Optical pacing of the embryonic heart

Advances in Biointegrated Wearable and Implantable Optoelectronic Devices for Cardiac Healthcare

With the prevalence of cardiovascular disease, it is imperative that medical monitoring and treatment become more instantaneous and comfortable for patients. Recently, wearable and implantable optoelectronic devices can be seamlessly integrated into human body to enable physiological monitoring and treatment in an imperceptible and spatiotemporally unconstrained manner, opening countless possibilities for the intelligent healthcare paradigm. To achieve biointegrated cardiac healthcare, researchers have focused on novel strategies for the construction of flexible/stretchable optoelectronic devices and systems. Here, we overview the progress of biointegrated flexible and stretchable optoelectronics for wearable and implantable cardiac healthcare devices. Firstly, the device design is addressed, including the mechanical design, interface adhesion, and encapsulation strategies. Next, the practical applications of optoelectronic devices for cardiac physiological monitoring, cardiac optogenetics, and nongenetic stimulation are presented. Finally, an outlook on biointegrated flexible and stretchable optoelectronic devices and systems for intelligent cardiac healthcare is discussed.

Near-infrared-triggered plasmonic regulation and cardiomyocyte-based biosensing system for in vitro bradyarrhythmia treatment

Bradyarrhythmia, a life-threatening cardiovascular disease, is an increasing burden for the healthcare system. Currently, surgery, implanted device, and drug are introduced to treat the bradyarrhythmia in clinical practice. However, these conventional therapeutic strategies suffer from the invasive surgery, power supply, or drug side effect, respectively, hence developing the alternative therapeutic strategy is necessarily imperative. Here, a convenient and effective strategy to treat the bradyarrhythmia is proposed using near-infrared-triggered Au nanorod (NR) based plasmonic photothermal effect (PPE). Moreover, electrophysiology of cardiomyocytes is dynamically monitored by the integrated biosensing-regulating system during and after the treatment. Cardiomyocyte-based bradyarrhythmia recover rhythmic for a long time by regulating plasmonic photothermal effect. Furthermore, the regulatory mechanism is qualitatively investigated to verify the significant thermal stimulation in the recovery process. This study establishes a reliable platform for long-term recording and evaluation of mild photothermal therapy for bradyarrhythmia in vitro, offering an efficient and non-invasive strategy for the potential clinical applications.

Quantifying tissue temperature changes induced by infrared neural stimulation: numerical simulation and MR thermometry

Infrared neural stimulation (INS) delivered via short pulse trains is an innovative tool that has potential for us use for studying brain function and circuitry, brain machine interface, and clinical use. The prevailing mechanism for INS involves the conversion of light energy into thermal transients, leading to neuronal membrane depolarization. Due to the potential risks of thermal damage, it is crucial to ensure that the resulting local temperature increases are within non-damaging limits for brain tissues. Previous studies have estimated damage thresholds using histological methods and have modeled thermal effects based on peripheral nerves. However, additional quantitative measurements and modeling studies are needed for the central nervous system. Here, we performed 7 T MRI thermometry on ex vivo rat brains following the delivery of infrared pulse trains at five different intensities from 0.1-1.0 J/cm2 (each pulse train 1,875 nm, 25 us/pulse, 200 Hz, 0.5 s duration, delivered through 200 µm fiber). Additionally, we utilized the General BioHeat Transfer Model (GBHTM) to simulate local temperature changes in perfused brain tissues while delivering these laser energies to tissue (with optical parameters of human skin) via three different sizes of optical fibers at five energy intensities. The simulation results clearly demonstrate that a 0.5 second INS pulse train induces an increase followed by an immediate drop in temperature at stimulation offset. The delivery of multiple pulse trains with 2.5 s interstimulus interval (ISI) leads to rising temperatures that plateau. Both thermometry and modeling results show that, using parameters that are commonly used in biological applications (200 µm diameter fiber, 0.1-1.0 J/cm2), the final temperature increase at the end of the 60 sec stimuli duration does not exceed 1°C with stimulation values of 0.1-0.5 J/cm2 and does not exceed 2°C with stimulation values of up to 1.0 J/cm2. Thus, the maximum temperature rise is consistent with the thermal damage threshold reported in previous studies. This study provides a quantitative evaluation of the temperature changes induced by INS, suggesting that existing practices pose minimal major safety concerns for biological tissues.

Shedding Light on Cardiac Excitation: In Vitro and In Silico Analysis of Native Ca2+ Channel Activation in Guinea Pig Cardiomyocytes Using Organic Photovoltaic Devices

OBJECTIVE

This study aims to explore the potential of organic electrolytic photocapacitors (OEPCs), an innovative photovoltaic device, in mediating the activation of native voltage-gated Cav1.2 channels (ICa,L) in Guinea pig ventricular cardiomyocytes.

METHODS

Whole-cell patch-clamp recordings were employed to examine light-triggered OEPC mediated ICa,L activation, integrating the channel's kinetic properties into a multicompartment cell model to take intracellular ion concentrations into account. A multidomain model was additionally incorporated to evaluate effects of OEPC-mediated stimulation. The final model combines external stimulation, multicompartmental cell simulation, and a patch-clamp amplifier equivalent circuit to assess the impact on achievable intracellular voltage changes.

RESULTS

Light pulses activated ICa,L, with amplitudes similar to voltage-clamp activation and high sensitivity to the L-type Ca2+ channel blocker, nifedipine. Light-triggered ICa,L inactivation exhibited kinetic parameters comparable to voltage-induced inactivation.

CONCLUSION

OEPC-mediated activation of ICa,L demonstrates their potential for nongenetic optical modulation of cellular physiology potentially paving the way for the development of innovative therapies in cardiovascular health. The integrated model proves the light-mediated activation of ICa,L and advances the understanding of the interplay between the patch-clamp amplifier and external stimulation devices.

SIGNIFICANCE

Treating cardiac conduction disorders by minimal-invasive means without genetic modifications could advance therapeutic approaches increasing patients' quality of life compared with conventional methods employing electronic devices.

Modulatory Effects on Laminar Neural Activity Induced by Near-Infrared Light Stimulation with a Continuous Waveform to the Mouse Inferior Colliculus In Vivo

Infrared neural stimulation (INS) is a promising area of interest for the clinical application of a neuromodulation method. This is in part because of its low invasiveness, whereby INS modulates the activity of the neural tissue mainly through temperature changes. Additionally, INS may provide localized brain stimulation with less tissue damage. The inferior colliculus (IC) is a crucial auditory relay nucleus and a potential target for clinical application of INS to treat auditory diseases and develop artificial hearing devices. Here, using continuous INS with low to high-power density, we demonstrate the laminar modulation of neural activity in the mouse IC in the presence and absence of sound. We investigated stimulation parameters of INS to effectively modulate the neural activity in a facilitatory or inhibitory manner. A mathematical model of INS-driven brain tissue was first simulated, temperature distributions were numerically estimated, and stimulus parameters were selected from the simulation results. Subsequently, INS was administered to the IC of anesthetized mice, and the modulation effect on the neural activity was measured using an electrophysiological approach. We found that the modulatory effect of INS on the spontaneous neural activity was bidirectional between facilitatory and inhibitory effects. The modulatory effect on sound-evoked responses produced only an inhibitory effect to all examined stimulus intensities. Thus, this study provides important physiological evidence on the response properties of IC neurons to INS. Overall, INS can be used for the development of new therapies for neurological disorders and functional support devices for auditory central processing.

The cardiac conduction system: History, development, and disease

The heart is the first organ to form during embryonic development, establishing the circulatory infrastructure necessary to sustain life and enable downstream organogenesis. Critical to the heart's function is its ability to initiate and propagate electrical impulses that allow for the coordinated contraction and relaxation of its chambers, and thus, the movement of blood and nutrients. Several specialized structures within the heart, collectively known as the cardiac conduction system (CCS), are responsible for this phenomenon. In this review, we discuss the discovery and scientific history of the mammalian cardiac conduction system as well as the key genes and transcription factors implicated in the formation of its major structures. We also describe known human diseases related to CCS development and explore existing challenges in the clinical context.

Nongenetic Optical Modulation of Pluripotent Stem Cells Derived Cardiomyocytes Function in the Red Spectral Range

Optical stimulation in the red/near infrared range recently gained increasing interest, as a not-invasive tool to control cardiac cell activity and repair in disease conditions. Translation of this approach to therapy is hampered by scarce efficacy and selectivity. The use of smart biocompatible materials, capable to act as local, NIR-sensitive interfaces with cardiac cells, may represent a valuable solution, capable to overcome these limitations. In this work, a far red-responsive conjugated polymer, namely poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl]] (PCPDTBT) is proposed for the realization of photoactive interfaces with cardiomyocytes derived from pluripotent stem cells (hPSC-CMs). Optical excitation of the polymer turns into effective ionic and electrical modulation of hPSC-CMs, in particular by fastening Ca2+ dynamics, inducing action potential shortening, accelerating the spontaneous beating frequency. The involvement in the phototransduction pathway of Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) and Na+ /Ca2+ exchanger (NCX) is proven by pharmacological assays and is correlated with physical/chemical processes occurring at the polymer surface upon photoexcitation. Very interestingly, an antiarrhythmogenic effect, unequivocally triggered by polymer photoexcitation, is also observed. Overall, red-light excitation of conjugated polymers may represent an unprecedented opportunity for fine control of hPSC-CMs functionality and can be considered as a perspective, noninvasive approach to treat arrhythmias.

Selective Infrared Neural Inhibition Can Be Reproduced by Resistive Heating

OBJECTIVES

Small-diameter afferent axons carry various sensory signals that are critical for vital physiological conditions but sometimes contribute to pathologies. Infrared (IR) neural inhibition (INI) can induce selective heat block of small-diameter axons, which holds potential for translational applications such as pain management. Previous research suggested that IR-heating-induced acceleration of voltage-gated potassium channel kinetics is the mechanism for INI. Therefore, we hypothesized that other heating methods, such as resistive heating (RH) in a cuff, could reproduce the selective inhibition observed in INI.

MATERIALS AND METHODS

We conducted ex vivo nerve-heating experiments on pleural-abdominal connective nerves of Aplysia californica using both IR and RH. We fabricated a transparent silicone nerve cuff for simultaneous IR heating, RH, and temperature measurements. Temperature elevations (ΔT) on the nerve surface were recorded for both heating modalities, which were tested over a range of power levels that cover a similar ΔT range. We recorded electrically evoked compound action potentials (CAPs) and segmented them into fast and slow subcomponents on the basis of conduction velocity differences between the large and small-diameter axonal subpopulations. We calculated the normalized inhibition strength and inhibition selectivity index on the basis of the rectified area under the curve of each subpopulation.

RESULTS

INI and RH showed a similar selective inhibition effect on CAP subcomponents for slow-conducting axons, confirmed by the inhibition probability vs ΔT dose-response curve based on approximately 2000 CAP measurements. The inhibition selectivity indexes of the two heating modalities were similar across six nerves. RH only required half the total electrical power required by INI to achieve a similar ΔT.

SIGNIFICANCE

We show that selective INI can be reproduced by other heating modalities such as RH. RH, because of its high energy efficiency and simple design, can be a good candidate for future implantable neural interface designs.

Skeletal muscle cells opto-stimulation by intramembrane molecular transducers

Optical stimulation and control of muscle cell contraction opens up a number of interesting applications in hybrid robotic and medicine. Here we show that recently designed molecular phototransducer can be used to stimulate C2C12 skeletal muscle cells, properly grown to exhibit collective behaviour. C2C12 is a skeletal muscle cell line that does not require animal sacrifice Furthermore, it is an ideal cell model for evaluating the phototransducer pacing ability due to its negligible spontaneous activity. We study the stimulation process and analyse the distribution of responses in multinuclear cells, in particular looking at the consistency between stimulus and contraction. Contractions are detected by using an imaging software for object recognition. We find a deterministic response to light stimuli, yet with a certain distribution of erratic behaviour that is quantified and correlated to light intensity or stimulation frequency. Finally, we compare our optical stimulation with electrical stimulation showing advantages of the optical approach, like the reduced cell stress.

Infrared light elicits endothelium-dependent vasodilation in isolated occipital arteries of the rat via soluble guanylyl cyclase-dependent mechanisms

The left and right occipital arteries provide blood supply to afferent cell bodies in the ipsilateral nodose and petrosal ganglia. This supply is free of an effective blood-ganglion barrier, so changes in occipital artery blood flow directly affect the access of circulating factors to the afferent cell bodies. The application of infrared (IR) light to modulate neural and other cell processes has yielded information about basic biological processes within tissues and is gaining traction as a potential therapy for a variety of disease processes. To address whether IR can directly modulate vascular function, we performed wire myography studies to determine the actions of IR on occipital arteries isolated from male Sprague-Dawley rats. Based on our previous research that functionally-important differences exist between occipital artery segments close to their origin at the external carotid artery (ECA) and those closer to the nodose ganglion, the occipital arteries were dissected into two segments, one closer to the ECA and the other closer to the nodose ganglion. Segments were constricted with 5-hydroxytryptamine to a level equal to 50% of the maximal response generated by the application of a high (80 mM) concentration of K+ ions. The direct application of pulsed IR (1,460 nm) for 5 s produced a rapid vasodilation in occipital arteries that was significantly more pronounced in segments closest to the ECA, although the ECA itself was minimally responsive. The vasodilation remained for a substantial time (at least 120 s) after cessation of IR application. The vasodilation during and following cessation of the IR application was markedly diminished in occipital arteries denuded of the endothelium. In addition, the vasodilation elicited by IR in endothelium-intact occipital arteries was substantially reduced in the presence of a selective inhibitor of the nitric oxide-sensitive guanylate cyclase, 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one (ODQ). It appears that IR causes endothelium-dependent, nitric-oxide-mediated vasodilation in the occipital arteries of the rat. The ability of IR to generate rapid and sustained vasodilation may provide new therapeutic approaches for restoring or improving blood flow to targeted tissues.

Graphene-based cardiac sensors and actuators

Graphene, a 2D carbon allotrope, is revolutionizing many biomedical applications due to its unique mechanical, electrical, thermal, and optical properties. When bioengineers realized that these properties could dramatically enhance the performance of cardiac sensors and actuators and may offer fundamentally novel technological capabilities, the field exploded with numerous studies developing new graphene-based systems and testing their limits. Here we will review the link between specific properties of graphene and mechanisms of action of cardiac sensors and actuators, analyze the performance of these systems from inaugural studies to the present, and offer future perspectives.

Infrared neural stimulation markedly enhances nerve functionality assessment during nerve monitoring

In surgical procedures where the risk of accidental nerve damage is prevalent, surgeons commonly use electrical stimulation (ES) during intraoperative nerve monitoring (IONM) to assess a nerve's functional integrity. ES, however, is subject to off-target stimulation and stimulation artifacts disguising the true functionality of the specific target and complicating interpretation. Lacking a stimulation artifact and having a higher degree of spatial specificity, infrared neural stimulation (INS) has the potential to improve upon clinical ES for IONM. Here, we present a direct comparison between clinical ES and INS for IONM performance in an in vivo rat model. The sensitivity of INS surpasses that of ES in detecting partial forms of damage while maintaining a comparable specificity and sensitivity to more complete forms. Without loss in performance, INS is readily compatible with existing clinical nerve monitoring systems. These findings underscore the clinical potential of INS to improve IONM and surgical outcomes.

Neural modulation with photothermally active nanomaterials

Modulating neural electrophysiology with high precision is essential for understanding neural communication and for the diagnosis and treatment of neural disorders. Photothermal modulation offers a remote and non-genetic method for neural modulation with high spatiotemporal resolution and specificity. This technique induces highly localized and transient temperature changes at the cell membrane interfaced with photothermally active nanomaterials. This rapid temperature change affects the electrical properties of the cell membrane or temperature-sensitive ion channels. In this Review, we discuss the fundamental material properties and illumination conditions that are necessary for nanomaterial-assisted photothermal neural excitation and inhibition. We examine how this versatile technique allows direct investigation of neural electrophysiology and signalling pathways in two-dimensional and three-dimensional cell cultures and tissues, and highlight the scientific and technological challenges in terms of cellular specificity, light delivery and biointerface stability on the road to clinical translation.

Infrared neural stimulation in human cerebral cortex

BACKGROUND

Modulation of brain circuits by electrical stimulation has led to exciting and powerful therapies for diseases such as Parkinson's. Because human brain organization is based in mesoscale (millimeter-scale) functional nodes, having a method that can selectively target such nodes could enable more precise, functionally specific stimulation therapies. Infrared Neural Stimulation (INS) is an emerging stimulation technology that stimulates neural tissue via delivery of tiny heat pulses. In nonhuman primates, this optical method provides focal intensity-dependent stimulation of the brain without tissue damage. However, whether INS application to the human central nervous system (CNS) is similarly effective is unknown.

OBJECTIVE

To examine the effectiveness of INS on human cerebral cortex in intraoperative setting and to evaluate INS damage threshholds.

METHODS

Five epileptic subjects undergoing standard lobectomy for epilepsy consented to this study. Cortical response to INS was assessed by intrinsic signal optical imaging (OI, a method that detects changes in tissue reflectance due to neuronal activity). A custom integrated INS and OI system was developed specifically for short-duration INS and OI acquisition during surgical procedures. Single pulse trains of INS with intensities from 0.2 to 0.8 J/cm² were delivered to the somatosensory cortex and responses were recorded via optical imaging. Following tissue resection, histological analysis was conducted to evaluate damage threshholds.

RESULTS

As assessed by OI, and similar to results in monkeys, INS induced responses in human cortex were highly focal (millimeter sized) and led to relative suppression of nearby cortical sites. Intensity dependence was observed at both stimulated and functionally connected sites. Histological analysis of INS-stimulated human cortical tissue provided damage threshold estimates.

CONCLUSION

This is the first study demonstrating application of INS to human CNS and shows feasibility for stimulating single cortical nodes and associated sites and provided INS damage threshold estimates for cortical tissue. Our results suggest that INS is a promising tool for stimulation of functionally selective mesoscale circuits in the human brain, and may lead to advances in the future of precision medicine.

Bio-hybrid electronic and photonic devices

Bio-hybrid devices, combining electronic and photonic components with cells, tissues, and organs, hold potential for advancing our understanding of biology, physiology, and pathologies and for treating a wide range of conditions and diseases. In this review, I describe the devices, materials, and technologies that enable bio-hybrid devices and provide examples of their utilization at multiple biological scales ranging from the subcellular to whole organs. Finally, I describe the outcomes of a National Science Foundation (NSF)-funded workshop envisioning potential applications of these technologies to improve health outcomes and quality of life.

A high spatial resolution osteogenic differentiation in human mesenchymal stem cells induced by femtosecond laser

A variety of physical and chemical methods have been developed in research laboratories for the induction of stem cell differentiation. However, the use of exogenous chemicals and materials may limit their widespread utility in clinics. To develop a clean and precise induction approach with minimal invasion, we reported here that 1-second stimulation by a tightly focused femtosecond laser (fsL) (140 mW/μm² , 200 fs) can modulate the signaling systems in human mesenchymal cells, such as intracellular calcium and reactive oxygen species. Upon stimulation on an automatic platform, hMSCs were found to express osteoblastic markers and form calcium-rich deposits. Moreover, tissue mineralization was observed when the fsL-illuminated hMSCs were ectopically transplanted into nude mice. Collectively, we described a novel and non-contact optical stimulation method for cell differentiation with high spatiotemporal resolution.

G-Optrode Bio-Interfaces for Non-Invasive Optical Cell Stimulation: Design and Evaluation

Biocompatibility and potential efficacy in biological applications rely on the bio-interactions of graphene nanoparticles with biological tissues. Analyzing and modulating cellular and device-level activity requires non-invasive electrical stimulation of cells. To address these needs, G-optrodes, bio-interfaces based on graphene, have been developed. These devices use light to stimulate cells without modifying their genetic code. Optoelectronic capabilities, in particular the capacity to transform light energy into electrical energy, will be maintained throughout the procedures of neural stimulation. G-optrodes have also been studied as thin films on a range of substrates, and they have been designed to function at a very small scale. This study examines the impact of G-optrode-based substrate designs on the optical stimulation of pheochromocytoma (PC-12). Graphene electrodes, known as G-optrodes, are responsible for converting light into electrical pulses with stimulating effects. G-optrode bio-interfaces provide a stimulus that is independent of wavelength range but is sensitive to changes in illuminance. The authors have performed a comprehensive investigation based on the correct effects of the medication in vitro, employing substrate-based G-optrode biointerfaces. In substrate-based systems, the authors have proven that graphene is biocompatible. PC-12 cells were cultured on graphene for 7 days. Based on the findings, 20-nm and 50-nm thick G-optrodes are being studied for possible use in biological and artificial retinal applications. The findings of this study highlight the significance of biocompatibility in the selection and use of G-optrodes for biomedical purposes.

Bidirectional modulation of evoked synaptic transmission by pulsed infrared light

Infrared (IR) neuromodulation (INM) has been demonstrated as a novel modulation modality of neuronal excitability. However, the effects of pulsed IR light on synaptic transmission have not been investigated systematically. In this report, the IR light (2 μm) is used to directly modulate evoked synaptic transmission at the crayfish opener neuromuscular junction. The extracellularly recorded terminal action potentials (tAPs) and evoked excitatory postsynaptic currents (EPSCs) modulated by localized IR light illumination (500 ms, 3–13 mW) aimed at the synapses are analyzed. The impact of a single IR light pulse on the presynaptic Ca²⁺ influx is monitored with Ca²⁺ indicators. The EPSC amplitude is enhanced, and its rising phase is accelerated under relatively low IR light power levels and localized temperature rises. Increasing the IR light power reversibly suppresses and eventually blocks the EPSCs. Meanwhile, the synaptic delay, tAP amplitude, and presynaptic Ca²⁺ influx decrease monotonously with higher IR light power. It is demonstrated for the first time that IR light illumination has bidirectional effects on evoked synaptic transmission. These results highlight the efficacy and flexibility of using pulsed IR light to directly control synaptic transmission and advance our understanding of INM of neural networks.

Following the Beat: Imaging the Valveless Pumping Function in the Early Embryonic Heart

In vertebrates, the coordinated beat of the early heart tube drives cardiogenesis and supports embryonic growth. How the heart pumps at this valveless stage marks a fascinating problem that is of vital significance for understanding cardiac development and defects. The developing heart achieves its function at the same time as continuous and dramatic morphological changes, which in turn modify its pumping dynamics. The beauty of this muti-time-scale process also highlights its complexity that requires interdisciplinary approaches to study. High-resolution optical imaging, particularly fast, four-dimensional (4D) imaging, plays a critical role in revealing the process of pumping, instructing numerical modeling, and enabling biomechanical analyses. In this review, we aim to connect the investigation of valveless pumping mechanisms with the recent advancements in embryonic cardiodynamic imaging, facilitating interactions between these two areas of study, in hopes of encouraging and motivating innovative work to further understand the early heartbeat.

Porosity-based heterojunctions enable leadless optoelectronic modulation of tissues

Homo- and heterojunctions play essential roles in semiconductor-based devices such as field-effect transistors, solar cells, photodetectors and light-emitting diodes. Semiconductor junctions have been recently used to optically trigger biological modulation via photovoltaic or photoelectrochemical mechanisms. The creation of heterojunctions typically involves materials with different doping or composition, which leads to high cost, complex fabrications and potential side effects at biointerfaces. Here we show that a porosity-based heterojunction, a largely overlooked system in materials science, can yield an efficient photoelectrochemical response from the semiconductor surface. Using self-limiting stain etching, we create a nanoporous/non-porous, soft-hard heterojunction in p-type silicon within seconds under ambient conditions. Upon surface oxidation, the heterojunction yields a strong photoelectrochemical response in saline. Without any interconnects or metal modifications, the heterojunction enables efficient non-genetic optoelectronic stimulation of isolated rat hearts ex vivo and sciatic nerves in vivo with optical power comparable to optogenetics, and with near-infrared capabilities.

Tissue-Like Optoelectronic Neural Interface Enabled by PEDOT:PSS Hydrogel for Cardiac and Neural Stimulation

Optoelectronic biointerfaces have made a significant impact on modern science and technology from understanding the mechanisms of the neurotransmission to the recovery of the vision for blinds. They are based on the cell interfaces made of organic or inorganic materials such as silicon, graphene, oxides, quantum dots, and π-conjugated polymers, which are dry and stiff unlike a cell/tissue environment. On the other side, wet and soft hydrogels have recently been started to attract significant attention for bioelectronics because of its high-level tissue-matching biomechanics and biocompatibility. However, it is challenging to obtain optimal opto-bioelectronic devices by using hydrogels requiring device, heterojunction, and hydrogel engineering. Here, an optoelectronic biointerface integrated with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, hydrogel that simultaneously achieves efficient, flexible, stable, biocompatible, and safe photostimulation of cells is demonstrated. Besides their interfacial tissue-like biomechanics, ≈34 kPa, and high-level biocompatibility, hydrogel-integration facilitates increase in charge injection amounts sevenfolds with an improved responsivity of 156 mA W^-1 , stability under mechanical bending , and functional lifetime over three years. Finally, these devices enable stimulation of individual hippocampal neurons and photocontrol of beating frequency of cardiac myocytes via safe charge-balanced capacitive currents. Therefore, hydrogel-enabled optoelectronic biointerfaces hold great promise for next-generation wireless neural and cardiac implants.

Integrated Au-Nanoroded Biosensing and Regulating Platform for Photothermal Therapy of Bradyarrhythmia

Bradyarrhythmia is a kind of cardiovascular disease caused by dysregulation of cardiomyocytes, which seriously threatens human life. Currently, treatment strategies of bradyarrhythmia mainly include drug therapy, surgery, or implantable cardioverter defibrillators, but these strategies are limited by drug side effect, surgical trauma, and instability of implanted devices. Here, we developed an integrated Au-nanoroded biosensing and regulating platform to investigate the photothermal therapy of cardiac bradyarrhythmia in vitro. Au-nanoroded electrode array can simultaneously accumulate energy from the photothermal regulation and monitor the electrophsiological state to restore normal rhythm of cardiomyocytes in real time. To treat the cardiomyocytes cultured on Au-nanoroded device by near-infrared (NIR) laser irradiation, cardiomyocytes return to normal for long term after irradiation of suitable NIR energy and maintenance. Compared with the conventional strategies, the photothermal strategy is more effective and convenient to regulate the cardiomyocytes. Furthermore, mRNA sequencing shows that the differential expression genes in cardiomyocytes are significantly increased after photothermal strategy, which are involved in the regulation of the heart rate, cardiac conduction, and ion transport. This work establishes a promising integrated biosensing and regulating platform for photothermal therapy of bradyarrhythmia in vitro and provides reliable evidence of photothermal regulation on cardiomyocytes for cardiological clinical studies.

The influence of light on the beat rate variability of murine embryonic stem cell derived cardiomyocytes

BACKGROUND

The human heart rhythm can be quantified by analyzing the heart rate variability (HRV). A major influencing factor of the HRV is the circadian rhythm. The ocular light and the hormone melatonin play decisive roles in the circadian rhythm. The beat rate variability (BRV) is considered to be the in vitro equivalent of the HRV. Previous studies have demonstrated the influence of melatonin on cardiomyocytes. Also, the influence of light on cardiomyocytes has been described before. Nevertheless, the effect of light on the BRV of cardiomyocytes has not yet been examined.

MATERIAL AND METHODS

The BRV of spontaneously beating cardiomyocytes was measured with microelectrode arrays over a time period of 30 min. The experiments were either performed with light exposure (with and without an infrared filter) or in complete darkness.

RESULTS

The BRV was higher and the beating frequency was lower when the cardiomyocytes were exposed to the full spectrum of light, compared to the measurements in darkness as well as to the measurements with an infrared filter. In contrast, the differences of BRV between the measurements in darkness and the measurements with an infrared filter were not as distinct.

CONCLUSIONS

This is the first study demonstrating the influence of light on the beating rhythm of heart tissue in vitro. The results indicate that especially the infrared spectrum of light alters the BRV. These findings could be of interest for clinical applications such as the field of optical pacing as well as in neonatal patient care.

Light Emitting Diodes Photobiomodulation Improves Cardiac Function by Promoting ATP Synthesis in Mice With Heart Failure

Heart failure (HF) is the common consequences of various cardiovascular diseases, often leading to severe cardiac output deficits with a high morbidity and mortality. In recent years, light emitting diodes-based therapy (LEDT) has been widely used in multiple cardiac diseases, while its modulatory effects on cardiac function with HF still remain unclear. Therefore, the objective of this study was to investigate the effects of LED-Red irradiation on cardiac function in mice with HF and to reveal its mechanisms. In this study, we constructed a mouse model of HF. We found that LED-Red (630 nm) was an effective wavelength for the treatment of HF. Meanwhile, the application of LED-Red therapy to treat HF mice improved cardiac function, ameliorate heart morphology, reduced pulmonary edema, as well as inhibited collagen deposition. Moreover, LED-Red therapy attenuated the extent of perivascular fibrosis. Besides, LED-Red irradiation promoted calcium transients in cardiomyocytes as well as upregulated ATP synthesis, which may have positive implications for contractile function in mice with HF. Collectively, we identified that LED-Red exerts beneficial effects on cardiac function in HF mice possibly by promoting the synthesis of ATP.

A Method for Recording the Bioelectrical Activity of Neural Axons upon Stimulation with Short Pulses of Infrared Laser Radiation

The aim of the study was to develop a method for long-term non-invasive recording of the bioelectrical activity induced in isolated neuronal axons irradiated with short infrared (IR) pulses and to study the effect of radiation on the occurrence of action potentials in axons of a neuron culture in vitro.

Materials and Methods

Hippocampal cells of mouse embryos (E18) were cultured in microfluidic chips made of polydimethylsiloxane and containing microchannels for axonal growth at a distance of up to 800 μm. We studied the electrophysiological activity of a neuronal culture induced by pulses of focused laser radiation in the IR range (1907 and 2095 nm). The electrophysiological activity of the neuronal culture was recorded using a multichannel recording system (Multi Channel Systems, Germany).

Results

The developed microfluidic chip and the optical stimulation system combined with the multichannel registration system made it possible to non-invasively record the action potentials caused by pulsed IR radiation in isolated neuronal axons in vitro. The propagation of action potentials in axons was detected using extracellular microelectrodes when the cells were irradiated with a laser at a wavelength of 1907 nm with a radiation power of 0.2-0.5 W for pulses with a duration of 6 ms and 0.5 W for pulses with a duration of 10 ms. It was shown that the radiation power positively correlated with the occurrence rate of axonal response. Moreover, the probability of a response evoked by optical stimulation increased at short optical pulses. In addition, we found that more responses could be evoked by irradiating the neuronal cell culture itself rather than the axon-containing microchannels.

Conclusion

The developed method makes it possible to isolate the axons growing from cultured neurons into a microfluidic chip, stimulate the neurons with infrared radiation, and non-invasively record the axonal spiking. The proposed approach allowed us to study the characteristics of neuronal responses in cell cultures over a long (weeks) period of time. The method can be used both in fundamental research into the brain signaling system and in the development of a non-invasive neuro-interface.

Opto-thermal technologies for microscopic analysis of cellular temperature-sensing systems

Could enzymatic activities and their cooperative functions act as cellular temperature-sensing systems? This review introduces recent opto-thermal technologies for microscopic analyses of various types of cellular temperature-sensing system. Optical microheating technologies have been developed for local and rapid temperature manipulations at the cellular level. Advanced luminescent thermometers visualize the dynamics of cellular local temperature in space and time during microheating. An optical heater and thermometer can be combined into one smart nanomaterial that demonstrates hybrid function. These technologies have revealed a variety of cellular responses to spatial and temporal changes in temperature. Spatial temperature gradients cause asymmetric deformations during mitosis and neurite outgrowth. Rapid changes in temperature causes imbalance of intracellular Ca2+ homeostasis and membrane potential. Among those responses, heat-induced muscle contractions are highlighted. It is also demonstrated that the short-term heating hyperactivates molecular motors to exceed their maximal activities at optimal temperatures. We discuss future prospects for opto-thermal manipulation of cellular functions and contributions to obtain a deeper understanding of the mechanisms of cellular temperature-sensing systems.

Optical neural stimulation using the thermoplasmonic effect of gold nano-hexagon

The use of nanoparticle photothermal effect as adjuvants in neuromodulation has recently received much attention, with many open questions about new nanostructures' effect on the action potential. The photothermal properties of hexagonal gold nanoparticles are investigated in this work, including the absorption peak wavelength and light-heat conversion rate, using both experimental and simulation methods. Furthermore, the ability to use these nanostructures in axonal neural stimulation and cardiac stimulation by measuring temperature changes of gold nano-hexagons under 532 nm laser irradiation is studied. In addition, their thermal effect on neural responses is investigated by modeling small-diameter unmyelinated axons and heart pacemaker cells. The results show that the increase in temperature caused by these nano-hexagons can successfully stimulate the small diameter axon and produce an action potential. Experiments have also demonstrated that the heat created by gold nano-hexagons affects toad cardiac rhythm and increases T wave amplitude. An increase in T wave amplitude on toad heart rhythm shows the thermal effect of nano hexagons heat on heart pacemaker cells and intracellular ion flows. This work demonstrates the feasibility of utilizing these nanostructures to create portable and compact medical devices, such as optical pacemakers or cardiac stimulation.

[Study on the temperature characteristics of fast capacitance in patch clamp experiments]

Patch clamp is a technique that can measure weak current in the level of picoampere (pA). It has been widely used for cellular electrophysiological recording in fundamental medical researches, such as membrane potential and ion channel currents recording, etc. In order to obtain accurate measurement results, both the resistance and capacitance of the pipette are required to be compensated. Capacitance compensations are composed of slow and fast capacitance compensation. The slow compensation is determined by the lipid bilayer of cell membrane, and its magnitude usually ranges from a few picofarads (pF) to a few microfarads (μF), depending on the cell size. The fast capacitance is formed by the distributed capacitance of the glass pipette, wires and solution, mostly ranging in a few picofarads. After the pipette sucks the cells in the solution, the positions of the glass pipette and wire have been determined, and only taking once compensation for slow and fast capacitance will meet the recording requirements. However, when the study needs to deal with the temperature characteristics, it is still necessary to make a recognition on the temperature characteristic of the capacitance. We found that the time constant of fast capacitance discharge changed with increasing temperature of bath solution when we studied the photothermal effect on cell membrane by patch clamp. Based on this phenomenon, we proposed an equivalent circuit to calculate the temperature-dependent parameters. Experimental results showed that the fast capacitance increased in a positive rate of 0.04 pF/℃, while the pipette resistance decreased. The fine data analysis demonstrated that the temperature rises of bath solution determined the kinetics of the fast capacitance mainly by changing the inner solution resistance of the glass pipette. This result will provide a good reference for the fine temperature characteristic study related to cellular electrophysiology based on patch clamp technique.

Nonthermal and reversible control of neuronal signaling and behavior by midinfrared stimulation

Various neuromodulation approaches have been employed to alter neuronal spiking activity and thus regulate brain functions and alleviate neurological disorders. Infrared neural stimulation (INS) could be a potential approach for neuromodulation because it requires no tissue contact and possesses a high spatial resolution. However, the risk of overheating and an unclear mechanism hamper its application. Here we show that midinfrared stimulation (MIRS) with a specific wavelength exerts nonthermal, long-distance, and reversible modulatory effects on ion channel activity, neuronal signaling, and sensorimotor behavior. Patch-clamp recording from mouse neocortical pyramidal cells revealed that MIRS readily provides gain control over spiking activities, inhibiting spiking responses to weak inputs but enhancing those to strong inputs. MIRS also shortens action potential (AP) waveforms by accelerating its repolarization, through an increase in voltage-gated K⁺ (but not Na⁺) currents. Molecular dynamics simulations further revealed that MIRS-induced resonance vibration of -C=O bonds at the K⁺ channel ion selectivity filter contributes to the K⁺ current increase. Importantly, these effects are readily reversible and independent of temperature increase. At the behavioral level in larval zebrafish, MIRS modulates startle responses by sharply increasing the slope of the sensorimotor input-output curve. Therefore, MIRS represents a promising neuromodulation approach suitable for clinical application.

Current Review of Optical Neural Interfaces for Clinical Applications

Neural interfaces, which enable the recording and stimulation of living neurons, have emerged as valuable tools in understanding the brain in health and disease, as well as serving as neural prostheses. While neural interfaces are typically based on electrical transduction, alternative energy modalities have been explored to create safe and effective approaches. Among these approaches, optical methods of linking neurons to the outside world have gained attention because light offers high spatial selectivity and decreased invasiveness. Here, we review the current state-of-art of optical neural interfaces and their clinical applications. Optical neural interfaces can be categorized into optical control and optical readout, each of which can be divided into intrinsic and extrinsic approaches. We discuss the advantages and disadvantages of each of these methods and offer a comparison of relative performance. Future directions, including their clinical opportunities, are discussed with regard to the optical properties of biological tissue.

Two-photon GCaMP6f imaging of infrared neural stimulation evoked calcium signals in mouse cortical neurons in vivo

Infrared neural stimulation is a promising tool for stimulating the brain because it can be used to excite with high spatial precision without the need of delivering or inserting any exogenous agent into the tissue. Very few studies have explored its use in the brain, as most investigations have focused on sensory or motor nerve stimulation. Using intravital calcium imaging with the genetically encoded calcium indicator GCaMP6f, here we show that the application of infrared neural stimulation induces intracellular calcium signals in Layer 2/3 neurons in mouse cortex in vivo. The number of neurons exhibiting infrared-induced calcium response as well as the amplitude of those signals are shown to be both increasing with the energy density applied. By studying as well the spatial extent of the stimulation, we show that reproducibility of the stimulation is achieved mainly in the central part of the infrared beam path. Stimulating in vivo at such a degree of precision and without any exogenous chromophores enables multiple applications, from mapping the brain's connectome to applications in systems neuroscience and the development of new therapeutic tools for investigating the pathological brain.

Infrared neurostimulation inex-vivorat sciatic nerve using 1470 nm wavelength

Objective.To design and implement a setup forex-vivooptical stimulation for exploring the effect of several key parameters (optical power and pulse duration), activation features (threshold, spatial selectivity) and recovery characteristics (repeated stimuli) in peripheral nerves.Approach.A nerve chamber allowing ex-vivo electrical and optical stimulation was designed and built. A 1470 nm light source was chosen to stimulate the nerve. A photodiode module was implemented for synchronization of the electrical and optical channels.Main results. Compound neural action potentials (CNAPs) were successfully generated with infrared light pulses of 200-2000µs duration and power in the range of 3-10 W. These parameters determine a radiant exposure for stimulation in the range 1.59-4.78 J cm^-2. Recruitment curves were obtained by increasing durations at a constant power level. Neural activation threshold is reached at a mean radiant exposure of 3.16 ± 0.68 J cm^-2and mean pulse energy of 3.79 ± 0.72 mJ. Repetition rates of 2-10 Hz have been explored. In eight out of ten sciatic nerves (SNs), repeated light stimuli induced a sensitization effect in that the CNAP amplitude progressively grows, representing an increasing number of recruited fibres. In two out of ten SNs, CNAPs were composed of a succession of peaks corresponding to different conduction velocities.Significance.The reported sensitization effect could shed light on the mechanism underlying infrared neurostimulation. Our results suggest that, in sharp contrast with electrical stimuli, optical pulses could recruit slow fibres early on. This more physiological order of recruitment opens the perspective for specific neuromodulation of fibre population who remained poorly accessible until now. Short high-power light pulses at wavelengths below 1.5µm offer interesting perspectives for neurostimulation.

Optimizing thermal block length during infrared neural inhibition to minimize temperature thresholds

Objective. Infrared neural inhibition (INI) is a method of blocking the generation or propagation of neural action potentials through laser heating with wavelengths strongly absorbed by water. Recent work has identified that the distance heated along axons, the block length (BL), modulates the temperature needed for inhibition; however, this relationship has not been characterized. This study explores how BL during INI can be optimized towards minimizing its temperature threshold.Approach. To understand the relationship between BL and the temperature required for INI, excised nerves fromAplysia californicawere laser-heated over different lengths of axon during electrical stimulation of compound action potentials. INI was provided by irradiation (λ= 1470 nm) from a custom probe (n= 6 nerves), and subsequent validation was performed by providing heat block using perfused hot media over nerves (n= 5 nerves).Main Results. Two BL regimes were identified. Short BLs (thermal full width at half maximum (tFWHM) = 0.81-1.13 mm) demonstrated that increasing the tFWHM resulted in lower temperature thresholds for INI (p< 0.0125), while longer BLs (tFWHM = 1.13-3.03 mm) showed no significant change between the temperature threshold and tFWHM (p> 0.0125). Validation of this longer regime was performed using perfused hot media over different lengths of nerves. This secondary heating method similarly showed no significant change (p> 0.025) in the temperature threshold (tFWHM = 1.25-4.42 mm).Significance. This work characterized how the temperature threshold for neural heat block varies with BL and identified an optimal BL around tFWHM = 1.13 mm which minimizes both the maximum temperature applied to tissue and the volume of tissue heated during INI. Understanding how to optimally target lengths of nerve to minimize temperature during INI can help inform the design of devices for longitudinal animal studies and human implementation.

Fiberoptic array for multiple channel infrared neural stimulation of the brain

Significance: We present a new optical method for modulating cortical activity in multiple locations and across multiple time points with high spatial and temporal precision. Our method uses infrared light and does not require dyes or transgenic modifications. It is compatible with a number of other stimulation and recording techniques. Aim: Infrared neural stimulation (INS) has been largely confined to single point stimuli. In this study, we expand upon this approach and develop a rapidly switched fiber array capable of generation of stimulus patterns. Our prototype is capable of stimulating at nine separate locations but is easily scalable. Approach: Our device is made of commercially available components: a solid-state infrared laser, a piezoelectric fiber coupled optical switch, and 200 - μ m diameter optical fibers. We validate it using intrinsic optical signal imaging of INS responses in macaque and squirrel monkey sensory cortical areas. Results: We demonstrate that our switched array can consistently generate responses in primate cortex, consistent with earlier single channel INS investigations. Conclusions: Our device can successfully target the cortical surface, either at one specific region or multiple points spread out across different areas. It is compatible with a host of other imaging and stimulation modalities.

Shining light on cardiac electrophysiology: From detection to intervention, from basic research to translational applications

Cardiac arrhythmias are an important group of cardiovascular diseases, which can occur alone or in association with other cardiovascular diseases. The development of cardiac arrhythmias cannot be separated from changes in cardiac electrophysiology, and the investigation and clarification of cardiac electrophysiological changes are beneficial for the treatment of cardiac arrhythmias. However, electrical energy-based pacemakers and defibrillators, which are widely used to treat arrhythmias, still have certain disadvantages. Thereby, optics promises to be used for optical manipulation and its use in biomedicine is increasing. Since visible light is readily absorbed and scattered in living tissues and tissue penetration is shallow, optical modulation for cells and tissues requires conversion media that convert light energy into bioelectrical activity. In this regard, fluorescent dyes, light-sensitive ion channels, and optical nanomaterials can assume this role, the corresponding optical mapping technology, optogenetics technology, and optical systems based on luminescent nanomaterials have been introduced into the research in cardiovascular field and are expected to be new tools for the study and treatment of cardiac arrhythmias. In addition, infrared and near-infrared light has strong tissue penetration, which is one of the excellent options of external trigger for achieving optical modulation, and is also widely used in the study of optical modulation of biological activities. Here, the advantages of optical applications are summarized, the research progresses and emerging applications of optical-based technologies as detection and intervention tools for cardiac electrophysiological are highlighted. Moreover, the prospects for future applications of optics in clinical diagnosis and treatment are discussed.

Isotonic ion replacement can lower the threshold for selective infrared neural inhibition

Significance: Infrared (IR) inhibition can selectively block peripheral sensory nerve fibers, a potential treatment for autonomic-dysfunction-related diseases (e.g., neuropathic pain and interstitial cystitis). Lowering the IR inhibition threshold can increase its translational potentials. Aim: Infrared induces inhibition by enhancing potassium channel activation. We hypothesized that the IR dose threshold could be reduced by combining it with isotonic ion replacement. Approach: We tested the IR inhibition threshold on the pleural-abdominal connective of Aplysia californica. Using a customized chamber system, the IR inhibition was applied either in normal saline or in isotonic ion-replaced saline, which could be high glucose saline, high choline saline, or high glucose/high choline saline. Each modified saline was at a subthreshold concentration for inhibiting neural conduction. Results: We showed that isotonically replacing ions in saline with glucose and/or choline can reduce the IR threshold and temperature threshold of neural inhibition. Furthermore, the size selectivity of IR inhibition was preserved when combined with high glucose/high choline saline. Conclusions: The present work of IR inhibition combined with isotonic ion replacement will guide further development of a more effective size-selective IR inhibition modality for future research and translational applications.

Identifying optimal parameters for infrared neural stimulation in the peripheral nervous system

Significance: Infrared neural stimulation (INS) utilizes pulsed infrared light to selectively elicit neural activity without exogenous compounds. Despite its versatility in a broad range of biomedical applications, no comprehensive comparison of factors pertaining to the efficacy and safety of INS such as wavelength, radiant exposure, and optical spot size exists in the literature. Aim: Here, we evaluate these parameters using three of the wavelengths commonly used for INS, 1450 nm, 1875 nm, and 2120 nm. Approach: In an in vivo rat sciatic nerve preparation, the stimulation threshold and transition rate to 100% activation probability were used to compare the effects of each parameter. Results: The pulsed diode lasers at 1450 nm and 1875 nm had a consistently higher ( ∼ 1.0    J / cm 2 ) stimulation threshold than that of the Ho:YAG laser at 2120 nm ( ∼ 0.7    J / cm 2 ). In addition, the Ho:YAG produced a faster transition rate to 100% activation probability compared to the diode lasers. Our data suggest that the superior performance of the Ho:YAG is a result of the high-intensity microsecond spike at the onset of the pulse. Acute histological evaluation of diode irradiated nerves revealed a safe range of radiant exposures for stimulation. Conclusion: Together, our results identify measures to improve the safety, efficacy, and accessibility of INS technology for research and clinical applications.

Infrared neuromodulation:a neuroengineering perspective

Infrared neuromodulation (INM) is a branch of photobiomodulation that offers direct or indirect control of cellular activity through elevation of temperature in a spatially confined region of the target tissue. Research on INM started about 15 ago and is gradually attracting the attention of the neuroscience community, as numerous experimental studies have provided firm evidence on the safe and reproducible excitation and inhibition of neuronal firing in both in vitro and in vivo conditions. However, its biophysical mechanism is not fully understood and several engineered interfaces have been created to investigate infrared stimulation in both the peripheral and central nervous system. In this review, recent applications and present knowledge on the effects of INM on cellular activity are summarized, and an overview of the technical approaches to deliver infrared light to cells and to interrogate the optically evoked response is provided. The micro- and nanoengineered interfaces used to investigate the influence of INM are described in detail.

Live mechanistic assessment of localized cardiac pumping in mammalian tubular embryonic heart

SIGNIFICANCE

Understanding how the valveless embryonic heart pumps blood is essential to elucidate biomechanical cues regulating cardiogenesis, which is important for the advancement of congenital heart defects research. However, methods capable of embryonic cardiac pumping analysis remain limited, and assessing this highly dynamic process in mammalian embryos is challenging. New approaches are critically needed to address this hurdle.

AIM

We report an imaging-based approach for functional assessment of localized pumping dynamics in the early tubular embryonic mouse heart.

APPROACH

Four-dimensional optical coherence tomography was used to obtain structural and Doppler hemodynamic imaging of the beating heart in live mouse embryos at embryonic day 9.25. The pumping assessment was performed based on the volumetric blood flow rate, flow resistance within the heart tube, and pressure gradient induced by heart wall movements. The relation between the blood flow, the pressure gradient, and the resistance to flow were evaluated through temporal analyses and Granger causality test.

RESULTS

In the ventricles, our method revealed connections between the temporal profiles of pressure gradient and volumetric blood flow rate. Statistically significant causal relation from the pressure gradient to the blood flow was demonstrated. Our analysis also suggests that cardiac pumping in the early ventricles is a combination of suction and pushing. In contrast, in the outflow tract, where the conduction wave is slower than the blood flow, we did not find significant causal relation from pressure to flow, suggesting that, different from ventricular regions, the local active contraction of the outflow tract is unlikely to drive the flow in that region.

CONCLUSIONS

We present an imaging-based approach that enables localized assessment of pumping dynamics in the mouse tubular embryonic heart. This method creates a new opportunity for functional analysis of the pumping mechanism underlying the developing mammalian heart at early stages and could be useful for studying biomechanical changes in mutant embryonic hearts that model congenital heart defects.

Optical stimulation of neural tissue

Electrical stimulation has been used for decades in devices such as pacemakers, cochlear implants and more recently for deep brain and retinal stimulation and electroceutical treatment of disease. However, current spread from the electrodes limits the precision of neural activation, leading to a low quality therapeutic outcome or undesired side-effects. Alternative methods of neural stimulation such as optical stimulation offer the potential to deliver higher spatial resolution of neural activation. Direct optical stimulation is possible with infrared light, while visible light can be used to activate neurons if the neural tissue is genetically modified with a light sensitive ion channel. Experimentally, both methods have resulted in highly precise stimulation with little spread of activation at least in the cochlea, each with advantages and disadvantages. Infrared neural stimulation does not require modification of the neural tissue, but has very high power requirements. Optogenetics can achieve precision of activation with lower power, but only in conjunction with targeted insertion of a light sensitive ion channel into the nervous system via gene therapy. This review will examine the advantages and limitations of optical stimulation of neural tissue, using the cochlea as an exemplary model and recent developments for retinal and deep brain stimulation.

Remote nongenetic optical modulation of neuronal activity using fuzzy graphene

Modulation of cellular electrophysiology helps develop an understanding of cellular development and function in healthy and diseased states. We modulate the electrophysiology of neuronal cells in two-dimensional (2D) and 3D assemblies with subcellular precision via photothermal stimulation using a multiscale fuzzy graphene nanostructure. Nanowire (NW)-templated 3D fuzzy graphene (NT-3DFG) nanostructures enable remote, nongenetic photothermal stimulation with laser energies as low as subhundred nanojoules without generating cellular stress. NT-3DFG serves as a powerful toolset for studies of cell signaling within and between in vitro 3D models (human-based organoids and spheroids) and can enable therapeutic interventions.

The ability to modulate cellular electrophysiology is fundamental to the investigation of development, function, and disease. Currently, there is a need for remote, nongenetic, light-induced control of cellular activity in two-dimensional (2D) and three-dimensional (3D) platforms. Here, we report a breakthrough hybrid nanomaterial for remote, nongenetic, photothermal stimulation of 2D and 3D neural cellular systems. We combine one-dimensional (1D) nanowires (NWs) and 2D graphene flakes grown out-of-plane for highly controlled photothermal stimulation at subcellular precision without the need for genetic modification, with laser energies lower than a hundred nanojoules, one to two orders of magnitude lower than Au-, C-, and Si-based nanomaterials. Photothermal stimulation using NW-templated 3D fuzzy graphene (NT-3DFG) is flexible due to its broadband absorption and does not generate cellular stress. Therefore, it serves as a powerful toolset for studies of cell signaling within and between tissues and can enable therapeutic interventions.

Nano-enabled cellular engineering for bioelectric studies

Engineered cells have opened up a new avenue for scientists and engineers to achieve specialized biological functions. Nanomaterials, such as silicon nanowires and quantum dots, can establish tight interfaces with cells either extra- or intracellularly, and they have already been widely used to control cellular functions. The future exploration of nanomaterials in cellular engineering may reveal numerous opportunities in both fundamental bioelectric studies and clinic applications. In this review, we highlight several nanomaterials-enabled non-genetic approaches to fabricating engineered cells. First, we briefly review the latest progress in engineered or synthetic cells, such as protocells that create cell-like behaviors from nonliving building blocks, and cells made by genetic or chemical modifications. Next, we illustrate the need for non-genetic cellular engineering with semiconductors and present some examples where chemical synthesis yields complex morphology or functions needed for biointerfaces. We then provide discussions in detail about the semiconductor nanostructure-enabled neural, cardiac, and microbial modulations. We also suggest the need to integrate tissue engineering with semiconductor devices to carry out more complex functions. We end this review by providing our perspectives for future development in non-genetic cellular engineering.

Intravital imaging of host-parasite interactions in organs of the thoracic and abdominopelvic cavities

Infections with protozoan and helminthic parasites affect multiple organs in the mammalian host. Imaging pathogens in their natural environment takes a more holistic view on biomedical aspects of parasitic infections. Here, we focus on selected organs of the thoracic and abdominopelvic cavities most commonly affected by parasites. Parasitic infections of these organs are often associated with severe medical complications or have health implications beyond the infected individual. Intravital imaging has provided a more dynamic picture of the host-parasite interplay and contributed not only to our understanding of the various disease pathologies, but has also provided fundamental insight into the biology of the parasites.

Near-infrared light driven tissue-penetrating cardiac optogenetics via upconversion nanoparticles in vivo

This study determines whether near-infrared (NIR) light can drive tissue-penetrating cardiac optical control with upconversion luminescent materials. Adeno-associated virus (AAV) encoding channelrhodopsin-2 (ChR2) was injected intravenously to rats to achieve ChR2 expression in the heart. The upconversion nanoparticles (UCNP) NaYF4:Yb/Tm or upconversion microparticles (UCMP) NaYF4 to upconvert blue light were selected to fabricate freestanding polydimethylsiloxane films. These were attached on the ventricle and covered with muscle tissue. Additionally, a 980-nm NIR laser was programmed and illuminated on the film or the tissue. The NIR laser successfully captured ectopic paced rhythm in the heart, which displays similar manipulation characteristics to those triggered by blue light. Our results highlight the feasibility of tissue-penetration cardiac optogenetics by NIR and demonstrate the potential to use external optical manipulation for non-invasive or weakly invasive applications in cardiovascular diseases.

Identifying the Role of Block Length in Neural Heat Block to Reduce Temperatures During Infrared Neural Inhibition

BACKGROUND AND OBJECTIVES

The objective of this study is to assess the hypothesis that the length of axon heated, defined here as block length (BL), affects the temperature required for thermal inhibition of action potential propagation applied using laser heating. The presence of such a phenomenon has implications for how this technique, called infrared neural inhibition (INI), may be applied in a clinically safe manner since it suggests that temperatures required for therapy may be reduced through the proper spatial application of light. Here, we validate the presence of this phenomenon by assessing how the peak temperatures during INI are reduced when two different BLs are applied using irradiation from either one or two adjacent optical fibers.

STUDY DESIGN/MATERIALS AND METHODS

Assessment of the role of BL was carried out over two phases. First, a computational proof of concept was performed in the neural conduction simulation environment, NEURON, simulating the response of action potentials to increased temperatures applied at different full-width at half-maxima (FWHM) along axons. Second, ex vivo validation of these predictions was performed by measuring the radiant exposure, peak temperature rise, and FWHM of heat distributions associated with INI from one or two adjacent optical fibers. Electrophysiological assessment of radiant exposures at inhibition threshold were carried out in ex vivo Aplysia californica (sea slug) pleural abdominal nerves ( n = 6), an invertebrate with unmyelinated axons. Measurement of the maximum temperature rise required for induced heat block was performed in a water bath using a fine wire thermocouple. Finally, magnetic resonance thermometry (MRT) was performed on a nerve immersed in saline to assess the elevated temperature distribution at these radiant exposures.

RESULTS

Computational modeling in NEURON provided a theoretical proof of concept that the BL is an important factor contributing to the peak temperature required during neural heat block, predicting a 11.7% reduction in temperature rise when the FWHM along an axon is increased by 42.9%. Experimental validation showed that, when using two adjacent fibers instead of one, a 38.5 ± 2.2% (mean ± standard error of the mean) reduction in radiant exposure per pulse per fiber threshold at the fiber output (P = 7.3E-6) is measured, resulting in a reduction in peak temperature rise under each fiber of 23.5  ± 2.1% ( P = 9.3E-5) and 15.0 ± 2.4% ( P = 1.4E-3) and an increase in the FWHM of heating by 37.7 ± 6.4% ( P = 1E-3), 68.4 ± 5.2% ( P = 2.4E-5), and 51.9  ± 9.9% ( P = 1.7E-3) in three MRT slices.

CONCLUSIONS

This study provides the first experimental evidence for a phenomenon during the heat block in which the temperature for inhibition is dependent on the BL. While more work is needed to further reduce the temperature during INI, the results highlight that spatial application of the temperature rise during INI must be considered. Optimized implementation of INI may leverage this cellular response to provide optical modulation of neural signals with lower temperatures over greater time periods, which may increase the utility of the technique for laboratory and clinical use. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Infrared Laser Pulses Excite Action Potentials in Primary Cortex Neurons In Vitro

Infrared neural modulation (INM) has been well studied in the peripheral nervous system (PNS) for potential clinical applications. However, limited research has been conducted on the central nervous systems (CNS). In this study, we aimed at investigating the feasibility of using pulsed infrared (IR) laser with a wavelength of 1940 nm to excite network activity of cultivated rat cortex neurons.We cultured rat cortex neurons, forming neural networks with spontaneous neural activity, on glass multi-electrode arrays (MEAs). Laser at a power of 600 mW and a pulse rate of 10 Hz were used to stimulate the neural networks using the optics of an inverted microscope. Pulse durations were varied from 200 μs to 1 ms. The spike rate was calculated to evaluate the change of the neural network activity during the IR stimuli and the corresponding frequency components of neural response were calculated to examine whether recorded spikes were evoked by the IR pulse or not. A temperature model was adapted from a previous study to estimate the temperature rise during laser pulsing.We observed that the IR irradiation with a pulse duration of 800 μs and 1 ms could excite neuronal action potentials. The temperature rose 18.5 and 23.9 °C, for pulse durations of 800 μs and 1 ms, respectively. Thus, in addition to previously shown inhibition of IR irradiation with a wavelength of 1550 nm, we demonstrate an optical method that can modulate neural network activity in vitro. The preliminary results from this paper also suggested that MEA recording technology coupled with a laser and microscope systems can be exploited as a new approach for future studies to understand mechanisms and characterize laser parameters of INM for CNS neurons.

Feasibility of Using Adjunctive Optogenetic Technologies in Cardiomyocyte Phenotyping - from the Single Cell to the Whole Heart

In 1791, Galvani established that electricity activated excitable cells. In the two centuries that followed, electrode stimulation of neuronal, skeletal and cardiac muscle became the adjunctive method of choice in experimental, electrophysiological, and clinical arenas. This approach underpins breakthrough technologies like implantable cardiac pacemakers that we currently take for granted. However, the contact dependence, and field stimulation that electrical depolarization delivers brings inherent limitations to the scope and experimental scale that can be achieved. Many of these were not exposed until reliable in vitro stem-cell derived experimental materials, with genotypes of interest, were produced in the numbers needed for multi-well screening platforms (for toxicity or efficacy studies) or the 2D or 3D tissue surrogates required to study propagation of depolarization within multicellular constructs that mimic clinically relevant arrhythmia in the heart or brain. Here the limitations of classical electrode stimulation are discussed. We describe how these are overcome by optogenetic tools which put electrically excitable cells under the control of light. We discuss how this enables studies in cardiac material from the single cell to the whole heart scale. We review the current commercial platforms that incorporate optogenetic stimulation strategies, and summarize the global literature to date on cardiac applications of optogenetics. We show that the advantages of optogenetic stimulation relevant to iPS-CM based screening include independence from contact, elimination of electrical stimulation artefacts in field potential measuring approaches such as the multi-electrode array, and the ability to print re-entrant patterns of depolarization at will on 2D cardiomyocyte monolayers.

Infrared inhibition and waveform modulation of action potentials in the crayfish motor axon

The infrared (IR) inhibition of axonal activities in the crayfish neuromuscular preparation is studied using 2 µm IR light pulses with varying durations. The intracellular neuronal activities are monitored with two-electrode current clamp, while the IR-induced temperature changes are measured by the open patch technique simultaneously. It is demonstrated that the IR pulses can reversibly shape or block locally initiated action potentials. Suppression of the AP amplitude and duration and decrease in axonal excitability by IR pulses are quantitatively analyzed. While the AP amplitude and duration decrease similarly during IR illumination, it is discovered that the recovery of the AP duration after the IR pulses is slower than that of the AP amplitude. An IR-induced decrease in the input resistance (8.8%) is detected and discussed together with the temperature dependent changes in channel kinetics as contributing factors for the inhibition reported here.