Gene Electrotransfer via Conductivity-Clamped Electric Field Focusing Pivots Sensori-Motor DNA Therapeutics: "A Spoonful of Sugar Helps the Medicine Go Down".

Viral vectors and lipofection-based gene therapies have dispersion-dependent transduction/transfection profiles that thwart precise targeting. The study describes the development of focused close-field gene electrotransfer (GET) technology, refining spatial control of gene expression. Integration of fluidics for precise delivery of "naked" plasmid deoxyribonucleic acid (DNA) in sucrose carrier within the focused electric field enables negative biasing of near-field conductivity ("conductivity-clamping"-CC), increasing the efficiency of plasma membrane molecular translocation. This enables titratable gene delivery with unprecedently low charge transfer. The clinic-ready bionics-derived CC-GET device achieved neurotrophin-encoding miniplasmid DNA delivery to the cochlea to promote auditory nerve regeneration; validated in deafened guinea pig and cat models, leading to improved central auditory tuning with bionics-based hearing. The performance of CC-GET is evaluated in the brain, an organ problematic for pulsed electric field-based plasmid DNA delivery, due to high required currents causing Joule-heating and damaging electroporation. Here CC-GET enables safe precision targeting of gene expression. In the guinea pig, reporter expression is enabled in physiologically critical brainstem regions, and in the striatum (globus pallidus region) delivery of a red-shifted channelrhodopsin and a genetically-encoded Ca2+ sensor, achieved photoactivated neuromodulation relevant to the treatment of Parkinson's Disease and other focal brain disorders.

Impedance Properties of Multi-Optrode Biopotential Sensing Arrays.

Recording and monitoring electrically-excitable cells is critical to understanding the complex cellular networking within organs as well as the processes underlying many electro-physiological pathologies. Biopotential recording using an optical-electrode (optrode) is a novel approach which has potential to significantly improve interface-instrumentation impedance mismatching as recording contact-sizes become smaller and smaller. Optrodes incorporate a conductive interface that can sense extracellular potential and an underlying layer of liquid crystals that passively transduces electrical signals into measurable optical signals. This study investigates the impedance properties of this optical technology by varying the diameter of recording sites and observing the corresponding changes in the impedance values. The results show that the liquid crystals in this optrode platform exhibit input impedance values (1 MΩ - 100 GΩ) that are three orders of magnitude higher than the corresponding interface impedance, which is appropriate for voltage sensing. The automatic scaling of the input impedance enabled within the optrode system maintains a relatively constant ratio between input and total system impedance of about one for sensing areas with diameters ranging from 40 µm to 1 mm, at which the calculated signal loss is predicted to be <1%. This feature preserves the interface-transducer impedance ratio, regardless of the size of the recording site, allowing development of passive optrode arrays capable of very high spatial-resolution recordings.

Electromechanical Stability and Transmission Behavior of Transparent Conductive Films for Biomedical Optoelectronic Devices.

The application of transparent conductive films to flexible biomedical optoelectronics is limited by stringent requirements on the candidate materials' electromechanical and optical properties as well as their biological performance. Thin films of graphene and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are sought as mechanically flexible alternatives to traditional indium tin oxide (ITO). However, they require more understanding of their suitability for biomedical optoelectronic devices in terms of transmission behavior and electromechanical stability. This study shows that the relative increase in sheet resistance under cyclic loading for ITO, graphene, and PEDOT:PSS was 3546±3908%,12±2.7%, and 62±68%, respectively. Moreover, graphene and PEDOT:PSS showed a transmission uniformity of 9.3% and 36.3% (380-2000 nm), respectively, compared with ITO film (61%). Understanding the optical, electrical, and mechanical limits of the transparent conductive films facilitates the optimization of flexible optoelectronic designs to fit multiple biomedical research and clinical applications.

Computational Modelling of the Effect of Infarct Stiffness on Regional Myocardial Mechanics.

Ventricular remodeling after myocardial infarction increases the rate of mortality and is highly associated with the extent of infarct transmurality. It is hypothesized that infarct stiffness alters regional mechanics and affects the likelihood of human ventricular remodeling. However, this is yet to be studied in detail. In this paper, we present simulations from an actively-contracting left ventricular model to investigate the effects of transmural infarct stiffness on myofiber regional mechanics. Results show that higher infarct stiffness reduces systolic stress at the infarct and border zones, minimizing infarct bulging but increasing the diastolic stress at the endocardial border zone. Determining a proper amount of infarct stiffness is required to achieve a balanced regional mechanics across the cardiac cycle that may be useful in therapy, such as myocardial hydrogel injection to adjust its stiffness and reduce stress to prevent ventricular remodeling.

A Multi-Domain Continuum Model of Electrical Stimulation of Healthy and Degenerate Retina.

A continuum multi-domain model of electrical stimulation of the retina is presented and validated against retinal ganglion cell (RGC) excitation thresholds reported in a recently published in vitro experimental study. We applied our model to investigate the response of the RGC layer to electrical stimulation during mid-to-late stage retinal degeneration for both epiretinal and suprachoroidal configurations. Interestingly, our model predicted that suprachoroidal stimulation of the degenerate retina required increased current thresholds, mainly because of the presence of the glial scar layer. In contrast, epiretinal stimulation thresholds were almost similar for both healthy and degenerate models. The latter finding implies that there is no influence of the glial scar layer on epiretinal stimulation current thresholds.

Computational Simulation of Array-based Electroporation in the Cochlea.

We present a computational model for predicting electric field distributions following array-based closed-loop electroporation in the cochlea. The model geometry was reconstructed from magnetic resonance images of the guinea pig cochlea and an eight-channel electrode array embedded within this geometry. The model's electrode voltage output waveform was obtained from electric potential mapping conducted in physiological solution following constant-current stimulation using the electrode array. Our simulations predict that a tandem electrode configuration with four ganged cathodes and four ganged anodes produces a larger area in target tissue where the electric field is within the range for successful gene transfer compared to an alternate paired anode-cathode electrode configuration. These findings corroborate published in vivo evidence comparing the two configurations and support the utility of the developed model as a tool to optimize the efficacy of electroporation electrodes.

High-amplitude electrical stimulation can reduce elicited neuronal activity in visual prosthesis.

Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of visual prostheses. As the conveyance of representation of complex visual scenes may require neighbouring electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high stimulating conditions in visual prostheses: (1) in vivo, using a suprachoroidal prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the stimulating electrode) being inhibited at certain stimulating amplitudes, whilst other groups (far from the stimulating electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.

Sensitivity analysis of left ventricle with dilated cardiomyopathy in fluid structure simulation.

Dilated cardiomyopathy (DCM) is the most common myocardial disease. It not only leads to systolic dysfunction but also diastolic deficiency. We sought to investigate the effect of idiopathic and ischemic DCM on the intraventricular fluid dynamics and myocardial wall mechanics using a 2D axisymmetrical fluid structure interaction model. In addition, we also studied the individual effect of parameters related to DCM, i.e. peak E-wave velocity, end systolic volume, wall compliance and sphericity index on several important fluid dynamics and myocardial wall mechanics variables during ventricular filling. Intraventricular fluid dynamics and myocardial wall deformation are significantly impaired under DCM conditions, being demonstrated by low vortex intensity, low flow propagation velocity, low intraventricular pressure difference (IVPD) and strain rates, and high-end diastolic pressure and wall stress. Our sensitivity analysis results showed that flow propagation velocity substantially decreases with an increase in wall stiffness, and is relatively independent of preload at low-peak E-wave velocity. Early IVPD is mainly affected by the rate of change of the early filling velocity and end systolic volume which changes the ventriculo:annular ratio. Regional strain rate, on the other hand, is significantly correlated with regional stiffness, and therefore forms a useful indicator for myocardial regional ischemia. The sensitivity analysis results enhance our understanding of the mechanisms leading to clinically observable changes in patients with DCM.

A generic ionic model of cardiac action potentials.

A generic cardiac ionic model employing membrane currents based on two-gate Hodgkin-Huxley kinetics is presented. Its generic nature allows it to accurately reproduce action potential waveforms in heterogeneous cardiac tissue by optimizing parameters governing ion channel kinetics and magnitudes. The model allows a user-defined number of voltage and time-dependent ion currents to be incorporated, in order to reproduce and predict electrophysiological action potential waveforms from multiple recordings in individual cardiac myocytes.

An anatomically realistic 3d model of atrial propagation based on experimentally recorded action potentials.

A three-dimensional anatomically and electro-physiologically realistic model of atrial propagation is developed utilizing generic cardiac ionic models fitted to experimentally recorded action potentials (APs). The atrial geometry incorporated realistic wall thickness and twelve anatomical structures, including the sino-atrial node (SAN), pulmonary veins, interatrial septum, Bachmann's bundle and coronary sinus as interatrial conduction pathways. The SAN was further subdivided into central and peripheral regions, characterized by different ionic parameters. These parameters were obtained by optimizing ionic models to fit spontaneous APs recorded intracellularly from intact rabbit in vitro sino-atrial tissue preparations. The SAN region in the 3D model was able to initiate spontaneous rhythmic APs and excite the surrounding atrium. The pattern of atrial activation was similar to that observed in humans. The use of model optimization allows direct incorporation of experimental data into anatomically realistic geometries and is a step towards developing patient-specific models for the treatment of atrial arrhythmias.

A morphologically realistic shell model of atrial propagation and ablation.

A three dimensional morphologically realistic model of atrial propagation is developed, based on the male Visible Human dataset and the Fitzhugh-Nagumo equations for cardiac excitation. The atrial shell geometry incorporates eleven different anatomical structures, including the pulmonary veins, and the septum, Bachmann's bundle and coronary sinus as interatrial conduction pathways. Although the model utilizes a simplified cellular model of cardiac excitation it is able to reproduce a variety of electrophysiological phenomena including: autorhythmicity of the sinoatrial node and its ability to excite surrounding atrial tissue, spiral re-entrant wavefronts, ectopic beats originating in the PV and their termination by circumferential ablation of the PV. The model is an important tool to quantitatively study atrial excitation under normal conditions and during atrial fibrillation.