Recent advances in bioprinting techniques: approaches, applications and future prospects

Recent adavances of functional modules for tooth regeneration

Dental diseases, such as dental caries and periodontal disorders, constitute a major global health challenge, affecting millions worldwide and often resulting in tooth loss. Traditional dental treatments, though beneficial, typically cannot fully restore the natural functions and structures of teeth. This limitation has prompted growing interest in innovative strategies for tooth regeneration methods. Among these, the use of dental stem cells to generate functional tooth modules represents an emerging and promising approach in dental tissue engineering. These modules aim to closely replicate the intricate morphology and essential physiological functions of dental tissues. Recent advancements in regenerative research have not only enhanced the assembly techniques for these modules but also highlighted their therapeutic potential in addressing various dental diseases. In this review, we discuss the latest progress in the construction of functional tooth modules, especially on regenerating dental pulp, periodontal tissue, and tooth roots.

3D bioprinting of liver models: A systematic scoping review of methods, bioinks, and reporting quality

Background

Effective communication is crucial for broad acceptance and applicability of alternative methods in 3R biomedical research and preclinical testing. 3D bioprinting is used to construct intricate biological structures towards functional liver models, specifically engineered for deployment as alternative models in drug screening, toxicological investigations, and tissue engineering. Despite a growing number of reviews in this emerging field, a comprehensive study, systematically assessing practices and reporting quality for bioprinted liver models is missing.

Methods

In this systematic scoping review we systematically searched MEDLINE (Ovid), EMBASE (Ovid) and BioRxiv for studies published prior to June 2nd, 2022. We extracted data on methodological conduct, applied bioinks, the composition of the printed model, performed experiments and model applications. Records were screened for eligibility and data were extracted from included articles by two independent reviewers from a panel of seven domain experts specializing in bioprinting and liver biology. We used RAYYAN for the screening process and SyRF for data extraction. We used R for data analysis, and R and Graphpad PRISM for visualization.

Results

Through our systematic database search we identified 1042 records, from which 63 met the eligibility criteria for inclusion in this systematic scoping review. Our findings revealed that extrusion-based printing, in conjunction with bioinks composed of natural components, emerged as the predominant printing technique in the bioprinting of liver models. Notably, the HepG2 hepatoma cell line was the most frequently employed liver cell type, despite acknowledged limitations. Furthermore, 51% of the printed models featured co-cultures with non-parenchymal cells to enhance their complexity. The included studies offered a variety of techniques for characterizing these liver models, with their primary application predominantly focused on toxicity testing. Among the frequently analyzed liver markers, albumin and urea stood out. Additionally, Cytochrome P450 (CYP) isoforms, primarily CYP3A and CYP1A, were assessed, and select studies employed nuclear receptor agonists to induce CYP activity.

Conclusion

Our systematic scoping review offers an evidence-based overview and evaluation of the current state of research on bioprinted liver models, representing a promising and innovative technology for creating alternative organ models. We conducted a thorough examination of both the methodological and technical facets of model development and scrutinized the reporting quality within the realm of bioprinted liver models. This systematic scoping review can serve as a valuable template for systematically evaluating the progress of organ model development in various other domains. The transparently derived evidence presented here can provide essential support to the research community, facilitating the adaptation of technological advancements, the establishment of standards, and the enhancement of model robustness. This is particularly crucial as we work toward the long-term objective of establishing new approach methods as reliable alternatives to animal testing, with extensive and versatile applications.

Droplet bioprinting of acellular and cell-laden structures at high-resolutions

Advances in digital light projection(DLP) based (bio) printers have made printing of intricate structures at high resolution possible using a wide range of photosensitive bioinks. A typical setup of a DLP bioprinter includes a vat or reservoir filled with liquid bioink, which presents challenges in terms of cost associated with bioink synthesis, high waste, and gravity-induced cell settling, contaminations, or variation in bioink viscosity during the printing process. Here, we report a vat-free, low-volume, waste-free droplet bioprinting method capable of rapidly printing 3D soft structures at high resolution using model bioinks and model cells. A multiphase many-body dissipative particle dynamics model was developed to simulate the dynamic process of droplet-based DLP printing and elucidate the roles of surface wettability and bioink viscosity. Process variables such as light intensity, photo-initiator concentration, and bioink formulations were optimized to print 3D soft structures (∼0.4-3 kPa) with a typical layer thickness of 50µm, an XY resolution of 38 ± 1.5μm and Z resolution of 237 ± 5.4µm. To demonstrate its versatility, droplet bioprinting was used to print a range of acellular 3D structures such as a lattice cube, a Mayan pyramid, a heart-shaped structure, and a microfluidic chip with endothelialized channels. Droplet bioprinting, performed using model C3H/10T1/2 cells, exhibited high viability (90%) and cell spreading. Additionally, microfluidic devices with internal channel networks lined with endothelial cells showed robust monolayer formation while osteoblast-laden constructs showed mineral deposition upon osteogenic induction. Overall, droplet bioprinting could be a low-cost, no-waste, easy-to-use, method to make customized bioprinted constructs for a range of biomedical applications.

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.

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.

3D bioprinting approaches for spinal cord injury repair

Regenerative healing of spinal cord injury (SCI) poses an ongoing medical challenge by causing persistent neurological impairment and a significant socioeconomic burden. The complexity of spinal cord tissue presents hurdles to successful regeneration following injury, due to the difficulty of forming a biomimetic structure that faithfully replicates native tissue using conventional tissue engineering scaffolds. 3D bioprinting is a rapidly evolving technology with unmatched potential to create 3D biological tissues with complicated and hierarchical structure and composition. With the addition of biological additives such as cells and biomolecules, 3D bioprinting can fabricate preclinical implants, tissue or organ-like constructs, andin vitromodels through precise control over the deposition of biomaterials and other building blocks. This review highlights the characteristics and advantages of 3D bioprinting for scaffold fabrication to enable SCI repair, including bottom-up manufacturing, mechanical customization, and spatial heterogeneity. This review also critically discusses the impact of various fabrication parameters on the efficacy of spinal cord repair using 3D bioprinted scaffolds, including the choice of printing method, scaffold shape, biomaterials, and biological supplements such as cells and growth factors. High-quality preclinical studies are required to accelerate the translation of 3D bioprinting into clinical practice for spinal cord repair. Meanwhile, other technological advances will continue to improve the regenerative capability of bioprinted scaffolds, such as the incorporation of nanoscale biological particles and the development of 4D printing.

Evaluation of Alginate Hydrogel Microstrands for Stromal Cell Encapsulation and Maintenance

Mesenchymal stromal cells (MSCs) have displayed potential in regenerating organ function due to their anti-fibrotic, anti-inflammatory, and regenerative properties. However, there is a need for delivery systems to enhance MSC retention while maintaining their anti-fibrotic characteristics. This study investigates the feasibility of using alginate hydrogel microstrands as a cell delivery vehicle to maintain MSC viability and phenotype. To accommodate cell implantation needs, we invented a Syringe-in-Syringe approach to reproducibly fabricate microstrands in small numbers with a diameter of around 200 µm and a porous structure, which would allow for transporting nutrients to cells by diffusion. Using murine NIH 3T3 fibroblasts and primary embryonic 16 (E16) salivary mesenchyme cells as primary stromal cell models, we assessed cell viability, growth, and expression of mesenchymal and fibrotic markers in microstrands. Cell viability remained higher than 90% for both cell types. To determine cell number within the microstrands prior to in vivo implantation, we have further optimized the alamarBlue assay to measure viable cell growth in microstrands. We have shown the effect of initial cell seeding density and culture period on cell viability and growth to accommodate future stromal cell delivery and implantation. Additionally, we confirmed homeostatic phenotype maintenance for E16 mesenchyme cells in microstrands.

Integrating bioprinting, cell therapies and drug delivery towards in vivo regeneration of cartilage, bone and osteochondral tissue

The biological and biomechanical functions of cartilage, bone and osteochondral tissue are naturally orchestrated by a complex crosstalk between zonally dependent cells and extracellular matrix components. In fact, this crosstalk involves biomechanical signals and the release of biochemical cues that direct cell fate and regulate tissue morphogenesis and remodelling in vivo. Three-dimensional bioprinting introduced a paradigm shift in tissue engineering and regenerative medicine, since it allows to mimic native tissue anisotropy introducing compositional and architectural gradients. Moreover, the growing synergy between bioprinting and drug delivery may enable to replicate cell/extracellular matrix reciprocity and dynamics by the careful control of the spatial and temporal patterning of bioactive cues. Although significant advances have been made in this direction, unmet challenges and open research questions persist. These include, among others, the optimization of scaffold zonality and architectural features; the preservation of the bioactivity of loaded active molecules, as well as their spatio-temporal release; the in vitro scaffold maturation prior to implantation; the pros and cons of each animal model and the graft-defect mismatch; and the in vivo non-invasive monitoring of new tissue formation. This work critically reviews these aspects and reveals the state of the art of using three-dimensional bioprinting, and its synergy with drug delivery technologies, to pattern the distribution of cells and/or active molecules in cartilage, bone and osteochondral engineered tissues. Most notably, this work focuses on approaches, technologies and biomaterials that are currently under in vivo investigations, as these give important insights on scaffold performance at the implantation site and its interaction/integration with surrounding tissues.

3D and 4D assembly of functional structures using shape-morphing materials for biological applications

3D structures are crucial to biological function in the human body, driving interest in their in vitro fabrication. Advances in shape-morphing materials allow the assembly of 3D functional materials with the ability to modulate the architecture, flexibility, functionality, and other properties of the final product that suit the desired application. The principles of these techniques correspond to the principles of origami and kirigami, which enable the transformation of planar materials into 3D structures by folding, cutting, and twisting the 2D structure. In these approaches, materials responding to a certain stimulus will be used to manufacture a preliminary structure. Upon applying the stimuli, the architecture changes, which could be considered the fourth dimension in the manufacturing process. Here, we briefly summarize manufacturing techniques, such as lithography and 3D printing, that can be used in fabricating complex structures based on the aforementioned principles. We then discuss the common architectures that have been developed using these methods, which include but are not limited to gripping, rolling, and folding structures. Then, we describe the biomedical applications of these structures, such as sensors, scaffolds, and minimally invasive medical devices. Finally, we discuss challenges and future directions in using shape-morphing materials to develop biomimetic and bioinspired designs.

Recent Developments in Bio-Ink Formulations Using Marine-Derived Biomaterials for Three-Dimensional (3D) Bioprinting

3D bioprinting is a disruptive, computer-aided, and additive manufacturing technology that allows the obtention, layer-by-layer, of 3D complex structures. This technology is believed to offer tremendous opportunities in several fields including biomedical, pharmaceutical, and food industries. Several bioprinting processes and bio-ink materials have emerged recently. However, there is still a pressing need to develop low-cost sustainable bio-ink materials with superior qualities (excellent mechanical, viscoelastic and thermal properties, biocompatibility, and biodegradability). Marine-derived biomaterials, including polysaccharides and proteins, represent a viable and renewable source for bio-ink formulations. Therefore, the focus of this review centers around the use of marine-derived biomaterials in the formulations of bio-ink. It starts with a general overview of 3D bioprinting processes followed by a description of the most commonly used marine-derived biomaterials for 3D bioprinting, with a special attention paid to chitosan, glycosaminoglycans, alginate, carrageenan, collagen, and gelatin. The challenges facing the application of marine-derived biomaterials in 3D bioprinting within the biomedical and pharmaceutical fields along with future directions are also discussed.

3D visualization and printing: An "Anatomical Engineering" trend revealing underlying morphology via innovation and reconstruction towards future of veterinary anatomy

The amalgamation of veterinary anatomy, technology and innovation has led to development of latest technological advancement in the field of veterinary medicine, i.e., three-dimensional (3D) imaging and reconstruction. 3D visualization technique followed by 3D reconstruction has been proven to enhance non-destructive 3D visualization grossly or microscopically, e.g., skeletal muscle, smooth muscle, ligaments, cartilage, connective tissue, blood vessels, nerves, lymph nodes, and glands. The core aim of this manuscript is to document non-invasive 3D visualization methods being adopted currently in veterinary anatomy to reveal underlying morphology and to reconstruct them by 3D softwares followed by printing, its applications, current challenges, trends and future opportunities. 3D visualization methods such as MRI, CT scans and micro-CT scans are utilised in revealing volumetric data and underlying morphology at microscopic levels as well. This will pave a way to transform and re-invent the future of teaching in veterinary medicine, in clinical cases as well as in exploring wildlife anatomy. This review provides novel insights into 3D visualization and printing as it is the future of veterinary anatomy, thus making it spread to become the plethora of opportunities for whole veterinary science.

Advantages and limitations of using cell viability assays for 3D bioprinted constructs

Bioprinting shows promise for bioengineered scaffolds and three-dimensional (3D) disease models, but assessing the viability of embedded cells is challenging. Conventional assays are limited by the technical problems that derive from using multi-layered bioink matrices dispersing cells in three dimensions. In this study, we tested bioprinted osteogenic bioinks as a model system. Alginate- or gelatin-based bioinks were loaded with/without ceramic microparticles and osteogenic cells (bone tumor cells, with or without normal bone cells). Despite demonstrating 80%-90% viability through manual counting and live/dead staining, this was time-consuming and operator-dependent. Moreover, for the alginate-bioprinted scaffold, cell spheroids could not be distinguished from single cells. The indirect assay (alamarBlue), was faster but less accurate than live/dead staining due to dependence on hydrogel permeability. Automated confocal microscope acquisition and cell counting of live/dead staining was more reproducible, reliable, faster, efficient, and avoided overestimates compared to manual cell counting by optical microscopy. Finally, for 1.2 mm thick 3D bioprints, dual-photon confocal scanning with vital staining greatly improved the precision of the evaluation of cell distribution and viability and cell-cell interactions through thez-axis. In summary, automated confocal microscopy and cell counting provided superior accuracy for the assessment of cell viability and interactions in 3D bioprinted models compared to most commonly and currently used techniques.

Embedded 3D bioprinting - An emerging strategy to fabricate biomimetic & large vascularized tissue constructs

Three-dimensional bioprinting is an advanced tissue fabrication technique that allows printing complex structures with precise positioning of multiple cell types layer-by-layer. Compared to other bioprinting methods, extrusion bioprinting has several advantages to print large-sized tissue constructs and complex organ models due to large build volume. Extrusion bioprinting using sacrificial, support and embedded strategies have been successfully employed to facilitate printing of complex and hollow structures. Embedded bioprinting is a gel-in-gel approach developed to overcome the gravitational and overhanging limits of bioprinting to print large-sized constructs with a micron-scale resolution. In embedded bioprinting, deposition of bioinks into the microgel or granular support bath will be facilitated by the sol-gel transition of the support bath through needle movement inside the granular medium. This review outlines various embedded bioprinting strategies and the polymers used in the embedded systems with advantages, limitations, and efficacy in the fabrication of complex vascularized tissues or organ models with micron-scale resolution. Further, the essential requirements of support bath systems like viscoelasticity, stability, transparency and easy extraction to print human scale organs are discussed. Additionally, the organs or complex geometries like vascular constructs, heart, bone, octopus and jellyfish models printed using support bath assisted printing methods with their anatomical features are elaborated. Finally, the challenges in clinical translation and the future scope of these embedded bioprinting models to replace the native organs are envisaged.

A Systematic Review of Fish-Based Biomaterial on Wound Healing and Anti-Inflammatory Processes

Objective: To conduct a systematic literature review to study the effects of fish-based biomaterials on wound healing in both in vivo and in vitro animal models. Approach: This review covers the study reported in different articles between 2016 and August 2022 concentrating mainly on the cytotoxicity evaluation of different fish-based biomaterials on inflammation, reepithelialization and wound healing. Significance: This review shows considerable amount of research work carried out with fish-based biomaterials and collagen for treating burn wounds. Surprisingly there are only a few commercial products developed so far in this particular regard for surgical purpose and therefore, there is a way out and need for developing medical support product from fish-based biomaterials to treat and cure wounds. Recent Advances: Three-dimensional skin bioprinting technique is a large-scale solution for severe burn wounds that requires collagen as a raw material for printing, wherein fish collagen can be used in place of bovine and porcine, as it is biocompatible, promotes cell proliferation, adhesion, and migration, and degrades enzymatically. In the recent times, there are a few fish-based surgical products that have been formulated by Kerecis in United States. Critical Issues: The different fish-based biomaterial products are all mere supplements taken in orally as food or supplements till date and there is no proper proven medications that has been formulated so far in the field of wound healing and inflammation based on fish biomaterials except the surgical products that can be finger counted. Future Directions: Fish-based biomaterials are known for the medicinal properties that are used throughout the world and further investigations should be carried out to understand the actual physiochemical properties of its derivatives for the discovery of novel products and drugs.

Drug-Releasing Tannic Acid-Mediated Adhesive PEG Hydrogel for Porous Titanium Implants

Porous titanium implants are commonly utilized for orthopedic surgery because they can mimic the mechanical properties and porous structure of human bone. However, the bioinertness of titanium (Ti) has been reported to obstruct biointegration processes, resulting in slower bone repair. Here, we propose a localized drug delivery system on Ti surfaces using adhesive hydrogel to enhance biological-Ti interactions. The hydrogel was fabricated from polyethylene glycol (PEG), which was cross-linked by the complex of tannic acid (TA) and 1,4-phenylenediboronic acid (PDBA) and stabilized by bovine serum albumin (BSA). The hydrogel was formed and attached to a Ti plate to investigate stability, biodegradability, controlled drug release, and biocompatibility. The stability and biodegradability of the hydrogel could be tuned by adjusting the concentrations of BSA and TA. The hydrogel lasted and remained adhered to the Ti surface after being submerged in PBS for at least 15 days. The controlled release of strontium ranelate (SrRan) and the release mechanism depended on the amount of TA since it was found to govern the hydrogel integrity and pore size. Additionally, in vitro biocompatibility was validated using L929 fibroblast and MC3T3-E1 osteoblast cells that showed greater than 70% viability. The adhesive hydrogel was further studied by injecting it into a 3D-printed Ti-scaffold that contained a porous structure mimicking natural human bone. The hydrogel completely filled and adhered to the inner porous structure of the scaffold. The biodegradation and drug release of the hydrogel in the scaffold occurred at a slower rate, suggesting sustainable drug release that is suitable for bone cell regeneration. The overall results in biodegradability, controlled drug release, and biocompatibility demonstrate the great potential of the drug-releasing TA-mediated adhesive PEG hydrogel as a Ti-enhancing biomaterial that supports osseointegration.

Multiblock Poly-ε-Caprolactones: One-Step Synthesis toward Programmable Properties

Control of monomer sequence enables predictable structure-property relationships in versatile polymeric materials. The facile synthesis of multiblock copolymers (MBCPs) with controlled chain structure is highly challenging, particularly for those prepared via one-pot copolymerization of mixed monomers. Herein, poly-ε-caprolactone MBCPs, a series of thermoplastic elastomers with tailored thermal, mechanical, rheological, and degradable properties, are synthesized by Janus polymerization. Melting temperature, tensile strength, ductility, viscosity, and enzymatic degradability are governed by block length which is in turn dictated by the monomer-to-catalyst feed ratio. The relationships between the physicochemical properties and the architectures are investigated in detail.

Controllable and biocompatible 3D bioprinting technology for microorganisms: Fundamental, environmental applications and challenges

3D bioprinting is a new 3D manufacturing technology, that can be used to accurately distribute and load microorganisms to form microbial active materials with multiple complex functions. Based on the 3D printing of human cells in tissue engineering, 3D bioprinting technology has been developed. Although 3D bioprinting technology is still immature, it shows great potential in the environmental field. Due to the precise programming control and multi-printing pathway, 3D bioprinting technology provides a high-throughput method based on micron-level patterning for a wide range of environmental microbiological engineering applications, which makes it an on-demand, multi-functional manufacturing technology. To date, 3D bioprinting technology has been employed in microbial fuel cells, biofilm material preparation, microbial catalysts and 4D bioprinting with time dimension functions. Nevertheless, current 3D bioprinting technology faces technical challenges in improving the mechanical properties of materials, developing specific bioinks to adapt to different strains, and exploring 4D bioprinting for intelligent applications. Hence, this review systematically analyzes the basic technical principles of 3D bioprinting, bioinks materials and their applications in the environmental field, and proposes the challenges and future prospects of 3D bioprinting in the environmental field. Combined with the current development of microbial enhancement technology in the environmental field, 3D bioprinting will be developed into an enabling platform for multifunctional microorganisms and facilitate greater control of in situ directional reactions.

Progress in bioprinting technology for tissue regeneration

In recent years, due to the increase in diseases that require organ/tissue transplantation and the limited donor, on the other hand, patients have lost hope of recovery and organ transplantation. Regenerative medicine is one of the new sciences that promises a bright future for these patients by providing solutions to repair, improve function, and replace tissue. One of the technologies used in regenerative medicine is three-dimensional (3D) bioprinters. Bioprinting is a new strategy that is the basis for starting a global revolution in the field of medical sciences and has attracted much attention. 3D bioprinters use a combination of advanced biology and cell science, computer science, and materials science to create complex bio-hybrid structures for various applications. The capacity to use this technology can be demonstrated in regenerative medicine to make various connective tissues, such as skin, cartilage, and bone. One of the essential parts of a 3D bioprinter is the bio-ink. Bio-ink is a combination of biologically active molecules, cells, and biomaterials that make the printed product. In this review, we examine the main bioprinting strategies, such as inkjet printing, laser, and extrusion-based bioprinting, as well as some of their applications.

Biodegradable Polymers in Biomedical Applications: A Review-Developments, Perspectives and Future Challenges

Biodegradable polymers are materials that, thanks to their remarkable properties, are widely understood to be suitable for use in scientific fields such as tissue engineering and materials engineering. Due to the alarming increase in the number of diagnosed diseases and conditions, polymers are of great interest in biomedical applications especially. The use of biodegradable polymers in biomedicine is constantly expanding. The application of new techniques or the improvement of existing ones makes it possible to produce materials with desired properties, such as mechanical strength, controlled degradation time and rate and antibacterial and antimicrobial properties. In addition, these materials can take virtually unlimited shapes as a result of appropriate design. This is additionally desirable when it is necessary to develop new structures that support or restore the proper functioning of systems in the body.

Droplet bioprinting of acellular and cell-laden structures at high-resolutions

Advances in Digital Light Processing (DLP) based (bio) printers have made printing of intricate structures at high resolution possible using a wide range of photosensitive bioinks. A typical setup of a DLP bioprinter includes a vat or reservoir filled with liquid bioink, which presents challenges in terms of cost associated with bioink synthesis, high waste, and gravity-induced cell settling, contaminations, or variation in bioink viscosity during the printing process. Here, we report a vat-free, low-volume, waste-free droplet bioprinting method capable of rapidly printing 3D soft structures at high resolution using model bioinks. A multiphase many-body dissipative particle dynamics (mDPD) model was developed to simulate the dynamic process of droplet-based DLP printing and elucidate the roles of surface wettability and bioink viscosity. Process variables such as light intensity, photo-initiator concentration, and bioink formulations were optimized to print 3D soft structures (∼0.4 to 3 kPa) with an XY resolution of 38 ± 1.5 μm and Z resolution of 237±5.4 μm. To demonstrate its versatility, droplet bioprinting was used to print a range of acellular 3D structures such as a lattice cube, a Mayan pyramid, a heart-shaped structure, and a microfluidic chip with endothelialized channels. Droplet bioprinting, performed using model C3H/10T1/2 cells, exhibited high viability (90%) and cell spreading. Additionally, microfluidic devices with internal channel network lined with endothelial cells showed robust monolayer formation while osteoblast-laden constructs showed mineral deposition upon osteogenic induction. Overall, droplet bioprinting could be a low-cost, no-waste, easy-to-use, method to make customized bioprinted constructs for a range of biomedical applications.

Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

The role of microfluidics and 3D-bioprinting in the future of exosome therapy

Exosome-based strategies constitute a promising tool for therapeutics, avoiding potential immunogenic and tumorigenic side-effects of cell therapies. However, the collection of a suitable exosome pool, and the need for high doses with conventional administration approaches, hamper their clinical translation. To overcome these challenges, versatile exosome collection strategies together with advanced delivery platforms may represent major progress in this field. Microfluidics enables large-scale gathering of both natural and synthetic exosomes for their implementation into bioinks, while 3D-bioprinting holds great promise in regenerative medicine with the use of exosome-loaded scaffolds that mimic the target tissue with controlled pharmacokinetics and pharmacodynamics. Hence, the combination of both strategies might become the key for the translation of exosome therapies to clinical practice.

Bioprinting-Enabled Biomaterials: A Cutting-Edge Strategy for Future Osteoarthritis Therapy

Bioprinting is an advanced technology that allows for the precise placement of cells and biomaterials in a controlled manner, making significant contributions in regenerative medicine. Notably, bioprinting-enabled biomaterials have found extensive application as drug delivery systems (DDS) in the treatment of osteoarthritis (OA). Despite the widespread utilization of these biomaterials, there has been limited comprehensive research summarizing the recent advances in this area. Therefore, this review aims to explore the noteworthy developments and challenges associated with utilizing bioprinting-enabled biomaterials as effective DDS for the treatment of OA. To begin, we provide an overview of the complex pathophysiology of OA, highlighting the shortcomings of current treatment modalities. Following this, we conduct a detailed examination of various bioprinting technologies and discuss the wide range of biomaterials employed in DDS applications for OA therapy. Finally, by placing emphasis on their transformative potential, we discuss the incorporation of crucial cellular components such as chondrocytes and mesenchymal stem cells into bioprinted constructs, which play a pivotal role in promoting tissue regeneration and repair.

Three-dimensional bioprinting in ophthalmic care

Three-dimensional (3D) bioprinting is widely used in ophthalmic clinic, including in diagnosis, surgery, prosthetics, medications, drug development and delivery, and medical education. Articles published in 2011-2022 into bioinks, printing technologies, and bioprinting applications in ophthalmology were reviewed and the strengths and limitations of bioprinting in ophthalmology highlighted. The review highlighted the trade-offs of printing technologies and bioinks in respect to, among others, material type cost, throughput, gelation technique, cell density, cell viability, resolution, and printing speed. There is already widespread ophthalmological application of bioprinting outside clinical settings, including in educational modelling, retinal imaging/visualization techniques and drug design/testing. In clinical settings, bioprinting has already found application in pre-operatory planning. Even so, the findings showed that even with its immense promise, actual translation to clinical applications remains distant, but relatively closer for the corneal (except stromal) tissues, epithelium, endothelium, and conjunctiva, than it was for the retina. This review similarly reflected on the critical on the technical, practical, ethical, and cost barrier to rapid progress of bioprinting in ophthalmology, including accessibility to the most sophisticated bioprinting technologies, choice, and suitability of bioinks, tissue viability and storage conditions. The extant research is encouraging, but more work is clearly required for the push towards clinical translation of research.

4D Bioprinting via Molecular Network Contraction for Membranous Tissue Fabrication

Generation of thin membranous tissues (TMT), such as the cornea, epidermis, and periosteum, presents a difficult fabrication challenge in tissue engineering (TE). TMTs consist of several cell layers that are less than 100 µm in thickness per layer. While traditional methods provide the necessary resolution for TMT fabrication, they require significant handling and incorporation of several layers is limited. Extrusion bioprinting offers precise control over deposition of different biomaterials and cell populations within the same construct but lacks the resolution to generate biomimetic TMTs. For the first time, a 4D bioprinting strategy that allows for the generation of cell-laden TMTs is developed. Anionic gelatin methacrylate (GelMA) hydrogels are treated with cationic poly-l-lysine (PLL), which induces charge attraction, microscale network collapse, and macroscale hydrogel shrinking. The impact of shrinking on hydrogel properties, print resolution, and cell viability is presented. Additionally, this work suggests that a novel mechanism is occurring, where PLL exhibits a contractile force on GelMA and PLL molecular weight drives GelMA shrinking capabilities. Finally, it is shown that this phenomenon can occur while maintaining an encapsulated cell population. These findings address a critical barrier by generating macroscale tissue structures with their microscale TMT counterparts in the same print.

Novel scaffold platforms for simultaneous induction osteogenesis and angiogenesis in bone tissue engineering: a cutting-edge approach

Despite the recent advances in the development of bone graft substitutes, treatment of critical size bone defects continues to be a significant challenge, especially in the elderly population. A current approach to overcome this challenge involves the creation of bone-mimicking scaffolds that can simultaneously promote osteogenesis and angiogenesis. In this context, incorporating multiple bioactive agents like growth factors, genes, and small molecules into these scaffolds has emerged as a promising strategy. To incorporate such agents, researchers have developed scaffolds incorporating nanoparticles, including nanoparticulate carriers, inorganic nanoparticles, and exosomes. Current paper provides a summary of the latest advancements in using various bioactive agents, drugs, and cells to synergistically promote osteogenesis and angiogenesis in bone-mimetic scaffolds. It also discusses scaffold design properties aimed at maximizing the synergistic effects of osteogenesis and angiogenesis, various innovative fabrication strategies, and ongoing clinical studies.

Utilization of 3D bioprinting technology in creating human tissue and organoid models for preclinical drug research - State-of-the-art

Rapid development of tissue engineering in recent years has increased the importance of three-dimensional (3D) bioprinting technology as novel strategy for fabrication functional 3D tissue and organoid models for pharmaceutical research. 3D bioprinting technology gives hope for eliminating many problems associated with traditional cell culture methods during drug screening. However, there is a still long way to wider clinical application of this technology due to the numerous difficulties associated with development of bioinks, advanced printers and in-depth understanding of human tissue architecture. In this review, the work associated with relatively well-known extrusion-based bioprinting (EBB), jetting-based bioprinting (JBB), and vat photopolymerization bioprinting (VPB) is presented and discussed with the latest advances and limitations in this field. Next we discuss state-of-the-art research of 3D bioprinted in vitro models including liver, kidney, lung, heart, intestines, eye, skin as well as neural and bone tissue that have potential applications in the development of new drugs.

New Insights into the Applications of 3D-Printed Biomaterial in Wound Healing and Prosthesis

Recently three-dimensional bioprinting (3D-bioP) has emerged as a revolutionary technique for numerous biomedical applications. 3D-bioP has facilitated the printing of advanced and complex human organs resulting in satisfactory therapeutic practice. One of the important biomedical applications of 3D-bioP is in tissue engineering, wound healing, and prosthetics. 3D-bioP is basically aimed to restore the natural extracellular matrix of human's damage due to wounds. The relevant search was explored using various scientific database, viz., PubMed, Web of Science, Scopus, and ScienceDirect. The objective of this review is to emphasize interpretations from the pre-executed studies and to assess the worth of employing 3D-bioP in wound healing as well as prosthetics in terms of patient compliance, clinical outcomes, and economic viability. Furthermore, the benefits of applying 3D-bioP in wound healing over traditional methods have been covered along with the biocompatible biomaterials employed as bioinks has been discussion. Additionally, the review expands about the clinical trials in 3D-bioP field, showing promise of biomedical applicability of this technique with growing advancement in recent years.

Role of three-dimensional cell culture in therapeutics and diagnostics: an updated review

Drug development and testing are a tedious and expensive process with a high degree of uncertainty in the clinical success and preclinical validation of manufactured therapeutic agents. Currently, to understand the drug action, disease mechanism, and drug testing, most therapeutic drug manufacturers use 2D cell culture models to validate the drug action. However, there are many uncertainties and limitations with the conventional use of 2D (monolayer) cell culture models for drug testing that are primarily attributed due to poor mimicking of cellular mechanisms, disturbance in environmental interaction, and changes in structural morphology. To overcome such odds and difficulties in the preclinical validation of therapeutic medications, newer in vivo drug testing cell culture models with higher screening efficiencies are required. One such promising and advanced cell culture model reported recently is the "three-dimensional cell culture model." The 3D cell culture models are reported to show evident benefits over conventional 2D cell models. This review article outlines and describes the current advancement in cell culture models, their types, significance in high-throughput screening, limitations, applications in drug toxicity screening, and preclinical testing methodologies to predict in vivo efficacy.

Conducting polymer-based nanostructured materials for brain-machine interfaces

As scientists discovered that raw neurological signals could translate into bioelectric information, brain-machine interfaces (BMI) for experimental and clinical studies have experienced massive growth. Developing suitable materials for bioelectronic devices to be used for real-time recording and data digitalizing has three important necessitates which should be covered. Biocompatibility, electrical conductivity, and having mechanical properties similar to soft brain tissue to decrease mechanical mismatch should be adopted for all materials. In this review, inorganic nanoparticles and intrinsically conducting polymers are discussed to impart electrical conductivity to systems, where soft materials such as hydrogels can offer reliable mechanical properties and a biocompatible substrate. Interpenetrating hydrogel networks offer more mechanical stability and provide a path for incorporating polymers with desired properties into one strong network. Promising fabrication methods, like electrospinning and additive manufacturing, allow scientists to customize designs for each application and reach the maximum potential for the system. In the near future, it is desired to fabricate biohybrid conducting polymer-based interfaces loaded with cells, giving the opportunity for simultaneous stimulation and regeneration. Developing multi-modal BMIs, Using artificial intelligence and machine learning to design advanced materials are among the future goals for this field. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

Bibliometric and visualized analysis of 3D printing bioink in bone tissue engineering

Background: Applying 3D printed bioink to bone tissue engineering is an emerging technology for restoring bone tissue defects. This study aims to evaluate the application of 3D printing bioink in bone tissue engineering from 2010 to 2022 through bibliometric analysis, and to predict the hotspots and developing trends in this field. Methods: We retrieved publications from Web of Science from 2010 to 2022 on 8 January 2023. We examined the retrieved data using the bibliometrix package in R software, and VOSviewer and CiteSpace were used for visualizing the trends and hotspots of research on 3D printing bioink in bone tissue engineering. Results: We identified 682 articles and review articles in this field from 2010 to 2022. The journal Biomaterials ranked first in the number of articles published in this field. In 2016, an article published by Hölzl, K in the Biofabrication journal ranked first in number of citations. China ranked first in number of articles published and in single country publications (SCP), while America surpassed China to rank first in multiple country publications (MCP). In addition, a collaboration network analysis showed tight collaborations among China, America, South Korea, Netherlands, and other countries, with the top 10 major research affiliations mostly from these countries. The top 10 high-frequency words in this field are consistent with the field's research hotspots. The evolution trend of the discipline indicates that most citations come from Physics/Materials/Chemistry journals. Factorial analysis plays an intuitive role in determining research hotspots in this sphere. Keyword burst detection shows that chitosan and endothelial cells are emerging research hotspots in this field. Conclusion: This bibliometric study maps out a fundamental knowledge structure including countries, affiliations, authors, journals and keywords in this field of research from 2010 to 2022. This study fills a gap in the field of bibliometrics and provides a comprehensive perspective with broad prospects for this burgeoning research area.

Fabrication Strategies for Engineered Thin Membranous Tissues

Thin membranous tissues (TMTs) are anatomical structures consisting of multiple stratified cell layers, each less than 100 μm in thickness. While these tissues are small in scale, they play critical roles in normal tissue function and healing. Examples of TMTs include the tympanic membrane, cornea, periosteum, and epidermis. Damage to these structures can be caused by trauma or congenital disabilities, resulting in hearing loss, blindness, dysfunctional bone development, and impaired wound repair, respectively. While autologous and allogeneic tissue sources for these membranes exist, they are significantly limited by availability and patient complications. Tissue engineering has therefore become a popular strategy for TMT replacement. However, due to their complex microscale architecture, TMTs are often difficult to replicate in a biomimetic manner. The critical challenge in TMT fabrication is balancing fine resolution with the ability to mimic complex target tissue anatomy. This Review reports existing TMT fabrication strategies, their resolution and material capabilities, cell and tissue response, and the advantages and disadvantages of each technique.

Characterization of 3D-Bioprinted In Vitro Lung Cancer Models Using RNA-Sequencing Techniques

OBJECTIVE

To construct an in vitro lung cancer model using 3D bioprinting and evaluate the feasibility of the model. Transcriptome sequencing was used to compare the differential genes and functions of 2D and 3D lung cancer cells.

METHODS

1. A549 cells were mixed with sodium alginate/gelatine/fibrinogen as 3D-printed biological ink to construct a hydrogel scaffold for the in vitro model of lung cancer; 2. A hydrogel scaffold was printed using a extrusion 3D bioprinter; 3. The printed lung cancer model was evaluated in vitro; and 4. A549 cells cultured in 2D and 3D tumour models in vitro were collected, and RNA-seq conducted bioinformatics analysis.

RESULTS

1. The in vitro lung cancer model printed using 3D-bioprinting technology was a porous microstructure model, suitable for the survival of A549 cells. Compared with the 2D cell-line model, the 3D model is closer to the fundamental human growth environment; 2. There was no significant difference in cell survival rate between the 2D and 3D groups; 3. In the cell proliferation rate measurement, it was found that the cells in the 2D group had a speedy growth rate in the first five days, but after five days, the growth rate slowed down. Cell proliferation showed a declining process after the ninth day of cell culture. However, cells in the 3D group showed a slow growth process at the beginning, and the growth rate reached a peak on the 12th day. Then, the growth rate showed a downward trend; and 4. RNA-seq compared A549 cells from 2D and 3D lung cancer models. A total of 3112 genes were differentially expressed, including 1189 up-regulated and 1923 down-regulated genes, with p-value ≤ 0.05 and |Log2Ratio| ≥ 1 as screening conditions. After functional enrichment analysis of differential genes, these differential genes affect the biological regulation of A549 cells, thus promoting lung cancer progression.

CONCLUSION

This study uses 3D-bioprinting technology to construct a tumour model of lung cancer that can grow sustainably in vitro. Three-dimensional bioprinting may provide a new research platform for studying the lung cancer TME mechanism and anticancer drug screening.

3D bioprinting patient-derived induced pluripotent stem cell models of Alzheimer's disease using a smart bioink

BACKGROUND

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is becoming increasingly prevalent as our population ages. It is characterized by the buildup of amyloid beta plaques and neurofibrillary tangles containing hyperphosphorylated-tau. The current treatments for AD do not prevent the long-term progression of the disease and pre-clinical models often do not accurately represent its complexity. Bioprinting combines cells and biomaterials to create 3D structures that replicate the native tissue environment and can be used as a tool in disease modeling or drug screening.

METHODS

This work differentiated both healthy and diseased patient-derived human induced pluripotent stems cells (hiPSCs) into neural progenitor cells (NPCs) that were bioprinted using the Aspect RX1 microfluidic printer into dome-shaped constructs. The combination of cells, bioink, and puromorphamine (puro)-releasing microspheres were used to mimic the in vivo environment and direct the differentiation of the NPCs into basal forebrain-resembling cholinergic neurons (BFCN). These tissue models were then characterized for cell viability, immunocytochemistry, and electrophysiology to evaluate their functionality and physiology for use as disease-specific neural models.

RESULTS

Tissue models were successfully bioprinted and the cells were viable for analysis after 30- and 45-day cultures. The neuronal and cholinergic markers β-tubulin III (Tuj1), forkhead box G1 (FOXG1), and choline acetyltransferase (ChAT) were identified as well as the AD markers amyloid beta and tau. Further, immature electrical activity was observed when the cells were excited with potassium chloride and acetylcholine.

CONCLUSIONS

This work shows the successful development of bioprinted tissue models incorporating patient derived hiPSCs. Such models can potentially be used as a tool to screen promising drug candidates for treating AD. Further, this model could be used to increase the understanding of AD progression. The use of patient derived cells also shows the potential of this model for use in personalized medicine applications.

Interfacial Polyelectrolyte Complexation-Inspired Bioprinting of Vascular Constructs

Bioprinting is a precise layer-by-layer manufacturing technology utilizing biomaterials, cells, and sometimes growth factors for the fabrication of customized three-dimensional (3D) biological constructs. In recent years, it has gained considerable interest in various biomedical studies. However, the translational application of bioprinting is currently impeded by the lack in efficient techniques for blood vessel fabrications. In this report, by systematically studying the previously reported phenomenon, interfacial polyelectrolyte complexation, an efficient blood vessel bioprinting technique based on the phenomenon, was proposed and subsequently investigated. In this technique, anionic hyaluronate and cationic lysine-based peptide amphiphiles were placed concentrically to bioprint with human umbilical endothelial cells for the fabrication of biological tubular constructs. These constructs demonstrated clear vascular features, which made them highly resemble blood vessels. In addition, to optimize the bioactivity of the printed constructs, this report also, for the first time, studied peptide sequencing's effect on the biocompatibility of the polyelectrolyte-peptide amphiphile complex. All these studies conducted in the report are highly relevant and interesting for research in vascular structure fabrication, which will eventually be beneficial for translational application development of bioprinting.

A digital light processing 3D-printed artificial skin model and full-thickness wound models using silk fibroin bioink

A three-dimensional (3D) artificial skin model offers diverse platforms for skin transplantation, disease mechanisms, and biomaterial testing for skin tissue. However, implementing physiological complexes such as the neurovascular system with living cells in this stratified structure is extremely difficult. In this study, full-thickness skin models were fabricated from methacrylated silk fibroin (Silk-GMA) and gelatin (Gel-GMA) seeded with keratinocytes, fibroblasts, and vascular endothelial cells representing the epidermis and dermis layers through a digital light processing (DLP) 3D printer. Printability, mechanical properties, and cell viability of the skin hydrogels fabricated with different concentrations of Silk-GMA and Gel-GMA were analyzed to find the optimal concentrations for the 3D printing of the artificial skin model. After the skin model was DLP-3D printed using Gel-GMA 15% + Silk-GMA 5% bioink, cultured, and air-lifted for four weeks, well-proliferated keratinocytes and fibroblasts were observed in histological analysis, and increased expressions of Cytokeratin 13, Phalloidin, and CD31 were noted in immunofluorescence staining. Furthermore, full-thickness skin wound models were 3D-printed to evaluate the wound-healing capabilities of the skin hydrogel. When the epidermal growth factor (EGF) was applied, enhanced wound healing in the epidermis and dermis layer with the proliferation of keratinocytes and fibroblasts was observed. Also, the semi-quantitative reverse transcription-polymerase chain reaction revealed increased expression of Cytokeratin 13, fibroblast growth factor, and CD31 in the EGF-treated group relative to the control group. The DLP 3D-printed artificial skin model was mechanically stable and biocompatible for more than four weeks, demonstrating the potential for application in skin tissue engineering. STATEMENT OF SIGNIFICANCE: A full-thickness artificial skin model was 3D-printed in this study with a digital light processing technique using silk fibroin and gelatin, which mimics the structural and cellular compositions of the human skin. The 3D-printed skin hydrogel ensured the viability of the cells in the skin layers that proliferated well after air-lifting cultivation, shown in the histological analysis and immunofluorescence stainings. Furthermore, full-thickness skin wound models were 3D-printed to evaluate the wound healing capabilities of the skin hydrogel, which demonstrated enhanced wound healing in the epidermis and dermis layer with the application of epidermal growth factor on the wound compared to the control. The bioengineered hydrogel expands the applicability of artificial skin models for skin substitutes, wound models, and drug testing.

3D Inkjet-Bioprinted Lung-on-a-Chip

There is an urgent need for physiologically relevant and customizable biochip models of human lung tissue to provide a niche for lung disease modeling and drug efficacy. Although various lung-on-a-chips have been developed, the conventional fabrication method has been limited in reconstituting a very thin and multilayered architecture and spatial arrangements of multiple cell types in a microfluidic device. To overcome these limitations, we developed a physiologically relevant human alveolar lung-on-a-chip model, effectively integrated with an inkjet-printed, micron-thick, and three-layered tissue. After bioprinting lung tissues inside four culture inserts layer-by-layer, the inserts are implanted into a biochip that supplies a flow of culture medium. This modular implantation procedure enables the formation of a lung-on-a-chip to facilitate the culture of 3D-structured inkjet-bioprinted lung models under perfusion at the air-liquid interface. The bioprinted models cultured on the chip maintained their structure with three layers of tens of micrometers and achieved a tight junction in the epithelial layer, the critical properties of an alveolar barrier. The upregulation of genes involved in the essential functions of alveoli was also confirmed in our model. Our culture insert-mountable organ-on-a-chip is a versatile platform that can be applied to various organ models by implanting and replacing culture inserts. It is amenable to mass production and the development of customized models through the convergence with bioprinting technology.

3D bioprinting tumor models mimic the tumor microenvironment for drug screening

Cancer is a severe threat to human life and health and represents the main cause of death globally. Drug therapy is one of the primary means of treating cancer; however, most anticancer medications do not proceed beyond preclinical testing because the conditions of actual human tumors are not effectively mimicked by traditional tumor models. Hence, bionic in vitro tumor models must be developed to screen for anticancer drugs. Three-dimensional (3D) bioprinting technology can produce structures with built-in spatial and chemical complexity and models with accurately controlled structures, a homogeneous size and morphology, less variation across batches, and a more realistic tumor microenvironment (TME). This technology can also rapidly produce such models for high-throughput anticancer medication testing. This review describes 3D bioprinting methods, the use of bioinks in tumor models, and in vitro tumor model design strategies for building complex tumor microenvironment features using biological 3D printing technology. Moreover, the application of 3D bioprinting in vitro tumor models in drug screening is also discussed.

Current Status and Future Outlook of Additive Manufacturing Technologies for the Reconstruction of the Trachea

Tracheal stenosis and defects occur congenitally and in patients who have undergone tracheal intubation and tracheostomy due to long-term intensive care. Such issues may also be observed during tracheal removal during malignant head and neck tumor resection. However, to date, no treatment method has been identified that can simultaneously restore the appearance of the tracheal skeleton while maintaining respiratory function in patients with tracheal defects. Therefore, there is an urgent need to develop a method that can maintain tracheal function while simultaneously reconstructing the skeletal structure of the trachea. Under such circumstances, the advent of additive manufacturing technology that can create customized structures using patient medical image data provides new possibilities for tracheal reconstruction surgery. In this study, the three-dimensional (3D) printing and bioprinting technologies used in tracheal reconstruction are summarized, and various research results related to the reconstruction of mucous membranes, cartilage, blood vessels, and muscle tissue, which are tissues required for tracheal reconstruction, are classified. The prospects for 3D-printed tracheas in clinical studies are also described. This review serves as a guide for the development of artificial tracheas and clinical trials using 3D printing and bioprinting.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

3D Bioprinting for Next-Generation Personalized Medicine

In the past decade, immense progress has been made in advancing personalized medicine to effectively address patient-specific disease complexities in order to develop individualized treatment strategies. In particular, the emergence of 3D bioprinting for in vitro models of tissue and organ engineering presents novel opportunities to improve personalized medicine. However, the existing bioprinted constructs are not yet able to fulfill the ultimate goal: an anatomically realistic organ with mature biological functions. Current bioprinting approaches have technical challenges in terms of precise cell deposition, effective differentiation, proper vascularization, and innervation. This review introduces the principles and realizations of bioprinting with a strong focus on the predominant techniques, including extrusion printing and digital light processing (DLP). We further discussed the applications of bioprinted constructs, including the engraftment of stem cells as personalized implants for regenerative medicine and in vitro high-throughput drug development models for drug discovery. While no one-size-fits-all approach to bioprinting has emerged, the rapid progress and promising results of preliminary studies have demonstrated that bioprinting could serve as an empowering technology to resolve critical challenges in personalized medicine.

Space habitats for bioengineering and surgical repair: addressing the requirement for reconstructive and research tissues during deep-space missions

Numerous technical scenarios have been developed to facilitate a human return to the Moon, and as a testbed for a subsequent mission to Mars. Crews appointed with constructing and establishing planetary bases will require a superior level of physical ability to cope with the operational demands. However, the challenging environments of nearby planets (e.g. geological, atmospheric, gravitational conditions) as well as the lengthy journeys through microgravity, will lead to progressive tissue degradation and an increased susceptibility to injury. The isolation, distance and inability to evacuate in an emergency will require autonomous medical support, as well as a range of facilities and specialised equipment to repair tissue damage on-site. Here, we discuss the design requirements of such a facility, in the form of a habitat that would concomitantly allow tissue substitute production, maintenance and surgical implantation, with an emphasis on connective tissues. The requirements for the individual modules and their operation are identified. Several concepts are assessed, including the presence of adjacent wet lab and medical modules supporting the gradual implementation of regenerative biomaterials and acellular tissue substitutes, leading to eventual tissue grafts and, in subsequent decades, potential tissues/organ-like structures. The latter, currently in early phases of development, are assessed particularly for researching the effects of extreme conditions on representative analogues for astronaut health support. Technical solutions are discussed for bioengineering in an isolated planetary environment with hypogravity, from fluid-gel bath suspended manufacture to cryostorage, cell sourcing and on-site resource utilisation for laboratory infrastructure. Surgical considerations are also discussed.

Towards using 3D cellular cultures to model the activation and diverse functions of macrophages

The advent of 3D cell culture technology promises to enhance understanding of cell biology within tissue microenvironments. Whilst traditional cell culturing methods have been a reliable tool for decades, they inadequately portray the complex environments in which cells inhabit in vivo. The need for better disease models has pushed the development of effective 3D cell models, providing more accurate drug screening assays. There has been great progress in developing 3D tissue models in fields such as cancer research and regenerative medicine, driven by desires to recreate the tumour microenvironment for the discovery of new chemotherapies, or development of artificial tissues or scaffolds for transplantation. Immunology is one field that lacks optimised 3D models and the biology of tissue resident immune cells such as macrophages has yet to be fully explored. This review aims to highlight the benefits of 3D cell culturing for greater understanding of macrophage biology. We review current knowledge of macrophage interactions with their tissue microenvironment and highlight the potential of 3D macrophage models in the development of more effective treatments for disease.

3D bioprinting of heterogeneous tissue-engineered skin containing human dermal fibroblasts and keratinocytes

Three-dimensional (3D) printed skin substitutes have great potential for wound healing. However, current 3D printed skin models are limited in simulating heterogeneity and complexity of skin tissue due to the lack of customized bioinks optimized for different skin layers. Herein, different gelatin methacrylate (GelMA)/nano-cellulose (BNC) bioink formulations were used to develop heterogeneous tissue-engineered skin (HTS) containing layers of fibroblast networks with larger pores, basal layers with smaller pores, and multilayered keratinocytes. The results revealed that the 10%GelMA/0.3%BNC bioink was better to model bioprinted dermis due to its high printability and cell-friendly sparse microenvironment. Additionally, the 10%GelMA/1.5%BNC bioink as the basal layer presented a dense network and sufficient material stiffness to support the establishment of keratinocyte confluent monolayers. The HTS not only had the ability to remodel the extracellular matrix but also supported epidermis reconstruction and stratification in vitro, with the epidermal thickness growing to 80 μm after 14 days. Furthermore, the full-thickness wound healing experiments demonstrated that the HTS promoted granulation tissue regeneration and improved wound healing quality. The generated skin of the HTS group had hair follicles and early-stage rete ridge structures, which were similar to normal skin in vivo. The HTS may deliver effective skin grafts for future clinical treatments.

Research Progress of Three-Dimensional Bioprinting Artificial Cardiac Tissue

Cardiovascular disease is one of the main diseases that endanger human life and health, and heart failure often occurs when the cardiovascular disease develops to the end-stage. Heart transplantation is the most effective treatment. However, there has always been a shortage of living heart organs. With the development of regenerative medicine, researchers have turned to bioprinting technology that can build tissues and organs in vitro. A large number of relevant literature on three-dimensional (3D) bioprinted hearts were searched and screened in Google Scholar. 3D bioprinting technology can accurately print biomaterials containing living cells into 3D functional living tissues, providing a feasible solution to the shortage of transplantable organs. As one of the most important organs in the human body, the research on 3D bioprinting of the heart has currently become a hot topic. This paper briefly overviews 3D bioprinting technology and the progress in bioprinting cardiac tissue. It is believed that in the future, bio-printed hearts will become a reality, making a new way of providing artificial organs for heart transplantation.

Stereolithography apparatus and digital light processing-based 3D bioprinting for tissue fabrication

Three-dimensional (3D) bioprinting has emerged as a class of promising techniques in biomedical research for a wide range of related applications. Specifically, stereolithography apparatus (SLA) and digital light processing (DLP)-based vat-polymerization techniques are highly effective methods of bioprinting, which can be used to produce high-resolution and architecturally sophisticated structures. Our review aims to provide an overview of SLA- and DLP-based 3D bioprinting strategies, starting from factors that affect these bioprinting processes. In addition, we summarize the advances in bioinks used in SLA and DLP, including naturally derived and synthetic bioinks. Finally, the biomedical applications of both SLA- and DLP-based bioprinting are discussed, primarily centered on regenerative medicine and tissue modeling engineering.

Fabrication and Characterization Techniques of In Vitro 3D Tissue Models

The culturing of cells in the laboratory under controlled conditions has always been crucial for the advancement of scientific research. Cell-based assays have played an important role in providing simple, fast, accurate, and cost-effective methods in drug discovery, disease modeling, and tissue engineering while mitigating reliance on cost-intensive and ethically challenging animal studies. The techniques involved in culturing cells are critical as results are based on cellular response to drugs, cellular cues, external stimuli, and human physiology. In order to establish in vitro cultures, cells are either isolated from normal or diseased tissue and allowed to grow in two or three dimensions. Two-dimensional (2D) cell culture methods involve the proliferation of cells on flat rigid surfaces resulting in a monolayer culture, while in three-dimensional (3D) cell cultures, the additional dimension provides a more accurate representation of the tissue milieu. In this review, we discuss the various methods involved in the development of 3D cell culture systems emphasizing the differences between 2D and 3D systems and methods involved in the recapitulation of the organ-specific 3D microenvironment. In addition, we discuss the latest developments in 3D tissue model fabrication techniques, microfluidics-based organ-on-a-chip, and imaging as a characterization technique for 3D tissue models.

Recent Developments in 3D Bio-Printing and Its Biomedical Applications

The fast-developing field of 3D bio-printing has been extensively used to improve the usability and performance of scaffolds filled with cells. Over the last few decades, a variety of tissues and organs including skin, blood vessels, and hearts, etc., have all been produced in large quantities via 3D bio-printing. These tissues and organs are not only able to serve as building blocks for the ultimate goal of repair and regeneration, but they can also be utilized as in vitro models for pharmacokinetics, drug screening, and other purposes. To further 3D-printing uses in tissue engineering, research on novel, suitable biomaterials with quick cross-linking capabilities is a prerequisite. A wider variety of acceptable 3D-printed materials are still needed, as well as better printing resolution (particularly at the nanoscale range), speed, and biomaterial compatibility. The aim of this study is to provide expertise in the most prevalent and new biomaterials used in 3D bio-printing as well as an introduction to the associated approaches that are frequently considered by researchers. Furthermore, an effort has been made to convey the most pertinent implementations of 3D bio-printing processes, such as tissue regeneration, etc., by providing the most significant research together with a comprehensive list of material selection guidelines, constraints, and future prospects.