Sponge-like nanostructured conducting polymers for electrically controlled drug release

Drug delivery via a 3D electro-swellable conjugated polymer hydrogel

Spatiotemporal controlled drug delivery minimizes side-effects and enables therapies that require specific dosing patterns. Conjugated polymers (CP) can be used for electrically controlled drug delivery; however so far, most demonstrations were limited to molecules up to 500 Da. Larger molecules could be incorporated only during the CP polymerization and thus limited to a single delivery. This work harnesses the record volume changes of a glycolated polythiophene p(g3T2) for controlled drug delivery. p(g3T2) undergoes reversible volumetric changes of up to 300% during electrochemical doping, forming pores in the nm-size range, resulting in a conducting hydrogel. p(g3T2)-coated 3D carbon sponges enable controlled loading and release of molecules spanning molecular weights of 800-6000 Da, from simple dyes up to the hormone insulin. Molecules are loaded as a combination of electrostatic interactions with the charged polymer backbone and physical entrapment in the porous matrix. Smaller molecules leak out of the polymer while larger ones could not be loaded effectively. Finally, this work shows the temporally patterned release of molecules with molecular weight of 1300 Da and multiple reloading and release cycles without affecting the on/off ratio.

The Alphabet of Nanostructured Polypyrrole

This review is devoted to polypyrrole and its morphology, which governs the electroactivity of the material. The macroscopic properties of the material are strictly relevant to microscopic ordering observed at the local level. During the synthesis, various (nano)morphologies can be produced. The formation of the ordered structure is dictated by the ability of the local forces and effects to induce restraints that help shape the structure. This review covers the aspects of morphology and roughness and their impact on the final properties of the modified electrode activity in selected applications.

Recent development of polymer nanomicelles in the treatment of eye diseases

The eye, being one of the most intricate organs in the human body, hosts numerous anatomical barriers and clearance mechanisms. This highlights the importance of devising a secure and efficacious ocular medication delivery system. Over the past several decades, advancements have been made in the development of a nano-delivery platform based on polymeric micelles. These advancements encompass diverse innovations such as poloxamer, chitosan, hydrogel-encapsulated micelles, and contact lenses embedded with micelles. Such technological evolutions allow for sustained medication retention and facilitate enhanced permeation within the eye, thereby standing as the avant-garde in ocular medication technology. This review provides a comprehensive consolidation of ocular medications predicated on polymer nanomicelles from 2014 to 2023. Additionally, it explores the challenges they pose in clinical applications, a discussion intended to aid the design of future clinical research concerning ocular medication delivery formulations.

Conductive polymers and composites-based systems: An incipient stride in drug delivery and therapeutics realm

Novel therapies and drug delivery systems (DDS) emphasis on localized, personalized, triggered, and regulated drug administration have heavily implicated electrically responsive DDS. An ideal DDS must deliver drugs to the target region at therapeutically effective concentrations to elicit a pharmacological response, resulting in better prophylaxis of the disease and the treatment. Biodegradable polymers are frequently employed for in-vivo long-term release; however, dose dumping can be anticipated. As a result, current DDSs can be tagged as dubbed "Smart Biomaterials" since they only focus on an on-demand cargo release in response to a trigger or stimulation. These organic materials have been recognized for their metal-like conductivity, as well as their mechanical stability and ease of production. These biomaterials can be programmed to respond to both internal and external stimuli. External pulsed triggers are required for extrinsic stimuli-responsive materials, whereas intrinsic stimuli-responsive materials rely on localized changes in the tissue environment. Furthermore, these materials have the ability to deliver active pharmaceutical agents at a varied concentration levels and across a broad spectrum of action. Drug delivery, biomedical implant technology, biosensor technology, and tissue engineering can be listed as a few prominent applications that have sparked immense interest for conductive polymers-based research and advancements in academia as well as in industry. This review comprehensively covers a cutting-edge collection of electrically conductive polymers and composites, and provide detailed insights of recent trends and advancements allied to conductive polymers for their potential applicability in an array of diverse meadows primarily focusing on drug delivery, biosensing and therapeutics. Furthermore, progressions in their synthesis, structural and functional properties have been presented in conjunction with futuristic directions for the smooth clinical translations.

An Insight of Nanomaterials in Tissue Engineering from Fabrication to Applications

Tissue engineering is a research domain that deals with the growth of various kinds of tissues with the help of synthetic composites. With the culmination of nanotechnology and bioengineering, tissue engineering has emerged as an exciting domain. Recent literature describes its various applications in biomedical and biological sciences, such as facilitating the growth of tissue and organs, gene delivery, biosensor-based detection, etc. It deals with the development of biomimetics to repair, restore, maintain and amplify or strengthen several biological functions at the level of tissue and organs. Herein, the synthesis of nanocomposites based on polymers, along with their classification as conductive hydrogels and bioscaffolds, is comprehensively discussed. Furthermore, their implementation in numerous tissue engineering and regenerative medicine applications is also described. The limitations of tissue engineering are also discussed here. The present review highlights and summarizes the latest progress in the tissue engineering domain directed at functionalized nanomaterials.

Conductive Biomaterials as Bioactive Wound Dressing for Wound Healing and Skin Tissue Engineering

Conductive biomaterials based on conductive polymers, carbon nanomaterials, or conductive inorganic nanomaterials demonstrate great potential in wound healing and skin tissue engineering, owing to the similar conductivity to human skin, good antioxidant and antibacterial activities, electrically controlled drug delivery, and photothermal effect. However, a review highlights the design and application of conductive biomaterials for wound healing and skin tissue engineering is lacking. In this review, the design and fabrication methods of conductive biomaterials with various structural forms including film, nanofiber, membrane, hydrogel, sponge, foam, and acellular dermal matrix for applications in wound healing and skin tissue engineering and the corresponding mechanism in promoting the healing process were summarized. The approaches that conductive biomaterials realize their great value in healing wounds via three main strategies (electrotherapy, wound dressing, and wound assessment) were reviewed. The application of conductive biomaterials as wound dressing when facing different wounds including acute wound and chronic wound (infected wound and diabetic wound) and for wound monitoring is discussed in detail. The challenges and perspectives in designing and developing multifunctional conductive biomaterials are proposed as well.

Electroactive Biomaterials and Systems for Cell Fate Determination and Tissue Regeneration: Design and Applications

During natural tissue regeneration, tissue microenvironment and stem cell niche including cell-cell interaction, soluble factors, and extracellular matrix (ECM) provide a train of biochemical and biophysical cues for modulation of cell behaviors and tissue functions. Design of functional biomaterials to mimic the tissue/cell microenvironment have great potentials for tissue regeneration applications. Recently, electroactive biomaterials have drawn increasing attentions not only as scaffolds for cell adhesion and structural support, but also as modulators to regulate cell/tissue behaviors and function, especially for electrically excitable cells and tissues. More importantly, electrostimulation can further modulate a myriad of biological processes, from cell cycle, migration, proliferation and differentiation to neural conduction, muscle contraction, embryogenesis, and tissue regeneration. In this review, endogenous bioelectricity and piezoelectricity are introduced. Then, design rationale of electroactive biomaterials is discussed for imitating dynamic cell microenvironment, as well as their mediated electrostimulation and the applying pathways. Recent advances in electroactive biomaterials are systematically overviewed for modulation of stem cell fate and tissue regeneration, mainly including nerve regeneration, bone tissue engineering, and cardiac tissue engineering. Finally, the significance for simulating the native tissue microenvironment is emphasized and the open challenges and future perspectives of electroactive biomaterials are concluded.

Electrically Stimulated Tunable Drug Delivery From Polypyrrole-Coated Polyvinylidene Fluoride

Electrical stimulus-responsive drug delivery from conducting polymers such as polypyrrole (PPy) has been limited by lack of versatile polymerization techniques and limitations in drug-loading strategies. In the present study, we report an in-situ chemical polymerization technique for incorporation of biotin, as the doping agent, to establish electrosensitive drug release from PPy-coated substrates. Aligned electrospun polyvinylidene fluoride (PVDF) fibers were used as a substrate for the PPy-coating and basic fibroblast growth factor and nerve growth factor were the model growth factors demonstrated for potential applications in musculoskeletal tissue regeneration. It was observed that 18-h of continuous polymerization produced an optimal coating of PPy on the surface of the PVDF electrospun fibers with significantly increased hydrophilicity and no substantial changes observed in fiber orientation or individual fiber thickness. This PPy-PVDF system was used as the platform for loading the aforementioned growth factors, using streptavidin as the drug-complex carrier. The release profile of incorporated biotinylated growth factors exhibited electrosensitive release behavior while the PPy-PVDF complex proved stable for a period of 14 days and suitable as a stimulus responsive drug delivery depot. Critically, the growth factors retained bioactivity after release. In conclusion, the present study established a systematic methodology to prepare PPy coated systems with electrosensitive drug release capabilities which can potentially be used to encourage targeted tissue regeneration and other biomedical applications.

Soft Template Electropolymerization of Polypyrrole for Improved pH-Induced Drug Delivery

Chronic wounds are characterized by a localized pH change from acidic (healthy) to alkaline (unhealthy), which can be harnessed to act as a switch for drug release from a polymer medium covering the wound for improved healing. To realize this, a new polymer dressing material is needed to help heal chronic wounds. Polypyrrole (PPy) is a biocompatible electroactive polymer that has been proven as a successful drug delivery mechanism, but currently lacks the capacity for scalable clinical applications due to its poor processability. In this study, PPy films with and without microstructures were produced using electrochemical oxidation and subsequently doped with fluorescein, a model drug molecule. To increase the drug loading capacity, microstructures were created through soft template polymerization of pyrrole around hydrogen gas bubbles. Fluorescein release was measured using UV spectroscopy over a pH range of 2 to 11, showing increased release at higher pH values. Microstructured films showed an increased doping capacity compared to flat PPy films, attributed to the increase in drug incorporation sites. The pH-activated release mechanism was shown to be successful and can be applied as a pH-sensitive biosensor and drug delivery system in vitro.

Electro-responsive controlled drug delivery from melanin nanoparticles

Electro-responsive controlled drug delivery has been receiving an increasing interest as one of the on-demand drug delivery systems, aiming the improvement of the therapeutics efficacy by controlling the amount of drug release at a specific time and target site. Herein, we report a simple method to develop an electro-responsive controlled drug delivery system using functionalized melanin nanoparticles (FMNPs) with polydopamine and polypyrrole to precisely control the release of dexamethasone (Dex). Optimized FMNPs showed 376.77 ± 62.05 nm of particle size, a polydispersity index of 0.26 ± 0.09 and a zeta-potential (ZP) of -32.59 ± 3.61 mV. FMNPs evidenced a spherical shape, which was confirmed by scanning electron microscopy. Fourier-transform infrared spectrometry analysis confirmed the deposition of the polymers on the FMNPs' surface. The incorporation efficiency of the optimized Dex-loaded FMNPs was 94.45 ± 0.63% and the increase of ZP to -40.34 ± 4.65 mV was attributed to the anionic nature of Dex. In vitro Dex release studies without stimuli revealed a maximum Dex release below 10%. Applying electrical stimulation, Dex release was augmented, with a maximum of ca. 32% after 24 h. The designed FMNPs provide a powerful biomaterial-based technological tool for electro-responsive controlled drug delivery, capable of surpassing the associated lack of efficiency and stability of current carriers.

Unfolding the future: Self-controlled catalytic nanomotor in healthcare system

Nanomotors, multimetallic systems are biologically inspired self-propelled tiny engines able to perform difficult tasks of transporting cargos from one end to another in presence of hydrogen peroxide fuel. Nanomotors can revolutionize the drug delivery system at the desired target by converting chemical energy into mechanical energy. Nanomotors exhibit unique properties like moving at higher speed, self-propulsion and drilling into the complex cellular environment. The review focuses on fuel dependent and fuel-free nanomotors with their propulsion mechanism. Further, the review highlights the method of fabrication, biohybrid nanomotors, toxicities along with their application in the field of active drug delivery, diabetes, precise surgery, ischemic stroke therapy, diagnosis and treatment of coronavirus, microwave hyperthermia, zika virus detection, anti-bacterial activity, water treatment and sensing and challenges lying at the forefront in the development of these tiny nanomachines. Hydrogen peroxide is toxic to mankind; biohybrid motors give an extra edge of eliminating hydrogen peroxide as fuel for self-propulsion, this can be used for smart drug delivery by reducing toxicities as compared to artificial nanomotors. Cost-effective fabrication of nanomotors will extend their applications in commercial sector overcoming limitations like scale-up and regulatory approval. In near future, nanomotors will diversify in fields of restoring conductivity of electronic medical devices, 3D printing and theranostics.

Construction of a graphene/polypyrrole composite electrode as an electrochemically controlled release system

A biocompatible conductive composite electrode GN–PPy–FL can realize controlled release of a drug model triggered by low voltages.

Incorporation of Conductive Materials into Hydrogels for Tissue Engineering Applications

In the field of tissue engineering, conductive hydrogels have been the most effective biomaterials to mimic the biological and electrical properties of tissues in the human body. The main advantages of conductive hydrogels include not only their physical properties but also their adequate electrical properties, which provide electrical signals to cells efficiently. However, when introducing a conductive material into a non-conductive hydrogel, a conflicting relationship between the electrical and mechanical properties may develop. This review examines the strengths and weaknesses of the generation of conductive hydrogels using various conductive materials such as metal nanoparticles, carbons, and conductive polymers. The fabrication method of blending, coating, and in situ polymerization is also added. Furthermore, the applications of conductive hydrogel in cardiac tissue engineering, nerve tissue engineering, and bone tissue engineering and skin regeneration are discussed in detail.

Ultra-low voltage triggered release of an anti-cancer drug from polypyrrole nanoparticles

We have synthesized polypyrrole nanoparticles using three different oxidizing agents (hydrogen peroxide, chloroauric acid and ferric chloride) and shown that films assembled from these nanoparticles have significantly different drug release profiles. When ferric chloride is used as the oxidizing agent, it is possible to release drugs at voltages as low as -0.05 V, almost an order of magnitude lower than typically used voltages. These ultra-low voltage responsive nanoparticles widen the window of operation of conducting polymers and enable delivery of redox active drugs. As an example, we have shown pulsed release of the chemotherapeutic methotrexate at voltages as low as -0.075 V, demonstrating the potential application of these nanoparticles in cancer treatment. We have also verified the anti-tumor efficacy of the released drug using PC12 cell cultures.

Electroactive biomaterials: Vehicles for controlled delivery of therapeutic agents for drug delivery and tissue regeneration

Electrical stimulation for delivery of biochemical agents such as genes, proteins and RNA molecules amongst others, holds great potential for controlled therapeutic delivery and in promoting tissue regeneration. Electroactive biomaterials have the capability of delivering these agents in a localized, controlled, responsive and efficient manner. These systems have also been combined for the delivery of both physical and biochemical cues and can be programmed to achieve enhanced effects on healing by establishing control over the microenvironment. This review focuses on current state-of-the-art research in electroactive-based materials towards the delivery of drugs and other therapeutic signalling agents for wound care treatment. Future directions and current challenges for developing effective electroactive approach based therapies for wound care are discussed.

Micelle directed chemical polymerization of polypyrrole particles for the electrically triggered release of dexamethasone base and dexamethasone phosphate

Conducting polymers such as polypyrrole (PPy) can be used as electrically responsive drug delivery systems typically prepared by electrochemical polymerisation, however, the amount of drug that can be delivered is typically low. To increase drug delivery capacity and prepare larger amounts of polymer, PPy nanoparticles were produced by chemical polymerisation over drug-loaded micelles. Two forms of dexamethasone were included to increase total drug loading and to explore the mechanisms of loading and release. The particles produced were approximately 50 nm in size and their conductivity and reversible redox activity were demonstrated. Loading of the hydrophobic dexamethasone base was more efficient than for the more hydrophilic phosphate salt. After pressing the particles into the desired form, electrically-responsive drug release was achieved with a pulsed potential signal being the most effective way to trigger release. Notably, the anionic phosphate salt of the drug was more sensitive to electrically stimulated release than the uncharged base of dexamethasone, highlighting the role of electrostatic forces in driving drug release. This system has potential to be loaded with different drugs widening the scope of application of these smart particles to treat a range of disease states.

A Materials Roadmap to Functional Neural Interface Design

Advancement in neurotechnologies for electrophysiology, neurochemical sensing, neuromodulation, and optogenetics are revolutionizing scientific understanding of the brain while enabling treatments, cures, and preventative measures for a variety of neurological disorders. The grand challenge in neural interface engineering is to seamlessly integrate the interface between neurobiology and engineered technology, to record from and modulate neurons over chronic timescales. However, the biological inflammatory response to implants, neural degeneration, and long-term material stability diminish the quality of interface overtime. Recent advances in functional materials have been aimed at engineering solutions for chronic neural interfaces. Yet, the development and deployment of neural interfaces designed from novel materials have introduced new challenges that have largely avoided being addressed. Many engineering efforts that solely focus on optimizing individual probe design parameters, such as softness or flexibility, downplay critical multi-dimensional interactions between different physical properties of the device that contribute to overall performance and biocompatibility. Moreover, the use of these new materials present substantial new difficulties that must be addressed before regulatory approval for use in human patients will be achievable. In this review, the interdependence of different electrode components are highlighted to demonstrate the current materials-based challenges facing the field of neural interface engineering.

Visual Prosthesis: Interfacing Stimulating Electrodes with Retinal Neurons to Restore Vision

The bypassing of degenerated photoreceptors using retinal neurostimulators is helping the blind to recover functional vision. Researchers are investigating new ways to improve visual percepts elicited by these means as the vision produced by these early devices remain rudimentary. However, several factors are hampering the progression of bionic technologies: the charge injection limits of metallic electrodes, the mechanical mismatch between excitable tissue and the stimulating elements, neural and electric crosstalk, the physical size of the implanted devices, and the inability to selectively activate different types of retinal neurons. Electrochemical and mechanical limitations are being addressed by the application of electromaterials such as conducting polymers, carbon nanotubes and nanocrystalline diamonds, among other biomaterials, to electrical neuromodulation. In addition, the use of synthetic hydrogels and cell-laden biomaterials is promising better interfaces, as it opens a door to establishing synaptic connections between the electrode material and the excitable cells. Finally, new electrostimulation approaches relying on the use of high-frequency stimulation and field overlapping techniques are being developed to better replicate the neural code of the retina. All these elements combined will bring bionic vision beyond its present state and into the realm of a viable, mainstream therapy for vision loss.

Electrically-responsive core-shell hybrid microfibers for controlled drug release and cell culture

It is an active research field to develop fiber-shaped smart materials for biomedical applications. Here we report the development of the multifunctional core-shell hybrid microfibers with excellent mechanical and electrical performance as a new smart biomaterial. The microfibers were synthesized using a combination of co-axial spinning with a microfluidic device and subsequent dip-coating, containing a hydrogel core of bacterial cellulose (BC) and a conductive polymer shell layer of poly(3,4-ethylenedioxythiophene) (PEDOT). The hybrid microfibers were featured with a well-controlled microscopic morphology, exhibiting enhanced mechanic properties. A model drug, diclofenac sodium, can be loaded in the core layer of the microfibers in situ during the process of synthesis. Our experiments suggested that the releasing behaviors of the drug molecules from the microfibers were enhanced by external electrical stimulation. Interestingly, we demonstrated an excellent biocompatibility and electroactivity of the hybrid microfibers for PC12 cell culture, thus promising a flexible template for the reconstruction of electrically-responsive tissues mimicking muscle fibers or nerve networks.

STATEMENT OF SIGNIFICANCE

Fiber-shaped biomaterials are useful in creating various functional objects from one dimensional to three-dimensional. The fabrication of microfibers with integrated physicochemical properties and bio-performance has drawn an increasing attention on researchers from chemical to biomedical. This study combined biocompatible bacterial cellulose with electroconductive poly(3,4-ethylenedioxythiophene) and further reduced them to a highly electroactive BC/PEDOT core-shell microfiber electrode for electrochemical actuator design. The result showed that the microfibers were well fabricated and the release of drugs from the microfibers was enhanced and could be controlled under electrical stimulation externally. Considering the excellent biocompatibility and electroactive toward PC12 cells, these microfibers may find use as templates for the reconstruction of fiber-shaped functional tissues that mimic muscle fibers, blood vessels or nerve networks in vivo.

Self-powered therapeutic release from conducting polymer/graphene oxide films on magnesium

Magnesium's complete in vivo degradation is appealing for medical implant applications. Rapid corrosion and hydrogen bubble generation along with inflammatory host tissue response have limited its clinical use. Here we electropolymerized a poly (3,4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) film directly on Mg surface. GO acted as nano-drug carrier to carry anti-inflammatory drug dexamethasone (Dex). PEDOT/GO/Dex coatings improved Mg corrosion resistance and decreased the rate of hydrogen production. Dex could be released driven by the electrical current generated from Mg corrosion. The anti-inflammatory activity of the released Dex was confirmed in microglia cultures. This PEDOT/GO/Dex film displayed the ability to both control Mg corrosion and act as an on demand release coating that delivers Dex at the corrosion site to minimize detrimental effects of corrosion byproducts. Such multi-functional smart coating will improve the clinical use of Mg implants. Furthermore, the PEDOT/GO/Drug/Mg system may be developed into self-powered implantable drug delivery devices.

A Simple Approach for Molecular Controlled Release based on Atomic Layer Deposition Hybridized Organic-Inorganic Layers

On-demand release of bioactive substances with high spatial and temporal control offers ground-breaking possibilities in the field of life sciences. However, available strategies for developing such release systems lack the possibility of combining efficient control over release with adequate storage capability in a reasonably compact system. In this study we present a new approach to target this deficiency by the introduction of a hybrid material. This organic-inorganic material was fabricated by atomic layer deposition of ZnO into thin films of polyethylene glycol, forming the carrier matrix for the substance to be released. Sub-surface growth mechanisms during this process converted the liquid polymer into a solid, yet water-soluble, phase. This layer permits extended storage for various substances within a single film of only a few micrometers in thickness, and hence demands minimal space and complexity. Improved control over release of the model substance Fluorescein was achieved by coating the hybrid material with a conducting polymer film. Single dosage and repetitive dispensing from this system was demonstrated. Release was controlled by applying a bias potential of ±0.5 V to the polymer film enabling or respectively suppressing the expulsion of the model drug. In vitro tests showed excellent biocompatibility of the presented system.

Nano-engineered electro-responsive drug delivery systems

Nano-engineering is exploited to address the slow drug release and low drug loading of electro-responsive drug delivery systems.

A Review of Patterned Organic Bioelectronic Materials and their Biomedical Applications

Organic electronic materials are rapidly emerging as superior replacements for a number of conventional electronic materials, such as metals and semiconductors. Conducting polymers, carbon nanotubes, graphenes, organic light-emitting diodes, and diamond films fabricated via chemical vapor deposition are the most popular organic bioelectronic materials that are currently under active research and development. Besides the capability to translate biological signals to electrical signals or vice versa, organic bioelectronic materials entail greater biocompatibility and biodegradability compared to conventional electronic materials, which makes them more suitable for biomedical applications. When patterned, these materials bring about numerous capabilities to perform various tasks in a more-sophisticated and high-throughput manner. Here, we provide an overview of the unique properties of organic bioelectronic materials, different strategies applied to pattern these materials, and finally their applications in the field of biomedical engineering, particularly biosensing, cell and tissue engineering, actuators, and drug delivery.

Electro-responsive macroporous polypyrrole scaffolds for triggered dexamethasone delivery

Corticosteroids such as dexamethasone are first line ophthalmic treatment for non-infectious posterior uveitis. Corticosteroids are often administered via intravitreal injection to treat this condition with frequent injections associated with poor treatment adherence and complications such as endophthalmitis. Current ocular implants provide sustained corticosteroid release at predetermined rates and lack the ability for dose individualisation. This study describes the successful fabrication of electrically responsive macroporous polypyrrole (PPy) thin films, and their subsequent application to triggered dexamethasone release. Colloidal crystal films composed of 370nm polymethylmethacrylate colloids were first deposited on ITO coated glass substrates, and subsequently used as sacrificial templates for the fabrication of high surface area, 3-dimensionally ordered macroporous PPy inverse opal (PPy IO) thin films. SEM, UV-Vis reflectance and cyclic voltammetry measurements established that the redox state of the PPy IO films could be controlled via electrical stimulation, which in turn influences both porosity and optical properties of the films. Incorporation of the anti-inflammatory corticosteroid, dexamethasone phosphate (DexP), in the PPy IO films during their fabrication resulted in an effective delivery platform for triggered DexP release. A sustained release profile was observed for the PPy IO-DexP films, bursts of release could be triggered by electrical stimulation. The amount of DexP released from the PPy IO-DexP films was significantly higher than that released from the conventional non-porous PPy-DexP films of comparable mass. Results suggest that electrically responsive PPy IO structures are highly suitable for on-demand drug delivery applications. This technology may enable physicians to fine-tune the required dose according to disease state and patients' needs to enhance the safety and efficacy of corticosteroid treatment.

Biomaterials for Bone Regenerative Engineering

Strategies for bone tissue regeneration have been continuously evolving for the last 25 years since the introduction of the "tissue engineering" concept. The convergence of the life, physical, and engineering sciences has brought in several advanced technologies available to tissue engineers and scientists. This resulted in the creation of a new multidisciplinary field termed as "regenerative engineering". In this article, the role of biomaterials in bone regenerative engineering is systematically reviewed to elucidate the new design criteria for the next generation of biomaterials for bone regenerative engineering. The exemplary design of biomaterials harnessing various materials characteristics towards successful bone defect repair and regeneration is highlighted. Particular attention is given to the attempts of incorporating advanced materials science, stem cell technologies, and developmental biology into biomaterials design to engineer and develop the next generation bone grafts.

Photoelectric artefact from optogenetics and imaging on microelectrodes and bioelectronics: New Challenges and Opportunities

Bioelectronics, electronic technologies that interface with biological systems, are experiencing rapid growth in terms of technology development and applications, especially in neuroscience and neuroprosthetic research. The parallel growth with optogenetics and in vivo multi-photon microscopy has also begun to generate great enthusiasm for simultaneous applications with bioelectronic technologies. However, emerging research showing artefact contaminated data highlight the need for understanding the fundamental physical principles that critically impact experimental results and complicate their interpretation. This review covers four major topics: 1) material dependent properties of the photoelectric effect (conductor, semiconductor, organic, photoelectric work function (band gap)); 2) optic dependent properties of the photoelectric effect (single photon, multiphoton, entangled biphoton, intensity, wavelength, coherence); 3) strategies and limitations for avoiding/minimizing photoelectric effects; and 4) advantages of and applications for light-based bioelectronics (photo-bioelectronics).

Elastic, conductive, polymeric hydrogels and sponges

As a result of inherent rigidity of the conjugated macromolecular chains resulted from the delocalized π-electron system along the polymer backbone, it has been a huge challenge to make conducting polymer hydrogels elastic by far. Herein elastic and conductive polypyrrole hydrogels with only conducting polymer as the continuous phase have been simply synthesized in the indispensable conditions of 1) mixed solvent, 2) deficient oxidant, and 3) monthly secondary growth. The elastic mechanism and oxidative polymerization mechanism on the resulting PPy hydrogels have been discussed. The resulting hydrogels show some novel properties, e.g., shape memory elasticity, fast functionalization with various guest objects, and fast removal of organic infectants from aqueous solutions, all of which cannot be observed from traditional non-elastic conducting polymer counterparts. What's more, light-weight, elastic, and conductive organic sponges with excellent stress-sensing behavior have been successfully achieved via using the resulting polypyrrole hydrogels as precursors.

Anti-inflammatory polymer electrodes for glial scar treatment: bringing the conceptual idea to future results

Conducting polymer films offer a convenient route for the functionalization of implantable microelectrodes without compromising their performance as excellent recording units. A micron thick coating, deposited on the surface of a regular metallic electrode, can elute anti-inflammatory drugs for the treatment of glial scarring as well as growth factors for the support of surrounding neurons. Electro-activation of the polymer drives the release of the substance and should ideally provide a reliable method for controlling quantity and timing of release. Driving signals in the form of a constant potential (CP), a slow redox sweep or a fast pulse are all represented in literature. Few studies present such release in vivo from actual recording and stimulating microelectronic devices. It is essential to bridge the gap between studies based on release in vitro, and the intended application, which would mean release into living and highly delicate tissue. In the biological setting, signals are limited both by available electronics and by the biological safety. Driving signals must not be harmful to tissue and also not activate the tissue in an uncontrolled manner. This review aims at shedding more light on how to select appropriate driving parameters for the polymer electrodes for the in vivo setting. It brings together information regarding activation thresholds for neurons, as well as injury thresholds, and puts this into context with what is known about efficient driving of release from conducting polymer films.

A review of organic and inorganic biomaterials for neural interfaces

Recent advances in nanotechnology have generated wide interest in applying nanomaterials for neural prostheses. An ideal neural interface should create seamless integration into the nervous system and performs reliably for long periods of time. As a result, many nanoscale materials not originally developed for neural interfaces become attractive candidates to detect neural signals and stimulate neurons. In this comprehensive review, an overview of state-of-the-art microelectrode technologies provided fi rst, with focus on the material properties of these microdevices. The advancements in electro active nanomaterials are then reviewed, including conducting polymers, carbon nanotubes, graphene, silicon nanowires, and hybrid organic-inorganic nanomaterials, for neural recording, stimulation, and growth. Finally, technical and scientific challenges are discussed regarding biocompatibility, mechanical mismatch, and electrical properties faced by these nanomaterials for the development of long-lasting functional neural interfaces.

Generalized green synthesis and formation mechanism of sponge-like ferrite micro-polyhedra with tunable structure and composition

This paper describes a green versatile glucose-engineered precipitation-sintering process that allows for the selective and mass preparation of spongy porous ferrite (M = Fe, Zn, Co, Ni, Mn, etc.) micro-polyhedra with tunable morphology, texture, and composition. Some kinetic factors, such as the molar ratio of glucose to metal nitrates, reaction temperature, sintering temperature and time, and type of metal nitrates, can be expediently employed to modulate their aspect ratio, shape, size, composition, and textural properties. In this protocol, glucose functions as a reductant, protecting agent, structure-directing agent, and a sacrificial template to guide the assembly of sheet-like nuclei into polyhedral precursors and the formation of spongy porous structures. Owing to larger EM parameters, multiresonant behavior, and dissipative current, spongy porous Fe3O4 polyhedra exhibited enhanced microwave-absorbing properties. This endows them with important potential applications in magnetic devices, catalysis, sorption, photoluminescence, electromagnetic wave absorbing materials, anode materials, and so on. Meanwhile, this general approach can be extended to synthesize other porous sponges with regular geometric configuration because it is simple, inexpensive, environmentally benign, and suitable for extensive production.

Poly(3,4-ethylenedioxythiophene)/multiwall carbon nanotube composite coatings for improving the stability of microelectrodes in neural prostheses applications

With the purpose of improving the stability of microelectrodes under continuous high charge density stimulation, which is required for neural prostheses applications such as visual prostheses, multiwall carbon nanotube (MWCNT)-doped poly(3,4-ethylenedioxythiophene) (PEDOT) composite films were coated onto a platinum microelectrode by electrochemical polymerization. Galvanostatically polymerized PEDOT/MWCNT films demonstrated superior characteristics compared to polystyrene sulfonate doping and potentiostatic polymerization, including a three-dimensional cone morphology and enhanced electrochemical performance (the safe charge injection limit reached 6.2 mC cm(-2) for cathodic-first pulses). Most important of all, the improved stability of the coatings has been revealed through stimulation for 96 h using 3.0 mCc m(-2) current pulses in bicarbonate- and phosphate-buffered saline solution. Cell assays revealed that PEDOT/MWCNT films could promote the adhesion and neurite outgrowth of rat pheochromocytoma cells. Finally, platinum wires coated with PEDOT/MWCNT films were implanted into rat cortex for 6 weeks for histological evaluation. Glial fibrillary acidic protein and neuronal nuclei staining revealed that the films elicit a lower tissue response compared to platinum implants. These results suggest that the galvanostatically polymerized PEDOT/MWCNT films can improve the stability of stimulation microelectrodes and that PEDOT/MWCNT is an excellent candidate material for electrode coating for neural prostheses applications.

Advances in Drug-delivery Systems Based on Intrinsically Conducting Polymers

Intrinsically conducting polymers (ICPs) are organic polymers with unique capabilities including the ability to conduct electricity. The release of drugs from ICP-based drug delivery systems can be controlled using electrical signaling to alter the redox state of the ICP, leading to subsequent changes in polymer charge and volume. The increasing use of ICPs in drug delivery systems can be attributed to their biocompatible nature and the ability to regulate drug release electrically. Drug can be easily incorporated into these polymers by physical and chemical means. As the release of the drugs from ICPs is in accordance with electrical stimulus the therapeutic effect can be maximized with a reduction in the side effects. In this chapter a general overview of ICPs, their electrochemical properties and the techniques used to characterize these materials with specifics pertaining to drug delivery is provided. Emphasis is given to advances in methods and technology to enhance the drug-loading capacity of these polymers and to achieve precise controlled therapy. The chapter discusses some of the exciting applications of ICPs as devices for controlled delivery of drugs to desired locations.

Organic bioelectronics for electronic-to-chemical translation in modulation of neuronal signaling and machine-to-brain interfacing

BACKGROUND

A major challenge when creating interfaces for the nervous system is to translate between the signal carriers of the nervous system (ions and neurotransmitters) and those of conventional electronics (electrons).

SCOPE OF REVIEW

Organic conjugated polymers represent a unique class of materials that utilizes both electrons and ions as charge carriers. Based on these materials, we have established a series of novel communication interfaces between electronic components and biological systems. The organic electronic ion pump (OEIP) presented in this review is made of the polymer-polyelectrolyte system poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The OEIP translates electronic signals into electrophoretic migration of ions and neurotransmitters.

MAJOR CONCLUSIONS

We demonstrate how spatio-temporally controlled delivery of ions and neurotransmitters can be used to modulate intracellular Ca(2+) signaling in neuronal cells in the absence of convective disturbances. The electronic control of delivery enables strict control of dynamic parameters, such as amplitude and frequency of Ca(2+) responses, and can be used to generate temporal patterns mimicking naturally occurring Ca(2+) oscillations. To enable further control of the ionic signals we developed the electrophoretic chemical transistor, an analog of the traditional transistor used to amplify and/or switch electronic signals. Finally, we demonstrate the use of the OEIP in a new "machine-to-brain" interface by modulating brainstem responses in vivo.

GENERAL SIGNIFICANCE

This review highlights the potential of communication interfaces based on conjugated polymers in generating complex, high-resolution, signal patterns to control cell physiology. We foresee widespread applications for these devices in biomedical research and in future medical devices within multiple therapeutic areas. This article is part of a Special Issue entitled Organic Bioelectronics-Novel Applications in Biomedicine.