Cell Electrospinning: a Review of Materials and Methodologies for Biofabrication

The process of electrohydrodynamic living cell microencapsulation inside a scaffold during the electrospinning (ES) process is called cell electrospinning (CE). Several studies demonstrate the feasibility of using cell electrospinning for biomedical applications, allowing for the direct biofabrication of living cells to be encapsulated in fibers for the formation of active biological scaffolds. In this review, a comprehensive overview of the materials and methodologies used in cell electrospinning, as well as their biomedical application in tissue engineering, is provided. Cell ES represents an innovative technique for automated application in regenerative medicine.

Cell Electrospinning: A Mini-Review of the Critical Processing Parameters and Its Use in Biomedical Applications

Functional tissue engineering is a widely studied area of research with increasing importance in regenerative medicine, as well as in the development of in vitro models used for drug discovery and mimicking diseased tissues, among other applications. Electrospinning (ES) is one of the most widely used methods in these fields. It has attracted considerable interest because it can produce materials resembling the extracellular matrix of native tissues. The micro/nanofibers produced by this method provide a cell-friendly environment that promotes cellular activities. Cell electrospinning (C-ES) is based on the fundamental ES process and enables the encapsulation of viable cells in a micro/nanofibrous mesh. In this review, the process of C-ES and the materials used in this process are discussed. This work also discusses the applications of C-ES in tissue engineering, focusing on recent advances in this field.

Electrospinning and Cell Fibers in Biomedical Applications

Human body tissues such as muscle, blood vessels, tendon/ligaments, and nerves have fiber-like fascicle morphologies, where ordered organization of cells and extracellular matrix (ECM) within the bundles in specific 3D manners orchestrates cells and ECM to provide tissue functions. Through engineering cell fibers (which are fibers containing living cells) as living building blocks with the help of emerging "bottom-up" biomanufacturing technologies, it is now possible to reconstitute/recreate the fiber-like fascicle morphologies and their spatiotemporally specific cell-cell/cell-ECM interactions in vitro, thereby enabling the modeling, therapy, or repair of these fibrous tissues. In this article, a concise review is provided of the "bottom-up" biomanufacturing technologies and materials usable for fabricating cell fibers, with an emphasis on electrospinning that can effectively and efficiently produce thin cell fibers and with properly designed processes, 3D cell-laden structures that mimic those of native fibrous tissues. The importance and applications of cell fibers as models, therapeutic platforms, or analogs/replacements for tissues for areas such as drug testing, cell therapy, and tissue engineering are highlighted. Challenges, in terms of biomimicry of high-order hierarchical structures and complex dynamic cellular microenvironments of native tissues, as well as opportunities for cell fibers in a myriad of biomedical applications, are discussed.

Electrohydrodynamic 3D Printing of Aqueous Solutions

Among the various electrohydrodynamic (EHD) processing techniques, electrowriting (EW) produces the most complex 3D structures. Aqueous solution EW similarly retains the potential for additive manufacturing well-resolved 3D structures, while providing new opportunities for processing biologically derived polymers and eschewing organic solvents. However, research on aqueous-based EHD processing is still limited. To summarize the field and advocate for increased use of aqueous bio-based materials, this review summarizes the most significant contributions of aqueous solution processing. Special emphasis has been placed on understanding the effects of different printing parameters, the prospects for 3D processing new materials, and future challenges.

Advancement of Nanofibrous Mats and Common Useful Drug Delivery Applications

Electrospinning enables simple and cost-effective production of polymer nanofibers from different polymer materials. Drug delivery systems are capable of achieving maximum drug treatment benefits by significantly reducing adverse complications. Electrospun nanofibers have recently attracted considerable attention owing to their distinctive properties, including flexibility and biocompatibility. The implementation of functional constituents within nanostructure fibers blends is an effective technique for the administration of a variety of drugs in animal research, broadening the nanofiber capability and reliability. The nanofibrous mesh and its various application purposes are discussed in terms of a summary of recent research, emphasizing the ease of streaming and a large number of combinations of this approach, which could lead to a breakthrough in targeted therapy.

Bio-electrospraying assessment toward in situ chondrocyte-laden electrospun scaffold fabrication

Electrospinning has been widely used to fabricate fibrous scaffolds for cartilage tissue engineering, but their small pores severely restrict cell infiltration, resulting in an uneven distribution of cells across the scaffold, particularly in three-dimensional designs. If bio-electrospraying is applied, direct chondrocyte incorporation into the fibers during electrospinning may be a solution. However, before this approach can be effectively employed, it is critical to identify whether chondrocytes are adversely affected. Several electrospraying operating settings were tested to determine their effect on the survival and function of an immortalized human chondrocyte cell line. These chondrocytes survived through an electric field formed by low needle-to-collector distances and low voltage. No differences in chondrocyte viability, morphology, gene expression, or proliferation were found. Preliminary data of the combination of electrospraying and polymer electrospinning disclosed that chondrocyte integration was feasible using an alternated approach. The overall increase in chondrocyte viability over time indicated that the embedded cells retained their proliferative capacity. Besides the cell line, primary chondrocytes were also electrosprayed under the previously optimized operational conditions, revealing the higher sensitivity degree of these cells. Still, their post-electrosprayed viability remained considerably high. The data reported here further suggest that bio-electrospraying under the optimal operational conditions might be a promising alternative to the existent cell seeding techniques, promoting not only cells safe delivery to the scaffold, but also the development of cellularized cartilage tissue constructs.

Conformal single cell hydrogel coating with electrically induced tip streaming of an AC cone

Encapsulation of single cells in a thin hydrogel provides a more precise control of stem cell niches and better molecular transport. Despite the recent advances in microfluidic technologies to allow encapsulation of single cells, existing methods rely on special crosslinking agents that are pre-coated on the cell surface and subject to the variation of the cell membrane, which limits their widespread adoption. This work reports a high-throughput single-cell encapsulation method based on the "tip streaming" mode of alternating current (AC) electrospray, with encapsulation efficiencies over 80% after tuned centrifugation. Dripping with multiple cells is curtailed due to gating by the sharp conic meniscus of the tip streaming mode that only allows one cell to be ejected at a time. Moreover, the method can be universally applied to both natural and synthetic hydrogels, as well as various cell types, including human multipotent mesenchymal stromal cells (hMSCs). Encapsulated hMSCs maintain good cell viability over an extended culture period and exhibit robust differentiation potential into osteoblasts and adipocytes. Collectively, electrically induced tip streaming enables high-throughput encapsulation of single cells with high efficiency and universality, which is applicable for various applications in cell therapy, pharmacokinetic studies, and regenerative medicine.

Electrospraying: Possibilities and Challenges of Engineering Carriers for Biomedical Applications-A Mini Review

Electrospraying, a liquid atomization-based technique, has been used to produce and formulate micro/nanoparticular cargo carriers for various biomedical applications, including drug delivery, biomedical imaging, implant coatings, and tissue engineering. In this mini review, we begin with the main features of electrospraying methods to engineer carriers with various bioactive cargos, including genes, growth factors, and enzymes. In particular, this review focuses on the improvement of traditional electrospraying technology for the fabrication of carriers for living cells and providing a suitable condition for gene transformation. Subsequently, the major applications of the electrosprayed carriers in the biomedical field are highlighted. Finally, we finish with conclusions and future perspectives of electrospraying for high efficiency and safe production.

Electrospraying an enabling technology for pharmaceutical and biomedical applications: A review

Electrospraying (ES) is a robust and versatile technique for the fabrication of micro- and nanoparticulate materials of various compositions, morphologies, shapes, textures and sizes. The physics of ES provides a great degree of flexibility towards the materials design of choice with desired physicochemical and biological properties. Not surprising, this technology has become an important tool for the production of micro- and nanostructured materials, especially in the pharmaceutical and biomedical arena. In this review, a basic introduction to the fundamentals of ES along with a brief description of the experimental parameters that can be manipulated to obtain micro- and nanostructured materials of desired composition, size, and configuration are outlined. A greater focus of this review is to bring to light the broad range of electrosprayed materials and their applications in drug delivery, biomedical imaging, implant coating, tissue engineering, and sensing. Taken together, this review will provide an appreciation of this unique technology, which can be used to fabricate micro- and nanostructured materials with tremendous applications in the pharmaceutical and biomedical fields.

Encapsulation of mesenchymal stem cells in glycosaminoglycans-chitosan polyelectrolyte microcapsules using electrospraying technique: Investigating capsule morphology and cell viability

Polyelectrolyte microcapsules are modular constructs which facilitate cell handling and assembly of cell‐based tissue constructs. In this study, an electrospray (ES) encapsulation apparatus was developed for the encapsulation of mesenchymal stem cells (MSCs). Ionic complexation between glycosaminoglycans (GAGs) and chitosan formed a polyelectrolyte complex membrane at the interface. To optimize the capsules, the effect of voltage, needle size and GAG formulation on capsule size were investigated. It was observed that by increasing the voltage and decreasing the needle size, the capsule size would decrease but at voltages above 12 kV, capsule size distribution broadened significantly which yields lower circularity. Increase in GAG viscosity resulted in larger microcapsules and cell viability exhibited no significant changes during the encapsulation procedure. These results suggest that ES is a highly efficient, and scalable approach to the encapsulation of MSCs for subsequent use in bioprinting and other modular tissue engineering or regenerative medicine applications.

Development of a bio-electrospray system for cell and non-viral gene delivery

The NVG-BES system facilitated to introduce DNA to cells and delivered cells to a target simultaneously. In this method, a cationic polymer was used as non-viral carrier with electric force by bio-electrospray (BES) system to electrospray living cells onto a target.

Cardiac tissue engineering: renewing the arsenal for the battle against heart disease

The development of therapies that lead to the regeneration or functional repair of compromised cardiac tissue is the most important challenge facing translational cardiovascular research today.

Recent advancements in tissue engineering for stem cell-based cardiac therapies

Advances in cardiac tissue engineering have recently focused on utilizing stem cells to regenerate infarcted and scarred myocardium. Due to their proliferative nature and tremendous potential for differentiation, stem cells are presently being investigated for clinical applications. Unfortunately, limiting factors such as massive cell death and poor retention have hampered clinical outcomes. Consequently, the development of an efficient delivery system for stem cells to the target site is essential. The use of innovative tissue engineering techniques has opened up new horizons within the field of cellular cardiomyoplasty. This paper will present a comprehensive overview of the recent advancements in stem cell technology destined for myocardial tissue repair. In addition, the multidisciplinary approach to tissue engineering presented here will provide the reader with insight into the clinical realization of cellular cardiomyoplasty.

Bio-Rapid-Prototyping of Tissue Engineering Scaffolds and the Process-Induced Cell Damage

Tissue scaffolds play a vital role in tissue engineering by providing a native tissue-mimicking environment for cell proliferation and differentiation as well as tissue regeneration. Fabrication of tissue scaffolds has been drawing increasing research attention and a number of fabrication techniques have been developed. To better mimic the microenvironment of native tissues, novel techniques have emerged in recent years to encapsulate cells into the engineered scaffolds during the scaffold fabrication process. Among them, bio-Rapid-Prototyping (bioRP) techniques, by which scaffolds with encapsulated cells can be fabricated with controlled internal microstructure and external shape, shows significant promise. It is noted in the bioRP processes, cells may be continuously subjected to environmental stresses such as mechanical, electrical forces and laser exposure. If the stress is greater than a certain level, the cell membrane may be ruptured, leading to the so-called process-induced cell damage. This paper reviews various cell encapsulation techniques for tissue scaffold fabrication, with emphasis on the bioRP technologies and their technical features. To understand the process-induced cell damage in the bioRP processes, this paper also surveys the cell damage mechanisms under different stresses. The process-induced cell damage models are also examined to provide a cue to the cell viability preservation in the fabrication process. Discussions on further improvements of bioRP technologies are given and ongoing research into mechanical cell damage mechanism are also suggested in this review.

Microscale Strategies for Generating Cell-Encapsulating Hydrogels

Hydrogels in which cells are encapsulated are of great potential interest for tissue engineering applications. These gels provide a structure inside which cells can spread and proliferate. Such structures benefit from controlled microarchitectures that can affect the behavior of the enclosed cells. Microfabrication-based techniques are emerging as powerful approaches to generate such cell-encapsulating hydrogel structures. In this paper we introduce common hydrogels and their crosslinking methods and review the latest microscale approaches for generation of cell containing gel particles. We specifically focus on microfluidics-based methods and on techniques such as micromolding and electrospinning.

Bio-electrospraying and cell electrospinning: progress and opportunities for basic biology and clinical sciences

Engineering of functional tissues is a fascinating and fertile arena of research and development. This flourishing enterprise weaves together many areas of research to tackle the most complex question faced to date, namely how to design and reconstruct a synthetic three-dimensional fully functional tissue on demand. At present our healthcare is under threat by several social and economical issues together with those of a more scientific and clinical nature. One such issue arises from our increasing life expectancy, resulting in an ageing society. This steeply growing ageing society requires functional organotypic tissues on demand for repair, replacement, and rejuvenation (R(3) ). Several approaches are pioneered and developed to assist conventional tissue/organ transplantation. In this Progress Report, "non-contact jet-based" approaches for engineering functional tissues are introduced and bio-electrosprays and cell electrospinning, i.e., biotechniques that have demonstrated as being benign for directly handling living cells and whole organisms, are highlighted. These biotechniques possess the ability to directly handle heterogeneous cell populations as suspensions with a biopolymer and/or other micro/nanomaterials for directly forming three-dimensional functional living reconstructs. These discoveries and developments have provided a promising biotechnology platform with far-reaching ramifications for a wide range of applications in basic biological laboratories to their utility in the clinic.

Bio-electrosprayed living composite matrix implanted into mouse models

We show that composite de novo structures can be generated using bio-electrosprays. Mouse lung fibroblasts are bio-electrosprayed directly with a biopolymer to form cell-bearing matrices, which are viable even when implanted subcutaneously into murine hosts. Generated cell-bearing matrices are assessed in-vitro and found to undergo all expected cellular behaviour. Subsequent in-vivo studies demonstrate the implanted living matrices integrating as expected with the surrounding microenvironment. The in-vitro and in-vivo studies elucidate and validate the ability for either bio-electrosprays or cell electrospinning to form a desired living architecture for undergoing investigation for repairing, replacing and rejuvenating damaged and/or ageing tissues.

Electrospun cellular microenvironments: Understanding controlled release and scaffold structure

Electrospinning is a versatile technique in tissue engineering for the production of scaffolds. To guide tissue development, scaffolds must provide specific biochemical, structural and mechanical cues to cells and deliver them in a controlled fashion over time. Electrospun scaffold design thus includes aspects of both controlled release and structural cues. Controlled multicomponent and multiphasic drug delivery can be achieved by the careful application and combination of novel electrospinning techniques, i.e., emulsion and co-axial electrospinning. Drug distribution and polymer properties influence the resulting release kinetics. Pore size is far more relevant as a structural parameter than previously recognized. It enables cell proliferation and ingrowth, whereas fiber diameter predominantly influences cell fate. Both parameters can be exploited by combining multiple fiber types in the form of multifiber and multilayer scaffolds. Such scaffolds are required to reproduce more complex tissue structures.

Pressure driven spinning: A multifaceted approach for preparing nanoscaled functionalized fibers, scaffolds, and membranes with advanced materials

Electrospinning, a flexible jet-based fiber, scaffold, and membrane fabrication approach, has been elucidated as having significance to the heath sciences. Its capabilities have been most impressive as it possesses the ability to spin composite fibers ranging from the nanometer to the micrometer scale. Nonetheless, electrospinning has limitations and hazards, negating its wider exploration, for example, the inability to handle highly conducting suspensions, to its hazardous high voltage. Hence, to date electrospinning has undergone an exhaustive research regime to a point of cliché. Thus, in the work reported herein we unveil a competing technique to electrospinning, which has overcome the above limitations and hazards yet comparable in capabilities. The fiber preparation approach unearthed herein is referred to as "pressure driven spinning (PDS)." The driving mechanism exploited in this fiber spinning process is the pressurized by-pass flow. This mechanism allows the drawing of either micro- or nanosized fibers while processing polymeric suspensions containing a wide range of advanced materials spanning structural, functional, and biological entities. Similar to electrospinning if the collection time of these continuous formed fibers is varied, composite scaffolds and membranes are generated. In keeping with our interests, multicompositional structural entities such as these could have several applications in biology and medicine, for example, ranging from the development of three-dimensional cultures (including disease models) to the development of synthetic tissues and organ structures to advanced approaches for controlled and targeted therapeutics.