Instructive Conductive 3D Silk Foam-Based Bone Tissue Scaffolds Enable Electrical Stimulation of Stem Cells for Enhanced Osteogenic Differentiation

Silk fibroin as a surfactant for water-based nanofabrication

Water-based processing plays a crucial role in high technology, especially in electronics, material sciences and life sciences, with important implications in the development of high-quality reliable devices, fabrication efficiency, safety and sustainability. At the micro- and nanoscale, water is uniquely enabling as a bridge between biological and technological systems. However, new approaches are needed to overcome fundamental challenges that arise from the high surface tension of water, which hinders wetting and, thus, fabrication at the bio-nano interface. Here we report the use of silk fibroin as a surfactant to enable water-based processing of nanoscale devices. Even in minute quantities (for example, 0.01 w/v%), silk fibroin considerably enhances surface coverage and outperforms commercial surfactants in precisely controlling interfacial energy between water-based solutions and hydrophobic surfaces. This effect is ascribed to the amphiphilic nature of the silk molecule and its adaptive adsorption onto substrates with diverse surface energy, facilitating intermolecular interactions between unlikely pairs of materials. The approach's versatility is highlighted by manufacturing water-processed nanodevices, ranging from transistors to photovoltaic cells. Its performance is found to be equivalent to analogous vacuum-processed devices, underscoring the utility and versatility of this approach for water-based nanofabrication.

Synergy between 3D-extruded electroconductive scaffolds and electrical stimulation to improve bone tissue engineering strategies

In this work, we propose a simple, reliable, and versatile strategy to create 3D electroconductive scaffolds suitable for bone tissue engineering (TE) applications with electrical stimulation (ES). The proposed scaffolds are made of 3D-extruded poly(ε-caprolactone) (PCL), subjected to alkaline treatment, and of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), anchored to PCL with one of two different crosslinkers: (3-glycidyloxypropyl)trimethoxysilane (GOPS) and divinyl sulfone (DVS). Both cross-linkers allowed the formation of a homogenous and continuous coating of PEDOT:PSS to PCL. We show that these PEDOT:PSS coatings are electroconductive (11.3-20.1 S cm-1), stable (up to 21 days in saline solution), and allow the immobilization of gelatin (Gel) to further improve bioactivity. In vitro mineralization of the corresponding 3D conductive scaffolds was greatly enhanced (GOPS(NaOH)-Gel - 3.1 fold, DVS(NaOH)-Gel - 2.0 fold) and cell colonization and proliferation were the highest for the DVS(NaOH)-Gel scaffold. In silico modelling of ES application in DVS(NaOH)-Gel scaffolds indicates that the electrical field distribution is homogeneous, which reduces the probability of formation of faradaic products. Osteogenic differentiation of human bone marrow derived mesenchymal stem/stromal cells (hBM-MSCs) was performed under ES. Importantly, our results clearly demonstrated a synergistic effect of scaffold electroconductivity and ES on the enhancement of MSC osteogenic differentiation, particularly on cell-secreted calcium deposition and the upregulation of osteogenic gene markers such as COL I, OC and CACNA1C. These scaffolds hold promise for future clinical applications, including manufacturing of personalized bone TE grafts for transplantation with enhanced maturation/functionality or bioelectronic devices.

Biomedical applications of silk and its role for intervertebral disc repair

Intervertebral disc (IVD) degeneration (IDD) is the main contributor to chronic low back pain. To date, the present therapies mainly focus on treating the symptoms caused by IDD rather than addressing the problem itself. For this reason, researchers have searched for a suitable biomaterial to repair and/or regenerate the IVD. A promising candidate to fill this gap is silk, which has already been used as a biomaterial for many years. Therefore, this review aims first to elaborate on the different origins from which silk is harvested, the individual composition, and the characteristics of each silk type. Another goal is to enlighten why silk is so suitable as a biomaterial, discuss its functionalization, and how it could be used for tissue engineering purposes. The second part of this review aims to provide an overview of preclinical studies using silk-based biomaterials to repair the inner region of the IVD, the nucleus pulposus (NP), and the IVD's outer area, the annulus fibrosus (AF). Since the NP and the AF differ fundamentally in their structure, different therapeutic approaches are required. Consequently, silk-containing hydrogels have been used mainly to repair the NP, and silk-based scaffolds have been used for the AF. Although most preclinical studies have shown promising results in IVD-related repair and regeneration, their clinical transition is yet to come.

Instructive electroactive electrospun silk fibroin-based biomaterials for peripheral nerve tissue engineering

Aligned sub-micron fibres are an outstanding surface for orienting and promoting neurite outgrowth; therefore, attractive features to include in peripheral nerve tissue scaffolds. A new generation of peripheral nerve tissue scaffolds is under development incorporating electroactive materials and electrical regimes as instructive cues in order to facilitate fully functional regeneration. Herein, electroactive fibres composed of silk fibroin (SF) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) were developed as a novel peripheral nerve tissue scaffold. Mats of SF with sub-micron fibre diameters of 190 ± 50 nm were fabricated by double layer electrospinning with thicknesses of ∼100 μm (∼70-80 μm random fibres and ∼20-30 μm aligned fibres). Electrospun SF mats were modified with interpenetrating polymer networks (IPN) of PEDOT:PSS in various ratios of PSS/EDOT (α) and the polymerisation was assessed by hard X-ray photoelectron spectroscopy (HAXPES). The mechanical properties of electrospun SF and IPNs mats were characterised in the wet state tensile and the electrical properties were examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The cytotoxicity and biocompatibility of the optimal IPNs (α = 2.3 and 3.3) mats were ascertained via the growth and neurite extension of mouse neuroblastoma x rat glioma hybrid cells (NG108-15) for 7 days. The longest neurite outgrowth of 300 μm was observed in the parallel direction of fibre alignment on laminin-coated electrospun SF and IPN (α = 2.3) mats which is the material with the lowest electron transfer resistance (R_et, ca. 330 Ω). These electrically conductive composites with aligned sub-micron fibres exhibit promise for axon guidance and also have the potential to be combined with electrical stimulation treatment as a further step for the effective regeneration of nerves.

Controlled Bioactive Delivery Using Degradable Electroactive Polymers

Biomaterials capable of precisely controlling the delivery of agrochemicals/biologics/drugs/fragrances have significant markets in the agriscience/healthcare industries. Here, we report the development of degradable electroactive polymers and their application for the controlled delivery of a clinically relevant drug (the anti-inflammatory dexamethasone phosphate, DMP). Electroactive copolymers composed of blocks of polycaprolactone (PCL) and naturally occurring electroactive pyrrole oligomers (e.g., bilirubin, biliverdin, and hemin) were prepared and solution-processed to produce films (optionally doped with DMP). A combination of in silico/in vitro/in vivo studies demonstrated the cytocompatibility of the polymers. The release of DMP in response to the application of an electrical stimulus was observed to be enhanced by ca. 10–30% relative to the passive release from nonstimulated samples in vitro. Such stimuli-responsive biomaterials have the potential for integration devices capable of delivering a variety of molecules for technical/medical applications.

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.

Electrical Stimulation and Conductive Polymers as a Powerful Toolbox for Tailoring Cell Behaviour in vitro

Electrical stimulation (ES) is a well-known method for guiding the behaviour of nerve cells in in vitro systems based on the response of these cells to an electric field. From this perspective, understanding how the electrochemical stimulus can be tuned for the design of a desired cell response is of great importance. Most biomedical studies propose the application of an electrical potential to cell culture arrays while examining the cell response regarding viability, morphology, and gene expression. Conversely, various studies failed to evaluate how the fine physicochemical properties of the materials used for cell culture influence the observed behaviours. Among the various materials used for culturing cells under ES, conductive polymers (CPs) are widely used either in pristine form or in addition to other polymers. CPs themselves do not possess the optimal surface for cell compatibility because of their hydrophobic nature, which leads to poor protein adhesion and, hence, poor bioactivity. Therefore, understanding how to tailor the chemical properties on the material surface will determine the obtention of improved ES platforms. Moreover, the structure of the material, either in a thin film or in porous electrospun scaffolds, also affects the biochemical response and needs to be considered. In this review, we examine how materials based on CPs influence cell behaviour under ES, and we compile the various ES setups and physicochemical properties that affect cell behaviour. This review concerns the culture of various cell types, such as neurons, fibroblasts, osteoblasts, and Schwann cells, and it also covers studies on stem cells prone to ES. To understand the mechanistic behaviour of these devices, we also examine studies presenting a more detailed biomolecular level of interaction. This review aims to guide the design of future ES setups regarding the influence of material properties and electrochemical conditions on the behaviour of in vitro cell studies.

ZnO Nanosheet-Coated TiZrPdSiNb Alloy as a Piezoelectric Hybrid Material for Self-Stimulating Orthopedic Implants

A Ti-based alloy (Ti₄₅Zr₁₅Pd₃₀Si₅Nb₅) with already proven excellent mechanical and biocompatibility features has been coated with piezoelectric zinc oxide (ZnO) to induce the electrical self-stimulation of cells. ZnO was grown onto the pristine alloy in two different morphologies: a flat dense film and an array of nanosheets. The effect of the combined material on osteoblasts (electrically stimulable cells) was analyzed in terms of proliferation, cell adhesion, expression of differentiation markers and induction of calcium transients. Although both ZnO structures were biocompatible and did not induce inflammatory response, only the array of ZnO nanosheets was able to induce calcium transients, which improved the proliferation of Saos-2 cells and enhanced the expression of some early differentiation expression genes. The usual motion of the cells imposes strain to the ZnO nanosheets, which, in turn, create local electric fields owing to their piezoelectric character. These electric fields cause the opening of calcium voltage gates and boost cell proliferation and early differentiation. Thus, the modification of the Ti₄₅Zr₁₅Pd₃₀Si₅Nb₅ surface with an array of ZnO nanosheets endows the alloy with smart characteristics, making it capable of electric self-stimulation.

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.

Pure polylysine-based foamy scaffolds and their interaction with MC3T3-E1 cells and osteogenesis

Polypeptide-derived copolymers have widely been exploited for drug/gene delivery due to their pendant functional groups and non-toxic degradation products. However, fabrication of polypeptide-based scaffolds for tissue engineering has seldom been reported. In this study, foamy poly(N _ε -benzyl formateoxycarbonyl-L-Lysine) (PZL) and poly(N _ε -benzyl formateoxycarbonyl-L-lysine-co-L-phenylalanine) (PZLP) scaffolds were successfully prepared by a combination of ring-opening polymerization of α-amino acid N-carboxyanhydride and negative porous NaCl templating approach. The physicochemical properties of these scaffolds including glass transition temperature, contact angle, compression modulus and degradation behavior were characterized. Both in vitro and in vivo biocompatibility of the scaffolds were evaluated by MC3T3-E1 cell culture and SD subcutaneous model, respectively. The results from live-dead staining, MTT and ALP activity assays indicated that PZL scaffolds were more conducive to the adhesion, proliferation and osteoblastic differentiation of MC3T3-E1 cells compared to PZLP scaffolds in the initial culture period due to their specific surface properties. While porous structure rather than surface properties of scaffolds played a decisive role in the later stage of cell culture. The results of in vivo studies including H&E, Masson's trichrome and CD34 staining further demonstrated that PZL scaffolds supported the ingrowth of microvessels than PZLP scaffolds due to their surface property difference. Collectively, PZL scaffolds displayed good biocompatibility and could be a promising candidate for tissue engineering application.

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.

Conductive biomaterials for muscle tissue engineering

Muscle tissues are soft tissues that are of great importance in force generation, body movements, postural support and internal organ function. Muscle tissue injuries would not only result in the physical and psychological pain and disability to the patient, but also become a severe social problem due to the heavy financial burden they laid on the governments. Current treatments for muscle tissue injuries all have their own severe limitations and muscle tissue engineering has been proposed as a promising therapeutic strategy to treat with this problem. Conductive biomaterials are good candidates as scaffolds in muscle tissue engineering due to their proper conductivity and their promotion on muscle tissue formation. However, a review of conductive biomaterials function in muscle tissue engineering, including the skeletal muscle tissue, cardiac muscle tissue and smooth muscle tissue regeneration is still lacking. Here we reviewed the recent progress of conductive biomaterials for muscle regeneration. The recent synthesis and fabrication methods of conductive scaffolds containing conductive polymers (mainly polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene), carbon-based nanomaterials (mainly graphene and carbon nanotube), and metal-based biomaterials were systematically discussed, and their application in a variety of forms (such as hydrogels, films, nanofibers, and porous scaffolds) for different kinds of muscle tissues formation (skeletal muscle, cardiac muscle and smooth muscle) were summarized. Furthermore, the mechanism of how the conductive biomaterials affect the muscle tissue formation was discussed and the future development directions were included.

Injectable and Conductive Granular Hydrogels for 3D Printing and Electroactive Tissue Support

Conductive hydrogels are attractive to mimic electrophysiological environments of biological tissues and toward therapeutic applications. Injectable and conductive hydrogels are of particular interest for applications in 3D printing or for direct injection into tissues; however, current approaches to add conductivity to hydrogels are insufficient, leading to poor gelation, brittle properties, or insufficient conductivity. Here, an approach is developed using the jamming of microgels to form injectable granular hydrogels, where i) hydrogel microparticles (i.e., microgels) are formed with water-in-oil emulsions on microfluidics, ii) microgels are modified via an in situ metal reduction process, and iii) the microgels are jammed into a solid, permitting easy extrusion from a syringe. Due to the presence of metal nanoparticles at the jammed interface with high surface area in this unique design, the granular hydrogels have greater conductivity than non-particle (i.e., bulk) hydrogels treated similarly or granular hydrogels either without metal nanoparticles or containing encapsulated nanoparticles. The conductivity of the granular hydrogels is easily modified through mixing conductive and non-conductive microgels during fabrication and they can be applied to the 3D printing of lattices and to bridge muscle defects. The versatility of this conductive granular hydrogel will permit numerous applications where conductive materials are needed.

Hierarchically designed bone scaffolds: From internal cues to external stimuli

Bone tissue engineering utilizes three critical elements - cells, scaffolds, and bioactive factors - to recapitulate the bone tissue microenvironment, inducing the formation of new bone. Recent advances in materials development have enabled the production of scaffolds that more effectively mimic the hierarchical features of bone matrix, ranging from molecular composition to nano/micro-scale biochemical and physical features. This review summarizes recent advances within the field in utilizing these features of native bone to guide the hierarchical design of materials and scaffolds. Biomimetic strategies discussed in this review cover several levels of hierarchical design, including the development of element-doped compositions of bioceramics, the usage of molecular templates for in vitro biomineralization at the nanoscale, the fabrication of biomimetic scaffold architecture at the micro- and nanoscale, and the application of external physical stimuli at the macroscale to regulate bone growth. Developments at each level are discussed with an emphasis on their in vitro and in vivo outcomes in promoting osteogenic tissue development. Ultimately, these hierarchically designed scaffolds can complement or even replace the usage of cells and biological elements, which present clinical and regulatory barriers to translation. As the field progresses ever closer to clinical translation, the creation of viable therapies will thus benefit from further development of hierarchically designed materials and scaffolds.

Photolithographic Masking Method to Chemically Pattern Silk Film Surfaces

A method has been developed for selectively patterning silk surfaces using a photolithographic process to mask off sections of silk films, which allows selective and precise patterning of features down to 40 μm. This process is highly versatile, utilizes only low-cost equipment and can be used to rapidly prototype flat silk substrates with spatially controlled chemical patterns. Here we demonstrate the usefulness of this technique to deposit fluorescent dyes, labeled proteins and conducting polymers or to modify the surface charge of the silk protein in desired regions on a silk film surface.

Biomimetic Polymer-Based Engineered Scaffolds for Improved Stem Cell Function

Scaffolds are considered promising materials for tissue engineering applications due to their unique physiochemical properties. The high porosity and adequate mechanical properties of the scaffolds facilitate greater cell adhesion, proliferation, and differentiation. Stem cells are frequently applied in tissue engineering applications due to their excellent potential. It has been noted that cell functions are profoundly affected by the nature of the extracellular matrix (ECM). Naturally derived ECM contains the bioactive motif that also influences the immune response of the organism. The properties of polymer scaffolds mean they can resemble the native ECM and can regulate cellular responses. Various techniques such as electrospinning and 3D printing, among others, are frequently used to fabricate polymer scaffolds, and their cellular responses are different with each technique. Furthermore, enhanced cell viability, as well as the differentiation ability of stem cells on the surface of scaffolds, opens a fascinating approach to the formation of ECM-like environments for tissue engineering applications.

A Mussel-Inspired Persistent ROS-Scavenging, Electroactive, and Osteoinductive Scaffold Based on Electrochemical-Driven In Situ Nanoassembly

Conductive polymers are promising for bone regeneration because they can regulate cell behavior through electrical stimulation; moreover, they are antioxidative agents that can be used to protect cells and tissues from damage originating from reactive oxygen species (ROS). However, conductive polymers lack affinity to cells and osteoinductivity, which limits their application in tissue engineering. Herein, an electroactive, cell affinitive, persistent ROS-scavenging, and osteoinductive porous Ti scaffold is prepared by the on-surface in situ assembly of a polypyrrole-polydopamine-hydroxyapatite (PPy-PDA-HA) film through a layer-by-layer pulse electrodeposition (LBL-PED) method. During LBL-PED, the PPy-PDA nanoparticles (NPs) and HA NPs are in situ synthesized and uniformly coated on a porous scaffold from inside to outside. PDA is entangled with and doped into PPy to enhance the ROS scavenging rate of the scaffold and realize repeatable, efficient ROS scavenging over a long period of time. HA and electrical stimulation synergistically promote osteogenic cell differentiation on PPy-PDA-HA films. Ultimately, the PPy-PDA-HA porous scaffold provides excellent bone regeneration through the synergistic effects of electroactivity, cell affinity, and antioxidative activity of the PPy-PDA NPs and the osteoinductivity of HA NPs. This study provides a new strategy for functionalizing porous scaffolds that show great promise as implants for tissue regeneration.

Conductive nanostructured Si biomaterials enhance osteogeneration through electrical stimulation

It is well known that the differentiation of stem cells is affected by the cell culture medium, the scaffold surface and electrochemical signals. However, stimulation of patterned biomaterials seeded with stem cell cultures has not been explored. Herein the effect of electrical stimulation on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (rBMSCs) cultured on solid and nanoporous micropyramid patterned Si surfaces was evaluated. It was found that both stimulation and scaffold patterning significantly enhanced osteo-differentiation. The stimulated nanoporous micropyramid scaffolds were more promising compared to the stimulated solid micropyramid surfaces, as they significantly promoted the osteogenic differentiation of rBMSCs via BMP/Smad signaling pathway. Particularly, as compared to the unstimulated patterned biomaterials, the stimulated patterned scaffolds allowed for a significant increase in core binding factor alpha l, alkaline phosphatase, the alpha l chain of type I Col, osteocalcin, and osteonectin, all of which are characteristic for osteo-differentiation. The proposed combination of electrical stimulation with scaffold patterning may provide novel promising strategies for bone tissue engineering and regenerative medicine.

Hybrid polymer biomaterials for bone tissue regeneration

Native tissues possess unparalleled physiochemical and biological functions, which can be attributed to their hybrid polymer composition and intrinsic bioactivity. However, there are also various concerns or limitations over the use of natural materials derived from animals or cadavers, including the potential immunogenicity, pathogen transmission, batch to batch consistence and mismatch in properties for various applications. Therefore, there is an increasing interest in developing degradable hybrid polymer biomaterials with controlled properties for highly efficient biomedical applications. There have been efforts to mimic the extracellular protein structure such as nanofibrous and composite scaffolds, to functionalize scaffold surface for improved cellular interaction, to incorporate controlled biomolecule release capacity to impart biological signaling, and to vary physical properties of scaffolds to regulate cellular behavior. In this review, we highlight the design and synthesis of degradable hybrid polymer biomaterials and focus on recent developments in osteoconductive, elastomeric, photoluminescent and electroactive hybrid polymers. The review further exemplifies their applications for bone tissue regeneration.

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.

Engineering the Future of Silk Materials through Advanced Manufacturing

Silk is a natural fiber renowned for its outstanding mechanical properties that have enabled the manufacturing of ultralight and ultrastrong textiles. Recent advances in silk processing and manufacturing have underpinned a re-interpretation of silk from textiles to technological materials. Here, it is argued that silk materials-optimized by selective pressure to work in the environment at the biotic-abiotic interface-can be harnessed by human micro- and nanomanufacturing technology to impart new functionalities and opportunities. A critical overview of recent progress in silk technology is presented with emphasis on high-tech applications enabled by recent innovations in multilevel modifications, multiscale manufacturing, and multimodal characterization of silk materials. These advances have enabled successful demonstrations of silk materials across several disciplines, including tissue engineering, drug delivery, implantable medical devices, and biodissolvable/degradable devices.

Looking into the Future: Toward Advanced 3D Biomaterials for Stem-Cell-Based Regenerative Medicine

Stem-cell-based therapies have the potential to provide novel solutions for the treatment of a variety of diseases, but the main obstacles to such therapies lie in the uncontrolled differentiation and functional engraftment of implanted tissues. The physicochemical microenvironment controls the self-renewal and differentiation of stem cells, and the key step in mimicking the stem cell microenvironment is to construct a more physiologically relevant 3D culture system. Material-based 3D assemblies of stem cells facilitate the cellular interactions that promote morphogenesis and tissue organization in a similar manner to that which occurs during embryogenesis. Both natural and artificial materials can be used to create 3D scaffolds, and synthetic organic and inorganic porous materials are the two main kinds of artificial materials. Nanotechnology provides new opportunities to design novel advanced materials with special physicochemical properties for 3D stem cell culture and transplantation. Herein, the advances and advantages of 3D scaffold materials, especially with respect to stem-cell-based therapies, are first outlined. Second, the stem cell biology in 3D scaffold materials is reviewed. Third, the progress and basic principles of developing 3D scaffold materials for clinical applications in tissue engineering and regenerative medicine are reviewed.

Charge injection based electrical stimulation on polypyrrole planar electrodes to regulate cellular osteogenic differentiation

This study reveals that the Q_inj on electrodes is a more significant factor than applied voltage for electrical stimulation to regulate cellular osteogenic differentiation, and the charge injection capacity can be tuned by thickness of Ppy.

Conductive nanofibrous composite scaffolds based on in-situ formed polyaniline nanoparticle and polylactide for bone regeneration

Conducting polymers and biodegradable polylactide (PLA) scaffolds are both promising biomaterials applied in bone tissue engineering. It is necessary to develop a composite scaffold combining their properties of osteogenic differentiation promotion and three-dimension matrix. To conquer the problem of poor processability of conductive polymers, we use a novel in-situ polymerization/thermal induced phase separation (TIPS) method to fabricate conductive nanofibrous PLA scaffolds with well-distributed polyaniline (PANI) nano-structures. The simple preparation technique provides the possibility to scale-up production of these conductive nanofibrous composite scaffolds. The scaffold structure and content of in-situ formed polyaniline nanoparticles was thoroughly characterized with ¹H NMR, FT-IR, XPS, TGA, SEM and UV-vis, and the conductivity/electrochemical properties of the composite scaffolds were controlled with varied feed ratios of aniline to PLA. Meanwhile, the good cytocompatibility of these composite scaffolds was evaluated by culturing bone marrow derived mesenchymal stem cells (BMSCs) on them. The effect of conductive nanofibrous scaffolds on osteogenic differentiation was studied with expression levels of alkaline phosphatase (Alp), osteocalcin (Ocn) and runt-related transcription factor 2 (Runx2) during the culture of BMSCs for three weeks. The calcium mineralization of BMSCs is determined by alizarin red staining. These results indicated that a moderate content of PANI in the conductive nanofibrous scaffolds significantly promoted osteogenic differentiation of BMSCs for engineering bone tissues.

UV Cross-Linkable Graphene/Poly(trimethylene Carbonate) Composites for 3D Printing of Electrically Conductive Scaffolds

Conductive, flexible graphene/poly(trimethylene carbonate) (PTMC) composites were prepared. Addition of just 3 wt % graphene to PTMC oligomers functionalized with methacrylate end-groups followed by UV cross-linking resulted in more than 100% improvement in tensile strength and enhanced electrical conductivity by orders of magnitude without altering the processability of the host material. The addition of graphene also enhanced mesenchymal stem cell (MSC) attachment and proliferation. When electrical stimulation via the composite material was applied, MSC viability was not compromised, and osteogenic markers were upregulated. Using additive fabrication techniques, the material was processed into multilayer 3D scaffolds which supported MSC attachment. These conducting composites with excellent processability and compatibility with MSCs are promising biomaterials to be used as versatile platforms for biomedical applications.

Biomineralization of Engineered Spider Silk Protein-Based Composite Materials for Bone Tissue Engineering

Materials based on biodegradable polyesters, such as poly(butylene terephthalate) (PBT) or poly(butylene terephthalate-co-poly(alkylene glycol) terephthalate) (PBTAT), have potential application as pro-regenerative scaffolds for bone tissue engineering. Herein, the preparation of films composed of PBT or PBTAT and an engineered spider silk protein, (eADF4(C16)), that displays multiple carboxylic acid moieties capable of binding calcium ions and facilitating their biomineralization with calcium carbonate or calcium phosphate is reported. Human mesenchymal stem cells cultured on films mineralized with calcium phosphate show enhanced levels of alkaline phosphatase activity suggesting that such composites have potential use for bone tissue engineering.

Research trends in biomimetic medical materials for tissue engineering: commentary

We introduce our active experts’ communications and reviews (Part II) of 2015 Korea-China Joint Symposium on Biomimetic Medical Materials in Republic of Korea, which reflect their perspectives on current research trends of biomimetic medical materials for tissue regeneration in both Korea and China. The communications covered three topics of biomimetics, i.e., 1) hydrogel for therapeutics and extracellular matrix environments, 2) design of electrical polymers for communications between electrical sources and biological systems and 3) design of biomaterials for nerve tissue engineering. The reviews in the Part II will cover biomimetics of 3D bioprinting materials, surface modifications, nano/micro-technology as well as clinical aspects of biomaterials for cartilage.

Novel three-dimensional, conducting, biocompatible, porous, and elastic polyaniline-based scaffolds for regenerative therapies

Fabrication of two novel three-dimensional, conducting, biocompatible, porous, and elastic scaffolds composed of hyperbranched aliphatic polyesters, polyaniline, and poly(ε-caprolactone) for tissue engineering applications.

Conducting polymer-based multilayer films for instructive biomaterial coatings

Aim:

To demonstrate the design, fabrication and testing of conformable conducting biomaterials that encourage cell alignment.

Materials & methods:

Thin conducting composite biomaterials based on multilayer films of poly(3.4-ethylenedioxythiophene) derivatives, chitosan and gelatin were prepared in a layer-by-layer fashion. Fibroblasts were observed with fluorescence microscopy and their alignment (relative to the dipping direction and direction of electrical current passed through the films) was determined using ImageJ.

Results:

Fibroblasts adhered to and proliferated on the films. Fibroblasts aligned with the dipping direction used during film preparation and this was enhanced by a DC current.

Conclusion:

We report the preparation of conducting polymer-based films that enhance the alignment of fibroblasts on their surface which is an important feature of a variety of tissues.

Lay abstract: Cells inhabit environments known as the extracellular matrix (ECM) which consists of a mixture of different biomolecules, and the precise composition and topographical properties are different in different tissues (e.g., bone, brain, muscle, skin). Cells interact intimately with the ECM, not only constructing the biomolecules, but assist its organization in 3D space, and its degradation (which is important for tissue remodeling); reciprocally, cells respond to the ECM (e.g., by modifying their size, shape, etc). Cellular alignment is observed in organs and tissues such as bones, muscles and skin, and this alignment is important for the healthy functioning of the organ/tissue. Here, we present a novel method of aligning cells on biomaterials, simply by applying an electrical current through the biomaterial.

Electrical Stimulation of Human Mesenchymal Stem Cells on Conductive Nanofibers Enhances their Differentiation toward Osteogenic Outcomes

Tissue scaffolds allowing the behavior of the cells that reside within them to be controlled are of particular interest for tissue engineering. Herein, the preparation of conductive fiber-based bone tissue scaffolds (nonwoven mats of electrospun polycaprolactone with an interpenetrating network of polypyrrole and polystyrenesulfonate) is described that enable the electrical stimulation of human mesenchymal stem cells to enhance their differentiation toward osteogenic outcomes.