Mini-review: advances in 3D bioprinting of vascularized constructs

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

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

The crisscross between p53 and metabolism in cancer

As the guardian of the genome, p53 is well known for its tumor suppressor function in humans, controlling cell proliferation, senescence, DNA repair and cell death in cancer through transcriptional and non-transcriptional activities. p53 is the most frequently mutated gene in human cancer, but how its mutation or depletion leads to tumorigenesis still remains poorly understood. Recently, there has been increasing evidence that p53 plays a vital role in regulating cellular metabolism as well as in metabolic adaptation to nutrient starvation. In contrast, mutant p53 proteins, especially those harboring missense mutations, have completely different functions compared to wild-type p53. In this review, we briefly summarize what is known about p53 mediating anabolic and catabolic metabolism in cancer, and in particular discuss recent findings describing how metabolites regulate p53 functions. To illustrate the variability and complexity of p53 function in metabolism, we will also review the differential regulation of metabolism by wild-type and mutant p53.

A Porous Gelatin Methacrylate-Based Material for 3D Cell-Laden Constructs

3D constructs are fundamental in tissue engineering and cancer modeling, generating a demand for tailored materials creating a suitable cell culture microenvironment and amenable to be bioprinted. Gelatin methacrylate (GelMA) is a well-known functionalized natural polymer with good printability and binding motifs allowing cell adhesion; however, its tight micropores induce encapsulated cells to retain a non-physiological spherical shape. To overcome this problem, blended GelMa is here blended with Pluronic F-127 (PLU) to modify the hydrogel internal porosity by inducing the formation of larger mesoscale pores. The change in porosity also leads to increased swelling and a slight decrease in Young's modulus. All blends form stable hydrogels both when cast in annular molds and bioprinted in complex structures. Embedded cells maintain high viability, and while Neuroblastoma cancer cells typically aggregate inside the mesoscale pores, Mesenchymal Stem Cells stretch in all three dimensions, forming cell-cell and cell-ECM interactions. The results of this work prove that the combination of tailored porous materials with bioprinting techniques enables to control both the micro and macro architecture of cell-laden constructs, a fundamental aspect for the development of clinically relevant in vitro constructs.

Myocardial infarction from a tissue engineering and regenerative medicine point of view: A comprehensive review on models and treatments

In the modern world, myocardial infarction is one of the most common cardiovascular diseases, which are responsible for around 18 million deaths every year or almost 32% of all deaths. Due to the detrimental effects of COVID-19 on the cardiovascular system, this rate is expected to increase in the coming years. Although there has been some progress in myocardial infarction treatment, translating pre-clinical findings to the clinic remains a major challenge. One reason for this is the lack of reliable and human representative healthy and fibrotic cardiac tissue models that can be used to understand the fundamentals of ischemic/reperfusion injury caused by myocardial infarction and to test new drugs and therapeutic strategies. In this review, we first present an overview of the anatomy of the heart and the pathophysiology of myocardial infarction, and then discuss the recent developments on pre-clinical infarct models, focusing mainly on the engineered three-dimensional cardiac ischemic/reperfusion injury and fibrosis models developed using different engineering methods such as organoids, microfluidic devices, and bioprinted constructs. We also present the benefits and limitations of emerging and promising regenerative therapy treatments for myocardial infarction such as cell therapies, extracellular vesicles, and cardiac patches. This review aims to overview recent advances in three-dimensional engineered infarct models and current regenerative therapeutic options, which can be used as a guide for developing new models and treatment strategies.

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.

3D In Vitro Platform for Cell and Explant Culture in Liquid-like Solids

Existing 3D cell models and technologies have offered tools to elevate cell culture to a more physiologically relevant dimension. One mechanism to maintain cells cultured in 3D is by means of perfusion. However, existing perfusion technologies for cell culture require complex electronic components, intricate tubing networks, or specific laboratory protocols for each application. We have developed a cell culture platform that simply employs a pump-free suction device to enable controlled perfusion of cell culture media through a bed of granular microgels and removal of cell-secreted metabolic waste. We demonstrated the versatile application of the platform by culturing single cells and keeping tissue microexplants viable for an extended period. The human cardiomyocyte AC16 cell line cultured in our platform revealed rapid cellular spheroid formation after 48 h and ~90% viability by day 7. Notably, we were able to culture gut microexplants for more than 2 weeks as demonstrated by immunofluorescent viability assay and prolonged contractility.

Three-Dimensional Bioprinting of Organs: Modern Trends

The paper presents an overview of some modern technologies for three-dimensional (3D) bioprinting of human tissues and organs. 3D bioprinting of human organs is increasingly used for the production and transplantation of artificial biological organs. Existing technologies of 3D bioprinting using bioink on a special substrate are considered. The features of the production of bioinks using biocompatible polymer compounds, hydrogels are given, some popular modern bioprinters are noted. Modern technologies of bioprinting of tissues of human organs are considered: skin, liver, lungs, heart, brain, existing technological problems in this area are given. Based on the analysis, the future prospects for the development of bioprinting technology for human organs are noted.

Long-Fiber Embedded Hydrogel 3D Printing for Structural Reinforcement

Hydrogels are candidate building blocks in a wide range of biomaterial applications including soft and biohybrid robotics, microfluidics, and tissue engineering. Recent advances in embedded 3D printing have broadened the design space accessible with hydrogel additive manufacturing. Specifically, the Freeform Reversible Embedding of Suspended Hydrogels (FRESH) technique has enabled the fabrication of complex 3D structures using extremely soft hydrogels, e.g., alginate and collagen, by assembling hydrogels within a fugitive support bath. However, the low structural rigidity of FRESH printed hydrogels limits their applications, especially those that require operation in nonaqueous environments. In this study, we demonstrated long-fiber embedded hydrogel 3D printing using a multihead printing platform consisting of a custom-built fiber extruder and an open-source FRESH bioprinter with high embedding fidelity. Using this process, fibers were embedded in 3D printed hydrogel components to achieve significant structural reinforcement (e.g., tensile modulus improved from 56.78 ± 8.76 to 382.55 ± 25.29 kPa and tensile strength improved from 9.44 ± 2.28 to 45.05 ± 5.53 kPa). In addition, we demonstrated the versatility of this technique by using fibers of a wide range of sizes and material types and implementing different 2D and 3D embedding patterns, such as embedding a conical helix using electrochemically aligned collagen fiber via nonplanar printing. Moreover, the technique was implemented using low-cost material and is compatible with open-source software and hardware, which facilitates its adoption and modification for new research applications.

Modelling Human Physiology on-Chip: Historical Perspectives and Future Directions

For centuries, animal experiments have contributed much to our understanding of mechanisms of human disease, but their value in predicting the effectiveness of drug treatments in the clinic has remained controversial. Animal models, including genetically modified ones and experimentally induced pathologies, often do not accurately reflect disease in humans, and therefore do not predict with sufficient certainty what will happen in humans. Organ-on-chip (OOC) technology and bioengineered tissues have emerged as promising alternatives to traditional animal testing for a wide range of applications in biological defence, drug discovery and development, and precision medicine, offering a potential alternative. Recent technological breakthroughs in stem cell and organoid biology, OOC technology, and 3D bioprinting have all contributed to a tremendous progress in our ability to design, assemble and manufacture living organ biomimetic systems that more accurately reflect the structural and functional characteristics of human tissue in vitro, and enable improved predictions of human responses to drugs and environmental stimuli. Here, we provide a historical perspective on the evolution of the field of bioengineering, focusing on the most salient milestones that enabled control of internal and external cell microenvironment. We introduce the concepts of OOCs and Microphysiological systems (MPSs), review various chip designs and microfabrication methods used to construct OOCs, focusing on blood-brain barrier as an example, and discuss existing challenges and limitations. Finally, we provide an overview on emerging strategies for 3D bioprinting of MPSs and comment on the potential role of these devices in precision medicine.

Fluid Bath-Assisted 3D Printing for Biomedical Applications: From Pre- to Postprinting Stages

Fluid bath-assisted three-dimensional (3D) printing is an innovative 3D printing strategy that extrudes liquid ink materials into a fluid bath to form various 3D configurations. Since the support bath can provide in situ support, extruded filaments are able to freely construct complex 3D structures. Meanwhile, the supporting function of the fluid bath decreases the dependence of the ink material's cross-linkability, thus broadening the material selections for biomedical applications. Fluid bath-assisted 3D printing can be divided into two subcategories: embedded 3D printing and support bath-enabled 3D printing. This review will introduce and discuss three main manufacturing processes, or stages, for these two strategies. The stages that will be discussed include preprinting, printing, and postprinting. In the preprinting stage, representative fluid bath materials are introduced and the bath material preparation methods are also discussed. In addition, the design criteria of fluid bath materials including biocompatibility, rheological properties, physical/chemical stability, hydrophilicity/hydrophobicity, and other properties are proposed in order to guide the selection and design of future fluid bath materials. For the printing stage, some key technical issues discussed in this review include filament formation mechanisms in a fluid bath, effects of nozzle movement on printed structures, and design strategies for printing paths. In the postprinting stage, some commonly used postprinting processes are introduced. Finally, representative biomedical applications of fluid bath-assisted 3D printing, such as standalone organoids/tissues, biomedical microfluidic devices, and wearable and bionic devices, are summarized and presented.

Understanding p53 tumour suppressor network

The mutation of TP53 gene affects half of all human cancers, resulting in impairment of the regulation of several cellular functions, including cell cycle progression and cell death in response to genotoxic stress. In the recent years additional p53-mediated tumour suppression mechanisms have been described, questioning the contribution of its canonical pathway for tumour suppression. These include regulation of alternative cell death modalities (i.e. ferroptosis), cell metabolism and the emerging role in RNA stability. Here we briefly summarize our knowledge on p53 “canonical DNA damage response” and discuss the most relevant recent findings describing potential mechanistic explanation of p53-mediated tumour suppression.

Bio-assembling and Bioprinting for Engineering Microvessels from the Bottom Up

Blood vessels are essential in transporting nutrients, oxygen, metabolic wastes, and maintaining the homeostasis of the whole human body. Mass of engineered microvessels is required to deliver nutrients to the cells included in the constructed large three-dimensional (3D) functional tissues by diffusion. It is a formidable challenge to regenerate microvessels and build a microvascular network, mimicking the cellular viabilities and activities in the engineered organs with traditional or existing manufacturing techniques. Modular tissue engineering adopting the "bottom-up" approach builds one-dimensional (1D) or two-dimensional (2D) modular tissues in micro scale first and then uses these modules as building blocks to generate large tissues and organs with complex but indispensable microstructural features. Building the microvascular network utilizing this approach could be appropriate and adequate. In this review, we introduced existing methods using the "bottom-up" concept developed to fabricate microvessels including bio-assembling powered by different micromanipulation techniques and bioprinting utilizing varied solidification mechanisms. We compared and discussed the features of the artificial microvessels engineered by these two strategies from multiple aspects. Regarding the future development of engineering the microvessels from the bottom up, potential directions were also concluded.

Current Insights Into 3D Bioprinting: An Advanced Approach for Eye Tissue Regeneration

Three-dimensional (3D) printing is a game changer technology that holds great promise for a wide variety of biomedical applications, including ophthalmology. Through this emerging technique, specific eye tissues can be custom-fabricated in a flexible and automated way, incorporating different cell types and biomaterials in precise anatomical 3D geometries. However, and despite the great progress and possibilities generated in recent years, there are still challenges to overcome that jeopardize its clinical application in regular practice. The main goal of this review is to provide an in-depth understanding of the current status and implementation of 3D bioprinting technology in the ophthalmology field in order to manufacture relevant tissues such as cornea, retina and conjunctiva. Special attention is paid to the description of the most commonly employed bioprinting methods, and the most relevant eye tissue engineering studies performed by 3D bioprinting technology at preclinical level. In addition, other relevant issues related to use of 3D bioprinting for ocular drug delivery, as well as both ethical and regulatory aspects, are analyzed. Through this review, we aim to raise awareness among the research community and report recent advances and future directions in order to apply this advanced therapy in the eye tissue regeneration field.