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 via a robust physical route for biological applications.

Micro- and nano-particles are elemental for many current and developing technologies. Specifically, these particles are being used extensively in biological studies and applications, which include imaging, drug delivery and therapeutics. Recent advances have led to the development of multifunctional particles, which have the potential to further enhance their effectiveness, enabling novel applications. Therefore, many efforts have been devoted to producing well-defined particles for specific needs. However, the conventional fabrication methodologies used to develop particles are time consuming, making it extremely challenging to fine-tune the properties of the particles for multifunctional applications. Herein, we present a simple and facile method to fabricate dome-shaped micron- and nano-sized particles via a robust physical route. The presented method enables particles to be designed using a vast range of materials, with different sizes and compositions. The versatility of this method enables the engineering of multifunctional particles with pre-defined properties that can be adjusted to a specific biological application. We demonstrate the fabrication of dome-shaped particles using physical vapor deposition (PVD) and a polystyrene-bead-monolayer-based mechanical mask. We show domes from several materials and coatings; in particular, we demonstrate the development process for biocompatible magnetic iron oxide domes. We find that our magnetic domes exhibit an Fe3O4 structure with a high magnetization saturation. In addition, we examine the biocompatibility of the magnetic domes by performing viability tests and morphological analysis. The ability to design and fabricate micro- and nano-particles upon request in a simple and relatively high-throughput manner opens possibilities for the development of new smart multifunctional particles for both therapeutic and diagnostic applications.

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.

Axial Confocal Tomography of Capillary-Contained Colloidal Structures.

Confocal microscopy is widely used for three-dimensional (3D) sample reconstructions. Arguably, the most significant challenge in such reconstructions is posed by the resolution along the optical axis being significantly lower than in the lateral directions. In addition, the imaging rate is lower along the optical axis in most confocal architectures, prohibiting reliable 3D reconstruction of dynamic samples. Here, we demonstrate a very simple, cheap, and generic method of multiangle microscopy, allowing high-resolution high-rate confocal slice collection to be carried out with capillary-contained colloidal samples in a wide range of slice orientations. This method, realizable with any common confocal architecture and recently implemented with macroscopic specimens enclosed in rotatable cylindrical capillaries, allows 3D reconstructions of colloidal structures to be verified by direct experiments and provides a solid testing ground for complex reconstruction algorithms. In this paper, we focus on the implementation of this method for dense nonrotatable colloidal samples, contained in complex-shaped capillaries. Additionally, we discuss strategies to minimize potential pitfalls of this method, such as the artificial appearance of chain-like particle structures.