3D Bioprinting of Neurovascular Tissue Modeling with Collagen-Based Low-Viscosity Composites

Stiffness-tunable biomaterials provide a good extracellular matrix environment for axon growth and regeneration

Neuronal growth, extension, branching, and formation of neural networks are markedly influenced by the extracellular matrix-a complex network composed of proteins and carbohydrates secreted by cells. In addition to providing physical support for cells, the extracellular matrix also conveys critical mechanical stiffness cues. During the development of the nervous system, extracellular matrix stiffness plays a central role in guiding neuronal growth, particularly in the context of axonal extension, which is crucial for the formation of neural networks. In neural tissue engineering, manipulation of biomaterial stiffness is a promising strategy to provide a permissive environment for the repair and regeneration of injured nervous tissue. Recent research has fine-tuned synthetic biomaterials to fabricate scaffolds that closely replicate the stiffness profiles observed in the nervous system. In this review, we highlight the molecular mechanisms by which extracellular matrix stiffness regulates axonal growth and regeneration. We highlight the progress made in the development of stiffness-tunable biomaterials to emulate in vivo extracellular matrix environments, with an emphasis on their application in neural repair and regeneration, along with a discussion of the current limitations and future prospects. The exploration and optimization of the stiffness-tunable biomaterials has the potential to markedly advance the development of neural tissue engineering.

Recent Advances in the Development and Application of Cell-Loaded Collagen Scaffolds

Tissue engineering techniques aim to improve or replace biological tissues or organs by utilizing the extracellular matrix to facilitate the repair of damaged tissues or organs. Collagen-based scaffolds offer numerous advantages, including excellent biocompatibility, low immunogenicity, biodegradability, hemostatic properties, and mechanical strength. Collagen scaffolds can reconstruct the extracellular microenvironment, promote cell adhesion, migration, proliferation, and differentiation, and play a critical role in cell-to-cell and cell-to-matrix interactions. Collagen has been extensively utilized in tissue engineering to facilitate tissue repair and organ reconstruction. This review examines the properties of collagen, including its composition, structure, biological characteristics, and role in regulating various cellular behaviors. Additionally, the preparation of cell-loaded collagen scaffolds is discussed, along with a comprehensive overview of their applications in various tissues, including skin, nerve, bone/cartilage, heart, liver, and others. Emerging strategies and future perspectives for clinical tissue repair are also presented. This review provides a comprehensive synthesis of the mechanisms underlying the use of cell-loaded collagen scaffolds as advanced biomaterials, emphasizing their potential to expand the clinical applications of collagen.

Multi-Nozzles 3D Bioprinting Collagen/Thermoplastic Elasto-Mer Scaffold with Interconnect Pores

Scaffolds play a crucial role in tissue engineering as regenerative templates. Fabricating scaffolds with good biocompatibility and appropriate mechanical properties remains a major challenge in this field. This study proposes a method for preparing multi-material scaffolds, enabling the 3D printing of collagen and thermoplastic elastomers at room temperature. Addressing the previous challenges such as the poor printability of pure collagen and the difficulty of maintaining structural integrity during multilayer printing, this research improved the printability of collagen by optimizing its concentration and pH value and completed the large-span printing of thermoplastic elastomer using a precise temperature-control system. The developed hybrid scaffold has an interconnected porous structure, which can support the adhesion and proliferation of fibroblasts. The scaffolds were further treated with different post-treatment methods, and it was proven that the neutralized and cross-linked collagen scaffold, which has both nano-fibers and a certain rigidity, can better support the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). The research results show that the collagen thermoplastic elastomer hybrid scaffold has significant clinical application potential in soft tissue and hard tissue regeneration, providing a versatile solution to meet the diverse needs of tissue engineering.

Hydrogel-Based Bioinks for Coaxial and Triaxial Bioprinting: A Review of Material Properties, Printing Techniques, and Applications

Three-dimensional bioprinting technology has emerged as a rapidly advancing multidisciplinary field with significant potential for tissue engineering applications. This technology enables the formation of complex tissues and organs by utilizing hydrogels, with or without cells, as scaffolds or structural supports. Among various bioprinting methods, advanced bioprinting using coaxial and triaxial nozzles stands out as a promising technique. Coaxial bioprinting technique simultaneously deposits two material streams through a coaxial nozzle, enabling controlled formation of an outer shell and inner core construct. In contrast, triaxial bioprinting utilizes three material streams namely the outer shell, inner shell and inner core to fabricate more complex constructs. Despite the growing interest in 3D bioprinting, the development of suitable cell-laden bioinks for creating complex tissues remains unclear. To address this gap, a systematic review was conducted using the preferred reporting items for systematic reviews and meta-analyses (PRISMA) flowchart, collecting 1621 papers from various databases, including Web of Science, PUBMED, SCOPUS, and Springer Link. After careful selection, 85 research articles focusing on coaxial and triaxial bioprinting were included in the review. Specifically, 77 research articles concentrated on coaxial bioprinting and 11 focused on triaxial bioprinting, with 3 covering both techniques. The search, conducted between 1 April and 30 September 2023, had no restrictions on publication date, and no meta-analyses were carried out due to the heterogeneity of studies. The primary objective of this review is to assess and identify the most commonly occurring cell-laden bioinks critical for successful advancements in bioprinting technologies. Specifically, the review focuses on delineating the commonly explored bioinks utilized in coaxial and triaxial bioprinting approaches. It focuses on evaluating the inherent merits of these bioinks, systematically comparing them while emphasizing their classifications, essential attributes, properties, and potential limitations within the domain of tissue engineering. Additionally, the review considers the applications of these bioinks, offering comprehensive insights into their efficacy and utility in the field of bioprinting technology. Overall, this review provides a comprehensive overview of some conditions of the relevant hydrogel bioinks used for coaxial and triaxial bioprinting of tissue constructs. Future research directions aimed at advancing the field are also briefly discussed.

Application progress of bio-manufacturing technology in kidney organoids

Kidney transplantation remains a pivotal treatment modality for kidney disease, yet its progress is significantly hindered by the scarcity of donor kidneys and ethical dilemmas surrounding their procurement. As organoid technology evolves and matures, the creation of bionic human kidney organoids offers profound potential for advancing kidney disease research, drug nephrotoxicity screening, and regenerative medicine. Nevertheless, current kidney organoid models grapple with limitations such as constrained cellular differentiation, underdeveloped functional structures, and a crucial absence of vascularization. This deficiency in vascularization, in particular, stunts organoid development, restricts their size, diminishes filtration capabilities, and may trigger immune inflammatory reactions through the resulting ischemic microenvironment. Hence, the achievement of vascularization within kidney organoids and the successful establishment of functional microvascular networks constitutes a paramount goal for their future progression. In this review, we provide an overview of recent advancements in biotechnology domains, encompassing organ-on-a-chip technology, biomimetic matrices, and bioprinting, with the aim of catalyzing technological breakthroughs that can enhance the vascularization of kidney organoids and broaden their applicability. These technologies hold the key to unlocking the full potential of kidney organoids as a transformative therapeutic option for kidney disease.

Advances and Challenges of Bioassembly Strategies in Neurovascular In Vitro Modeling: An Overview of Current Technologies with a Focus on Three-Dimensional Bioprinting

Bioassembly encompasses various techniques such as bioprinting, microfluidics, organoids, and self-assembly, enabling advances in tissue engineering and regenerative medicine. Advancements in bioassembly technologies have enabled the precise arrangement and integration of various cell types to more closely mimic the complexity functionality of the neurovascular unit (NVU) and that of other biodiverse multicellular tissue structures. In this context, bioprinting offers the ability to deposit cells in a spatially controlled manner, facilitating the construction of interconnected networks. Scaffold-based assembly strategies provide structural support and guidance cues for cell growth, enabling the formation of complex bio-constructs. Self-assembly approaches utilize the inherent properties of cells to drive the spontaneous organization and interaction of neuronal and vascular components. However, recreating the intricate microarchitecture and functional characteristics of a tissue/organ poses additional challenges. Advancements in bioassembly techniques and materials hold great promise for addressing these challenges. The further refinement of bioprinting technologies, such as improved resolution and the incorporation of multiple cell types, can enhance the accuracy and complexity of the biological constructs; however, developing bioinks that support the growth of cells, viability, and functionality while maintaining compatibility with the bioassembly process remains an unmet need in the field, and further advancements in the design of bioactive and biodegradable scaffolds will aid in controlling cell adhesion, differentiation, and vascularization within the engineered tissue. Additionally, integrating advanced imaging and analytical techniques can provide real-time monitoring and characterization of bioassembly, aiding in quality control and optimization. While challenges remain, ongoing research and technological advancements propel the field forward, paving the way for transformative developments in neurovascular research and tissue engineering. This work provides an overview of the advancements, challenges, and future perspectives in bioassembly for fabricating neurovascular constructs with an add-on focus on bioprinting technologies.

Gel-Based Suspension Medium Used in 3D Bioprinting for Constructing Tissue/Organ Analogs

Constructing tissue/organ analogs with natural structures and cell types in vitro offers a valuable strategy for the in situ repair of damaged tissues/organs. Three-dimensional (3D) bioprinting is a flexible method for fabricating these analogs. However, extrusion-based 3D bioprinting faces the challenge of balancing the use of soft bioinks with the need for high-fidelity geometric shapes. To address these challenges, recent advancements have introduced various suspension mediums based on gelatin, agarose, and gellan gum microgels. The emergence of these gel-based suspension mediums has significantly advanced the fabrication of tissue/organ constructs using 3D bioprinting. They effectively stabilize and support soft bioinks, enabling the formation of complex spatial geometries. Moreover, they provide a stable, cell-friendly environment that maximizes cell viability during the printing process. This minireview will summarize the properties, preparation methods, and potential applications of gel-based suspension mediums in constructing tissue/organ analogs, while also addressing current challenges and providing an outlook on the future of 3D bioprinting.

Innovative 3D bioprinting approaches for advancing brain science and medicine: a literature review

The rapid advancements in 3D printing technology have revolutionized the field of tissue engineering, particularly in the development of neural tissues for the treatment of nervous system diseases. Brain neural tissue, composed of neurons and glial cells, plays a crucial role in the functioning of the brain, spinal cord, and peripheral nervous system by transmitting nerve impulses and processing information. By leveraging 3D bioprinting and bioinks, researchers can create intricate neural scaffolds that facilitate the proliferation and differentiation of nerve cells, thereby promoting the repair and regeneration of damaged neural tissues. This technology allows for the precise spatial arrangement of various cell types and scaffold materials, enabling the construction of complex neural tissue models that closely mimic the natural architecture of the brain. Human-induced pluripotent stem cells (hiPSCs) have emerged as a groundbreaking tool in neuroscience research and the potential treatment of neurological diseases. These cells can differentiate into diverse cell types within the nervous system, including neurons, astrocytes, microglia, oligodendrocytes, and Schwann cells, providing a versatile platform for studying neural networks, neurodevelopment, and neurodegenerative disorders. The use of hiPSCs also opens new avenues for personalized medicine, allowing researchers to model diseases and develop targeted therapies based on individual patient profiles. Despite the promise of direct hiPSC injections for therapeutic purposes, challenges such as poor localization and limited integration have led to the exploration of biomaterial scaffolds as supportive platforms for cell delivery and tissue regeneration. This paper reviews the integration of 3D bioprinting technologies and bioink materials in neuroscience applications, offering a unique platform to create complex brain and tissue architectures that mimic the mechanical, architectural, and biochemical properties of native tissues. These advancements provide robust tools for modelling, repair, and drug screening applications. The review highlights current research, identifies research gaps, and offers recommendations for future studies on 3D bioprinting in neuroscience. The investigation demonstrates the significant potential of 3D bioprinting to fabricate brain-like tissue constructs, which holds great promise for regenerative medicine and drug testing models. This approach offers new avenues for studying brain diseases and potential treatments.

Cation-crosslinkedκ-carrageenan sub-microgel medium for high-quality embedded bioprinting

Three-dimensional (3D) bioprinting embedded within a microgel bath has emerged as a promising strategy for creating intricate biomimetic scaffolds. However, it remains a great challenge to construct tissue-scale structures with high resolution by using embedded 3D bioprinting due to the large particle size and polydispersity of the microgel medium, as well as its limited cytocompatibility. To address these issues, novel uniform sub-microgels of cell-friendly cationic-crosslinked kappa-carrageenan (κ-Car) are developed through an easy-to-operate mechanical grinding strategy. Theseκ-Car sub-microgels maintain a uniform submicron size of around 642 nm and display a rapid jamming-unjamming transition within 5 s, along with excellent shear-thinning and self-healing properties, which are critical for the high resolution and fidelity in the construction of tissue architecture via embedded 3D bioprinting. Utilizing this new sub-microgel medium, various intricate 3D tissue and organ structures, including the heart, lungs, trachea, branched vasculature, kidney, auricle, nose, and liver, are successfully fabricated with delicate fine structures and high shape fidelity. Moreover, the bone marrow mesenchymal stem cells encapsulated within the printed constructs exhibit remarkable viability exceeding 92.1% and robust growth. Thisκ-Car sub-microgel medium offers an innovative avenue for achieving high-quality embedded bioprinting, facilitating the fabrication of functional biological constructs with biomimetic structural organizations.