Melt Electrospinning Writing of Poly-Hydroxymethylglycolide-co-ε-Caprolactone-Based Scaffolds for Cardiac Tissue Engineering

Biomimetic design and integrated biofabrication of an in-vitro three-dimensional multi-scale multilayer cortical model

The lack of accurate and reliable in vitro brain models hinders the development of brain science and research on brain diseases. Owing to the complex structure of the brain tissue and its highly nonlinear characteristics, the construction of brain-like in vitro tissue models remains one of the most challenging research fields in the construction of living tissues. This study proposes a multi-scale design of a brain-like model with a biomimetic cortical structure, which includes the macroscopic structural features of six layers of different cellular components, as well as micrometer-scale continuous fiber structures running through all layers vertically. To achieve integrated biomanufacturing of such a complex multi-scale brain-like model, a multi-material composite printing/culturing integrated bioprinting platform was developed in-house by integrating cell-laden hydrogel ink direct writing printing and electrohydrodynamic fiber 3D printing technologies. Through integrated bioprinting, multi-scale models with different cellular components and fiber structural parameters were prepared to study the effects of macroscopic and microscopic structural features on the directionality of neural cells, as well as the interaction between glial cells and neurons within the tissue model in a three-dimensional manner. The results revealed that the manufactured in vitro biomimetic cortical model achieved morphological connections between the layers of neurons, reflecting the structure and cellular morphology of the natural cortex. Micrometer-scale (10 μm) cross-layer fibers effectively guided and controlled the extension length and direction of the neurites of surrounding neural cells but had no significant effect on the migration of neurons. In contrast, glial cells significantly promoted the migration of surrounding PC12 cells towards the glial layer but did not contribute to the extension of neurites. This study provides a basis for the design and manufacture of accurate brain-like models for the functionalization of neuronal tissues.

Microstructured silk fiber scaffolds with enhanced stretchability

Despite extensive research, current methods for creating three-dimensional (3D) silk fibroin (SF) scaffolds lack control over molecular rearrangement, particularly in the formation of β-sheet nanocrystals that severely embrittle SF, as well as hierarchical fiber organization at both micro- and macroscale. Here, we introduce a fabrication process based on electrowriting of aqueous SF solutions followed by post-processing using an aqueous solution of sodium dihydrogen phosphate (NaH2PO4). This approach enables gelation of SF chains via controlled β-sheet formation and partial conservation of compliant random coil structures. Moreover, this process allows for precise architecture control in microfiber scaffolds, enabling the creation of 3D flat and tubular macro-geometries with square-based and crosshatch microarchitectures, featuring inter-fiber distances of 400 μm and ∼97% open porosity. Remarkably, the crosslinked printed structures demonstrated a balanced coexistence of β-sheet and random coil conformations, which is uncommon for organic solvent-based crosslinking methods. This synergy of printing and post-processing yielded stable scaffolds with high compliance (modulus = 0.5-15 MPa) and the ability to support elastic cyclic loading up to 20% deformation. Furthermore, the printed constructs supported in vitro adherence and growth of human renal epithelial and endothelial cells with viability above 95%. These cells formed homogeneous monolayers that aligned with the fiber direction and deposited type-IV collagen as a specific marker of healthy extracellular matrix, indicating that both cell types attach, proliferate, and organize their own microenvironment within the SF scaffolds. These findings represent a significant development in fabricating organized stable SF scaffolds with unique microfiber structures and mechanical and biological properties that make them highly promising for tissue engineering applications.

Biomimetic Dual-Network Collagen Fibers with Porous and Mechanical Cues Reconstruct Neural Stem Cell Niche via AKT/YAP Mechanotransduction after Spinal Cord Injury

Tissue engineering scaffolds can mediate the maneuverability of neural stem cell (NSC) niche to influence NSC behavior, such as cell self-renewal, proliferation, and differentiation direction, showing the promising application in spinal cord injury (SCI) repair. Here, dual-network porous collagen fibers (PCFS) are developed as neurogenesis scaffolds by employing biomimetic plasma ammonia oxidase catalysis and conventional amidation cross-linking. Following optimizing the mechanical parameters of PCFS, the well-matched Young's modulus and physiological dynamic adaptability of PCFS (4.0 wt%) have been identified as a neurogenetic exciter after SCI. Remarkably, porous topographies and curving wall-like protrusions are generated on the surface of PCFS by simple and non-toxic CO2 bubble-water replacement. As expected, PCFS with porous and matched mechanical properties can considerably activate the cadherin receptor of NSCs and induce a series of serine-threonine kinase/yes-associated protein mechanotransduction signal pathways, encouraging cellular orientation, neuron differentiation, and adhesion. In SCI rats, implanted PCFS with matched mechanical properties further integrated into the injured spinal cords, inhibited the inflammatory progression and decreased glial and fibrous scar formation. Wall-like protrusions of PCFS drive multiple neuron subtypes formation and even functional neural circuits, suggesting a viable therapeutic strategy for nerve regeneration and functional recovery after SCI.

Artificial Trabecular Meshwork Structure Combining Melt Electrowriting and Solution Electrospinning

The human trabecular meshwork (HTM) is responsible for regulating intraocular pressure (IOP) by means of gradient porosity. Changes in its physical properties, like increases in stiffness or alterations in the extracellular matrix (ECM), are associated with increases in the IOP, which is the primary cause of glaucoma. The complexity of its structure limits the engineered models to one-layered and simple approaches, which do not accurately replicate the biological and physiological cues related to glaucoma. Here, a combination of melt electrowriting (MEW) and solution electrospinning (SE) is explored as a biofabrication technique used to produce a gradient porous scaffold that mimics the multi-layered structure of the native HTM. Polycaprolactone (PCL) constructs with a height of 20-710 µm and fiber diameters of 0.7-37.5 µm were fabricated. After mechanical characterization, primary human trabecular meshwork cells (HTMCs) were seeded over the scaffolds within the subsequent 14-21 days. In order to validate the system's responsiveness, cells were treated with dexamethasone (Dex) and the rho inhibitor Netarsudil (Net). Scanning electron microscopy and immunochemistry staining were performed to evaluate the expected morphological changes caused by the drugs. Cells in the engineered membranes exhibited an HTMC-like morphology and a correct drug response. Although this work demonstrates the utility of combining MEW and SE in reconstructing complex morphological features like the HTM, new geometries and dimensions should be tested, and future works need to be directed towards perfusion studies.

Hypothermic and cryogenic preservation of cardiac tissue-engineered constructs

Cardiac tissue engineering (cTE) has already advanced towards the first clinical trials, investigating safety and feasibility of cTE construct transplantation in failing hearts. However, the lack of well-established preservation methods poses a hindrance to further scalability, commercialization, and transportation, thereby reducing their clinical implementation. In this study, hypothermic preservation (4 °C) and two methods for cryopreservation (i.e., a slow and fast cooling approach to -196 °C and -150 °C, respectively) were investigated as potential solutions to extend the cTE construct implantation window. The cTE model used consisted of human induced pluripotent stem cell-derived cardiomyocytes and human cardiac fibroblasts embedded in a natural-derived hydrogel and supported by a polymeric melt electrowritten hexagonal scaffold. Constructs, composed of cardiomyocytes of different maturity, were preserved for three days, using several commercially available preservation protocols and solutions. Cardiomyocyte viability, function (beat rate and calcium handling), and metabolic activity were investigated after rewarming. Our observations show that cardiomyocytes' age did not influence post-rewarming viability, however, it influenced construct function. Hypothermic preservation with HypoThermosol® ensured cardiomyocyte viability and function. Furthermore, fast freezing outperformed slow freezing, but both viability and function were severely reduced after rewarming. In conclusion, whereas long-term preservation remains a challenge, hypothermic preservation with HypoThermosol® represents a promising solution for cTE construct short-term preservation and potential transportation, aiding in off-the-shelf availability, ultimately increasing their clinical applicability.

Research Progress in the Field of Tumor Model Construction Using Bioprinting: A Review

The development of therapeutic drugs and methods has been greatly facilitated by the emergence of tumor models. However, due to their inherent complexity, establishing a model that can fully replicate the tumor tissue situation remains extremely challenging. With the development of tissue engineering, the advancement of bioprinting technology has facilitated the upgrading of tumor models. This article focuses on the latest advancements in bioprinting, specifically highlighting the construction of 3D tumor models, and underscores the integration of these two technologies. Furthermore, it discusses the challenges and future directions of related techniques, while also emphasizing the effective recreation of the tumor microenvironment through the emergence of 3D tumor models that resemble in vitro organs, thereby accelerating the development of new anticancer therapies.

Electrohydrodynamic Direct-Writing Micro/Nanofibrous Architectures: Principle, Materials, and Biomedical Applications

Electrohydrodynamic (EHD) direct-writing has recently gained attention as a highly promising additive manufacturing strategy for fabricating intricate micro/nanoscale architectures. This technique is particularly well-suited for mimicking the extracellular matrix (ECM) present in biological tissue, which serves a vital function in facilitating cell colonization, migration, and growth. The integration of EHD direct-writing with other techniques has been employed to enhance the biological performance of scaffolds, and significant advancements have been made in the development of tailored scaffold architectures and constituents to meet the specific requirements of various biomedical applications. Here, a comprehensive overview of EHD direct-writing is provided, including its underlying principles, demonstrated materials systems, and biomedical applications. A brief chronology of EHD direct-writing is provided, along with an examination of the observed phenomena that occur during the printing process. The impact of biomaterial selection and architectural topographic cues on biological performance is also highlighted. Finally, the major limitations associated with EHD direct-writing are discussed.

Materials and Strategies to Enhance Melt Electrowriting Potential

Melt electrowriting (MEW) is an emerging additive manufacturing (AM) technology that enables the precise deposition of continuous polymeric microfibers, allowing for the creation of high-resolution constructs. In recent years, MEW has undergone a revolution, with the introduction of active properties or additional functionalities through novel polymer processing strategies, the incorporation of functional fillers, postprocessing, or the combination with other techniques. While extensively explored in biomedical applications, MEW's potential in other fields remains untapped. Thus, this review explores MEW's characteristics from a materials science perspective, emphasizing the diverse range of materials and composites processed by this technique and their current and potential applications. Additionally, the prospects offered by postprinting processing techniques are explored, together with the synergy achieved by combining melt electrowriting with other manufacturing methods. By highlighting the untapped potentials of MEW, this review aims to inspire research groups across various fields to leverage this technology for innovative endeavors.

Melt electrowritten poly-lactic acid /nanodiamond scaffolds towards wound-healing patches

Multifunctional wound dressings, enriched with biologically active agents for preventing or treating infections and promoting wound healing, along with cell delivery capability, are highly needed. To address this issue, composite scaffolds with potential in wound dressing applications were fabricated in this study. The poly-lactic acid/nanodiamonds (PLA/ND) scaffolds were first printed using melt electrowriting (MEW) and then coated with quaternized β-chitin (QβC). The NDs were well-dispersed in the printed filaments and worked as fillers and bioactive additions to PLA material. Additionally, they improved coating effectiveness due to the interaction between their negative charges (from NDs) and positive charges (from QβC). NDs not only increased the thermal stability of PLA but also benefitted cellular behavior and inhibited the growth of bacteria. Scaffolds coated with QβC increased the effect of bacteria growth inhibition and facilitated the proliferation of human dermal fibroblasts. Additionally, we have observed rapid extracellular matrix (ECM) remodeling on QβC-coated PLA/NDs scaffolds. The scaffolds provided support for cell adhesion and could serve as a valuable tool for delivering cells to chronic wound sites. The proposed PLA/ND scaffold coated with QβC holds great potential for achieving fast healing in various types of wounds.

3D-printed electrospun fibres for wound healing

Wound management for acute and chronic wounds has become a serious clinical problem worldwide, placing considerable pressure on public health systems. Owing to the high-precision, adjustable pore structure, and repeatable manufacturing process, 3D-printed electrospun fibre (3DP-ESF) has attracted widespread attention for fabricating wound dressing. In addition, in comparison with 2D electrospun fibre membranes fabricated by traditional electrospinning, the 3D structures provide additional guidance on cell behaviour. In this perspective article, we first summarise the basic manufacturing principles and methods to fabricate 3DP-ESF. Then, we discuss the function of 3DP-ESF in manipulating the different stages of wound healing, including anti-bacteria, anti-inflammation, and promotion of cell migration and proliferation, as well as the construction of tissue-engineered scaffolds. In the end, we provide the current challenge faced by 3DP-ESF in the application of skin wound regeneration and its promising future directions.

Biodegradable Electrospun Membranes for Sustainable Industrial Applications

The escalating demand for sustainable industrial practices has driven the exploration of innovative materials, prominently exemplified by biodegradable electrospun membranes (BEMs). This review elucidates the pivotal role of these membranes across diverse industrial applications, addressing the imperative for sustainability. Furthermore, a comprehensive overview of biodegradable materials underscores their significance in electrospinning and their role in minimizing the environmental impact through biodegradability. The application of BEMs in various industrial sectors, including water treatment, food packaging, and biomedical applications, are extensively discussed. The environmental impact and sustainability analysis traverse the lifecycle of BEMs, evaluating their production to disposal and emphasizing reduced waste and resource conservation. This review demonstrates the research about BEMs toward an eco-conscious industrial landscape for a sustainable future.

3D Printed Magneto-Active Microfiber Scaffolds for Remote Stimulation and Guided Organization of 3D In Vitro Skeletal Muscle Models

This work reports the rational design and fabrication of magneto-active microfiber meshes with controlled hexagonal microstructures via melt electrowriting (MEW) of a magnetized polycaprolactone-based composite. In situ iron oxide nanoparticle deposition on oxidized graphene yields homogeneously dispersed magnetic particles with sizes above 0.5 µm and low aspect ratio, preventing cellular internalization and toxicity. With these fillers, homogeneous magnetic composites with high magnetic content (up to 20 weight %) are obtained and processed in a solvent-free manner for the first time. MEW of magnetic composites enabled the creation of skeletal muscle-inspired design of hexagonal scaffolds with tunable fiber diameter, reconfigurable modularity, and zonal distribution of magneto-active and nonactive material, with elastic tensile deformability. External magnetic fields below 300 mT are sufficient to trigger out-of-plane reversible deformation. In vitro culture of C2C12 myoblasts on three-dimensional (3D) Matrigel/collagen/MEW scaffolds showed that microfibers guided the formation of 3D myotube architectures, and the presence of magnetic particles does not significantly affect viability or differentiation rates after 8 days. Centimeter-sized skeletal muscle constructs allowed for reversible, continued, and dynamic magneto-mechanical stimulation. Overall, these innovative microfiber scaffolds provide magnetically deformable platforms suitable for dynamic culture of skeletal muscle, offering potential for in vitro disease modeling.

Melt electrowritten scaffold architectures to mimic tissue mechanics and guide neo-tissue orientation

All human tissues present with unique mechanical properties critical to their function. This is achieved in part through the specific architecture of the extracellular matrix (ECM) fibres within each tissue. An example of this is seen in the walls of the vasculature where each layer presents with a unique ECM orientation critical to its functions. Current adopted vascular grafts to bypass a stenosed/damaged vessel fail to recapitulate this unique mechanical behaviour, particularly in the case of small diameter vessels (<6 mm), leading to failure. Therefore, in this study, melt-electrowriting (MEW) was adopted to produce a range of fibrous scaffolds to mimic the extracellular matrix (ECM) architecture of the tunica media of the vasculature, in an attempt to match the mechanical and biological behaviour of the native porcine tissue. Initially, the range of collagen architectures within the native vessel was determined, and subsequently replicated using MEW (winding angles (WA) 45°, 26.5°, 18.4°, 11.3°). These scaffolds recapitulated the anisotropic, non-linear mechanical behaviour of native carotid blood vessels. Moreover, these grafts facilitated human mesenchymal stem cell (hMSC) infiltration, differentiation, and ECM deposition that was independent of WA. The bioinspired MEW fibre architecture promoted cell alignment and preferential neo-tissue orientation in a manner similar to that seen in native tissue, particularly for WA 18.4° and 11.3°, which is a mandatory requirement for long-term survival of the regenerated tissue post-scaffold degradation. Lastly, the WA 18.4° was translated to a tubular graft and was shown to mirror the mechanical behaviour of small diameter vessels within physiological strain. Taken together, this study demonstrates the capacity to use MEW to fabricate bioinspired scaffolds to mimic the tunica media of vessels and recapitulate vascular mechanics which could act as a framework for small diameter graft development to guide tissue regeneration and orientation.

Hybrid Biofabrication of Heterogeneous 3D Constructs Using Low-Viscosity Bioinks

The application of cytocompatible hydrogels supporting extensive cellular activities to three-dimensional (3D) bioprinting is crucial for recreating complex physiological environments with high biomimicry. However, the poor printability and tunability of such natural hydrogels diminish the versatility and resolution of bioprinters. In this study, we propose a novel approach for the hybrid biofabrication of complex and heterogeneous 3D constructs using low-viscosity bioinks. Poly(lactic acid) (PLA) filament is extruded by fused deposition modeling on a micromesh to create PLA-framed micromesh substrates onto which fibrinogen is printed by microextrusion bioprinting. The micromesh supports the printed hydrogel with a capillary pinning effect to enable high-resolution bioprinting. Accordingly, the micromesh-bioink layers are aligned and stacked to form volumetric constructs. This approach, called the 3D micromesh-bioink overlaid structure and interlocked culture (3D MOSAIC) platform, enables the fabrication of complicated and multimaterial 3D structures, including overhangs and voids. Endothelial cells cultured under vasculogenic conditions in the platform self-organize within the biologically functional hydrogel to form vascular networks, and cancer cell migration can be observed across the layers. The multidisciplinary 3D MOSAIC platform is an important step toward the biofabrication of complex constructs with high biological and structural significance and functionality.

Construction of cardiac fibrosis for biomedical research

Cardiac remodeling is critical for effective tissue recuperation, nevertheless, excessive formation and deposition of extracellular matrix components can result in the onset of cardiac fibrosis. Despite the emergence of novel therapies, there are still no lifelong therapeutic solutions for this issue. Understanding the detrimental cardiac remodeling may aid in the development of innovative treatment strategies to prevent or reverse fibrotic alterations in the heart. Further combining the latest understanding of disease pathogenesis with cardiac tissue engineering has provided the conversion of basic laboratory studies into the therapy of cardiac fibrosis patients as an increasingly viable prospect. This review presents the current main mechanisms and the potential tissue engineering of cardiac fibrosis. Approaches using biomedical materials-based cardiac constructions are reviewed to consider key issues for simulating in vitro cardiac fibrosis, outlining a future perspective for preclinical applications.

Volumetric Printing Across Melt Electrowritten Scaffolds Fabricates Multi-Material Living Constructs with Tunable Architecture and Mechanics

Major challenges in biofabrication revolve around capturing the complex, hierarchical composition of native tissues. However, individual 3D printing techniques have limited capacity to produce composite biomaterials with multi-scale resolution. Volumetric bioprinting recently emerged as a paradigm-shift in biofabrication. This ultrafast, light-based technique sculpts cell-laden hydrogel bioresins into 3D structures in a layerless fashion, providing enhanced design freedom over conventional bioprinting. However, it yields prints with low mechanical stability, since soft, cell-friendly hydrogels are used. Herein, the possibility to converge volumetric bioprinting with melt electrowriting, which excels at patterning microfibers, is shown for the fabrication of tubular hydrogel-based composites with enhanced mechanical behavior. Despite including non-transparent melt electrowritten scaffolds in the volumetric printing process, high-resolution bioprinted structures are successfully achieved. Tensile, burst, and bending mechanical properties of printed tubes are tuned altering the electrowritten mesh design, resulting in complex, multi-material tubular constructs with customizable, anisotropic geometries that better mimic intricate biological tubular structures. As a proof-of-concept, engineered tubular structures are obtained by building trilayered cell-laden vessels, and features (valves, branches, fenestrations) that can be rapidly printed using this hybrid approach. This multi-technology convergence offers a new toolbox for manufacturing hierarchical and mechanically tunable multi-material living structures.

3D Printed Conductive Multiscale Nerve Guidance Conduit with Hierarchical Fibers for Peripheral Nerve Regeneration

Nerve guidance conduits (NGCs) have become a promising alternative for peripheral nerve regeneration; however, the outcome of nerve regeneration and functional recovery is greatly affected by the physical, chemical, and electrical properties of NGCs. In this study, a conductive multiscale filled NGC (MF-NGC) consisting of electrospun poly(lactide-co-caprolactone) (PCL)/collagen nanofibers as the sheath, reduced graphene oxide /PCL microfibers as the backbone, and PCL microfibers as the internal structure for peripheral nerve regeneration is developed. The printed MF-NGCs presented good permeability, mechanical stability, and electrical conductivity, which further promoted the elongation and growth of Schwann cells and neurite outgrowth of PC12 neuronal cells. Animal studies using a rat sciatic nerve injury model reveal that the MF-NGCs promote neovascularization and M2 transition through the rapid recruitment of vascular cells and macrophages. Histological and functional assessments of the regenerated nerves confirm that the conductive MF-NGCs significantly enhance peripheral nerve regeneration, as indicated by improved axon myelination, muscle weight increase, and sciatic nerve function index. This study demonstrates the feasibility of using 3D-printed conductive MF-NGCs with hierarchically oriented fibers as functional conduits that can significantly enhance peripheral nerve regeneration.

Electric-Field-Driven Printed 3D Highly Ordered Microstructure with Cell Feature Size Promotes the Maturation of Engineered Cardiac Tissues

Engineered cardiac tissues (ECTs) derived from human induced pluripotent stem cells (hiPSCs) are viable alternatives for cardiac repair, patient-specific disease modeling, and drug discovery. However, the immature state of ECTs limits their clinical utility. The microenvironment fabricated using 3D scaffolds can affect cell fate, and is crucial for the maturation of ECTs. Herein, the authors demonstrate an electric-field-driven (EFD) printed 3D highly ordered microstructure with cell feature size to promote the maturation of ECTs. The simulation and experimental results demonstrate that the EFD jet microscale 3D printing overcomes the jet repulsion without any prior requirements for both conductive and insulating substrates. Furthermore, the 3D highly ordered microstructures with a fiber diameter of 10-20 µm and spacing of 60-80 µm have been fabricated by maintaining a vertical jet, achieving the largest ratio of fiber diameter/spacing of 0.29. The hiPSCs-derived cardiomyocytes formed ordered ECTs with their sarcomere growth along the fiber and developed synchronous functional ECTs inside the 3D-printed scaffold with matured calcium handling compared to the 2D coverslip. Therefore, the EFD jet 3D microscale printing process facilitates the fabrication of scaffolds providing a suitable microenvironment to promote the maturation of ECTs, thereby showing great potential for cardiac tissue engineering.

Melt Electrowriting of Liquid Crystal Elastomer Scaffolds with Programmed Mechanical Response

Recently, significant advances have been achieved to precisely program the response of liquid crystal elastomers (LCEs) through extrusion-based additive manufacturing techniques; however, important challenges remain, especially when well-defined scaffolds based on ultrafine fibers are required. Here the melt electrowriting of reactive liquid crystalline inks, leading, after ultraviolet-light-induced crosslinking, to digitally positioned uniform LCE fibers with diameters ranging from hundreds of nanometers to tens of micrometers is presented, which is hardly accessible with conventional extrusion-based printing techniques. The electrowriting process induces the preferential alignment of the mesogens parallel to the fiber's axis. Such an alignment, defined by the printing path, determines the mechanical response of the crosslinked material upon stimulation. This manufacturing platform allows the preparation of open square lattice scaffolds with ultrafine fibers (a few micrometers in diameter), periods as small as 90 µm, and well-defined morphology. Additionally, the combination of accurate fiber stacking (up to 50 layers) and fiber fusion between layers leads to unprecedented microstructures composed of high-aspect-ratio LCE thin walls. The possibility of digitally controlling the printing of fibers allows the preparation complex fiber-based scaffolds with programmed and reversible shape-morphing, thus opening new avenues to prepare miniaturized actuators and smart structures for soft robotics and biomedical applications.

Biomimetic natural biomaterials for tissue engineering and regenerative medicine: new biosynthesis methods, recent advances, and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering (TE) and regenerative medicine. In contrast to conventional biomaterials or synthetic materials, biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix (ECM). Additionally, such materials have mechanical adaptability, microstructure interconnectivity, and inherent bioactivity, making them ideal for the design of living implants for specific applications in TE and regenerative medicine. This paper provides an overview for recent progress of biomimetic natural biomaterials (BNBMs), including advances in their preparation, functionality, potential applications and future challenges. We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM. Moreover, we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications. Finally, we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Composite Graded Melt Electrowritten Scaffolds for Regeneration of the Periodontal Ligament-to-Bone Interface

Periodontitis is a ubiquitous chronic inflammatory, bacteria-triggered oral disease affecting the adult population. If left untreated, periodontitis can lead to severe tissue destruction, eventually resulting in tooth loss. Despite previous efforts in clinically managing the disease, therapeutic strategies are still lacking. Herein, melt electrowriting (MEW) is utilized to develop a compositionally and structurally tailored graded scaffold for regeneration of the periodontal ligament-to-bone interface. The composite scaffolds, consisting of fibers of polycaprolactone (PCL) and fibers of PCL-containing magnesium phosphate (MgP) were fabricated using MEW. To maximize the bond between bone (MgP) and ligament (PCL) regions, we evaluated two different fiber architectures in the interface area. These were a crosshatch pattern at a 0/90° angle and a random pattern. MgP fibrous scaffolds were able to promote in vitro bone formation even in culture media devoid of osteogenic supplements. Mechanical properties after MgP incorporation resulted in an increase of the elastic modulus and yield stress of the scaffolds, and fiber orientation in the interfacial zone affected the interfacial toughness. Composite graded MEW scaffolds enhanced bone fill when they were implanted in an in vivo periodontal fenestration defect model in rats. The presence of an interfacial zone allows coordinated regeneration of multitissues, as indicated by higher expression of bone, ligament, and cementoblastic markers compared to empty defects. Collectively, MEW-fabricated scaffolds having compositionally and structurally tailored zones exhibit a good mimicry of the periodontal complex, with excellent regenerative capacity and great potential as a defect-specific treatment strategy.

Unveiling the potential of melt electrowriting in regenerative dental medicine

For nearly three decades, tissue engineering strategies have been leveraged to devise effective therapeutics for dental, oral, and craniofacial (DOC) regenerative medicine and treat permanent deformities caused by many debilitating health conditions. In this regard, additive manufacturing (AM) allows the fabrication of personalized scaffolds that have the potential to recapitulate native tissue morphology and biomechanics through the utilization of several 3D printing techniques. Among these, melt electrowriting (MEW) is a versatile direct electrowriting process that permits the development of well-organized fibrous constructs with fiber resolutions ranging from micron to nanoscale. Indeed, MEW offers great prospects for the fabrication of scaffolds mimicking tissue specificity, healthy and pathophysiological microenvironments, personalized multi-scale transitions, and functional interfaces for tissue regeneration in medicine and dentistry. Excitingly, recent work has demonstrated the potential of converging MEW with other AM technologies and/or cell-laden scaffold fabrication (bioprinting) as a favorable route to overcome some of the limitations of MEW for DOC tissue regeneration. In particular, such convergency fabrication strategy has opened great promise in terms of supporting multi-tissue compartmentalization and predetermined cell commitment. In this review, we offer a critical appraisal on the latest advances in MEW and its convergence with other biofabrication technologies for DOC tissue regeneration. We first present the engineering principles of MEW and the most relevant design aspects for transition from flat to more anatomically relevant 3D structures while printing highly-ordered constructs. Secondly, we provide a thorough assessment of contemporary achievements using MEW scaffolds to study and guide soft and hard tissue regeneration, and draw a parallel on how to extrapolate proven concepts for applications in DOC tissue regeneration. Finally, we offer a combined engineering/clinical perspective on the fabrication of hierarchically organized MEW scaffold architectures and the future translational potential of site-specific, single-step scaffold fabrication to address tissue and tissue interfaces in dental, oral, and craniofacial regenerative medicine. STATEMENT OF SIGNIFICANCE: Melt electrowriting (MEW) techniques can further replicate the complexity of native tissues and could be the foundation for novel personalized (defect-specific) and tissue-specific clinical approaches in regenerative dental medicine. This work presents a unique perspective on how MEW has been translated towards the application of highly-ordered personalized multi-scale and functional interfaces for tissue regeneration, targeting the transition from flat to anatomically-relevant three-dimensional structures. Furthermore, we address the value of convergence of biofabrication technologies to overcome the traditional manufacturing limitations provided by multi-tissue complexity. Taken together, this work offers abundant engineering and clinical perspectives on the fabrication of hierarchically MEW architectures aiming towards site-specific implants to address complex tissue damage in regenerative dental medicine.

Tailoring micro/nano-fibers for biomedical applications

Nano/micro fibers have evoked much attention of scientists and have been researched as cutting edge and hotspot in the area of fiber science in recent years due to the rapid development of various advanced manufacturing technologies, and the appearance of fascinating and special functions and properties, such as the enhanced mechanical strength, high surface area to volume ratio and special functionalities shown in the surface, triggered by the nano or micro-scale dimensions. In addition, these outstanding and special characteristics of the nano/micro fibers impart fiber-based materials with wide applications, such as environmental engineering, electronic and biomedical fields. This review mainly focuses on the recent development in the various nano/micro fibers fabrication strategies and corresponding applications in the biomedical fields, including tissue engineering scaffolds, drug delivery, wound healing, and biosensors. Moreover, the challenges for the fabrications and applications and future perspectives are presented.

Breaking the resolution limits of 3D bioprinting: future opportunities and present challenges

Bioprinting aims to produce 3D structures from which embedded cells can receive mechanical and chemical stimuli that influence their behavior, direct their organization and migration, and promote differentiation, in a similar way to what happens within the native extracellular matrix. However, limited spatial resolution has been a bottleneck for conventional 3D bioprinting approaches. Reproducing fine features at the cellular scale, while maintaining a reasonable printing volume, is necessary to enable the biofabrication of more complex and functional tissue and organ models. In this opinion article we recount the emergence of, and discuss the most promising, high-definition (HD) bioprinting techniques to achieve this goal, discussing which obstacles remain to be overcome, and which applications are envisioned in the tissue engineering field.

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

Biomimetic design of bioartificial scaffolds for the in vitro modelling of human cardiac fibrosis

In vitro models of pathological cardiac tissue have attracted interest as predictive platforms for preclinical validation of therapies. However, models reproducing specific pathological features, such as cardiac fibrosis size (i.e., thickness and width) and stage of development are missing. This research was aimed at engineering 2D and 3D models of early-stage post-infarct fibrotic tissue (i.e., characterized by non-aligned tissue organization) on bioartificial scaffolds with biomimetic composition, design, and surface stiffness. 2D scaffolds with random nanofibrous structure and 3D scaffolds with 150 µm square-meshed architecture were fabricated from polycaprolactone, surface-grafted with gelatin by mussel-inspired approach and coated with cardiac extracellular matrix (ECM) by 3 weeks culture of human cardiac fibroblasts. Scaffold physicochemical properties were thoroughly investigated. AFM analysis of scaffolds in wet state, before cell culture, confirmed their close surface stiffness to human cardiac fibrotic tissue. Following 3 weeks culture, biomimetic biophysical and biochemical scaffold properties triggered the activation of myofibroblast phenotype. Upon decellularization, immunostaining, SEM and two-photon excitation fluorescence microscopy showed homogeneous decoration of both 2D and 3D scaffolds with cardiac ECM. The versatility of the approach was demonstrated by culturing ventricular or atrial cardiac fibroblasts on scaffolds, thus suggesting the possibility to use the same scaffold platforms to model both ventricular and atrial cardiac fibrosis. In the future, herein developed in vitro models of cardiac fibrotic tissue, reproducing specific pathological features, will be exploited for a fine preclinical tuning of therapies.

Surface Functionalization of Nanofibers: The Multifaceted Approach for Advanced Biomedical Applications

Nanocarriers are gaining significant importance in the modern era of drug delivery. Nanofiber technology is one of the prime paradigms in nanotechnology for various biomedical and theranostic applications. Nanofibers obtained after successful electrospinning subjected to surface functionalized for drug delivery, biomedical, tissue engineering, biosensing, cell imaging and wound dressing application. Surface functionalization entirely changes physicochemical and biological properties of nanofibers. In physicochemical properties, wettability, melting point, glass transition temperature, and initial decomposition temperature significantly change offer several advantageous for nanofibers. Similarly, biological properties include cell adhesion, biocompatibility, and proliferation, also changes by functionalization of nanofibers. Various natural and synthetic materials polymers, metals, carbon materials, functional groups, proteins, and peptides, are currently used for surface modification of nanofibers. Various research studies across the globe demonstrated the usefulness of surface functionalized nanofibers in tissue engineering, wound healing, skin cancers, melanoma, and disease diagnosis. The delivery of drug through surface functionalized nanofibers results in improved permeation and bioavailability of drug which is important for better targeting of disease and therapeutic efficacy. This review provides a comprehensive insight about various techniques of surface functionalization of nanofibers along with its biomedical applications, toxicity assessment and global patent scenario.

Melt Electrowriting of Graded Porous Scaffolds to Mimic the Matrix Structure of the Human Trabecular Meshwork

The permeability of the human trabecular meshwork (HTM) regulates eye pressure via a porosity gradient across its thickness modulated by stacked layers of matrix fibrils and cells. Changes in HTM porosity are associated with increases in intraocular pressure and the progress of diseases such as glaucoma. Engineered HTMs could help to understand the structure-function relation in natural tissues and lead to new regenerative solutions. Here, melt electrowriting (MEW) is explored as a biofabrication technique to produce fibrillar, porous scaffolds that mimic the multilayer, gradient structure of native HTM. Poly(caprolactone) constructs with a height of 125-500 μm and fiber diameters of 10-12 μm are printed. Scaffolds with a tensile modulus between 5.6 and 13 MPa and a static compression modulus in the range of 6-360 kPa are obtained by varying the scaffold design, that is, the density and orientation of the fibers and number of stacked layers. Primary HTM cells attach to the scaffolds, proliferate, and form a confluent layer within 8-14 days, depending on the scaffold design. High cell viability and cell morphology close to that in the native tissue are observed. The present work demonstrates the utility of MEW for reconstructing complex morphological features of natural tissues.

Recent Advances in Cardiac Patches: Materials, Preparations, and Properties

Cardiac patches are biomaterials that can be used for transplantation and repair of damaged myocardium by combining seed cells with the ability to form cardiomyocytes and suitable scaffold materials. On the one hand, they provide temporary support to the infarcted area, and on the other hand, they repair the damaged myocardium by delivering cells or bioactive factors to integrate with the host, which have gradually become a hot research topic in recent years. This paper summarizes the structural properties of natural myocardium and reviews the recent research progress of cardiac patches, including the seed cells and scaffold materials used in patch preparation, as well as the main methods of scaffold preparation and the structure properties of various scaffolds. In addition, a comprehensive analysis of the problems faced in the clinical implementation of cardiac patches is presented. Finally, we look forward to the development of cardiac patches and point out that precisely tunable anisotropic tissue engineering scaffolds close to natural myocardial tissue will become an important direction for future research.

Fabrication of human myocardium using multidimensional modelling of engineered tissues

Biofabrication of human tissues has seen a meteoric growth triggered by recent technical advancements such as human induced pluripotent stem cells (hiPSCs) and additive manufacturing. However, generation of cardiac tissue is still hampered by lack of addequate mechanical properties and crucially by the often unpredictable post-fabrication evolution of biological components. In this study we employ melt electrowriting (MEW) and hiPSC-derived cardiac cells to generate fibre-reinforced human cardiac minitissues. These are thoroughly characterized in order to build computational models and simulations able to predict their post-fabrication evolution. Our results show that MEW-based human minitissues display advanced maturation 28 post-generation, with a significant increase in the expression of cardiac genes such as MYL2, GJA5, SCN5A and the MYH7/MYH6 and MYL2/MYL7 ratios. Human iPSC-cardiomyocytes are significantly more aligned within the MEW-based 3D tissues, as compared to conventional 2D controls, and also display greater expression of CX43. These are also correlated with a more mature functionality in the form of faster conduction velocity. We used these data to develop simulations capable of accurately reproducing the experimental performance. In-depth gauging of the structural disposition (cellular alignment) and intercellular connectivity (CX43) allowed us to develop an improved computational model able to predict the relationship between cardiac cell alignment and functional performance. This study lays down the path for advancing in the development of in silico tools to predict cardiac biofabricated tissue evolution after generation, and maps the route towards more accurate and biomimetic tissue manufacture.

Advancing Engineered Heart Muscle Tissue Complexity with Hydrogel Composites

A heart attack results in the permanent loss of heart muscle and can lead to heart disease, which kills more than 7 million people worldwide each year. To date, outside of heart transplantation, current clinical treatments cannot regenerate lost heart muscle or restore full function to the damaged heart. There is a critical need to create engineered heart tissues with structural complexity and functional capacity needed to replace damaged heart muscle. The inextricable link between structure and function suggests that hydrogel composites hold tremendous promise as a biomaterial-guided strategy to advance heart muscle tissue engineering. Such composites provide biophysical cues and functionality as a provisional extracellular matrix that hydrogels cannot on their own. This review describes the latest advances in the characterization of these biomaterial systems and using them for heart muscle tissue engineering. The review integrates results across the field to provide new insights on critical features within hydrogel composites and perspectives on the next steps to harnessing these promising biomaterials to faithfully reproduce the complex structure and function of native heart muscle.

Recent advances in melt electro writing for tissue engineering for 3D printing of microporous scaffolds for tissue engineering

Melt electro writing (MEW) is a high-resolution 3D printing technique that combines elements of electro-hydrodynamic fiber attraction and melts extrusion. The ability to precisely deposit micro- to nanometer strands of biocompatible polymers in a layer-by-layer fashion makes MEW a promising scaffold fabrication method for all kinds of tissue engineering applications. This review describes possibilities to optimize multi-parametric MEW processes for precise fiber deposition over multiple layers and prevent printing defects. Printing protocols for nonlinear scaffolds structures, concrete MEW scaffold pore geometries and printable biocompatible materials for MEW are introduced. The review discusses approaches to combining MEW with other fabrication techniques with the purpose to generate advanced scaffolds structures. The outlined MEW printer modifications enable customizable collector shapes or sacrificial materials for non-planar fiber deposition and nozzle adjustments allow redesigned fiber properties for specific applications. Altogether, MEW opens a new chapter of scaffold design by 3D printing.

Medical Applications of Porous Biomaterials: Features of Porosity and Tissue-Specific Implications for Biocompatibility

Porosity is an important material feature commonly employed in implants and tissue scaffolds. The presence of material voids permits the infiltration of cells, mechanical compliance, and outward diffusion of pharmaceutical agents. Various studies have confirmed that porosity indeed promotes favorable tissue responses, including minimal fibrous encapsulation during the foreign body reaction (FBR). However, increased biofilm formation and calcification is also described to arise due to biomaterial porosity. Additionally, the relevance of host responses like the FBR, infection, calcification, and thrombosis are dependent on tissue location and specific tissue microenvironment. In this review, the features of porous materials and the implications of porosity in the context of medical devices is discussed. Common methods to create porous materials are also discussed, as well as the parameters that are used to tune pore features. Responses toward porous biomaterials are also reviewed, including the various stages of the FBR, hemocompatibility, biofilm formation, and calcification. Finally, these host responses are considered in tissue specific locations including the subcutis, bone, cardiovascular system, brain, eye, and female reproductive tract. The effects of porosity across the various tissues of the body is highlighted and the need to consider the tissue context when engineering biomaterials is emphasized.

The Technological Advancement to Engineer Next-Generation Stent-Grafts: Design, Material, and Fabrication Techniques

Endovascular treatment of aortic disorders has gained wide acceptance due to reduced physiological burden to the patient compared to open surgery, and ongoing stent-graft evolution has made aortic repair an option for patients with more complex anatomies. To date, commercial stent-grafts are typically developed from established production techniques with simple design structures and limited material ranges. Despite the numerous updated versions of stent-grafts by manufacturers, the reoccurrence of device-related complications raises questions about whether the current manfacturing methods are technically able to eliminate these problems. The technology trend to produce efficient medical devices, including stent-grafts and all similar implants, should eventually change direction to advanced manufacturing techniques. It is expected that through recent advancements, especially the emergence of 4D-printing and smart materials, unprecedented features can be defined for cardiovascular medical implants, like shape change and remote battery-free self-monitoring. 4D-printing technology promises adaptive functionality, a highly desirable feature enabling printed cardiovascular implants to physically transform with time to perform a programmed task. This review provides a thorough assessment of the established technologies for existing stent-grafts and provides technical commentaries on known failure modes. They then discuss the future of advanced technologies and the efforts needed to produce next-generation endovascular implants.

Bioengineering approaches to treat the failing heart: from cell biology to 3D printing

Successfully engineering a functional, human, myocardial pump would represent a therapeutic alternative for the millions of patients with end-stage heart disease and provide an alternative to animal-based preclinical models. Although the field of cardiac tissue engineering has made tremendous advances, major challenges remain, which, if properly resolved, might allow the clinical implementation of engineered, functional, complex 3D structures in the future. In this Review, we provide an overview of state-of-the-art studies, challenges that have not yet been overcome and perspectives on cardiac tissue engineering. We begin with the most clinically relevant cell sources used in this field and discuss the use of topological, biophysical and metabolic stimuli to obtain mature phenotypes of cardiomyocytes, particularly in relation to organized cytoskeletal and contractile intracellular structures. We then move from the cellular level to engineering planar cardiac patches and discuss the need for proper vascularization and the main strategies for obtaining it. Finally, we provide an overview of several different approaches for the engineering of volumetric organs and organ parts - from whole-heart decellularization and recellularization to advanced 3D printing technologies.

New Forms of Electrospun Nanofibers Applied in Cardiovascular Field

Cardiovascular disease (CVD) is one of the leading causes of death worldwide. In recent years, regenerative medicine, tissue engineering and the development of new materials have become the focus of attention this field, and electrospinning technology to prepare nanofibrous materials for the treatment of cardiovascular diseases has attracted people's attention. Unlike previous reviews, this research enumerates the experimental methods and applications of electrospinning technology combined with nanofibrous materials in the directions of myocardial infarction repair, artificial heart valves, artificial blood vessels and cardiovascular patches from the perspective of cardiovascular surgery. In the end, this review also summarizes the limitations, unresolved technical challenges, and possible future directions of this technology for cardiovascular disease applications.

Fabrication of bioinspired grid-crimp micropatterns by melt electrospinning writing for bone-ligament interface study

Many strategies have been adopted to engineer bone-ligament interface, which is of great value to both the tissue regeneration and the mechanism understanding underlying interface regeneration. However, how to recapitulate the complexity and heterogeneity of the native bone-ligament interface including the structural, cellular and mechanical gradients is still challenging. In this work, a bioinspired grid-crimp micropattern fabricated by melt electrospinning writing (MEW) was proposed to mimic the native structure of bone-ligament interface. The printing strategy of crimped fiber micropattern was developed and the processing parameters were optimized, which were used to mimic the crimp structure of the collagen fibrils in ligament. The guidance effect of the crimp angle and fiber spacing on the orientation of fibroblasts was studied, and both of them showed different levels of cell alignment effect.. MEW grid micropatterns with different fiber spacings were fabricated as bone region. Both the alkaling phosphatase activity and calcium mineralization results demonstrated the higher osteoinductive ability of the MEW grid structures, especially for that with smaller fiber spacing. The combined grid-crimp micropatterns were applied for the co-culture of fibroblasts and osteoblasts. The results showed that more cells were observed to migrate into the in-between interface region for the pattern with smaller fiber spacing, suggested the faster migration speed of cells. Finally, a cylindrical triphasic scaffold was successfully generated by rolling the grid-crimp micropatterns up, showing both structural and mechanical similarity to the native bone-ligament interface. In summary, the proposed strategy is reliable to fabricate grid-crimp triphasic micropatterns with controllable structural parameters to mimic the native bone-to-ligament structure, and the generated 3D scaffold shows great potential for the further bone-ligament interface tissue engineering.

The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period.

Recent advances on bioengineering approaches for fabrication of functional engineered cardiac pumps: A review

The field of cardiac tissue engineering has advanced over the past decades; however, most research progress has been limited to engineered cardiac tissues (ECTs) at the microscale with minimal geometrical complexities such as 3D strips and patches. Although microscale ECTs are advantageous for drug screening applications because of their high-throughput and standardization characteristics, they have limited translational applications in heart repair and the in vitro modeling of cardiac function and diseases. Recently, researchers have made various attempts to construct engineered cardiac pumps (ECPs) such as chambered ventricles, recapitulating the geometrical complexity of the native heart. The transition from microscale ECTs to ECPs at a translatable scale would greatly accelerate their translational applications; however, researchers are confronted with several major hurdles, including geometrical reconstruction, vascularization, and functional maturation. Therefore, the objective of this paper is to review the recent advances on bioengineering approaches for fabrication of functional engineered cardiac pumps. We first review the bioengineering approaches to fabricate ECPs, and then emphasize the unmatched potential of 3D bioprinting techniques. We highlight key advances in bioprinting strategies with high cell density as researchers have begun to realize the critical role that the cell density of non-proliferative cardiomyocytes plays in the cell-cell interaction and functional contracting performance. We summarize the current approaches to engineering vasculatures both at micro- and meso-scales, crucial for the survival of thick cardiac tissues and ECPs. We showcase a variety of strategies developed to enable the functional maturation of cardiac tissues, mimicking the in vivo environment during cardiac development. By highlighting state-of-the-art research, this review offers personal perspectives on future opportunities and trends that may bring us closer to the promise of functional ECPs.

3D bioprinting: current status and trends—a guide to the literature and industrial practice

The multidisciplinary research field of bioprinting combines additive manufacturing, biology and material sciences to create bioconstructs with three-dimensional architectures mimicking natural living tissues. The high interest in the possibility of reproducing biological tissues and organs is further boosted by the ever-increasing need for personalized medicine, thus allowing bioprinting to establish itself in the field of biomedical research, and attracting extensive research efforts from companies, universities, and research institutes alike. In this context, this paper proposes a scientometric analysis and critical review of the current literature and the industrial landscape of bioprinting to provide a clear overview of its fast-changing and complex position. The scientific literature and patenting results for 2000–2020 are reviewed and critically analyzed by retrieving 9314 scientific papers and 309 international patents in order to draw a picture of the scientific and industrial landscape in terms of top research countries, institutions, journals, authors and topics, and identifying the technology hubs worldwide. This review paper thus offers a guide to researchers interested in this field or to those who simply want to understand the emerging trends in additive manufacturing and 3D bioprinting.

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A suspended layer additive manufacturing approach to the bioprinting of tri-layered skin equivalents

Skin exhibits a complex structure consisting of three predominant layers (epidermis, dermis, and hypodermis). Extensive trauma may result in the loss of these structures and poor repair, in the longer term, forming scarred tissue and associated reduction in function. Although a number of skin replacements exist, there have been no solutions that recapitulate the chemical, mechanical, and biological roles that exist within native skin. This study reports the use of suspended layer additive manufacturing to produce a continuous tri-layered implant, which closely resembles human skin. Through careful control of the bioink composition, gradients (chemical and cellular) were formed throughout the printed construct. Culture of the model demonstrated that over 21 days, the cellular components played a key role in remodeling the supporting matrix into architectures comparable with those of healthy skin. Indeed, it has been demonstrated that even at seven days post-implantation, the integration of the implant had occurred, with mobilization of the adipose tissue from the surrounding tissue into the construct itself. As such, it is believed that these implants can facilitate healing, commencing from the fascia, up toward the skin surface-a mechanism recently shown to be key within deep wounds.

The Importance of Interfaces in Multi-Material Biofabricated Tissue Structures

Biofabrication exploits additive manufacturing techniques for creating 3D structures with a precise geometry that aim to mimic a physiological cellular environment and to develop the growth of native tissues. The most recent approaches of 3D biofabrication integrate multiple technologies into a single biofabrication platform combining different materials within different length scales to achieve improved construct functionality. However, the importance of interfaces between the different material phases, has not been adequately explored. This is known to determine material's interaction and ultimately mechanical and biological performance of biofabricated parts. In this review, this gap is bridged by critically examining the interface between different material phases in (bio)fabricated structures, with a particular focus on how interfacial interactions can compromise or define the mechanical (and biological) properties of the engineered structures. It is believed that the importance of interfacial properties between the different constituents of a composite material, deserves particular attention in its role in modulating the final characteristics of 3D tissue-like structures.

Renal Biology Driven Macro- and Microscale Design Strategies for Creating an Artificial Proximal Tubule Using Fiber-Based Technologies

Chronic kidney disease affects one in six people worldwide. Due to the scarcity of donor kidneys and the complications associated with hemodialysis (HD), a cell-based bioartificial kidney (BAK) device is desired. One of the shortcomings of HD is the lack of active transport of solutes that would normally be performed by membrane transporters in kidney epithelial cells. Specifically, proximal tubule (PT) epithelial cells play a major role in the active transport of metabolic waste products. Therefore, a BAK containing an artificial PT to actively transport solutes between the blood and the filtrate could provide major therapeutic advances. Creating such an artificial PT requires a biocompatible tubular structure which supports the adhesion and function of PT-specific epithelial cells. Ideally, this scaffold should structurally replicate the natural PT basement membrane which consists mainly of collagen fibers. Fiber-based technologies such as electrospinning are therefore especially promising for PT scaffold manufacturing. This review discusses the use of electrospinning technologies to generate an artificial PT scaffold for ex vivo/in vivo cellularization. We offer a comparison of currently available electrospinning technologies and outline the desired scaffold properties required to serve as a PT scaffold. Discussed also are the potential technologies that may converge in the future, enabling the effective and biomimetic incorporation of synthetic PTs in to BAK devices and beyond.