Bioelectronic Devices for Targeted Drug Delivery and Monitoring of Microbial Electrogenesis

Abstract: Despite a range of pain therapies available in the market, 70% of patients report so-called “breakthrough pain”. Coupled with global issues like opioid crisis, there is a clear need for advanced therapies and technologies for pain management. In this thesis we aim to develop a novel pain management therapy based on precise, fluid-flow-free delivery of anesthetic drugs directly to the peripheral nervous system (PNS) using organic electronic ion pumps (OEIPs). OEIPs are devices that can transport charged drug molecules through a permselective ion exchange membrane (IEM) under an applied electric field. In this work we used primary dorsal root ganglion (DRG) neurons as an in vitro PNS model system for neuropathic pain. The IEM was made up of custom synthesized hyberbranched polyglycerols (HPGs), which enabled the delivery of large aromatic anesthetic drug such as bupivacaine for the first time in an OEIP. Bupivacaine is a common local nerve blocker which if delivered to DRGs effectively blocks their neuronal activity which in turn blocks the pain signal to travel to the central nervous system (CNS) thereby blocking the sensation of pain. Two types of OEIP devices were fabricated and characterized in this context: capillary-based OEIPs with a probe-like form factor, and inkjet-printed flexible OEIPs with a potential towards implantable form factor. The results showed that both types of OEIP devices could deliver bupivacaine locally (delivery radius ~ 75 µm) to DRG neurons at concentrations close to 40000 times lower than the bulk/bolus means. The results demonstrated that OEIPs could achieve long-lasting and reversible nerve blockage without causing tissue damage or systemic side effects. These studies lay the foundation for future demonstrations of “iontronic” PNS pain relief in living/awake animals.  On the other end of the spectrum, most of today’s modern communication is based upon our understanding of how electrons move through semiconductors. This allows one to mediate the flow of electrons by designing complex integrated circuits in the form of microchips which gives rise to smart devices such as mobile phones and computers. Likewise, in many organism’s electron transfer plays a critical role in metabolic processes in eukaryotes, which includes animals all the way down to microbes. In most of these metabolic processes, the role of the final electron acceptor is played by oxygen (aerobic respiration). However, there are few families of bacterial cells that we know today have evolved in special ways allowing them to respire or “breathe” through metals/metal oxides when exposed to anaerobic conditions. In electromicrobiology, this is termed as extracellular electron transfer (EET), wherein the microbes shuttle electrons from inside of their cells to the outside, in presence of favorable extracellular electron acceptors. The EET process has thus been exploited in various microbial electrochemical systems (MESs) such as microbial fuel cells (MFCs), biosensors, and bio-photovoltaic cells to name a few. In this thesis, we have carried out a detailed study examining the EET process in MESs and ways to amplify such signals in broadly two major approaches: Bioelectrochemical and device optimization. Under bioelectrochemical means, we have shown that we can amplify EET signal of exoelectrogens such as Shewanella oneidensis MR-1 in a standard microbial bioreactor set up containing fumarate (a common carbon food source) by up to 50x times without the excess cell growth in the reactor. This study helped to unravel few unknown mysteries of the EET and bust few of its well-studied myths in the process. However, to record EET, traditionally one still requires large area/volume of electrodes with sufficiently high concentration of bacteria to remain well above the threshold signal-to-noise ratio. So under device optimization route, we combined S.oneidensis with an electrochemical transistor termed as Organic Microbial Electrochemical Transistor (OMECT). With OMECT we successfully monitored and amplified EET events from small number of microbial cells on a microscale area (500 µm x 500 µm) in real time without the need big/bulky/expensive signal amplifying instruments. Interestingly, the OMECT platform also revealed an order of magnitude faster EET response of S. oneidensis MR-1 to lactate compared to studies using classical electrochemical approaches thus underlying one of the major advantages of the miniaturized bioelectronic device.