Graphene has exciting potential for use in various implants and other medical applications, but since graphene is stiff and biological tissues are soft, there is a concern among scientists that a graphene implant could suddenly heat up and "fry" the surrounding cells when any power is applied to make it function. Researchers from MIT and Tsinghua University in China have simulated the way in which electrical power produces heat between a simple cell membrane and a single layer of graphene, to find if it is possible to prevent the heat buildup.

The team found that this is possible by using a very thin, in-between layer of water. By controlling the thickness of this in-between water layer, the collaborative team could carefully manipulate the quantity of heat transferred between biological tissue and graphene. They also fixed the critical power required to apply to the graphene layer, without causing the cell membrane to burn. The researchers attempted to accurately characterize the way heat moves, at the level of individual atoms, between the biological tissue and graphene. They applied classical molecular dynamics - a mathematical technique based on a “force field” potential operation, or a simplified version of the interactions between atoms - that enabled them to efficiently calculate interactions within bigger atomic systems.

As the stiffness of graphene and biological tissue is so diverse, the researchers anticipated that heat would conduct quite weakly between the two materials, increasing sharply in the graphene before overflowing and overheating the cell membrane. However, the in-between water layer helped disperse this heat, easing its conduction and preventing a sharp rise in the temperature in the cell membrane.

By closely observing the interactions within this interface, the researchers stumbled upon a finding: Within the sandwich model, the water - pressed against chicken-wire pattern of graphene - transformed into a similar crystal-like structure. The team altered the thickness of the in-between water layer in simulations, and discovered that a 1 nm-wide layer of water helped to disperse heat very efficiently. In connection with the power applied to the system, they calculated that approximately a megawatt of power per meter squared, applied in small, microsecond bursts, was the most power that could be supplied to the interface without frying the cell membrane.

Going forward, the team states that implant designers can use the team’s model and simulations to establish the vital power requirements for graphene devices of varied dimensions. As for the way they might practically manipulate the thickness of the in-between water layer, the surface of graphene may be altered to attract a certain number of water molecules.

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