3D Bioprinting: from Benches to Translational Applications

Advances in Cell-Rich Inks for Biofabricating Living Architectures

Advancing biofabrication toward manufacturing living constructs with well-defined architectures and increasingly biologically relevant cell densities is highly desired to mimic the biofunctionality of native human tissues. The formulation of tissue-like, cell-dense inks for biofabrication remains, however, challenging at various levels of the bioprinting process. Promising advances have been made toward this goal, achieving relatively high cell densities that surpass those found in conventional platforms, pushing the current boundaries closer to achieving tissue-like cell densities. On this focus, herein the overarching challenges in the bioprocessing of cell-rich living inks into clinically grade engineered tissues are discussed, as well as the most recent advances in cell-rich living ink formulations and their processing technologies are highlighted. Additionally, an overview of the foreseen developments in the field is provided and critically discussed.

Manufacturing 3D Biomimetic Tissue: A Strategy Involving the Integration of Electrospun Nanofibers with a 3D-Printed Framework for Enhanced Tissue Regeneration

3D printing and electrospinning are versatile techniques employed to produce 3D structures, such as scaffolds and ultrathin fibers, facilitating the creation of a cellular microenvironment in vitro. These two approaches operate on distinct working principles and utilize different polymeric materials to generate the desired structure. This review provides an extensive overview of these techniques and their potential roles in biomedical applications. Despite their potential role in fabricating complex structures, each technique has its own limitations. Electrospun fibers may have ambiguous geometry, while 3D-printed constructs may exhibit poor resolution with limited mechanical complexity. Consequently, the integration of electrospinning and 3D-printing methods may be explored to maximize the benefits and overcome the individual limitations of these techniques. This review highlights recent advancements in combined techniques for generating structures with controlled porosities on the micro-nano scale, leading to improved mechanical structural integrity. Collectively, these techniques also allow the fabrication of nature-inspired structures, contributing to a paradigm shift in research and technology. Finally, the review concludes by examining the advantages, disadvantages, and future outlooks of existing technologies in addressing challenges and exploring potential opportunities.

Assessment and process optimization of high throughput biofabrication of immunocompetent breast cancer model for drug screening applications

Recent advancements in 3D cancer modeling have significantly enhanced our ability to delve into the intricacies of carcinogenesis. Despite the pharmaceutical industry's substantial investment of both capital and time in the drug screening and development pipeline, a concerning trend persists: drug candidates screened on conventional cancer models exhibit a dismal success rate in clinical trials. One pivotal factor contributing to this discrepancy is the absence of drug testing on pathophysiologically biomimetic 3D cancer models during pre-clinical stages. Unfortunately, current manual methods of 3D cancer modeling, such as spheroids and organoids, suffer from limitations in reproducibility and scalability. In our study, we have meticulously developed 3D bioprinted breast cancer model utilizing decellularized adipose tissue-based hydrogel obtained via a detergent-free decellularization method. Our innovative printing techniques allows for rapid, high-throughput fabrication of 3D cancer models in a 96-well plate format, demonstrating unmatched scalability and reproducibility. Moreover, we have conducted extensive validation, showcasing the efficacy of our platform through drug screening assays involving two potent anti-cancer drugs, 5-Fluorouracil and PRIMA-1Met. Notably, our platform facilitates effortless imaging and gene expression analysis, streamlining the evaluation process. In a bid to enhance the relevance of our cancer model, we have introduced a heterogeneous cell population into the DAT-based bioink. Through meticulous optimization and characterization, we have successfully developed a biomimetic immunocompetent breast cancer model, complete with microenvironmental cues and diverse cell populations. This breakthrough paves the way for rapid multiplex drug screening and the development of personalized cancer models, marking a paradigm shift in cancer research and pharmaceutical development.

3D Bioprinting of Biomimetic Alginate/Gelatin/Chondroitin Sulfate Hydrogel Nanocomposites for Intrinsically Chondrogenic Differentiation of Human Mesenchymal Stem Cells

3D-printed hydrogel scaffolds biomimicking the extracellular matrix (ECM) are key in cartilage tissue engineering as they can enhance the chondrogenic differentiation of mesenchymal stem cells (MSCs) through the presence of active nanoparticles such as graphene oxide (GO). Here, biomimetic hydrogels were developed by cross-linking alginate, gelatin, and chondroitin sulfate biopolymers in the presence of GO as a bioactive filler, with excellent processability for developing bioactive 3D printed scaffolds and for the bioprinting process. A novel bioink based on our hydrogel with embedded human MSCs presented a cell survival rate near 100% after the 3D bioprinting process. The effects of processing and filler concentration on cell differentiation were further quantitatively evaluated. The nanocomposited hydrogels render high MSC proliferation and viability, exhibiting intrinsic chondroinductive capacity without any exogenous factor when used to print scaffolds or bioprint constructs. The bioactivity depended on the GO concentration, with the best performance at 0.1 mg mL-1. These results were explained by the rational combination of the three biopolymers, with GO nanoparticles having carboxylate and sulfate groups in their structures, therefore, biomimicking the highly negatively charged ECM of cartilage. The bioactivity of this biomaterial and its good processability for 3D printing scaffolds and 3D bioprinting techniques open up a new approach to developing novel biomimetic materials for cartilage repair.

Modular photoorigami-based 4D manufacturing of vascular junction elements

Four-dimensional (4D) printing, combining three-dimensional (3D) printing with time-dependent stimuli-responsive shape transformation, eliminates the limitations of the conventional 3D printing technique for the fabrication of complex hollow constructs. However, existing 4D printing techniques have limitations in terms of the shapes that can be created using a single shape-changing object. In this paper, we report an advanced 4D fabrication approach for vascular junctions, particularly T-junctions, using the 4D printing technique based on coordinated sequential folding of two or more specially designed shape-changing elements. In our approach, the T-junction is split into two components, and each component is 4D printed using different synthesized shape memory polyurethanes and their nanohybrids, which have been synthesized with varying hard segment contents and by incorporating different weight percentages of photo-responsive copper sulfide-polyvinyl pyrrolidone nanoparticles. The formation of a T-junction is demonstrated by assigning different shape memory behaviors to each component of the T-junction. A cell culture study with human umbilical vein endothelial cells reveals that the cells proliferate over time, and almost 90% of cells remain viable on day 7. Finally, the formation of the T-junction in the presence of near-infrared light has been demonstrated after seeding the endothelial cells on the programmed flat surface of the two components and fluorescence microscopy at day 3 and 7 reveals that the cells adhered well and continue to proliferate over time. Hence, the proposed alternative approach has huge potential and can be used to fabricate vascular junctions in the future.

Bioprinted Human Lung Cancer-Mimics for Tissue Diagnostics Applications

Developing a reproducible and secure supply of customizable control tissues that standardizes for the cell type, tissue architecture, and preanalytics of interest for usage in applications including diagnostic, prognostic, and predictive assays, is critical for improving our patient care and welfare. The conventionally adopted control tissues directly obtained from patients are not ideal because they oftentimes have different amounts of normal and neoplastic elements, differing cellularity, differing architecture, and unknown preanalytics, in addition to the limited supply availability and thus associated high costs. In this study, we demonstrated a strategy to stably produce tissue-mimics for diagnostics purposes by taking advantage of the three-dimensional (3D) bioprinting technology. Specifically, we take anaplastic lymphoma kinase-positive (Alk+) lung cancer as an example, where a micropore-forming bioink laden with tumor cells was combined with digital light processing-based bioprinting for developing native-like Alk+ lung cancer tissue-mimics with both structural and functional relevancy. It is anticipated that our proposed methodology will pave new avenues for both fields of tissue diagnostics and 3D bioprinting significantly expanding their capacities, scope, and sustainability.

Research progress of photo-crosslink hydrogels in ophthalmology: A comprehensive review focus on the applications

Hydrogel presents a three-dimensional polymer network with high water content. Over the past decade, hydrogel has developed from static material to intelligent material with controllable response. Various stimuli are involved in the formation of hydrogel network, among which photo-stimulation has attracted wide attention due to the advantages of controllable conditions, which has a good application prospect in the treatment of ophthalmic diseases. This paper reviews the application of photo-crosslink hydrogels in ophthalmology, focusing on the types of photo-crosslink hydrogels and their applications in ophthalmology, including drug delivery, tissue engineering and 3D printing. In addition, the limitations and future prospects of photo-crosslink hydrogels are also provided.

Applications of 3D Bioprinting Technology to Brain Cells and Brain Tumor Models: Special Emphasis to Glioblastoma

Primary brain tumor is one of the most fatal diseases. The most malignant type among them, glioblastoma (GBM), has low survival rates. Standard treatments reduce the life quality of patients due to serious side effects. Tumor aggressiveness and the unique structure of the brain render the removal of tumors and the development of new therapies challenging. To elucidate the characteristics of brain tumors and examine their response to drugs, realistic systems that mimic the tumor environment and cellular crosstalk are desperately needed. In the past decade, 3D GBM models have been presented as excellent platforms as they allowed the investigation of the phenotypes of GBM and testing innovative therapeutic strategies. In that scope, 3D bioprinting technology offers utilities such as fabricating realistic 3D bioprinted structures in a layer-by-layer manner and precisely controlled deposition of materials and cells, and they can be integrated with other technologies like the microfluidics approach. This Review covers studies that investigated 3D bioprinted brain tumor models, especially GBM using 3D bioprinting techniques and essential parameters that affect the result and quality of the study like frequently used cells, the type and physical characteristics of hydrogel, bioprinting conditions, cross-linking methods, and characterization techniques.

Advanced 3D imaging and organoid bioprinting for biomedical research and therapeutic applications

Organoid cultures offer a valuable platform for studying organ-level biology, allowing for a closer mimicry of human physiology compared to traditional two-dimensional cell culture systems or non-primate animal models. While many organoid cultures use cell aggregates or decellularized extracellular matrices as scaffolds, they often lack precise biochemical and biophysical microenvironments. In contrast, three-dimensional (3D) bioprinting allows precise placement of organoids or spheroids, providing enhanced spatial control and facilitating the direct fusion for the formation of large-scale functional tissues in vitro. In addition, 3D bioprinting enables fine tuning of biochemical and biophysical cues to support organoid development and maturation. With advances in the organoid technology and its potential applications across diverse research fields such as cell biology, developmental biology, disease pathology, precision medicine, drug toxicology, and tissue engineering, organoid imaging has become a crucial aspect of physiological and pathological studies. This review highlights the recent advancements in imaging technologies that have significantly contributed to organoid research. Additionally, we discuss various bioprinting techniques, emphasizing their applications in organoid bioprinting. Integrating 3D imaging tools into a bioprinting platform allows real-time visualization while facilitating quality control, optimization, and comprehensive bioprinting assessment. Similarly, combining imaging technologies with organoid bioprinting can provide valuable insights into tissue formation, maturation, functions, and therapeutic responses. This approach not only improves the reproducibility of physiologically relevant tissues but also enhances understanding of complex biological processes. Thus, careful selection of bioprinting modalities, coupled with appropriate imaging techniques, holds the potential to create a versatile platform capable of addressing existing challenges and harnessing opportunities in these rapidly evolving fields.

Three-dimensional bioprinting of tissue-engineered skin: Biomaterials, fabrication techniques, challenging difficulties, and future directions: A review

As an emerging new manufacturing technology, Three-dimensional (3D) bioprinting provides the potential for the biomimetic construction of multifaceted and intricate architectures of functional integument, particularly functional biomimetic dermal structures inclusive of cutaneous appendages. Although the tissue-engineered skin with complete biological activity and physiological functions is still cannot be manufactured, it is believed that with the advances in matrix materials, molding process, and biotechnology, a new generation of physiologically active skin will be born in the future. In pursuit of furnishing readers and researchers involved in relevant research to have a systematic and comprehensive understanding of 3D printed tissue-engineered skin, this paper furnishes an exegesis on the prevailing research landscape, formidable obstacles, and forthcoming trajectories within the sphere of tissue-engineered skin, including: (1) the prevalent biomaterials (collagen, chitosan, agarose, alginate, etc.) routinely employed in tissue-engineered skin, and a discerning analysis and comparison of their respective merits, demerits, and inherent characteristics; (2) the underlying principles and distinguishing attributes of various current printing methodologies utilized in tissue-engineered skin fabrication; (3) the present research status and progression in the realm of tissue-engineered biomimetic skin; (4) meticulous scrutiny and summation of the extant research underpinning tissue-engineered skin inform the identification of prevailing challenges and issues.

Advancing cardiac regeneration through 3D bioprinting: methods, applications, and future directions

Cardiovascular diseases (CVDs) represent a paramount global mortality concern, and their prevalence is on a relentless ascent. Despite the effectiveness of contemporary medical interventions in mitigating CVD-related fatality rates and complications, their efficacy remains curtailed by an array of limitations. These include the suboptimal efficiency of direct cell injection and an inherent disequilibrium between the demand and availability of heart transplantations. Consequently, the imperative to formulate innovative strategies for cardiac regeneration therapy becomes unmistakable. Within this context, 3D bioprinting technology emerges as a vanguard contender, occupying a pivotal niche in the realm of tissue engineering and regenerative medicine. This state-of-the-art methodology holds the potential to fabricate intricate heart tissues endowed with multifaceted structures and functionalities, thereby engendering substantial promise. By harnessing the prowess of 3D bioprinting, it becomes plausible to synthesize functional cardiac architectures seamlessly enmeshed with the host tissue, affording a viable avenue for the restitution of infarcted domains and, by extension, mitigating the onerous yoke of CVDs. In this review, we encapsulate the myriad applications of 3D bioprinting technology in the domain of heart tissue regeneration. Furthermore, we usher in the latest advancements in printing methodologies and bioinks, culminating in an exploration of the extant challenges and the vista of possibilities inherent to a diverse array of approaches.

High Throughput Bioprinting Using Decellularized Adipose Tissue-Based Hydrogels for 3D Breast Cancer Modeling

3D bioprinting allows rapid automated fabrication and can be applied for high throughput generation of biomimetic constructs for in vitro drug screening. Decellularized extracellular matrix (dECM) hydrogel is a popular biomaterial choice for tissue engineering and studying carcinogenesis as a tumor microenvironmental mimetic. This study proposes a method for high throughput bioprinting with decellularized adipose tissue (DAT) based hydrogels for 3D breast cancer modeling. A comparative analysis of decellularization protocol using detergent-based and detergent-free decellularization methods for caprine-origin adipose tissue is performed, and the efficacy of dECM hydrogel for 3D cancer modeling is assessed. Histological, biochemical, morphological, and biological characterization and analysis showcase the cytocompatibility of DAT hydrogel. The rheological property of DAT hydrogel and printing process optimization is assessed to select a bioprinting window to attain 3D breast cancer models. The bioprinted tissues are characterized for cellular viability and tumor cell-matrix interactions. Additionally, an approach for breast cancer modeling is shown by performing rapid high throughput bioprinting in a 96-well plate format, and in vitro drug screening using 5-fluorouracil is performed on 3D bioprinted microtumors. The results of this study suggest that high throughput bioprinting of cancer models can potentially have downstream clinical applications like multi-drug screening platforms and personalized disease models.

Replace or Regenerate? Diverse Approaches to Biomaterials for Treating Corneal Lesions

The inner structures of the eye are protected by the cornea, which is a transparent membrane exposed to the external environment and subjected to the risk of lesions and diseases, sometimes resulting in impaired vision and blindness. Several eye pathologies can be treated with a keratoplasty, a surgical procedure aimed at replacing the cornea with tissues from human donors. Even though the success rate is high (up to 90% for the first graft in low-risk patients at 5-year follow-up), this approach is limited by the insufficient number of donors and several clinically relevant drawbacks. Alternatively, keratoprosthesis can be applied in an attempt to restore minimal functions of the cornea: For this reason, it is used only for high-risk patients. Recently, many biomaterials of both natural and synthetic origin have been developed as corneal substitutes to restore and replace diseased or injured corneas in low-risk patients. After illustrating the traditional clinical approaches, the present paper aims to review the most innovative solutions that have been recently proposed to regenerate the cornea, avoiding the use of donor tissues. Finally, innovative approaches to biological tissue 3D printing and xenotransplantation will be mentioned.

Magnetically driven formation of 3D freestanding soft bioscaffolds

3D soft bioscaffolds have great promise in tissue engineering, biohybrid robotics, and organ-on-a-chip engineering applications. Though emerging three-dimensional (3D) printing techniques offer versatility for assembling soft biomaterials, challenges persist in overcoming the deformation or collapse of delicate 3D structures during fabrication, especially for overhanging or thin features. This study introduces a magnet-assisted fabrication strategy that uses a magnetic field to trigger shape morphing and provide remote temporary support, enabling the straightforward creation of soft bioscaffolds with overhangs and thin-walled structures in 3D. We demonstrate the versatility and effectiveness of our strategy through the fabrication of bioscaffolds that replicate the complex 3D topology of branching vascular systems. Furthermore, we engineered hydrogel-based bioscaffolds to support biohybrid soft actuators capable of walking motion triggered by cardiomyocytes. This approach opens new possibilities for shaping hydrogel materials into complex 3D morphologies, which will further empower a broad range of biomedical applications.

Rapid Volumetric Bioprinting of Decellularized Extracellular Matrix Bioinks

Decellularized extracellular matrix (dECM)-based hydrogels are widely applied to additive biomanufacturing strategies for relevant applications. The extracellular matrix components and growth factors of dECM play crucial roles in cell adhesion, growth, and differentiation. However, the generally poor mechanical properties and printability have remained as major limitations for dECM-based materials. In this study, heart-derived dECM (h-dECM) and meniscus-derived dECM (Ms-dECM) bioinks in their pristine, unmodified state supplemented with the photoinitiator system of tris(2,2-bipyridyl) dichlororuthenium(II) hexahydrate and sodium persulfate, demonstrate cytocompatibility with volumetric bioprinting processes. This recently developed bioprinting modality illuminates a dynamically evolving light pattern into a rotating volume of the bioink, and thus decouples the requirement of mechanical strengths of bioprinted hydrogel constructs with printability, allowing for the fabrication of sophisticated shapes and architectures with low-concentration dECM materials that set within tens of seconds. As exemplary applications, cardiac tissues are volumetrically bioprinted using the cardiomyocyte-laden h-dECM bioink showing favorable cell proliferation, expansion, spreading, biomarker expressions, and synchronized contractions; whereas the volumetrically bioprinted Ms-dECM meniscus structures embedded with human mesenchymal stem cells present appropriate chondrogenic differentiation outcomes. This study supplies expanded bioink libraries for volumetric bioprinting and broadens utilities of dECM toward tissue engineering and regenerative medicine.

Engineering Cardiac Tissue for Advanced Heart-On-A-Chip Platforms

Cardiovascular disease is a major cause of mortality worldwide, and current preclinical models including traditional animal models and 2D cell culture models have limitations in replicating human native heart physiology and response to drugs. Heart-on-a-chip (HoC) technology offers a promising solution by combining the advantages of cardiac tissue engineering and microfluidics to create in vitro 3D cardiac models, which can mimic key aspects of human microphysiological systems and provide controllable microenvironments. Herein, recent advances in HoC technologies are introduced, including engineered cardiac microtissue construction in vitro, microfluidic chip fabrication, microenvironmental stimulation, and real-time feedback systems. The development of cardiac tissue engineering methods is focused for 3D microtissue preparation, advanced strategies for HoC fabrication, and current applications of these platforms. Major challenges in HoC fabrication are discussed and the perspective on the potential for these platforms is provided to advance research and clinical applications.

Breaking the stromal barrier in pancreatic cancer: Advances and challenges

Pancreatic cancer (PC) remains a leading cause of mortality worldwide due to the absence of early detection methods and the low success rates of traditional therapeutic strategies. Drug resistance in PC is driven by its desmoplastic stroma, which creates a barrier that shields cancer niches and prevents the penetration of drugs. The PC stroma comprises heterogeneous cellular populations and non-cellular components involved in aberrant ECM deposition, immunosuppression, and drug resistance. These components can influence PC development through intricate and complex crosstalk with the PC cells. Understanding how stromal components and cells interact with and influence the invasiveness and refractoriness of PC cells is thus a prerequisite for developing successful stroma-modulating strategies capable of remodeling the PC stroma to alleviate drug resistance and enhance therapeutic outcomes. In this review, we explore how non-cellular and cellular stromal components, including cancer-associated fibroblasts and tumor-associated macrophages, contribute to the immunosuppressive and tumor-promoting effects of the stroma. We also examine the signaling pathways underlying their activation, tumorigenic effects, and interactions with PC cells. Finally, we discuss recent pre-clinical and clinical work aimed at developing and testing novel stroma-modulating agents to alleviate drug resistance and improve therapeutic outcomes in PC.

The Art of Building Living Tissues: Exploring the Frontiers of Biofabrication with 3D Bioprinting

The scope of three-dimensional printing is expanding rapidly, with innovative approaches resulting in the evolution of state-of-the-art 3D bioprinting (3DbioP) techniques for solving issues in bioengineering and biopharmaceutical research. The methods and tools in 3DbioP emphasize the extrusion process, bioink formulation, and stability of the bioprinted scaffold. Thus, 3DbioP technology augments 3DP in the biological world by providing technical support to regenerative therapy, drug delivery, bioengineering of prosthetics, and drug kinetics research. Besides the above, drug delivery and dosage control have been achieved using 3D bioprinted microcarriers and capsules. Developing a stable, biocompatible, and versatile bioink is a primary requisite in biofabrication. The 3DbioP research is breaking the technical barriers at a breakneck speed. Numerous techniques and biomaterial advancements have helped to overcome current 3DbioP issues related to printability, stability, and bioink formulation. Therefore, this Review aims to provide an insight into the technical challenges of bioprinting, novel biomaterials for bioink formulation, and recently developed 3D bioprinting methods driving future applications in biofabrication research.

Tissue Bioprinting: Promise and Challenges

In recent years, we have witnessed remarkable progress in the field of regenerative medicine, in large part fuelled by developments in advanced biofabrication technologies such as three-dimensional (3D) bioprinting [...].

Development of Electro-Conductive Composite Bioinks for Electrohydrodynamic Bioprinting with Microscale Resolution

Bioprinting has attracted extensive attention in the field of tissue engineering due to its unique capability in constructing biomimetic tissue constructs in a highly controlled manner. However, it is still challenging to reproduce the physical and structural properties of native electroactive tissues due to the poor electroconductivity of current bioink systems as well as the limited printing resolution of conventional bioprinting techniques. In this work, an electro-conductive hydrogel is prepared by introducing poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) into an RGD (GGGGRGDSP)-functionalized alginate and fibrin system (RAF), and then electrohydrodynamic (EHD)-bioprinted to form living tissue constructs with microscale resolution. The addition of 0.1 (w/v%) PEDOT: PSS increases the electroconductivity to 1.95 ± 0.21 S m-1 and simultaneously has little effect on cell viability. Compared with pure RAF bioink, the presence of PEDOT: PSS expands the printable parameters for EHD-bioprinting, and hydrogel filaments with the smallest feature size of 48.91 ± 3.44 µm can be obtained by further optimizing process parameters. Furthermore, the EHD-bioprinted electro-conductive living tissue constructs with improved resolution show good viability (>85%). The synergy of the advanced electro-conductive hydrogel and EHD-bioprinting presented here may provide a promising approach for engineering electro-conductive and cell-laden constructs for electroactive tissue engineering.

Application of 4D printing and bioprinting in cardiovascular tissue engineering

Cardiovascular diseases have remained the leading cause of death worldwide for the past 20 years. The current clinical therapeutic measures, including bypass surgery, stent implantation and pharmacotherapy, are not enough to repair the massive loss of cardiomyocytes after myocardial ischemia. Timely replenishment with functional myocardial tissue via biomedical engineering is the most direct and effective means to improve the prognosis and survival rate of patients. It is widely recognized that 4D printing technology introduces an additional dimension of time in comparison with traditional 3D printing. Additionally, in the context of 4D bioprinting, both the printed material and the resulting product are designed to be biocompatible, which will be the mainstream of bioprinting in the future. Thus, this review focuses on the application of 4D bioprinting in cardiovascular diseases, discusses the bottleneck of the development of 4D bioprinting, and finally looks forward to the future direction and prospect of this revolutionary technology.

The Porous Structure of Peripheral Nerve Guidance Conduits: Features, Fabrication, and Implications for Peripheral Nerve Regeneration

Porous structure is an important three-dimensional morphological feature of the peripheral nerve guidance conduit (NGC), which permits the infiltration of cells, nutrients, and molecular signals and the discharge of metabolic waste. Porous structures with precisely customized pore sizes, porosities, and connectivities are being used to construct fully permeable, semi-permeable, and asymmetric peripheral NGCs for the replacement of traditional nerve autografts in the treatment of long-segment peripheral nerve injury. In this review, the features of porous structures and the classification of NGCs based on these characteristics are discussed. Common methods for constructing 3D porous NGCs in current research are described, as well as the pore characteristics and the parameters used to tune the pores. The effects of the porous structure on the physical properties of NGCs, including biodegradation, mechanical performance, and permeability, were analyzed. Pore structure affects the biological behavior of Schwann cells, macrophages, fibroblasts, and vascular endothelial cells during peripheral nerve regeneration. The construction of ideal porous structures is a significant advancement in the regeneration of peripheral nerve tissue engineering materials. The purpose of this review is to generalize, summarize, and analyze methods for the preparation of porous NGCs and their biological functions in promoting peripheral nerve regeneration to guide the development of medical nerve repair materials.

Sequential Dual-Biofactor Release from the Scaffold of Mesoporous HA Microspheres and PLGA Matrix for Boosting Endogenous Bone Regeneration

The combined design of scaffold structure and multi-biological factors is a prominent strategy to promote bone regeneration. Herein, a composite scaffold of mesoporous hydroxyapatite (HA) microspheres loaded with the bone morphogenetic protein-2 (BMP-2) and a poly(DL-lactic-co-glycolic acid) (PLGA) matrix is constructed by 3D printing. Furthermore, the chemokine stromal cell-derived factor-1α (SDF-1α) is adsorbed on a scaffold surface to achieve the sequential release of the dual-biofactors. The results indicate that the rapid release of SDF-1α chemokine on the scaffold surface effectively recruits bone marrow-derived mesenchymal stem cells (BMSCs) to the target defect area, whereas the long-term sustained release of BMP-2 from the HA microspheres in the degradable PLGA matrix successfully triggers the osteogenic differentiation in the recruited BMSCs, significantly promoting bone regeneration and reconstruction. In addition, these structures/biofactors specially combining scaffold exhibit significantly better biological performance than that of other combined scaffolds, including the bare HA/PLGA scaffold, the scaffold loaded with SDF-1α or BMP-2 biofactor alone, and the scaffold with surface SDF-1α and BMP-2 dual-biofactors. The utilization of mesoporous HA, the assembly method, and sequential release of the two biofactors in the 3D printed composite scaffold present a new method for future design of high-performance bone repairing scaffolds.

In vitro high-content tissue models to address precision medicine challenges

The field of precision medicine allows for tailor-made treatments specific to a patient and thereby improve the efficiency and accuracy of disease prevention, diagnosis, and treatment and at the same time would reduce the cost, redundant treatment, and side effects of current treatments. Here, the combination of organ-on-a-chip and bioprinting into engineering high-content in vitro tissue models is envisioned to address some precision medicine challenges. This strategy could be employed to tackle the current coronavirus disease 2019 (COVID-19), which has made a significant impact and paradigm shift in our society. Nevertheless, despite that vaccines against COVID-19 have been successfully developed and vaccination programs are already being deployed worldwide, it will likely require some time before it is available to everyone. Furthermore, there are still some uncertainties and lack of a full understanding of the virus as demonstrated in the high number new mutations arising worldwide and reinfections of already vaccinated individuals. To this end, efficient diagnostic tools and treatments are still urgently needed. In this context, the convergence of bioprinting and organ-on-a-chip technologies, either used alone or in combination, could possibly function as a prominent tool in addressing the current pandemic. This could enable facile advances of important tools, diagnostics, and better physiologically representative in vitro models specific to individuals allowing for faster and more accurate screening of therapeutics evaluating their efficacy and toxicity. This review will cover such technological advances and highlight what is needed for the field to mature for tackling the various needs for current and future pandemics as well as their relevancy towards precision medicine.

In Situ Imaging and Anti-inflammation of 3D Printed Scaffolds Enabled by AIEgen

Three-dimensional (3D) printed bioactive scaffolds have been widely used in the field of bone tissue engineering. However, its in vivo visualization and bacterial inflammation are intractable issues during the surgery and treatment. Herein, we first synthesized an aggregation-induced emission-active luminogen (AIEgen) named 4BC with efficient reactive oxygen species (ROS) generation. Then, a series of 3D bioactive scaffolds loaded with 4BC were fabricated by a precipitation adsorption method, namely 4BC@scaffolds, which showed good in situ imaging performance for the implanted scaffolds by using simple UV light irradiation. Among them, the 4BC@TMP scaffold composed of trimagnesium phosphate (TMP) had excellent bactericidal ability for Escherichia coli and Staphylococcus aureus in vitro and resisted bacterial inflammation in vivo through photodynamic action. H&E and immunofluorescence staining were performed to further evaluate the inhibitory effect of bacterial inflammation in vivo. This work verified that AIEgen-based 3D scaffolds are promising bioactive frameworks for bioimaging and antibacterial applications.

Additive Manufacturing and Physicomechanical Characteristics of PEGDA Hydrogels: Recent Advances and Perspective for Tissue Engineering

In this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices.

Placing biofabrication into the context of human disease modeling

The field of biofabrication has seen tremendous advances in the past decade. More recently, the emerging role of biofabrication in allowing faithful generation of models of human tissues in their healthy and diseased states has been demonstrated and has rapidly expanded. These biomimetic models are potentially widely applicable in a range of research and translational areas including but not limited to fundamental biology studies as well as screening of chemical compounds, such as therapeutic agents. The United States Food and Drug Administration Modernization Act 2.0, which now no longer requires animal tests before approving human drug trials, will likely further boost the field in the years to come. This Special Issue, with a collection of 11 excellent research articles, thus focuses on showcasing the latest developments of biofabrication towards human disease modeling, spanning from 3D (bo)printing to organ-on-a-chip as well as their integration.

Electro-Biofabrication. Coupling Electrochemical and Biomolecular Methods to Create Functional Bio-Based Hydrogels

Twenty years ago, this journal published a review entitled "Biofabrication with Chitosan" based on the observations that (i) chitosan could be electrodeposited using low voltage electrical inputs (typically less than 5 V) and (ii) the enzyme tyrosinase could be used to graft proteins (via accessible tyrosine residues) to chitosan. Here, we provide a progress report on the coupling of electronic inputs with advanced biological methods for the fabrication of biopolymer-based hydrogel films. In many cases, the initial observations of chitosan's electrodeposition have been extended and generalized: mechanisms have been established for the electrodeposition of various other biological polymers (proteins and polysaccharides), and electrodeposition has been shown to allow the precise control of the hydrogel's emergent microstructure. In addition, the use of biotechnological methods to confer function has been extended from tyrosinase conjugation to the use of protein engineering to create genetically fused assembly tags (short sequences of accessible amino acid residues) that facilitate the attachment of function-conferring proteins to electrodeposited films using alternative enzymes (e.g., transglutaminase), metal chelation, and electrochemically induced oxidative mechanisms. Over these 20 years, the contributions from numerous groups have also identified exciting opportunities. First, electrochemistry provides unique capabilities to impose chemical and electrical cues that can induce assembly while controlling the emergent microstructure. Second, it is clear that the detailed mechanisms of biopolymer self-assembly (i.e., chitosan gel formation) are far more complex than anticipated, and this provides a rich opportunity both for fundamental inquiry and for the creation of high performance and sustainable material systems. Third, the mild conditions used for electrodeposition allow cells to be co-deposited for the fabrication of living materials. Finally, the applications have been expanded from biosensing and lab-on-a-chip systems to bioelectronic and medical materials. We suggest that electro-biofabrication is poised to emerge as an enabling additive manufacturing method especially suited for life science applications and to bridge communication between our biological and technological worlds.

Three-dimensional bioprinting of artificial blood vessel: Process, bioinks, and challenges

The coronary artery bypass grafting is a main treatment for restoring the blood supply to the ischemic site by bypassing the narrow part, thereby improving the heart function of the patients. Autologous blood vessels are preferred in coronary artery bypass grafting, but their availability is often limited by due to the underlying disease. Thus, tissue-engineered vascular grafts that are devoid of thrombosis and have mechanical properties comparable to those of natural vessels are urgently required for clinical applications. Most of the commercially available artificial implants are made from polymers, which are prone to thrombosis and restenosis. The biomimetic artificial blood vessel containing vascular tissue cells is the most ideal implant material. Due to its precision control ability, three-dimensional (3D) bioprinting is a promising method to prepare biomimetic system. In the 3D bioprinting process, the bioink is at the core state for building the topological structure and keeping the cell viable. Therefore, in this review, the basic properties and viable materials of the bioink are discussed, and the research of natural polymers in bioink, including decellularized extracellular matrix, hyaluronic acid, and collagen, is emphasized. Besides, the advantages of alginate and Pluronic F127, which are the mainstream sacrificial material during the preparation of artificial vascular graft, are also reviewed. Finally, an overview of the applications in the field of artificial blood vessel is also presented.

Marine Collagen-Based Bioink for 3D Bioprinting of a Bilayered Skin Model

Marine organisms (i.e., fish, jellyfish, sponges or seaweeds) represent an abundant and eco-friendly source of collagen. Marine collagen, compared to mammalian collagen, can be easily extracted, is water-soluble, avoids transmissible diseases and owns anti-microbial activities. Recent studies have reported marine collagen as a suitable biomaterial for skin tissue regeneration. The aim of this work was to investigate, for the first time, marine collagen from basa fish skin for the development of a bioink for extrusion 3D bioprinting of a bilayered skin model. The bioinks were obtained by mixing semi-crosslinked alginate with 10 and 20 mg/mL of collagen. The bioinks were characterised by evaluating the printability in terms of homogeneity, spreading ratio, shape fidelity and rheological properties. Morphology, degradation rate, swelling properties and antibacterial activity were also evaluated. The alginate-based bioink containing 20 mg/mL of marine collagen was selected for 3D bioprinting of skin-like constructs with human fibroblasts and keratinocytes. The bioprinted constructs showed a homogeneous distribution of viable and proliferating cells at days 1, 7 and 14 of culture evaluated by qualitative (live/dead) and qualitative (XTT) assays, and histological (H&E) and gene expression analysis. In conclusion, marine collagen can be successfully used to formulate a bioink for 3D bioprinting. In particular, the obtained bioink can be printed in 3D structures and is able to support fibroblasts and keratinocytes viability and proliferation.

Recent Advances in Decellularized Extracellular Matrix-Based Bioinks for 3D Bioprinting in Tissue Engineering

In recent years, three-dimensional (3D) bioprinting has been widely utilized as a novel manufacturing technique by more and more researchers to construct various tissue substitutes with complex architectures and geometries. Different biomaterials, including natural and synthetic materials, have been manufactured into bioinks for tissue regeneration using 3D bioprinting. Among the natural biomaterials derived from various natural tissues or organs, the decellularized extracellular matrix (dECM) has a complex internal structure and a variety of bioactive factors that provide mechanistic, biophysical, and biochemical signals for tissue regeneration and remodeling. In recent years, more and more researchers have been developing the dECM as a novel bioink for the construction of tissue substitutes. Compared with other bioinks, the various ECM components in dECM-based bioink can regulate cellular functions, modulate the tissue regeneration process, and adjust tissue remodeling. Therefore, we conducted this review to discuss the current status of and perspectives on dECM-based bioinks for bioprinting in tissue engineering. In addition, the various bioprinting techniques and decellularization methods were also discussed in this study.

Photothermal Responsive Digital Polymerase Chain Reaction Resolving Exosomal microRNAs Expression in Liver Cancer

Exosomal microRNAs have been studied as a good source of noninvasive biomarkers due to their functions in genetic exchange between cells and have been already well documented in many biological activities; however, inaccuracy remains a key challenge for liver cancer surveillance. Herein, a versatile duplex photothermal digital polymerase chain reaction (PCR) strategy combined with a lipid nanoparticle-based exosome capture approach is proposed to profile microRNAs expression through a 3-h easy-to-operate process. The microfluidically-generated molybdenum disulfide-nanocomposite-doped gelatin microcarriers display attractive properties as a 2-4 °C s^-1 ramping-up rate triggered by near-infrared and reversible sol-gel transforming in step with PCR activation. To achieve PCR thermocycling, the corresponding irradiation coordinating with fan cooling are automatically performed via a homemade control module with programs. Thus, taking the multiplexing capability of dual-color labeling, 19-31 folds higher in exosomal microRNA-200b-3p and microRNA-21-5p, and tenfold lower in microRNA-22-3p expressions relative to the control microRNA-26a-5p are quantified in two liver cancer cells (Huh7 and HepG2) than in those from the healthy cells. It is believed that this exosomal microRNA genotyping method would be highly applicable for liver cancer diagnostics.

Properties of Poly (Lactic-co-Glycolic Acid) and Progress of Poly (Lactic-co-Glycolic Acid)-Based Biodegradable Materials in Biomedical Research

In recent years, biodegradable polymers have gained the attention of many researchers for their promising applications, especially in drug delivery, due to their good biocompatibility and designable degradation time. Poly (lactic-co-glycolic acid) (PLGA) is a biodegradable functional polymer made from the polymerization of lactic acid (LA) and glycolic acid (GA) and is widely used in pharmaceuticals and medical engineering materials because of its biocompatibility, non-toxicity, and good plasticity. The aim of this review is to illustrate the progress of research on PLGA in biomedical applications, as well as its shortcomings, to provide some assistance for its future research development.

The Next Frontier of 3D Bioprinting: Bioactive Materials Functionalized by Bacteria

3D bioprinting has become a flexible technical means used in many fields. Currently, research on 3D bioprinting is mainly focused on the use of mammalian cells to print organ and tissue models, which has greatly promoted progress in the fields of tissue engineering, regenerative medicine, and pharmaceuticals. In recent years, bacterial bioprinting has gradually become a rapidly developing research fields, with a wide range of potential applications in basic research, biomedicine, bioremediation, and other field. Here, this works reviews new research on bacterial bioprinting, and discuss its future research direction.

Application of Nanomaterials in Stem Cell-Based Therapeutics for Cardiac Repair and Regeneration

Cardiovascular disease is a leading cause of disability and death worldwide. Although the survival rate of patients with heart diseases can be improved with contemporary pharmacological treatments and surgical procedures, none of these therapies provide a significant improvement in cardiac repair and regeneration. Stem cell-based therapies are a promising approach for functional recovery of damaged myocardium. However, the available stem cells are difficult to differentiate into cardiomyocytes, which result in the extremely low transplantation efficiency. Nanomaterials are widely used to regulate the myocardial differentiation of stem cells, and play a very important role in cardiac tissue engineering. This study discusses the current status and limitations of stem cells and cell-derived exosomes/micro RNAs based cardiac therapy, describes the cardiac repair mechanism of nanomaterials, summarizes the recent advances in nanomaterials used in cardiac repair and regeneration, and evaluates the advantages and disadvantages of the relevant nanomaterials. Besides discussing the potential clinical applications of nanomaterials in cardiac therapy, the perspectives and challenges of nanomaterials used in stem cell-based cardiac repair and regeneration are also considered. Finally, new research directions in this field are proposed, and future research trends are highlighted.

(Bio)printing in Personalized Medicine—Opportunities and Potential Benefits

The global development of technologies now enters areas related to human health, with a transition from conventional to personalized medicine that is based to a significant extent on (bio)printing. The goal of this article is to review some of the published scientific literature and to highlight the importance and potential benefits of using 3D (bio)printing techniques in contemporary personalized medicine and also to offer future perspectives in this research field. The article is prepared according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Web of Science, PubMed, Scopus, Google Scholar, and ScienceDirect databases were used in the literature search. Six authors independently performed the search, study selection, and data extraction. This review focuses on 3D bio(printing) in personalized medicine and provides a classification of 3D bio(printing) benefits in several categories: overcoming the shortage of organs for transplantation, elimination of problems due to the difference between sexes in organ transplantation, reducing the cases of rejection of transplanted organs, enhancing the survival of patients with transplantation, drug research and development, elimination of genetic/congenital defects in tissues and organs, and surgery planning and medical training for young doctors. In particular, we highlight the benefits of each 3D bio(printing) applications included along with the associated scientific reports from recent literature. In addition, we present an overview of some of the challenges that need to be overcome in the applications of 3D bioprinting in personalized medicine. The reviewed articles lead to the conclusion that bioprinting may be adopted as a revolution in the development of personalized, medicine and it has a huge potential in the near future to become a gold standard in future healthcare in the world.

Reflections on the Biology of Cell Culture Models: Living on the Edge of Oxidative Metabolism in Cancer Cells

Nowadays, the study of cell metabolism is a hot topic in cancer research. Many studies have used 2D conventional cell cultures for their simplicity and the facility to infer mechanisms. However, the limitations of bidimensional cell cultures to recreate architecture, mechanics, and cell communication between tumor cells and their environment, have forced the development of other more realistic in vitro methodologies. Therefore, the explosion of 3D culture techniques and the necessity to reduce animal experimentation to a minimum has attracted the attention of researchers in the field of cancer metabolism. Here, we revise the limitations of actual culture models and discuss the utility of several 3D culture techniques to resolve those limitations.

Optimization of methacrylated gelatin /layered double hydroxides nanocomposite cell-laden hydrogel bioinks with high printability for 3D extrusion bioprinting

Layered double hydroxides (LDHs) offer unique source of inspiration for design of bone mimetic biomaterials due to their superior mechanical properties, drug delivery capability and regulation cellular behaviors, particularly by divalent metal cations in their structure. Three-dimensional (3D) bioprinting of LDHs holds great promise as a novel strategy thanks to highly tunable physiochemical properties and shear-thinning ability of LDHs, which allow shape fidelity after deposition. Herein, we introduce a straightforward strategy for extrusion bioprinting of cell laden nanocomposite hydrogel bioink of gelatin methacryloyl (GelMA) biopolymer and LDHs nanoparticles. First, we synthesized LDHs by co-precipitation process and systematically examined the effect of LDHs addition on printing parameters such as printing pressure, extrusion rate, printing speed, and finally bioink printability in creating grid-like constructs. The developed hydrogel bioinks provided precise control over extrudability, extrusion uniformity, and structural integrity after deposition. Based on the printability and rheological analysis, the printability could be altered by controlling the concentration of LDHs, and printability was found to be ideal with the addition of 3 wt % LDHs. The addition of LDHs resulted in remarkably enhanced compressive strength from 652 kPa (G-LDH0) to 1168 kPa (G-LDH3). It was shown that the printed nanocomposite hydrogel scaffolds were able to support encapsulated osteoblast survival, spreading, and proliferation in the absence of any osteoinductive factors taking advantage of LDHs. In addition, cells encapsulated in G-LDH3 had a larger cell spreading area and higher cell aspect ratio than those encapsulated in G-LDH0. Altogether, the results demonstrated that the developed GelMA/LDHs nanocomposite hydrogel bioink revealed a high potential for extrusion bioprinting with high structural fidelity to fabricate implantable 3D hydrogel constructs for repair of bone defects.

Effect of porosity on mechanical and biological properties of bioprinted scaffolds

Treatment of tissue defects commonly represents a major problem in clinics due to difficulties involving a shortage of donors, inappropriate sizes, abnormal shapes, and immunological rejection. While many scaffold parameters such as pore shape, porosity percentage, and pore connectivity could be adjusted to achieve desired mechanical and biological properties. These parameters are crucial scaffold parameters that can be accurately produced by 3D bioprinting technology based on the damaged tissue. In the present research, the effect of porosity percentage (40%, 50%, and 60%) and different pore shapes (square, star, and gyroid) on the mechanical (e.g., stiffness, compressive and tensile behavior) and biological (e.g., biodegradation, and cell viability) properties of porous polycaprolactone (PCL) scaffolds coated with gelatin have been investigated. Moreover, human foreskin fibroblast cells were cultured on the scaffolds in the in-vitro procedures. MTT assay (4, 7, and 14 days) was utilized to determine the cytotoxicity of the porous scaffolds. It is revealed that the porous scaffolds produced by the bioprinter did not produce a cytotoxic effect. Among all the porous scaffolds, scaffolds with a pore size of about 500 μm and porosity of 50% showed the best cell proliferation compared to the controls after 14 days. The results demonstrated that the pore shape, porosity percentage, and pore connectivity have an important role in improving the mechanical and biological properties of porous scaffolds. These 3D bioprinted biodegradable scaffolds exhibit potential for future application as polymeric scaffolds in hard tissue engineering applications.

Volumetric additive manufacturing of pristine silk-based (bio)inks

Volumetric additive manufacturing (VAM) enables fast photopolymerization of three-dimensional constructs by illuminating dynamically evolving light patterns in the entire build volume. However, the lack of bioinks suitable for VAM is a critical limitation. This study reports rapid volumetric (bio)printing of pristine, unmodified silk-based (silk sericin (SS) and silk fibroin (SF)) (bio)inks to form sophisticated shapes and architectures. Of interest, combined with post-fabrication processing, the (bio)printed SS constructs reveal properties including reversible as well as repeated shrinkage and expansion, or shape-memory; whereas the (bio)printed SF constructs exhibit tunable mechanical performances ranging from a few hundred Pa to hundreds of MPa. Both types of silk-based (bio)inks are cytocompatible. This work supplies expanded bioink libraries for VAM and provides a path forward for rapid volumetric manufacturing of silk constructs, towards broadened biomedical applications.

Preparation and properties of a photocrosslinked MCl n -doped PDMA-g-PSMA hydrogel

To treat damaged joint areas, photocrosslinked hydrophobically associating PDMA-g-PSMA hydrogels can act as mild and easily regulated materials due to their rich pore structure, which have been widely applied in articular cartilage replacement research. In this study, the effects of ADS-MCl _n (ADS-NaCl, ADS-MgCl₂ and ADS-CaCl₂) doping systems on the micro morphology, mechanical, self-healing, and friction properties and cytotoxicity of PDMA-g-PSMA hydrogels were studied. The results showed that the solubilization behavior of the ADS-MCl _n ionic micelles affected the hydrophobic association stability, thereby changing the toughness, self-healing and friction properties of the hydrogel. Ca²⁺-doping resulted in the crystallization and precipitation of the anionic surfactants, destroying the solubilization ability of the ionic micelles for the hydrophobic units, and thus hydrogels with high hardness, low toughness and no self-healing function were obtained. Doping with Na⁺ greatly improved the dissolving power of the ADS micelles for SMA, yielding PDMA-g-PSMA hydrogels with good mechanical strength and good self-healing ability. However, in this case, a drawback is that the Na⁺-doped system will lose its components during the swelling process, leading to the degradation of its self-healing performance. Interestingly, Mg²⁺ doping resulted in the formation of highly stable ADS micellar aggregates, and then PDMA-g-PSMA hydrogels with a lower friction coefficient (0.023), less wear (35.0 mg), higher elongation at break and 100% self-healing efficiency were obtained. The hydrogel products obtained from the three doping systems all exhibited good biocompatibility. Our research provides important guidelines for the design and preparation of anti-friction artificial articular cartilage.

Recent advances of three-dimensional bioprinting technology in hepato-pancreato-biliary cancer models

Hepato-pancreato-biliary (HPB) cancer is a serious category of cancer including tumors originating in the liver, pancreas, gallbladder and biliary ducts. It is limited by two-dimensional (2D) cell culture models for studying its complicated tumor microenvironment including diverse contents and dynamic nature. Recently developed three-dimensional (3D) bioprinting is a state-of-the-art technology for fabrication of biological constructs through layer-by-layer deposition of bioinks in a spatially defined manner, which is computer-aided and designed to generate viable 3D constructs. 3D bioprinting has the potential to more closely recapitulate the tumor microenvironment, dynamic and complex cell-cell and cell-matrix interactions compared to the current methods, which benefits from its precise definition of positioning of various cell types and perfusing network in a high-throughput manner. In this review, we introduce and compare multiple types of 3D bioprinting methodologies for HPB cancer and other digestive tumors. We discuss the progress and application of 3D bioprinting in HPB and gastrointestinal cancers, focusing on tumor model manufacturing. We also highlight the current challenges regarding clinical translation of 3D bioprinting and bioinks in the field of digestive tumor research. Finally, we suggest valuable perspectives for this advanced technology, including combination of 3D bioprinting with microfluidics and application of 3D bioprinting in the field of tumor immunology.

3D cancer models: One step closer to in vitro human studies

Cancer immunotherapy is the great breakthrough in cancer treatment as it displayed prolonged progression-free survival over conventional therapies, yet, to date, in only a minority of patients. In order to broad cancer immunotherapy clinical applicability some roadblocks need to be overcome, first among all the lack of preclinical models that faithfully depict the local tumor microenvironment (TME), which is known to dramatically affect disease onset, progression and response to therapy. In this review, we provide the reader with a detailed overview of current 3D models developed to mimick the complexity and the dynamics of the TME, with a focus on understanding why the TME is a major target in anticancer therapy. We highlight the advantages and translational potentials of tumor spheroids, organoids and immune Tumor-on-a-Chip models in disease modeling and therapeutic response, while outlining pending challenges and limitations. Thinking forward, we focus on the possibility to integrate the know-hows of micro-engineers, cancer immunologists, pharmaceutical researchers and bioinformaticians to meet the needs of cancer researchers and clinicians interested in using these platforms with high fidelity for patient-tailored disease modeling and drug discovery.

Development of a high-performance open-source 3D bioprinter

The application of 3D printing to biological research has provided the tissue engineering community with a method for organizing cells and biological materials into complex 3D structures. While many commercial bioprinting platforms exist, they are expensive, ranging from $5000 to over $1,000,000. This high cost of entry prevents many labs from incorporating 3D bioprinting into their research. Due to the open-source nature of desktop plastic 3D printers, an alternative option has been to convert low-cost plastic printers into bioprinters. Several open-source modifications have been described, but there remains a need for a user-friendly, step-by-step guide for converting a thermoplastic printer into a bioprinter using components with validated performance. Here we convert a low-cost 3D printer, the FlashForge Finder, into a bioprinter using our Replistruder 4 syringe pump and the Duet3D Duet 2 WiFi for total cost of less than $900. We demonstrate that the accuracy of the bioprinter's travel is better than 35 µm in all three axes and quantify fidelity by printing square lattice collagen scaffolds with average errors less than 2%. We also show high fidelity reproduction of clinical-imaging data by printing a scaffold of a human ear using collagen bioink. Finally, to maximize accessibility and customizability, all components we have designed for the bioprinter conversion are provided as open-source 3D models, along with instructions for further modifying the bioprinter for additional use cases, resulting in a comprehensive guide for the bioprinting field.

3D printing of bone and cartilage with polymer materials

Damage and degeneration to bone and articular cartilage are the leading causes of musculoskeletal disability. Commonly used clinical and surgical methods include autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement. 3D bio printing technology to construct implants by layer-by-layer printing of biological materials, living cells, and other biologically active substances in vitro, which is expected to replace the repair mentioned above methods. Researchers use cells and biomedical materials as discrete materials. 3D bio printing has largely solved the problem of insufficient organ donors with the ability to prepare different organs and tissue structures. This paper mainly discusses the application of polymer materials, bio printing cell selection, and its application in bone and cartilage repair.

Sound-based assembly of a microcapillary network in a saturn-like tumor model for drug testing

The tumor microenvironment (TME), consisting of extracellular matrix, proteins, stromal cells, and a vascular system, is reported to have a key role in cancer progression and prognosis. Thereby, the interaction between the vascular network and tumor mass is an important feature of the TME since the anticancer agents which are delivered to the TME can trigger the vascular response and influence the therapeutic outcome of the treatment. To identify and develop new therapeutic strategies, 3D in vitro models that recapitulate the complexity of the TME are urgently needed. Among them, vascularized tumor models are a promising approach, allowing to target tumor angiogenesis and reduce tumor growth. By using sound patterning, cells can be condensed locally into highly reproducible patterns through the action of mild hydrodynamic forces. Here, we use a soundwave-driven cell assembly approach to create a ring-shaped microcapillary network in fibrin hydrogel. Then, we generate a 3D vascularized tumor model by combining a tumor heterotypic spheroid, consisting of fibroblasts and Malignant Pleural Mesothelioma (MPM) cells, with the surrounding vascular ring. Based on its shape, we name it Saturn-like vascularized Tumor Model (STM). The growth of the microcapillary network is monitored over time by fluorescence imaging. The area covered by the microcapillary network, and its continuous increase in presence of the heterotypic tumor spheroid was monitored. Interestingly, this effect is enhanced when treating the STM with the anticancer agent Cisplatin. Overall, we show the use of sound patterning as a fast and cell-friendly approach to spatially organize and condense cells, to generate a 3D in vitro platform from which simple readouts of drug tests can be extracted by image analysis, with the potential to provide a model system for tailored tumor therapy.

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Reproducible ring-shaped microcapillary networks were created by sound assembly.

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Ring microcapillary network and tumor spheroid formed the Saturn-like tumor model.

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‘Radial profile’ analysis was used to monitor the ring microcapillary networks.

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Growth of the microcapillaries was modulated by tumor spheroid and anticancer drug.

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Anticancer drug upregulated pro-angiogenic related genes in the tumor spheroid.

Current trends and research topics regarding liver 3D bioprinting: A bibliometric analysis research

Introduction: Over recent years, 3D bioprinting has changed dramatically. The articles related to liver 3D bioprinting have not been quantitatively analyzed. In this article, we screen all articles related to liver 3D bioprinting until January 2022 and analyzed them using bibliometric citation analysis to characterize the current trends in liver 3D bioprinting. Methods: The articles were identified and analyzed from the Clarivate Analytics Web of Science Core Collection database. Results: Until 1 January 2022, 71 articles focusing on liver 3D bioprinting were identified. There was an increase in the number of articles in 2015. Most articles came from the USA (n = 27), followed by South Korea (n = 22), China (n = 16), and Japan (n = 5). The printing technology of liver 3D printing was the most studied topic (n = 29). Biofabrication published the highest number of papers (n = 16) with 1,524 total citations. Conclusion: Based on bibliometric analysis of the articles until January 2022, a comprehensive analysis of the liver 3D bioprinting articles highlighted the current trends and research topics of this field. The data should provide clinicians and researchers insight into future directions relative to the liver 3D bioprinting.

Application of 3D-bioprinted nanocellulose and cellulose derivative-based bio-inks in bone and cartilage tissue engineering

212Three-dimensional (3D) printing is a modern, computer-aided, design-based technology that allows the layer-by-layer deposition of 3D structures. Bioprinting, a 3D printing technology, has attracted increasing attention because of its capacity to produce scaffolds for living cells with extreme precision. Along with the rapid development of 3D bioprinting technology, the innovation of bio-inks, which is recognized as the most challenging aspect of this technology, has demonstrated tremendous promise for tissue engineering and regenerative medicine. Cellulose is the most abundant polymer in nature. Various forms of cellulose, nanocellulose, and cellulose derivatives, including cellulose ethers and cellulose esters, are common bioprintable materials used to develop bio-inks in recent years, owing to their biocompatibility, biodegradability, low cost, and printability. Although various cellulose-based bio-inks have been investigated, the potential applications of nanocellulose and cellulose derivative-based bio-inks have not been fully explored. This review focuses on the physicochemical properties of nanocellulose and cellulose derivatives as well as the recent advances in bio-ink design for 3D bioprinting of bone and cartilage. In addition, the current advantages and disadvantages of these bio-inks and their prospects in 3D printing-based tissue engineering are comprehensively discussed. We hope to offer helpful information for the logical design of innovative cellulose-based materials for use in this sector in the future.

Three-dimensional printing of smart constructs using stimuli-responsive biomaterials: A future direction of precision medicine

Three-dimensional (3D) printing, which is a valuable technique for the fabrication of tissue-engineered constructs and biomedical devices with complex architectures, has brought about considerable progress in regenerative medicine, drug delivery, and diagnosis of diseases. However, because of the static and inanimate properties of conventional 3D-printed structures, it is difficult to use them in therapies for active and precise medicine, such as improved tissue regeneration, targeted or controlled drug delivery, and advanced pathophysiological monitoring. The integration of stimuli-responsive biomaterials into 3D printing provides a potential strategy for designing and building smart constructs that exhibit programmed functions and controllable changes in properties in response to exogenous and autogenous stimuli. These features make 3D-printed smart constructs the next generation of tissue-engineered products. In this review, we introduce the prevalent 3D printing techniques (with an emphasis on the differences between 3D printing and bioprinting, and biomaterials and bioink), the working principle of each technique, and the advantages of using 3D printing for the fabrication of smart constructs. Stimuli-responsive biomaterials that are widely used for 3D printing of smart constructs are categorized, followed by a summary of their applications in tissue regeneration, drug delivery, and biosensors. Finally, the challenges and future perspectives of 3D-printed smart constructs are discussed.

State-of-the-art techniques for promoting tissue regeneration: Combination of three-dimensional bioprinting and carbon nanomaterials

181Biofabrication approaches, such as three-dimensional (3D) bioprinting of hydrogels, have recently garnered increasing attention, especially in the construction of 3D structures that mimic the complexity of tissues and organs with the capacity for cytocompatibility and post-printing cellular development. However, some printed gels show poor stability and maintain less shape fidelity if parameters such as polymer nature, viscosity, shear-thinning behavior, and crosslinking are affected. Therefore, researchers have incorporated various nanomaterials as bioactive fillers into polymeric hydrogels to address these limitations. Carbon-family nanomaterials (CFNs), hydroxyapatites, nanosilicates, and strontium carbonates have been incorporated into printed gels for application in various biomedical fields. In this review, following the compilation of research publications on CFNs-containing printable gels in various tissue engineering applications, we discuss the types of bioprinters, the prerequisites of bioink and biomaterial ink, as well as the progress and challenges of CFNs-containing printable gels in this field.