Browsing by Author "Alrashdan, Fatima"

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    A wireless millimetric magnetoelectric implant for the endovascular stimulation of peripheral nerves
    (Springer Nature, 2022) Chen, Joshua C.; Kan, Peter; Yu, Zhanghao; Alrashdan, Fatima; Garcia, Roberto; Singer, Amanda; Lai, C.S. Edwin; Avants, Ben; Crosby, Scott; Li, Zhongxi; Wang, Boshuo; Felicella, Michelle M.; Robledo, Ariadna; Peterchev, Angel V.; Goetz, Stefan M.; Hartgerink, Jeffrey D.; Sheth, Sunil A.; Yang, Kaiyuan; Robinson, Jacob T.; Applied Physics Program
    Implantable bioelectronic devices for the simulation of peripheral nerves could be used to treat disorders that are resistant to traditional pharmacological therapies. However, for many nerve targets, this requires invasive surgeries and the implantation of bulky devices (about a few centimetres in at least one dimension). Here we report the design and in vivo proof-of-concept testing of an endovascular wireless and battery-free millimetric implant for the stimulation of specific peripheral nerves that are difficult to reach via traditional surgeries. The device can be delivered through a percutaneous catheter and leverages magnetoelectric materials to receive data and power through tissue via a digitally programmable 1 mm × 0.8 mm system-on-a-chip. Implantation of the device directly on top of the sciatic nerve in rats and near a femoral artery in pigs (with a stimulation lead introduced into a blood vessel through a catheter) allowed for wireless stimulation of the animals’ sciatic and femoral nerves. Minimally invasive magnetoelectric implants may allow for the stimulation of nerves without the need for open surgery or the implantation of battery-powered pulse generators.
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    Magnetoelectrics for Implantable Bioelectronics: Progress to Date
    (American Chemical Society, 2024) Alrashdan, Fatima; Yang, Kaiyuan; Robinson, Jacob T.; Applied Physics Program
    ConspectusThe coupling of magnetic and electric properties manifested in magnetoelectric (ME) materials has unlocked numerous possibilities for advancing technologies like energy harvesting, memory devices, and medical technologies. Due to this unique coupling, the magnetic properties of these materials can be tuned by an electric field; conversely, their electric polarization can be manipulated through a magnetic field.Over the past seven years, our lab work has focused on leveraging these materials to engineer implantable bioelectronics for various neuromodulation applications. One of the main challenges for bioelectronics is to design miniaturized solutions that can be delivered with minimally invasive procedures and yet can receive sufficient power to directly stimulate tissue or power electronics to perform functions like communication and sensing.Magnetoelectric coupling in ME materials is strongest when the driving field matches a mechanical resonant mode. However, miniaturized ME transducers typically have resonance frequencies >100 kHz, which is too high for direct neuromodulation as neurons only respond to low frequencies (typically <1 kHz). We discuss two approaches that have been proposed to overcome this frequency mismatch: operating off-resonance and rectification. The off-resonance approach is most common for magnetoelectric nanoparticles (MENPs) that typically have resonance frequencies in the gigahertz range. In vivo experiments on rat models have shown that MENPs could induce changes in neural activity upon excitation with <200 Hz magnetic fields. However, the neural response has latencies of several seconds due to the weak coupling in the off-resonance regime.To stimulate neural responses with millisecond precision, we developed methods to rectify the ME response so that we could drive the materials at their resonant frequency but still produce the slowly varying voltages needed for direct neural stimulation. The first version of the stimulator combined a ME transducer and analog electronics for rectification. To create even smaller solutions, we introduced the first magnetoelectric metamaterial (MNM) that exhibits self-rectification. Both designs have effectively induced neural modulation in rat models with less than 5 ms latency.Based on our experience with in vivo testing of the rectified ME stimulators, we found it challenging to deliver the precisely controlled therapy required for clinical applications, given the ME transducer’s sensitivity to the external transmitter alignment. To overcome this challenge, we developed the ME-BIT (MagnetoElectric BioImplanT), a digitally programmable stimulator that receives wireless power and data through the ME link.We further expanded the utility of this technology to neuromodulation applications that require high stimulation thresholds by introducing the DOT (Digitally programmable Overbrain Therapeutic). The DOT has voltage compliance up to 14.5 V. We have demonstrated the efficacy of these designs through various in vivo studies for applications like peripheral nerve stimulation and epidural cortical stimulation.To further improve these systems to be adaptive and enable a network of coordinated devices, we developed a bidirectional communication system to transmit data to and from the implant. To enable even greater miniaturization, we developed a way to use the same ME transducer for wireless power and data communication by developing the first ME backscatter communication protocol.
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    Miniature battery-free epidural cortical stimulators
    (AAAS, 2024) Woods, Joshua E.; Singer, Amanda L.; Alrashdan, Fatima; Tan, Wendy; Tan, Chunfeng; Sheth, Sunil A.; Sheth, Sameer A.; Robinson, Jacob T.; Applied Physics Program
    Miniaturized neuromodulation systems could improve the safety and reduce the invasiveness of bioelectronic neuromodulation. However, as implantable bioelectronic devices are made smaller, it becomes difficult to store enough power for long-term operation in batteries. Here, we present a battery-free epidural cortical stimulator that is only 9 millimeters in width yet can safely receive enough wireless power using magnetoelectric antennas to deliver 14.5-volt stimulation bursts, which enables it to stimulate cortical activity on-demand through the dura. The device has digitally programmable stimulation output and centimeter-scale alignment tolerances when powered by an external transmitter. We demonstrate that this device has enough power and reliability for real-world operation by showing acute motor cortex activation in human patients and reliable chronic motor cortex activation for 30 days in a porcine model. This platform opens the possibility of simple surgical procedures for precise neuromodulation.
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    Wireless Magnetoelectric Communication for Bioelectronics
    (2024-04-19) Alrashdan, Fatima; Robinson , Jacob
    Implantable bioelectronics hold great potential to improve the diagnosis and treatment of myriad chronic health conditions. Wireless bioelectronic implants that continuously monitor the patient’s physiological state and transmit these data in real-time without tethers would improve diagnosis and facilitate adaptive therapeutic interventions. However, existing wireless communication modalities, such as Bluetooth, radio frequency, and ultrasound, have performance trade-offs regarding implant size, misalignment tolerance, power consumption, and operational distance. In this dissertation, I present the first wireless backscatter magnetoelectric communication system that features a miniaturized size, ultra-low power consumption, and deep operational distance with high misalignment tolerance. The system leverages two fundamental characteristics of the magnetoelectric transducers. Firstly, magnetoelectric materials generate a backscattered magnetic field when excited by an external field; we exploit these fields as a carrier signal. The magnetoelectric implant consumes negligible power for carrier generation since the external field that induces this signal is generated outside the body. Secondly, the characteristics of the backscattered field can be modulated by an external electric load; thus, we can use load modulation for digital data encoding. This design enables continuous, real-time data transmission from a mm-sized magnetoelectric. bioimplant to a custom-designed external transceiver. Our benchtop testing shows that the system can support an operational range within 55 mm while maintaining a bit error rate (BER) of less than 1E-6. Furthermore, the system is robust to translational misalignment; the system performance is maintained with a misalignment of more than 10 mm. To validate the system reliability in real-life applications and facilitate the clinical translation of this technology, we tested the system operation in a porcine model. We have shown two demonstrations of in-vivo studies: wireless monitoring of stimulation electrode impedance for cortical brain implants and real-time remote monitoring of electrical intracardiac signals for cardiac implants. The proposed technology could enable the design of next-generation bioelectronics that feature real-time physiology monitoring for more precise diagnosis, as well as closed-loop systems for personalized therapies.