This study describes the development of

This study describes the development of an EW fiber-optic sensor for the detection of matrix metalloproteinase 2 (MMP-2) and 9 (MMP-9) activities. In the context of pressure and venous leg ulcers, an elevated and persistent activity of these proteases has been associated with a loss of extracellular matrix (ECM) homeostasis and a chronic inflammatory state, which result in the disruption of the wound healing process [8,30–32]. The protease-sensitive film consists in glutaraldehyde (GTA)-crosslinked cold water fish gelatin deposited by dip-coating on the core of a poly(methyl methacrylate) (PMMA) optical fiber. Gelatin was chosen due to its recognized biocompatibility, non-immunogenicity [33], low price, excellent film forming properties [34,35], and degradation by most MMPs involved in the ECM remodeling process, principally MMP-2 and MMP-9 [36]. As such, it has been widely used to quantify the overall proteolytic activity [37,38,19,39]. The gelatin film was stained with chlorophyllin copper sodium salt to visualize its degradation by the enzyme using EW retinoid x receptor of transmitted light. The system was integrated as a portable autonomous device, providing a new point-of-care diagnostic tool to identify large protease imbalances in the wound bed, which will complete clinical symptom evaluation and support treatment decisions.
Experimental
Results and discussion
Conclusions In summary, we reported on the use of optical fibers as valuable transducers to quantify protease activity based on the enzymatic degradation of thin polymer films. Cold water fish gelatin solutions mixed with GTA as a crosslinker led to convenient formulations for film preparation by dip-coating at room temperature, resulting in water resistant films, which served as a substrate for MMP-2 and MMP-9. Staining the films with chlorophyllin copper allowed detection of film degradation using the absorption of the EW in the portion where the gelatin film replaced the fiber cladding. The resulting variations in light transmission were measured using a simple setup based on LEDs and PD as light sources and photodetectors and simple signal processing. Signal variation rates proportional to enzyme concentration enabled direct monitoring of the activity of MMP-2 and -9 down to 2 and 10μg/mL, respectively, in approximately 10min, without the need for sensor calibration for each experimental setup. The investigation of the influence of the preparation conditions on the sensor behavior revealed that sensitivity was optimal in the case of the thinnest gelatin film with the lowest crosslinker concentration. Furthermore, it demonstrated that the film degradation rate can be slowed down by increasing the crosslinker concentration in the initial formulation, which highlights possibilities for tuning the sensitivity and operational time of the sensor. Finally, the sensor reproducibility appeared to strongly depend on the storage conditions, with best results upon storage at a low relative humidity, i.e. in the glassy state. Thanks to the biocompatibility of the film components and the small size and flexibility of optical fibers, this system is truly adapted as a point-of-care device for monitoring in biological fluids directly. In the context of chronic wounds notably, integration in wound dressings will permit in situ quantification of protease activity that will support assessment of the wound status and of the potential role of protease-modulating treatments on chronic wounds outcome.
Conflict of interest
Acknowledgement The authors gratefully acknowledge the Swiss Nano-Tera initiative (TecInTex project) and European Commission (SWAN-iCare project: FP7-ICT-2011-8-317894) for their financial support. In addition, they would also like to acknowledge the Adolphe Merkle Institute for FTIR and viscosimetry measurements, and Dr. Rolf Steiger for useful discussion.
Introduction