Combining surface-sensitive microscopies for analysis of biological tissues after neural device implantation (original) (raw)
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In vitro assessment of bioactive coatings for neural implant applications
Journal of Biomedical Materials Research, 2004
Recent efforts in our laboratory have focused on developing methods for immobilizing bioactive peptides to low cell-adhesive dextran monolayer coatings and promoting biospecific cell adhesion for biomaterial implant applications. In the current study, this dextran-based bioactive coating technology was developed for silicon, polyimide, and gold, the base materials utilized to fabricate our prototype neural implants. Chemical composition of all modified surfaces was verified by X-ray photoelectron spectroscopy (XPS). We observed that surface-immobilized dextran supported very little cell adhesion in vitro (24-h incubation with serum-supplemented medium) on all base materials. Inactive nonadhesion-promoting Gly-Arg-Ala-Asp-Ser-Pro peptides immobilized on dextran-coated materials promoted adhesion and spreading at low levels not significantly different from dextran-coated substrates. Arg-Gly-Asp (RGD) peptide-grafted surfaces were observed to promote substantial fibroblast and glial cell adhesion with minimal PC12 (neuronal cell) adhesion. In contrast, dextran-coated materials with surface-grafted laminin-based, neurite-promoting Ile-Lys-Val-Ala-Val (IKVAV) peptide promoted substantial neuron cell adhesion and minimal fibroblast and glial cell adhesion. It was concluded that neuron-selective substrates are feasible using dextran-based surface chemistry strategies. The chemical surface modifications could be utilized to establish a stable neural tissue-implant interface for longterm performance of neural prosthetic devices.
Coating flexible probes with an ultra fast degrading polymer to aid in tissue insertion
Biomedical microdevices, 2015
We report a fabrication process for coating neural probes with an ultrafast degrading polymer to create consistent and reproducible devices for neural tissue insertion. The rigid polymer coating acts as a probe insertion aid, but resorbs within hours post-implantation. Despite the feasibility for short term neural recordings from currently available neural prosthetic devices, most of these devices suffer from long term gliosis, which isolates the probes from adjacent neurons, increasing the recording impedance and stimulation threshold. The size and stiffness of implanted probes have been identified as critical factors that lead to this long term gliosis. Smaller, more flexible probes that match the mechanical properties of brain tissue could allow better long term integration by limiting the mechanical disruption of the surrounding tissue during and after probe insertion, while being flexible enough to deform with the tissue during brain movement. However, these small flexible prob...
Objective. Despite the feasibility of short-term neural recordings using implantable microelectrodes, attaining reliable, chronic recordings remains a challenge. Most neural recording devices suffer from a long-term tissue response, including gliosis, at the device–tissue interface. It was hypothesized that smaller, more flexible intracortical probes would limit gliosis by providing a better mechanical match with surrounding tissue. Approach. This paper describes the in vivo evaluation of flexible parylene microprobes designed to improve the interface with the adjacent neural tissue to limit gliosis and thereby allow for improved recording longevity. The probes were coated with an ultrafast degrading tyrosine-derived polycarbonate (E5005(2K)) polymer that provides temporary mechanical support for device implantation, yet degrades within 2 h post-implantation. A parametric study of probes of varying dimensions and polymer coating thicknesses were implanted in rat brains. The glial tissue response and neuronal loss were assessed from 72 h to 24 weeks post-implantation via immunohistochemistry. Main results. Experimental results suggest that both probe and polymer coating sizes affect the extent of gliosis. When an appropriate sized coating dimension (100 µm × 100 µm) and small probe (30 µm × 5 µm) was implanted, a minimal post-implantation glial response was observed. No discernible gliosis was detected when compared to tissue where a sham control consisting of a solid degradable polymer shuttle of the same dimensions was inserted. A larger polymer coating (200 µm × 200 µm) device induced a more severe glial response at later time points, suggesting that the initial insertion trauma can affect gliosis even when the polymer shuttle degrades rapidly. A larger degree of gliosis was also observed when comparing a larger sized probe (80 µm × 5 µm) to a smaller probe (30 µm × 5 µm) using the same polymer coating size (100 µm × 100 µm). There was no significant neuronal loss around the implantation sites for most device candidates except the group with largest polymer coating and probe sizes. Significance. These results suggest that: (1) the degree of mechanical trauma at device implantation and mechanical mismatches at the probe-tissue interface affect long term gliosis; (2) smaller, more flexible probes may minimize the glial response to provide improved tissue biocompatibility when used for chronic neural signal recording; and (3) some degree of glial scarring did not significantly affect neuronal distribution around the probe.
Journal of Neuroscience Methods, 2009
Penetrating microscale microelectrodes made from flexible polymers tend to bend or deflect and may fail to reach their target location. The development of flexible neural probes requires methods for reliable and controlled insertion into the brain. Previous approaches for implanting flexible probes into the cortex required modifications that negate the flexibility, limit the functionality, or restrict the design of the probe. This study investigated the use of an electronegative selfassembled monolayer (SAM) as a coating on a stiff insertion shuttle to carry a polymer probe into the cerebral cortex, and then the detachment of the shuttle from the probe by altering the shuttle's hydrophobicity.
Peptide-based coatings for flexible implantable neural interfaces
Scientific reports, 2018
In the last decade, the use of flexible biosensors for neuroprosthetic and translational applications has widely increased. Among them, the polyimide (PI)-based thin-film electrodes got a large popularity. However, the usability of these devices is still hampered by a non-optimal tissue-device interface that usually compromises the long-term quality of neural signals. Advanced strategies able to improve the surface properties of these devices have been developed in the recent past. Unfortunately, most of them are not easy to be developed and combined with micro-fabrication processes, and require long-term efforts to be testable with human subjects. Here we show the results of the design and in vitro testing of an easy-to-implement and potentially interesting coating approach for thin-film electrodes. In particular, two biocompatible coatings were obtained via covalent conjugation of a laminin-derived peptide, CAS-IKVAV-S (IKV), with polyimide sheets that we previously functionalized...
Dextran as a Resorbable Coating Material for Flexible Neural Probes
Micromachines
In the quest for chronically reliable and bio-tolerable brain interfaces there has been a steady evolution towards the use of highly flexible, polymer-based electrode arrays. The reduced mechanical mismatch between implant and brain tissue has shown to reduce the evoked immune response, which in turn has a positive effect on signal stability and noise. Unfortunately, the low stiffness of the implants also has practical repercussions, making surgical insertion extremely difficult. In this work we explore the use of dextran as a coating material that temporarily stiffens the implant, preventing buckling during insertion. The mechanical properties of dextran coated neural probes are characterized, as well as the different parameters which influence the dissolution rate. Tuning parameters, such as coating thickness and molecular weight of the used dextran, allows customization of the stiffness and dissolution time to precisely match the user’s needs. Finally, the immunological response ...
Polymeric Thin Film Technology for Neural Interfaces: Review and Perspectives
Polymer Thin Films, 2010
An important and exciting direction of research in nanomedicine would be to gain a fundamental understanding of how living cells respond to nanostructures. At this aim, thin film technology plays a key role in helping to understand the cell-surface interactions. Generally, thin films are deposited onto bulk materials to achieve properties unattainable or not easily attainable in the substrate alone. In particularly, in biomedicine, polymeric thin films are used such as coating to improve the properties of biocompatibility, thus avoiding typical inflammatory response of immunitary system, especially when the system have to be permanently implanted (Jeong et al., 1986). Various biodegradable polymeric drug delivery devices have been developed for the sustained release of a variety of drugs, which include micro and nanoparticles, films, foams, wafers, discs, and micro-and nanofibers (Jain, 2000) Among them, films have gained growing interest in various applications.
Intact Histological Characterization of Brain-implanted Microdevices and Surrounding Tissue
Journal of Visualized Experiments, 2013
Research into the design and utilization of brain-implanted microdevices, such as microelectrode arrays, aims to produce clinically relevant devices that interface chronically with surrounding brain tissue. Tissue surrounding these implants is thought to react to the presence of the devices over time, which includes the formation of an insulating "glial scar" around the devices. However, histological analysis of these tissue changes is typically performed after explanting the device, in a process that can disrupt the morphology of the tissue of interest.
Neurobiochemical changes in the vicinity of a nanostructured neural implant
Scientific Reports, 2016
Neural interface technologies including recording and stimulation electrodes are currently in the early phase of clinical trials aiming to help patients with spinal cord injuries, degenerative disorders, strokes interrupting descending motor pathways, or limb amputations. Their lifetime is of key importance; however, it is limited by the foreign body response of the tissue causing the loss of neurons and a reactive astrogliosis around the implant surface. Improving the biocompatibility of implant surfaces, especially promoting neuronal attachment and regeneration is therefore essential. In our work, bioactive properties of implanted black polySi nanostructured surfaces (520-800 nm long nanopillars with a diameter of 150-200 nm) were investigated and compared to microstructured Si surfaces in eightweek-long in vivo experiments. Glial encapsulation and local neuronal cell loss were characterised using GFAP and NeuN immunostaining respectively, followed by systematic image analysis. Regarding the severity of gliosis, no significant difference was observed in the vicinity of the different implant surfaces, however, the number of surviving neurons close to the nanostructured surface was higher than that of the microstructured ones. Our results imply that the functionality of implanted microelectrodes covered by Si nanopillars may lead to improved long-term recordings. Neural interface technologies are currently being introduced in preclinical applications aiming for the treatment of patients with spinal cord injuries 1 , degenerative disorders 2 , brainstem strokes 3 , amyotrophic lateral sclerosis 4 , tetraplegia 5 and/or limb amputation(s) 6. Recording the action potentials of many individual neurons is impossible with non-invasive brain-machine-interfaces (BMI) e.g. EEG, because the neuronal spiking is lost by averaging and filtering across the scalp 1. The lifetime of invasive, intracortical recording devices such as microfabricated neural probes, however, is limited due to the foreign body response (FBR) of the central nervous system 7-9. FBR results in the formation of a glial scar, which electrically insulates neurons 10. On the other hand, reactive astrocytes release proinflammatory and neurotoxic factors that either lead to neuronal death and degeneration, or may inhibit axonal regrowth and regeneration 10. The immune response around the neural implant can modify the appropriate interpretation of in vivo recordings 8 , since it leads to reduced sensitivity, stability and very often to device failure. Huge efforts are made to overcome the limitation of the chronic use of microelectrodes by improving the biocompatibility of the implant surfaces using bioactive coatings 10-13 , however, cellular behaviour is influenced both by chemical and physical properties of the environment. Surface topography has been shown to play a role in the biocompatibility of certain materials in vitro 14-20. Furthermore, it has been demonstrated to clearly modify cellular behaviour: adhesion, migration and differentiation 21. Since the extracellular matrix (ECM) consists of nanostructured fibrous protein assemblies, the theory that neurons may prefer a similar topography rather than a smooth implant surface seems to be reasonable. Several groups have investigated the effect of nanostructuring on neurons and glial cells in vitro aiming for enhanced in vivo neural implant efficiency. Most of them used porous Si 19,22,23 or etched Si surfaces with nanometre scale structures 17,18,24-26. In other cases, various other materials have been applied, such as GaP 27 or polymers 28. In the past few years, by altering the specific surface area, the wetting properties and the pattern regularity
Visualization of the intact interface between neural tissue and implanted microelectrode arrays
Journal of Neural Engineering, 2005
This research presents immunohistochemical strategies for assessing the interactions at the immediate interface between micro-scale implanted devices and the surrounding brain tissue during inflammatory astrogliotic reactions. This includes preparation, microscopy and analysis techniques for obtaining images of the intimate contact between neural cells and the surface of implantable micro-electromechanical systems (MEMS) devices. The ability to visualize the intact interface between an implant and the surrounding tissue allows researchers to examine tissue that is unchanged from its native implanted state. Conversely, current popular techniques involve removing the implant. This tends to cause damage to the tissue immediately surrounding the implant and can hinder one's ability to differentiate inflammatory responses to the implant versus physical damage occurring from removal of the implant from the tissue. Due to advances in microscopy and staining techniques, it is now possible to visualize the intact tissue-implant interface. This paper presents the development of imaging techniques for visualizing the intact interface between neural tissue and implanted devices. This is particularly important for understanding both the acute and chronic neuroinflammatory responses to devices intended for long-term use in a prosthetic system. Non-functional, unbonded devices were imaged in vitro and in vivo at different times post-implantation via a range of techniques. Using these techniques, detailed interactions could be seen between delicate cellular processes and the electrode surface, which would have been destroyed using conventional histology processes.