Cell encapsulation in gelatin bioink impairs 3D bioprinting resolution

Advances in 3D bioprinting for regenerative medicine applications

Biofabrication techniques allow for the construction of biocompatible and biofunctional structures composed from biomaterials, cells and biomolecules. Bioprinting is an emerging 3D printing method which utilizes biomaterial-based mixtures with cells and other biological constituents into printable suspensions known as bioinks. Coupled with automated design protocols and based on different modes for droplet deposition, 3D bioprinters are able to fabricate hydrogel-based objects with specific architecture and geometrical properties, providing the necessary environment that promotes cell growth and directs cell differentiation towards application-related lineages. For the preparation of such bioinks, various water-soluble biomaterials have been employed, including natural and synthetic biopolymers, and inorganic materials. Bioprinted constructs are considered to be one of the most promising avenues in regenerative medicine due to their native organ biomimicry. For a successful application, the bioprinted constructs should meet particular criteria such as optimal biological response, mechanical properties similar to the target tissue, high levels of reproducibility and printing fidelity, but also increased upscaling capability. In this review, we highlight the most recent advances in bioprinting, focusing on the regeneration of various tissues including bone, cartilage, cardiovascular, neural, skin and other organs such as liver, kidney, pancreas and lungs. We discuss the rapidly developing co-culture bioprinting systems used to resemble the complexity of tissues and organs and the crosstalk between various cell populations towards regeneration. Moreover, we report on the basic physical principles governing 3D bioprinting, and the ideal bioink properties based on the biomaterials' regenerative potential. We examine and critically discuss the present status of 3D bioprinting regarding its applicability and current limitations that need to be overcome to establish it at the forefront of artificial organ production and transplantation.

DeepFreeze 3D-biofabrication for Bioengineering and Storage of Stem Cells in Thick and Large-Scale Human Tissue Analogs

3D bioprinting holds great promise for meeting the increasing need for transplantable tissues and organs. However, slow printing, interlayer mixing, and the extended exposure of cells to non-physiological conditions in thick structures still hinder clinical applications. Here the DeepFreeze-3D (DF-3D) procedure and bioink for creating multilayered human-scale tissue mimetics is presented for the first time. The bioink is tailored to support stem cell viability, throughout the rapid freeform DF-3D biofabrication process. While the printer nozzle is warmed to room temperature, each layer solidifies at contact with the stage (-80 °C), or the subsequent layers, ensuring precise separation. After thawing, the encapsulated stem cells remain viable without interlayer mixing or delamination. The composed cell-laden constructs can be cryogenically stored and thawed when needed. Moreover, it is shown that under inductive conditions the stem cells differentiate into bone-like cells and grow for months after thawing, to form large tissue-mimetics in the scale of centimeters. This is important, as this approach allows the generation and storage of tissue mimetics in the size and thickness of human tissues. Therefore, DF-3D biofabrication opens new avenues for generating off-the-shelf human tissue analogs. It further holds the potential for regenerative treatments and for studying tissue pathologies caused by disease, tumor, or trauma.

Prediction of Clinical Precision Chemotherapy by Patient-Derived 3D Bioprinting Models of Colorectal Cancer and Its Liver Metastases

Methods accurately predicting the responses of colorectal cancer (CRC) and colorectal cancer liver metastasis (CRLM) to personalized chemotherapy remain limited due to tumor heterogeneity. This study introduces an innovative patient-derived CRC and CRLM tumor model for preclinical investigation, utilizing 3d-bioprinting (3DP) technology. Efficient construction of homogeneous in vitro 3D models of CRC/CRLM is achieved through the application of patient-derived primary tumor cells and 3D bioprinting with bioink. Genomic and histological analyses affirm that the CRC/CRLM 3DP tumor models effectively retain parental tumor biomarkers and mutation profiles. In vitro tests evaluating chemotherapeutic drug sensitivities reveal substantial tumor heterogeneity in chemotherapy responses within the 3DP CRC/CRLM models. Furthermore, a robust correlation is evident between the drug response in the CRLM 3DP model and the clinical outcomes of neoadjuvant chemotherapy. These findings imply a significant potential for the application of patient-derived 3DP cancer models in precision chemotherapy prediction and preclinical research for CRC/CRLM.

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.

Rise of tissue- and species-specific 3D bioprinting based on decellularized extracellular matrix-derived bioinks and bioresins

Thanks to its natural complexity and functionality, decellularized extracellular matrix (dECM) serves as an excellent foundation for creating highly cell-compatible bioinks and bioresins. This enables the bioprinted cells to thrive in an environment that closely mimics their native ECM composition and offers customizable biomechanical properties. To formulate dECM bioinks and bioresins, one must first pulverize and/or solubilize the dECM into non-crosslinked fragments, which can then be chemically modified as needed. In bioprinting, the solubilized dECM-derived material is typically deposited and/or crosslinked in a layer-by-layer fashion to build 3D hydrogel structures. Since the introduction of the first liver-derived dECM-based bioinks, a wide variety of decellularized tissue have been employed in bioprinting, including kidney, heart, cartilage, and adipose tissue among others. This review aims to summarize the critical steps involved in tissue-derived dECM bioprinting, starting from the decellularization of the ECM to the standardized formulation of bioinks and bioresins, ultimately leading to the reproducible bioprinting of tissue constructs. Notably, this discussion also covers photocrosslinkable dECM bioresins, which are particularly attractive due to their ability to provide precise spatiotemporal control over the gelation in bioprinting. Both in extrusion printing and vat photopolymerization, there is a need for more standardized protocols to fully harness the unique properties of dECM-derived materials. In addition to mammalian tissues, the most recent bioprinting approaches involve the use of microbial extracellular polymeric substances in bioprinting of bacteria. This presents similar challenges as those encountered in mammalian cell printing and represents a fascinating frontier in bioprinting technology.

Cell encapsulation in gelatin methacryloyl bioinks impairs microscale diffusion properties

Light-assisted bioprinted gelatin methacryloyl (GelMA) constructs have been used for cell-laden microtissues and organoids. GelMA can be loaded by desired cells, which can regulate the biophysical properties of bioprinted constructs. We study how the degree of methacrylation (MA degree), GelMA mass concentration, and cell density change mass transport properties. We introduce a fluorescent-microscopy-based method of biotransport testing with improved sensitivity compared to the traditional particle tracking methods. The diffusion capacity of GelMA with a higher MA significantly decreased compared to a lower MA. Opposed to a steady range of linear elastic moduli, the diffusion coefficient in GelMA varied when cell densities ranged from 0 to 10 × 106 cells/ml. A comparative study of different cell sizes showed a higher diffusivity coefficient for the case of larger cells. The results of this study can help bioengineers and scientists to better control the biotransport characteristics in light-assisted bioprinted microtissues and organoids.

Fabrication and characterization of bioprints with Lactobacillus crispatus for vaginal application

Bacterial vaginosis (BV) is characterized by low levels of lactobacilli and overgrowth of potential pathogens in the female genital tract. Current antibiotic treatments often fail to treat BV in a sustained manner, and > 50% of women experience recurrence within 6 months post-treatment. Recently, lactobacilli have shown promise for acting as probiotics by offering health benefits in BV. However, as with other active agents, probiotics often require intensive administration schedules incurring difficult user adherence. Three-dimensional (3D)-bioprinting enables fabrication of well-defined architectures with tunable release of active agents, including live mammalian cells, offering the potential for long-acting probiotic delivery. One promising bioink, gelatin alginate has been previously shown to provide structural stability, host compatibility, viable probiotic incorporation, and cellular nutrient diffusion. This study formulates and characterizes 3D-bioprinted Lactobacillus crispatus-containing gelatin alginate scaffolds for gynecologic applications. Different weight to volume (w/v) ratios of gelatin alginate were bioprinted to determine formulations with highest printing resolution, and different crosslinking reagents were evaluated for effect on scaffold integrity via mass loss and swelling measurements. Post-print viability, sustained-release, and vaginal keratinocyte cytotoxicity assays were conducted. A 10:2 (w/v) gelatin alginate formulation was selected based on line continuity and resolution, while degradation and swelling experiments demonstrated greatest structural stability with dual genipin and calcium crosslinking, showing minimal mass loss and swelling over 28 days. 3D-bioprinted L. crispatus-containing scaffolds demonstrated sustained release and proliferation of live bacteria over 28 days, without impacting viability of vaginal epithelial cells. This study provides in vitro evidence for 3D-bioprinted scaffolds as a novel strategy to sustain probiotic delivery with the ultimate goal of restoring vaginal lactobacilli following microbiological disturbances.

Cell Encapsulation and 3D Bioprinting for Therapeutic Cell Transplantation

The promise of cell therapy has been augmented by introducing biomaterials, where intricate scaffold shapes are fabricated to accommodate the cells within. In this review, we first discuss cell encapsulation and the promising potential of biomaterials to overcome challenges associated with cell therapy, particularly cellular function and longevity. More specifically, cell therapies in the context of autoimmune disorders, neurodegenerative diseases, and cancer are reviewed from the perspectives of preclinical findings as well as available clinical data. Next, techniques to fabricate cell-biomaterials constructs, focusing on emerging 3D bioprinting technologies, will be reviewed. 3D bioprinting is an advancing field that enables fabricating complex, interconnected, and consistent cell-based constructs capable of scaling up highly reproducible cell-biomaterials platforms with high precision. It is expected that 3D bioprinting devices will expand and become more precise, scalable, and appropriate for clinical manufacturing. Rather than one printer fits all, seeing more application-specific printer types, such as a bioprinter for bone tissue fabrication, which would be different from a bioprinter for skin tissue fabrication, is anticipated in the future.

Thermo-Responsive Nanocomposite Bioink with Growth-Factor Holding and its Application to Bone Regeneration

Three-dimensional (3D) bioprinting, which is being increasingly used in tissue engineering, requires bioinks with tunable mechanical properties, biological activities, and mechanical strength for in vivo implantation. Herein, a growth-factor-holding poly(organophosphazene)-based thermo-responsive nanocomposite (TNC) bioink system is developed. The mechanical properties of the TNC bioink are easily controlled within a moderate temperature range (5-37 °C). During printing, the mechanical properties of the TNC bioink, which determine the 3D printing resolution, can be tuned by varying the temperature (15-30 °C). After printing, TNC bioink scaffolds exhibit maximum stiffness at 37 °C. Additionally, because of its shear-thinning and self-healing properties, TNC bioinks can be extruded smoothly, demonstrating good printing outcomes. TNC bioink loaded with bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta1 (TGF-β1), key growth factors for osteogenesis, is used to print a scaffold that can stimulate biological activity. A biological scaffold printed using TNC bioink loaded with both growth factors and implanted on a rat calvarial defect model reveals significantly improved bone regenerative effects. The TNC bioink system is a promising next-generation bioink platform because its mechanical properties can be tuned easily for high-resolution 3D bioprinting with long-term stability and its growth-factor holding capability has strong clinical applicability.

Egg white improves the biological properties of an alginate-methylcellulose bioink for 3D bioprinting of volumetric bone constructs

Three-dimensional microextrusion bioprinting has attracted great interest for fabrication of hierarchically structured, functional tissue substitutes with spatially defined cell distribution. Despite considerable progress, several significant limitations remain such as a lack of suitable bioinks which combine favorable cell response with high shape fidelity. Therefore, in this work a novel bioink of alginate-methylcellulose (AlgMC) blend functionalized with egg white (EW) was developed with the aim of solving this limitation. In this regard, a stepwise strategy was proposed to improve and examine the cell response in low-viscosity alginate inks (3%, w/v) with different EW concentrations, and in high-viscosity inks after gradual methylcellulose addition for enhancing printability. The rheological properties and printability of these cell-responsive bioinks were characterized to obtain an optimized formulation eliciting balanced physicochemical and biological properties for fabrication of volumetric scaffolds. The bioprinted AlgMC + EW constructs exhibited excellent shape fidelity while encapsulated human mesenchymal stem cells showed high post-printing viability as well as adhesion and spreading within the matrix. In a proof-of-concept experiment, the impact of these EW-mediated effects on osteogenesis of bioprinted primary human pre-osteoblasts (hOB) was evaluated. Results confirmed a high viability of hOB (93.7 ± 0.15%) post-fabrication in an EW-supported AlgMC bioink allowing cell adhesion, proliferation and migration. EW even promoted the expression of osteogenic genes, coding for bone sialoprotein (integrin binding sialoprotein/bone sialoprotein precursor (IBSP)) and osteocalcin (BGLAP) on mRNA level. To demonstrate the suitability of the novel ink for future fabrication of multi-zonal bone substitutes, AlgMC + EW was successfully co-printed together with a pasty calcium phosphate bone cement biomaterial ink to achieve a partly mineralized 3D volumetric environment with good cell viability and spreading. Along with the EW-mediated positive effects within bioprinted AlgMC-based scaffolds, this highlighted the promising potential of this novel ink for biofabrication of bone tissue substitutes in clinically relevant dimensions.

Advances in the development of tubular structures using extrusion-based 3D cell-printing technology for vascular tissue regenerative applications

Until recent, there are no ideal small diameter vascular grafts available on the market. Most of the commercialized vascular grafts are used for medium to large-sized blood vessels. As a solution, vascular tissue engineering has been introduced and shown promising outcomes. Despite these optimistic results, there are limitations to commercialization. This review will cover the need for extrusion-based 3D cell-printing technique capable of mimicking the natural structure of the blood vessel. First, we will highlight the physiological structure of the blood vessel as well as the requirements for an ideal vascular graft. Then, the essential factors of 3D cell-printing including bioink, and cell-printing system will be discussed. Afterwards, we will mention their applications in the fabrication of tissue engineered vascular grafts. Finally, conclusions and future perspectives will be discussed.

Rheological characterization of cell-laden alginate-gelatin hydrogels for 3D biofabrication

Biofabrication of tissue models that closely mimic the tumor microenvironment is necessary for high-throughput anticancer therapeutics. Extrusion-based bioprinting of heterogeneous cell-laden hydrogels has shown promise in advancing rapid artificial tissue development. A major bottleneck limiting the rapid production of physiologically relevant tissue models is the current limitation in effectively printing large populations of cells. However, by significantly increasing hydrogel cell-seeding densities, the time required to produce tissues could be effectively reduced. Here, we explore the effects of increasing cell seeding densities on the viscoelastic properties, printability, and cell viability of two different alginate-gelatin hydrogel compositions. Rheological analysis of hydrogels of varying cell seeding densities reveals an inverse relationship between cell concentration and zero-shear viscosity. We also observe that as cell seeding densities increases, the storage moduli decrease, thus lowering the required printing pressures for gel extrusion. We also observe that increasing cell concentration can negatively impact the structural properties of the extruded material by increasing post-print line spreading. We find that hydrogels composed of higher molecular weight alginates and the highest cell-seeding densities (107 cells/mL) yield higher cell viability (>80%) and structural uniformity after printing. The optimized printing parameters determined for the alginate-gelatin bioinks explored may aid in the future rapid fabrication of functional tissue models for therapeutic screening.

Extrusion of Cell Encapsulated in Boron Nitride Nanotubes Reinforced Gelatin—Alginate Bioink for 3D Bioprinting

Three-dimensional (3D) bioprinting, an innovative technology, has gained the attention of researchers as a promising technique for the redevelopment of complex tissue or organ structures. Despite significant advancements, a major challenge in 3D bioprinting is the limited number of suitable bioinks that fulfil the physiochemical requirements to produce complicated structures. Therefore, there is a demand for the production of bioinks for 3D bioprinting techniques. In this short communication, THP-1 cells encapsulated in boron nitride nanotubes (BNNTs) reinforced gelatin and alginate bioink was prepared. The study investigated the impact on the cells during printing using a fluorescence cell image. The results showed that the pure polymer bioinks demonstrated poor printability properties with the incorporation of cells. However, BNNT-combined bioink showed a significant increase in structural integrity even after the incorporation of cells. Furthermore, the scaffold structure was successfully printed with the cells incorporated bioink, and a considerable number of live cells were observed. With further studies, BNNTs as a promising nanomaterial for formulating bioink encapsulated with cells can be understood fully.

Gelatin-methacryloyl hydrogels containing turnip mosaic virus for fabrication of nanostructured materials for tissue engineering

Current tissue engineering techniques frequently rely on hydrogels to support cell growth, as these materials strongly mimic the extracellular matrix. However, hydrogels often need ad hoc customization to generate specific tissue constructs. One popular strategy for hydrogel functionalization is to add nanoparticles to them. Here, we present a plant viral nanoparticle the turnip mosaic virus (TuMV), as a promising additive for gelatin methacryloyl (GelMA) hydrogels for the engineering of mammalian tissues. TuMV is a flexuous, elongated, tubular protein nanoparticle (700–750 nm long and 12–15 nm wide) and is incapable of infecting mammalian cells. These flexuous nanoparticles spontaneously form entangled nanomeshes in aqueous environments, and we hypothesized that this nanomesh structure could serve as a nanoscaffold for cells. Human fibroblasts loaded into GelMA-TuMV hydrogels exhibited similar metabolic activity to that of cells loaded in pristine GelMA hydrogels. However, cells cultured in GelMA-TuMV formed clusters and assumed an elongated morphology in contrast to the homogeneous and confluent cultures seen on GelMA surfaces, suggesting that the nanoscaffold material per se did not favor cell adhesion. We also covalently conjugated TuMV particles with epidermal growth factor (EGF) using a straightforward reaction scheme based on a Staudinger reaction. BJ cells cultured on the functionalized scaffolds increased their confluency by approximately 30% compared to growth with unconjugated EGF. We also provide examples of the use of GelMA-TuMV hydrogels in different biofabrication scenarios, include casting, flow-based-manufacture of filaments, and bioprinting. We envision TuMV as a versatile nanobiomaterial that can be useful for tissue engineering.

Extrusion 3D bioprinting of functional self-supporting neural constructs using a photoclickable gelatin bioink

Many in vitro models of neural physiology utilize neuronal networks established on two-dimensional substrates. Despite the simplicity of these 2D neuronal networks, substrate stiffness may influence cell morphology, network interactions and how neurons communicate and function. With this perspective, 3D gel encapsulation is a powerful to recapitulating aspects of in vivo features, yet such an approach is often limited in terms of the level of resolution and feature size relevant for modelling aspects of brain architecture. Here, we report 3D bioplotting of rat primary cortical neural cells using a hydrogel system comprising gelatin norbornene (GelNB) and poly (ethylene glycol) dithiol (PEGdiSH). This bioink benefits from a rapid photo-click chemistry, yielding 8-layer crosshatch neural scaffolds and a filament width of 350 µm. The printability of this system depends on hydrogel concentration, printing temperature, extrusion pressure and speed. These parameters were studied via quantitative comparison between rheology and filament dimensions to determine the optimal printing conditions. Under optimal conditions, cell viability of bioprinted primary cortical neurons at day 1 (68 ± 2%) and at day 7 (68 ± 1%) were comparable to the 2D control group (72 ± 7%). The present study relates material rheology and filament dimensions to generate compliant free-standing neural constructs through bioplotting of low-concentration GelNB-PEGdiSH, which may provide a step forward to study 3D neuronal function and network formation.

Natural Hydrogel-Based Bio-Inks for 3D Bioprinting in Tissue Engineering: A Review

Three-dimensional (3D) printing is well acknowledged to constitute an important technology in tissue engineering, largely due to the increasing global demand for organ replacement and tissue regeneration. In 3D bioprinting, which is a step ahead of 3D biomaterial printing, the ink employed is impregnated with cells, without compromising ink printability. This allows for immediate scaffold cellularization and generation of complex structures. The use of cell-laden inks or bio-inks provides the opportunity for enhanced cell differentiation for organ fabrication and regeneration. Recognizing the importance of such bio-inks, the current study comprehensively explores the state of the art of the utilization of bio-inks based on natural polymers (biopolymers), such as cellulose, agarose, alginate, decellularized matrix, in 3D bioprinting. Discussions regarding progress in bioprinting, techniques and approaches employed in the bioprinting of natural polymers, and limitations and prospects concerning future trends in human-scale tissue and organ fabrication are also presented.

Bioink Rheology Regulates Stability of Bioprinted Strands

Extrusion three-dimensional (3D) bioprinting typically requires an ad-hoc trial-and-error optimization of the bioink composition towards enhanced resolution. The bioink solutions are solidified after leaving cone-shaped or cylindrical nozzles. The presence of bioink instability not only hampers the extrusion resolution but also affects the behavior of embedded cellular components. This is a key factor in selecting bioinks and bioprinting design parameters for well-established desktop and handheld bioprinters. In this work, we developed an analytical solution for the process of bioink deposition and compared its predictions against numerical simulations of the deposition. We estimated the onset of bioink instability as a function of bioink rheological properties and nozzle geometry. Both analytical and simulation results demonstrated that enhancing shear-thinning behavior of the bioink stabilizes the printing process whereas bioink shear-thickening behavior induces an opposite effect through extending the toe region of the deposition. The present study serves as a benchmark for detailed simulations of the extrusion process for optimal bioprinting.

Exploring the Patent Landscape and Innovation of Hydrogel-based Bioinks Used for 3D Bioprinting

BACKGROUND

This paper provides a comprehensive overview of the patent situation for hydrogel- based bioinks used for 3D bioprinting globally. It encapsulates information which could be used as a reference by researchers in the fields of 3D bioprinting, biomaterials, tissue engineering, and biomedical engineering, as well as those interested in biomaterials, especially in the formulation of hydrogels. It can also inform policy discussions, strategic research planning, or technology transfer in this area. The findings presented hereinafter are considered novel research aspects regarding the used hydrogels, their preparation methods, and their formulations, as well as the 3D bioprinting process using hydrogels. Furthermore, the novel part, synthesized patents, is regarded as a breakthrough in hydrogel- based bioinks.

METHODS

The following research aspects of this study are based on data collection from selected patent databases. The search results are then analyzed according to publication years, classification, inventors, applicants, and owners, as well as jurisdictions.

RESULTS

Based on the earliest priority date, it is possible to precisely assume that 2004 is considered the starting year of patenting of hydrogel-based bioinks. Furthermore, 2020 was the year with the most patent documents. According to the findings, the United States, China, and the Republic of Korea are the most prolific countries in terms of patenting on hydrogel-based bioinks. The most prolific patenting companies are from the United States, Sweden, and Australia, while universities from the Republic of Korea and the United States are the academic institutions leading the way. Most inventions of hydrogel- based bioinks intended for hydrogels or hydrocolloids used as materials for prostheses or for coating prostheses are characterized by their function or physical properties.

CONCLUSION

The state has been reviewed by introducing what has been patented concerning hydrogelbased bioinks. Knowledge clusters and expert driving factors indicate that the research based on biomaterials, tissue engineering, and biofabrication is concentrated in the most common patent documents. Finally, this paper, which gives a competitive analysis of the past, present, and future trends in hydrogel-based bioinks, leads to various recommendations that could help one to plan and innovate research strategies.

Multi-material digital light processing bioprinting of hydrogel-based microfluidic chips

Recent advancements in digital-light-processing (DLP)-based bioprinting and hydrogel engineering have enabled novel developments in organs-on-chips. In this work, we designed and developed a multi-material, DLP-based bioprinter for rapid, one-step prototyping of hydrogel-based microfluidic chips. A composite hydrogel bioink based on poly-ethylene-glycol-diacrylate (PEGDA) and gelatin methacryloyl (GelMA) was optimized through varying the bioprinting parameters such as light exposure time, bioink composition, and layer thickness. We showed a wide range of mechanical properties of the microfluidic chips for various ratios of PEGDA:GelMA. Microfluidic features of hydrogel-based chips were then tested using dynamic flow experiments. Human-derived tumor cells were encapsulated in 3D bioprinted structures to demonstrate their bioactivity and cell-friendly environment. Cell seeding experiments then validated the efficacy of the selected bioinks for vascularized micro-tissues. Our biofabrication approach offers a useful tool for the rapid integration of micro-tissue models into organs-on-chips and high-throughput drug screening platforms.

Double network laminarin-boronic/alginate dynamic bioink for 3D bioprinting cell-laden constructs

The design of dynamically crosslinked hydrogel bioinks for three-dimensional (3D) bioprinting is emerging as a valuable strategy to advance the fabrication of mechanically tuneable cell-laden constructs for 3Din vitrodisease modelling and tissue engineering applications. Herein, a dynamic bioink comprising boronic acid-functionalised laminarin and alginate is explored for bioprinting 3D constructs under physiologically relevant conditions. The formulated bioink takes advantage of a double crosslinked network that combines covalent but reversible boronate ester bonds and ionic gelation via divalent cations. Moreover, it exhibits suitable rheological properties and improved mechanical features owing to its modular crosslinking chemistry, yielding stable constructs with user-programmable architecture. We explored such dynamic bioink as a supporting matrix for different cell classes, namely osteoblast precursors, fibroblasts and breast cancer cells. The resulting cell-laden bioprinted hydrogels display a homogeneous cell distribution post-printing and exceptional cell viability (>90%) that can be maintained for prolonged time periods in culture (14 days) for all cell lines. This simple and chemically versatile approach is envisaged to accelerate the development of multifunctional bioinks and contribute towards the fabrication of biomimetic 3D scaffolds with applicability in a wide range of predictive or exploratory biomedical platforms.

Advances in 3D bioprinting technology for cardiac tissue engineering and regeneration

Cardiovascular disease is still one of the leading causes of death in the world, and heart transplantation is the current major treatment for end-stage cardiovascular diseases. However, because of the shortage of heart donors, new sources of cardiac regenerative medicine are greatly needed. The prominent development of tissue engineering using bioactive materials has creatively laid a direct promising foundation. Whereas, how to precisely pattern a cardiac structure with complete biological function still requires technological breakthroughs. Recently, the emerging three-dimensional (3D) bioprinting technology for tissue engineering has shown great advantages in generating micro-scale cardiac tissues, which has established its impressive potential as a novel foundation for cardiovascular regeneration. Whether 3D bioprinted hearts can replace traditional heart transplantation as a novel strategy for treating cardiovascular diseases in the future is a frontier issue. In this review article, we emphasize the current knowledge and future perspectives regarding available bioinks, bioprinting strategies and the latest outcome progress in cardiac 3D bioprinting to move this promising medical approach towards potential clinical implementation.

Printability in extrusion bioprinting

Extrusion bioprinting has been widely used to extrude continuous filaments of bioink (or the mixture of biomaterial and living cells), layer-by-layer, to build three-dimensional (3D) constructs for biomedical applications. In extrusion bioprinting, printability is an important parameter used to measure the difference between the designed construct and the one actually printed. This difference could be caused by the extrudability of printed bioink and/or the structural formability and stability of printed constructs. Although studies have reported in characterizing printability based on the bioink properties and printing process, the concept of printability is often confusingly and, sometimes, conflictingly used in the literature. The objective of this perspective is to define the printability for extrusion bioprinting in terms of extrudability, filament fidelity, and structural integrity, as well as to review the effect of bioink properties, bioprinting process, and construct design on the printability. Challenges related to the printability of extrusion bioprinting are also discussed, along with recommendations for improvements.

Cell preservation methods and its application to studying rare disease

The ability to preserve and transport human cells in a stable medium over long distances is critical to collaborative efforts and the advancement of knowledge in the study of human disease. This is particularly important in the study of rare diseases. Recently, advancements in the understanding of renal ciliopathies has been achieved via the use of patient urine-derived cells (UDCs). However, the traditional method of cryopreservation, although considered as the gold standard, can result in decreased sample viability of many cell types, including UDCs. Delays in transportation can have devastating effects upon the viability of samples, and may even result in complete destruction of cells following evaporation of dry ice or liquid nitrogen, leaving samples in cryoprotective agents, which are cytotoxic at room temperature. The loss of any patient sample in this manner is detrimental to research, however it is even more so when samples are from patients with a rare disease. In order to overcome the associated limitations of traditional practices, new methods of preservation and shipment, including cell encapsulation within hydrogels, and transport in specialised devices are continually being investigated. Here we summarise and compare traditional methods with emerging novel alternatives for the preservation and shipment of cells, and consider the effectiveness of such methods for use with UDCs to further enable the study and understanding of kidney diseases.

Biomechanical factors in three-dimensional tissue bioprinting

3D bioprinting techniques have shown great promise in various fields of tissue engineering and regenerative medicine. Yet, creating a tissue construct that faithfully represents the tightly regulated composition, microenvironment, and function of native tissues is still challenging. Among various factors, biomechanics of bioprinting processes play fundamental roles in determining the ultimate outcome of manufactured constructs. This review provides a comprehensive and detailed overview on various biomechanical factors involved in tissue bioprinting, including those involved in pre, during, and post printing procedures. In preprinting processes, factors including viscosity, osmotic pressure, and injectability are reviewed and their influence on cell behavior during the bioink preparation is discussed, providing a basic guidance for the selection and optimization of bioinks. In during bioprinting processes, we review the key characteristics that determine the success of tissue manufacturing, including the rheological properties and surface tension of the bioink, printing flow rate control, process-induced mechanical forces, and the in situ cross-linking mechanisms. Advanced bioprinting techniques, including embedded and multi-material printing, are explored. For post printing steps, general techniques and equipment that are used for characterizing the biomechanical properties of printed tissue constructs are reviewed. Furthermore, the biomechanical interactions between printed constructs and various tissue/cell types are elaborated for both in vitro and in vivo applications. The review is concluded with an outlook regarding the significance of biomechanical processes in tissue bioprinting, presenting future directions to address some of the key challenges faced by the bioprinting community.

Screen Printing to Create 3D Tissue Models

3D printing has revolutionized making tissue models, but the instruments are often quite expensive, and the approach can involve heat and/or shear forces that can damage cells. As a complement to more traditional 3D printing approaches, we looked at screen printing. Screen printing is an additive manufacturing technique used to pattern inks through screens supporting patterns onto different surfaces. It has a wide range of applications ranging from traditional printing to printing electric circuit boards. Taking cues from this we have developed a process of screen printing live cells along with a suitable scaffold on to different surfaces to generate in vitro models. The process is not only inexpensive and simple to use, but it also offers a wide range of advantages like the ability to use a range of bioinks limited only by their gelation time, printing on different surfaces, and the ability to autoclave all of the major components. In this paper, we present the screen assembly and the setup we used to print the cells along with the resolution and limits of features printed and the effect of the printing on the cells.

Guidelines for establishing a 3-D printing biofabrication laboratory

Advanced manufacturing and 3D printing are transformative technologies currently undergoing rapid adoption in healthcare, a traditionally non-manufacturing sector. Recent development in this field, largely enabled by merging different disciplines, has led to important clinical applications from anatomical models to regenerative bioscaffolding and devices. Although much research to-date has focussed on materials, designs, processes, and products, little attention has been given to the design and requirements of facilities for enabling clinically relevant biofabrication solutions. These facilities are critical to overcoming the major hurdles to clinical translation, including solving important issues such as reproducibility, quality control, regulations, and commercialization. To improve process uniformity and ensure consistent development and production, large-scale manufacturing of engineered tissues and organs will require standardized facilities, equipment, qualification processes, automation, and information systems. This review presents current and forward-thinking guidelines to help design biofabrication laboratories engaged in engineering model and tissue constructs for therapeutic and non-therapeutic applications.

Printability and Shape Fidelity of Bioinks in 3D Bioprinting

Three-dimensional bioprinting uses additive manufacturing techniques for the automated fabrication of hierarchically organized living constructs. The building blocks are often hydrogel-based bioinks, which need to be printed into structures with high shape fidelity to the intended computer-aided design. For optimal cell performance, relatively soft and printable inks are preferred, although these undergo significant deformation during the printing process, which may impair shape fidelity. While the concept of good or poor printability seems rather intuitive, its quantitative definition lacks consensus and depends on multiple rheological and chemical parameters of the ink. This review discusses qualitative and quantitative methodologies to evaluate printability of bioinks for extrusion- and lithography-based bioprinting. The physicochemical parameters influencing shape fidelity are discussed, together with their importance in establishing new models, predictive tools and printing methods that are deemed instrumental for the design of next-generation bioinks, and for reproducible comparison of their structural performance.

New gellan gum-graft-poly(d,l-lactide-co-glycolide) copolymers as promising bioinks: Synthesis and characterization

This research focused on the aim of tackling the urgent demand of printable biomaterials, hence we synthetized and characterized three gellan gum-graft-poly(d,l-lactide-co-glycolide) copolymers (GGm-PLGA a, b and c) which differed in the graft substitution degree. We investigated the effect of the polyester chain grafted onto hydrophilic backbone of gellan gum in terms of physicochemical properties and the ability of the system to print 3D cell laden constructs. In particular, we evaluated thermo-rheological, ionotropic crosslinking, shear thinning, swelling and stability properties of these copolymers and their derived biomaterials and findings related to the degree of functionalization. Moreover, the optimization of the 3D process parameters and the effect of different water/DPBS mixtures was investigated, demonstrating the feasibility of the system to print 3D constructs. Finally, biological tests revealed that fibroblasts and chondrocytes remained viable after printing and over a culture period of seven days into scaffolds.