Stretchable microelectronic fibers and their assemblies as multifunctional bioelectronic interfaces for whole organs
A soft, stretchable, multifunctional bioelectronic interface can be used to monitor and/or modulate an entire organ, such as a stomach, heart, bladder, or spinal cord. The interface's softness translates to reduced mechanical mismatch with the tissue, and the interface's stretchability reduces interfacial stress with dynamically expanding and contracting organs. The electronics are stretchable thanks in part to liquid-metal conductors sealed within hollow channels of elastomeric fibers embedded in the interface. The liquid metal is largely strain-insensitive, non-toxic, and has a melting point of less than 37° C., so it remains liquid when implanted in a mammalian body. The liquid metal conductors connect microelectronic components, such as micro light-emitting diodes (μLEDs), electrodes, photodiodes, and temperature sensors, to a flexible printed circuit board (fPCB) at one end of the fiber. The interface may include other microelectronic components, such as piezoelectric strain sensors, that are also coupled to the fPCB.
1 . An implantable apparatus for interfacing with an organ, the implantable apparatus comprising:
an elastomeric substrate having a channel formed in a surface thereof;
an elastomeric fiber disposed in the channel, the elastomeric fiber defining a hollow channel;
liquid metal disposed in the hollow channel;
a plurality of layers disposed on the surface of the elastomeric substrate over the channel; and
a microelectronic component, disposed on an outer layer of the plurality of layers and in electrical communication with the liquid metal, to stimulate and/or sense the organ in response to an electrical signal and/or electrical power conducted by the liquid metal.
2 . The implantable apparatus of claim 1 , wherein the liquid metal comprises at least one of Gallium, eutectic Gallium-Indium, or Gallium-Indium-Tin alloy.
3 . The implantable apparatus of claim 1 , wherein the liquid metal is non-toxic and has a melting point of less than 37° C.
4 . The implantable apparatus of claim 1 , further comprising a micro light-emitting diode to optically stimulate the organ.
5 . The implantable apparatus of claim 1 , further comprising a temperature sensor to sense a temperature of the organ.
6 . The implantable apparatus of claim 1 , wherein at least one layer of the plurality of layers comprises:
at least one silicone layer disposed on the elastomeric substrate over the channel.
7 . The implantable apparatus of claim 6 , wherein at least one layer of the plurality of layers comprises:
an adhesive layer, disposed on the at least one silicone layer, to adhere the implantable apparatus to a surface of the organ.
8 . The implantable apparatus of claim 7 , further comprising:
a strain sensor, disposed between the elastomeric substrate and the adhesive layer, to sense strain experienced by the organ.
9 . The implantable apparatus of claim 7 , wherein at least one layer of the plurality of layers comprises:
a functionalization layer, disposed between on the at least one silicone layer and the adhesive layer, to increase adhesion of on the at least one silicone layer to the adhesive layer.
10 . The implantable apparatus of claim 6 , wherein the at least one silicone layer comprises at least four silicone layers, each having a thickness of at least 200 μm.
11 . The implantable apparatus of claim 6 , wherein the at least one silicone layer comprises at least eight silicone layers, each having a thickness of about 1000 μm.
12 . The implantable apparatus of claim 1 , further comprising:
an optically absorbing material plugging a length of the hollow channel.
13 . A method of making an implantable apparatus for interfacing with an organ, the method comprising:
forming a preform comprising an elastomeric core and a sacrificial outer layer, the elastomeric core defining a hollow channel;
drawing the preform to form an elastomeric fiber having the hollow channel oriented along a length of the elastomeric fiber;
removing the sacrificial outer layer from the elastomeric fiber;
disposing liquid metal in the hollow channel;
forming an electrical connection between the liquid metal and a microelectronic component, the microelectronic component in electrical communication with the liquid metal and adapted to stimulate and/or sense the organ in response to an electrical signal and/or electrical power conducted by the liquid metal; and
integrating the elastomeric fiber with an elastomeric substrate, wherein integrating the elastomeric fiber with the elastomeric substrate comprises:
disposing the elastomeric fiber in a channel formed on a surface of the elastomeric substrate; and
disposing a plurality of layers over the elastomeric substrate and the channel.
14 . The method of claim 13 , wherein the liquid metal is non-toxic and has a melting point of less than 37° C.
15 . The method of claim 13 , wherein forming the preform comprises:
defining a groove along a length of the elastomeric core; and
plugging the groove lengthwise with an optically absorbing material to form the hollow channel.
16 . The method of claim 15 , wherein forming the electrical connection comprises:
ablating a hole in the optically absorbing material to expose a portion of the liquid metal;
disposing the microelectronic component in electrical communication with the liquid metal through the hole; and
forming a seal about the hole to prevent the liquid metal from leaking out of the hollow channel.
17 . The method of claim 15 , wherein the elastomeric core comprises a poly[styrene-(ethylene-co-butylene-styrene] triblock copolymer (SEBS), the optically absorbing material comprises carbon-doped SEBS, and the sacrificial outer layer comprises polymethyl methacrylate (PMMA).
18 . The method of claim 13 , wherein disposing the liquid metal in the hollow channel comprises disposing the liquid metal in the hollow channel before drawing the preform.
19 . The method of claim 13 , wherein disposing the liquid metal in the hollow channel comprises disposing the liquid metal in the hollow channel after drawing the preform.
20 . A multi-layer implantable apparatus for interfacing with an organ, the multi-layer implantable apparatus comprising:
an elastomeric substrate with a groove extending along an outer surface of the elastomeric substrate;
a microelectronic fiber disposed in the groove, the microelectronic fiber comprising a liquid metal conductor;
a plurality of layers disposed over the outer surface of the elastomeric substrate and sealing the microelectronic fiber in the groove; and
at least one of a sensor or an actuator disposed on an outer surface of the multi-layer implantable apparatus and electrically coupled to the microelectronic fiber, to stimulate and/or sense the organ in response to an electrical signal and/or electrical power conducted by the liquid metal conductor.