Fabrication of conductive electrospun silk fibroin scaffolds by coating with polypyrrole for biomedical applications

Electrically conductive coatings in tissue engineering

Recent interest in tissue engineering (TE) has focused on electrically conductive biomaterials. This has been inspired by the characteristics of the cells' microenvironment where signalling is supported by electrical stimulation. Numerous studies have demonstrated the positive influence of electrical stimulation on cell excitation to proliferate, differentiate, and deposit extracellular matrix. Even without external electrical stimulation, research shows that electrically active scaffolds can improve tissue regeneration capacity. Tissues like bone, muscle, and neural contain electrically excitable cells that respond to electrical cues provided by implanted biomaterials. To introduce an electrical pathway, TE scaffolds can incorporate conductive polymers, metallic nanoparticles, and ceramic nanostructures. However, these materials often do not meet implantation criteria, such as maintaining mechanical durability and degradation characteristics, making them unsuitable as scaffold matrices. Instead, depositing conductive layers on TE scaffolds has shown promise as an efficient alternative to creating electrically conductive structures. A stratified scaffold with an electroactive surface synergistically excites the cells through active top-pathway, with/without electrical stimulation, providing an ideal matrix for cell growth, proliferation, and tissue deposition. Additionally, these conductive coatings can be enriched with bioactive or pharmaceutical components to enhance the scaffold's biomedical performance. This review covers recent developments in electrically active biomedical coatings for TE. The physicochemical and biological properties of conductive coating materials, including polymers (polypyrrole, polyaniline and PEDOT:PSS), metallic nanoparticles (gold, silver) and inorganic (ceramic) particles (carbon nanotubes, graphene-based materials and Mxenes) are examined. Each section explores the conductive coatings' deposition techniques, deposition parameters, conductivity ranges, deposit morphology, cell responses, and toxicity levels in detail. Furthermore, the applications of these conductive layers, primarily in bone, muscle, and neural TE are considered, and findings from in vitro and in vivo investigations are presented. STATEMENT OF SIGNIFICANCE: Tissue engineering (TE) scaffolds are crucial for human tissue replacement and acceleration of healing. Neural, muscle, bone, and skin tissues have electrically excitable cells, and their regeneration can be enhanced by electrically conductive scaffolds. However, standalone conductive materials often fall short for TE applications. An effective approach involves coating scaffolds with a conductive layer, finely tuning surface properties while leveraging the scaffold's innate biological and physical support. Further enhancement is achieved by modifying the conductive layer with pharmaceutical components. This review explores the under-reviewed topic of conductive coatings in tissue engineering, introducing conductive biomaterial coatings and analyzing their biological interactions. It provides insights into enhancing scaffold functionality for tissue regeneration, bridging a critical gap in current literature.

Polypyrrole-based structures for activation of cellular functions under electrical stimulation

Polypyrrole (Ppy) is an electroconductive polymer used in various applications, including in vitro experiments with cell cultures under electrical stimulation (ES). Ppy can be applied in various forms and most importantly, it is biocompatible with cells. Ppy specifically directs ES to cells, which makes Ppy a potential polymer for the development of novel technologies for targeted tissue regeneration. The high potential of ES in combination with different Ppy-based systems, such as hydrogels, scaffolds, or Ppy-layers is advantageous to stimulate cellular differentiation towards neurogenic, cardiac, muscle, and osteogenic lineages. Different in-house devices and the principles of ES application used to stimulate cellular functions are reviewed and summarized. The focus of this review is to observe the most relevant studies and their in-house techniques regarding the application of Ppy-based materials for the use of bone, neural, cardiac, and muscle tissue regeneration under ES. Different types of Ppy materials, such as Ppy particles, layers/films, membranes, and 3D-shaped synthetic and natural scaffolds, as well as combining Ppy with different active molecules are reviewed.

From Nature to Technology: Exploring Bioinspired Polymer Actuators via Electrospinning

Nature has always been a source of inspiration for the development of novel materials and devices. In particular, polymer actuators that mimic the movements and functions of natural organisms have been of great interest due to their potential applications in various fields, such as biomedical engineering, soft robotics, and energy harvesting. During recent years, the development and actuation performance of electrospun fibrous meshes with the advantages of high permeability, surface area, and easy functional modification, has received extensive attention from researchers. This review covers the recent progress in the state-of-the-art electrospun actuators based on commonly used polymers such as stimuli-sensitive hydrogels, shape-memory polymers (SMPs), and electroactive polymers. The design strategies inspired by nature such as hierarchical systems, layered structures, and responsive interfaces to enhance the performance and functionality of these actuators, including the role of biomimicry to create devices that mimic the behavior of natural organisms, are discussed. Finally, the challenges and future directions in the field, with a focus on the development of more efficient and versatile electrospun polymer actuators which can be used in a wide range of applications, are addressed. The insights gained from this review can contribute to the development of advanced and multifunctional actuators with improved performance and expanded application possibilities.

Electrical Stimulation Increases Axonal Growth from Dorsal Root Ganglia Co-Cultured with Schwann Cells in Highly Aligned PLA-PPy-Au Microfiber Substrates

Nerve regeneration is a slow process that needs to be guided for distances greater than 5 mm. For this reason, different strategies are being studied to guide axonal growth and accelerate the axonal growth rate. In this study, we employ an electroconductive fibrillar substrate that is able to topographically guide axonal growth while accelerating the axonal growth rate when subjected to an exogenous electric field. Dorsal root ganglia were seeded in co-culture with Schwann cells on a substrate of polylactic acid microfibers coated with the electroconductive polymer polypyrrole, adding gold microfibers to increase its electrical conductivity. The substrate is capable of guiding axonal growth in a highly aligned manner and, when subjected to an electrical stimulation, an improvement in axonal growth is observed. As a result, an increase in the maximum length of the axons of 19.2% and an increase in the area occupied by the axons of 40% were obtained. In addition, an upregulation of the genes related to axon guidance, axogenesis, Schwann cells, proliferation and neurotrophins was observed for the electrically stimulated group. Therefore, our device is a good candidate for nerve regeneration therapies.

The Contribution of Silk Fibroin in Biomedical Engineering

Silk fibroin (SF) is a natural protein (biopolymer) extracted from the cocoons of Bombyx mori L. (silkworm). It has many properties of interest in the field of biotechnology, the most important being biodegradability, biocompatibility and robust mechanical strength with high tensile strength. SF is usually dissolved in water-based solvents and can be easily reconstructed into a variety of material formats, including films, mats, hydrogels, and sponges, by various fabrication techniques (spin coating, electrospinning, freeze-drying, and physical or chemical crosslinking). Furthermore, SF is a feasible material used in many biomedical applications, including tissue engineering (3D scaffolds, wounds dressing), cancer therapy (mimicking the tumor microenvironment), controlled drug delivery (SF-based complexes), and bone, eye and skin regeneration. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the main methods used for ecological extraction and processing of SF that make it a green material are discussed. Lastly, technological advances in the use of SF-based materials are addressed, especially in healthcare applications such as tissue engineering and cancer therapeutics.

Atomistic Simulation of Water Incorporation and Mobility in Bombyx mori Silk Fibroin

Bombyx mori silk fibroin (SF) is a biopolymer that can be processed into materials with attractive properties (e.g., biocompatibility and degradability) for use in a multitude of technical and medical applications (including textiles, sutures, drug delivery devices, tissue scaffolds, etc.). Utilizing the information from experimental and computational SF studies, a simplified SF model has been produced (alanine-glycine [Ala-Gly] _n crystal structure), enabling the application of both molecular dynamic and density functional theory techniques to offer a unique insight into SF-based materials. The secondary structure of the computational model has been evaluated using Ramachandran plots under different environments (e.g., different temperatures and ensembles). In addition, the mean square displacement of water incorporated into the SF model was investigated: the diffusion coefficients, activation energies, most and least favorable positions of water, and trajectory of water diffusion through the SF model are obtained. With further computational study and in combination with experimental data, the behavior/degradation of SF (and similar biomaterials) can be elucidated. Consequently, greater control of the aforementioned technologies may be achieved and positively affect their potential applications.

In Situ Construction of Co-MoS2/Pd Nanosheets on Polypyrrole-Derived Nitrogen-Doped Carbon Microtubes as Multifunctional Catalysts with Enhanced Catalytic Performance

The structural design of multiple functional components could integrate synergistic effects to enhance the catalytic performance of MoS₂-based composites for catalytic applications. Herein, one-dimensional (1D) Co-MoS₂/Pd@NCMTs composites were designed to prepare Co-doped MoS₂/Pd nanosheets (NSs) on N-doped carbon microtubes (NCMTs) from tubular polypyrrole (PPy) as multifunctional catalysts. The Co-MoS₂/Pd@NCMTs composites integrated the synergistic effects of Co-doping, a 1D tubular structure, and noble-metal Pd decoration. Thus, a higher catalytic activity was observed in 4-nitrophenol (4-NP) reduction and peroxidase-like catalysis than other components, such as MoS₂, MoS₂@NCMTs, and Co-MoS₂@NCMTs. Remarkably, the results indicated that the dissolution, diffusion, and redistribution led to the dissolution of MoO₃@ZIF-67 cores and generation of Co-doped MoS₂ NSs. Benefiting from the synergistic effect from these components, Co-MoS₂/Pd@NCMTs were considered as a facile colorimetric sensing platform for detecting tannic acid. Moreover, outstanding performance was realized in the reduction of 4-NP with the composites. Thus, we provide a simple synthetic strategy for simultaneously integrating electronic engineering and structural advantages to develop an efficient MoS₂-based multifunctional catalyst.

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.

Bioengineering silk into blood vessels

The rising incidence of cardiovascular disease has increased the demand for small diameter (<6 mm) synthetic vascular grafts for use in bypass surgery. Clinically available synthetic grafts (polyethylene terephthalate and expanded polytetrafluorethylene) are incredibly strong, but also highly hydrophobic and inelastic, leading to high rates of failure when used for small diameter bypass. The poor clinical outcomes of commercial synthetic grafts in this setting have driven significant research in search of new materials that retain favourable mechanical properties but offer improved biocompatibility. Over the last several decades, silk fibroin derived from Bombyx mori silkworms has emerged as a promising biomaterial for use in vascular applications. Progress has been driven by advances in silk manufacturing practices which have allowed unprecedented control over silk strength, architecture, and the ensuing biological response. Silk can now be manufactured to mimic the mechanical properties of native arteries, rapidly recover the native endothelial cell layer lining vessels, and direct positive vascular remodelling through the regulation of local inflammatory responses. This review summarises the advances in silk purification, processing and functionalisation which have allowed the production of robust vascular grafts with promise for future clinical application.

Nerve guidance conduit development for primary treatment of peripheral nerve transection injuries: A commercial perspective

Commercial nerve guidance conduits (NGCs) for repair of peripheral nerve discontinuities are of little use in gaps larger than 30 mm, and for smaller gaps they often fail to compete with the autografts that they are designed to replace. While recent research to develop new technologies for use in NGCs has produced many advanced designs with seemingly positive functional outcomes in animal models, these advances have not been translated into viable clinical products. While there have been many detailed reviews of the technologies available for creating NGCs, none of these have focussed on the requirements of the commercialisation process which are vital to ensure the translation of a technology from bench to clinic. Consideration of the factors essential for commercial viability, including regulatory clearance, reimbursement processes, manufacturability and scale up, and quality management early in the design process is vital in giving new technologies the best chance at achieving real-world impact. Here we have attempted to summarise the major components to consider during the development of emerging NGC technologies as a guide for those looking to develop new technology in this domain. We also examine a selection of the latest academic developments from the viewpoint of clinical translation, and discuss areas where we believe further work would be most likely to bring new NGC technologies to the clinic. STATEMENT OF SIGNIFICANCE: NGCs for peripheral nerve repairs represent an adaptable foundation with potential to incorporate modifications to improve nerve regeneration outcomes. In this review we outline the regulatory processes that functionally distinct NGCs may need to address and explore new modifications and the complications that may need to be addressed during the translation process from bench to clinic.

Conductive Polyaniline Patterns on Electrospun Polycaprolactone/Hydroxyapatite Scaffolds for Bone Tissue Engineering

Currently, the challenge for bone tissue engineering is to design a scaffold that would mimic the structure and biological functions of the extracellular matrix and would be able to direct the appropriate response of cells through electrochemical signals, thus stimulate faster bone formation. The purpose of the presented research was to perform and evaluate PCL/n-HAp scaffolds locally modified with a conductive polymer-polyaniline. The material was obtained using electrospinning, and a simple ink-jet printing method was applied to receive the conductive polyaniline patterns on the surface of the electrospun materials. The samples of scaffolds were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal analysis (DSC, TGA), and infrared spectroscopy (FTIR) before and after immersion of the material in Simulated Body Fluid. The effect of PANI patterns on changes in the SBF mineralization process and cell morphology was evaluated in order to prove that the presented material enables the growth and proliferation of bone cells.

Intrinsically Conductive Polymers for Striated Cardiac Muscle Repair

One of the most important features of striated cardiac muscle is the excitability that turns on the excitation-contraction coupling cycle, resulting in the heart blood pumping function. The function of the heart pump may be impaired by events such as myocardial infarction, the consequence of coronary artery thrombosis due to blood clots or plaques. This results in the death of billions of cardiomyocytes, the formation of scar tissue, and consequently impaired contractility. A whole heart transplant remains the gold standard so far and the current pharmacological approaches tend to stop further myocardium deterioration, but this is not a long-term solution. Electrically conductive, scaffold-based cardiac tissue engineering provides a promising solution to repair the injured myocardium. The non-conductive component of the scaffold provides a biocompatible microenvironment to the cultured cells while the conductive component improves intercellular coupling as well as electrical signal propagation through the scar tissue when implanted at the infarcted site. The in vivo electrical coupling of the cells leads to a better regeneration of the infarcted myocardium, reducing arrhythmias, QRS/QT intervals, and scar size and promoting cardiac cell maturation. This review presents the emerging applications of intrinsically conductive polymers in cardiac tissue engineering to repair post-ischemic myocardial insult.

Critical review on microfibrous composites for applications in chemical engineering

Microfibrous composites (MCs) are novel materials with unique structures and excellent functional properties, showing great potential in industrial applications. The investigation of the physicochemical properties of MCs is significant for accommodating the rapid development of high-efficiency chemical engineering industries. In this review, the characteristics, synthesis and applications of different types of previously reported MCs are discussed according to the constituent fibres, including polymers, metals and nonmetals. Among the different types of MCs, polymer MCs have a facile synthesis process and adjustable fibre composition, making them suitable for many complex situations. The high thermal and electrical conductivity of metal MCs enables their application in strong exothermic, endothermic and electrochemical reactions. Nonmetallic MCs are usually stable and corrosion resistant when reducing and oxidizing environments. The disadvantages of MCs, such as complicated synthesis processes compared to those of particles or powders, high cost, insufficient thorough study, and unsatisfactory regeneration effects, are also summarized. As a result, a more systematic investigation of MCs remains necessary. Despite the advantages and great application potential of microfibrous composites, much effort remains necessary to advance them to the industrial level in the chemical engineering industry.

Conductive polypyrrole-encapsulated silk fibroin fibers for cardiac tissue engineering

Polypyrrole (PPy) has been utilized in smart scaffolds to improve the functionality of the engineered cardiac tissue. Compared to the commonly used aqueous coating, here, PPy was blended into silk fibroin (SF) solution to electrospin conductive PPy-encapsulated SF nanofibers. Combinations of various SF concentrations (5%, 7%, and 12%) and different PPy-to-SF ratios (15:85, 30:70, and 40:60) were compared. PPy reduced the fiber diameter (0.431 ± 0.060 μm), better-mimicking the myocardium fibrils. Conductive mats with 7% SF showed the closest mechanical properties (1.437 ± 0.044 MPa) to the native myocardium; meanwhile, a PPy-to-SF ratio of 15:85 exhibited sufficient electrical conductivity for cardiomyocytes (CMs). In vitro studies using three different types of CM demonstrated that the hybrid mats support CM contraction. Primary neonatal rat CMs on the mat with a PPy-to-SF ratio of 15:85 were elongated and orientated anisotropically with locally organized sarcomeric striations. By contrast, human-induced pluripotent stem cell derived-CMs on the mat with a PPy-to-SF ratio of 30:70 exhibited the strongest contractions. Contraction synchrony was further improved by external stimulation. Taken together, these findings indicated the great potential of the PPy-encapsulated SF electrospun mat for cardiac tissue engineering.

Redox Polymers for Tissue Engineering

This review will focus on the targeted design, synthesis and application of redox polymers for use in regenerative medicine and tissue engineering. We define redox polymers to encompass a variety of polymeric materials, from the multifunctional conjugated conducting polymers to graphene and its derivatives, and have been adopted for use in the engineering of several types of stimulus responsive tissues. We will review the fundamental properties of organic conducting polymers (OCPs) and graphene, and how their properties are being tailored to enhance material - biological interfacing. We will highlight the recent development of high-resolution 3D fabrication processes suitable for biomaterials, and how the fabrication of intricate scaffolds at biologically relevant scales is providing exciting opportunities for the application of redox polymers for both in-vitro and in-vivo tissue engineering. We will discuss the application of OCPs in the controlled delivery of bioactive compounds, and the electrical and mechanical stimulation of cells to drive behaviour and processes towards the generation of specific functional tissue. We will highlight the relatively recent advances in the use of graphene and the exploitation of its physicochemical and electrical properties in tissue engineering. Finally, we will look forward at the future of organic conductors in tissue engineering applications, and where the combination of materials development and fabrication processes will next unite to provide future breakthroughs.

Conductive Materials for Healing Wounds: Their Incorporation in Electroactive Wound Dressings, Characterization, and Perspectives

The use of conductive materials to promote the activity of electrically responsive cells is an effective means of accelerating wound healing. This article focuses on recent advancements in conductive materials, with emphasis on overviewing their incorporation with non-conducting polymers to fabricate electroactive wound dressings. The characteristics of these electroactive dressings are deliberated, and the mechanisms on how they accelerate the wound healing process are discussed. Potential directions for the future development of electroactive wound dressings and their potential in monitoring the course of wound healing in vivo concomitantly are also proposed.

BDNF-Gene Transfected Schwann Cell-Assisted Axonal Extension and Sprouting on New PLA-PPy Microfiber Substrates

The work here reported analyzes the effect of increased efficiency of brain-derived neurotrophic factor (BDNF) production by electroporated Schwann cells (SCs) on the axonal extension in a coculture system on a biomaterial platform that can be of interest for the treatment of injuries of the nervous system, both central and peripheral. Rat SCs are electrotransfected with a plasmid coding for the BDNF protein in order to achieve an increased expression and release of this protein into the culture medium of the cells, performing the best balance between the level of transfection and the number of living cells. Gene-transfected SCs show an about 100-fold increase in the release of BDNF into the culture medium, compared to nonelectroporated SCs. Cocultivation of electroporated SCs with rat dorsal root ganglia (DRG) is performed on highly aligned substrates of polylactic acid (PLA) microfibers coated with the electroconductive polymer polypyrrol (PPy). The coculture of DRG with electrotransfected SCs increase both the axonal extension and the axonal sprouting from DRG neurons compared to the coculture of DRG with nonelectroporated SCs. Therefore, the use of PLA-PPy highly aligned microfiber substrates preseeded with electrotransfected SCs with an increased BDNF secretion is capable of both guiding and accelerating axonal growth.

Scale-up of Electrospinning: Market Overview of Products and Devices for Pharmaceutical and Biomedical Purposes

Recently, the electrospinning (ES) process has been extensively studied due to its potential applications in various fields, particularly pharmaceutical and biomedical purposes. The production rate using typical ES technology is usually around 0.01-1 g/h, which is lower than pharmaceutical industry production requirements. Therefore, different companies have worked to develop electrospinning equipment, technological solutions, and electrospun materials into large-scale production. Different approaches have been explored to scale-up the production mainly by increasing the nanofiber jet through multiple needles, free-surface technologies, and hybrid methods that use an additional energy source. Among them, needleless and centrifugal methods have gained the most attention and applications. Besides, the production rate reached (450 g/h in some cases) makes these methods feasible in the pharmaceutical industry. The present study overviews and compares the most recent ES approaches successfully developed for nanofibers' large-scale production and accompanying challenges with some examples of applied approaches in drug delivery systems. Besides, various types of commercial products and devices released to the markets have been mentioned.

Effects of surface condition of conductive electrospun nanofiber mats on cell behavior for nerve tissue engineering

Electrospun nanofibrous scaffold is a promising implant for peripheral nerve regeneration. Herein, to investigate the effect of surface morphological features and electrical properties of scaffolds on nerve cell behavior, we modified electrospun cellulose (EC) fibrous mats with four kind of soluble conductive polymers derivates (poly (N-(methacryl ethyl) pyrrole) (PMAEPy), poly (N-(2-hydroxyethyl) pyrrole) (PHEPy), poly (3-(Ethoxycarbonyl) thiophene) (P3ECT) and poly (3-thiophenethanol) (P3TE)) by an in-situ polymerization method. The morphological characterization showed that conductive polymers formed aggregated nanoparticles and coatings on the EC nanofibers with the increased fiber diameter further affected the surface properties. Compared with pure EC scaffold, more PC12 cells were adhered and grown on modified mats, with more integral and clearer cell morphology. The results of protein adsorption study indicated that modified EC mats could provide more protein adsorption site due to their characteristic surface morphology, which is beneficial to cell adhesion and growth. The results in this study suggested that these conductive polymers modified scaffolds with special surface morphology have potential applications in neural tissue engineering.

Silkworm and spider silk electrospinning: a review

Issues of fossil fuel and plastic pollution are shifting public demand toward biopolymer-based textiles. For instance, silk, which has been traditionally used during at least 5 milleniums in China, is re-emerging in research and industry with the development of high-tech spinning methods. Various arthropods, e.g. insects and arachnids, produce silky proteinic fiber of unique properties such as resistance, elasticity, stickiness and toughness, that show huge potential for biomaterial applications. Compared to synthetic analogs, silk presents advantages of low density, degradability and versatility. Electrospinning allows the creation of nonwoven mats whose pore size and structure show unprecedented characteristics at the nanometric scale, versus classical weaving methods or modern techniques such as melt blowing. Electrospinning has recently allowed to produce silk scaffolds, with applications in regenerative medicine, drug delivery, depollution and filtration. Here we review silk production by the spinning apparatus of the silkworm Bombyx mori and the spiders Aranea diadematus and Nephila Clavipes. We present the biotechnological procedures to get silk proteins, and the preparation of a spinning dope for electrospinning. We discuss silk's mechanical properties in mats obtained from pure polymer dope and multi-composites. This review highlights the similarity between two very different yarn spinning techniques: biological and electrospinning processes.

Multifunctional Conductive Biomaterials as Promising Platforms for Cardiac Tissue Engineering

Adult cardiomyocytes are terminally differentiated cells that result in minimal intrinsic potential for the heart to self-regenerate. The introduction of novel approaches in cardiac tissue engineering aims to repair damages from cardiovascular diseases. Recently, conductive biomaterials such as carbon- and gold-based nanomaterials, conductive polymers, and ceramics that have outstanding electrical conductivity, acceptable mechanical properties, and promoted cell-cell signaling transduction have attracted attention for use in cardiac tissue engineering. Nevertheless, comprehensive classification of conductive biomaterials from the perspective of cardiac cell function is a subject for discussion. In the present review, we classify and summarize the unique properties of conductive biomaterials considered beneficial for cardiac tissue engineering. We attempt to cover recent advances in conductive biomaterials with a particular focus on their effects on cardiac cell functions and proposed mechanisms of action. Finally, current problems, limitations, challenges, and suggested solutions for applications of these biomaterials are presented.

Application of conductive PPy/SF composite scaffold and electrical stimulation for neural tissue engineering

Electrical stimulation (ES) with conductive polymers can dramatically enhance neurite outgrowth and promote neural regeneration. However, besides ES, the practical applications of neural repair is also highly dependent on the nerve cell functionality and response to substrate conductivity. Therefore, the combination of the ES and suitable materials, such as tissue scaffolds, has been applied to facilitate treatment of neural injuries and demonstrated great potential in peripheral nerve regeneration. In this study, polypyrrole/silk fibroin (PPy/SF) conductive composite scaffold was fabricated by 3D bioprinting and electrospinning. Schwann cells seeded on these scaffolds were electrically stimulated and hence demonstrated enhanced viability, proliferation and migration, as well as upregulated expression of neurotrophic factors. Furthermore, the constructed PPy/SF conductive nerve guidance conduits accompanying with ES could effectively promote axonal regeneration and remyelination in vivo. Moreover, we found that the MAPKs signal transduction pathway was activated by ES at the conductive conduit. Our findings demonstrate that the PPy/SF conductive composite scaffolds with longitudinal guidance exhibit favorable properties for clinical use and promotes nerve regeneration and functional recovery.

Polypyrrole-Incorporated Conducting Constructs for Tissue Engineering Applications: A Review

Conductive polymers have recently attracted interest in biomedical applications because of their excellent intrinsic electrical conductivity and satisfactory biocompatibility. Polypyrrole (PPy) is one of the most popular among these conductive polymers due to its high conductivity under physiological conditions, and it can be chemically modified to allow biomolecules conjugation. PPy has been used in fabricating biocompatible stimulus-responsive scaffolds for tissue engineering applications, especially for repair and regeneration of electroactive tissues, such as the bone, neuron, and heart. This review provides a comprehensive overview of the basic properties and synthesis methods of PPy, as well as a summary of the materials that have been integrated with PPy. These composite scaffolds are comparatively evaluated with regard to their mechanical properties, biocompatibility, and usage in tissue engineering.

Silk fibres exhibiting biodegradability & superhydrophobicity for recovery of petroleum oils from oily wastewater

Present study reports superhydrophobic-oleophilic, environment-friendly, & biodegradable silk material derived from Bombyx mori silkworm, for practical oil-water separation and oil recovery applications. In this study, raw silk fibers were degummed using water and Na₂CO₃ (at 100 °C), for removal of outer gummy sericin protein layer, which was confirmed using FTIR & FE-SEM analysis. The water & Na₂CO₃ degummed silk fibers showed superhydrophobicity with water contact angles (WCA) of 153° & 158°, respectively, demonstrating Wenzel & Cassi-Baxter states. Degummed silk fibers showed superoleophilicity (OCA∼0°) towards petroleum oils like Petrol, Diesel, & Engine oil. The water & Na₂CO₃ degummed silk fibers showed oil-water separation efficiencies of 95 % & 87.5 %, respectively. Both degummed silk fibers showed more than 50 % efficiency till 10 separation cycles. Further, raw & degummed silk fibers showed an environmental biocompatibility, by their biodegradation under in-house developed biotic de-compost culture consisting of biodegrading micro-organisms. Their analysis showed that biotic de-compost culture rendered biodegradation weight loss of 11 % and 18 %, respectively, in 35 days. Successive results showed that, degummed silk fibers can be effectively utilized for practical oil-water separation, and further, they can be environmentally biodegraded, thereby mitigating their waste generation and disposal problem.

Photocatalytic Performance of Electrospun Silk Fibroin/ZnO Mats to Remove Pesticide Residues from Water under Natural Sunlight

We have evaluated the efficiency of silk fibroin (SF) coated with ZnO nanoparticles in the photocatalytic disappearance of one acaricide (etoxazole) and three fungicides (difenoconazole, myclobutanil and penconazole) in water exposed to sunlight irradiation. Electrospun SF/ZnO mats were successfully synthesized by electrospinning technique and characterized by XRD, FE-SEM, XPS, XDS, FTIR, and BET. The influence of catalyst loading on the degradation kinetics of the different pesticides was examined in order to gain knowledge of maximum degradation efficiency. A significant increment in degradation rates was observed with the addition of ZnO. SF mats with 25 mg of ZnO were finally selected since no significant differences (p < 0.05) were detected when the loading was enlarged from 25 to 50 mg for the majority of the compounds. In the experimental conditions, the half-lives ranged from 33 min to 93 min for etoxazole and myclobutanil, respectively. The comparison of SF materials coated with similar amount of TiO2 and ZnO showed that the later was slightly more efficient to remove pesticide residues. Hence, the use of electrospun SF/ZnO nanostructures would provide an environmentally friendly approach with photocatalytic activity to be applied in the reclamation of water polluted by pesticides.

Natural polypeptides-based electrically conductive biomaterials for tissue engineering

Fabrication of an appropriate scaffold is the key fundamental step required for a successful tissue engineering (TE). The artificial scaffold as extracellular matrix in TE has noticeable role in the fate of cells in terms of their attachment, proliferation, differentiation, orientation and movement. In addition, chemical and electrical stimulations affect various behaviors of cells such as polarity and functionality. Therefore, the fabrication approach and materials used for the preparation of scaffold should be more considered. Various synthetic and natural polymers have been used extensively for the preparation of scaffolds. The electrically conductive polymers (ECPs), moreover, have been used in combination with other polymers to apply electric fields (EF) during TE. In this context, composites of natural polypeptides and ECPs can be taken into account as context for the preparation of suitable scaffolds with superior biological and physicochemical features. In this review, we overviewed the simultaneous usage of natural polypeptides and ECPs for the fabrication of scaffolds in TE.

Progressive trends in heavy metal ions and dyes adsorption using silk fibroin composites

Thriving industrialization for human lifestyle headway has seeded the roots of water intoxication with harmful and hazardous toxic metal ions and dyes, which may ingress into food chains and become homicidal or mutation causing for creatures. The degummed functionalized silk fibroin composites with different biomaterials and synthetic materials are able to show adsorption efficiencies equivalent to 52.5%, 90%, 81.1%, 93.75%, 84.2%, and 98.9% for chromium, copper, cadmium, lead, thorium, and uranium ions, respectively, and adsorption capacity of 88.5 mg/g, 74.63 mg/g, 76.34 mg/g, and 72 mg/L for acid yellow 11, naphthol orange, direct orange S, and methylene blue, respectively, which make them desirable solution for water toxicants removal. This review is intended to describe the ability of silk fibroins to adsorb and abolish toxic heavy metal ions and dyes from water reservoirs, thus, providing a way to step toward water sanitation and wholesome living. Graphical abstract.

Electrospun silk fibroin/TiO2 mats. Preparation, characterization and efficiency for the photocatalytic solar treatment of pesticide polluted water

The photocatalytic properties of silk fibroin (SF) incorporating TiO₂ nanoparticles using an electrospinning technique were examined. Electrospun SF/TiO₂ mats were successfully prepared and characterized by different techniques (XRD, FE-SEM, XPS, XDS, FTIR and BET). The photocatalytic efficiency of these materials were assessed by their ability to degrade four pesticides (boscalid, hexythiazox, pyraclostrobin and trifloxystrobin) in water exposed to solar irradiation. The effect of catalyst loading on the disappearance kinetics of the different pesticides was studied in order to determine the maximum degradation efficiency. The degradation rate significantly increases upon adding the TiO₂. However, no significant differences (p < 0.05) were observed when the TiO₂ loading was increased from 25 to 50 mg for most compounds. Thus, SF mats with 25 mg of TiO₂ were selected. Therefore, a new and simple approach to produce materials with photocatalytic activity, safety and potential application in the purification of water contaminated by pesticides has been developed.

The photocatalytic properties of silk fibroin (SF) incorporating TiO₂ nanoparticles using an electrospinning technique were examined.

A Comprehensive Review on Bio-Nanomaterials for Medical Implants and Feasibility Studies on Fabrication of Such Implants by Additive Manufacturing Technique

Nanomaterials have allowed significant breakthroughs in bio-engineering and medical fields. In the present paper a holistic assessment on diverse biocompatible nanocomposites are studied. Their compatibility with advanced fabrication methods such as additive manufacturing for the design of functional medical implants is also critically reviewed. The significance of nanocomposites and processing techniques is also envisaged comprehensively in regard with the needs and futures of implantable medical device industries.

Design of Self-Healing and Electrically Conductive Silk Fibroin-Based Hydrogels

Self-healing and electrically conductive silk fibroin (SF)-based hydrogels were developed based on the dynamic assembly/disassembly nature of supramolecular complexes and the conductive nature of polypyrrole (PPy). The self-healing properties of the hydrogels were achieved through host-guest interactions between β-cyclodextrin and amino acid side chains (tyrosine, tryptophan, phenylalanine, and histidine) on SF. PPy deposition was achieved via in situ polymerization of pyrrole using ammonium persulfate as an oxidant and laccase as a catalyst. The PPy-coated hydrogels behaved as an elastomer and displayed excellent electrical properties, with adjustable electrical conductivities ranging from 0.8 ± 0.2 to (1.0 ± 0.3) × 10^-3 S·cm^-1. Furthermore, possibility of potential utilization of the hydrogels in electrochemistry applications as flexible yet self-healable electrode materials was explored. This study not only shows great potential in expanding the role of silk-based devices for various applications but also provides a useful approach for designing multifunctional self-healing protein-based hydrogels.

Flexible and Stretchable PEDOT-Embedded Hybrid Substrates for Bioengineering and Sensory Applications

Herein, we introduce a flexible, biocompatible, robust and conductive electrospun fiber mat as a substrate for flexible and stretchable electronic devices for various biomedical applications. To impart the electrospun fiber mats with electrical conductivity, poly(3,4-ethylenedioxythiophene) (PEDOT), a conductive polymer, was interpenetrated into nitrile butadiene rubber (NBR) and poly(ethylene glycol) dimethacrylate (PEGDM) crosslinked electrospun fiber mats. The mats were fabricated with tunable fiber orientation, random and aligned, and displayed elastomeric mechanical properties and high conductivity. In addition, bending the mats caused a reversible change in their resistance. The cytotoxicity studies confirmed that the elastomeric and conductive electrospun fiber mats support cardiac cell growth, and thus are adaptable to a wide range of applications, including tissue engineering, implantable sensors and wearable bioelectronics.

Conjugated Polymer Actuators and Devices: Progress and Opportunities

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or "artificial muscles" for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.

Silk fibroin scaffolds seeded with Wharton's jelly mesenchymal stem cells enhance re-epithelialization and reduce formation of scar tissue after cutaneous wound healing

Background

The treatment of extensive and/or chronic skin wounds is a widespread and costly public health problem. Mesenchymal stem cells (MSCs) have been proposed as a potential cell therapy for inducing wound healing in different clinical settings, alone or in combination with biosynthetic scaffolds. Among them, silk fibroin (SF) seeded with MSCs has been shown to have increased efficacy in skin wound healing experimental models.

Methods

In this report, we investigated the wound healing effects of electrospun SF scaffolds cellularized with human Wharton’s jelly MSCs (Wj-MSCs-SF) using a murine excisional wound splinting model.

Results

Immunohistopathological examination after transplant confirmed the presence of infiltrated human fibroblast-like CD90-positive cells in the dermis of the Wj-MSCs-SF-treated group, yielding neoangiogenesis, decreased inflammatory infiltrate and myofibroblast proliferation, less collagen matrix production, and complete epidermal regeneration.

Conclusions

These findings indicate that Wj-MSCs transplanted in the wound bed on a silk fibroin scaffold contribute to the generation of a well-organized and vascularized granulation tissue, enhance reepithelization of the wound, and reduce the formation of fibrotic scar tissue, highlighting the potential therapeutic effects of Wj-MSC-based tissue engineering approaches to non-healing wound treatment.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1229-6) contains supplementary material, which is available to authorized users.

Roles of electrical stimulation in promoting osteogenic differentiation of BMSCs on conductive fibers

The strategy of using conductive materials in regenerating bone defects is attractive, benefiting from the bioelectricity feature of natural bone tissues. Thereby, POP conductive fibers were fabricated by coating polypyrrole (PPY) onto electrospun poly(l-lactide) (PLLA) fibers, and their potentials in promoting osteogenic differentiation of bone mesenchymal stromal cells (BMSCs) were investigated. Different from the smooth-surfaced PLLA fibers, POP fibers were rough-surfaced and favorable for protein adsorption and mineralization nucleation. When electrical stimulation (ES) was applied, the surface charges on the conductive POP fibers further promoted the protein adsorption and the mineral deposition, while the non-conductive PLLA fibers displayed no such promotion. When BMSCs were cultured on these fibers, strong cell viability was detected, indicating their good biocompatibility and cell affinity. In osteogenic differentiation studies, BMSCs demonstrated the strongest ability in differentiating toward osteoblasts when they were cultured on the POP fibers under ES, followed by the case without ES. In comparison with the conductive POP fibers, the non-conductive PLLA fibers displayed significantly weaker ability in inducing the osteogenic differentiation of BMSCs with ES being applied or not. Alongside the differentiation, both the calcium deposition on BMSC/material complexes and the intracellular Ca²⁺ concentration were identified the most abundant when BMSCs grew on the POP fibers under ES. These findings suggested that the surface charges of conductive fibers played roles in regulating protein adsorption, ion migration and nucleation, particularly under ES, which contributed much to the increased intracellular Ca²⁺ ions, and thus accelerated the osteogenic differentiation of the seeded cells. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Macroscale Biomolecular Electronics and Ionics

The conduction of ions and electrons over multiple length scales is central to the processes that drive the biological world. The multidisciplinary attempts to elucidate the physics and chemistry of electron, proton, and ion transfer in biological charge transfer have focused primarily on the nano- and microscales. However, recently significant progress has been made on biomolecular materials that can support ion and electron currents over millimeters if not centimeters. Likewise, similar transport phenomena in organic semiconductors and ionics have led to new innovations in a wide variety of applications from energy generation and storage to displays and bioelectronics. Here, the underlying principles of conduction on the macroscale in biomolecular materials are discussed, highlighting recent examples, and particularly the establishment of accurate structure-property relationships to guide rationale material and device design. The technological viability of biomolecular electronics and ionics is also discussed.

Bioactive Silk-Based Nerve Guidance Conduits for Augmenting Peripheral Nerve Repair

Repair of peripheral nerve injuries depends upon complex biology stemming from the manifold and challenging injury-healing processes of the peripheral nervous system. While surgical treatment options are available, they tend to be characterized by poor clinical outcomes for the injured patients. This is particularly apparent in the clinical management of a nerve gap whereby nerve autograft remains the best clinical option despite numerous limitations; in addition, effective repair becomes progressively more difficult with larger gaps. Nerve conduit strategies based on tissue engineering approaches and the use of silk as scaffolding material have attracted much attention in recent years to overcome these limitations and meet the clinical demand of large gap nerve repair. This review examines the scientific advances made with silk-based conduits for peripheral nerve repair. The focus is on enhancing bioactivity of the conduits in terms of physical guidance cues, inner wall and lumen modification, and imbuing novel conductive functionalities.

Conductive Silk-Polypyrrole Composite Scaffolds with Bioinspired Nanotopographic Cues for Cardiac Tissue Engineering

We report on the development of bioinspired cardiac scaffolds made from electroconductive acid-modified silk fibroin-poly(pyrrole) (AMSF+PPy) substrates patterned with nanoscale ridges and grooves reminiscent of native myocardial extracellular matrix (ECM) topography to enhance the structural and functional properties of cultured human pluripotent stem cells (hPSC)-derived cardiomyocytes. Nanopattern fidelity was maintained throughout the fabrication and functionalization processes, and no loss in conductive behavior occurred due to the presence of the nanotopographical features. AMSF+PPy substrates were biocompatible and stable, maintaining high cell viability over a 21-day culture period while displaying no signs of PPy delamination. The presence of anisotropic topographical cues led to increased cellular organization and sarcomere development, and electroconductive cues promoted a significant improvement in the expression and polarization of connexin 43 (Cx43), a critical regulator of cell-cell electrical coupling. The combination of biomimetic topography and electroconductivity also increased the expression of genes that encode key proteins involved in regulating the contractile and electrophysiological function of mature human cardiac tissue.

Novel conductive polypyrrole/silk fibroin scaffold for neural tissue repair

Three dimensional (3D) bioprinting, which involves depositing bioinks (mixed biomaterials) layer by layer to form computer-aided designs, is an ideal method for fabricating complex 3D biological structures. However, it remains challenging to prepare biomaterials with micro-nanostructures that accurately mimic the nanostructural features of natural tissues. A novel nanotechnological tool, electrospinning, permits the processing and modification of proper nanoscale biomaterials to enhance neural cell adhesion, migration, proliferation, differentiation, and subsequent nerve regeneration. The composite scaffold was prepared by combining 3D bioprinting with subsequent electrochemical deposition of polypyrrole and electrospinning of silk fibroin to form a composite polypyrrole/silk fibroin scaffold. Fourier transform infrared spectroscopy was used to analyze scaffold composition. The surface morphology of the scaffold was observed by light microscopy and scanning electron microscopy. A digital multimeter was used to measure the resistivity of prepared scaffolds. Light microscopy was applied to observe the surface morphology of scaffolds immersed in water or Dulbecco's Modified Eagle's Medium at 37°C for 30 days to assess stability. Results showed characteristic peaks of polypyrrole and silk fibroin in the synthesized conductive polypyrrole/silk fibroin scaffold, as well as the structure of the electrospun nanofiber layer on the surface. The electrical conductivity was 1 × 10-5-1 × 10-3 S/cm, while stability was 66.67%. A 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay was employed to measure scaffold cytotoxicity in vitro. Fluorescence microscopy was used to observe EdU-labeled Schwann cells to quantify cell proliferation. Immunohistochemistry was utilized to detect S100β immunoreactivity, while scanning electron microscopy was applied to observe the morphology of adherent Schwann cells. Results demonstrated that the polypyrrole/silk fibroin scaffold was not cytotoxic and did not affect Schwann cell proliferation. Moreover, filopodia formed on the scaffold and Schwann cells were regularly arranged. Our findings verified that the composite polypyrrole/silk fibroin scaffold has good biocompatibility and may be a suitable material for neural tissue engineering.