## 3 Treatments for Spinal Cord Injury
### 'SMART' Implants and Devices  
Researchers at the University of Pittsburgh, Swansea, have been developing a 'SMART' spinal implant device [30]. This study introduces a \"self-aware\" metamaterial implant designed for spinal cord injury treatment, integrating energy-harvesting and self-sensing functionalities. Utilising triboelectric nanogenerators (TENGs), the implant converts body motion into electrical energy, allowing it to operate without external power sources [31]. Constructed with triboelectric auxetic microstructures, the device autonomously collects real-time data on its environment, enhancing its monitoring capabilities. The prototype consisted of an interbody fusion cage, which demonstrated success in synthetic and cadaveric spinal models by generating up to 9.2 volts and 4.9 nanoamperes while monitoring bone healing. Mechanical fatigue testing revealed a reduction in elastic modulus (from 1.76 MPa to 1.4 MPa) and voltage output (from 2.69 volts to approximately 1 volt) after 40,000 loading cycles, indicating the need for more robust fabrication methods. By providing continuous, real-time tracking of spinal fusion progress, this device can record data that can be obtained with an ultrasonic probe [31]. This self-powered implant addresses critical gaps in spinal cord injury care. Its ability to function without external power enhances patient monitoring and recovery outcomes. Though this is a self-aware implant that can gather data in response to mechanical stimulus, these data cannot be wirelessly logged, making it difficult to adapt the implant to the patient's unique movements. In future designs, this device may be tested on a larger cohort of clinical human trials and have a more unique patient-specific approach to spinal cord injury. Another 'SMART' device was produced by a group of researchers at the University of Cambridge. This study tested a flexible circumferential spinal cord implant, enabling it to simulate and record 360 degrees around the spinal cord [32]. The device itself stimulates the spinal cord through ventral stimulation, which has been shown to be more efficient in muscle activation, through a 32-electrode array organised in a staggered linear configuration. Figure 4, below, illustrates the device concept and optical images. The '360' device was fabricated from a parylene-C-based array, which included titanium and gold electrical structures. Furthermore, to enhance the performance of the device, the impedances were decreased as polymer poly (3,4-ethylene) dioxythiophene (PEDOT) was used with a counterion, poly (styrene sulfonate) (PSS). Due to the thin nature of the device, at 4 um, it was able to completely rotate 360 degrees around the spinal cord implant. The implant was tested on rats and human cadavers. The animal spinal cord recording showed signal altitudes across the 32 channels, mapping the diverse patterns of evoked potentials at equal intervals. The researchers used a thresholding method to allow for the filtration of these signals based on peak amplitude and then the extraction of the signals in preparation for data analysis. The study used a supervised machine learning approach, which used a k-nearest neighbours (KNN) algorithm to locate the origins of the evoked potentials. As a result, the device showed very low latency while stimulating limb movement in a rat, which showed that the device may be able to record signals and stimulation of the spinal cord in humans. The potential application for this device includes treating paralysis, as it does not require brain surgery and could allow for spinal cord signals to be sent across a damaged spinal cord site [33]. However, there are a few limitations to this method. The study is in early stages, meaning clinical trials on humans have not yet been conducted; therefore, the effectiveness on a live human remains unknown. Furthermore, the longevity and durability of this device hasnot been mentioned in the research, nor has the power source for the device. This could mean various wires emitting from the patient's spinal cord.