and penicillin solutions by means of impedance-spectroscopy, capacitance-voltage and constant-capacitance methods.
a b s t r a c tFor the development of new biopolymers and implantable biomedical devices with predicted biodegradability, simple, non-destructive, fast and inexpensive techniques capable for real-time in situ testing of the degradation kinetics of polymers are highly appreciated. In this work, a capacitive field-effect electrolyte-insulator-semiconductor (EIS) sensor has been applied for real-time in situ monitoring of degradation of thin poly(d,l-lactic acid) (PDLLA) films over a long-time period of one month. Generally, the polymer-modified EIS (PMEIS) sensor is capable of detecting any changes in the bulk, surface and interface properties of the polymer (e.g., thickness, coverage, dielectric constant, surface potential) induced by degradation processes. The time-dependent capacitance-voltage (C-V) characteristics of PMEIS structures were used as an indicator of the polymer degradation. To accelerate the PDLLA degradation, experiments were performed in alkaline buffer solution of pH 10.6. The results of these degradation measurements with the EIS sensor were verified by the detection of lactic acid (product of the PDLLA degradation) in the degradation medium. In addition, the micro-structural and morphological changes of the polymer surface induced by the polymer degradation have been systematically studied by means of scanning-electron microscopy, atomic-force microscopy, optical microscopy, and contact-angle measurements.
It is well known that the degradation environment can strongly influence the biodegradability and kinetics of biodegradation processes of polymers. Therefore, besides the monitoring of the degradation process, it is also necessary to control the medium in which the degradation takes place. In this work, a micromachined multi‐parameter sensor chip for the control of the polymer‐degradation medium has been developed. The chip combines a capacitive field‐effect pH sensor, a four‐electrode electrolyte‐conductivity sensor and a thin‐film Pt‐temperature sensor. The results of characterization of individual sensors are presented. In addition, the multi‐parameter sensor chip together with an impedimetric polymer‐degradation sensor was simultaneously characterized in degradation solutions with different pH and electrolyte conductivity. The obtained results demonstrate the feasibility of the multi‐parameter sensor chip for the control of the polymer‐degradation medium.
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