Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Adhesion to wet and dynamic surfaces, including biological tissues, is important in many fields but has proven to be extremely challenging. Existing adhesives are cytotoxic, adhere weakly to tissues, or cannot be used in wet environments. We report a bioinspired design for adhesives consisting of two layers: an adhesive surface and a dissipative matrix. The former adheres to the substrate by electrostatic interactions, covalent bonds, and physical interpenetration. The latter amplifies energy dissipation through hysteresis. The two layers synergistically lead to higher adhesion energies on wet surfaces as compared with those of existing adhesives. Adhesion occurs within minutes, independent of blood exposure and compatible with in vivo dynamic movements. This family of adhesives may be useful in many areas of application, including tissue adhesives, wound dressings, and tissue repair.

Tough adhesives for diverse wet surfaces

Generation of thick vascularized tissues that fully match the patient still remains an unmet challenge in cardiac tissue engineering. Here, a simple approach to 3D-print thick, vascularized, and perfusable cardiac patches that completely match the immunological, cellular, biochemical, and anatomical properties of the patient is reported. To this end, a biopsy of an omental tissue is taken from patients. While the cells are reprogrammed to become pluripotent stem cells, and differentiated to cardiomyocytes and endothelial cells, the extracellular matrix is processed into a personalized hydrogel. Following, the two cell types are separately combined with hydrogels to form bioinks for the parenchymal cardiac tissue and blood vessels. The ability to print functional vascularized patches according to the patient's anatomy is demonstrated. Blood vessel architecture is further improved by mathematical modeling of oxygen transfer. The structure and function of the patches are studied in vitro, and cardiac cell morphology is assessed after transplantation, revealing elongated cardiomyocytes with massive actinin striation. Finally, as a proof of concept, cellularized human hearts with a natural architecture are printed. These results demonstrate the potential of the approach for engineering personalized tissues and organs, or for drug screening in an appropriate anatomical structure and patient-specific biochemical microenvironment.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201900344

3D Printing of Personalized Thick and Perfusable Cardiac Patches and Hearts

Recent advances in soft materials and system integration technologies have provided a unique opportunity to design various types of wearable flexible hybrid electronics (WFHE) for advanced human healthcare and human-machine interfaces. The hybrid integration of soft and biocompatible materials with miniaturized wireless wearable systems is undoubtedly an attractive prospect in the sense that the successful device performance requires high degrees of mechanical flexibility, sensing capability, and user-friendly simplicity. Here, the most up-to-date materials, sensors, and system-packaging technologies to develop advanced WFHE are provided. Details of mechanical, electrical, physicochemical, and biocompatible properties are discussed with integrated sensor applications in healthcare, energy, and environment. In addition, limitations of the current materials are discussed, as well as key challenges and the future direction of WFHE. Collectively, an all-inclusive review of the newly developed WFHE along with a summary of imperative requirements of material properties, sensor capabilities, electronics performance, and skin integrations is provided.

Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment.

Most bacteria release membrane vesicles (MVs) that contain specific cargo molecules and have diverse functions, including the transport of virulence factors, DNA transfer, interception of bacteriophages, antibiotics and eukaryotic host defence factors, cell detoxification and bacterial communication. MVs not only are abundant in nature but also show great promise for applications in biomedicine and nanotechnology. MVs were first discovered to originate from controlled blebbing of the outer membrane of Gram-negative bacteria and are therefore often called outer-membrane vesicles (OMVs). However, recent work has shown that Gram-positive bacteria can produce MVs, that different types of MVs besides OMVs exist and that, in addition to membrane blebbing, MVs can also be formed by endolysin-triggered cell lysis. In this Review, we provide an overview of the structures and compositions of the various vesicle types and discuss novel formation routes, which may lead to distinct vesicle types that serve particular functions.

Types and origins of bacterial membrane vesicles.

In cardiac tissue engineering approaches to treat myocardial infarction, cardiac cells are seeded within three-dimensional porous scaffolds to create functional cardiac patches. However, current cardiac patches do not allow for online monitoring and reporting of engineered-tissue performance, and do not interfere to deliver signals for patch activation or to enable its integration with the host. Here, we report an engineered cardiac patch that integrates cardiac cells with flexible, freestanding electronics and a 3D nanocomposite scaffold. The patch exhibited robust electronic properties, enabling the recording of cellular electrical activities and the on-demand provision of electrical stimulation for synchronizing cell contraction. We also show that electroactive polymers containing biological factors can be deposited on designated electrodes to release drugs in the patch microenvironment on demand. We expect that the integration of complex electronics within cardiac patches will eventually provide therapeutic control and regulation of cardiac function.

Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function

Unlike lytic phages, temperate phages that enter lysogeny maintain a long-term association with their bacterial host. In this context, mutually beneficial interactions can evolve that support efficient reproduction of both phages and bacteria. Temperate phages are integrated into the bacterial chromosome as large DNA insertions that can disrupt gene expression, and they may pose a fitness burden on the cell. However, they have also been shown to benefit their bacterial hosts by providing new functions in a bacterium-phage symbiotic interaction termed lysogenic conversion. In this Opinion article, we discuss another type of bacterium-phage interaction, active lysogeny, in which phages or phage-like elements are integrated into the bacterial chromosome within critical genes or operons and serve as switches that regulate bacterial genes via genome excision.

A new perspective on lysogeny: prophages as active regulatory switches of bacteria

Advances in electronic devices have opened opportunities for extracting a variety of data from the human body, and for the treatment of diseases. In this Review, tissue properties affecting device integration are described and electronic systems interfacing with organs and engineered tissues are highlighted.

Tissue–electronics interfaces: from implantable devices to engineered tissues

Coiled perimysial fibers within the heart muscle provide it with the ability to contract and relax efficiently. Here, we report on a new nanocomposite scaffold for cardiac tissue engineering, integrating coiled electrospun fibers with gold nanoparticles. Cultivation of cardiac cells within the hybrid scaffolds promoted cell organization into elongated and aligned tissues generating a strong contraction force, high contraction rate and low excitation threshold.

Coiled fiber scaffolds embedded with gold nanoparticles improve the performance of engineered cardiac tissues

The development of scaffolding materials that recapitulate the cellular microenvironment and provide cells with physicochemical cues is crucial for successfully engineering functional tissues that can aid in repairing damaged organs. The use of gold nanoparticles for tissue engineering and regenerative medicine has raised great interest in recent years. In this mini review, we describe the shape-dependent properties of gold nanoparticles, and their versatile use in creating tunable nanocomposite scaffolds with improved mechanical and electrical properties for tissue engineering. We further describe using gold nanoparticle-integrated scaffolds to achieve improved stem cells proliferation and differentiation. Finally, we discuss the main challenges and prospects for clinical translation of gold nanoparticles-hybrid scaffolds.

Ron Feiner

Papers

Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function

A new perspective on lysogeny: prophages as active regulatory switches of bacteria

Tissue–electronics interfaces: from implantable devices to engineered tissues

Coiled fiber scaffolds embedded with gold nanoparticles improve the performance of engineered cardiac tissues

Gold Nanoparticle-Integrated Scaffolds for Tissue Engineering and Regenerative Medicine