Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> C. Electromagnetic Far-field Based Wireless Power System <s> Small, lightweight LED implants and a radio-frequency transducer as a power source enable wireless optogenetic stimulation in the brain, spinal cord and peripheral nervous system of behaving mice. <s> BIB001 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> C. Electromagnetic Far-field Based Wireless Power System <s> Optogenetic studies of the peripheral nervous system and spinal cord are enabled by soft, wirelessly powered biocompatible devices. <s> BIB002 </s> Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review <s> C. Electromagnetic Far-field Based Wireless Power System <s> Combination of optogenetics and pharmacology represents a unique approach to dissect neural circuitry with high specificity and versatility. However, conventional tools available to perform these experiments, such as optical fibers and metal cannula, are limited due to their tethered operation and lack of biomechanical compatibility. To address these issues, a miniaturized, battery-free, soft optofluidic system that can provide wireless drug delivery and optical stimulation for spatiotemporal control of the targeted neural circuit in freely behaving animals is reported. The device integrates microscale inorganic light-emitting diodes and microfluidic drug delivery systems with a tiny stretchable multichannel radiofrequency antenna, which not only eliminates the need for bulky batteries but also offers fully wireless, independent control of light and fluid delivery. This design enables a miniature (125 mm3 ), lightweight (220 mg), soft, and flexible platform, thus facilitating seamless implantation and operation in the body without causing disturbance of naturalistic behavior. The proof-of-principle experiments and analytical studies validate the feasibility and reliability of the fully implantable optofluidic systems for use in freely moving animals, demonstrating its potential for wireless in vivo pharmacology and optogenetics. <s> BIB003
As compared to the stiff implant of Montgomery et al. BIB001 , advancement in soft and flexible electronics empowered to develop an energy harvesting system, which is stretchable, flexible (PDMS encapsulated), and fully implantable BIB002 , as shown in Fig. 8(c) . The implant consists of four key parts: a power harvester, rectifier circuit along with a voltage multiplier, and a very small 470 nm LED. PDMS encapsulation of the implant ensures not only protection from the adjacent tissues but also forms a physical and mechanical alliance with the tissue. Due to smaller size (6 × 3.8 × 0.7 mm 3 ) and lightweight (16 mg), the device is available to implant subdermally in numerous crucial areas of peripheral and central nervous systems to support in vivo optogenetics. By reducing the thickness of the PDMS encapsulation, the implant can achieve lighter, slimmer, and bendable profile to facilitate the biointegration with tissue. A stretchable antenna having a miniaturized surface area of 3 × 3 mm 2 , resonating at 2.3 GHz with a 200 MHz bandwidth, is a key component of this device to harvest the RF energy. Due to the significant higher bandwidth than the traditional patch antenna, this type of receiver antenna can enhance the energy harvesting efficiency. The transmitted RF signal is generated by another antenna from the base station. Identical RF signals are applied to energy harvesting as well as control signalling to power the LED. Despite the unique characteristics, the resonant frequency of the stretchable antenna may change due to deformity caused by the animal motions, and therefore, requires further optimization. Furthermore, the footprint of the device is too big to recognize a large-scale distributed optogenetics system. Recently, this work is further developed to a thinner and lighter device to steer up to four channels using a modified antenna BIB003 .