Liquid 3D Microneedles for Cardiac Recording and Stimulation

Implantable cardiac devices for recording the electrocardiograms (ECGs) are essential for the diagnosis of cardiovascular diseases such as arrhythmia, bradycardia, or atrial fibrillation. Also, these implantable devices that can stimulate the heart electrically have been developed for therapeutic solutions. Conventional implantable devices using rigid metals with high moduli (>1 GPa) have limitations in forming a tight interface with the heart tissue (<100 KPa) and the discordance of mechanical properties that can result in immune responses. Additionally, the fatty layer of the epicardium adjoining the myocardium, where most implantable devices are attached, can limit the clear recording of the ECG signals. Therefore, the development of a soft and injectable three-dimensional (3D) device that can penetrate the epicardium to minimize the unwanted noise levels is important for accurate and long-term recording. Here, we demonstrate the high-resolution arrays of liquid 3D microneedles for both functions of cardiac recording and stimulating, with their tattooable, injectable, and biocompatible properties. The liquid form of these 3D microneedles are advantageous to minimize the damage in tissues with offering their reliable operations. As a result of in-vivo rabbit experiment, these liquid microneedle arrays are capable of recording clearer signals compared to the cases of previous planar electrodes using solid metals, and of transmitting electrical stimulus to a live heart for recovering from bradycardia to a normal rhythm.