Implantable device for Prevention of late-Phase Hemorrhagic Shock Using a Novel Non-enzymatic Fuel Cell

Here we present an autonomous implantable device for vasopressin monitoring and prevention of latephase hemorrhagic shock powered using a novel non-enzymatic fuel cell unit. The device consists of a biosensor, drug delivery device and fuel cell unit. The innovative stacked single-layer fuel cell (SLFC) design allows to achieve small packaging volume and reduces oxygen cross-over at the anode resulting in a power density of 46 μWcm-3, a large improvement over the state of the art for non-enzymatic fuel cells [1]. In addition, it is demonstrated for the first time, that non-enzymatic fuel cell can be used to directly monitor changes in vasopressin levels by supplying current to an aptamer-based biosensor. Summary of Research: Fuel Cell. Glucose fuel cells produce electricity through the coupling of glucose oxidation and oxygen reduction reactions. The biggest challenge with non-enzymatic fuel cells has been the lack of selective catalysts for glucose oxidation in the presence of oxygen at the anode. Most groups have tackled this issue by having a stacked electrode design, meaning that a porous cathode is placed in front of the anode in order to reduce the amount of oxygen that interferes with the glucose oxidation reaction [2, 3]. This approach, although potentially useful as a coating layer for implantable devices, had the disadvantage being thick and impractical for low volume applications. Here we present a fuel cell unit composed of stacked SLFCs printed on each side of a 500 μm thick fused silica wafer. Each SLFC consists of a platinum nickel alloy anode surrounded by an oxygen-selective platinum aluminum alloy cathode. By itself, when tested in vitro at physiological levels of glucose and oxygen, the SLFC achieves low power output (0.6 μW), because of oxygen cross over at the anode, however when the layers are stacked 500 μm apart, the oxygen gets depleted at the cathode before it reaches the anode. Consequently, due to a reduction in oxygen crossover, two stacked fuel cells in parallel can achieve 4.6 μW (or 46 μWcm-3 power density) — almost eight times higher power output than a SLFC (Figure 3a). The fabrications steps for the fuel cells described here were performed at the Cornell NanoScale Facility. The single-layer fuel cells (SLFC) used in this paper are fabricated on fused silica substrates using multiple patterning steps (Figure 2). In order to achieve high surface area, a Raney-type alloy process is used for both the anode and the cathode. The process — first demonstrated by Gebhardt, et al. [1] — involves the annealing of a thin layer of platinum with a non-noble metal followed by the chemical etching of the non-alloyed outer metal layer. In this paper, nickel was used as the non-noble metal at the anode and aluminum at the cathode. We use a Ni/Pt alloy as anode for glucose oxidation because it has been shown elsewhere to exhibit grater selectivity towards glucose than other catalysts. 20 nm of Ti was used as adhesion layer followed by the deposition 100 nm of Pt and 300 nm of Ni. Experiments with several anneal temperatures in the range 400°C-600°C have demonstrated that the roughness that can be obtained using a Reney-type process peaks when the annealing temperature is 500°C. For the cathode, a high surface area Pt surface was obtained by annealing Pt/Al at a low-temperature of 300°C and subsequently etching the Al with NaOH. Figure 1: a) Implantable autonomous device. b) structure of single layer fuel cell (SLFC) and SEM images of the electrodes. c) oxygenglucose separation at the anode due to stacked SLFC design. d) biosensor for vasopressin detection.