A streptavidin-biotin system combined with magnetic actuators for remote neuronal guidance

The ability to control neuronal mobility and organization is of great importance in developing neuronal interfaces and novel therapeutic approaches. An emerging promising method is the manipulation of neuronal cells from afar via magnetic forces. Nevertheless, using magnetic iron oxide nanoparticles as internal actuators may lead to biotoxicity, adverse influence on intracellular processes, and thus requires prerequisite considerations for therapeutic approaches. Magnetizing the cells via the incorporation of magnetic particles that can be applied extracellularly is advantageous. Herein, we have developed a magnetic system based on streptavidin-biotin interaction to decorate cellular membrane with magnetic elements. In this model, superparamagnetic microparticles, coated with streptavidin, were specifically bound to biotinylated PC12 cells. We demonstrated that cell movement can be directed remotely by the forces produced by pre-designed magnetic fields. First, using time lapse imaging, we analyzed the kinetics of cell migration towards the higher flux zone. Next, to form organized networks of cells we designed and fabricated micro-patterned magnetic devices. The fabricated devices were composed of a variety of ferromagnetic shapes, sputter-deposited onto glass substrates. Cells that were conjugated to the magnetic particles were plated atop the micro-patterned substrates, attracted to the magnetic actuators and became fixed onto the magnetic patterns. In all, our study presents a novel system based on a well-known molecular technology combined with nanotechnology that may well lead to the expansion of implantable magnetic actuators to organize and direct cellular growth.

Controlled synthesis of multifunctional dome-shaped micro- and nano-structures by a robust physical route for biological applications

Micro- and Nano-particles are elemental for many current and developing technologies. Specifically, these particles are being extensively used in biological studies and applications, including imaging, drug delivery and therapeutics. Recent...

Remote photonic sensing of action potential in mammalian nerve cells via histogram-based analysis of temporal spatial acoustic vibrations

Label free and remote action potential detection in neurons can be of great importance in the neuroscience research field. This paper presents a novel label free imaging modality based on the detection of temporal vibrations of speckle patterns illuminating the sample. We demonstrated the feasibility of detecting action potentials originating from spontaneous and stimulated activity in cortical cell culture. The spatiotemporal vibrations of isolated cortical cells were extracted by illuminating the culture with a laser beam while the vibrations of the random back scattered secondary speckle patterns are captured by a camera. The postulated action potentials were estimated following correlation-based analysis on the captured vibrations, where the variance deviation of the signal from a Gaussian distribution is directly associated with the action potential events. The technique was validated in a series of experiments in which the optical signals were acquired concurrently with microelectrode array (MEA) recordings. Our results demonstrate the ability of detecting action potential events in mammalian cells remotely via extraction of acoustic vibrations.

A predictive model for personalization of nanotechnology-based phototherapy in cancer treatment

A major challenge in radiation oncology is the prediction and optimization of clinical responses in a personalized manner. Recently, nanotechnology-based cancer treatments are being combined with photodynamic therapy (PDT) and photothermal therapy (PTT). Predictive models based on machine learning techniques can be used to optimize the clinical setup configuration, including such parameters as laser radiation intensity, treatment duration, and nanoparticle features. In this article we demonstrate a methodology that can be used to identify the optimal treatment parameters for PDT and PTT by collecting data from in vitro cytotoxicity assay of PDT/PTT-induced cell death using a single nanocomplex. We construct three machine learning prediction models, employing regression, interpolation, and low- degree analytical function fitting, to predict the laser radiation intensity and duration settings that maximize the treatment efficiency. To examine the accuracy of these prediction models, we construct a dedicated dataset for PDT, PTT, and a combined treatment; this dataset is based on cell death measurements after light radiation treatment and is divided into training and test sets. The preliminary results show that the performance of all three models is sufficient, with death rate errors of 0.09, 0.15, and 0.12 for the regression, interpolation, and analytical function fitting approaches, respectively. Nevertheless, due to its simple form, the analytical function method has an advantage in clinical application and can be used for further analysis of the sensitivity of performance to the treatment parameters. Overall, the results of this study form a baseline for a future personalized prediction model based on machine learning in the domain of combined nanotechnology- and phototherapy-based cancer treatment.

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

Fabrication of Magnetic Platforms for Micron-Scale Organization of Interconnected Neurons

The ability to direct neurons into organized neural networks has great implications for regenerative medicine, tissue engineering, and bio-interfacing. Many studies have aimed at directing neurons using chemical and topographical cues. However, reports of organizational control on a micron-scale over large areas are scarce. Here, an effective method has been described for placing neurons in preset sites and guiding neuronal outgrowth with micron-scale resolution, using magnetic platforms embedded with micro-patterned, magnetic elements. It has been demonstrated that loading neurons with magnetic nanoparticles (MNPs) converts them into sensitive magnetic units that can be influenced by magnetic gradients. Following this approach, a unique magnetic platform has been fabricated on which PC12 cells, a common neuron-like model, were plated and loaded with superparamagnetic nanoparticles. Thin films of ferromagnetic (FM) multilayers with stable perpendicular magnetization were deposited to provide effective attraction forces toward the magnetic patterns. These MNP-loaded PC12 cells, plated and differentiated atop the magnetic platforms, were preferentially attached to the magnetic patterns, and the neurite outgrowth was well aligned with the pattern shape, forming oriented networks. Quantitative characterization methods of the magnetic properties, cellular MNP uptake, cell viability, and statistical analysis of the results are presented. This approach enables the control of neural network formation and improves neuron-to-electrode interface through the manipulation of magnetic forces, which can be an effective tool for in vitro studies of networks and may offer novel therapeutic biointerfacing directions.

Patterning of Particles and Live Cells at Single Cell Resolution

The ability to manipulate and selectively position cells into patterns or distinct microenvironments is an important component of many single cell experimental methods and biological engineering applications. Although a variety of particles and cell patterning methods have been demonstrated, most of them deal with the patterning of cell populations, and are either not suitable or difficult to implement for the patterning of single cells. Here, we describe a bottom-up strategy for the micropatterning of cells and cell-sized particles. We have configured a micromanipulator system, in which a pneumatic microinjector is coupled to a holding pipette capable of physically isolating single particles and cells from different types, and positioning them with high accuracy in a predefined position, with a resolution smaller than 10 µm. Complementary DNA sequences were used to stabilize and hold the patterns together. The system is accurate, flexible, and easy-to-use, and can be automated for larger-scale tasks. Importantly, it maintains the viability of live cells. We provide quantitative measurements of the process and offer a file format for such assemblies.

Axonal Tree Morphology and Signal Propagation Dynamics Improve Interneuron Classification

Neurons are diverse and can be differentiated by their morphological, electrophysiological, and molecular properties. Current morphology-based classification approaches largely rely on the dendritic tree structure or on the overall axonal projection layout. Here, we use data from public databases of neuronal reconstructions and membrane properties to study the characteristics of the axonal and dendritic trees for interneuron classification. We show that combining signal propagation patterns observed by biophysical simulations of the activity along ramified axonal trees with morphological parameters of the axonal and dendritic trees, significantly improve classification results compared to previous approaches. The classification schemes introduced here can be utilized for robust neuronal classification. Our work paves the way for understanding and utilizing form-function principles in realistic neuronal reconstructions.

Large-scale acoustic-driven neuronal patterning and directed outgrowth

Acoustic manipulation is an emerging non-invasive method enabling precise spatial control of cells in their native environment. Applying this method for organizing neurons is invaluable for neural tissue engineering applications. Here, we used surface and bulk standing acoustic waves for large-scale patterning of Dorsal Root Ganglia neurons and PC12 cells forming neuronal cluster networks, organized biomimetically. We showed that by changing parameters such as voltage intensity or cell concentration we were able to affect cluster properties. We examined the effects of acoustic arrangement on cells atop 3D hydrogels for up to 6 days and showed that assembled cells spontaneously grew branches in a directed manner towards adjacent clusters, infiltrating the matrix. These findings have great relevance for tissue engineering applications as well as for mimicking architectures and properties of native tissues.

Magnetic Targeting of mTHPC To Improve the Selectivity and Efficiency of Photodynamic Therapy

Photodynamic therapy (PDT) is a promising recognized treatment for cancer. To date, PDT drugs are injected systemically, and the tumor area is irradiated to induce cell death. Current clinical protocols have several drawbacks, including limited accessibility to solid tumors and insufficient selectivity of drugs. Herein, we propose an alternative approach to improve PDT effectiveness by magnetic targeting of responsive carriers conjugated to the PDT drug. We coordinatively attached a meso-tetrahydroxyphenylchlorin (mTHPC) photosensitizer to Ce-doped-γ-Fe₂O₃ maghemite nanoparticles (MNPs). These MNPs are superparamagnetic and biocompatible, and the resulting mTHPC-MNPs nanocomposites are stable in aqueous suspensions. MDA-MB231 (human breast cancer) cells incubated with the mTHPC-MNPs showed high uptake and high death rates in cell population after PDT. The exposure to external magnetic forces during the incubation period directed the nanocomposites to selected sites enhancing drug accumulation that was double that of cells with no magnetic exposure. Next, breast cancer tumors were induced subcutaneously in mice and treated magnetically. In vivo results showed accelerated drug accumulation in tumors of mice injected with mTHPC-MNP nanocomposites, compared to the free drug. PDT irradiation led to a decrease in tumor size of both groups, whereas treatment with the focused magnetic nanocomposites led to significant tumor regression. Our results demonstrate a method to improve the current PDT treatments by applying magnetic forces to effectively direct the drug to cancerous tissue. This approach leads to a highly localized and effective PDT process, opening new directions for clinical PDT protocols.

Neuroprotective Effect of Nerve Growth Factor Loaded in Porous Silicon Nanostructures in an Alzheimer's Disease Model and Potential Delivery to the Brain

Nerve growth factor (NGF) plays a vital role in reducing the loss of cholinergic neurons in Alzheimer's disease (AD). However, its delivery to the brain remains a challenge. Herein, NGF is loaded into degradable oxidized porous silicon (PSiO₂ ) carriers, which are designed to carry and continuously release the protein over a 1 month period. The released NGF exhibits a substantial neuroprotective effect in differentiated rat pheochromocytoma PC12 cells against amyloid-beta (Aβ)-induced cytotoxicity, which is associated with Alzheimer's disease. Next, two potential localized administration routes of the porous carriers into murine brain are investigated: implantation of PSiO₂ chips above the dura mater, and biolistic bombardment of PSiO₂ microparticles through an opening in the skull using a pneumatic gene gun. The PSiO₂ -implanted mice are monitored for a period of 8 weeks and no inflammation or adverse effects are observed. Subsequently, a successful biolistic delivery of these highly porous microparticles into a live-mouse brain is demonstrated for the first time. The bombarded microparticles are observed to penetrate the brain and reach a depth of 150 µm. These results pave the way for using degradable PSiO₂ carriers as potential localized delivery systems for NGF to the brain.

Fluorescent metal-doped carbon dots for neuronal manipulations

There is a growing need for biocompatible nanocomposites that may efficiently interact with biological tissues through multiple modalities. Carbon dots (CDs) could serve as biocompatible fluorescence nanomaterials for targeted tissue/cell imaging. Important goals toward this end are to enhance the fluorescence quantum yields of the CDs and to increase their targetability to cells. Here, sonochemistry was used to develop a one-pot synthesis of CDs, including metal-doped CDs (M@CDs), demonstrating how various experimental parameters, such as sonication time, temperature, and power of sonication affect the size of the CDs (2-10 nm) and their fluorescence properties. The highest measured quantum yield of emission was ∼16%. Similarly, we synthesized CDs doped with different metals (M@CDs) including Ga, Sn, Zn, Ag, and Au. The interaction of M@CDs with neuron-like cells was examined and showed efficient uptake and low cytotoxicity. Moreover, the influence of the M@CDs on the improvement of neurites during initiation and elongation growth phases were compared with pristine CDs. Our research demonstrates the use of M@CDs for imaging and for neuronal interactions. The M@CD nanocomposites are promising due to their biocompatibility, photo-stability and potential selective affinity, paving the way for multifunctional biomedical applications.

Comparing Transcriptome Profiles of Neurons Interfacing Adjacent Cells and Nanopatterned Substrates Reveals Fundamental Neuronal Interactions

Developing neuronal axons are directed by chemical and physical signals toward a myriad of target cells. According to current dogma, the resulting network architecture is critically shaped by electrical interconnections, the synapses; however, key mechanisms translating neuronal interactions into neuronal growth behavior during network formation are still unresolved. To elucidate these mechanisms, we examined neurons interfacing nanopatterned substrates and compared them to natural interneuron interactions. We grew similar neuronal populations under three connectivity conditions, (1) the neurons are isolated, (2) the neurons are interconnected, and (3) the neurons are connected only to artificial substrates, then quantitatively compared both the cell morphologies and the transcriptome-expression profiles. Our analysis shows that whereas axon-guidance signaling pathways in isolated neurons are predominant, in isolated neurons interfacing nanotopography, these pathways are downregulated, similar to the interconnected neurons. Moreover, in nanotopography, interfacing neuron genes related to synaptogenesis and synaptic regulation are highly expressed, that is, again resembling the behavior of interconnected neurons. These molecular findings demonstrate that interactions with nanotopographies, although not leading to electrical coupling, play a comparable functional role in two major routes, neuronal guidance and network formation, with high relevance to the design of regenerative interfaces.

Designing Porous Silicon Films as Carriers of Nerve Growth Factor

Despite the great potential of NGF for treating neurodegenerative diseases, its therapeutic administration represents a significant challenge as the protein does not cross the blood-brain barrier, owing to its chemical properties, and thus requires long-term delivery to the brain to have a biological effect. This work describes fabrication of nanostructured PSi films as degradable carriers of NGF for sustained delivery of this sensitive protein. The PSi carriers are specifically tailored to obtain high loading efficacy and continuous release of NGF for a period of four weeks, while preserving its biological activity. The behavior of the NGF-PSi carriers as a NGF delivery system is investigated in vitro by examining their capability to induce neuronal differentiation and outgrowth of PC12 cells and dissociated DRG neurons. Cell viability in the presence of neat and NGF-loaded PSi carriers is evaluated. The bioactivity of NGF released from the PSi carriers is compared to the conventional treatment of repetitive free NGF administrations. PC12 cell differentiation is analyzed and characterized by the measurement of three different morphological parameters of differentiated cells; (i) the number of neurites extracting from the soma (ii) the total neurites' length and (iii) the number of branching points. PC12 cells treated with the NGF-PSi carriers demonstrate a profound differentiation throughout the release period. Furthermore, DRG neuronal cells cultured with the NGF-PSi carriers show an extensive neurite initiation, similar to neurons treated with repetitive free NGF administrations. The studied tunable carriers demonstrate the long-term implants for NGF release with a therapeutic potential for neurodegenerative diseases.

Magnetic Targeting of Growth Factors Using Iron Oxide Nanoparticles

Growth factors play an important role in nerve regeneration and repair. An attractive drug delivery strategy, termed “magnetic targeting”, aims to enhance therapeutic efficiency by directing magnetic drug carriers specifically to selected cell populations that are suitable for the nervous tissues. Here, we covalently conjugated nerve growth factor to iron oxide nanoparticles (NGF-MNPs) and used controlled magnetic fields to deliver the NGF–MNP complexes to target sites. In order to actuate the magnetic fields a modular magnetic device was designed and fabricated. PC12 cells that were plated homogenously in culture were differentiated selectively only in targeted sites out of the entire dish, restricted to areas above the magnetic “hot spots”. To examine the ability to guide the NGF-MNPs towards specific targets in vivo, we examined two model systems. First, we injected and directed magnetic carriers within the sciatic nerve. Second, we injected the MNPs intravenously and showed a significant accumulation of MNPs in mouse retina while using an external magnet that was placed next to one of the eyes. We propose a novel approach to deliver drugs selectively to injured sites, thus, to promote an effective repair with minimal systemic side effects, overcoming current challenges in regenerative therapeutics.

Frontline Science: Elevated nuclear lamin A is permissive for granulocyte transendothelial migration but not for motility through collagen I barriers

Transendothelial migration (TEM) of lymphocytes and neutrophils is associated with the ability of their deformable nuclei to displace endothelial cytoskeletal barriers. Lamin A is a key intermediate filament component of the nuclear lamina that is downregulated during granulopoiesis. When elevated, lamin A restricts nuclear squeezing through rigid confinements. To determine if the low lamin A expression by leukocyte nuclei is critical for their exceptional squeezing ability through endothelial barriers, we overexpressed this protein in granulocyte-like differentiated HL-60 cells. A 10-fold higher lamin A expression did not interfere with chemokinetic motility of these granulocytes on immobilized CXCL1. Furthermore, these lamin A high leukocytes exhibited normal chemotaxis toward CXCL1 determined in large pore transwell barriers, but poorly squeezed through 3 μm pores toward identical CXCL1 gradients. Strikingly, however, these leukocytes successfully completed paracellular TEM across inflamed endothelial monolayers under shear flow, albeit with a small delay in nuclear squeezing into their sub-endothelial pseudopodia. In contrast, CXCR2 mediated granulocyte motility through collagen I barriers was dramatically delayed by lamin A overexpression due to a failure of lamin A high nuclei to translocate into the pseudopodia of the granulocytes. Collectively, our data predict that leukocytes maintain a low lamin A content in their nuclear lamina in order to optimize squeezing through extracellular collagen barriers but can tolerate high lamin A content when crossing the highly adaptable barriers presented by the endothelial cytoskeleton.

Ultrafine Highly Magnetic Fluorescent γ-Fe2O3/NCD Nanocomposites for Neuronal Manipulations

In this work, we describe a low-cost, two-step synthesis of composites of nitrogen-doped carbon quantum dots (NCDs) with γ-Fe2O3 (NCDs/γ-Fe2O3), which is based on a hydrothermal cum co-precipitation method. The product is a fine powder of particles having an average diameter of 9 ± 3 nm. The physical and chemical properties of NCDs/γ-Fe2O3 were studied, as well as the superconducting quantum interference device and Mossbauer analysis of the magnetic properties of these nanocomposites. The interaction of NCDs/γ-Fe2O3 nanocomposites with neuron-like cells was examined, showing efficient uptake and low toxicity. Our research demonstrates the use of the nanocomposites for imaging and for controlling the cellular motility. The NCDs/γ-Fe2O3 nanocomposites are promising because of their biocompatibility, photostability, and potential selective affinity, paving the way for multifunctional biomedical applications.

meso-Tetrahydroxyphenylchlorin-Conjugated Gold Nanoparticles as a Tool To Improve Photodynamic Therapy

Photodynamic therapy (PDT) is a promising therapeutic modality for cancer. However, current protocols using bare drugs suffer from several limitations that impede its beneficial clinical effects. Here, we introduce a new approach for an efficient PDT treatment. It involves conjugating a PDT agent, meso-tetrahydroxyphenylchlorin (mTHPC) photosensitizer, to gold nanoparticles (AuNPs) that serve as carriers for the drug. AuNPs have a number of characteristics that make them highly suitable to function as drug carriers: they are biocompatible, serve as biomarkers, and function as contrast agents in vitro and in vivo. We synthesized AuNPs and covalently conjugated the mTHPC drug molecules through a linker. The resultant functional complex, AuNP-mTHPC, is a stable, soluble compound. SH-SY5Y human neuroblastoma cells were incubated with the complex, showing possible administration of higher doses of drug when conjugated to the AuNPs. Then cells were irradiated with a laser beam at 650 nm to mimic the PDT procedure. Our study shows higher rates of cell death in cells incubated with the AuNP-mTHPC complex compared to the incubation with the free drug. Using the new complex may form the basis for a better PDT strategy for a wide range of cancers.

Topographical impact of silver nanolines on the morphology of neuronal SH-SY5Y Cells

An extracellular environment is critical in neuronal development and growth. Changes in neuronal morphology, neuron adhesion, and even the rate of neurite formation, can be modified by both the chemical and physical properties of interfacing substrates. Topography has a major impact on neuronal growth. Neuronal behavior and morphology are affected by the size, shape and pattern of the topographic elements. Combining topography with active materials may lead to enhanced influence. This paper demonstrates the effects of silver nanolines (AgNLs) on the growth pattern of SH-SY5Y cells. The morphology of the cells atop the nanotopographical substrates is measured, revealing a significant promoting effect. The number of neurites initiating from the soma is larger in SH-SY5Y cells plated on AgNLs than in control samples. The cells also exhibit an increase in neurite branching points towards more complex structures. These results indicate that substrates decorated with nanotopography affect cellular growth in a way that may be useful for enhanced regeneration, opening new possibilities for electrode and implant design.

Branching morphology determines signal propagation dynamics in neurons

Computational modeling of signal propagation in neurons is critical to our understanding of basic principles underlying brain organization and activity. Exploring these models is used to address basic neuroscience questions as well as to gain insights for clinical applications. The seminal Hodgkin Huxley model is a common theoretical framework to study brain activity. It was mainly used to investigate the electrochemical and physical properties of neurons. The influence of neuronal structure on activity patterns was explored, however, the rich dynamics observed in neurons with different morphologies is not yet fully understood. Here, we study signal propagation in fundamental building blocks of neuronal branching trees, unbranched and branched axons. We show how these simple axonal elements can code information on spike trains, and how asymmetric responses can emerge in axonal branching points. This asymmetric phenomenon has been observed experimentally but until now lacked theoretical characterization. Together, our results suggest that axonal morphological parameters are instrumental in activity modulation and information coding. The insights gained from this work lay the ground for better understanding the interplay between function and form in real-world complex systems. It may also supply theoretical basis for the development of novel therapeutic approaches to damaged nervous systems.

Interactions of Neurons with Physical Environments

Nerve growth strongly relies on multiple chemical and physical signals throughout development and regeneration. Currently, a cure for injured neuronal tissue is an unmet need. Recent advances in fabrication technologies and materials led to the development of synthetic interfaces for neurons. Such engineered platforms that come in 2D and 3D forms can mimic the native extracellular environment and create a deeper understanding of neuronal growth mechanisms, and ultimately advance the development of potential therapies for neuronal regeneration. This progress report aims to present a comprehensive discussion of this field, focusing on physical feature design and fabrication with additional information about considerations of chemical modifications. We review studies of platforms generated with a range of topographies, from micro-scale features down to topographical elements at the nanoscale that demonstrate effective interactions with neuronal cells. Fabrication methods are discussed as well as their biological outcomes. This report highlights the interplay between neuronal systems and the important roles played by topography on neuronal differentiation, outgrowth, and development. The influence of substrate structures on different neuronal cells and parameters including cell fate, outgrowth, intracellular remodeling, gene expression and activity is discussed. Matching these effects to specific needs may lead to the emergence of clinical solutions for patients suffering from neuronal injuries or brain-machine interface (BMI) applications.

Mechanically Oriented 3D Collagen Hydrogel for Directing Neurite Growth

Recent studies in the field of neuro-tissue engineering have demonstrated the promising effects of aligned contact guidance cue to scaffolds of enhancement and direction of neuronal growth. In vivo, neurons grow and develop neurites in a complex three-dimensional (3D) extracellular matrix (ECM) surrounding. Studies have utilized hydrogel scaffolds derived from ECM molecules to better simulate natural growth. While many efforts have been made to control neuronal growth on 2D surfaces, the development of 3D scaffolds with an elaborate oriented topography to direct neuronal growth still remains a challenge. In this study, we designed a method for growing neurons in an aligned and oriented 3D collagen hydrogel. We aligned collagen fibers by inducing controlled uniaxial strain on gels. To examine the collagen hydrogel as a suitable scaffold for neuronal growth, we evaluated the physical properties of the hydrogel and measured collagen fiber properties. By combining the neuronal culture in 3D collagen hydrogels with strain-induced alignment, we were able to direct neuronal growth in the direction of the aligned collagen matrix. Quantitative evaluation of neurite extension and directionality within aligned gels was performed. The analysis showed neurite growth aligned with collagen matrix orientation, while maintaining the advantageous 3D growth.

Sonochemically-fabricated Ga@C-dots@Ga nanoparticle-aided neural growth

In this paper, we report the fabrication of an antibacterial material, Ga-doped C-dots on Ga nanoparticles (Ga@C-dots@Ga NPs), which is deposited on a glass substrate for neural growth. A one-step sonochemical process is applied for the simultaneous fabrication and coating of Ga@C-dots@Ga NPs using PEG 400 and molten gallium. The physical and chemical characteristics of the synthesized materials were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), fluorescence analysis, dynamic light scattering (DLS) and other techniques. SH-SY5Y cells were plated on the substrates. The effect of the Ga@C-dots@Ga NPs on the development of neurites during the initiation and elongation growth phases was studied and compared with C-dots, Ga@C-dots and Ga NPs. Our research focuses on the influence of the physical and chemical properties of composites on neurite growth. We observed that cells grown on a Ga@C-dots@Ga-coated substrate exhibit a 97% increase in the number of branches originating from the soma. We found that surface modification and particle morphology play a significant role in the neural growth.

Iron oxide nanoparticles for neuronal cell applications: uptake study and magnetic manipulations

Background

The ability to direct and manipulate neuronal cells has important potential in therapeutics and neural network studies. An emerging approach for remotely guiding cells is by incorporating magnetic nanoparticles (MNPs) into cells and transferring the cells into magnetic sensitive units. Recent developments offer exciting possibilities of magnetic manipulations of MNPs-loaded cells by external magnetic fields. In the present study, we evaluated and characterized uptake properties for optimal loading of cells by MNPs. We examined the interactions between MNPs of different cores and coatings, with primary neurons and neuron-like cells.

Results

We found that uncoated-maghemite iron oxide nanoparticles maximally interact and penetrate into cells with no cytotoxic effect. We observed that the cellular uptake of the MNPs depends on the time of incubation and the concentration of nanoparticles in the medium. The morphology patterns of the neuronal cells were not affected by MNPs uptake and neurons remained electrically active. We theoretically modeled magnetic fluxes and demonstrated experimentally the response of MNP-loaded cells to the magnetic fields affecting cell motility. Furthermore, we successfully directed neurite growth orientation along regeneration.

Conclusions

Applying mechanical forces via magnetic mediators is a useful approach for biomedical applications. We have examined several types of MNPs and studied the uptake behavior optimized for magnetic neuronal manipulations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-016-0190-0) contains supplementary material, which is available to authorized users.

Gold Nanoparticle-Decorated Scaffolds Promote Neuronal Differentiation and Maturation

Engineered 3D neuronal networks are considered a promising approach for repairing the damaged spinal cord. However, the lack of a technological platform encouraging axonal elongation over branching may jeopardize the success of such treatment. To address this issue we have decorated gold nanoparticles on the surface of electrospun nanofiber scaffolds, characterized the composite material, and investigated their effect on the differentiation, maturation, and morphogenesis of primary neurons and on an immature neuronal cell line. We have shown that the nanocomposite scaffolds have encouraged a longer outgrowth of the neurites, as judged by the total length of the branching trees and the length and total distance of neurites. Moreover, neurons grown on the nanocomposite scaffolds had less neurites originating out of the soma and lower number of branches. Taken together, these results indicate that neurons cultivated on the gold nanoparticle scaffolds prefer axonal elongation over forming complex branching trees. We envision that such cellular constructs may be useful in the future as implantable cellular devices for repairing damaged neuronal tissues, such as the spinal cord.

Remote Magnetic Orientation of 3D Collagen Hydrogels for Directed Neuronal Regeneration

Hydrogel matrices are valuable platforms for neuronal tissue engineering. Orienting gel fibers to achieve a directed scaffold is important for effective functional neuronal regeneration. However, current methods are limited and require treatment of gels prior to implantation, ex-vivo, without taking into consideration the pathology in the injured site. We have developed a method to control gel orientation dynamically and remotely in situ. We have mixed into collagen hydrogels magnetic nanoparticles then applied an external magnetic field. During the gelation period the magnetic particles aggregated into magnetic particle strings, leading to the alignment of the collagen fibers. We have shown that neurons within the 3D magnetically induced gels exhibited normal electrical activity and viability. Importantly, neurons formed elongated cooriented morphology, relying on the particle strings and fibers as supportive cues for growth. The ability to inject the mixed gel directly into the injured site as a solution then to control scaffold orientation remotely opens future possibilities for therapeutic engineered scaffolds.

Engineered Promoters for Potent Transient Overexpression

The core promoter, which is generally defined as the region to which RNA Polymerase II is recruited to initiate transcription, plays a pivotal role in the regulation of gene expression. The core promoter consists of different combinations of several short DNA sequences, termed core promoter elements or motifs, which confer specific functional properties to each promoter. Earlier studies that examined the ability to modulate gene expression levels via the core promoter, led to the design of strong synthetic core promoters, which combine different core elements into a single core promoter. Here, we designed a new core promoter, termed super core promoter 3 (SCP3), which combines four core promoter elements (the TATA box, Inr, MTE and DPE) into a single promoter that drives prolonged and potent gene expression. We analyzed the effect of core promoter architecture on the temporal dynamics of reporter gene expression by engineering EGFP expression vectors that are driven by distinct core promoters. We used live cell imaging and flow cytometric analyses in different human cell lines to demonstrate that SCPs, particularly the novel SCP3, drive unusually strong long-term EGFP expression. Importantly, this is the first demonstration of long-term expression in transiently transfected mammalian cells, indicating that engineered core promoters can provide a novel non-viral strategy for biotechnological as well as gene-therapy-related applications that require potent expression for extended time periods.

Fluorescence life-time imaging and steady state polarization for examining binding of fluorophores to gold nanoparticles

Nanocomposites as multifunctional agents are capable of combing imaging and cell biology technologies. The conventional methods used for validation of the conjugation process of nanoparticles (NPs) to fluorescent molecules such as spectroscopy analysis and surface potential measurements, are not sufficient. In this paper we present a new and highly sensitive procedure that uses the combination of (1) fluorescence spectrum, (2) fluorescence lifetime, and (3) steady state fluorescence polarization measurements. We characterize and analyze gold NPs with Lucifer yellow (LY) surface coating as a model. We demonstrate the ability to differentiate between LY-GNP (the conjugated complex) and a mixture of coated NP and free dyes. We suggest the approach for neuroscience applications where LY is used for detecting and labeling cells, studying morphology and intracellular communications. Histograms of Fluorescence lifetime imaging (FLIM) of free LY dye (Left) in comparison to the conjugated dye to gold nanoparticles, LY-GNP (Middle) enable the differentiation between LY-GNP (the conjugated complex) and a mixture of coated NP and free dyes (Right).

Magnetic micro-device for manipulating PC12 cell migration and organization

Directing neuronal migration and growth has an important impact on potential post traumatic therapies. Magnetic manipulation is an advantageous method for remotely guiding cells. In the present study, we have generated highly localized magnetic fields with controllable magnetic flux densities to manipulate neuron-like cell migration and organization at the microscale level. We designed and fabricated a unique miniaturized magnetic device composed of an array of rectangular ferromagnetic bars made of permalloy (Ni80Fe20), sputter-deposited onto glass substrates. The asymmetric shape of the magnets enables one to design a magnetic landscape with high flux densities at the poles. Iron oxide nanoparticles were introduced into PC12 cells, making the cells magnetically sensitive. First, we manipulated the cells by applying an external magnetic field. The magnetic force was strong enough to direct PC12 cell migration in culture. Based on time lapse observations, we analysed the movement of the cells and estimated the amount of MNPs per cell. We plated the uploaded cells on the micro-patterned magnetic device. The cells migrated towards the high magnetic flux zones and aggregated at the edges of the patterned magnets, corroborating that the cells with magnetic nanoparticles are indeed affected by the micro-magnets and attracted to the bars' magnetic poles. Our study presents an emerging method for the generation of pre-programmed magnetic micro-'hot spots' to locate and direct cellular growth, setting the stage for implanted magnetic devices.

De novo transcriptome assembly databases for the central nervous system of the medicinal leech

The study of non-model organisms stands to benefit greatly from genetic and genomic data. For a better understanding of the molecular mechanisms driving neuronal development, and to characterize the entire leech Hirudo medicinalis central nervous system (CNS) transcriptome we combined Trinity for de-novo assembly and Illumina HiSeq2000 for RNA-Seq. We present a set of 73,493 de-novo assembled transcripts for the leech, reconstructed from RNA collected, at a single ganglion resolution, from the CNS. This set of transcripts greatly enriches the available data for the leech. Here, we share two databases, such that each dataset allows a different type of search for candidate homologues. The first is the raw set of assembled transcripts. This set allows a sequence-based search. A comprehensive analysis of which revealed 22,604 contigs with high e-values, aligned versus the Swiss-Prot database. This analysis enabled the production of the second database, which includes correlated sequences to annotated transcript names, with the confidence of BLAST best hit.

Promotion of neural sprouting using low-level green light-emitting diode phototherapy

We irradiated neuroblastoma SH-SY5Y cell line with low-level light-emitting diode (LED) illumination at a visible wavelength of 520 nm (green) and intensity of 100 mW∕cm2. We captured and analyzed the cell morphology before LED treatment, immediately after, and 12 and 24 h after treatment. Our study demonstrated that LED illumination increases the amount of sprouting dendrites in comparison to the control untreated cells. This treatment also resulted in more elongated cells after treatment in comparison to the control cells and higher levels of expression of a differentiation related gene. This result is a good indication that the proposed method could serve in phototherapy treatment for increasing sprouting and enhancing neural network formation.

NGF-conjugated iron oxide nanoparticles promote differentiation and outgrowth of PC12 cells

The search for regenerative agents that promote neuronal differentiation and repair is of great importance. Nerve growth factor (NGF) which is an essential contributor to neuronal differentiation has shown high pharmacological potential for the treatment of central neurodegenerative diseases such as Alzheimer's and Parkinson's. However, growth factors undergo rapid degradation, leading to a short biological half-life. In our study, we describe a new nano-based approach to enhance the NGF activity resulting in promoted neuronal differentiation. We covalently conjugated NGF to iron oxide nanoparticles (NGF-NPs) and studied the effect of the novel complex on the differentiation of PC12 cells. We found that the NGF-NP treatment, at the same concentration as free NGF, significantly promoted neurite outgrowth and increased the complexity of the neuronal branching trees. Examination of neuronal differentiation gene markers demonstrated higher levels of expression in PC12 cells treated with the conjugated factor. By manipulating the NGF specific receptor, TrkA, we have demonstrated that NGF-NPs induce cell differentiation via the regular pathway. Importantly, we have shown that NGF-NPs undergo slower degradation than free NGF, extending their half-life and increasing NGF availability. Even a low concentration of conjugated NGF treatment has led to an effective response. We propose the use of the NGF-NP complex which has magnetic characteristics, also as a useful method to enhance NGF efficiency and activity, thus, paving the way for substantial neuronal repair therapeutics.

Neuronal growth on L- and D-cysteine self-assembled monolayers reveals neuronal chiral sensitivity

Studying the interaction between neuronal cells and chiral molecules is fundamental for the design of novel biomaterials and drugs. Chirality influences all biological processes that involve intermolecular interaction. One common method used to study cellular interactions with different enantiomeric targets is the use of chiral surfaces. Based on previous studies that demonstrated the importance of cysteine in the nervous system, we studied the effect of L- and D-cysteine on single neuronal growth. L-Cysteine, which normally functions as a neuromodulator or a neuroprotective antioxidant, causes damage at elevated levels, which may occur post trauma. In this study, we grew adult neurons in culture enriched with L- and D-cysteine as free compounds or as self-assembled monolayers of chiral surfaces and examined the effect on the neuronal morphology and adhesion. Notably, we have found that exposure to the L-cysteine enantiomer inhibited, and even prevented, neuronal attachment more severely than exposure to the D-cysteine enantiomer. Atop the L-cysteine surfaces, neuronal growth was reduced and degenerated. Since the cysteine molecules were attached to the surface via the thiol groups, the neuronal membrane was exposed to the molecular chiral site. Thus, our results have demonstrated high neuronal chiral sensitivity, revealing chiral surfaces as indirect regulators of neuronal cells and providing a reference for studying chiral drugs.

Substrates coated with silver nanoparticles as a neuronal regenerative material

Much effort has been devoted to the design of effective biomaterials for nerve regeneration. Here, we report the novel use of silver nanoparticles (AgNPs) as regenerative agents to promote neuronal growth. We grew neuroblastoma cells on surfaces coated with AgNPs and studied the effect on the development of the neurites during the initiation and the elongation growth phases. We find that the AgNPs function as favorable anchoring sites, and the growth on the AgNP-coated substrates leads to a significantly enhanced neurite outgrowth. Cells grown on substrates coated with AgNPs have initiated three times more neurites than cells grown on uncoated substrates, and two times more than cells grown on substrates sputtered with a plain homogenous layer of silver. The growth of neurites on AgNPs in the elongation phase was enhanced as well. A comparison with substrates coated with gold nanoparticles (AuNPs) and zinc oxide nanoparticles (ZnONPs) demonstrated a clear silver material-driven promoting effect, in addition to the nanotopography. The growth on substrates coated with AgNPs has led to a significantly higher number of initiating neurites when compared to substrates coated with AuNPs or ZnONPs. All nanoparticle-coated substrates affected and promoted the elongation of neurites, with a significant positive maximal effect for the AgNPs. Our results, combined with the well-known antibacterial effect of AgNPs, suggest the use of AgNPs as an attractive nanomaterial – with dual activity – for neuronal repair studies.

Spatial regulation dominates gene function in the ganglia chain

MOTIVATION

To understand the molecular mechanisms of neurons, it is imperative to identify genomic dissimilarities within the heterogeneity of the neural system. This is especially true for neuronal disorders in which spatial considerations are of critical nature. For this purpose, Hirudo medicinalis provides here an ideal system in which we are able to follow gene expression along the central nervous system, to affiliate location with gene behavior.

RESULTS

In all, 221.1 million high-quality short reads were sequenced on the Illumina Hiseq2000 platform at the single ganglion level. Thereafter, a de novo assembly was performed using two state-of-the-art assemblers, Trinity and Trans-ABySS, to reconstruct a comprehensive de novo transcriptome. Classification of Trinity and Trans-ABySS transcripts produced a non-redundant set of 76 845 and 268 355 transcripts (>200 bp), respectively. Remarkably, using Trinity, 82% of the published medicinal leech messenger RNAs was identified. For the innexin family, all of the 21 recently reported genes were identified. Spatial regulation analysis across three ganglia throughout the entire central nervous system revealed distinct patterns of gene expression. These transcriptome data were combined with expression distribution to produce a spatio-transcripto map along the ganglia chain. This study provides a resource for gene discovery and gene regulation in future studies.

Thermal degradation of DNA

In this article, we investigate the thermal degradation of deoxyribonucleic acid (DNA). We find that under dry conditions, complete DNA degradation occurs at above 190°C. In addition, as the boiling temperature of water is pressure dependent, we have investigated the thermal degradation of the DNA in water for different applied partial pressures. This information is important for fundamental understanding of DNA structure and energetics, and can be useful for biomedical applications such as thermal targeting of DNA in cancer cells, as well as for basic research.

Gold nanoparticles-based biosensing of single nucleotide DNA mutations

Detection of DNA mutations is critical for scientific research and diagnostic procedures. Here, we propose a novel interdisciplinary method for rapid and simple detection of DNA mutations. We show that heating a solution containing DNA and gold nanoparticles results in degradation of the DNA. Surprisingly, we found that the DNA can be protected against degradation, if an oligonucleotide that matches the DNA is added to the solution. Moreover, the level of degradation indicates the presence of mutations in the DNA. The method is sensitive enough to indicate even a single nucleotide difference, and has the potential to ultimately replace initial medical genetic tests. As proof of concept, we demonstrate a clear detection of two of the most common mutations leading to Cystic Fibrosis.

Bombarding cancer: biolistic delivery of therapeutics using porous Si carriers

A new paradigm for an effective delivery of therapeutics into cancer cells is presented. Degradable porous silicon carriers, which are tailored to carry and release a model anti-cancer drug, are biolistically bombarded into in-vitro cancerous targets. We demonstrate the ability to launch these highly porous microparticles by a pneumatic capillary gene gun, which is conventionally used to deliver cargos by heavy metal carriers. By optimizing the gun parameters e.g., the accelerating gas pressure, we have successfully delivered the porous carriers, to reach deep targets and to cross a skin barrier in a highly spatial resolution. Our study reveals significant cytotoxicity towards the target human breast carcinoma cells following the delivery of drug-loaded carriers, while administrating empty particles results in no effect on cell viability. The unique combination of biolistics with the temporal control of payload release from porous carriers presents a powerful and non-conventional platform for designing new therapeutic strategies.

Localized RNAi and ectopic gene expression in the medicinal leech

In this video, we show the use of a pneumatic capillary gun for the accurate biolistic delivery of reagents into live tissue. We use the procedure to perturb gene expression patterns in selected segments of leech embryos, leaving the untreated segments as internal controls. The pneumatic capillary gun can be used to reach internal layers of cells at early stages of development without opening the specimen. As a method for localized introduction of substances into living tissues, the biolistic delivery with the gun has several advantages: it is fast, contact-free and non-destructive. In addition, a single capillary gun can be used for independent delivery of different substances. The delivery region can have lateral dimensions of approximately 50-150 microm and extends over approximately 15 microm around the mean penetration depth, which is adjustable between 0 and 50 microm. This delivery has the advantage of being able to target a limited number of cells in a selected location intermediate between single cell knock down by microinjection and systemic knockdown through extracellular injections or by means of genetic approaches. For knocking down or knocking in the expression of the axon guidance molecule Netrin, which is naturally expressed by some central neurons and in the ventral body wall, but not the dorsal domain, we deliver molecules of dsRNA or plasmid-DNA into the body wall and central ganglia. This procedure includes the following steps: (i) preparation of the experimental setup for a specific assay (adjusting the accelerating pressure), (ii) coating the particles with molecules of dsRNA or DNA, (iii) loading the coated particles into the gun, up to two reagents in one assay, (iv) preparing the animals for the particle delivery, (v) delivery of coated particles into the target tissue (body wall or ganglia), and (vi) processing the embryos (immunostaining, immunohistochemistry and neuronal labeling) to visualize the results, usually 2 to 3 days after the delivery. When the particles were coated with netrin dsRNA, they caused clearly visible knock-down of netrin expression that only occurred in cells containing particles (usually, 1-2 particles per cell). Particles coated with a plasmid encoding EGFP induced fluorescence in neuronal cells when they stopped in their nuclei.