Multifunctional cell-culture platform for aligned cell sheet monitoring, transfer printing, and therapy

The biological and therapeutic assessment of a P(3HB-co-4HB)-bioactive glass-graphene composite biomaterial for tissue regeneration

An ideal wound dressing should create a healing environment that relieves pain, protects against infections, maintains moisture, removes debris, and speeds up wound closure and repair. However, conventional options like gauze often fall short in fulfilling these requirements, especially for chronic or nonhealing wounds. Hence there is a critical need for inventive formulations that offer efficient, cost-effective, and eco-friendly alternatives. This study focuses on assessing the innovative formulation based on a microbial-derived copolymer known as poly(3-hydroxybutyrate-co-4-hydroxybutyrate), P(3HB-co-4HB) bioactive glass and graphene particles, and exploring their biological response in vitro and in vivo-to find the best combination that promotes cell adhesion and enhances wound healing. The formulation optimized at concentration of bioactive glass (1 w/w%) and graphene (0.01 w/w%) showed accelerated degradation and enhanced blood vessel formation. Meanwhile biocompatibility was evaluated using murine osteoblasts, human dermal fibroblasts, and standard cell culture assays, demonstrating no adverse effects after 7 days of culture and well-regulated inflammatory kinetics. Whole thickness skin defect using mice indicated the feasibility of the biocomposites for a faster wound closure and reduced inflammation. Overall, this biocomposite appears promising as an ideal wound dressing material and positively influencing wound healing rates.

Phase-Modulated Elastic Properties of 2D Magnetic FeTe: Hexagonal and Tetragonal Polymorphs

2D layered magnets, such as iron chalcogenides, have emerged these years as a new family of unconventional superconductors and provided the key insights to understand the phonon-electron interaction and pairing mechanism. Their mechanical properties are of strategic importance for the potential applications in spintronics and optoelectronics. However, there is still a lack of efficient approach to tune the elastic modulus despite the extensive studies. Herein, the modulated elastic modulus of 2D magnetic FeTe and its thickness-dependence is reported via phase engineering. The grown 2D FeTe by chemical vapor deposition can present various polymorphs, that is tetragonal FeTe (t-FeTe, antiferromagnetic) and hexagonal FeTe (h-FeTe, ferromagnetic). The measured Young's modulus of t-FeTe by nanoindentation method shows an obvious thickness-dependence, from 290.9 ± 9.2 to 113.0 ± 8.7 GPa when the thicknesses increased from 13.2 to 42.5 nm, respectively. In comparison, the elastic modulus of h-FeTe remains unchanged. These results can shed light on the efficient modulation of mechanical properties of 2D magnetic materials and pave the avenues for their practical applications in nanodevices.

Recent advances in two-dimensional nanomaterials for sustainable wearable electronic devices

The widespread adoption of smart terminals has significantly boosted the market potential for wearable electronic devices. Two-dimensional (2D) nanomaterials show great promise for flexible, wearable electronics of next-generation electronic materials and have potential in energy, optoelectronics, and electronics. First, this review focuses on the importance of functionalization/defects in 2D nanomaterials, a discussion of different kinds of 2D materials for wearable devices, and the overall structure-property relationship of 2D materials. Then, in this comprehensive review, we delve into the burgeoning realm of emerging applications for 2D nanomaterial-based flexible wearable electronics, spanning diverse domains such as energy, medical health, and displays. A meticulous exploration is presented, elucidating the intricate processes involved in tailoring material properties for specific applications. Each research direction is dissected, offering insightful perspectives and dialectical evaluations that illuminate future trajectories and inspire fruitful investigations in this rapidly evolving field.

Regulated Behavior in Living Cells with Highly Aligned Configurations on Nanowrinkled Graphene Oxide Substrates: Deep Learning Based on Interplay of Cellular Contact Guidance

Micro-/nanotopographical cues have emerged as a practical and promising strategy for controlling cell fate and reprogramming, which play a key role as biophysical regulators in diverse cellular processes and behaviors. Extracellular biophysical factors can trigger intracellular physiological signaling via mechanotransduction and promote cellular responses such as cell adhesion, migration, proliferation, gene/protein expression, and differentiation. Here, we engineered a highly ordered nanowrinkled graphene oxide (GO) surface via the mechanical deformation of an ultrathin GO film on an elastomeric substrate to observe specific cellular responses based on surface-mediated topographical cues. The ultrathin GO film on the uniaxially prestrained elastomeric substrate through self-assembly and subsequent compressive force produced GO nanowrinkles with periodic amplitude. To examine the acute cellular behaviors on the GO-based cell interface with nanostructured arrays of wrinkles, we cultured L929 fibroblasts and HT22 hippocampal neuronal cells. As a result, our developed cell-culture substrate obviously provided a directional guidance effect. In addition, based on the observed results, we adapted a deep learning (DL)-based data processing technique to precisely interpret the cell behaviors on the nanowrinkled GO surfaces. According to the learning/transfer learning protocol of the DL network, we detected cell boundaries, elongation, and orientation and quantitatively evaluated cell velocity, traveling distance, displacement, and orientation. The presented experimental results have intriguing implications such that the nanotopographical microenvironment could engineer the living cells' morphological polarization to assemble them into useful tissue chips consisting of multiple cell types.

Mimicked Spinal Cord Fibers Trigger Axonal Regeneration and Remyelination after Injury

Spinal cord injury (SCI) causes tissue structure damage and composition changes of the neural parenchyma, resulting in severe consequences for spinal cord function. Mimicking the components and microstructure of spinal cord tissues holds promise for restoring the regenerative microenvironment after SCI. Here, we have utilized electrospinning technology to develop aligned decellularized spinal cord fibers (A-DSCF) without requiring synthetic polymers or organic solvents. A-DSCF preserves multiple types of spinal cord extracellular matrix proteins and forms a parallel-oriented structure. Compared to aligned collagen fibers (A-CF), A-DSCF exhibits stronger mechanical properties, improved enzymatic stability, and superior functionality in the adhesion, proliferation, axonal extension, and myelination of differentiated neural progenitor cells (NPCs). Notably, axon extension or myelination has been primarily linked to Agrin (AGRN), Laminin (LN), or Collagen type IV (COL IV) proteins in A-DSCF. When transplanted into rats with complete SCI, A-DSCF loaded with NPCs improves the survival, maturation, axon regeneration, and motor function of the SCI rats. These findings highlight the potential of structurally and compositionally biomimetic scaffolds to promote axonal extension and remyelination after SCI.

Applications of flexible electronics related to cardiocerebral vascular system

Ensuring accessible and high-quality healthcare worldwide requires field-deployable and affordable clinical diagnostic tools with high performance. In recent years, flexible electronics with wearable and implantable capabilities have garnered significant attention from researchers, which functioned as vital clinical diagnostic-assisted tools by real-time signal transmission from interested targets in vivo. As the most crucial and complex system of human body, cardiocerebral vascular system together with heart-brain network attracts researchers inputting profuse and indefatigable efforts on proper flexible electronics design and materials selection, trying to overcome the impassable gulf between vivid organisms and rigid inorganic units. This article reviews recent breakthroughs in flexible electronics specifically applied to cardiocerebral vascular system and heart-brain network. Relevant sensor types and working principles, electronics materials selection and treatment methods are expounded. Applications of flexible electronics related to these interested organs and systems are specially highlighted. Through precedent great working studies, we conclude their merits and point out some limitations in this emerging field, thus will help to pave the way for revolutionary flexible electronics and diagnosis assisted tools development.

Fibrinogen-based cell and spheroid sheets manipulating and delivery for mouse hindlimb ischemia

In this research, we introduced a novel strategy for fabricating cell sheets (CSs) prepared by simply adding a fibrinogen solution to growth medium without using any synthetic polymers or chemical agents. We confirmed that the fibrinogen-based CS could be modified for target tissue regardless of size, shape, and cell types. Also, fibrinogen-based CSs were versatile and could be used to form three-dimensional (3D) CSs such as multi-layered CSs and those mimicking native blood vessels. We also prepared fibrinogen-based spheroid sheets for the treatment of ischemic disease. The fibrinogen-based spheroid sheets had much higherin vitrotubule formation and released more angiogenic factors compared to other types of platform in this research. We transplanted fibrinogen-based spheroid sheets into a mouse hindlimb ischemia model and found that fibrinogen-based spheroid sheets showed significantly improved physiological function and blood perfusion rates compared to the other types of platform in this research.

Esophageal wound healing by aligned smooth muscle cell-laden nanofibrous patch

The esophagus exhibits peristalsis via contraction of circularly and longitudinally aligned smooth muscles, and esophageal replacement is required if there is a critical-sized wound. In this study, we proposed to reconstruct esophageal tissues using cell electrospinning (CE), an advanced technique for encapsulating living cells into fibers that allows control of the direction of fiber deposition. After treatment with transforming growth factor-β, mesenchymal stem cell-derived smooth muscle cells (SMCs) were utilized for cell electrospinning or three-dimensional bioprinting to compare the effects of aligned micropatterns on cell morphology. CE resulted in SMCs with uniaxially arranged and elongated cell morphology with upregulated expression levels of SMC-specific markers, including connexin 43, smooth muscle protein 22 alpha (SM22α), desmin, and smoothelin. When SMC-laden nanofibrous patches were transplanted into a rat esophageal defect model, the SMC patch promoted regeneration of esophageal wounds with an increased number of newly formed blood vessels and enhanced the SMC-specific markers of SM22α and vimentin. Taken together, CE with its advantages, such as guidance of highly elongated, aligned cell morphology and accelerated SMC differentiation, can be an efficient strategy to reconstruct smooth muscle tissues and treat esophageal perforation.

Fabrication of Biohybrid Nanofibers by the Green Electrospinning Technique and Their Antibacterial Activity

The development of bioactive polymer nanofiber sheets based on eco-friendly components is required to meet the needs of various medical applications as well as to preserve the environment. This study aimed to fabricate biohybrid nanofibers based on water-soluble polymers and aqueous extract of myrrh. The myrrh extract was incorporated into poly(vinyl alcohol)/tragacanth gum nanofiber mats (myrrh@PVA/TG) by the green electrospinning technique. Various characteristics of the prepared fibers such as morphology, fiber diameter distribution, crystallinity, and thermal stability were studied. The results confirmed that the morphology of biohybrid nanofibers was uniform without beads and tragacanth gum plays an important role in controlling the average diameter of fibers and the crystallinity. The antibacterial properties of the developed biohybrid nanofibers were investigated against common pathogens of Gram-positive and Gram-negative bacteria by the standard disc diffusion method. A significant antibacterial activity was observed toward bacterial strains after incorporation of aqueous myrrh extract into nanofibers, which increased on increasing the extract ratio. Due to their eco-friendly components and significant antibacterial activity, the prepared biohybrid nanofibers will open new avenues toward incorporating aqueous herbal extracts into degradable polymer fibers for use in many antibacterial applications.

Multifunctional Injectable Hydrogel for In Vivo Diagnostic and Therapeutic Applications

Injectable hydrogels show high potential for in vivo biomedical applications owing to their distinctive mode of administration into the human body. In this study, we propose a material design strategy for developing a multifunctional injectable hydrogel with good adhesiveness, stretchability, and bioresorbability. Its multifunctionality, whereupon multiple reactions occur simultaneously during its injection into the body without requiring energy stimuli and/or additives, was realized through meticulous engineering of bioresorbable precursors based on hydrogel chemistry. The multifunctional injectable hydrogel can be administered through a minimally invasive procedure, form a conformal adhesive interface with the target tissue, dynamically stretch along with the organ motions with minimal mechanical constraints, and be resorbed in vivo after a specific period. Further, the incorporation of functional nanomaterials into the hydrogel allows for various in vivo diagnostic and therapeutic applications, without compromising the original multifunctionality of the hydrogel. These features are verified through theranostic case studies on representative organs, including the skin, liver, heart, and bladder.

Soft Bioelectronics Based on Nanomaterials

Recent advances in nanostructured materials and unconventional device designs have transformed the bioelectronics from a rigid and bulky form into a soft and ultrathin form and brought enormous advantages to the bioelectronics. For example, mechanical deformability of the soft bioelectronics and thus its conformal contact onto soft curved organs such as brain, heart, and skin have allowed researchers to measure high-quality biosignals, deliver real-time feedback treatments, and lower long-term side-effects in vivo. Here, we review various materials, fabrication methods, and device strategies for flexible and stretchable electronics, especially focusing on soft biointegrated electronics using nanomaterials and their composites. First, we summarize top-down material processing and bottom-up synthesis methods of various nanomaterials. Next, we discuss state-of-the-art technologies for intrinsically stretchable nanocomposites composed of nanostructured materials incorporated in elastomers or hydrogels. We also briefly discuss unconventional device design strategies for soft bioelectronics. Then individual device components for soft bioelectronics, such as biosensing, data storage, display, therapeutic stimulation, and power supply devices, are introduced. Afterward, representative application examples of the soft bioelectronics are described. A brief summary with a discussion on remaining challenges concludes the review.

Research Progress of Microtransfer Printing Technology for Flexible Electronic Integrated Manufacturing

In recent years, with the rapid development of the flexible electronics industry, there is an urgent need for a large-area, multilayer, and high-production integrated manufacturing technology for scalable and flexible electronic products. To solve this technical demand, researchers have proposed and developed microtransfer printing technology, which picks up and prints inks in various material forms from the donor substrate to the target substrate, successfully realizing the integrated manufacturing of flexible electronic products. This review retrospects the representative research progress of microtransfer printing technology for the production of flexible electronic products and emphasizes the summary of seal materials, the basic principles of various transfer technology and fracture mechanics models, and the influence of different factors on the transfer effect. In the end, the unique functions, technical features, and related printing examples of each technology are concluded and compared, and the prospects of further research work on microtransfer printing technology is finally presented.

Mechanomaterials: A Rational Deployment of Forces and Geometries in Programming Functional Materials

The knowledge of mechanics of materials has been extensively implemented in developing functional materials, giving rise to recent advances in soft actuators, flexible electronics, mechanical metamaterials, tunable mechanochromics, regenerative mechanomedicine, etc. While conventional mechanics of materials offers passive access to mechanical properties of materials in existing forms, a paradigm shift is emerging toward proactive programming of materials' functionality by leveraging the force-geometry-property relationships. Here, such a rising field is coined as "mechanomaterials". To profile the concept, the design principles in this field at four scales is first outlined, namely the atomic scale, the molecular scale, the manipulation of nanoscale materials, and the microscale design of structural materials. A variety of techniques have been recruited to deliver the multiscale programming of functional mechanomaterials, such as strain engineering, capillary assembly, topological interlocking, kirigami, origami, to name a few. Engineering optical and biological functionalities have also been achieved by implementing the fundamentals of mechanochemistry and mechanobiology. Nonetheless, the field of mechanomaterials is still in its infancy, with many open challenges and opportunities that need to be addressed. The authors hope this review can serve as a modest spur to attract more researchers to further advance this field.

Wearable and Implantable Soft Bioelectronics: Device Designs and Material Strategies

High-performance wearable and implantable devices capable of recording physiological signals and delivering appropriate therapeutics in real time are playing a pivotal role in revolutionizing personalized healthcare. However, the mechanical and biochemical mismatches between rigid, inorganic devices and soft, organic human tissues cause significant trouble, including skin irritation, tissue damage, compromised signal-to-noise ratios, and limited service time. As a result, profuse research efforts have been devoted to overcoming these issues by using flexible and stretchable device designs and soft materials. Here, we summarize recent representative research and technological advances for soft bioelectronics, including conformable and stretchable device designs, various types of soft electronic materials, and surface coating and treatment methods. We also highlight applications of these strategies to emerging soft wearable and implantable devices. We conclude with some current limitations and offer future prospects of this booming field.

Nanomaterial Additives for Fabrication of Stimuli-Responsive Skeletal Muscle Tissue Engineering Constructs

Volumetric muscle loss necessitates novel tissue engineering strategies for skeletal muscle repair, which have traditionally involved cells and extracellular matrix-mimicking scaffolds and have thus far been unable to successfully restore physiologically relevant function. However, the incorporation of various nanomaterial additives with unique physicochemical properties into scaffolds has recently been explored as a means of fabricating constructs that are responsive to electrical, magnetic, and photothermal stimulation. Herein, several classes of nanomaterials that are used to mediate external stimulation to tissue engineered skeletal muscle are reviewed and the impact of these stimuli-responsive biomaterials on cell growth and differentiation and in vivo muscle repair is discussed. The degradation kinetics and biocompatibilities of these nanomaterial additives are also briefly examined and their potential for incorporation into clinically translatable skeletal muscle tissue engineering strategies is considered. Overall, these nanomaterial additives have proven efficacious and incorporation in tissue engineering scaffolds has resulted in enhanced functional skeletal muscle regeneration.

Graphene Templated DNA Arrays and Biotin-Streptavidin Sensitive Bio-Transistors Patterned by Dynamic Self-Assembly of Polymeric Films Confined within a Roll-on-Plate Geometry

Patterning of surfaces with a simple strategy provides insights into the functional interfaces by suitable modification of the surface by novel techniques. Especially, highly ordered structural topographies and chemical features from the wide range of interfaces have been considered as important characteristics to understand the complex relationship between the surface chemistries and biological systems. Here, we report a simple fabrication method to create patterned surfaces over large areas using evaporative self-assembly that is designed to produce a sacrificial template and lithographic etch masks of polymeric stripe patterns, ranging from micrometer to nanoscale. By facilitating a roll-on-plate geometry, the periodically patterned surface structures formed by repetitive slip-stick motions were thoroughly examined to be used for the deposition of the Au nanoparticles decorated graphene oxide (i.e., AuNPs, ~21 nm) and the formation of conductive graphene channels. The fluorescently labeled thiol-modified DNA was applied on the patterned arrays of graphene oxide (GO)/AuNPs, and biotin-streptavidin sensitive devices built with graphene-based transistors (GFETs, effective mobility of ~320 cm² V^-1 s^-1) were demonstrated as examples of the platform for the next-generation biosensors with the high sensing response up to ~1 nM of target analyte (i.e., streptavidin). Our strategy suggests that the stripe patterned arrays of polymer films as sacrificial templates can be a simple route to creating highly sensitive biointerfaces and highlighting the development of new chemically patterned surfaces composed of graphene-based nanomaterials.

Material-Based Approaches for the Fabrication of Stretchable Electronics

Stretchable electronics are mechanically compatible with a variety of objects, especially with the soft curvilinear contours of the human body, enabling human-friendly electronics applications that could not be achieved with conventional rigid electronics. Therefore, extensive research effort has been devoted to the development of stretchable electronics, from research on materials and unit device, to fully integrated systems. In particular, material-processing technologies that encompass the synthesis, assembly, and patterning of intrinsically stretchable electronic materials have been actively investigated and have provided many notable breakthroughs for the advancement of stretchable electronics. Here, the latest studies of such material-based approaches are reviewed, mainly focusing on intrinsically stretchable electronic nanocomposites that generally consist of conducting/semiconducting filler materials inside or on elastomer backbone matrices. Various approaches for fabricating these intrinsically stretchable electronic materials are presented, including the blending of electronic fillers into elastomer matrices, the formation of bi-layered heterogeneous electronic-layer and elastomer support-layer structures, and modifications to polymeric molecular structures in order to impart stretchability. Detailed descriptions of the various conducting/semiconducting composites prepared by each method are provided, along with their electrical/mechanical properties and examples of device applications. To conclude, a brief future outlook is presented.

Large scale and integrated platform for digital mass culture of anchorage dependent cells

Industrial applications of anchorage-dependent cells require large-scale cell culture with multifunctional monitoring of culture conditions and control of cell behaviour. Here, we introduce a large-scale, integrated, and smart cell-culture platform (LISCCP) that facilitates digital mass culture of anchorage-dependent cells. LISCCP is devised through large-scale integration of ultrathin sensors and stimulator arrays in multiple layers. LISCCP provides real-time, 3D, and multimodal monitoring and localized control of the cultured cells, which thereby allows minimizing operation labour and maximizing cell culture performance. Wireless integration of multiple LISCCPs across multiple incubators further amplifies the culture scale and enables digital monitoring and local control of numerous culture layers, making the large-scale culture more efficient. Thus, LISCCP can transform conventional labour-intensive and high-cost cell cultures into efficient digital mass cell cultures. This platform could be useful for industrial applications of cell cultures such as in vitro toxicity testing of drugs and cosmetics and clinical scale production of cells for cell therapy.

Large scale culture of adherent cells would benefit from a platform for continuous monitoring and control of cell growth and culture conditions. Here the authors develop an integrated, smart cell culture platform where cells are grown on multiple layers of thin sensors that can be wirelessly integrated across several incubators.

Hierarchically Porous Hydroxyapatite Hybrid Scaffold Incorporated with Reduced Graphene Oxide for Rapid Bone Ingrowth and Repair

Hydroxyapatite (HA), the traditional bone tissue replacement material was widely used in the clinical treatment of bone defects because of its excellent biocompatibility. However, the processing difficulty and poor osteoinductive ability greatly limit the application of HA. Although many strategies have been reported to improve the machinability and osteointegration ability, the performance including mechanical strength, porosity, cell adhesion, etc. of material still can not meet the requirements. In this work, a soft template method was developed and a porous scaffold with hierarchical pore structure, nano surface morphology, suitable porosity and pore size, and good biomechanical strength was successfully prepared. The hierarchical pore structure is beneficial for cell adhesion, fluid transfer, and cell ingrowth. Moreover, the loaded reduced graphene oxide (rGO) can improve the adhesion and promote the proliferation and spontaneous osteogenic differentiation bone marrow mesenchymal stem cells. The scaffold is then crushed, degraded and wrapped by the newly formed bone and the newly formed bone gradually replaces the scaffold. The degradation rate of the scaffold well matches the rate of the new bone formation. The hierarchical porous HA/rGO composite scaffolds can greatly accelerate the bone ingrowth in the scaffold and bone repair in critical bone defects, thus providing a clinical potential candidate for large segment bone tissue engineering.

Sensor-Instrumented Scaffold Integrated with Microporous Spongelike Ultrabuoy for Long-Term 3D Mapping of Cellular Behaviors and Functions

Real-time monitoring of cellular behaviors and functions with sensor-instrumented scaffolds can provide a profound impact on fundamental studies of the underlying biophysics and disease modeling. Although quantitative measurement of predictive data for in vivo tests and physiologically relevant information in these contexts is important, the long-term reliable monitoring of cellular functions in three-dimensional (3D) environments is limited by the required set under wet cell culture conditions that are unfavorable to electronic instrument settings. Here, we introduce an ultrabuoyant 3D instrumented scaffold that can remain afloat on the surface of culture medium and thereby provides favorable environments for the entire electronic components in the air while the cells reside and grow underneath. This setting enables high-fidelity recording of electrical cell-substrate impedance and electrophysiological signals for a long period of time (weeks). Comprehensive in vitro studies reveal the utility of this platform as an effective tool for drug screening and tissue development.

Bioresorbable Electronic Implants: History, Materials, Fabrication, Devices, and Clinical Applications

Medical implants, either passive implants for structural support or implantable devices with active electronics, have been widely used for the diagnosis and treatment of various diseases and clinical issues. These implants offer various functions, including mechanical support of biological structures in orthopedic and dental applications, continuous electrophysiological monitoring and feedback of electrical stimulation in neuronal and cardiac applications, and controlled drug delivery while maintaining arterial structure in drug-eluting stents. Although these implants exhibit long-term biocompatibility, surgery for their retrieval is often required, which imposes physical, biological, and economical burdens on the patients. Therefore, as an alternative to such secondary surgeries, bioresorbable implants that disappear after a certain period of time inside the body, including bioresorbable active electronics, have been highlighted recently. This review first discusses the historical background of medical implants and briefly define related terminology. Representative examples of non-degradable medical implants for passive structural support and/or for diagnosis and therapy with active electronics are also provided. Then, recent progress in bioresorbable active implants composed of biosignal sensors, actuators for therapeutics, wireless power supply components, and their integrated systems are reviewed. Finally, clinical applications of these bioresorbable electronic implants are exemplified with brief conclusion and future outlook.

Wearable and Implantable Soft Bioelectronics Using Two-Dimensional Materials

Soft bioelectronics intended for application to wearable and implantable biomedical devices have attracted great attention from material scientists, device engineers, and clinicians because of their extremely soft mechanical properties that match with a variety of human organs and tissues, including the brain, heart, skin, eye, muscles, and neurons, as well as their wide diversity in device designs and biomedical functions that can be finely tuned for each specific case of applications. These unique features of the soft bioelectronics have allowed minimal mechanical and biological damage to organs and tissues integrated with bioelectronic devices and reduced side effects including inflammation, skin irritation, and immune responses even after long-term biointegration. These favorable properties for biointegration have enabled long-term monitoring of key biomedical indicators with high signal-to-noise ratio, reliable diagnosis of the patient's health status, and in situ feedback therapy with high treatment efficacy optimized for the requirements of each specific disease model. These advantageous device functions and performances could be maximized by adopting novel high-quality soft nanomaterials, particularly ultrathin two-dimensional (2D) materials, for soft bioelectronics. Two-dimensional materials are emerging material candidates for the channels and electrodes in electronic devices (semiconductors and conductors, respectively). They can also be applied to various biosensors and therapeutic actuators in soft bioelectronics. The ultrathin vertically layered nanostructure, whose layer number can be controlled in the synthesis step, and the horizontally continuous planar molecular structure, which can be found over a large area, have conferred unique mechanical, electrical, and optical properties upon the 2D materials. The atomically thin nanostructure allows mechanical softness and flexibility and high optical transparency of the device, while the large-area continuous thin film structure allows efficient carrier transport within the 2D plane. In addition, the quantum confinement effect in the atomically thin 2D layers introduces interesting optoelectronic properties and superb photodetecting capabilities. When fabricated as soft bioelectronic devices, these interesting and useful material features of the 2D materials enable unconventional device functions in biological and optical sensing, as well as superb performance in electrical and biochemical therapeutic actuations. In this Account, we first summarize the distinctive characteristics of the 2D materials in terms of the mechanical, optical, chemical, electrical, and biomedical aspects and then present application examples of the 2D materials to soft bioelectronic devices based on each aforementioned unique material properties. Among various kinds of 2D materials, we particularly focus on graphene and MoS₂. The advantageous material features of graphene and MoS₂ include ultrathin thickness, facile functionalization, large surface-to-volume ratio, biocompatibility, superior photoabsorption, and high transparency, which allow the development of high-performance multifunctional soft bioelectronics, such as a wearable glucose patch, a highly sensitive humidity sensor, an ultrathin tactile sensor, a soft neural probe, a soft retinal prosthesis, a smart endoscope, and a cell culture platform. A brief comparison of their characteristics and performances is also provided. Finally, this Account concludes with a future outlook on next-generation soft bioelectronics based on 2D materials.

Asymmetric multifunctional 3D cell microenvironments by capillary force assembly

The fabrication and characterization of advanced 3D cell culture microenvironments that enable systematic structure–property relationship studies are reported.

Thermally-triggered fabrication of cell sheets for tissue engineering and regenerative medicine

Cell transplantation is a promising approach for promoting tissue regeneration in the treatment of damaged tissues or organs. Although cells have conventionally been delivered by direct injection to damaged tissues, cell injection has limited efficiency to deliver therapeutic cells to the target sites. Progress in tissue engineering has moved scaffold-based cell/tissue delivery into the mainstream of tissue regeneration. A variety of scaffolds can be fabricated from natural or synthetic polymers to provide the appropriate culture conditions for cell growth and achieve in-vitro tissue formation. Tissue engineering has now become the primary approach for cell-based therapies. However, there are still serious limitations, particularly for engineering of cell-dense tissues. "Cell sheet engineering" is a scaffold-free tissue technology that holds even greater promise in the field of tissue engineering and regenerative medicine. Thermoresponsive poly(N-isopropylacrylamide)-grafted surfaces allow the fabrication of a tissue-like cell monolayer, a "cell sheet", and efficiently delivers this cell-dense tissue to damaged sites without the use of scaffolds. At present, this unique approach has been applied to human clinical studies in regenerative medicine. Furthermore, this thermally triggered cell manipulation system allows us to produce various types of 3D tissue models not only for regenerative medicine but also for tissue modeling, which can be used for drug discovery. Here, new cell sheet-based technologies are described including vascularization for scaled-up 3D tissue constructs, induced pluripotent stem (iPS) cell technology for human cell sheet fabrication and microfabrication for arranging tissue microstructures, all of which are expected to produce more complex tissues based on cell sheet tissue engineering.

Highly Tunable and Scalable Fabrication of 3D Flexible Graphene Micropatterns for Directing Cell Alignment

Patterning graphene allows to precisely tune its properties to manufacture flexible functional materials or miniaturized devices for electronic and biomedical applications. However, conventional lithographic techniques are cumbersome for scalable production of time- and cost-effective graphene patterns, thus greatly impeding their practical applications. Here, we present a simple scalable fabrication of wafer-scale three-dimensional (3D) graphene micropatterns by direct laser tuning graphene oxide reduction and expansion using a LightScribe DVD writer. This one-step laser-scribing process can produce custom-made 3D graphene patterns on the surface of a disk with dimensions ranging from microscale up to decimeter scale in about 20 min. Through control over laser-scribing parameters, the resulting various 3D graphene patterns are exploited as scaffolds for controlling cell alignment. The 3D graphene patterns demonstrate their potential to biomedical applications, beyond the fields of electronics and photonics, which will allow to incorporate flexible graphene patterns for 3D cell or tissue culture to promote tissue engineering and drug testing applications.

Multifaceted Biomedical Applications of Functional Graphene Nanomaterials to Coated Substrates, Patterned Arrays and Hybrid Scaffolds

Because of recent research advances in nanoscience and nanotechnology, there has been a growing interest in functional nanomaterials for biomedical applications, such as tissue engineering scaffolds, biosensors, bioimaging agents and drug delivery carriers. Among a great number of promising candidates, graphene and its derivatives-including graphene oxide and reduced graphene oxide-have particularly attracted plenty of attention from researchers as novel nanobiomaterials. Graphene and its derivatives, two-dimensional nanomaterials, have been found to have outstanding biocompatibility and biofunctionality as well as exceptional mechanical strength, electrical conductivity and thermal stability. Therefore, tremendous studies have been devoted to employ functional graphene nanomaterials in biomedical applications. Herein, we focus on the biological potentials of functional graphene nanomaterials and summarize some of major literature concerning the multifaceted biomedical applications of functional graphene nanomaterials to coated substrates, patterned arrays and hybrid scaffolds that have been reported in recent years.

Control of cell growth on 3D-printed cell culture platforms for tissue engineering

Biocompatible tissue growth has excellent prospects for tissue engineering. These tissues are built over scaffolds, which can influence aspects such as cell adhesion, proliferation rate, morphology, and differentiation. However, the ideal 3D biological structure has not been developed yet. Here, we applied the electro-hydrodynamic jet (E-jet) 3D printing technology using poly-(lactic-co-glycolic acid, PLGA) solution to print varied culture platforms for engineered tissue structures. The effects of different parameters (electrical voltage, plotting speed, and needle sizes) on the outcome were investigated. We compared the biological compatibility of the 3D printed culture platforms with that of random fibers. Finally, we used the 3D-printed PLGA platforms to culture fibroblasts, the main cellular components of loose connective tissue. The results show that the E-jet printed platforms could guide and improve cell growth. These highly aligned fibers were able to support cellular alignment and proliferation. Cell angle was consistent with the direction of the fibers, and cells cultured on these fibers showed a much faster migration, potentially enhancing wound healing performance. Thus, the potential of this technology for 3D biological printing is large. This process can be used to grow biological scaffolds for the engineering of tissues. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3281-3292, 2017.

Programmable Nano-Bio Interfaces for Functional Biointegrated Devices

A large amount of evidence has demonstrated the revolutionary role of nanosystems in the screening and shielding of biological systems. The explosive development of interfacing bioentities with programmable nanomaterials has conveyed the intriguing concept of nano-bio interfaces. Here, recent advances in functional biointegrated devices through the precise programming of nano-bio interactions are outlined, especially with regard to the rational assembly of constituent nanomaterials on multiple dimension scales (e.g., nanoparticles, nanowires, layered nanomaterials, and 3D-architectured nanomaterials), in order to leverage their respective intrinsic merits for different functions. Emerging nanotechnological strategies at nano-bio interfaces are also highlighted, such as multimodal diagnosis or "theragnostics", synergistic and sequential therapeutics delivery, and stretchable and flexible nanoelectronic devices, and their implementation into a broad range of biointegrated devices (e.g., implantable, minimally invasive, and wearable devices). When utilized as functional modules of biointegrated devices, these programmable nano-bio interfaces will open up a new chapter for precision nanomedicine.

Leveraging a temperature-tunable, scale-like microstructure to produce multimodal, supersensitive sensors

The microstructure of a flexible film plays an important role in its sensing capability. Here, we fabricate a temperature-dependent wrinkled single-walled carbon nanotube (SWCNT)/polydimethyl-siloxane (PDMS) film (WSPF) and a wrinkle-dependent scale-like SWCNT/PDMS film (SSPF) successfully, and address the formation and evolution mechanisms of each film. The low elastic modulus and high coefficient of thermal expansion of the PDMS layer combined with the excellent piezoresistive behavior of the SWCNT film motivated us to investigate how the scale-like microstructure of the SSPF could be used to design multimodal-sensing devices with outstanding capabilities. The results show that SSPFs present supersensitive performance in mechanical loading (an effective sensitivity of up to 740.7 kPa^-1) and in temperature (a tunable thermal index of up to 29.9 × 10³ K). These exceptional properties were demonstrated in practical applications in a programmable flexile pressure sensor, thermal/light monitor or switch, etc., and were further explained through the macroscopic and microscopic piezoresistive behaviors of scale-like SWCNT coatings.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Stem cell-derived cell-sheets for connective tissue engineering

Cell-sheet technology involves the recovery of cells with its secreted ECM and cell-cell junctions intact, and thereby harvesting them in a single contiguous layer. Temperature changes coupled with a thermoresponsive polymer grafted culture plate surface are typically used to induce detachment of this cell-matrix layer by controlling the hydrophobicity and hydrophilicity properties of the culture surface. This review article details the genesis and development of this technique as a critical tissue-engineering tool, with a comprehensive discussion on connective tissue applications. This includes applications in the myocardial, vascular, cartilage, bone, tendon/ligament, and periodontal areas among others discussed. In particular, further focus will be given to the use of stem cells-derived cell-sheets, such as those involving bone marrow-derived and adipose tissue-derived mesenchymal stem cells. In addition, some of the associated challenges faced by approaches using stem cells-derived cell-sheets will also be discussed. Finally, recent advances pertaining to technologies forming, detaching, and manipulating cell-sheets will be covered in view of the potential impact they will have on shaping the way cell-sheet technology will be utilized in the future as a tissue-engineering technique.

Recent Advances in Flexible and Stretchable Bio-Electronic Devices Integrated with Nanomaterials

Flexible and stretchable electronics and optoelectronics configured in soft, water resistant formats uniquely address seminal challenges in biomedicine. Over the past decade, there has been enormous progress in the materials, designs, and manufacturing processes for flexible/stretchable system subcomponents, including transistors, amplifiers, bio-sensors, actuators, light emitting diodes, photodetector arrays, photovoltaics, energy storage elements, and bare die integrated circuits. Nanomaterials prepared using top-down processing approaches and synthesis-based bottom-up methods have helped resolve the intrinsic mechanical mismatch between rigid/planar devices and soft/curvilinear biological structures, thereby enabling a broad range of non-invasive, minimally invasive, and implantable systems to address challenges in biomedicine. Integration of therapeutic functional nanomaterials with soft bioelectronics demonstrates therapeutics in combination with unconventional diagnostics capabilities. Recent advances in soft materials, devices, and integrated systems are reviewes, with representative examples that highlight the utility of soft bioelectronics for advanced medical diagnostics and therapies.

Deformable devices with integrated functional nanomaterials for wearable electronics

As the market and related industry for wearable electronics dramatically expands, there are continuous and strong demands for flexible and stretchable devices to be seamlessly integrated with soft and curvilinear human skin or clothes. However, the mechanical mismatch between the rigid conventional electronics and the soft human body causes many problems. Therefore, various prospective nanomaterials that possess a much lower flexural rigidity than their bulk counterparts have rapidly established themselves as promising electronic materials replacing rigid silicon and/or compound semiconductors in next-generation wearable devices. Many hybrid structures of multiple nanomaterials have been also developed to pursue both high performance and multifunctionality. Here, we provide an overview of state-of-the-art wearable devices based on one- or two-dimensional nanomaterials (e.g., carbon nanotubes, graphene, single-crystal silicon and oxide nanomembranes, organic nanomaterials and their hybrids) in combination with zero-dimensional functional nanomaterials (e.g., metal/oxide nanoparticles and quantum dots). Starting from an introduction of materials strategies, we describe device designs and the roles of individual ones in integrated systems. Detailed application examples of wearable sensors/actuators, memories, energy devices, and displays are also presented.

Enhanced Osteogenesis by Reduced Graphene Oxide/Hydroxyapatite Nanocomposites

Recently, graphene-based nanomaterials, in the form of two dimensional substrates or three dimensional foams, have attracted considerable attention as bioactive scaffolds to promote the differentiation of various stem cells towards specific lineages. On the other hand, the potential advantages of using graphene-based hybrid composites directly as factors inducing cellular differentiation as well as tissue regeneration are unclear. This study examined whether nanocomposites of reduced graphene oxide (rGO) and hydroxyapatite (HAp) (rGO/HAp NCs) could enhance the osteogenesis of MC3T3-E1 preosteoblasts and promote new bone formation. When combined with HAp, rGO synergistically promoted the spontaneous osteodifferentiation of MC3T3-E1 cells without hindering their proliferation. This enhanced osteogenesis was corroborated from determination of alkaline phosphatase activity as early stage markers of osteodifferentiation and mineralization of calcium and phosphate as late stage markers. Immunoblot analysis showed that rGO/HAp NCs increase the expression levels of osteopontin and osteocalcin significantly. Furthermore, rGO/HAp grafts were found to significantly enhance new bone formation in full-thickness calvarial defects without inflammatory responses. These results suggest that rGO/HAp NCs can be exploited to craft a range of strategies for the development of novel dental and orthopedic bone grafts to accelerate bone regeneration because these graphene-based composite materials have potentials to stimulate osteogenesis.

Nanofiber Yarn/Hydrogel Core-Shell Scaffolds Mimicking Native Skeletal Muscle Tissue for Guiding 3D Myoblast Alignment, Elongation, and Differentiation

Designing scaffolds that can mimic native skeletal muscle tissue and induce 3D cellular alignment and elongated myotube formation remains an ongoing challenge for skeletal muscle tissue engineering. Herein, we present a simple technique to generate core-shell composite scaffolds for mimicking native skeletal muscle structure, which comprise the aligned nanofiber yarn (NFY) core and the photocurable hydrogel shell. The aligned NFYs are prepared by the hybrid composition including poly(caprolactone), silk fibroin, and polyaniline via a developed dry-wet electrospinning method. A series of core-shell column and sheet composite scaffolds are ultimately obtained by encapsulating a piece and layers of aligned NFY cores within the hydrogel shell after photo-cross-linking. C2C12 myoblasts are seeded within the core-shell scaffolds, and the good biocompatibility of these scaffolds and their ability to induce 3D cellular alignment and elongation are successfully demonstrated. Furthermore, the 3D elongated myotube formation within core-shell scaffolds is also performed after long-term cultivation. These data suggest that these core-shell scaffolds combine the aligned NFY core that guides the myoblast alignment and differentiation and the hydrogel shell that provides a suitable 3D environment for nutrition exchange and mechanical protection to perform a great practical application for skeletal muscle regeneration.

Current applications of graphene oxide in nanomedicine

Graphene has attracted the attention of the entire scientific community due to its unique mechanical and electrochemical, electronic, biomaterial, and chemical properties. The water-soluble derivative of graphene, graphene oxide, is highly prized and continues to be intensely investigated by scientists around the world. This review seeks to provide an overview of the currents applications of graphene oxide in nanomedicine, focusing on delivery systems, tissue engineering, cancer therapies, imaging, and cytotoxicity, together with a short discussion on the difficulties and the trends for future research regarding this amazing material.

A hierarchical rippled and crumpled PLA microstructure generated through double emulsion: the interesting roles of Pickering nanoparticles

The delicate roles of Pickering nanoparticles for the in situ creation of hierarchical rippled and crumpled textures upon biomedical polymers were uncovered and demonstrated.