Electrical percolation in extrinsically conducting, poly(ε-decalactone) composite neural interface materials

Conducting polymer-based nanostructured materials for brain-machine interfaces

As scientists discovered that raw neurological signals could translate into bioelectric information, brain-machine interfaces (BMI) for experimental and clinical studies have experienced massive growth. Developing suitable materials for bioelectronic devices to be used for real-time recording and data digitalizing has three important necessitates which should be covered. Biocompatibility, electrical conductivity, and having mechanical properties similar to soft brain tissue to decrease mechanical mismatch should be adopted for all materials. In this review, inorganic nanoparticles and intrinsically conducting polymers are discussed to impart electrical conductivity to systems, where soft materials such as hydrogels can offer reliable mechanical properties and a biocompatible substrate. Interpenetrating hydrogel networks offer more mechanical stability and provide a path for incorporating polymers with desired properties into one strong network. Promising fabrication methods, like electrospinning and additive manufacturing, allow scientists to customize designs for each application and reach the maximum potential for the system. In the near future, it is desired to fabricate biohybrid conducting polymer-based interfaces loaded with cells, giving the opportunity for simultaneous stimulation and regeneration. Developing multi-modal BMIs, Using artificial intelligence and machine learning to design advanced materials are among the future goals for this field. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

In Vivo Chronic Brain Cortex Signal Recording Based on a Soft Conductive Hydrogel Biointerface

In neuroscience, the acquisition of neural signals from the brain cortex is crucial to analyze brain processes, detect neurological disorders, and offer therapeutic brain-computer interfaces. The design of neural interfaces conformable to the brain tissue is one of today's major challenges since the insufficient biocompatibility of those systems provokes a fibrotic encapsulation response, leading to an inaccurate signal recording and tissue damage precluding long-term/permanent implants. The design and production of a novel soft neural biointerface made of polyacrylamide hydrogels loaded with plasmonic silver nanocubes are reported herein. Hydrogels are surrounded by a silicon-based template as a supporting element for guaranteeing an intimate neural-hydrogel contact while making possible stable recordings from specific sites in the brain cortex. The nanostructured hydrogels show superior electroconductivity while mimicking the mechanical characteristics of the brain tissue. Furthermore, in vitro biological tests performed by culturing neural progenitor cells demonstrate the biocompatibility of hydrogels along with neuronal differentiation. In vivo chronic neuroinflammation tests on a mouse model show no adverse immune response toward the nanostructured hydrogel-based neural interface. Additionally, electrocorticography acquisitions indicate that the proposed platform permits long-term efficient recordings of neural signals, revealing the suitability of the system as a chronic neural biointerface.

Nanomaterial-based microelectrode arrays for in vitro bidirectional brain-computer interfaces: a review

A bidirectional in vitro brain-computer interface (BCI) directly connects isolated brain cells with the surrounding environment, reads neural signals and inputs modulatory instructions. As a noninvasive BCI, it has clear advantages in understanding and exploiting advanced brain function due to the simplified structure and high controllability of ex vivo neural networks. However, the core of ex vivo BCIs, microelectrode arrays (MEAs), urgently need improvements in the strength of signal detection, precision of neural modulation and biocompatibility. Notably, nanomaterial-based MEAs cater to all the requirements by converging the multilevel neural signals and simultaneously applying stimuli at an excellent spatiotemporal resolution, as well as supporting long-term cultivation of neurons. This is enabled by the advantageous electrochemical characteristics of nanomaterials, such as their active atomic reactivity and outstanding charge conduction efficiency, improving the performance of MEAs. Here, we review the fabrication of nanomaterial-based MEAs applied to bidirectional in vitro BCIs from an interdisciplinary perspective. We also consider the decoding and coding of neural activity through the interface and highlight the various usages of MEAs coupled with the dissociated neural cultures to benefit future developments of BCIs.

Simulation of electrical conductivity for polymer silver nanowires systems

A simple model is developed for the conductivity of polymeric systems including silver nanowires (AgNWs). This model reveals the effects of interphase thickness, tunneling distance, waviness and aspect ratio of nanowires, as well as effective filler volume fraction on the percolation and electrical conductivity of AgNW-reinforced samples. The validity of this model is tested by using the measured data from several samples. Based on this model, the conductivity calculations are in proper accordance with the measured values. A large network and a low percolation onset are produced by nanowires with a high aspect ratio developing the nanocomposite conductivity. The results also show that a thicker interphase expands the network, thereby increasing the electrical conductivity. Furthermore, non-waved AgNWs exhibit more conductivity compared to wavy nanowires. It is concluded that the surface energies of polymer medium and nanowires have no effect on the conductivity of samples. On the other hand, the volume fraction and aspect ratio of nanowires, in addition to the interphase thickness and tunneling distance have the greatest influences on the conductivity of nanocomposites.

Modeling and characterization of the electrical conductivity on metal nanoparticles/carbon nanotube/polymer composites

Flexible conductive films have good deformability and conductivity, and are expected to be used in flexible electronic devices. In this paper, four kinds of flexible conductive films were successfully prepared by compounding nano-sized metal (Ni, Cu, Au or AuCu alloy) particles to CNT surface and then dispersing to polydimethylsiloxane matrix. Experiment results show that the conductivity of these prepared films are almost two orders of magnitude higher than that of CNT/polydimethylsiloxane films with the same CNT loadings. A simulation model based on percolation network theory and Monte Carlo technology is introduced to study the influence of nanoparticles on the composite conductivity. Results confirmed that the introduction of nanoparticles effectively reduces the effective resistance of CNT and the tunnelling resistance at CNT junctions. The intrinsic conductivity and the length diameter ratio of CNT, the intrinsic conductivity, the size and the coverage ratio of nanoparticles are the core parameters affecting the conductivity of composite. Compared with CNT/polydimethylsiloxane films, the optimized theoretical conductivity of these nano-sized particles enhanced composites can be further improved.

Strategies for interface issues and challenges of neural electrodes

Neural electrodes, as a bridge for bidirectional communication between the body and external devices, are crucial means for detecting and controlling nerve activity. The electrodes play a vital role in monitoring the state of neural systems or influencing it to treat disease or restore functions. To achieve high-resolution, safe and long-term stable nerve recording and stimulation, a neural electrode with excellent electrochemical performance (e.g., impedance, charge storage capacity, charge injection limit), and good biocompatibility and stability is required. Here, the charge transfer process in the tissues, the electrode-tissue interfaces and the electrode materials are discussed respectively. Subsequently, the latest research methods and strategies for improving the electrochemical performance and biocompatibility of neural electrodes are reviewed. Finally, the challenges in the development of neural electrodes are proposed. It is expected that the development of neural electrodes will offer new opportunities for the evolution of neural prosthesis, bioelectronic medicine, brain science, and so on.

Synthesis of copolyesters based on substituted and non-substituted lactones towards the control of their crystallinity and their potential effect on hydrolytic degradation in the design of soft medical devices

ROP synthesis of polyesters at different molar ratios of monomers ε-caprolactone (ε-CL) in combination with alkyl substituted lactones δ-decalactone (δ-DL), ε-decalactone (ε-DL) and δ-dodecalactone (δ-DD), as well copolymers based on ε-DL and δ-DD.

Bifunctional conducting polymer matrices with antibacterial and neuroprotective effects

Current trends in the field of neural tissue engineering include the design of advanced biomaterials combining excellent electrochemical performance with versatile biological characteristics. The purpose of this work was to develop an antibacterial and neuroprotective coating based on a conducting polymer - poly(3,4-ethylenedioxypyrrole) (PEDOP), loaded with an antibiotic agent - tetracycline (Tc). Employing an electrochemical technique to immobilize Tc within a growing polymer matrix allowed to fabricate robust PEDOP/Tc coatings with a high charge storage capacity (63.65 ± 6.05 mC/cm²), drug release efficiency (629.4 µg/cm² ± 62.7 µg/cm²), and low charge transfer resistance (2.4 ± 0.1 kΩ), able to deliver a stable electrical signal. PEDOP/Tc were found to exhibit strong antimicrobial effects against Gram-negative bacteria Escherichia coli, expressed through negligible adhesion, reduction in viability, and a characteristic elongation of bacterial cells. Cytocompatibility and neuroprotective effects were evaluated using a rat neuroblastoma B35 cell line, and were analyzed using MTT, cell cycle, and Annexin-V apoptosis assays. The presence of Tc was found to enhance neural cell viability and neurite outgrowth. The results confirmed that PEDOP/Tc can serve as an efficient neural electrode coating able to enhance charge transfer, as well as to exhibit bifunctional biological characteristics, different for eukaryotic and prokaryotic cells.