Research Proposal On Developing High Definition (HD) Graphene Three Dimensional (3D) Manipulators
This proposal focuses on developing new tools to fabricate high definition (HD) graphene three dimensional (3D) manipulators reinforced with biocompatible polymers designed to probe the interior and surrounding of cells with electrical and light stimuli.
Understanding and communicating with biological systems and other living organisms has important implications for artificial intelligence, biomedical engineering and nanomedicine. This requires devices that interface live biological material with adhesive, sensing and stimulation tools, such as single electrode and arrays. In this position, graphene becomes the ‘’connection’’, the solid-state interface between living organisms and computer machines. By using the remarkable properties of graphene (transparency, high electrical conduction, and mechanical properties) as well as its biocompatibility, one of our goals is to develop a sharp needle with a tip radius of 1 µm, a diameter body of 100 to 300 µm and an overall length of 1 or 2 cm to facilitate its insertion into a soft body. This probe will be internally reinforced with biocompatible polymers such as poly (methyl metacrylate) and polydimethylsiloxane, externally coated with parylene and attached to a copper wire and to an optical fiber. It will be capable to pierce through tissues and membranes and penetrate inside most cells to deliver electricity and light with the precision of one to ten micrometers. The probe will be designed to sustain pressure from puncture and tested for its strength, its flexibility and its rupture limit.
Also, its ability to detect flow of ions in biological tissues and their photo response will be measured using amperometry and voltammetry to evaluate its potential for light-dependant electrophysiology. Because 3D printing of graphene and other metals needs binders and chemical agents to stick particles together in the process, it cannot deliver high purity materials. This introduces potentially harmful contaminants for the biological systems and also for the electric system of the device itself. Furthermore, 3D printing uses large injection nozzles to prevent blocking in continuous operations and this limits spatial resolution to hundreds of microns. For these reasons, it is generally difficult to implement a strategy based on this emergent technology to fabricate templates and materials with the required spatial resolution and purity to probe and connect with smaller living organisms. To overcome this, we will therefore combine 3D printing, electro-etching and casting techniques to create a copper cylinder substrate (the negative mold) with a hole inside of it having the shape of the desired graphene probe. The hole is created by casting a HD-master object (pre-normal image) into a 99. 5% purity copper mass (sintered powder or liquid melt) at high temperature (1000-1100 oC) under reduced atmosphere, then by removing the master either by mechanical force or selective electro-etching.
To create the mold, bulk tungsten materials with rough details (wires, rods, objects obtained from 3D printing, machining, etc. ) are masked and etched under anodic conditions in a solution of potassium hydroxide until size and profile are refined to match the microworld. This shows great potential because tungsten tips are inexpensive, easily available or prepared in the laboratory with atomic scale resolution, they can resist to hot melted copper, have excellent strength and hardness and more importantly, they show very low adhesion values for copper surface. Once in hand, the copper substrate is used to catalyse the deposition of graphene from methane. Before etching the copper in ammonium persulfate solution, the inside only of the copper mold is filled with polymers to reinforce the coating of graphene attached to it. Once the copper is completely dissolved, a transparent 3D graphene-polymers replicate is recuperated floating in solution.
The last challenge consists in applying a final coating of parylene using physical vapor deposition on the exterior to insulate the body in the presence of a photoresist mask placed in a way, that once removed, it will expose the tip. This operation will be performed in the microfabrication lab. It is noteworthy, that this technique to create 3D copper substrates can replicate large 3D objects with submicron details. It is inexpensive, requires a conventional chemical vapour deposition system, a 12 VDC power supply and no precision tool. It shows great promise to replicate complex tungsten micro components (arrows, blades, screws, tweezers, multiheaded probes, spears, arrays, etc. ).
For now, most of graphene growth is performed on commercial copper foil and praised for its surface applications (2D). There is only little work how to melt and shape high purity copper molds and on creating 3D graphene geometries for similar applications. There is no doubt that we will develop a powerful and versatile tool to create any 3D graphene objects that will go beyond the proof of concept.
