Softening and flexible hybrid electronics integration for biomedical applications

Rocha-Flores, Pedro Emanuel; Guerrero, Edgar; Rodriguez‐Lopez, Ovidio; Chitrakar, Chandani; Parikh, Ankit; Pancrazio, Joseph J.; Cogan, Stuart F.; Ecker, Melanie; Voit, Walter

doi:10.1557/s43579-023-00431-5

Cited by 3 publications

(1 citation statement)

References 30 publications

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“…This choice of a 1 kΩ load resistance was based on the consideration that, at frequencies of 1 kHz and above, the impedance of the electrode/electrolyte interface for a typical 500 μm TiN electrode is approximately 1 kΩ. [32] As shown in Figure 3d,e, both types of transistors exhibited similar behavior as the frequency increased from 1 to 100 kHz, with 100 kHz being the highest frequency at which the TFTs could efficiently respond. By measuring between the 50% transition point of the input signals and the output waveforms of the TFTs at the load resistance at the different frequencies, we calculate the propagation delay (t p ).…”

Section: Resultsmentioning

confidence: 99%

Flexible a‐IGZO TFT‐Based Circuit for Active Addressing in Neural Stimulation Electrode Arrays

Rodriguez‐Lopez,

Rocha‐Flores,

Maeng

et al. 2023

Adv Materials Technologies

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Neural interfaces have undergone significant advancements in recent decades, aiming for flexible, compact, and high‐density electrode arrays with a large number of channels. However, the scalability of these devices is often hindered by the number of wires needed to separately connect each electrode to external electronics. To address this limitation, thin‐film transistor (TFT)‐based electronic circuits offer a promising solution by enabling active addressing of stimulation electrodes and potentially increasing the channel count with fewer interconnections. This paper presents the integration of a circuit comprising two amorphous indium–gallium–zinc‐oxide (a‐IGZO) TFTs and a titanium nitride (TiN) electrode on a flexible polymer platform. This circuit precisely controls the electrode's On/Off states and the delivery of current for nerve stimulation. Characterization studies involving frequency and electrochemical analysis demonstrate the TFT‐based circuit's capability to operate at high frequencies, deliver biphasic stimulation pulses to the electrode, and store sufficient charge for effective neural stimulation. Moreover, the a‐IGZO TFTs exhibit remarkable stability during repeated gate voltage sweeps with minimal changes in electrical performance. This circuit has the potential to be extended to active‐matrix devices that enable electrode arrays with a high number of channels and enhanced spatial resolution, which is crucial for selective neural stimulation.

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Section: Resultsmentioning

confidence: 99%

Flexible a‐IGZO TFT‐Based Circuit for Active Addressing in Neural Stimulation Electrode Arrays

Rodriguez‐Lopez,

Rocha‐Flores,

Maeng

et al. 2023

Adv Materials Technologies

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Softening, Conformable, and Stretchable Conductors for Implantable Bioelectronics Interfaces

Rocha‐Flores,

Chitrakar,

Rodriguez‐Lopez

et al. 2024

Adv Materials Technologies

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Neural implantable devices serve as electronic interfaces facilitating communication between the body and external electronic systems. These bioelectronic systems ideally possess stable electrical conductivity, flexibility, and stretchability to accommodate dynamic movements within the body. However, achieving both high electrical conductivity and mechanical compatibility remains a challenge. Effective electrical conductors tend to be rigid and stiff, leading to a substantial mechanical mismatch with bodily tissues. On the other hand, highly stretchable polymers, while mechanically compatible, often suffer from limited compatibility with lithography techniques and reduced electrical stability. Therefore, there exists a pressing need to develop electromechanically stable neural interfaces that enable precise communication with biological tissues. In this study, a polymer that is softening, flexible, conformal, and compatible with lithography to microfabricate perforated thin‐film architectures is utilized. These architectures offer stretchability and improved mechanical compatibility. Three distinct geometries are evaluated both mechanically and electrically under in vitro conditions that simulate physiological environments. Notably, the Peano structure demonstrates minimal changes in resistance, varying less than 1.5× even when subjected to ≈150% strain. Furthermore, devices exhibit a maximum mechanical elongation before fracture, reaching 220%. Finally, the application of multi‐electrode spinal cord leads employing titanium nitride for neural stimulation in rat models is demonstrated.

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Development and Characterization of Compliant Bioelectronic Devices for Gastrointestinal Stimulation

Chitrakar

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In this research, we aimed to develop thin-film devices on a polymer substrate and an alternative 3D-printed device with macroelectrodes for treating gastrointestinal (GI) conditions. First, the fabrication of thin-film devices was demonstrated on a softening thiol-ene/acrylate polymer utilizing titanium nitride (TiN) as electrode material. This was achieved by utilizing cleanroom fabrication processes such as photolithography, wet and dry etching. The functionality of the device was shown by performing electrochemical characterization tests, mainly cyclic voltammetry, electrochemical impedance spectroscopy, and voltage transient. We synthesized a novel thiol-ene/acrylate polymer based on 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), trimethylolpropanetris (3-mercaptopropionate) (TMTMP), and polyethylene glycol diacrylate (PEGDA). We show that this stretchable shape memory polymer substrate is well suited for cleanroom processes. Finally, for the high throughput of the wearable devices with electrodes size 10 mm in diameter, we implemented single electrode fabrication using printed circuit boards (PCBs) and depositing gold (Au) and TiN on the plated side of PCBs utilizing the sputtering tool. This step was followed by the assembly of those single electrodes on the flexible 3D printed device. We showed that the TiN electrode material performed better in terms of charge storage capacity and charge injection capacity than the widely used stainless steel electrode material for wearables.

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Softening and flexible hybrid electronics integration for biomedical applications

Cited by 3 publications

References 30 publications

Flexible a‐IGZO TFT‐Based Circuit for Active Addressing in Neural Stimulation Electrode Arrays

Flexible a‐IGZO TFT‐Based Circuit for Active Addressing in Neural Stimulation Electrode Arrays

Softening, Conformable, and Stretchable Conductors for Implantable Bioelectronics Interfaces

Development and Characterization of Compliant Bioelectronic Devices for Gastrointestinal Stimulation

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