Future biomedical devices may enable chronic sensing or stimulation of body tissue through stable interfaces between soft tissue and high-performance electronics. We demonstrate flexible organic thin-film transistors (OTFTs) on physiologically-responsive smart polymer substrates with shape-changing and softening properties that can mechanically-adapt after implantation for creating soft bioelectronic interfaces while maintain initial electrical properties. Additionally, 3D deployable structures are demonstrated with large geometry changes based on the release of stored applied stresses.
Shape memory polymers (SMPs) are smart polymers which respond to stimuli, such as a temperature change, to soften and change shape. We synthesize SMP substrates which can adapt in vivo to autonomously form secure interfaces with target tissue via a two order of magnitude drop in modulus when exposed to physiological conditions, which reduces the modulus mismatch between the device and soft tissue. Reduction in the mechanical mismatch between biomedical implants and soft tissue through soft materials has been shown to extend the long-term viability of biotic/abiotic interfaces. Acute in vivo stability of an OTFT which adapts to the morphology of soft tissue is shown, with only small changes in device performance after implantation for 24 hours.
OTFTs fabricated on SMP substrates are demonstrated which can autonomously deploy to programmed 3D shapes 15× larger than the insertion footprint of the device, as well as conform to 3D surfaces with radii as small as 500 µm when triggered by a small temperature change. Flexural stability of the OTFTs is demonstrated down to 1 mm radius for four bending configurations; with some devices remaining operational at radii as small as 100 µm. The flexible low-voltage transistors (2 V) based on the air-stable organic semiconductor, dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (DNTT), are demonstrated with a measured average mobility of 1.5 cm^2V^-1s^-1 and an on/off current ratio of 10^4, which is suitable for sensing small biosignals at low operating voltages.
The University of Tokyo, The University of Texas at Dallas
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