Multitasking smart hydrogels based on the combination of alginate and poly(3,4-ethylenedioxythiophene) properties: A review

Poly(3,4-ethylenedioxythiophene) (PEDOT), a very stable and biocompatible conducting polymer, and alginate (Alg), a natural water-soluble polysaccharide mainly found in the cell wall of various species of brown algae, exhibit very different but at the same complementary properties. In the last few years, the remarkable capacity of Alg to form hydrogels and the electro-responsive properties of PEDOT have been combined to form not only layered composites (PEDOT-Alg) but also interpenetrated multi-responsive PEDOT/Alg hydrogels. These materials have been found to display outstanding properties, such as electrical conductivity, piezoelectricity, biocompatibility, self-healing and re-usability properties, pH and thermoelectric responsiveness, among others. Consequently, a wide number of applications are being proposed for PEDOT-Alg composites and, especially, PEDOT/Alg hydrogels, which should be considered as a new kind of hybrid material because of the very different chemical nature of the two polymeric components. This review summarizes the applications of PEDOT-Alg and PEDOT/Alg in tissue interfaces and regeneration, drug delivery, sensors, microfluidics, energy storage and evaporators for desalination. Special attention has been given to the discussion of multi-tasking applications, while the new challenges to be tackled based on aspects not yet considered in either of the two polymers have also been highlighted.Peer ReviewedPostprint (published version

A Graphene Oxide Nanocomposite for Neural Interfacing Applications

Advanced neural interfacing technologies have the ability to communicate with the central nervous system (CNS) and provide researchers with valuable information about the complex physiology of the brain. Traditional neural electrodes interact with nervous tissue electrically, either through recording or stimulation, but are limited in their potential to chemically interface with the CNS. This dissertation describes the development of a conductive neural biomaterial with the capability of recording neurochemical signals in addition to providing both immobilized and soluble chemical cues to influence cell behavior. The material consists of a graphene oxide/conducting polymer (GO/CP) nanocomposite deposited onto the surface of metal or carbon electrodes for improved, multimodal interfacing capabilities with neurons and neural stem cells (NSCs). The GO/CP nanocomposite demonstrated good biocompatibility with neurons and NSCs and improved neuronal differentiation and neurite outgrowth as a result of its chemical and morphological properties. Additionally, the GO nanosheets present at the nanocomposite surface enabled patterning with bioactive molecules to further influence cell growth. The electrochemical properties of the GO/CP nanocomposite enabled highly controllable, on-demand drug delivery, and the chemical properties contributed by the GO nanosheets created a platform for highly sensitive and selective dopamine detection. With an eye toward developing a highly customizable device that incorporates the versatile chemical interfacing capabilities of GO/CP with the electrical recording ability of planar multielectrode arrays, this body of work concluded with the characterization of an in vitro cultured neuronal network (CNN) damage model for investigating the pathobiology of neuronal injury. A crush injury applied to the CNN interrupted the normal activity patterns of the network and the addition of NSCs to the injury site demonstrated the ability to protect the network from developing dysfunctional circuitry, making the model an exciting platform for exploring neuronal regeneration. While the work here focuses solely on the potential of the nanocomposite in neural interfacing applications, its uses are not limited to the CNS but span all systems in the body and, as a result of its extremely unique chemical and electrical properties, extend to fields outside biomedicine

Design and development of an implantable biohybrid device for muscle stimulation following lower motor neuron injury

In the absence of innervation caused by complete lower motor neuron injuries, skeletal muscle undergoes an inexorable course of degeneration and atrophy. The most apparent and debilitating clinical outcome of denervation is the immediate loss of voluntary use of muscle. However, these injuries are associated with secondary complications of bones, skin and cardiovascular system that, if untreated, may be fatal. Electrical stimulation has been implemented as a clinical rehabilitation technique in patients with denervated degenerated muscles offering remarkable improvements in muscle function. Nevertheless, this approach has limitations and side effects triggered by the delivery of high intensity electrical pulses. Combining innovative approaches in the fields of cell therapy and implanted electronics offers the opportunity to develop a biohybrid device to stimulate muscles in patients with lower motor neuron injuries. Incorporation of stem cell-derived motor neurons into implantable electrodes, could allow muscles to be stimulated in a physiological manner and circumvent problems associated with direct stimulation of muscle. The hypothesis underpinning this project is that artificially-grown motor neurons can serve as an intermediate between stimulator and muscle, converting the electrical stimulus into a biological action potential and re-innervating muscle via neuromuscular interaction. Here, a suitable stem cell candidate with therapeutic potential was identified and a differentiation protocol developed to generate motor neuron-like cells. Thick-film technology and laser micromachining were implemented to manufacture electrode arrays with features and dimensions suitable for implantation. Manufactured electrodes were electrochemically characterised, and motor neuron-like cells incorporated to create biohybrid devices. In vitro results indicate manufactured electrodes support motor neuron-like cell growth and neurite extension. Moreover, electrochemical characterisation suggests electrodes are suitable for stimulation. Preliminary in vivo testing explored implantation in a rat muscle denervation model. Overall, this thesis demonstrates initial development of a novel approach for fabricating biohybrid devices that may improve stimulation of denervated muscles

Nanomaterials for Neural Interfaces

This review focuses on the application of nanomaterials for neural interfacing. The junction between nanotechnology and neural tissues can be particularly worthy of scientific attention for several reasons: (i) Neural cells are electroactive, and the electronic properties of nanostructures can be tailored to match the charge transport requirements of electrical cellular interfacing. (ii) The unique mechanical and chemical properties of nanomaterials are critical for integration with neural tissue as long-term implants. (iii) Solutions to many critical problems in neural biology/medicine are limited by the availability of specialized materials. (iv) Neuronal stimulation is needed for a variety of common and severe health problems. This confluence of need, accumulated expertise, and potential impact on the well-being of people suggests the potential of nanomaterials to revolutionize the field of neural interfacing. In this review, we begin with foundational topics, such as the current status of neural electrode (NE) technology, the key challenges facing the practical utilization of NEs, and the potential advantages of nanostructures as components of chronic implants. After that the detailed account of toxicology and biocompatibility of nanomaterials in respect to neural tissues is given. Next, we cover a variety of specific applications of nanoengineered devices, including drug delivery, imaging, topographic patterning, electrode design, nanoscale transistors for high-resolution neural interfacing, and photoactivated interfaces. We also critically evaluate the specific properties of particular nanomaterials—including nanoparticles, nanowires, and carbon nanotubes—that can be taken advantage of in neuroprosthetic devices. The most promising future areas of research and practical device engineering are discussed as a conclusion to the review.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64336/1/3970_ftp.pd

Bipolar Electroactive Conducting Polymers for Wireless Cell Stimulation

Electrochemical stimulation (ES) promotes wound healing and tissue regeneration in biomedical applications and clinical studies and is central to the emerging field of electroceuticals. Traditional ES such as deep brain stimulation for Parkinson’s disease, utilises metal electrodes that are hard wired to a power supply to deliver the stimulation. Bipolar electrochemistry (BPE) introduces an innovative approach to cell stimulation that is wireless. Developing conducting polymers (CPs)-based stimulation platforms wireless powdered by BPE bipolar will provide an exciting new dimension to medical bionics. In this project, Chapter 2 deals with development of a bipolar electrochemical activity testing system and bipolar electrochemical stimulation (BPES) system. Then, bipolar electroactive and biocompatible CPs grown on FTO substrate are successfully synthesised, modified, and characterised in Chapter 3 and Chapter 4 using the above systems prior to using for wireless cell stimulation. Furthermore, free standing and soft CP templates are developed (Chapter 5). More importantly, all these bipolar electroactive CPs have been applied to wireless cell stimulation using BPE (all research Chapters). Significant increase in both cell number and neurite growth has been demonstated, suggesting that the BPES system is highly efficient for stimulation of animal PC 12 cell and human SH-SY5Y cell. More specific information is presented in each chapter as below. In Chapter 3, a CP-based bipolar electrochemical stimulation (BPES) system for cell stimulation was present. Polypyrrole (PPy) films with different dopants have demonstrated reversible and recoverable bipolar electrochemical activity under a low driving DC voltage

Developing a new generation of neuro-prosthetic interfaces: structure-function correlates of viable retina-CNT biohybrids

PhD ThesisOne of the many challenges in the development of neural prosthetic devices is the choice of electrode material. Electrodes must be biocompatible, and at the same time, they must be able to sustain repetitive current injections in a highly corrosive physiological environment. We investigated the suitability of carbon nanotube (CNT) electrodes for retinal prosthetics by studying prolonged exposure to retinal tissue and repetitive electrical stimulation of retinal ganglion cells (RGCs). Experiments were performed on retinal wholemounts isolated from the Cone rod homeobox (CRX) knockout mouse, a model of Leber congenital amaurosis. Retinas were interfaced at the vitreo-retinal juncture with CNT assemblies and maintained in physiological conditions for up to three days to investigate any anatomical (immunohistochemistry and electron microscopy) and electrophysiological changes (multielectrode array stimulation and recordings; electrodes were made of CNTs or commercial titanium nitride). Anatomical characterisation of the inner retina, including RGCs, astrocytes and Müller cells as well as cellular matrix and inner retinal vasculature, provide strong evidence of a gradual remodelling of the retina to incorporate CNT assemblies, with very little indication of an immune response. Prolonged electrophysiological recordings, performed over the course of three days, demonstrate a gradual increase in signal amplitudes, lowering of stimulation thresholds and an increase in cellular recruitment for RGCs interfaced with CNT electrodes, but not with titanium nitride electrodes. These results provide for the first time electrophysiological, ultrastructural and cellular evidence of the time-dependent formation of strong and viable bio-hybrids between the RGC layer and CNT arrays in intact retinas. We conclude that CNTs are a promising material for inclusion in retinal prosthetic devices

Out-of-plane graphene materials for enhanced cell-chip coupling

Bioelectronic devices interact directly with biological systems to monitor cellular electrical activity and promote cell reaction to electrical stimulation. The capabilities of such devices, in terms of recording and stimulation, are affected by the effective cell-platform coupling. Therefore, during the last years, the development of engineered 2.5-3D micro and nanostructures has improved the effectiveness of biosensors using protruding structures to achieve a more intimate contact between cells and substrates. The vertical structures, due to their surface curvature, can actively modulate the cell-material interaction and the coupling conditions by regulating peculiar cellular processes at the interface such as membrane bending, ruffling, which ultimately reduce the distance between the electroactive materials and the biological components. In parallel, the rising of carbon-based materials (i.e., graphene) for bioelectronics has gained attention during the last years because of their outstanding chemical properties which allow improved cell-device interfacing. Given this scenario, 3D out-of-the-plane graphene structures has been designed and grown on planar platforms, exploiting the electrical, mechanical and optical features of this promising material. 3D fuzzy graphene (3DFG) and two nanowire-templated arrangements (NT-3DFG collapsed and non-collapsed) were realized to ultimately increase the dimensionality at the interface with cells through nanoscale features and wire-based architectures. Here we report a comprehensive study of the electrogenic cells-material interface by using fluorescence and electron microscopy for characterizing cell-graphene materials interactions at micro and nanoscale. First, we investigated the biocompatibility and the adhesion effect (cell stretching and outgrowth) of the diverse graphene-based pseudo-3D surfaces coupled to cardiomyocytes-like cells and primary cortical neuronal cells. Then, we examined the membrane deformation and the actual cell-device coupling via scanning electron microscopy/focused ion beam sectioning. We found out an enhanced cells adhesion on the substrates, suggesting that out-of-the-plane platform could improve the coupling between cells and sensors not only for electrophysiology application but also to modulate cellular functionalities and outgrowth

Interfacing graphene with peripheral neurons: influence of neurite outgrowth and NGF axonal transport

Graphene displays properties that make it appealing for neuroregenerative medicine, yet the potential of large-scale highly-crystalline graphene as a conductive peripheral neural interface has been scarcely investigated. In particular, pristine graphene offers enhanced electrical properties that can be advantageous for nervous system regeneration applications. In this work, we investigate graphene potential as peripheral nerve interface. First, we perform an unprecedented analysis aimed at revealing how the typical polymeric coatings for neural cultures distribute on graphene at the nanometric scale. Second, we examine the impact of graphene on the culture of two established cellular models for peripheral nervous system: PC12 cell line and primary embryonic rat dorsal root ganglion (DRG) neurons, showing a better and faster axonal elongation using graphene. We then observe that the axon elongation in the first days of culture correlates to an altered nerve growth factor (NGF) axonal transport, with a reduced number of retrogradely moving NGF vesicles in favor of stalled vesicles. We thus hypothesize that the axon elongation observed in the first days of culture could be mediated by this pool of NGF vesicles locally retained in the medial/distal parts of axons. Furthermore, we investigate electrophysiological properties and cytoskeletal structure of peripheral neurons. We observe a reduced neural excitability and altered membrane potential together with a reduced inter-microtubular distance on graphene and correlate these electrophysiological and structural reorganizations of axon physiology to the observed vesicle stalling. Finally, the potential of another 2D material as neural interface, tungsten disulfide, is explored