The billion cell construct: will three-dimensional printing get us there?

A Microgel-Hydrogel Hybrid for Functional Compensation and Mechanical Stability in 3D Printed Cell-Dense Vascularized Liver Tissue

3D bioprinting of liver tissue with high cell density (HCD) shows great promise for restoring function in cases of acute liver failure, where a substantial number of functional cells are required to perform essential physiological tasks. Direct vascular anastomosis is critical for the successful implantation of these bioprinted vascularized tissues into the host vasculature, allowing for rapid functional compensation and addressing various acute conditions. However, conventional hydrogels used to encapsulate high-density cells often lack the mechanical properties needed to withstand the shear forces of physiological blood flow, often resulting in implantation failure. In this study, a heterogeneous microgel-hydrogel hybrid is developed to carry HCD hepatocytes and support the embedded bioprinting of hierarchical vascular structures. By optimizing the ratio of microgel to biomacromolecule, the covalently crosslinked network offers mechanical integrity and enables direct vascular anastomosis, ensuring efficient nutrient and oxygen exchange. The bioprinted thick, vascularized constructs, containing HCD hepatocytes, are successfully implanted in rats after 85% hepatectomy, leading to swift functional recovery and prolonged survival. This study presents a strategy to enhance regenerative therapy outcomes through advanced bioprinting and vascular integration techniques.

Meta-analysis of the make-up and properties of in vitro models of the healthy and diseased blood-brain barrier

In vitro models of the human blood-brain barrier (BBB) are increasingly used to develop therapeutics that can cross the BBB for treating diseases of the central nervous system. Here we report a meta-analysis of the make-up and properties of transwell and microfluidic models of the healthy BBB and of BBBs in glioblastoma, Alzheimer's disease, Parkinson's disease and inflammatory diseases. We found that the type of model, the culture method (static or dynamic), the cell types and cell ratios, and the biomaterials employed as extracellular matrix are all crucial to recapitulate the low permeability and high expression of tight-junction proteins of the BBB, and to obtain high trans-endothelial electrical resistance. Specifically, for models of the healthy BBB, the inclusion of endothelial cells and pericytes as well as physiological shear stresses (~10-20 dyne cm-2) are necessary, and when astrocytes are added, astrocytes or pericytes should outnumber endothelial cells. We expect this meta-analysis to facilitate the design of increasingly physiological models of the BBB.

Scalable tissue biofabrication via perfusable hollow fiber arrays for cultured meat applications

Creating perfusable channels within engineered tissues is crucial for the development of large-scale tissues. Unfortunately, existing technologies have not achieved uniformly distributed, perfusable networks on a large scale. To overcome this, we developed a method using a hollow fiber bioreactor (HFB) equipped with an array of closely packed semipermeable hollow fibers that function as artificial circulation systems, ensuring uniform nutrient and oxygen distribution throughout the tissue. Furthermore, the HFB includes microfabricated anchors for promoting cell alignment. When using active perfusion, biofabricated centimeter-scale chicken muscle tissue exhibited an elevated level of marker protein expression and sarcomere formation throughout the tissue, along with improved texture and flavor. In addition, a robotic-assisted fiber threading system was developed to achieve efficient assembly of the HFBs. Future full automation of this approach may revolutionize both the cultured meat industry and the tissue engineering field, which aims to create large-scale, tissue-engineered organs.

Three-dimensional bio-derived materials for biomedical applications: challenges and opportunities

Three-dimensional (3D) bio-derived materials are emerging as a promising approach to enhance wound healing therapies. These innovative materials can be tailored to meet the specific needs of various wound types and patients, facilitating the controlled release of therapeutic agents such as growth factors and antibiotics, which promote cell growth and tissue regeneration. Despite their potential, significant challenges remain in achieving optimal biocompatibility, ensuring structural integrity, and maintaining precise release mechanisms. Additionally, issues such as scalability, cost-effectiveness, and regulatory compliance pose substantial barriers to widespread use. However, recent advances in materials science and interdisciplinary research offer new opportunities to overcome these challenges. This review provides a comprehensive analysis of the current state of 3D bio-derived materials in biomedical applications, highlighting the types of materials available, their advantages and limitations, and the progress made in their design and development. It also outlines new directions for future research aimed at bridging the gap between scientific discoveries and their practical applications in injury healing strategies. The findings of this review underscore the significant potential of 3D bio-derived materials in revolutionizing wound healing and advancing personalized therapeutic approaches.

Extrusion bioprinting: meeting the promise of human tissue biofabrication?

Extrusion is the most popular bioprinting platform. Predictions of human tissue and whole-organ printing have been made for the technology. However, after decades of development, extruded constructs lack the essential microscale resolution and heterogeneity observed in most human tissues. Extrusion bioprinting has had little clinical impact with the majority of research directed away from the tissues most needed by patients. The distance between promise and reality is a result of technology hype and inherent design flaws that limit the shape, scale and survival of extruded features. By more widely adopting resolution innovations and softening its ambitions the biofabrication field could define a future for extrusion bioprinting that more closely aligns with its capabilities.

Mechanistic origins of temperature scaling in the early embryonic cell cycle

Temperature profoundly impacts organismal physiology and ecological dynamics, particularly affecting ectothermic species and making them especially vulnerable to climate changes. Although complex physiological processes usually involve dozens of enzymes, empirically it is found that the rates of these processes often obey the Arrhenius equation, which was originally proposed for individual chemical reactions. Here we have examined the temperature scaling of the early embryonic cell cycle, with the goal of understanding why the Arrhenius equation approximately holds and why it breaks down at temperature extremes. Using experimental data from Xenopus laevis, Xenopus tropicalis, and Danio rerio, plus published data from Caenorhabditis elegans, Caenorhabditis briggsae, and Drosophila melanogaster, we find that the apparent activation energies (E a values) for the early embryonic cell cycle for diverse ectotherms are all similar, 75 ± 7 kJ/mol (mean ± std.dev., n = 6), which corresponds to aQ 10 value at 20°C of 2.8 ± 0.2 (mean ± std.dev., n = 6). Using computational models, we find that the approximate Arrhenius scaling and the deviations from it at high and low temperatures can be accounted for by biphasic temperature scaling in critical individual components of the cell cycle oscillator circuit, by imbalances in theE a values for different partially rate-determining enzymes, or by a combination of both. Experimental studies of cycling Xenopus extracts indicate that both of these mechanisms contribute to the general scaling of temperature, and in vitro studies of individual cell cycle regulators confirm that there is in fact a substantial imbalance in theirE a values. These findings provide mechanistic insights into the dynamic interplay between temperature and complex biochemical processes, and into why biological systems fail at extreme temperatures.

SEGUID v2: Extending SEGUID checksums for circular, linear, single- and double-stranded biological sequences

Background

Synthetic biology involves combining different DNA fragments, each containing functional biological parts, to address specific problems. Fundamental gene-function research often requires cloning and propagating DNA fragments, such as those from the iGEM Parts Registry or Addgene, typically distributed as circular plasmids.Addgene's repository alone offers around 150,000 plasmids. To ensure data integrity, cryptographic checksums can be calculated for the sequences. Each sequence has a unique checksum, making checksums useful for validation and quick lookups of associated annotations. For example, the SEGUID checksum, uniquely identifies protein sequences with a 27-character string.

Objectives

The original SEGUID, while effective for protein sequences and single-stranded DNA (ssDNA), is not suitable for circular and double-stranded DNA (dsDNA) due to topological differences. Challenges include how to uniquely represent linear dsDNA, circular ssDNA, and circular dsDNA. To meet these needs, we propose SEGUID v2, which extends the original SEGUID to handle additional types of sequences.

Conclusions

SEGUID v2 produces orientation and rotation invariant checksums for single-stranded, double-stranded, possibly staggered, linear, and circular DNA and RNA sequences. Customizable alphabets allow for other types of sequences. In contrast to the original SEGUID, which uses Base64, SEGUID v2 uses Base64url to encode the SHA-1 hash. This ensures SEGUID v2 checksums can be used as-is in filenames, regardless of platform, and in URLs, with minimal friction.

Availability

SEGUID v2 is readily available for major programming languages, distributed under the MIT license. JavaScript package seguid is available on npm, Python package seguid on PyPi, R package seguid on CRAN, and a Tcl script on GitHub. These tools, along with documentation, examples, and an online SEGUID Calculator , can be found at https://www.seguid.org .

Bridging the Gap: Advances and Challenges in Heart Regeneration from In Vitro to In Vivo Applications

Cardiovascular diseases, particularly ischemic heart disease, area leading cause of morbidity and mortality worldwide. Myocardial infarction (MI) results in extensive cardiomyocyte loss, inflammation, extracellular matrix (ECM) degradation, fibrosis, and ultimately, adverse ventricular remodeling associated with impaired heart function. While heart transplantation is the only definitive treatment for end-stage heart failure, donor organ scarcity necessitates the development of alternative therapies. In such cases, methods to promote endogenous tissue regeneration by stimulating growth factor secretion and vascular formation alone are insufficient. Techniques for the creation and transplantation of viable tissues are therefore highly sought after. Approaches to cardiac regeneration range from stem cell injections to epicardial patches and interposition grafts. While numerous preclinical trials have demonstrated the positive effects of tissue transplantation on vasculogenesis and functional recovery, long-term graft survival in large animal models is rare. Adequate vascularization is essential for the survival of transplanted tissues, yet pre-formed microvasculature often fails to achieve sufficient engraftment. Recent studies report success in enhancing cell survival rates in vitro via tissue perfusion. However, the transition of these techniques to in vivo models remains challenging, especially in large animals. This review aims to highlight the evolution of cardiac patch and stem cell therapies for the treatment of cardiovascular disease, identify discrepancies between in vitro and in vivo studies, and discuss critical factors for establishing effective myocardial tissue regeneration in vivo.

Embedding Biomimetic Vascular Networks via Coaxial Sacrificial Writing into Functional Tissue

Printing human tissues and organs replete with biomimetic vascular networks is of growing interest. While it is possible to embed perfusable channels within acellular and densely cellular matrices, they do not currently possess the biomimetic architectures found in native vessels. Here, coaxial sacrificial writing into functional tissues (co-SWIFT) is developed, an embedded bioprinting method capable of generating hierarchically branching, multilayered vascular networks within both granular hydrogel and densely cellular matrices. Coaxial printheads are designed with an extended core-shell configuration to facilitate robust core-core and shell-shell interconnections between printed branching vessels during embedded bioprinting. Using optimized core-shell ink combinations, biomimetic vessels composed of a smooth muscle cell-laden shell that surrounds perfusable lumens are coaxially printed into granular matrices composed of: 1) transparent alginate microparticles, 2) sacrificial microparticle-laden collagen, or 3) cardiac spheroids derived from human induced pluripotent stem cells. Biomimetic blood vessels that exhibit good barrier function are produced by seeding these interconnected lumens with a confluent layer of endothelial cells. Importantly, it is found that co-SWIFT cardiac tissues mature under perfusion, beat synchronously, and exhibit a cardio-effective drug response in vitro. This advance opens new avenues for the scalable biomanufacturing of vascularized organ-specific tissues for drug testing, disease modeling, and therapeutic use.

Efficient fabrication of 3D bioprinted functional sensory neurons using an inducible Neurogenin-2 human pluripotent stem cell line

Three-dimensional (3D) tissue models have gained recognition for their improved ability to mimic the native cell microenvironment compared to traditional two-dimensional models. This progress has been driven by advances in tissue-engineering technologies such as 3D bioprinting, a promising method for fabricating biomimetic living tissues. While bioprinting has succeeded in generating various tissues to date, creating neural tissue models remains challenging. In this context, we present an accelerated approach to fabricate 3D sensory neuron (SN) structures using a transgenic human pluripotent stem cell (hPSC)-line that contains an inducible Neurogenin-2 (NGN2) expression cassette. The NGN2 hPSC line was first differentiated to neural crest cell (NCC) progenitors, then incorporated into a cytocompatible gelatin methacryloyl-based bioink for 3D bioprinting. Upregulated NGN2 expression in the bioprinted NCCs resulted in induced SN (iSN) populations that exhibited specific cell markers, with 3D analysis revealing widespread neurite outgrowth through the scaffold volume. Calcium imaging demonstrated functional activity of iSNs, including membrane excitability properties and voltage-gated sodium channel (NaV) activity. This efficient approach to generate 3D bioprinted iSN structures streamlines the development of neural tissue models, useful for the study of neurodevelopment and disease states and offering translational potential.

Contemporary management of mesothelioma

Pleural mesothelioma (PM) is an aggressive asbestos-associated thoracic malignancy with a median survival of 12-18 months. Due to continued asbestos use in many nations, global incidence is rising. Causes due to non-occupational, environmental exposure are also rising in many countries despite utilisation bans. For many years, platinum--pemetrexed chemotherapy was the solitary licensed therapy, but first-line combination immune checkpoint blockade has recently demonstrated improved outcomes, with both regimes tested in predominantly late-stage cohorts. In the second-line setting, single-agent nivolumab has been shown to extend survival and is now available for routine use in some regions, while second-line chemotherapy has no proven role and opportunities for clinical trials should be maximised in relapsed disease. Surgery for "technically resectable" disease has been offered for decades in many expert centres, but the recent results from the phase III MARS2 trial have challenged this approach. There remains no robustly proven standard of care for early-stage PM. The clinical trial landscape for PM is complex and increasingly diverse, making further development of specialist PM multidisciplinary teams an important priority in all countries. The observation of improving outcomes in centres that have adopted this service model emphasises the importance of high-quality diagnostics and equitable access to therapies and trials. Novel therapies targeting a range of aberrations are being evaluated; however, a better understanding of the molecular drivers and their associated vulnerabilities is required to identify and prioritise treatment targets.

Coaxial 3D Bioprinting Process Research and Performance Tests on Vascular Scaffolds

Three-dimensionally printed vascularized tissue, which is suitable for treating human cardiovascular diseases, should possess excellent biocompatibility, mechanical performance, and the structure of complex vascular networks. In this paper, we propose a method for fabricating vascularized tissue based on coaxial 3D bioprinting technology combined with the mold method. Sodium alginate (SA) solution was chosen as the bioink material, while the cross-linking agent was a calcium chloride (CaCl2) solution. To obtain the optimal parameters for the fabrication of vascular scaffolds, we first formulated theoretical models of a coaxial jet and a vascular network. Subsequently, we conducted a simulation analysis to obtain preliminary process parameters. Based on the aforementioned research, experiments of vascular scaffold fabrication based on the coaxial jet model and experiments of vascular network fabrication were carried out. Finally, we optimized various parameters, such as the flow rate of internal and external solutions, bioink concentration, and cross-linking agent concentration. The performance tests showed that the fabricated vascular scaffolds had levels of satisfactory degradability, water absorption, and mechanical properties that meet the requirements for practical applications. Cellular experiments with stained samples demonstrated satisfactory proliferation of human umbilical vein endothelial cells (HUVECs) within the vascular scaffold over a seven-day period, observed under a fluorescent inverted microscope. The cells showed good biocompatibility with the vascular scaffold. The above results indicate that the fabricated vascular structure initially meet the requirements of vascular scaffolds.

Cardiac organoid: multiple construction approaches and potential applications

The human cardiac organoid (hCO) is three-dimensional tissue model that is similar to an in vivo organ and has great potential on heart development biology, disease modeling, drug screening and regenerative medicine. However, the construction of hCO presents a unique challenge compared with other organoids such as the lung, small intestine, pancreas, liver. Since heart disease is the dominant cause of death and the treatment of such disease is one of the most unmet medical needs worldwide, developing technologies for the construction and application of hCO is a critical task for the scientific community. In this review, we discuss the current classification and construction methods of hCO. In addition, we describe its applications in drug screening, disease modeling, and regenerative medicine. Finally, we propose the limitations of the cardiac organoid and future research directions. A detailed understanding of hCO will provide ways to improve its construction and expand its applications.

A dive into the bath: embedded 3D bioprinting of freeform in vitro models

Designing functional, vascularized, human scale in vitro models with biomimetic architectures and multiple cell types is a highly promising strategy for both a better understanding of natural tissue/organ development stages to inspire regenerative medicine, and to test novel therapeutics on personalized microphysiological systems. Extrusion-based 3D bioprinting is an effective biofabrication technology to engineer living constructs with predefined geometries and cell patterns. However, bioprinting high-resolution multilayered structures with mechanically weak hydrogel bioinks is challenging. The advent of embedded 3D bioprinting systems in recent years offered new avenues to explore this technology for in vitro modeling. By providing a stable, cell-friendly and perfusable environment to hold the bioink during and after printing, it allows to recapitulate native tissues' architecture and function in a well-controlled manner. Besides enabling freeform bioprinting of constructs with complex spatial organization, support baths can further provide functional housing systems for their long-term in vitro maintenance and screening. This minireview summarizes the recent advances in this field and discuss the enormous potential of embedded 3D bioprinting technologies as alternatives for the automated fabrication of more biomimetic in vitro models.

Unleashing the Power of the Right Brain

We envision a paradigm shift where our profession no longer follows but leads the charge to develop a whole mind approach in our pharmacists. Left brain skills remain critical but are no longer sufficient to combat the current threats of abundance, automation, and outsourcing within the pharmacy landscape. It is vital that pharmacists be skilled problem solvers and empathizers. We must capitalize on characteristics that make pharmacists essential while innovating new opportunities and jobs. We call on the Academy to reimagine curricular design and offer deliberate messaging and modeling that fosters a higher priority on right brain skill development.

Large-Scale Production of Wholly Cellular Bioinks via the Optimization of Human Induced Pluripotent Stem Cell Aggregate Culture in Automated Bioreactors

Combining the sustainable culture of billions of human cells and the bioprinting of wholly cellular bioinks offers a pathway toward organ-scale tissue engineering. Traditional 2D culture methods are not inherently scalable due to cost, space, and handling constraints. Here, the suspension culture of human induced pluripotent stem cell-derived aggregates (hAs) is optimized using an automated 250 mL stirred tank bioreactor system. Cell yield, aggregate morphology, and pluripotency marker expression are maintained over three serial passages in two distinct cell lines. Furthermore, it is demonstrated that the same optimized parameters can be scaled to an automated 1 L stirred tank bioreactor system. This 4-day culture results in a 16.6- to 20.4-fold expansion of cells, generating approximately 4 billion cells per vessel, while maintaining >94% expression of pluripotency markers. The pluripotent aggregates can be subsequently differentiated into derivatives of the three germ layers, including cardiac aggregates, and vascular, cortical and intestinal organoids. Finally, the aggregates are compacted into a wholly cellular bioink for rheological characterization and 3D bioprinting. The printed hAs are subsequently differentiated into neuronal and vascular tissue. This work demonstrates an optimized suspension culture-to-3D bioprinting pipeline that enables a sustainable approach to billion cell-scale organ engineering.

3D-bioprinted human tissue and the path toward clinical translation

Three-dimensional (3D) bioprinting is a transformative technology for engineering tissues for disease modeling and drug screening and building tissues and organs for repair, regeneration, and replacement. In this Viewpoint, we discuss technological advances in 3D bioprinting, key remaining challenges, and essential milestones toward clinical translation.

Biomimetic Vasculatures by 3D-Printed Porous Molds

Despite recent advances in biofabrication, recapitulating complex architectures of cell-laden vascular constructs remains challenging. To date, biofabricated vascular models have not yet realized four fundamental attributes of native vasculatures simultaneously: freestanding, branching, multilayered, and perfusable. In this work, a microfluidics-enabled molding technique combined with coaxial bioprinting to fabricate anatomically relevant, cell-laden vascular models consisting of hydrogels is developed. By using 3D porous molds of poly(ethylene glycol) diacrylate as casting templates that gradually release calcium ions as a crosslinking agent, freestanding, and perfusable vascular constructs of complex geometries are fabricated. The bioinks can be tailored to improve the compatibility with specific vascular cells and to tune the mechanical modulus mimicking native blood vessels. Crucially, the integration of relevant vascular cells (such as smooth muscle cells and endothelial cells) in a multilayer and biomimetic configuration is highlighted. It is also demonstrated that the fabricated freestanding vessels are amenable for testing percutaneous coronary interventions (i.e., drug-eluting balloons and stents) under physiological mechanical states such as stretching and bending. Overall, a versatile fabrication technique with multifaceted possibilities of generating biomimetic vascular models that can benefit future research in mechanistic understanding of cardiovascular diseases and the development of therapeutic interventions is introduced.

Advances in three-dimensional bioprinted stem cell-based tissue engineering for cardiovascular regeneration

Three-dimensional (3D) bioprinting of cellular or biological components are an emerging field to develop tissue structures that mimic the spatial, mechanochemical and temporal characteristics of cardiovascular tissues. 3D multi-cellular and multi-domain organotypic biological constructs can better recapitulate in vivo physiology and can be utilized in a variety of applications. Such applications include in vitro cellular studies, high-throughput drug screening, disease modeling, biocompatibility analysis, drug testing and regenerative medicine. A major challenge of 3D bioprinting strategies is the inability of matrix molecules to reconstitute the complexity of the extracellular matrix and the intrinsic cellular morphologies and functions. An important factor is the inclusion of a vascular network to facilitate oxygen and nutrient perfusion in scalable and patterned 3D bioprinted tissues to promote cell viability and functionality. In this review, we summarize the new generation of 3D bioprinting techniques, the kinds of bioinks and printing materials employed for 3D bioprinting, along with the current state-of-the-art in engineered cardiovascular tissue models. We also highlight the translational applications of 3D bioprinting in engineering the myocardium cardiac valves, and vascular grafts. Finally, we discuss current challenges and perspectives of designing effective 3D bioprinted constructs with native vasculature, architecture and functionality for clinical translation and cardiovascular regeneration.

A sound approach to advancing healthcare systems: the future of biomedical acoustics

Newly developed acoustic technologies are playing a transformational role in life science and biomedical applications ranging from the activation and inactivation of mechanosensitive ion channels for fundamental physiological processes to the development of contact-free, precise biofabrication protocols for tissue engineering and large-scale manufacturing of organoids. Here, we provide our perspective on the development of future acoustic technologies and their promise in addressing critical challenges in biomedicine.

Application Status of Sacrificial Biomaterials in 3D Bioprinting

Additive manufacturing, also known as three-dimensional (3D) printing, relates to several rapid prototyping (RP) technologies, and has shown great potential in the manufacture of organoids and even complex bioartificial organs. A major challenge for 3D bioprinting complex org unit ans is the competitive requirements with respect to structural biomimeticability, material integrability, and functional manufacturability. Over the past several years, 3D bioprinting based on sacrificial templates has shown its unique advantages in building hierarchical vascular networks in complex organs. Sacrificial biomaterials as supporting structures have been used widely in the construction of tubular tissues. The advent of suspension printing has enabled the precise printing of some soft biomaterials (e.g., collagen and fibrinogen), which were previously considered unprintable singly with cells. In addition, the introduction of sacrificial biomaterials can improve the porosity of biomaterials, making the printed structures more favorable for cell proliferation, migration and connection. In this review, we mainly consider the latest developments and applications of 3D bioprinting based on the strategy of sacrificial biomaterials, discuss the basic principles of sacrificial templates, and look forward to the broad prospects of this approach for complex organ engineering or manufacturing.

Biomanufacturing human tissues via organ building blocks

The construction of human organs on demand remains a tantalizing vision to solve the organ donor shortage. Yet, engineering tissues that recapitulate the cellular and architectural complexity of native organs is a grand challenge. The use of organ building blocks (OBBs) composed of multicellular spheroids, organoids, and assembloids offers an important pathway for creating organ-specific tissues with the desired cellular-to-tissue-level organization. Here, we review the differentiation, maturation, and 3D assembly of OBBs into functional human tissues and, ultimately, organs for therapeutic repair and replacement. We also highlight future challenges and areas of opportunity for this nascent field.

A review on 3D printing functional brain model

Modern neuroscience increasingly relies on 3D models to study neural circuitry, nerve regeneration, and neural disease. Several different biofabrication approaches have been explored to create 3D neural tissue model structures. Among them, 3D bioprinting has shown to have great potential to emerge as a high-throughput/high precision biofabrication strategy that can address the growing need for 3D neural models. Here, we have reviewed the design principles for neural tissue engineering. The main challenge to adapt printing technologies for biofabrication of neural tissue models is the development of neural bioink, i.e., a biomaterial with printability and gelation properties and also suitable for neural tissue culture. This review shines light on a vast range of biomaterials as well as the fundamentals of 3D neural tissue printing. Also, advances in 3D bioprinting technologies are reviewed especially for bioprinted neural models. Finally, the techniques used to evaluate the fabricated 2D and 3D neural models are discussed and compared in terms of feasibility and functionality.

Scaffolding Biomaterials for 3D Cultivated Meat: Prospects and Challenges

Cultivating meat from stem cells rather than by raising animals is a promising solution to concerns about the negative externalities of meat production. For cultivated meat to fully mimic conventional meat's organoleptic and nutritional properties, innovations in scaffolding technology are required. Many scaffolding technologies are already developed for use in biomedical tissue engineering. However, cultivated meat production comes with a unique set of constraints related to the scale and cost of production as well as the necessary attributes of the final product, such as texture and food safety. This review discusses the properties of vertebrate skeletal muscle that will need to be replicated in a successful product and the current state of scaffolding innovation within the cultivated meat industry, highlighting promising scaffold materials and techniques that can be applied to cultivated meat development. Recommendations are provided for future research into scaffolds capable of supporting the growth of high-quality meat while minimizing production costs. Although the development of appropriate scaffolds for cultivated meat is challenging, it is also tractable and provides novel opportunities to customize meat properties.

Projection-based stereolithography for direct 3D printing of heterogeneous ultrasound phantoms

Modern ultrasound (US) imaging is increasing its clinical impact, particularly with the introduction of US-based quantitative imaging biomarkers. Continued development and validation of such novel imaging approaches requires imaging phantoms that recapitulate the underlying anatomy and pathology of interest. However, current US phantom designs are generally too simplistic to emulate the structure and variability of the human body. Therefore, there is a need to create a platform that is capable of generating well-characterized phantoms that can mimic the basic anatomical, functional, and mechanical properties of native tissues and pathologies. Using a 3D-printing technique based on stereolithography, we fabricated US phantoms using soft materials in a single fabrication session, without the need for material casting or back-filling. With this technique, we induced variable levels of stable US backscatter in our printed materials in anatomically relevant 3D patterns. Additionally, we controlled phantom stiffness from 7 to >120 kPa at the voxel level to generate isotropic and anisotropic phantoms for elasticity imaging. Lastly, we demonstrated the fabrication of channels with diameters as small as 60 micrometers and with complex geometry (e.g., tortuosity) capable of supporting blood-mimicking fluid flow. Collectively, these results show that projection-based stereolithography allows for customizable fabrication of complex US phantoms.

Engineering the niche to differentiate and deploy cardiovascular cells

Applications for stem cells have ranged from therapeutic interventions to more conventional screening and in vitro modeling, but significant limitations to each is due to the lack of maturity from decades old monolayer protocols. While those methods remain the 'gold standard,' newer three-dimensional methods, when combined with engineered niche, stand to significantly improve cell maturity and enable new applications. Here in three parts, we first discuss past methods, and where and why we believe those methods produced suboptimal myocytes. Second, we note how newer methods are moving the field into an era of cell mechanical, electrical, and biological maturity. Finally, we highlight how these improvements will solve issues of scale and engraftment to yield clinical success. It is our conclusion that only through a combination of diverse cell populations and engineered niche will we create an engineered heart tissue with the maturity and vasculature to integrate successfully into a host.

Resolution of 3D bioprinting inside bulk gel and granular gel baths

Three-dimensional (3D) bioprinting has rapidly developed in the last decade, playing an increasingly important role in applications including pharmacokinetics research, tissue engineering, and organ regeneration. As a cutting-edge technology in 3D printing, gel bath-supported 3D bioprinting enables the freeform construction of complex structures with soft and water-containing materials, facilitating the in vitro fabrication of live tissue or organ models. To realize in vivo-like organs or tissues in terms of biological functions and complex structures by 3D printing, high resolution and fidelity are prerequisites. Although a wide range of gel matrices have recently been developed as supporting materials, the effect of bath properties and printing parameters on the print resolution is still not clearly understood. This review systematically introduces the decisive factors for resolution in both bulk gel bath systems and granular microgel bath systems, providing guidelines for high-resolution 3D bioprinting based on bath properties and printing parameters.

Blood Flow Within Bioengineered 3D Printed Vascular Constructs Using the Porcine Model

Recently developed biofabrication technologies are enabling the production of three-dimensional engineered tissues containing vascular networks which can deliver oxygen and nutrients across large tissue volumes. Tissues at this scale show promise for eventual regenerative medicine applications; however, the implantation and integration of these constructs in vivo remains poorly studied. Here, we introduce a surgical model for implantation and direct in-line vascular connection of 3D printed hydrogels in a porcine arteriovenous shunt configuration. Utilizing perfusable poly(ethylene glycol) diacrylate (PEGDA) hydrogels fabricated through projection stereolithography, we first optimized the implantation procedure in deceased piglets. Subsequently, we utilized the arteriovenous shunt model to evaluate blood flow through implanted PEGDA hydrogels in non-survivable studies. Connections between the host femoral artery and vein were robust and the patterned vascular channels withstood arterial pressure, permitting blood flow for 6 h. Our study demonstrates rapid prototyping of a biocompatible and perfusable hydrogel that can be implanted in vivo as a porcine arteriovenous shunt, suggesting a viable surgical approach for in-line implantation of bioprinted tissues, along with design considerations for future in vivo studies. We further envision that this surgical model may be broadly applicable for assessing whether biomaterials optimized for 3D printing and cell function can also withstand vascular cannulation and arterial blood pressure. This provides a crucial step toward generated transplantable engineered organs, demonstrating successful implantation of engineered tissues within host vasculature.

Perfusion and endothelialization of engineered tissues with patterned vascular networks

As engineered tissues progress toward therapeutically relevant length scales and cell densities, it is critical to deliver oxygen and nutrients throughout the tissue volume via perfusion through vascular networks. Furthermore, seeding of endothelial cells within these networks can recapitulate the barrier function and vascular physiology of native blood vessels. In this protocol, we describe how to fabricate and assemble customizable open-source tissue perfusion chambers and catheterize tissue constructs inside them. Human endothelial cells are seeded along the lumenal surfaces of the tissue constructs, which are subsequently connected to fluid pumping equipment. The protocol is agnostic with respect to biofabrication methodology as well as cell and material composition, and thus can enable a wide variety of experimental designs. It takes ~14 h over the course of 3 d to prepare perfusion chambers and begin a perfusion experiment. We envision that this protocol will facilitate the adoption and standardization of perfusion tissue culture methods across the fields of biomaterials and tissue engineering.

Three-dimensional Printing in Orthopaedic Surgery: Current Applications and Future Developments

Three-dimensional (3D) printing is an exciting form of manufacturing technology that has transformed the way we can treat various medical pathologies. Also known as additive manufacturing, 3D printing fuses materials together in a layer-by-layer fashion to construct a final 3D product. This technology allows flexibility in the design process and enables efficient production of both off-the-shelf and personalized medical products that accommodate patient needs better than traditional manufacturing processes. In the field of orthopaedic surgery, 3D printing implants and instrumentation can be used to address a variety of pathologies that would otherwise be challenging to manage with products made from traditional subtractive manufacturing. Furthermore, 3D bioprinting has significantly impacted bone and cartilage restoration procedures and has the potential to completely transform how we treat patients with debilitating musculoskeletal injuries. Although costs can be high, as technology advances, the economics of 3D printing will improve, especially as the benefits of this technology have clearly been demonstrated in both orthopaedic surgery and medicine as a whole. This review outlines the basics of 3D printing technology and its current applications in orthopaedic surgery and ends with a brief summary of 3D bioprinting and its potential future impact.

Designer Self-Assembling Peptide Hydrogels to Engineer 3D Cell Microenvironments for Cell Constructs Formation and Precise Oncology Remodeling in Ovarian Cancer

Designer self-assembling peptides form the entangled nanofiber networks in hydrogels by ionic-complementary self-assembly. This type of hydrogel has realistic biological and physiochemical properties to serve as biomimetic extracellular matrix (ECM) for biomedical applications. The advantages and benefits are distinct from natural hydrogels and other synthetic or semisynthetic hydrogels. Designer peptides provide diverse alternatives of main building blocks to form various functional nanostructures. The entangled nanofiber networks permit essential compositional complexity and heterogeneity of engineering cell microenvironments in comparison with other hydrogels, which may reconstruct the tumor microenvironments (TMEs) in 3D cell cultures and tissue-specific modeling in vitro. Either ovarian cancer progression or recurrence and relapse are involved in the multifaceted TMEs in addition to mesothelial cells, fibroblasts, endothelial cells, pericytes, immune cells, adipocytes, and the ECM. Based on the progress in common hydrogel products, this work focuses on the diverse designer self-assembling peptide hydrogels for instructive cell constructs in tissue-specific modeling and the precise oncology remodeling for ovarian cancer, which are issued by several research aspects in a 3D context. The advantages and significance of designer peptide hydrogels are discussed, and some common approaches and coming challenges are also addressed in current complex tumor diseases.

The Research on Multi-material 3D Vascularized Network Integrated Printing Technology

Three-dimensional bioprinting has emerged as one of the manufacturing approaches that could potentially fabricate vascularized channels, which is helpful to culture tissues in vitro. In this paper, we report a novel approach to fabricate 3D perfusable channels by using the combination of extrusion and inkjet techniques in an integrated manufacture process. To achieve this, firstly we investigate the theoretical model to analyze influencing factors of structural dimensions of the printed parts like the printing speed, pressure, dispensing time, and voltage. In the experiment, photocurable hydrogel was printed to form a self-supporting structure with internal channel grooves. When the desired height of hydrogel was reached, the dual print-head was switched to the piezoelectric nozzle immediately, and the sacrificial material was printed by the changed nozzle on the printed hydrogel layer. Then, the extrusion nozzle was switched to print the next hydrogel layer. Once the printing of the internal construct was finished, hydrogel was extruded to wrap the entire structure, and the construct was immersed in a CaCl2 solution to crosslink. After that, the channel was formed by removing the sacrificial material. This approach can potentially provide a strategy for fabricating 3D vascularized channels and advance the development of culturing thick tissues in vitro.

Cross-Linkable Microgel Composite Matrix Bath for Embedded Bioprinting of Perfusable Tissue Constructs and Sculpting of Solid Objects

Tissue engineering is a rapidly growing field, which requires advanced fabrication technologies to generate cell-laden tissue analogues with a wide range of internal and external physical features including perfusable channels, cavities, custom shapes, and spatially varying material and/or cell compositions. A versatile embedded printing methodology is proposed in this work for creating custom biomedical acellular and cell-laden hydrogel constructs by utilizing a biocompatible microgel composite matrix bath. A sacrificial material is patterned within a biocompatible hydrogel precursor matrix bath using extrusion printing to create three-dimensional features; after printing, the matrix bath is cross-linked, and the sacrificial material is flushed away to create perfusable channels within the bulk composite hydrogel matrix. The composite matrix bath material consists of jammed cross-linked hydrogel microparticles (microgels) to control rheology during fabrication along with a fluid hydrogel precursor, which is cross-linked after fabrication to form the continuous phase of the composite hydrogel. For demonstration, gellan or enzymatically cross-linked gelatin microgels are utilized with a continuous gelatin hydrogel precursor solution to make the composite matrix bath herein; the composite hydrogel matrix is formed by cross-linking the continuous gelatin phase enzymatically after printing. A variety of features including discrete channels, junctions, networks, and external contours are fabricated in the proposed composite matrix bath using embedded printing. Cell-laden constructs with printed features are also evaluated; the microgel composite hydrogel matrices support cell activity, and printed channels enhance proliferation compared to solid constructs even in static culture. The proposed method can be expanded as a solid object sculpting method to sculpt external contours by printing a shell of sacrificial ink and further discarding excess composite hydrogel matrix after printing and cross-linking. While aqueous alginate solution is used as a sacrificial ink, more advanced sacrificial materials can be utilized for better printing resolution.

A FRESH Take on Resolution in 3D Bioprinting

Recent innovations in the materials used for bioprinting have enabled transformative gains in the resolution and architecture of 3D-printed engineered tissues. We focus here on one of these innovations, reported by Lee et al., which lowers the resolution limit for printing soft biomaterials.

Biomanufacturing of organ-specific tissues with high cellular density and embedded vascular channels

Engineering organ-specific tissues for therapeutic applications is a grand challenge, requiring the fabrication and maintenance of densely cellular constructs composed of ~10⁸ cells/ml. Organ building blocks (OBBs) composed of patient-specific-induced pluripotent stem cell-derived organoids offer a pathway to achieving tissues with the requisite cellular density, microarchitecture, and function. However, to date, scant attention has been devoted to their assembly into 3D tissue constructs. Here, we report a biomanufacturing method for assembling hundreds of thousands of these OBBs into living matrices with high cellular density into which perfusable vascular channels are introduced via embedded three-dimensional bioprinting. The OBB matrices exhibit the desired self-healing, viscoplastic behavior required for sacrificial writing into functional tissue (SWIFT). As an exemplar, we created a perfusable cardiac tissue that fuses and beats synchronously over a 7-day period. Our SWIFT biomanufacturing method enables the rapid assembly of perfusable patient- and organ-specific tissues at therapeutic scales.

Monitoring Oxygen Levels within Large, Tissue-Engineered Constructs Using Porphyin-Hydrogel Microparticles

A major barrier to the creation of engineered organs is the limited diffusion of oxygen through biological tissues. Advances in biofabrication bring us increasingly closer to complex vascular networks capable of supplying oxygen to large cellularized scaffolds. However, technologies for monitoring oxygen levels in engineered tissues do not accommodate imaging depths of more than a few dozen micrometers. Here, we report the creation of fluorescent porphyrin-hydrogel microparticles that can be used at depths of 2 mm into artificial tissues. By combining an oxygen-responsive porphyrin dye with a reference dye, the microparticles generate a ratiometric signal that is photostable, unaffected by attenuation from biological material, and responsive to physiological change in oxygen concentration. These microparticles can measure long-distance oxygen gradients within 3D, cellularized constructs and accurately report cellular oxygen consumption rates. Furthermore, they are compatible with a number of hydrogel polymerization chemistries and cell types, including primary human cells. We believe this technology will significantly advance efforts to visualize oxygen gradients in cellularized constructs and inform efforts to tissue engineer solid organs.

3D bioprinting of collagen to rebuild components of the human heart

Collagen is the primary component of the extracellular matrix in the human body. It has proved challenging to fabricate collagen scaffolds capable of replicating the structure and function of tissues and organs. We present a method to 3D-bioprint collagen using freeform reversible embedding of suspended hydrogels (FRESH) to engineer components of the human heart at various scales, from capillaries to the full organ. Control of pH-driven gelation provides 20-micrometer filament resolution, a porous microstructure that enables rapid cellular infiltration and microvascularization, and mechanical strength for fabrication and perfusion of multiscale vasculature and tri-leaflet valves. We found that FRESH 3D-bioprinted hearts accurately reproduce patient-specific anatomical structure as determined by micro–computed tomography. Cardiac ventricles printed with human cardiomyocytes showed synchronized contractions, directional action potential propagation, and wall thickening up to 14% during peak systole.

When bodies think: panpsychism, pluralism, biopolitics

Cultivating a speculative orientation to the medical humanities, the aim of this essay is to explore some dimensions of the recent calls for more participatory forms of medicine and healthcare under the sign of what, after Michel Foucault, I call the 'biopolitical problematic'. That is, the divergent encounter between techniques of biopower that seek to take hold of life and the body, and a plurality of living bodies that persistently respond, challenge and escape its grasp. If critics of 'participatory medicine' have warned that the turn to 'participation' in healthcare functions as a form of biopower that seeks to gain access to bodies, and in so doing take a better hold of life, in this essay, I propose we experiment with the question of what kinds of conceptual tools may be required to make perceptible the ways in which a plurality of participating bodies may become capable of responding, challenging and escaping 'participation's' grasp. After problematising the ontology of participation involved in contemporary debates around participatory medicine, I draw on the work of William James and Alfred North Whitehead, among others, to argue for the need to reclaim a pluralistic panpsychism-in short, the proposition that all things think-as a pragmatic tool to envisage the possibility of a plurality of thinking bodies capable of unruly forms of participation all the way down.

Support-Free Ceramic Stereolithography of Complex Overhanging Structures Based on an Elasto-viscoplastic Suspension Feedstock

Ceramic stereolithography (CSL) is an additive manufacturing method for creating ceramic three-dimensional (3D) objects via the layer-by-layer photopolymerization of a ceramic suspension. A key challenge in CSL is that support structures are required for building overhanging structures to prevent part damage or deformation caused by gravity or process-induced shears. Removing the support structures can result in issues such as poor surface quality, high risk of cracking, etc. To overcome this challenge, this article presents a new CSL-based ceramic fabrication method that uses an elasto-viscoplastic ceramic suspension as the feedstock material. The suspension's inherently strong interparticle resistive force can support overhangs without the need for building additional support structures; a temperature-controlled layer-coating module is designed to dynamically form a localized suspension bridge above the free surface of previously deposited materials, which allows for the application of fresh thin layers with a controlled shear force. The article presents material design and characterizations and discusses key process parameters and their effects on the geometry retention of fabricated overhangs. This new process provides the potential for fabricating ceramic 3D objects with complex overhangs, such as vascular networks, biomimetic heat exchangers, and microreactors.

Macroporous Dual-compartment Hydrogels for Minimally Invasive Transplantation of Primary Human Hepatocytes

BACKGROUND

Given the shortage of available organs for whole or partial liver transplantation, hepatocyte cell transplantation has long been considered a potential strategy to treat patients suffering from various liver diseases. Some of the earliest approaches that attempted to deliver hepatocytes via portal vein or spleen achieved little success due to poor engraftment. More recent efforts include transplantation of cell sheets or thin hepatocyte-laden synthetic hydrogels. However, these implants must remain sufficiently thin to ensure that nutrients can diffuse into the implant.

METHODS

To circumvent these limitations, we investigated the use of a vascularizable dual-compartment hydrogel system for minimally invasive transplantation of primary hepatocytes. The dual-compartment system features a macroporous outer polyethylene glycol diacrylate/hyaluronic acid methacrylate hydrogel compartment for seeding supportive cells and facilitating host cell infiltration and vascularization and a hollow inner core to house the primary human hepatocytes.

RESULTS

We show that the subcutaneous implantation of these cell-loaded devices in NOD/SCID mice facilitated vascular formation while supporting viability of the transplanted cells. Furthermore, the presence of human serum albumin in peripheral blood and the immunostaining of excised implants indicated that the hepatocytes maintained function in vivo for at least 1 month, the longest assayed time point.

CONCLUSIONS

Cell transplantation devices that assist the anastomosis of grafts with the host can be potentially used as a minimally invasive ectopic liver accessory to augment liver-specific functions as well as potentially treat various pathologies associated with compromised functions of liver, such as hemophilia B or alpha-1 antitrypsin deficiency.

Microfabrication of AngioChip, a biodegradable polymer scaffold with microfluidic vasculature

Microengineered biomimetic systems for organ-on-a-chip or tissue engineering purposes often fail as a result of an inability to recapitulate the in vivo environment, specifically the presence of a well-defined vascular system. To address this limitation, we developed an alternative method to cultivate three-dimensional (3D) tissues by incorporating a microfabricated scaffold, termed AngioChip, with a built-in perfusable vascular network. Here, we provide a detailed protocol for fabricating the AngioChip scaffold, populating it with endothelial cells and parenchymal tissues, and applying it in organ-on-a-chip drug testing in vitro and surgical vascular anastomosis in vivo. The fabrication of the AngioChip scaffold is achieved by a 3D stamping technique, in which an intricate microchannel network can be embedded within a 3D scaffold. To develop a vascularized tissue, endothelial cells are cultured in the lumen of the AngioChip network, and parenchymal cells are encapsulated in hydrogels that are amenable to remodeling around the vascular network to form functional tissues. Together, these steps yield a functional, vascularized network in vitro over a 14-d period. Finally, we demonstrate the functionality of AngioChip-vascularized hepatic and cardiac tissues, and describe direct surgical anastomosis of the AngioChip vascular network on the hind limb of a Lewis rat model.

Brain Capillary Networks Across Species: A few Simple Organizational Requirements Are Sufficient to Reproduce Both Structure and Function

Despite the key role of the capillaries in neurovascular function, a thorough characterization of cerebral capillary network properties is currently lacking. Here, we define a range of metrics (geometrical, topological, flow, mass transfer, and robustness) for quantification of structural differences between brain areas, organs, species, or patient populations and, in parallel, digitally generate synthetic networks that replicate the key organizational features of anatomical networks (isotropy, connectedness, space-filling nature, convexity of tissue domains, characteristic size). To reach these objectives, we first construct a database of the defined metrics for healthy capillary networks obtained from imaging of mouse and human brains. Results show that anatomical networks are topologically equivalent between the two species and that geometrical metrics only differ in scaling. Based on these results, we then devise a method which employs constrained Voronoi diagrams to generate 3D model synthetic cerebral capillary networks that are locally randomized but homogeneous at the network-scale. With appropriate choice of scaling, these networks have equivalent properties to the anatomical data, demonstrated by comparison of the defined metrics. The ability to synthetically replicate cerebral capillary networks opens a broad range of applications, ranging from systematic computational studies of structure-function relationships in healthy capillary networks to detailed analysis of pathological structural degeneration, or even to the development of templates for fabrication of 3D biomimetic vascular networks embedded in tissue-engineered constructs.

Accurate flow in augmented networks (AFAN): an approach to generating three-dimensional biomimetic microfluidic networks with controlled flow

In vivo, microvasculature provides oxygen, nutrients, and soluble factors necessary for cell survival and function. The highly tortuous, densely-packed, and interconnected three-dimensional (3D) architecture of microvasculature ensures that cells receive these crucial components. The ability to duplicate microvascular architecture in tissue-engineered models could provide a means to generate large-volume constructs as well as advanced microphysiological systems. Similarly, the ability to induce realistic flow in engineered microvasculature is crucial to recapitulating in vivo-like flow and transport. Advanced biofabrication techniques are capable of generating 3D, biomimetic microfluidic networks in hydrogels, however, these models can exhibit systemic aberrations in flow due to incorrect boundary conditions. To overcome this problem, we developed an automated method for generating synthetic augmented channels that induce the desired flow properties within three-dimensional microfluidic networks. These augmented inlets and outlets enforce the appropriate boundary conditions for achieving specified flow properties and create a three-dimensional output useful for image-guided fabrication techniques to create biomimetic microvascular networks.

Bioprinting in Vascularization Strategies

Three-dimensional (3D) printing technology has revolutionized tissue engineering field because of its excellent potential of accurately positioning cell-laden constructs. One of the main challenges in the formation of functional engineered tissues is the lack of an efficient and extensive network of microvessels to support cell viability. By printing vascular cells and appropriate biomaterials, the 3D printing could closely mimic in vivo conditions to generate blood vessels. In vascular tissue engineering, many various approaches of 3D printing have been developed, including selective laser sintering and extrusion methods, etc. The 3D printing is going to be the integral part of tissue engineering approaches; in comparison with other scaffolding techniques, 3D printing has two major merits: automation and high cell density. Undoubtedly, the application of 3D printing in vascular tissue engineering will be extended if its resolution, printing speed, and available materials can be improved.

An Update on the Use of Alginate in Additive Biofabrication Techniques

BACKGROUND

Solid free forming (SFF) technique also called additive manufacturing process is immensely popular for biofabrication owing to its high accuracy, precision and reproducibility.

METHOD

SFF techniques like stereolithography, selective laser sintering, fused deposition modeling, extrusion printing, and inkjet printing create three dimension (3D) structures by layer by layer processing of the material. To achieve desirable results, selection of the appropriate technique is an important aspect and it is based on the nature of biomaterial or bioink to be processed.

RESULT & CONCLUSION

Alginate is a commonly employed bioink in biofabrication process, attributable to its nontoxic, biodegradable and biocompatible nature; low cost; and tendency to form hydrogel under mild conditions. Furthermore, control on its rheological properties like viscosity and shear thinning, makes this natural anionic polymer an appropriate candidate for many of the SFF techniques. It is endeavoured in the present review to highlight the status of alginate as bioink in various SFF techniques.

Bioprinting in Vascularization Strategies

Three-dimensional (3D) printing technology has revolutionized tissue engineering field because of its excellent potential of accurately positioning cell-laden constructs. One of the main challenges in the formation of functional engineered tissues is the lack of an efficient and extensive network of microvessels to support cell viability. By printing vascular cells and appropriate biomaterials, the 3D printing could closely mimic in vivo conditions to generate blood vessels. In vascular tissue engineering, many various approaches of 3D printing have been developed, including selective laser sintering and extrusion methods, etc. The 3D printing is going to be the integral part of tissue engineering approaches; in comparison with other scaffolding techniques, 3D printing has two major merits: automation and high cell density. Undoubtedly, the application of 3D printing in vascular tissue engineering will be extended if its resolution, printing speed, and available materials can be improved.