Direct coupled electrical stimulation towards improved osteogenic differentiation of human mesenchymal stem/stromal cells: a comparative study of different protocols.

Electrical stimulation (ES) has been described as a promising tool for bone tissue engineering, being known to promote vital cellular processes such as cell proliferation, migration, and differentiation. Despite the high variability of applied protocol parameters, direct coupled electric fields have been successfully applied to promote osteogenic and osteoinductive processes in vitro and in vivo. Our work aims to study the viability, proliferation, and osteogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells when subjected to five different ES protocols. The protocols were specifically selected to understand the biological effects of different parts of the generated waveform for typical direct-coupled stimuli. In vitro culture studies evidenced variations in cell responses with different electric field magnitudes (numerically predicted) and exposure protocols, mainly regarding tissue mineralization (calcium contents) and osteogenic marker gene expression while maintaining high cell viability and regular morphology. Overall, our results highlight the importance of numerical guided experiments to optimize ES parameters towards improved in vitro osteogenesis protocols.

JANUS: an open-source 3D printable perfusion bioreactor and numerical model-based design strategy for tissue engineering.

Bioreactors have been employed in tissue engineering to sustain longer and larger cell cultures, managing nutrient transfer and waste removal. Multiple designs have been developed, integrating sensor and stimulation technologies to improve cellular responses, such as proliferation and differentiation. The variability in bioreactor design, stimulation protocols, and cell culture conditions hampered comparison and replicability, possibly hiding biological evidence. This work proposes an open-source 3D printable design for a perfusion bioreactor and a numerical model-driven protocol development strategy for improved cell culture control. This bioreactor can simultaneously deliver capacitive-coupled electric field and fluid-induced shear stress stimulation, both stimulation systems were validated experimentally and in agreement with numerical predictions. A preliminary in vitro validation confirmed the suitability of the developed bioreactor to sustain viable cell cultures. The outputs from this strategy, physical and virtual, are openly available and can be used to improve comparison, replicability, and control in tissue engineering applications.

How the Number and Distance of Electrodes Change the Induced Electric Field in the Cortex during Multichannel tDCS.

Multichannel transcranial direct current stimulation (tDCS) is a promising approach to target neuromodulation of neural networks by making use of variable number of electrodes and distances to facilitate/inhibit specific connectivity patterns. Optimization of the electric field (EF) spatial distribution through computational models can provide a more accurate definition of the stimulation settings that are more effective. In this study, we investigate the effect of increasing the number of cathodes around a central anode placed over the target. We demonstrate that anode-cathode distance has the largest influence in the EF and using more than 3 cathodes did not result in considerable changes in the EF magnitude and direction. This could be relevant for simultaneous tDCS-electroencephalography (EEG) applications, by saving electrode positions for EEG acquisition. Clinical Relevance- This study demonstrates that distance between electrodes is more relevant than electrode number in determining the electric field distribution, and that a highly-focused stimulation can be equally effective with fewer electrodes.

Respiratory function tests in amyotrophic lateral sclerosis: The role of maximal voluntary ventilation.

BACKGROUND: Pulmonary function tests are routinely used to measure progression in ALS. This study aimed to assess the change of various respiratory tests, in particular maximal voluntary ventilation (MVV), which evaluates respiratory endurance. METHODS: A group of 51 patients were assessed 3 times (T1, T2, T3, separated by 5.4 months), including slow (SVC) and forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow (PEF), maximal inspiratory (MIP) and expiratory (MEP) pressures, MVV, and sniff nasal inspiratory pressure (SNIP). In addition, body mass index (BMI), ALSFRS-R and phrenic nerve responses were obtained 4 times. Patients with dementia and marked bulbar involvement were excluded. RESULTS: Mean ALSFRS-R was high at entry (42.9) and its decline was moderately slow at 0.4/month. FVC and FEV1 declined significantly in the three time frames analysed. MVV reduced significantly only between T1-T3 and SVC between T2-T3, and MIP, MEP, PEF and SNIP did not change significantly. The amplitude and the latency of the motor response of the phrenic nerve changed significantly, and BMI declined significantly in most time periods, and ALSFRS-R changed significantly in the 4 time periods. We found a strong correlation between MVV, and FVC, SVC, FEV1, SNIP, phrenic nerve amplitude/area (p < 0.001), and markedly with PEF (rho = 0.821) and ALSFRS-R (rho = 0.713). CONCLUSIONS: Our study of early affected patients supports the use of a set of volitional and non-volitional respiratory tests to assess disease progression, rather than any single test. We found MVV a potentially useful marker of pulmonary function in ALS.

Effects of Scaffold Electrical Properties on Electric Field Delivery in Bioreactors.

In tissue engineering, cell culture scaffolds have been widely used in combination with electrical stimulation to promote multiple cellular outcomes, like differentiation and proliferation. Nevertheless, the influence of scaffolds on the electric field delivered inside a bioreactor is often ignored and requires a deeper study. By performing numerical analysis in a capacitively coupled setup, this work aimed to predict the effects of the scaffold presence on the electric field, considering multiple combinations of scaffold and culture medium electrical properties. We concluded that the effect of the scaffold on the electric field in the surrounding culture medium was determined by the difference in electrical conductivity of these two materials. The numerical simulations pointed to significant variations in local electric field patterns, which could lead to different cellular outcomes and confound the interpretation of the experimental results.

Transcutaneous spinal direct current stimulation of the lumbar and sacral spinal cord: a modelling study.

OBJECTIVE: Our aim was to perform a computational study of the electric field (E-field) generated by transcutaneous spinal direct current stimulation (tsDCS) applied over the thoracic, lumbar and sacral spinal cord, in order to assess possible neuromodulatory effects on spinal cord circuitry related with lower limb functions. APPROACH: A realistic volume conductor model of the human body consisting of 14 tissues was obtained from available databases. Rubber pad electrodes with a metallic connector and a conductive gel layer were modelled. The finite element (FE) method was used to calculate the E-field when a current of 2.5 mA was passed between two electrodes. The main characteristics of the E-field distributions in the spinal grey matter (spinal-GM) and spinal white matter (spinal-WM) were compared for seven montages, with the anode placed either over T10, T8 or L2 spinous processes (s.p.), and the cathode placed over right deltoid (rD), umbilicus (U) and right iliac crest (rIC) areas or T8 s.p. Anisotropic conductivity of spinal-WM and of a group of dorsal muscles near the vertebral column was considered. MAIN RESULTS: The average E-field magnitude was predicted to be above 0.15 V m-1 in spinal cord regions located between the electrodes. L2-T8 and T8-rIC montages resulted in the highest E-field magnitudes in lumbar and sacral spinal segments (>0.30 V m-1). E-field longitudinal component is 3 to 6 times higher than the ventral-dorsal and right-left components in both the spinal-GM and WM. Anatomical features such as CSF narrowing due to vertebrae bony edges or disks intrusions in the spinal canal correlate with local maxima positions. SIGNIFICANCE: Computational modelling studies can provide detailed information regarding the electric field in the spinal cord during tsDCS. They are important to guide the design of clinical tsDCS protocols that optimize stimulation of application-specific spinal targets.

Optimizing Electric-Field Delivery for tDCS: Virtual Humans Help to Design Efficient, Noninvasive Brain and Spinal Cord Electrical Stimulation.

Noninvasive electrical stimulation of the central nervous system is attracting increasing interest from the clinical and academic communities as well as from high-tech companies. This interest was sparked by two landmark studies conducted in 2000 and 2001 at the University of G?ttingen, Germany. Michael Nitsche and Walter Paulus showed that by passing a weak, almost imperceptible electric current between two electrodes on the scalp, they could alter the way the human brain responds to stimuli and that the effect persisted for some time after the current was stopped. These findings opened the prospect of therapeutic applications of transcranial direct-current stimulation (tDCS).

The effect of inter-electrode distance on the electric field distribution during transcutaneous lumbar spinal cord direct current stimulation.

Previous studies have indicated potential neuromodulation of the spinal circuitry by transcutaneous spinal direct current stimulation (tsDCS), such as changes in motor unit recruitment, shortening of the peripheral silent period and interference with supraspinal input to lower motor neurons. All of these effects were dependent on the polarity of the electrodes. The present study investigates how the distance between the electrodes during tsDCS influences the electric field's (E-field) spatial distribution in the lumbar and sacral spinal cord (SC). The electrodes were placed longitudinally along the SC, with the target electrode over the lumbar spine, and the return electrode above the former, considering four different distances (4, 8, 12 and 16 cm from the target). A fifth configuration was also tested with the return electrode over the right deltoid muscle. Peak values of the E-field's magnitude are found in the lumbo-sacral region of the SC for all tested configurations. Increasing the distance between the electrodes results in a wider spread of the E-field magnitude distribution along the SC, with larger maximum peak values and a smoother variation. The fifth configuration does not present the highest maximum values when compared to the other configurations. The results indicate that the choice of the return electrode position relative to the target can influence the distribution and the range of values of the E-field magnitude in the SC. Possible clinical significance of the observed effects will be discussed.

Evaluation of the electric field in the brain during transcranial direct current stimulation: A sensitivity analysis.

The use of computational modeling studies accounts currently for the best approach to predict the electric field (E-field) distribution in transcranial direct current stimulation. As with any model, the values attributed to the physical properties, namely the electrical conductivity of the tissues, affect the predicted E-field distribution. A wide range of values for the conductivity of most tissues is reported in the literature. In this work, we used the finite element method to compute the E-field induced in a realistic human head model for two electrode montages targeting the left dorso-lateral prefrontal cortex (DLPFC). A systematic analysis of the effect of different isotropic conductivity profiles on the E-field distribution was performed for the standard bipolar 7×5 cm2 electrodes configuration and also for an optimized multielectrode montage. Average values of the E-field's magnitude, normal and tangential components were calculated in the target region in the left DLPFC. Results show that the field decreases with increasing scalp, cerebrospinal fluid (CSF) and grey matter (GM) conductivities, while the opposite is observed for the skull and white matter conductivities. The tissues whose conductivity most affects the E-field in the cortex are the scalp and the CSF, followed by the GM and the skull. Uncertainties in the conductivity of individual tissues may affect electric field values by up to about 80%.

Investigating an alternative ring design of transducer arrays for tumor treating fields (TTFields).

Tumor treating fields (TTFields) is a therapy that inhibits cell proliferation and has been approved by the U.S Food and Drug Administration (FDA) for the treatment of Glioblastoma Multiforme. This anti-mitotic technique works non-invasively and regionally, and is associated with less toxicity and a better quality of life. Currently a device called Optune™ is clinically used which works with two perpendicular and alternating array pairs each consisting of 3×3 transducers. The aim of this study is to investigate a theoretical alternative array design which consists of two rings of 16 transducers and thus permits various field directions. A realistic human head model with isotropic tissues was used to simulate the electric field distribution induced by the two types of array layouts. One virtual tumour was modelled as a sphere in the white matter close to one lateral ventricle. Four alternative ring design directions were evaluated by activating arrays of 2×2 transducers on opposite sides of the head. The same amount of current was passed through active transducer arrays of the Optune system and the ring design. The electric field distribution in the brain differs for the various array configurations, with higher fields between activated transducer pairs and lower values in distant areas. Nonetheless, the average electric field strength values in the tumour are comparable for the various configurations. Values between 1.00 and 1.91 V/cm were recorded, which are above the threshold for effective treatment. Increasing the amount of field directions could possibly also increase treatment efficacy, because TTFields' effect on cancer cells is highest when the randomly distributed cell division axis is aligned with the field. The results further predict that slightly changing transducer positions only has a minor effect on the electric field. Thus patients might have some freedom to adjust array positions without major concern for treatment efficacy.

Influence of electrode configuration on the electric field distribution during transcutaneous spinal direct current stimulation of the cervical spine.

Transcutaneous spinal direct current stimulation (tsDCS) is a recent technique with promising neuromodulatory effects on spinal neuronal circuitry. The main objective of the present study was to perform a finite element analysis of the electric field distribution in tsDCS in the cervical spine region, with varying electrode configurations and geometry. A computational model of a human trunk was generated with nine tissue meshes. Three electrode configurations were tested: A) rectangular saline-soaked sponge target and return electrodes placed over C3 and T3 spinous processes, respectively; B1) circular saline-soaked sponge target and return electrodes placed over C7 spinous process and right deltoid muscle, respectively; B2) same configuration as B1, considering circular shaped electrodes with sponge and rubber layers and a small circular connector on the top surface. The electric field distribution for cervical tsDCS predicted higher magnitude in configurations B1 and B2, reaching a maximum of 0.71 V/m in the spinal white matter and 0.43 V/m in the spinal grey matter, with values above 0.15 V/m in the region of the spinal circuits related with upper limb innervation. In configuration A, the values were found to be <; 0.15 V/m through the entire spinal cord. Electric fields with magnitude above 0.15 V/m are thought to be effective in neuromodulation of the human cerebral cortex, so the configurations B1 and B2 could be an optimal choice for cervical tsDCS protocols. Computational studies using realistic models may be a powerful tool to predict physical effects of tsDCS on the cervical spinal cord and to optimize electrode placement focused on specific neurologic patient needs related with upper limb function.

Computational models of non-invasive brain and spinal cord stimulation.

Non-invasive brain and spinal cord stimulation techniques are increasingly used for diagnostic and therapeutic purposes. Knowledge of the spatial distribution of the induced electric field is necessary to interpret experimental results and to optimize field delivery. Since the induced electric field cannot be measured in vivo in humans, computational models play a fundamental role in determining the characteristics of the electric field. We produced computational models of the head and trunk to calculate the electric field induced in the brain and spinal cord by transcranial magnetic stimulation, transcranial direct current stimulation and transcutaneous spinal cord direct current stimulation. The field distribution is highly non-uniform and depends on the type of technique used, on the position of the stimulation sources, and on anatomy. In future these models may be improved by using more accurate and precise values for the physical parameters as they become available, by combining them with neuronal models to predict the outcome of stimulation, and by better segmentation and meshing techniques that make producing individual models practicable.