Control of Neuronal Survival and Development Using Conductive Diamond.

This study demonstrates the control of neuronal survival and development using nitrogen-doped ultrananocrystalline diamond (N-UNCD). We highlight the role of N-UNCD in regulating neuronal activity via near-infrared illumination, demonstrating the generation of stable photocurrents that enhance neuronal survival and neurite outgrowth and foster a more active, synchronized neuronal network. Whole transcriptome RNA sequencing reveals that diamond substrates improve cellular-substrate interaction by upregulating extracellular matrix and gap junction-related genes. Our findings underscore the potential of conductive diamond as a robust and biocompatible platform for noninvasive and effective neural tissue engineering.

Diamond electrodes for controlling stem cells.

Electrical stimulation is one of several methods for controlling differentiation and proliferation of stem cells. This work demonstrated the use of nitrogen-doped ultra-nanocrystalline diamond (N-UNCD) electrodes as a substrate for the growth of human mesenchymal stem cells (hMSCs). As well as exhibiting a high charge injection capacity, N-UNCD displays high cytocompatibility making it suitable electrode material for stem cell stimulation.Clinical Relevance-This work establishes that N-UNCD electrodes can support the growth of hMSCs.

Spectral and temporal detection of blood bilirubin level using a point-of-care device.

Bilirubin is a biomarker for liver inflammation used to assess liver functions. Its concentration in the blood has been measured using a range of techniques both in clinical and point-of-care settings. Existing point-of-care devices utilize a spectral approach, namely dual-wavelength absorption measurement, to assess the blood bilirubin concentration. This work examines a novel temporal approach based on the photodegradation of bilirubin in the blood sample. It demonstrates that combining photodegradation characteristics with dual-wavelength measurement produces a more accurate technique for measuring blood bilirubin concentration. Tracking the evolution of absorbed light as a function of time represents a low-cost and simple way of improving the accuracy of point-of-care devices for bilirubin measurements.Clinical Relevance - This work demonstrates a facile and cheap bilirubin monitoring approach that may allow bilirubin monitoring applications in homes after a patient is discharged from a hospital, which may decrease the burden on patients, families, and clinicians.

A purely solid-state based method for bilirubin levels determination in plasma.

In the past half-century, the advent of solid-state electronics, i.e., microcontrollers, transistors, photodiodes, light-emitting diodes and more, has led to the improvement of the tools we, as a human race, need and use in our daily lives. Solid-state electronics has specifically contributed significantly to the field of biomedical engineering and has allowed various round-the-clock point-of-care testing applications. These include handheld, wearable, and implantable sensors and devices for accelerated interventions. Furthermore, miniaturization has accelerated the implementation of low-cost and energy-efficient systems with increased performance. In this paper, we have used optical techniques along with the benefits of solid-state electronics to measure bilirubin concentration in plasma with concentrations projected from healthy individuals to hyperbilirubinemia (0 - 30 mg/dL). Traditionally, full-range spectrophotometry is the gold standard optical method and provides the most accurate results but suffers from instrument complexity. Thus, this paper proposes and investigates the measurement of bilirubin by using a dual-wavelength approach combined with photodegradation kinetics. By tracking the changes in the spectral characteristics of bilirubin for 10 minutes (~3 J/cm2), a new model was built to measure bilirubin concentrations and distinguish between low vs high and risky vs non-risky levels. Results show a high positive correlation between the optical responses and concentration (R-square > 0.93) with an average accuracy of ~1.4 mg/dL. On top of that, the technique's viability for point-of-care testing of bilirubin levels was studied using a system-on-chip optical module. Thus, this could help suggest neonatal therapeutic interventions, including enteral feeding, phototherapy, and blood transfusion.

Diamond Supercapacitors: Towards Durable, Safe, and Biocompatible Aqueous-Based Energy Storage.

Durable and safe energy storage is required for the next generation of miniature bioelectronic devices, in which aqueous electrolytes are preferred due to the advantages in safety, low cost, and high conductivity. While rechargeable aqueous batteries are among the primary choices with relatively low power requirements, their lifetime is generally limited to a few thousand charging/discharging cycles as the electrode material can degrade due to electrochemical reactions. Electrical double layer capacitors (EDLCs) possess increased cycling stability and power density, although with as-yet lower energy density, due to quick electrical adsorption and desorption of ions without involving chemical reactions. However, in aqueous solution, chemical reactions which cause electrode degradation and produce hazardous species can occur when the voltage is increased beyond its operation window to improve the energy density. Diamond is a durable and biocompatible electrode material for supercapacitors, while at the same time provides a larger voltage window in biological environments. For applications requiring higher energy density, diamond-based pseudocapacitors (PCs) have also been developed, which combine EDLCs with fast electrochemical reactions. Here we inspect the properties of diamond-related materials and discuss their advantages and disadvantages when used as EDLC and PC materials. We argue that further optimization of the diamond surface chemistry and morphology, guided by computational modelling of the interface, can lead to supercapacitors with enhanced performance. We envisage that such diamond-based supercapacitors could be used in a wide range of applications and in particular those requiring high performance in biomedical applications.

A Novel Optical Assay System for Bilirubin Concentration Measurement in Whole Blood.

As a biomarker for liver disease, bilirubin has been utilized in prognostic scoring systems for cirrhosis. While laboratory-based methods are used to determine bilirubin levels in clinical settings, they do not readily lend themselves to applications outside of hospitals. Consequently, bilirubin monitoring for cirrhotic patients is often performed only intermittently; thus, episodes requiring clinical interventions could be missed. This work investigates the feasibility of measuring bilirubin concentration in whole porcine blood samples using dual-wavelength transmission measurement. A compact and low-cost dual-wavelength transmission measurement setup is developed and optimized to measure whole blood bilirubin concentrations. Using small volumes of whole porcine blood (72 µL), we measured the bilirubin concentration within a range corresponding to healthy individuals and cirrhotic patients (1.2-30 mg/dL). We demonstrate that bilirubin levels can be estimated with a positive correlation (R-square > 0.95) and an accuracy of ±1.7 mg/dL, with higher reliability in cirrhotic bilirubin concentrations (> 4 mg/dL) - critical for high-risk patients. The optical and electronic components utilized are economical and can be readily integrated into a miniature, low-cost, and user-friendly system. This could provide a pathway for point-of-care monitoring of blood bilirubin outside of medical facilities (e.g., patient's home).

Advances in Carbon-Based Microfiber Electrodes for Neural Interfacing.

Neural interfacing devices using penetrating microelectrode arrays have emerged as an important tool in both neuroscience research and medical applications. These implantable microelectrode arrays enable communication between man-made devices and the nervous system by detecting and/or evoking neuronal activities. Recent years have seen rapid development of electrodes fabricated using flexible, ultrathin carbon-based microfibers. Compared to electrodes fabricated using rigid materials and larger cross-sections, these microfiber electrodes have been shown to reduce foreign body responses after implantation, with improved signal-to-noise ratio for neural recording and enhanced resolution for neural stimulation. Here, we review recent progress of carbon-based microfiber electrodes in terms of material composition and fabrication technology. The remaining challenges and future directions for development of these arrays will also be discussed. Overall, these microfiber electrodes are expected to improve the longevity and reliability of neural interfacing devices.

Eighty-Five Percent of Improved Optical Power Delivery to Epiretinal Prostheses Using Rigid Body Compensation Algorithm.

Vision impairment caused by degenerative retinal pathologies such as age-related macular degeneration can be treated using retinal implants. Such devices receive power and data using cables passing through a permanent surgical incision in the eye wall (sclera), which increases the risk to patients and surgical costs. A recently developed retinal implant design eliminates the necessity of the implant cable using a photonic power converter (PPC), which receives optical power and data through the pupil and is directed by an ellipsoidal reflector and micro-electromechanical mirror. We present a misalignment compensation algorithm model that accounts for rigid-body motions of the reflector relative to the eye and applies the correction to the mirror coordinates in the presence of angular misalignment of the reflector. We demonstrate that up to 85% of the nominal optical power can be delivered to the implant with axial reflector misalignments up to 30 deg using the compensation algorithm.

Mechanisms and Applications of Neuromodulation Using Surface Acoustic Waves-A Mini-Review.

The study of neurons is fundamental for basic neuroscience research and treatment of neurological disorders. In recent years ultrasound has been increasingly recognized as a viable method to stimulate neurons. However, traditional ultrasound transducers are limited in the scope of their application by self-heating effects, limited frequency range and cavitation effects during neuromodulation. In contrast, surface acoustic wave (SAW) devices, which are producing wavemodes with increasing application in biomedical devices, generate less self-heating, are smaller and create less cavitation. SAW devices thus have the potential to address some of the drawbacks of traditional ultrasound transducers and could be implemented as miniaturized wearable or implantable devices. In this mini review, we discuss the potential mechanisms of SAW-based neuromodulation, including mechanical displacement, electromagnetic fields, thermal effects, and acoustic streaming. We also review the application of SAW actuation for neuronal stimulation, including growth and neuromodulation. Finally, we propose future directions for SAW-based neuromodulation.

Laminin coated diamond electrodes for neural stimulation.

The performance of many implantable neural stimulation devices is degraded due to the loss of neurons around the electrodes by the body's natural biological responses to a foreign material. Coating of electrodes with biomolecules such as extracellular matrix proteins is one potential route to suppress the adverse responses that lead to loss of implant functionality. Concurrently, however, the electrochemical performance of the stimulating electrode must remain optimal to continue to safely provide sufficient charge for neural stimulation. We have previously found that oxygen plasma treated nitrogen included ultrananocrystalline diamond coated platinum electrodes exhibit superior charge injection capacity and electrochemical stability for neural stimulation (Sikder et al., 2019). To fabricate bioactive diamond electrodes, in this work, laminin, an extracellular matrix protein known to be involved in inter-neuron adhesion and recognition, was used as an example biomolecule. Here, laminin was covalently coupled to diamond electrodes. Electrochemical analysis found that the covalently coupled films were robust and resulted in minimal change to the charge injection capacity of diamond electrodes. The successful binding of laminin and its biological activity was further confirmed using primary rat cortical neuron cultures, and the coated electrodes showed enhanced cell attachment densities and neurite outgrowth. The method proposed in this work is versatile and adaptable to many other biomolecules for producing bioactive diamond electrodes, which are expected to show reduced the inflammatory responses in vivo.

Detection and identification of polyaromatic hydrocarbons (PAHs) contamination in soil using intrinsic fluorescence.

Polyaromatic hydrocarbons (PAHs), such as pyrene, benzo[a]pyrene, phenanthrene, and anthracene induce toxic, carcinogenic, and mutagenic effects on living organisms and are considered as primary pollutants. Traditional methods for their identification are often laborious and time-consuming and do not account for the heterogeneous nature of their distribution. Here we present confocal microscopy as a rapid and accurate technique for direct analysis of PAHs in soil samples without the complexity of sample pre-processing which might delay results for several days. The method uses the intrinsic fluorescence of PAHs for detection and their emission spectra for the identification of different PAHs. A clear difference was observed in the fluorescence spectral properties of phenanthrene, pyrene and naphthalene in real-time environmental samples. The post-processing of confocal scans obtained in the detection stage of PAHs was completed through the application of ImageJ software. Intrinsic fluorescence-based detections of PAHs may open new avenues in terms of rapid detection and identification of PAHs in heterogeneous complex soil samples.

Laser Driven Miniature Diamond Implant for Wireless Retinal Prostheses.

The design and benchtop operation of a wireless miniature epiretinal stimulator implant is reported. The implant is optically powered and controlled using safe illumination at near-infrared wavelengths. An application-specific integrated circuit (ASIC) hosting a digital control unit is used to control the implant's electrodes. The ASIC is powered using an advanced photovoltaic (PV) cell and programmed using a single photodiode. Diamond packaging technology is utilized to achieve high-density integration of the implant optoelectronic circuitry, as well as individual connections between a stimulator chip and 256 electrodes, within a 4.6 mm × 3.7 mm × 0.9 mm implant package. An ultrahigh efficiency PV cell with a monochromatic power conversion efficiency of 55% is used to power the implant. On-board photodetection circuity with a bandwidth of 3.7 MHz is used for forward data telemetry of stimulation parameters. In comparison to implants which utilize inductively coupled coils, laser power delivery enables a high degree of miniaturization and lower surgical complexity. The device presented combines the benefits of implant miniaturization and a flexible stimulation strategy provided by a dedicated stimulator chip. This development provides a route to fully wireless miniaturized minimally invasive implants with sophisticated functionalities.

In vivo feasibility of epiretinal stimulation using ultrananocrystalline diamond electrodes.

OBJECTIVE: Due to their increased proximity to retinal ganglion cells (RGCs), epiretinal visual prostheses present the opportunity for eliciting phosphenes with low thresholds through direct RGC activation. This study characterised the in vivo performance of a novel prototype monolithic epiretinal prosthesis, containing Nitrogen incorporated ultrananocrystalline (N-UNCD) diamond electrodes. APPROACH: A prototype implant containing up to twenty-five 120 × 120 µm N-UNCD electrodes was implanted into 16 anaesthetised cats and attached to the retina either using a single tack or via magnetic coupling with a suprachoroidally placed magnet. Multiunit responses to retinal stimulation using charge-balanced biphasic current pulses were recorded acutely in the visual cortex using a multichannel planar array. Several stimulus parameters were varied including; the stimulating electrode, stimulus polarity, phase duration, return configuration and the number of electrodes stimulated simultaneously. MAIN RESULTS: The rigid nature of the device and its form factor necessitated complex surgical procedures. Surgeries were considered successful in 10/16 animals and cortical responses to single electrode stimulation obtained in eight animals. Clinical imaging and histological outcomes showed severe retinal trauma caused by the device in situ in many instances. Cortical measures were found to significantly depend on the surgical outcomes of individual experiments, phase duration, return configuration and the number of electrodes stimulated simultaneously, but not stimulus polarity. Cortical thresholds were also found to increase over time within an experiment. SIGNIFICANCE: The study successfully demonstrated that an epiretinal prosthesis containing diamond electrodes could produce cortical activity with high precision, albeit only in a small number of cases. Both surgical approaches were highly challenging in terms of reliable and consistent attachment to and stabilisation against the retina, and often resulted in severe retinal trauma. There are key challenges (device form factor and attachment technique) to be resolved for such a device to progress towards clinical application, as current surgical techniques are unable to address these issues.

Minimizing axon bundle activation of retinal ganglion cells with oriented rectangular electrodes.

OBJECTIVE: Retinal prostheses aim to restore vision in patients with retinal degenerative diseases, such as age-related macular degeneration and retinitis pigmentosa. By implanting an array of microelectrodes, such a device creates percepts in patients through electrical stimulation of surviving retinal neurons. A challenge for retinal prostheses when trying to return high quality vision is the unintended activation of retinal ganglion cells through the stimulation of passing axon bundles, which leads to patients reporting large, elongated patches of light instead of focal spots. APPROACH: In this work, we used calcium imaging to record the responses of retinal ganglion cells to electrical stimulation in explanted retina using rectangular electrodes placed with different orientations relative to the axon bundles. MAIN RESULTS: We showed that narrow, rectangular electrodes oriented parallel to the axon bundles can achieve focal stimulation. To further improve the strategy, we studied the impact of different stimulation waveforms and electrode configurations. We found the selectivity for focal stimulation to be higher when using short (33 µs), anodic-first biphasic pulses, with long electrode lengths and at least 50 µm electrode-to-retinal separation. Focal stimulation was, in fact, less selective when the electrodes made direct contact with the retinal surface due to unwanted preferential stimulation of the proximal axon bundles. SIGNIFICANCE: When employed in retinal prostheses, the proposed stimulation strategy is expected to provide improved quality of vision to the blind.

Real-time detection and identification of nematode eggs genus and species through optical imaging.

Nematode eggs are pervasive pathogens that infect billions of people and livestock every year. Adult parasitic nematode worms can be distinguished based on their size and morphology. However, their eggs, particularly their species Ascaris lumbricoides and Ascaris suum cannot be identified from each other. Identifying eggs of helminths from wastewater and sludge is important from a public health perspective to minimize the spread of Ascaris infections. Numerous methods exist for nematode identification, from a morphological-based approach to high throughput sequencing technology. However, these techniques are not consistent and often laborious and time-consuming. In this study, we demonstrate that non-invasive real-time identification of eggs is possible based on their intrinsic fluorescence. Using confocal microscopy, we investigate the autofluorescence properties of five species of nematode eggs and observe clear differences between genus and for the first time their species in sludge samples. This non-invasive imaging technique could lead to better understanding of these species and may assist in early control of diseases.

Enhanced Widefield Quantum Sensing with Nitrogen-Vacancy Ensembles Using Diamond Nanopillar Arrays.

Surface micro- and nano-patterning techniques are often employed to enhance the optical interface to single photoluminescent emitters in diamond, but the utility of such surface structuring in applications requiring ensembles of emitters is still open to investigation. Here, we demonstrate scalable and fault-tolerant fabrication of closely packed arrays of fluorescent diamond nanopillars, each hosting its own dense, uniformly bright ensemble of near-surface nitrogen-vacancy centers. We explore the optimal sizes for these structures and realize enhanced spin and photoluminescence properties resulting in a 4.5 times increase in optically detected magnetic resonance sensitivity when compared to unpatterned surfaces. Utilizing the increased measurement sensitivity, we image the mechanical stress tensor in each diamond pillar across the arrays and show that the fabrication process has a negligible impact on in-built stress compared to the unpatterned surface. Our results represent a valuable pathway toward future multimodal and vector-resolved imaging studies, for instance in biological contexts.

Analysis of the capacitance of minimally insulated parallel wires implanted in biological tissue.

State of the art bioelectronic implants are using thin cables for therapeutic electrical stimulation. If cable insulation is thin, biological tissue surrounding cables can be unintentionally stimulated. The capacitance of the cable must be much less than the stimulating electrodes to ensure stimulating currents are delivered to the electrode-tissue interface. This work derives and experimentally validates a model to determine the capacitance of parallel cables implanted in biological tissue. Biological tissue has a high relative permittivity, so the capacitance of cabling implanted in the human body depends on cable insulation thickness. Simulations and measurements demonstrate that insulation thickness influences the capacitance of implanted parallel cables across almost two orders of magnitude: from 20 pF/m to 700 pF/m. The results are verified using four different methods: solving the Laplacian numerically from first principles, using a commercially available electrostatic solver, and measuring twelve different parallel pairs of wires using two different potentiostats. Cable capacitance simulations and measurements are performed in air, a porcine blood pool and porcine muscle tissue. The results do not differ by more than 30% for a given cable across simulation and measurement methodologies. The modelling in this work can be used to design cabling for minimally-invasive biomedical implants.

3D Diamond Electrode Array for High-Acuity Stimulation in Neural Tissue.

Innovations in micro- and nanofabrication technologies enable the manufacture of multielectrode arrays for use in neuromodulation and neural recording. Multielectrode arrays make possible medical implants such as pacemakers, deep-brain stimulators, or visual and hearing aids, to treat numerous neural disorders. An optimal neural interface requires a high density of electrodes to precisely record from and stimulate the nervous system while minimizing the overall size of the array. For example, people with retinal degenerative diseases can benefit from retinal prostheses implanted inside the eye. However, at present the visual acuity provided by such implants is well below the threshold for functional vision, mainly due to the limited spatial resolution. In this work, we present a design of 3D nanostructured conductive diamond electrodes, integrated within a polycrystalline diamond housing, offering a high electrode density and count, which simultaneously satisfies spatial resolution and biocompatibility goals. The array is composed of height adjustable pillar electrodes that are 80 µm in diameter and separated by 150 µm. A holistic characterization of the electrodes was performed and the device tested for stimulation performance in a whole-mounted retina. Electrochemical testing showed impedance of 20 kΩ and a wide water window of 2.47 V. The pillar structure allows the distance between the electrodes and the retinal ganglion cells to be reduced which is key to more confined stimulation at lower current levels, leading to potentially higher-acuity stimulation without damaging retinal tissue.

Hybrid diamond/ carbon fiber microelectrodes enable multimodal electrical/chemical neural interfacing.

Implantable medical devices are now in regular use to treat or ameliorate medical conditions, including movement disorders, chronic pain, cardiac arrhythmias, and hearing or vision loss. Aside from offering alternatives to pharmaceuticals, one major advantage of device therapy is the potential to monitor treatment efficacy, disease progression, and perhaps begin to uncover elusive mechanisms of diseases pathology. In an ideal system, neural stimulation, neural recording, and electrochemical sensing would be conducted by the same electrode in the same anatomical region. Carbon fiber (CF) microelectrodes are the appropriate size to achieve this goal and have shown excellent performance, in vivo. Their electrochemical properties, however, are not suitable for neural stimulation and electrochemical sensing. Here, we present a method to deposit high surface area conducting diamond on CF microelectrodes. This unique hybrid microelectrode is capable of recording single-neuron action potentials, delivering effective electrical stimulation pulses, and exhibits excellent electrochemical dopamine detection. Such electrodes are needed for the next generation of miniaturized, closed-loop implants that can self-tune therapies by monitoring both electrophysiological and biochemical biomarkers.

Improved visual acuity using a retinal implant and an optimized stimulation strategy.

OBJECTIVE: Retinal prosthetic devices hold great promise for the treatment of retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration. Through electrical stimulation of the surviving retinal neurons, these devices evoke visual signals that are then relayed to the brain. Currently, the visual prostheses used in clinical trials have few electrodes, thus limiting visual acuity. Electrode arrays with high electrode densities have been developed using novel technologies, including diamond growth and laser machining, and these may provide a more promising route to achieve high visual acuity in blind patients. APPROACH: Here, we studied the potential spatial resolution of electrical stimulation using diamond electrodes. We did this by labeling retinal ganglion cells in whole mount retina with a calcium indicator in wild-type rats and those with retinal degeneration. We imaged the ganglion cell responses to a range of stimulation parameters, including pulse duration and return electrode configuration. MAIN RESULTS: With sub-retinal stimulation, in which electrodes were in contact with the intact or degenerated photoreceptor layer, we found that biphasic pulses of 0.1 ms phase duration and a local return configuration was the most effective in confining the retinal ganglion cell activation patterns, while also remaining within the safety limits of the materials and providing the best power efficiency. SIGNIFICANCE: These results provide an optimized stimulation strategy for retinal implants, which if implemented in a retinal prosthetic is expected to improve the achievable visual acuity.