Engineering alginate as bioink for bioprinting

Bioprinting functional constructs for women's reproductive health: Utilizing tailored biomaterials and biopolymer macromolecules for drug delivery and tissue regeneration

The application of 3D bioprinting, combined with the versatility of biomaterials and biopolymers macromolecules is revolutionizing the landscape of women's reproductive health. Biomaterials, including both natural and synthetic variants, offer unmatched biocompatibility, degradability, and functional adaptability, enabling the development of innovative solutions for complex reproductive disorders. This review examines the pivotal role of biomaterials and biopolymers macromolecules in creating scaffolds, bioinks, and drug delivery systems tailored to address disorders such as endometriosis, polycystic ovary syndrome, gynecological cancers, and so on. By integrating biomaterials, 3D bioprinting overcomes anatomical and physiological challenges unique to the female reproductive tract, such as cyclic hormonal variations and diverse microbiomes, ensuring precise and personalized healthcare interventions. The potential of various polymer-based hydrogels (biomaterials and biopolymers) in sustained drug delivery and regenerative tissue applications is highlighted, along with advancements in tissue-engineered constructs for reproductive health restoration. This amalgamation of polymer science and 3D bioprinting not only enhances therapeutic outcomes but also paves the way for innovative advancements in women's healthcare, addressing long-standing challenges with unparalleled precision and efficacy.

3D Extrusion-Printed Alginate-Gelatin Hydrogel Modified with Nanoscale Hydroxyapatite: A Comprehensive Understanding of Process Science and Evaluation of the Antimicrobial Property

In developing hydrogel scaffolds for the soft tissue regeneration, a number of inorganic or carbonaceous fillers are embedded in alginate/gelatin-based hydrogel while manufacturing shape fidelity compliant constructs using three-dimensional (3D) extrusion printing. Among the spectrum of nanofillers, nanohydroxyapatite (nHAP), due to its intrinsic bioactivity, could promote mineralization and interaction with host tissues while conferring superior mechanical properties (strength and elastic modulus). Against this backdrop, this study demonstrates the effectiveness of nHAP reinforcement in tuning several clinically relevant properties such as rheological properties, mechanical properties, swelling, degradation, and antimicrobial properties. At higher concentrations of nHAP (0.75%) in the hydrogel matrix (3A5G0.75H), a 3.13-fold increment in the compressive strength was observed, with the gel stability window and the thermal stability of the cross-linked graft being extended to greater than 40 and 143 °C, respectively. This study demonstrated the printability of the nHAP-reinforced hydrogel ink by fabricating the matrix-shaped graft of dimension 20 mm in diameter and 10 mm in thickness, and the buildability was established by making the bulk-sized construct up to 62 layers (20 mm in height) with a well-maintained pore interconnectivity, as demonstrated using micro-CT analysis. Interestingly, the CFU study revealed a 2.9- and 1.5-fold improvement in the reduction of bacterial adhesion for 3A5G0.75H with respect to Escherichia coli and Staphylococcus aureus bacteria. Cell culture studies on the 3D printed scaffolds w.r.to NIH 3T3 fibroblast cell line demonstrated a consistent increase in cell viability and pronounced filopodial extensions, confirming the cytocompatibility of 3A5G0.75H scaffolds and their ability to support cellular growth during an in vitro culture. Taken together, the present study uncovers a process science-based understanding of the 3D buildability and biophysical properties of different concentrations of nHAP-reinforced hydrogel inks with clinically relevant properties.

Divalent metal ions enhance bone regeneration through modulation of nervous systems and metabolic pathways

The divalent metal cations promote new bone formation through modulation of sensory and sympathetic nervous systems (SNS) activities. In addition, acetylcholine (Ach), as a chief neurotransmitter released by the parasympathetic nervous system (PNS), also affects bone remodeling, so it is of worth to investigate if the divalent cations influence PNS activity. Of note, these cations are key co-enzymes modulating glucose metabolism. Aerobic glycolysis rather than oxidative phosphorylation favors osteogenesis of mesenchymal stem cells (MSCs), so it is of interest to study the effects of these cations on glucose metabolic pathway. Prior to biological function assessment, the tolerance limits of the divalent metal cations (Mg2+, Zn2+, and Ca2+) and their combinations were profiled. In terms of direct effects, these divalent cations potentially enhanced migration and adhesion capability of MSCs through upregulating Tgf-β1 and Integrin-β1 levels. Interestingly, the divalent cations alone did not influence osteogenesis and aerobic glycolysis of undifferentiated MSCs. However, once the osteogenic differentiation of MSCs was initiated by neurotransmitters or osteogenic differentiation medium, the osteogenesis of MSCs could be significantly promoted by the divalent cations, which was accompanied by the improved aerobic glycolysis. In terms of indirect effects, the divalent cations significantly upregulated levels of sensory nerve derived CGRP, PNS produced choline acetyltransferase and type H vessels, while significantly tuned down sympathetic activity in the defect zone in rats, thereby contributing to significantly increased bone formation relative to the control group. Together, the divalent cations favor bone regeneration via modulation of sensory-autonomic nervous systems and promotion of aerobic glycolysis-driven osteogenesis of MSCs after osteogenic initiation by neurotransmitters.

3D Bioprinting Models for Glioblastoma: From Scaffold Design to Therapeutic Application

Conventional in vitro models fail to accurately mimic the tumor in vivo characteristics, being appointed as one of the causes of clinical attrition rate. Recent advances in 3D culture techniques, replicating essential physical and biochemical cues such as cell-cell and cell-extracellular matrix interactions, have led to the development of more realistic tumor models. Bioprinting has emerged to advance the creation of 3D in vitro models, providing enhanced flexibility, scalability, and reproducibility. This is crucial for the development of more effective drug treatments, and glioblastoma (GBM) is no exception. GBM, the most common and deadly brain cancer, remains a major challenge, with a median survival of only 15 months post-diagnosis. This review highlights the key components needed for 3D bioprinted GBM models. It encompasses an analysis of natural and synthetic biomaterials, along with crosslinking methods to improve structural integrity. Also, it critically evaluates current 3D bioprinted GBM models and their integration into GBM-on-a-chip platforms, which hold noteworthy potential for drug screening and personalized therapies. A versatile development framework grounded on Quality-by-Design principles is proposed to guide the design of bioprinting models. Future perspectives, including 4D bioprinting and machine learning approaches, are discussed, along with the current gaps to advance the field further.

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.

Mucin-Based Dual Cross-Linkable IPN Hydrogel Bioink for 3D Bioprinting and Cartilage Tissue Engineering

The cartilage possesses limited regenerative capacity, necessitating advanced approaches for its repair. This study introduces a bioink designed for cartilage tissue engineering (TE) by incorporating ionically cross-linkable alginate into the photo-cross-linkable MuMA bioink, resulting in a double cross-linked interpenetrating network (IPN) hydrogel. Additionally, hyaluronic acid (HA), a natural component of cartilage and synovial fluid, was added to enhance the scaffold's properties. HA has been demonstrated to improve cartilage lubrication, regulate inflammation, promote cell proliferation, and support extracellular matrix (ECM) deposition and regeneration, making it valuable for cartilage TE. Comprehensive experiments were conducted to assess morphology, swelling, degradation, mechanical and rheological properties, printability, and biocompatibility. Results indicated that the double cross-linked scaffolds comprising MuMA, alginate, and HA exhibited compressive moduli comparable to native cartilage, unlike single cross-linked variants. The double cross-linking also influenced degradation, water uptake, and porosity, contributing to the scaffold durability and stability for chondrocyte support. Biocompatibility tests with C28/I2 cells demonstrated the cell-supportive and chondrogenic potential of the bioink. This study establishes mucin as a versatile material for specialized cartilage tissue engineering applications.

Bioinks for engineering gradient-based osteochondral and meniscal tissue substitutes: a review

Gradient tissues are anisotropic structure with gradual transition in structural and biological properties. The gradient in structural, mechanical and biochemical properties of osteochondral and meniscal tissues play a major role in defining tissue functions. Designing tissue substitutes that replicate these gradient properties is crucial to facilitate regeneration of tissue functions following injuries. Advanced manufacturing technologies such as 3D bioprinting hold great potentials for recreating gradient nature of tissues through using zone-specific bioinks and layer-by-layer deposition of spatially defined biomaterials, cell types and bioactive cues. This review highlighted the gradients in osteochondral and meniscal tissues in detail, elaborated on individual components of the bioink, and reviewed recent advancements in 3D gradient-based osteochondral and meniscal tissue substitutes. Finally, key challenges of the field and future perspectives for developing gradient-based tissue substitutes were discussed. The insights from these advances can broaden the possibilities for engineering gradient tissues.

Sodium Alginate/Poly (Acrylicacid) Hydrogel Composite, Potential Carrier for Fibroblast Growth Factor1 (FGF1) Delivery

Fibroblast growth factor1 is a powerful signaling molecule that plays a critical role in injury repair of diverse tissue by stimulating cell growth and angiogenesis. FGF1 has significant role in the cell fate and regulating inflammation with short half-life and poor in vivo stability. The encapsulation of the growth factor in the hydrogel led to peptide protect from the degradation and/or immune recognition and enable controlled drug delivery over a longer period of time. The aim of this study is to develop and evaluate a hydrogel carrier with adjustable release rate while maintaining bioactivity of FGF1. Here we describe an optimal ratio of sodium alginate and polyacrylic acid without additional cross linker containing optimum amount of FGF1 with the potential of sustained release to be used as a therapeutic agent. The carrier was characterized by FTIR, contact angle and swelling ratio. The activity of FGF1 after release from the hydrogel was confirmed by ELISA and Western blot. Further assessment of genes related to inflammation were evaluated by RTPCR. This hydrogel is able to deliver growth factors by restricting the essential proteins within the matrix to prevent rapid proteolysis and explosive release and is therefore widely applicable.

Decellularized cartilage tissue bioink formulation for osteochondral graft development

Articular cartilage and osteochondral defect repair and regeneration presents significant challenges to the field of tissue engineering (TE). TE and regenerative medicine strategies utilizing natural and synthetic-based engineered scaffolds have shown potential for repair, however, they face limitations in replicating the intricate native microenvironment and structure to achieve optimal regenerative capacity and functional recovery. Herein, we report the development of a cartilage extracellular matrix (ECM) as a printable biomaterial for tissue regeneration. The biomaterial was prepared through decellularization and solubilization of articular cartilage. The effects of two different viscosity modifiers, xanthan gum and Laponite®, and the introduction of a secondary photo-crosslinkable component on the rheological behavior and stability were studied. dcECM-Laponite® bioink formulations demonstrated storage modulus (G') ranging from 750 to 4000 Pa, which is three orders of magnitude higher than that of the dcECM-XG bioink formulations. The rheological evaluation of the bioinks demonstrated the tunability of the bioinks in terms of their viscosity and degree of shear thinning, allowing the formulations to be readily extruded during 3D printing. Also, a spreadable ink composition was identified to form a uniform cartilage layer post-printing. The choice of viscosity modifier along with UV cross-linking warrants shape fidelity of the structure post-printing, as well as improvements in the storage and loss moduli. The modified ECM-based bioink also significantly improved the stability and allowed for prolonged and sustained release of loaded growth factors through the addition of Laponite®. The ECM-based bioink supported human bone-marrow derived stromal cell and chondrocyte viability and increased chondrogenic differentiationin vitro. By forming decellularized cartilage ECM biomaterials in a printable and stable bioink form, we develop a 'Cartilage Ink' that can support cartilaginous tissue formation by closely resembling the native cartilage ECM in structure and function.

Development of Mg-Alginate Based Self Disassociative Bio-Ink for Magnetic Bio-Patterning of 3D Tumor Models

Alginate forms a hydrogel via physical cross-linking with divalent cations. In literature, Ca2+ is mostly utilized due to strong interactions but additional procedures are required to disassociate Ca-alginate hydrogels. On the other hand, Mg-alginate hydrogels disassociate spontaneously, which might benefit certain applications. This study introduces Mg-alginate as the main component of a bio-ink for the first time to obtain 3D tumor models by magnetic bio-patterning technique. The bio-ink contains magnetic nanoparticles (MNPs) for magnetic manipulation, Mg-alginate hydrogel as a sacrificial material, and cells. The applicability of the methodology is tested for the formation of 3D tumor models using HeLa, SaOS-2, and SH-SY5Y cells. Long-term cultures are examined by Live/dead and MTT analysis and revealed high cell viability. Subsequently, Collagen and F-actin expressions are observed successfully in 3D tumor models. Finally, the anti-cancer drug Doxorubicin (DOX) effect is investigated on 3D tumor models, and IC50 values is calculated to assess the drug response. As a result, significantly higher drug resistance is observed for bio-patterned 3D tumor models up to tenfold compared to 2D control. Overall, Mg-alginate hydrogel is successfully used to form bio-patterned 3D tumor models, and the applicability of the model is shown effectively, especially as a drug screening platform.

Engineering considerations in the design of tissue specific bioink for 3D bioprinting applications

Over eight million surgical procedures are conducted annually in the United Stats to address organ failure or tissue losses. In response to this pressing need, recent medical advancements have significantly improved patient outcomes, primarily through innovative reconstructive surgeries utilizing tissue grafting techniques. Despite tremendous efforts, repairing damaged tissues remains a major clinical challenge for bioengineers and clinicians. 3D bioprinting is an additive manufacturing technique that holds significant promise for creating intricately detailed constructs of tissues, thereby bridging the gap between engineered and actual tissue constructs. In contrast to non-biological printing, 3D bioprinting introduces added intricacies, including considerations for material selection, cell types, growth, and differentiation factors. However, technical challenges arise, particularly concerning the delicate nature of living cells in bioink for tissue construction and limited knowledge about the cell fate processes in such a complex biomechanical environment. A bioink must have appropriate viscoelastic and rheological properties to mimic the native tissue microenvironment and attain desired biomechanical properties. Hence, the properties of bioink play a vital role in the success of 3D bioprinted substitutes. This review comprehensively delves into the scientific aspects of tissue-centric or tissue-specific bioinks and sheds light on the current challenges of the translation of bioinks and bioprinting.

Leveraging printability and biocompatibility in materials for printing implantable vessel scaffolds

Vessel scaffolds are crucial for treating cardiovascular diseases (CVDs). It is currently feasible to fabricate vessel scaffolds from a variety of materials using traditional fabrication methods, but the risks of thrombus formation, chronic inflammation, and atherosclerosis associated with these scaffolds have led to significant limitations in the clinical usages. Bioprinting, as an emerging technology, has great potential in constructing implantable vessel scaffolds. During the fabrication of the constructs, the biomaterials used for bioprinting have offered significant contributions for the successful fabrications of the vessel scaffolds. Herein, we review recent advances in biomaterials for bioprinting implantable vessel scaffolds. First, we briefly introduce the requirements for implantable vessel scaffolds and its conventional manufacturing methods. Next, a brief overview of the classic methods for bioprinting vessel scaffolds is presented. Subsequently, we provide an in-depth analysis of the properties of the representative natural, synthetic, composite and hybrid biomaterials that can be used for bioprinting implantable vessel scaffolds. Ultimately, we underscore the necessity of leveraging biocompatibility and printability for biomaterials, and explore the unmet needs and potential applications of these biomaterials in the field of bioprinted implantable vessel scaffolds.

Advances in tumor microenvironment: Applications and challenges of 3D bioprinting

The tumor microenvironment (TME) assumes a pivotal role in the treatment of oncological diseases, given its intricate interplay of diverse cellular components and extracellular matrices. This dynamic ecosystem poses a serious challenge to traditional research methods in many ways, such as high research costs, inefficient translation, poor reproducibility, and low modeling success rates. These challenges require the search for more suitable research methods to accurately model the TME, and the emergence of 3D bioprinting technology is transformative and an important complement to these traditional methods to precisely control the distribution of cells, biomolecules, and matrix scaffolds within the TME. Leveraging digital design, the technology enables personalized studies with high precision, providing essential experimental flexibility. Serving as a critical bridge between in vitro and in vivo studies, 3D bioprinting facilitates the realistic 3D culturing of cancer cells. This comprehensive article delves into cutting-edge developments in 3D bioprinting, encompassing diverse methodologies, biomaterial choices, and various 3D tumor models. Exploration of current challenges, including limited biomaterial options, printing accuracy constraints, low reproducibility, and ethical considerations, contributes to a nuanced understanding. Despite these challenges, the technology holds immense potential for simulating tumor tissues, propelling personalized medicine, and constructing high-resolution organ models, marking a transformative trajectory in oncological research.

Factorial Design of Experiment Method to Characterize Bioprinting Process Parameters to Obtain the Targeted Scaffold Porosity

Due to its inbuilt ability to release biocompatible materials encapsulating living cells in a predefined location, 3D bioprinting is a promising technique for regenerating patient-specific tissues and organs. Among various 3D bioprinting techniques, extrusion-based 3D bioprinting ensures a higher percentage of cell release, ensuring suitable external and internal scaffold architectures. Scaffold architecture is mainly defined by filament geometry and width. A systematic selection of a set of process parameters, such as nozzle diameter, print speed, print distance, extrusion pressure, and material viscosity, can control the filament geometry and width, eventually confirming the user-defined scaffold porosity. For example, carefully selecting two sets of process parameters can result in a similar filament width (FW). However, the lack of availability of sufficient analytical relationships between printing process parameters and FW creates a barrier to achieving defined scaffold architectures with available resources. In this article, the factorial design of experiment (DoE) method has been adopted to obtain a relationship among scaffold properties that is, FW with 3D printing process parameters. The FW was determined using an image processing technique and an analytical relationship was developed, including various process parameters to maintain defined FW variation for different hydrogels within an acceptable range to confirm the overall geometric fidelity of the scaffold. The validation experiment results showed that our analytical relationship obtained from the DoE effectively predicts the scaffold's architectural property. Furthermore, the proposed analytical relationships can help achieve defined scaffold architectures with available resources.

Remote-Controlled Gene Delivery in Coaxial 3D-Bioprinted Constructs using Ultrasound-Responsive Bioinks

Introduction

Coaxial 3D bioprinting has advanced the formation of tissue constructs that recapitulate key architectures and biophysical parameters for in-vitro disease modeling and tissue-engineered therapies. Controlling gene expression within these structures is critical for modulating cell signaling and probing cell behavior. However, current transfection strategies are limited in spatiotemporal control because dense 3D scaffolds hinder diffusion of traditional vectors. To address this, we developed a coaxial extrusion 3D bioprinting technique using ultrasound-responsive gene delivery bioinks. These bioink materials incorporate echogenic microbubble gene delivery particles that upon ultrasound exposure can sonoporate cells within the construct, facilitating controllable transfection.

Methods

Phospholipid-coated gas-core microbubbles were electrostatically coupled to reporter transgene plasmid payloads and incorporated into cell-laden alginate bioinks at varying particle concentrations. These bioinks were loaded into the coaxial nozzle core for extrusion bioprinting with CaCl2 crosslinker in the outer sheath. Resulting bioprints were exposed to 2.25 MHz focused ultrasound and evaluated for microbubble activation and subsequent DNA delivery and transgene expression.

Results

Coaxial printing parameters were established that preserved the stability of ultrasound-responsive gene delivery particles for at least 48 h in bioprinted alginate filaments while maintaining high cell viability. Successful sonoporation of embedded cells resulted in DNA delivery and robust ultrasound-controlled transgene expression. The number of transfected cells was modulated by varying the number of focused ultrasound pulses applied. The size region over which DNA was delivered was modulated by varying the concentration of microbubbles in the printed filaments.

Conclusions

Our results present a successful coaxial 3D bioprinting technique designed to facilitate ultrasound-controlled gene delivery. This platform enables remote, spatiotemporally-defined genetic manipulation in coaxially bioprinted tissue constructs with important applications for disease modeling and regenerative medicine.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00818-x.

Mitochondria-engine with self-regulation to restore degenerated intervertebral disc cells via bioenergetic robust hydrogel design

Previous studies have confirmed that intervertebral disc degeneration (IDD) is closely associated with inflammation-induced reactive oxygen species (ROS) and resultant cell mitochondrial membrane potential (MMP) decline. Clearance of ROS in an inflammatory environment is essential for breaking the vicious cycle of MMP decline. Additionally, re-energizing the mitochondria damaged in the inflammatory milieu to restore their function, is equally important. Herein, we proposed an interesting concept of mitochondrion-engine equipped with coolant, which enables first to "cool-down" the inflammatory environment, next to restore the MMP, finally to allow cells to regain normal energy metabolism through materials design. As such, we developed a multi-functional composite composed of a reactive oxygen species (ROS)-responsive sodium alginate/gelatin hydrogel infused into a rigid 3D-printed thermoplastic polyurethane (TPU) scaffold. The TPU scaffold was coated with conductive polypyrrole (PPy) to electrophoretically deposit l-arginine, which could upregulate the Mammalian target of rapamycin (mTOR) pathway, thus increasing MMP and energy metabolism to stimulate extracellular matrix synthesis for IVD repair. While the ROS-responsive hydrogel acting as the "mito-engine coolant" could scavenge the excessive ROS to create a favorable environment for IVD cells recovery. Demonstrated by in vitro and in vivo evaluations, the mito-engine system markedly promoted the proliferation and collagen synthesis of nucleus pulposus cells while enhancing the mitochondrial respiration and MMP under oxidative stress. Radiological and histological assessments in vivo revealed the efficacy of this system in IVD repair. This unique bioinspired design integrated biomaterial science with mitochondrial biology, presents a promising paradigm for IDD treatment.

Mechanical and Biological Characterization of Ionic and Photo-Crosslinking Effects on Gelatin-Based Hydrogel for Cartilage Tissue Engineering Applications

Articular cartilage degeneration poses a significant public health challenge; techniques such as 3D bioprinting are being explored for its regeneration in vitro. Gelatin-based hydrogels represent one of the most promising biopolymers used in cartilage tissue engineering, especially for its collagen composition and tunable mechanical properties. However, there are no standard protocols that define process parameters such as the crosslinking method to apply. To this aim, a reproducible study was conducted for exploring the influence of different crosslinking methods on 3D bioprinted gelatin structures. This study assessed mechanical properties and cell viability in relation to various crosslinking techniques, revealing promising results particularly for dual (photo + ionic) crosslinking methods, which achieved high cell viability and tunable stiffness. These findings offer new insights into the effects of crosslinking methods on 3D bioprinted gelatin for cartilage applications. For example, ionic and photo-crosslinking methods provide softer materials, with photo-crosslinking supporting cell stretching and diffusion, while ionic crosslinking preserves a spherical stem cell morphology. On the other hand, dual crosslinking provides a stiffer, optimized solution for creating stable cartilage-like constructs. The results of this study offer a new perspective on the standardization of gelatin for cartilage bioprinting, bridging the gap between research and clinical applications.

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.

Bioinks for bioprinting using plant-derived biomaterials

Three-dimensional (3D) bioprinting has revolutionized tissue engineering by enabling the fabrication of complex and functional human tissues and organs. An essential component of successful 3D bioprinting is the selection of an appropriate bioink capable of supporting cell proliferation and viability. Plant-derived biomaterials, because of their abundance, biocompatibility, and tunable properties, hold promise as bioink sources, thus offering advantages over animal-derived biomaterials, which carry immunogenic concerns. This comprehensive review explores and analyzes the potential of plant-derived biomaterials as bioinks for 3D bioprinting of human tissues. Modification and optimization of these materials to enhance printability and biological functionality are discussed. Furthermore, cancer research and drug testing applications of the use of plant-based biomaterials in bioprinting various human tissues such as bone, cartilage, skin, and vascular tissues are described. Challenges and limitations, including mechanical integrity, cell viability, resolution, and regulatory concerns, along with potential strategies to overcome them, are discussed. Additionally, this review provides insights into the potential use of plant-based decellularized ECM (dECM) as bioinks, future prospects, and emerging trends in the use of plant-derived biomaterials for 3D bioprinting applications. The potential of plant-derived biomaterials as bioinks for 3D bioprinting of human tissues is highlighted herein. However, further research is necessary to optimize their processing, standardize their properties, and evaluate their long-termin vivoperformance. Continued advancements in plant-derived biomaterials have the potential to revolutionize tissue engineering and facilitate the development of functional and regenerative therapies for diverse clinical applications.

Light-Responsive and Antibacterial Graphenic Materials as a Holistic Approach to Tissue Engineering

While the continuous development of advanced bioprinting technologies is under fervent study, enhancing the regenerative potential of hydrogel-based constructs using external stimuli for wound dressing has yet to be tackled. Fibroblasts play a significant role in wound healing and tissue implants at different stages, including extracellular matrix production, collagen synthesis, and wound and tissue remodeling. This study explores the synergistic interplay between photothermal activity and nanomaterial-mediated cell proliferation. The use of different graphene-based materials (GBM) in the development of photoactive bioinks is investigated. In particular, we report the creation of a skin-inspired dressing for wound healing and regenerative medicine. Three distinct GBM, namely, graphene oxide (GO), reduced graphene oxide (rGO), and graphene platelets (GP), were rigorously characterized, and their photothermal capabilities were elucidated. Our investigations revealed that rGO exhibited the highest photothermal efficiency and antibacterial properties when irradiated, even at a concentration as low as 0.05 mg/mL, without compromising human fibroblast viability. Alginate-based bioinks alongside human fibroblasts were employed for the bioprinting with rGO. The scaffold did not affect the survival of fibroblasts for 3 days after bioprinting, as cell viability was not affected. Remarkably, the inclusion of rGO did not compromise the printability of the hydrogel, ensuring the successful fabrication of complex constructs. Furthermore, the presence of rGO in the final scaffold continued to provide the benefits of photothermal antimicrobial therapy without detrimentally affecting fibroblast growth. This outcome underscores the potential of rGO-enhanced hydrogels in tissue engineering and regenerative medicine applications. Our findings hold promise for developing game-changer strategies in 4D bioprinting to create smart and functional tissue constructs with high fibroblast proliferation and promising therapeutic capabilities in drug delivery and bactericidal skin-inspired dressings.

Click method preserves but EDC method compromises the therapeutic activities of the peptide-activated hydrogels for critical ischemic vessel regeneration

Peptide-functionalized hydrogel is one of commonly used biomaterials to introduce hydrogel-induced vessel regeneration. Despite many reports about the discoveries of high-active peptides (or ligands) for regeneration, the study on the conjugating methods for the hydrogel functionalization with peptides is limited. Here, we compared the vasculogenic efficacy of the peptide-functionalized hydrogels prepared by two commonly used conjugating methods, 1-ethyl-3-(3-dimethylamino propyl) carbodiimide (EDC) and Click methods, through cell models, organ-on-chips models, animal models, and RNA sequencing analysis. Two vascular-related cell types, the human umbilical vein endothelial cells (HUVECs) and the adipose-derived stem cells (ADSCs), have been cultured on the hydrogel surfaces prepared by EDC/Click methods. It showed that the hydrogels prepared by Click method supported the higher vasculogenic activities while the ones made by EDC method compromised the peptide activities on hydrogels. The vasculogenesis assays further revealed that hydrogels prepared by Click method promoted a better vascular network formation. In a critical ischemic hindlimb model, only the peptide-functionalized hydrogels prepared by Click method successfully salvaged the ischemic limb, significantly improved blood perfusion, and enhanced the functional recoveries (through gait analysis and animal behavior studies). RNA sequencing studies revealed that the hydrogels prepared by Click method significantly promoted the PI3K-AKT pathway activation compared to the hydrogels prepared by EDC method. All the results suggested that EDC method compromised the functions of the peptides, while Click method preserved the vascular regenerating capacities of the peptides on the hydrogels, illustrating the importance of the conjugating method during the preparation of the peptide-functionalized hydrogels.

Recent Advances in Hydrogel-Based 3D Bioprinting and Its Potential Application in the Treatment of Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect, requiring invasive surgery often before a child's first birthday. Current materials used during CHD surgery lack the ability to grow, remodel, and regenerate. To solve those limitations, 3D bioprinting is an emerging tool with the capability to create tailored constructs based on patients' own imaging data with the ability to grow and remodel once implanted in children with CHD. It has the potential to integrate multiple bioinks with several cell types and biomolecules within 3D-bioprinted constructs that exhibit good structural fidelity, stability, and mechanical integrity. This review gives an overview of CHD and recent advancements in 3D bioprinting technologies with potential use in the treatment of CHD. Moreover, the selection of appropriate biomaterials based on their chemical, physical, and biological properties that are further manipulated to suit their application are also discussed. An introduction to bioink formulations composed of various biomaterials with emphasis on multiple cell types and biomolecules is briefly overviewed. Vasculogenesis and angiogenesis of prefabricated 3D-bioprinted structures and novel 4D printing technology are also summarized. Finally, we discuss several restrictions and our perspective on future directions in 3D bioprinting technologies in the treatment of CHD.

Single-Step 3D Bioprinting of Alginate-Collagen Type I Hydrogel Fiber Rings to Promote Angiogenic Network Formation

In the advent of tissue engineering and regenerative medicine, the demand for innovative approaches to biofabricate complex vascular structures is increasing. We describe a single-step 3D bioprinting method leveraging Aspect Biosystems RX1 technology, which integrates the crosslinking step at a flow-focusing junction, to biofabricate immortalized adult rat brain endothelial cell (SV-ARBEC)-encapsulated alginate-collagen type I hydrogel rings. This single-step biofabrication process involves the strategic layer-by-layer assembly of hydrogel rings, encapsulating SV-ARBECs in a spatially controlled manner while optimizing access to media and nutrients. The spatial arrangement of the SV-ARBECs within the rings promotes spontaneous angiogenic network formation and the constrained deposition of cells within the hydrogel matrix facilitates tissue-like organized vascular-like network development. This approach provides a platform that can be adapted to many different endothelial cell types and leveraged to better understand the mechanisms driving angiogenesis and vascular-network formation in 3D bioprinted constructs supporting the development of more complex tissue and disease models for advancing drug discovery, tissue engineering, and regenerative medicine applications.

Biomaterials for extrusion-based bioprinting and biomedical applications

Amongst the range of bioprinting technologies currently available, bioprinting by material extrusion is gaining increasing popularity due to accessibility, low cost, and the absence of energy sources, such as lasers, which may significantly damage the cells. New applications of extrusion-based bioprinting are systematically emerging in the biomedical field in relation to tissue and organ fabrication. Extrusion-based bioprinting presents a series of specific challenges in relation to achievable resolutions, accuracy and speed. Resolution and accuracy in particular are of paramount importance for the realization of microstructures (for example, vascularization) within tissues and organs. Another major theme of research is cell survival and functional preservation, as extruded bioinks have cells subjected to considerable shear stresses as they travel through the extrusion apparatus. Here, an overview of the main available extrusion-based printing technologies and related families of bioprinting materials (bioinks) is provided. The main challenges related to achieving resolution and accuracy whilst assuring cell viability and function are discussed in relation to specific application contexts in the field of tissue and organ fabrication.

Bioinspired Bioinks for the Fabrication of Chemomechanically Relevant Standalone Disease Models of Hepatic Steatosis

Hepatotoxicity-related issues are poorly predicted during preclinical experimentation, as its relevance is limited by the inadequacy to screen all the non-physiological subclasses of the population. These pitfalls can be solved by implementing complex in vitro models of hepatic physiology and pathologies in the preclinical phase. To produce these platforms, extrusion-based bioprinting is focused on, since it allows to manufacture tridimensional cell-laden constructs with controlled geometries, in a high-throughput manner. Different bioinks, whose formulation is tailored to mimic the chemomechanical environment of hepatic steatosis, the most prevalent hepatic disorder worldwide, are proposed. Internally crosslinked alginate hydrogels are chosen as structural components of the inks. Their viscoelastic properties (G' = 512-730 Pa and G″ = 94-276 Pa, depending on frequency) are tuned to mimic those of steatotic liver tissue. Porcine hepatic ECM is introduced as a relevant biochemical cue. Sodium oleate is added to recall the accumulation of lipids in the tissue. Downstream analyses on 14-layered bioprinted structures cultured for 10 days reveal the establishment of steatotic-like features (intracellular lipid vesicles, viability decrease up to ≈50%) without needing external conditionings. The presented bioinks are thus suitable to fabricate complex models of hepatic steatosis to be implemented in a high-throughput experimental frame.

Development of 3D-Printable Albumin-Alginate Foam for Wound Dressing Applications

In this article, a method to develop 3D printable hybrid sodium alginate and albumin foam, crosslinked with calcium chloride mist is introduced. Using this method, highly porous structures are produced without the need of further postprocessing (such as freeze drying). The proposed method is particularly beneficial in the development of wound dressing as the printed foams show excellent lift-off and water absorption properties. Compared with methods that use liquid crosslinker, the use of mist prevents the leaching of biocompounds into the liquid crosslinker. 3D printing technique was chosen to provide more versatility over the wound dressing geometry. Calcium chloride and rhodamine B were used as the crosslinking material and the model drug, respectively. Various biomaterial inks were prepared by different concentrations of sodium alginate and albumin, and the fabricated scaffolds were crosslinked in mist, liquid, or kept without crosslinking. The effects of biomaterial composition and the crosslinking density on the wound dressing properties were assessed through printability studies. The mist-crosslinked biomaterial ink composed of 1% (w/v) sodium alginate and 12% (w/v) albumin showed the superior printability. The fabricated scaffolds were also characterized through porosity, mechanical, degradation, and drug release tests. The mist-crosslinked scaffolds showed superior mechanical properties and provided relatively prolonged drug release.

Application of 3D, 4D, 5D, and 6D bioprinting in cancer research: what does the future look like?

The application of three- and four-dimensional (3D/4D) printing in cancer research represents a significant advancement in understanding and addressing the complexities of cancer biology. 3D/4D materials provide more physiologically relevant environments compared to traditional two-dimensional models, allowing for a more accurate representation of the tumor microenvironment that enables researchers to study tumor progression, drug responses, and interactions with surrounding tissues under conditions similar to in vivo conditions. The dynamic nature of 4D materials introduces the element of time, allowing for the observation of temporal changes in cancer behavior and response to therapeutic interventions. The use of 3D/4D printing in cancer research holds great promise for advancing our understanding of the disease and improving the translation of preclinical findings to clinical applications. Accordingly, this review aims to briefly discuss 3D and 4D printing and their advantages and limitations in the field of cancer. Moreover, new techniques such as 5D/6D printing and artificial intelligence (AI) are also introduced as methods that could be used to overcome the limitations of 3D/4D printing and opened promising ways for the fast and precise diagnosis and treatment of cancer.

Nanofibrous polyelectrolyte complex incorporated BSA-alginate composite bioink for 3D bioprinting of bone mimicking constructs

Although several bioinks have been developed for 3D bioprinting applications, the lack of optimal printability, mechanical properties, and adequate cell response has limited their practical applicability. Therefore, this work reports the development of a composite bioink consisting of bovine serum albumin (BSA), alginate, and self-assembled nanofibrous polyelectrolyte complex aggregates of gelatin and chitosan (PEC-GC). The nanofibrous PEC-GC aggregates were prepared and incorporated into the bioink in varying concentrations (0 % to 3 %). The bioink samples were bioprinted and crosslinked post-printing by calcium chloride. The average nanofiber diameter of PEC-GC was 62 ± 15 nm. It was demonstrated that PEC-GC improves the printability and cellular adhesion of the developed bioink and modulates the swelling ratio, degradation rate, and mechanical properties of the fabricated scaffold. The in vitro results revealed that the bioink with 2 % PEC-GC had the best post-printing cell viability of the encapsulated MG63 osteosarcoma cells and well oragnized stress fibers, indicating enhanced cell adhesion. The cell viability was >90 %, as observed from the MTT assay. The composite bioink also showed osteogenic potential, as confirmed by the estimation of alkaline phosphatase activity and collagen synthesis assay. This study successfully fabricated a high-shape fidelity bioink with potential in bone tissue engineering.

Investigating the Effect of Processing and Material Parameters of Alginate Dialdehyde-Gelatin (ADA-GEL)-Based Hydrogels on Stiffness by XGB Machine Learning Model

To address the limitations of alginate and gelatin as separate hydrogels, partially oxidized alginate, alginate dialdehyde (ADA), is usually combined with gelatin to prepare ADA-GEL hydrogels. These hydrogels offer tunable properties, controllable degradation, and suitable stiffness for 3D bioprinting and tissue engineering applications. Several processing variables affect the final properties of the hydrogel, including degree of oxidation, gelatin content and type of crosslinking agent. In addition, in 3D-printed structures, pore size and the possible addition of a filler to make a hydrogel composite also affect the final physical and biological properties. This study utilized datasets from 13 research papers, encompassing 33 unique combinations of ADA concentration, gelatin concentration, CaCl2 and microbial transglutaminase (mTG) concentrations (as crosslinkers), pore size, bioactive glass (BG) filler content, and one identified target property of the hydrogels, stiffness, utilizing the Extreme Boost (XGB) machine learning algorithm to create a predictive model for understanding the combined influence of these parameters on hydrogel stiffness. The stiffness of ADA-GEL hydrogels is notably affected by the ADA to GEL ratio, and higher gelatin content for different ADA gel concentrations weakens the scaffold, likely due to the presence of unbound gelatin. Pore size and the inclusion of a BG particulate filler also have a significant impact on stiffness; smaller pore sizes and higher BG content lead to increased stiffness. The optimization of ADA-GEL composition and the inclusion of BG fillers are key determinants to tailor the stiffness of these 3D printed hydrogels, as found by the analysis of the available data.

Gelatin Methacryloyl (GelMA)-Based Biomaterial Inks: Process Science for 3D/4D Printing and Current Status

Tissue engineering for injured tissue replacement and regeneration has been a subject of investigation over the last 30 years, and there has been considerable interest in using additive manufacturing to achieve these goals. Despite such efforts, many key questions remain unanswered, particularly in the area of biomaterial selection for these applications as well as quantitative understanding of the process science. The strategic utilization of biological macromolecules provides a versatile approach to meet diverse requirements in 3D printing, such as printability, buildability, and biocompatibility. These molecules play a pivotal role in both physical and chemical cross-linking processes throughout the biofabrication, contributing significantly to the overall success of the 3D printing process. Among the several bioprintable materials, gelatin methacryloyl (GelMA) has been widely utilized for diverse tissue engineering applications, with some degree of success. In this context, this review will discuss the key bioengineering approaches to identify the gelation and cross-linking strategies that are appropriate to control the rheology, printability, and buildability of biomaterial inks. This review will focus on the GelMA as the structural (scaffold) biomaterial for different tissues and as a potential carrier vehicle for the transport of living cells as well as their maintenance and viability in the physiological system. Recognizing the importance of printability toward shape fidelity and biophysical properties, a major focus in this review has been to discuss the qualitative and quantitative impact of the key factors, including microrheological, viscoelastic, gelation, shear thinning properties of biomaterial inks, and printing parameters, in particular, reference to 3D extrusion printing of GelMA-based biomaterial inks. Specifically, we emphasize the different possibilities to regulate mechanical, swelling, biodegradation, and cellular functionalities of GelMA-based bio(material) inks, by hybridization techniques, including different synthetic and natural biopolymers, inorganic nanofillers, and microcarriers. At the close, the potential possibility of the integration of experimental data sets and artificial intelligence/machine learning approaches is emphasized to predict the printability, shape fidelity, or biophysical properties of GelMA bio(material) inks for clinically relevant tissues.

Photo-/thermo-responsive bioink for improved printability in extrusion-based bioprinting

Extrusion-based bioprinting has demonstrated significant potential for manufacturing constructs, particularly for 3D cell culture. However, there is a greatly limited number of bioink candidates exploited with extrusion-based bioprinting, as they meet the opposing requirements for printability with indispensable rheological features and for biochemical functionality with desirable microenvironment. In this study, a blend of silk fibroin (SF) and iota-carrageenan (CG) was chosen as a cell-friendly printable material. The SF/CG ink exhibited suitable viscosity and shear-thinning properties, coupled with the rapid sol-gel transition of CG. By employing photo-crosslinking of SF, the printability with Pr value close to 1 and structural integrity of the 3D constructs were significantly improved within a matter of seconds. The printed constructs demonstrated a Young's modulus of approximately 250 kPa, making them suitable for keratinocyte and myoblast cell culture. Furthermore, the high cell adhesiveness and viability (maximum >98%) of the loaded cells underscored the considerable potential of this 3D culture scaffold applied for skin and muscle tissues, which can be easily manipulated using an extrusion-based bioprinter.

Biofabrication of engineered blood vessels for biomedical applications

To successfully engineer large-sized tissues, establishing vascular structures is essential for providing oxygen, nutrients, growth factors and cells to prevent necrosis at the core of the tissue. The diameter scale of the biofabricated vasculatures should range from 100 to 1,000 µm to support the mm-size tissue while being controllably aligned and spaced within the diffusion limit of oxygen. In this review, insights regarding biofabrication considerations and techniques for engineered blood vessels will be presented. Initially, polymers of natural and synthetic origins can be selected, modified, and combined with each other to support maturation of vascular tissue while also being biocompatible. After they are shaped into scaffold structures by different fabrication techniques, surface properties such as physical topography, stiffness, and surface chemistry play a major role in the endothelialization process after transplantation. Furthermore, biological cues such as growth factors (GFs) and endothelial cells (ECs) can be incorporated into the fabricated structures. As variously reported, fabrication techniques, especially 3D printing by extrusion and 3D printing by photopolymerization, allow the construction of vessels at a high resolution with diameters in the desired range. Strategies to fabricate of stable tubular structures with defined channels will also be discussed. This paper provides an overview of the many advances in blood vessel engineering and combinations of different fabrication techniques up to the present time.

Differentiation of Human Adipose-derived Stem Cells to Exosome-affected Neural-like Cells Extracted from Human Cerebrospinal Fluid Using Bioprinting Process

BACKGROUND

Advancement in tissue engineering has provided novel solutions for creating scaffolds as well as applying induction factors in the differentiation of stem cells. The present research aimed to investigate the differentiation of human adipose-derived mesenchymal stem cells to neural-like cells using the novel bioprinting method, as well as the effect of cerebrospinal fluid exosomes.

METHODS

In the present study, the extent of neuronal proliferation and differentiation of adipose- derived stem cells were explored using the MTT method, immunocytochemistry, and real-- time PCR in the scaffolds created by the bioprinting process. Furthermore, in order to investigate the veracity of the identity of the CSF (Cerebrospinal fluid) derived exosomes, after the isolation of exosomes, dynamic light scattering (DLS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques were used.

RESULTS

MTT findings indicated survivability and proliferation of cells in the scaffolds created by the bioprinting process during a 14-day period. The results obtained from real-time PCR showed that the level of MAP2 gene (Microtubule Associated Protein 2) expression increased on days 7 and 14, while the expression of the Nestin gene (intermediate filament protein) significantly decreased compared to the control. The investigation to confirm the identity of exosomes indicated that the CSF-derived exosomes had a spherical shape with a 40-100 nm size.

CONCLUSION

CSF-derived exosomes can contribute to the neuronal differentiation of adipose- derived stem cells in alginate hydrogel scaffolds created by the bioprinting process.

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

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

Smart alginate inks for tissue engineering applications

Amazing achievements have been made in the field of tissue engineering during the past decades. However, we have not yet seen fully functional human heart, liver, brain, or kidney tissue emerge from the clinics. The promise of tissue engineering is thus still not fully unleashed. This is mainly related to the challenges associated with producing tissue constructs with similar complexity as native tissue. Bioprinting is an innovative technology that has been used to obliterate these obstacles. Nevertheless, natural organs are highly dynamic and can change shape over time; this is part of their functional repertoire inside the body. 3D-bioprinted tissue constructs should likewise adapt to their surrounding environment and not remain static. For this reason, the new trend in the field is 4D bioprinting - a new method that delivers printed constructs that can evolve their shape and function over time. A key lack of methodology for printing approaches is the scalability, easy-to-print, and intelligent inks. Alginate plays a vital role in driving innovative progress in 3D and 4D bioprinting due to its exceptional properties, scalability, and versatility. Alginate's ability to support 3D and 4D printing methods positions it as a key material for fueling advancements in bioprinting across various applications, from tissue engineering to regenerative medicine and beyond. Here, we review the current progress in designing scalable alginate (Alg) bioinks for 3D and 4D bioprinting in a "dry"/air state. Our focus is primarily on tissue engineering, however, these next-generation materials could be used in the emerging fields of soft robotics, bioelectronics, and cyborganics.

Translational biomaterials of four-dimensional bioprinting for tissue regeneration

Bioprinting is an additive manufacturing technique that combines living cells, biomaterials, and biological molecules to develop biologically functional constructs. Three-dimensional (3D) bioprinting is commonly used as anin vitromodeling system and is a more accurate representation ofin vivoconditions in comparison to two-dimensional cell culture. Although 3D bioprinting has been utilized in various tissue engineering and clinical applications, it only takes into consideration the initial state of the printed scaffold or object. Four-dimensional (4D) bioprinting has emerged in recent years to incorporate the additional dimension of time within the printed 3D scaffolds. During the 4D bioprinting process, an external stimulus is exposed to the printed construct, which ultimately changes its shape or functionality. By studying how the structures and the embedded cells respond to various stimuli, researchers can gain a deeper understanding of the functionality of native tissues. This review paper will focus on the biomaterial breakthroughs in the newly advancing field of 4D bioprinting and their applications in tissue engineering and regeneration. In addition, the use of smart biomaterials and 4D printing mechanisms for tissue engineering applications is discussed to demonstrate potential insights for novel 4D bioprinting applications. To address the current challenges with this technology, we will conclude with future perspectives involving the incorporation of biological scaffolds and self-assembling nanomaterials in bioprinted tissue constructs.

Hemostatic patch with ultra-strengthened mechanical properties for efficient adhesion to wet surfaces

Controlling traumatic bleeding from damaged internal organs while effectively sealing the wound is critical for saving the lives of patients. Existing bioadhesives suffer from blood incompatibility, insufficient adhesion to wet surfaces, weak mechanical properties, and complex application procedures. Here, we engineered a ready-to-use hemostatic bioadhesive with ultra-strengthened mechanical properties and fatigue resistance, robust adhesion to wet tissues within a few seconds of gentle pressing, deformability to accommodate physiological function and action, and the ability to stop bleeding efficiently. The engineered hydrogel, which demonstrated high elasticity (>900%) and toughness (>4600 kJ/m3), was formed by fine-tuning a series of molecular interactions and crosslinking mechanisms involving N-hydroxysuccinimide (NHS) conjugated alginate (Alg-NHS), poly (ethylene glycol) diacrylate (PEGDA), tannic acid (TA), and Fe3+ ions. Dual adhesive moieties including mussel-inspired pyrogallol/catechol and NHS synergistically enhanced wet tissue adhesion (>400 kPa in a wound closure test). In conjunction with physical sealing, the high affinity of TA/Fe3+ for blood could further augment hemostasis. The engineered bioadhesive demonstrated excellent in vitro and in vivo biocompatibility as well as improved hemostatic efficacy as compared to commercial Surgicel®. Overall, the hydrogel design strategy described herein holds great promise for overcoming existing obstacles impeding clinical translation of engineered hemostatic bioadhesives.

A bioactive microparticle-loaded osteogenically enhanced bioprinted scaffold that permits sustained release of BMP-2

Extrusion-based bioprinting technology is widely used for tissue regeneration and reconstruction. However, the method that uses only hydrogel as the bioink base material exhibits limited biofunctional properties and needs improvement to achieve the desired tissue regeneration. In this study, we present a three-dimensionally printed bioactive microparticle-loaded scaffold for use in bone regeneration applications. The unique structure of the microparticles provided sustained release of growth factor for > 4 weeks without the use of toxic or harmful substances. Before and after printing, the optimal particle ratio in the bioink for cell viability demonstrated a survival rate of ≥ 85% over 7 days. Notably, osteogenic differentiation and mineralization-mediated by human periosteum-derived cells in scaffolds with bioactive microparticles-increased over a 2-week interval. Here, we present an alternative bioprinting strategy that uses the sustained release of bioactive microparticles to improve biofunctional properties in a manner that is acceptable for clinical bone regeneration applications.

Development of lumen-based perfusable 3D liver in vitro model using single-step bioprinting with composite bioinks

Hepatic sinusoids are uniquely organized structures that help maintain a spectrum of hepatic functions. Although several in vitro liver models have been developed to replicate liver sinusoids, most of these platforms require complex, multi-step fabrication methods making it difficult to achieve truly three-dimensional (3D) channel geometries. In this study, a single-step bioprinting technique was demonstrated to simultaneously print a chip platform and develop a perfusable vascularized liver sinusoid in vitro model. The integrated system uses a co-axial-based bioprinting approach to develop a liver sinusoid-like model that consists of a sacrificial core compartment containing a perfusable pre-vascular structure and an alginate-collagen-based shell compartment containing hepatocytes. The lumen-based perfusable 3D liver sinusoid-on-a-chip (LSOC-P) demonstrated significantly better hepatocyte viability, proliferation, and liver-specific gene and protein expression compared to a 3D hepatocyte-based core/shell model with static media and the standard hepatocyte-based 2D sandwich culture system. A drug toxicity evaluation of hepatotoxins highlighted the comparatively higher sensitivity of the LSOC system with a close estimation of the therapeutic range of safe drug concentrations for humans. In conclusion, the current findings indicate that the combinatorial single-step co-axial bioprinting technique is a promising fabrication approach for the development of a perfusable LSOC platform for drug screening applications.

Harnessing decellularised extracellular matrix microgels into modular bioinks for extrusion-based bioprinting with good printability and high post-printing cell viability

The printability of bioink and post-printing cell viability is crucial for extrusion-based bioprinting. A proper bioink not only provides mechanical support for structural fidelity, but also serves as suitable three-dimensional (3D) microenvironment for cell encapsulation and protection. In this study, a hydrogel-based composite bioink was developed consisting of gelatin methacryloyl (GelMA) as the continuous phase and decellularised extracellular matrix microgels (DMs) as the discrete phase. A flow-focusing microfluidic system was employed for the fabrication of cell-laden DMs in a high-throughput manner. After gentle mixing of the DMs and GelMA, both rheological characterisations and 3D printing tests showed that the resulting DM-GelMA hydrogel preserved the shear-thinning nature, mechanical properties, and good printability from GelMA. The integration of DMs not only provided an extracellular matrix-like microenvironment for cell encapsulation, but also considerable shear-resistance for high post-printing cell viability. The DM sizes and inner diameters of the 3D printer needles were correlated and optimised for nozzle-based extrusion. Furthermore, a proof-of-concept bioink composedg of RSC96 Schwann cells encapsulated DMs and human umbilical vein endothelial cell-laden GelMA was successfully bioprinted into 3D constructs, resulting in a modular co-culture system with distinct cells/materials distribution. Overall, the modular DM-GelMA bioink provides a springboard for future precision biofabrication and will serve in numerous biomedical applications such as tissue engineering and drug screening.

Architecting oxidized alginate methacrylate hydrogels with tunable characteristics by altering the sequence of the cross-linking steps, methacrylation reaction time, and polymer concentration

In this study, biodegradable oxidized methacrylated alginate (OMA) hydrogels with controllable mechanical properties were engineered. An ionic and photo cross-linking combination was employed to fabricate dual cross-linked hydrogels. By altering the degree of methacrylation and polymer concentration, hydrogels with an elastic modulus of 4.85 ± 0.13 to 21.02 ± 0.91 kPa, controllable swelling, and degradation kinetics, and cross-link density in the range of 1.0 × 10^-5 to 6.5 × 10^-5 mol/cm³ were obtained. Moreover, evaluating the effect of cross-linking sequence on the hydrogels' mechanical properties demonstrated that in comparison to the hydrogels fabricated by ionic cross-linking followed by photo-polymerization, hydrogels produced by photo-polymerization followed by ionic cross-linking retain a stiffer gel network with more compact structure. Cytocompatibility examination was performed via MTT assay against L929 fibroblasts, and all the hydrogel samples demonstrated high cell viability (>80%). The findings demonstrate the significant effect of the sequence of cross-linking as a novel tool to tune the OMA hydrogel's final properties which can serve as a useful platform for tissue engineering applications.

3D Bioprinting of Hyaline Articular Cartilage: Biopolymers, Hydrogels, and Bioinks

The musculoskeletal system, consisting of bones and cartilage of various types, muscles, ligaments, and tendons, is the basis of the human body. However, many pathological conditions caused by aging, lifestyle, disease, or trauma can damage its elements and lead to severe disfunction and significant worsening in the quality of life. Due to its structure and function, articular (hyaline) cartilage is the most susceptible to damage. Articular cartilage is a non-vascular tissue with constrained self-regeneration capabilities. Additionally, treatment methods, which have proven efficacy in stopping its degradation and promoting regeneration, still do not exist. Conservative treatment and physical therapy only relieve the symptoms associated with cartilage destruction, and traditional surgical interventions to repair defects or endoprosthetics are not without serious drawbacks. Thus, articular cartilage damage remains an urgent and actual problem requiring the development of new treatment approaches. The emergence of biofabrication technologies, including three-dimensional (3D) bioprinting, at the end of the 20th century, allowed reconstructive interventions to get a second wind. Three-dimensional bioprinting creates volume constraints that mimic the structure and function of natural tissue due to the combinations of biomaterials, living cells, and signal molecules to create. In our case-hyaline cartilage. Several approaches to articular cartilage biofabrication have been developed to date, including the promising technology of 3D bioprinting. This review represents the main achievements of such research direction and describes the technological processes and the necessary biomaterials, cell cultures, and signal molecules. Special attention is given to the basic materials for 3D bioprinting-hydrogels and bioinks, as well as the biopolymers underlying the indicated products.

3D Bioprinting as a Powerful Technique for Recreating the Tumor Microenvironment

In vitro three-dimensional models aim to reduce and replace animal testing and establish new tools for oncology research and the development and testing of new anticancer therapies. Among the various techniques to produce more complex and realistic cancer models is bioprinting, which allows the realization of spatially controlled hydrogel-based scaffolds, easily incorporating different types of cells in order to recreate the crosstalk between cancer and stromal components. Bioprinting exhibits other advantages, such as the production of large constructs, the repeatability and high resolution of the process, as well as the possibility of vascularization of the models through different approaches. Moreover, bioprinting allows the incorporation of multiple biomaterials and the creation of gradient structures to mimic the heterogeneity of the tumor microenvironment. The aim of this review is to report the main strategies and biomaterials used in cancer bioprinting. Moreover, the review discusses several bioprinted models of the most diffused and/or malignant tumors, highlighting the importance of this technique in establishing reliable biomimetic tissues aimed at improving disease biology understanding and high-throughput drug screening.

Current advancements in bio-ink technology for cartilage and bone tissue engineering

In tissue engineering, the fate of a particular organ/tissue regeneration and repair mainly depends on three pillars - 3D architecture, cells used, and stimulus provided. 3D cell supportive structure development is one of the crucial pillars necessary for defining organ/tissue geometry and shape. In recent years, the advancements in 3D bio-printing (additive manufacturing) made it possible to develop very precise 3D architectures with the help of industrial software like Computer-Aided Design (CAD). The main requirement for the 3D printing process is the bio-ink, which can act as a source for cell support, proliferation, drug (growth factors, stimulators) delivery, and organ/tissue shape. The selection of the bio-ink depends upon the type of 3D tissue of interest. Printing tissues like bone and cartilage is always challenging because it is difficult to find printable biomaterial that can act as bio-ink and mimic the strength of the natural bone and cartilage tissues. This review describes different biomaterials used to develop bio-inks with different processing variables and cell-seeding densities for bone and cartilage 3D printing applications. The review also discusses the advantages, limitations, and cell bio-ink compatibility in each biomaterial section. The emphasis is given to bio-inks reported for 3D printing cartilage and bone and their applications in orthopedics and orthodontists. The critical/important performance and the architectural morphology requirements of desired bone and cartilage bio-inks were compiled in summary.

Global hotspots and emerging trends in 3D bioprinting research

Three-dimensional (3D) bioprinting is an advanced tissue engineering technique that has received a lot of interest in the past years. We aimed to highlight the characteristics of articles on 3D bioprinting, especially in terms of research hotspots and focus. Publications related to 3D bioprinting from 2007 to 2022 were acquired from the Web of Science Core Collection database. We have used VOSviewer, CiteSpace, and R-bibliometrix to perform various analyses on 3,327 published articles. The number of annual publications is increasing globally, a trend expected to continue. The United States and China were the most productive countries with the closest cooperation and the most research and development investment funds in this field. Harvard Medical School and Tsinghua University are the top-ranked institutions in the United States and China, respectively. Dr. Anthony Atala and Dr. Ali Khademhosseini, the most productive researchers in 3D bioprinting, may provide cooperation opportunities for interested researchers. Tissue Engineering Part A contributed the largest publication number, while Frontiers in Bioengineering and Biotechnology was the most attractive journal with the most potential. As for the keywords in 3D bioprinting, Bio-ink, Hydrogels (especially GelMA and Gelatin), Scaffold (especially decellularized extracellular matrix), extrusion-based bioprinting, tissue engineering, and in vitro models (organoids particularly) are research hotspots analyzed in the current study. Specifically, the research topics "new bio-ink investigation," "modification of extrusion-based bioprinting for cell viability and vascularization," "application of 3D bioprinting in organoids and in vitro model" and "research in personalized and regenerative medicine" were predicted to be hotspots for future research.

Multi-thermo responsive double network composite hydrogel for 3D printing medical hydrogel mask

3D printing of multifunctional hydrogels offers great opportunities for developing innovative biomedical technologies as it can provide custom-designed shapes and structures conformal to arbitrary contours. There have been significant improvements of the 3D printing techniques, but the available printable hydrogel materials limit the progress. Here, we investigated the use of a poloxamer diacrylate (Pluronic P123) to augment the thermo-responsive network composed of poly(N-isopropylacrylamide) and develop a multi-thermoresponsive hydrogel for photopolymerization 3D printing. The hydrogel precursor resin was synthesised to be printable with high-fidelity of fine structures and once cured can form a robust thermo-responsive hydrogel. By utilizing N-isopropyl acrylamide monomer and a Pluronic P123 diacrylate crosslinker as 2 separate thermo-responsive components it was found that the final hydrogel displayed 2 distinct lower critical solution temperature (LCST) switches. This enables the loading of hydrophilic drugs at fridge temperature and improving the strength of the hydrogel at room temperature while still maintaining a drug release at body temperature. The thermo-responsive material properties of this multifunctional hydrogel material system were investigated, showing a significant promise as a medical hydrogel mask. Furthermore, it is demonstrated that it can be printed in sizes large enough to fit and adhere to a human face at 1:1 scale with high dimensional accuracy, as well as its ability to load with hydrophilic drugs.

Bioprinting: a focus on improving bioink printability and cell performance based on different process parameters

Three dimensional (3D) bioprinting is an emerging biofabrication technique that shows great potential in the field of tissue engineering, regenerative medicine and advanced drug delivery. Despite the current advancement of bioprinting technology, it faces several obstacles such as the challenge of optimizing the printing resolution of 3D constructs while retaining cell viability before, during, and after bioprinting. Therefore, it is of great significance to fully understand factors that influence the shape fidelity of printed structures and the performance of cells encapsulated in bioinks. This review presents a comprehensive analysis of bioprinting process parameters that influence bioink printability and cell performance, including bioink properties (composition, concentration, and component ratio), printing speed and pressure, nozzle charateristics (size, length, and geometry), and crosslinking parameters (crosslinker types, concentration, and crosslinking time). Key examples are provided to analyze how these parameters could be tailored to achieve the optimal printing resolution as well as cell performance. Finally, future prospects of bioprinting technology, including correlating process parameters to particular cell types with predefined applications, applying statistical analysis and artificial intelligence (AI)/machine learning (ML) technique in parameter screening, and optimizing 4D bioprinting process parameters, are highlighted.

Three-dimensional bioprinting of artificial blood vessel: Process, bioinks, and challenges

The coronary artery bypass grafting is a main treatment for restoring the blood supply to the ischemic site by bypassing the narrow part, thereby improving the heart function of the patients. Autologous blood vessels are preferred in coronary artery bypass grafting, but their availability is often limited by due to the underlying disease. Thus, tissue-engineered vascular grafts that are devoid of thrombosis and have mechanical properties comparable to those of natural vessels are urgently required for clinical applications. Most of the commercially available artificial implants are made from polymers, which are prone to thrombosis and restenosis. The biomimetic artificial blood vessel containing vascular tissue cells is the most ideal implant material. Due to its precision control ability, three-dimensional (3D) bioprinting is a promising method to prepare biomimetic system. In the 3D bioprinting process, the bioink is at the core state for building the topological structure and keeping the cell viable. Therefore, in this review, the basic properties and viable materials of the bioink are discussed, and the research of natural polymers in bioink, including decellularized extracellular matrix, hyaluronic acid, and collagen, is emphasized. Besides, the advantages of alginate and Pluronic F127, which are the mainstream sacrificial material during the preparation of artificial vascular graft, are also reviewed. Finally, an overview of the applications in the field of artificial blood vessel is also presented.

Three-Dimensional Bioprinting Applications for Bone Tissue Engineering

The skeletal system is a key support structure within the body. Bones have unique abilities to grow and regenerate after injury. Some injuries or degeneration of the tissues cannot rebound and must be repaired by the implantation of foreign objects following injury or disease. This process is invasive and does not always improve the quality of life of the patient. New techniques have arisen that can improve bone replacement or repair. 3D bioprinting employs a printer capable of printing biological materials in multiple directions. 3D bioprinting potentially requires multiple steps and additional support structures, which may include the use of hydrogels for scaffolding. In this review, we discuss normal bone physiology and pathophysiology and how bioprinting can be adapted to further the field of bone tissue engineering.

Modification, 3D printing process and application of sodium alginate based hydrogels in soft tissue engineering: A review

Sodium alginate (SA) is an inexpensive and biocompatible biomaterial with fast and gentle crosslinking that has been widely used in biological soft tissue repair/regeneration. Especially with the advent of 3D bioprinting technology, SA hydrogels have been applied more deeply in tissue engineering due to their excellent printability. Currently, the research on material modification, molding process and application of SA-based composite hydrogels has become a hot topic in tissue engineering, and a lot of fruitful results have been achieved. To better help readers have a comprehensive understanding of the development status of SA based hydrogels and their molding process in tissue engineering, in this review, we summarized SA modification methods, and provided a comparative analysis of the characteristics of various SA based hydrogels. Secondly, various molding methods of SA based hydrogels were introduced, the processing characteristics and the applications of different molding methods were analyzed and compared. Finally, the applications of SA based hydrogels in tissue engineering were reviewed, the challenges in their applications were also analyzed, and the future research directions were prospected. We believe this review is of great helpful for the researchers working in biomedical and tissue engineering.