Carbon Microelectrodes for Real Time Osteoporosis Drug Screenings

Osteoporosis is a disabling skeletal disorder affecting 200 million people worldwide 1 . Presently, the main challenge is to develop new more effective drugs with reduced long-term side effects. Monitoring the interactions of diseased bone tissues with drugs is fundamental for osteoporosis drug development and screening. In vitro cytotoxicity assays represent the most commonly used approach for screening and validation of drug candidates in the early stage of drug discovery 2 . Most of these assays rely on two dimensional (2D) cell culture systems which do not allow for complex three dimensional (3D) spatial interactions (i.e. cell-cell and cell-extracellular matrix (ECM) interactions) typical in living bone and crucial for accurate results in toxicological testing 3 . Moreover, conventional 2D cytotoxicity screenings do not provide temporal information of the cellular response to drugs. Thus, there is a need for new and complementary 3D in vitro systems that can better mimic the in vivo microenvironment of bone architecture and enable in situ monitoring of bone cell response to osteoporosis drugs in real time. Conductive 3D substrates and scaffolds (e.g. based on metal, carbon, conductive polymers, etc.) offer the possibility for in-situ electrical sensing while providing a more in-vivo like microenvironment for real-time monitoring of cell population processes 4 . In the fabrication of 3D electrodes, limitations for high throughput, reproducibility, large-scale production and costs still remain a critical issue. Carbonaceous materials 5 , such as graphene, graphene foam, CNTs, diamond-like carbon, carbon composites and pyrolysed carbon are emerging for development of 2D and 3D electrodes. The carbon MEMS (C-MEMS) technique is a very simple and cost-effective method for electrode fabrication 6 , where a patterned polymer template is heated to temperatures above 900 °C in inert atmosphere to produce pyrolysed carbon electrodes. This process enables easy and reproducible fabrication of carbon electrodes with possibility for tailoring ad-hoc designs and sensitivities for specific applications 7 . Moreover, pyrolysed carbon electrodes exhibit a wide electrochemical potential window, chemical inertness towards a range of solvents and electrolytes, good biocompatibility, and the possibility to tune the electrical and mechanical properties of the electrodes. In order to monitor bone cell response to drugs in real time, 2D interdigitated pyrolysed carbon electrod