Contents I. Introduction
Wireless implantable devices can continuously monitor vital physiological signals within the human body and assist doctors in effectively treating diseases. In recent years, significant advancements have been made in implantable techniques. For example, a cervical spinal stimulator has been developed to improve motor control in the arms and legs [1], while an inner retinal implant has been created to stimulate nerve cells and induce visual perception [2], electrodes have been utilized to interpret brain waves and achieve a brain-computer interface (BCI) [3]. These innovations have greatly contributed to medical treatment. When implanting devices in delicate organs such as the spine [1], retina [2], or blood vessels [3], it is crucial to minimize invasiveness in order to reduce negative effects on the human body. A promising approach to achieve minimal invasion is the use of syringes with thin needles to inject implants [4]. The commonly used needle diameter is approximately 3–4 mm [5], [6], necessitating the implant to have a small width in order to be accommodated. Furthermore, in minimal invasive implants, flexible devices printed on ultra-thin substrates are preferred due to their advantages of low profile, lightweight, and flexibility when twisting.
