Natural Biomaterials and Their Use as Bioinks for Printing Tissues

Advances in bioink-based 3D printed scaffolds: optimizing biocompatibility and mechanical properties for bone regeneration

The development of bioink-based 3D-printed scaffolds has revolutionized bone tissue engineering (BTE) by enabling patient-specific and biomimetic constructs for bone regeneration. This review focuses on the biocompatibility and mechanical properties essential for scaffold performance, highlighting advancements in bioink formulations, material combinations, and printing techniques. The key biomaterials, including natural polymers (gelatin, collagen, alginate), synthetic polymers (polycaprolactone, polyethylene glycol), and bioactive ceramics (hydroxyapatite, calcium phosphate), are discussed concerning their osteoconductivity, printability, and structural integrity. Despite significant progress, challenges remain in achieving optimal mechanical strength, degradation rates, and cellular interactions. The review explores emerging strategies such as gene-activated bioinks, nanocomposite reinforcements, and crosslinking techniques to enhance scaffold durability and bioactivity. By synthesizing recent developments, this work provides insights into future directions for bioink-based scaffolds, paving the way for more effective and personalized bone regenerative therapies.

The Recent Applications of Stem Cell-Derived Exosomes and Hydrogels in Neurological Disorders

Neurological disorders such as Alzheimer's disease, Parkinson's disease, and stroke pose significant challenges for conventional therapy due to the complexities of the blood-brain barrier (BBB) and the restricted delivery of drugs to the central nervous system. Exosomes, a type of small extracellular vesicle secreted by nearly all cell types, hold substantial promise as delivery vehicles for therapeutic agents in treating these conditions. Notably, stem cell-secreted exosomes have emerged as particularly effective due to their regenerative potential and natural ability to cross the BBB. Similarly, hydrogels have gained recognition as versatile biomaterials capable of supporting sustained release and targeted delivery of therapeutics. The combination of the regenerative properties of stem cell-derived exosomes (SC-Exos) with the structural and functional benefits of hydrogels offers a promising approach for enhancing neurogenesis, modulating neuroinflammation, and facilitating tissue repair. This review explores the origin, structure, and modifications of exosomes as well as the synthesis and incorporation methods of hydrogels in the therapeutic context for debilitating neurological disorders. It highlights recent advancements in using SC-Exos and hydrogels for therapeutic delivery, addressing both current challenges and future applications. Improving our understanding of hydrogels loaded with SC-Exos for cargo transportation and neural tissue regeneration may pave the way for novel therapeutic strategies.

Advances and Challenges in 3D Bioprinted Cancer Models: Opportunities for Personalized Medicine and Tissue Engineering

Cancer is the second leading cause of death worldwide, after cardiovascular disease, claiming not only a staggering number of lives but also causing considerable health and economic devastation, particularly in less-developed countries. Therapeutic interventions are impeded by differences in patient-to-patient responses to anti-cancer drugs. A personalized medicine approach is crucial for treating specific patient groups and includes using molecular and genetic screens to find appropriate stratifications of patients who will respond (and those who will not) to treatment regimens. However, information on which risk stratification method can be used to hone in on cancer types and patients who will be likely responders to a specific anti-cancer agent remains elusive for most cancers. Novel developments in 3D bioprinting technology have been widely applied to recreate relevant bioengineered tumor organotypic structures capable of mimicking the human tissue and microenvironment or adequate drug responses in high-throughput screening settings. Parts are autogenously printed in the form of 3D bioengineered tissues using a computer-aided design concept where multiple layers include different cell types and compatible biomaterials to build specific configurations. Patient-derived cancer and stromal cells, together with genetic material, extracellular matrix proteins, and growth factors, are used to create bioprinted cancer models that provide a possible platform for the screening of new personalized therapies in advance. Both natural and synthetic biopolymers have been used to encourage the growth of cells and biological materials in personalized tumor models/implants. These models may facilitate physiologically relevant cell-cell and cell-matrix interactions with 3D heterogeneity resembling real tumors.

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.

3D bioprinting technology for modeling vascular diseases and its application

In vitromodeling of vascular diseases provides a useful platform for drug screening and mechanistic studies, by recapitulating the essential structures and physiological characteristics of the native tissue. Bioprinting is an emerging technique that offers high-resolution 3D capabilities, which have recently been employed in the modeling of various tissues and associated diseases. Blood vessels are composed of multiple layers of distinct cell types, and experience different mechanical conditions depending on the vessel type. The intimal layer, in particular, is directly exposed to such hemodynamic conditions inducing shear stress, which in turn influence vascular physiology. 3D bioprinting techniques have addressed the structural limitations of the previous vascular models, by incorporating supporting cells such as smooth muscle cells, geometrical properties such as dilation, curvature, or branching, or mechanical stimulation such as shear stress and pulsatile pressure. This paper presents a review of the physiology of blood vessels along with the pathophysiology of the target diseases including atherosclerosis, thrombosis, aneurysms, and tumor angiogenesis. Additionally, it discusses recent advances in fabricatingin vitro3D vascular disease models utilizing bioprinting techniques, while addressing the current challenges and future perspectives for the potential clinical translation into therapeutic interventions.

Harnessing native blueprints for designing bioinks to bioprint functional cardiac tissue

Cardiac tissue lacks regenerative capacity, making heart transplantation the primary treatment for end-stage heart failure. Engineered cardiac tissues developed through three-dimensional bioprinting (3DBP) offer a promising alternative. However, reproducing the native structure, cellular diversity, and functionality of cardiac tissue requires advanced cardiac bioinks. Major obstacles in CTE (cardiac tissue engineering) include accurately characterizing bioink properties, replicating the cardiac microenvironment, and achieving precise spatial organization. Optimizing bioink properties to closely mimic the extracellular matrix (ECM) is essential, as deviations may result in pathological effects. This review encompasses the rheological and electromechanical properties of bioinks and the function of the cardiac microenvironment in the design of functional cardiac constructs. Furthermore, it focuses on improving the rheological characteristics, printability, and functionality of bioinks, offering valuable perspectives for developing new bioinks especially designed for CTE.

Optimizing Flexor Digitorum Profundus Tendon Repair: A Narrative Review

Zone II flexor digitorum profundus (FDP) tendon injuries are complex, and present significant challenges in hand surgery, due to the need to balance strength and flexibility during repair. Traditional suture techniques often lead to complications such as adhesions or tendon rupture, prompting the exploration of novel strategies to improve outcomes. This review investigates the use of flexor digitorum superficialis (FDS) tendon autografts to reinforce FDP repairs, alongside the integration of biomaterials to enhance mechanical strength without sacrificing FDS tissue. Key biomaterials, including collagen-polycaprolactone (PCL) composites, are evaluated for their biocompatibility, mechanical integrity, and controlled degradation properties. Collagen-PCL emerges as a leading candidate, offering the potential to reduce adhesions and promote tendon healing. Although nanomaterials such as nanofibers and nanoparticles show promise in preventing adhesions and supporting cellular proliferation, their application remains limited by manufacturing challenges. By combining advanced repair techniques with biomaterials like collagen-PCL, this approach aims to improve surgical outcomes and minimize complications. Future research will focus on validating these findings in biological models, assessing tendon healing through imaging, and comparing the cost-effectiveness of biomaterial-enhanced repairs with traditional methods. This review underscores the potential for biomaterial-based approaches to transform FDP tendon repair.

Bioprinted Hydrogels as Vehicles for the Application of Extracellular Vesicles in Regenerative Medicine

Three-dimensional bioprinting is a new advance in tissue engineering and regenerative medicine. Bioprinting allows manufacturing three-dimensional (3D) structures that mimic tissues or organs. The bioinks used are mainly made of natural or synthetic polymers that must be biocompatible, printable, and biodegradable. These bioinks may incorporate progenitor cells, favoring graft implantation and regeneration of injured tissues. However, the natures of biomaterials, bioprinting processes, a lack of vascularization, and immune responses are factors that limit the viability and functionality of implanted cells and the regeneration of damaged tissues. These limitations can be addressed by incorporating extracellular vesicles (EV) into bioinks. Indeed, EV from progenitor cells may have regenerative capacities, being similar to those of their source cells. Therefore, their combinations with biomaterials can be used in cell-free therapies. Likewise, they can complement the manufacture of bioinks by increasing the viability, differentiation, and regenerative ability of incorporated cells. Thus, the main objective of this review is to show how the use of 3D bioprinting technology can be used for the application of EV in regenerative medicine by incorporating these nanovesicles into hydrogels used as bioinks. To this end, the latest advances derived from in vitro and in vivo studies have been described. Together, these studies show the high therapeutic potential of this strategy in regenerative medicine.

Synthesis and characterization of dextran palmitate for extrusion 3D printing

The fabrication of objects with complex shape and geometry has been greatly facilitated with the advancements in additive manufacturing. While synthetic polymers like ABS and PLA have found widespread use in extrusion 3D printing, other biobased thermoplastics that are both biodegradable and biocompatible could offer strategic advantages over traditional synthetic materials. In this work dextran of low (20 kDa) and medium (40 kDa) molecular weight (MW) was modified with palmitic acid to obtain meltable polymers for extrusion 3D printing/fused deposition modeling additive manufacturing. The dextran derivatives were characterized by FTIR, NMR and elemental analysis. The degree of substitution (DS) varied between 0.94 ± 0.31 and 1.36 ± 0.16. Our findings reveal a melting temperature near 40 °C, independent of the DS or MW. Extrudability varied depending on the DS. Cubes with dimensions of 15 × 15 × 10 mm3 were printed from the dextran palmitate. The swelling degree of the cubes in water remained limited, up to 0.17 ± 0.02 g/g. This work demonstrates the great potential of dextran palmitate as biobased and biodegradable polymers for 3D printing for future applications in human health.

3D printed sodium alginate/gelatin/tannic acid/calcium chloride scaffolds laden bone marrow mesenchymal stem cells to repair defective thyroid cartilage plate

Due to the absence of blood vessels, cartilage exhibits extremely limited self-repair capacity. Currently, repairing laryngeal cartilage defects, resulting from conditions such as laryngeal tumors, injury, and congenital structural abnormalities, remains a significant challenge in the Department of Otolaryngology, Head and Neck Surgery. Previous research has often focused on enhancing the mechanical properties of synthetic materials. However, their low biological activity and weak cell adhesion necessitate compensatory measures. This study aims to capitalize on the advantages of natural materials in cartilage tissue engineering. Sodium alginate, gelatin, tannic acid, and calcium chloride were utilized to prepare bioinks through cross-linking for application in 3D printing cartilage scaffolds. Bone marrow mesenchymal stem cells with multidirectional differentiation potential were chosen as seed cells, with appropriate growth factors incorporated to promote their differentiation into cartilage during in vitro culture. The scaffold laden cells was subsequently implanted into rabbit thyroid cartilage plate defects at the appropriate time. HE staining, toluidine blue staining, Masson staining, and collagen type II staining were employed to assess cartilage defect repair at 4, 8, and 12 weeks, respectively. Results demonstrated that scaffolds made from natural materials could emulate the mechanical properties of fresh cartilage with commendable biocompatibility. Stained sections further confirmed the efficacy of the composite hydrogel scaffolds identified in this study in promoting rabbit thyroid cartilage plate restoration. In summary, this study successfully fabricated a natural material scaffold for rabbit laryngeal cartilage tissue engineering, thereby furnishing a new idea and experience for the clinical application of laryngeal cartilage defect reconstruction.

The Properties and Applicability of Bioprinting in the Field of Maxillofacial Surgery

Perhaps the most innovative branch of medicine is represented by regenerative medicine. It deals with regenerating or replacing tissues damaged by disease or aging. The innovative frontier of this branch is represented by bioprinting. This technology aims to reconstruct tissues, organs, and anatomical structures, such as those in the head and neck region. This would mean revolutionizing therapeutic and surgical approaches in the management of multiple conditions in which a conspicuous amount of tissue is lost. The application of bioprinting for the reconstruction of anatomical areas removed due to the presence of malignancy would represent a revolutionary new step in personalized and precision medicine. This review aims to investigate recent advances in the use of biomaterials for the reconstruction of anatomical structures of the head-neck region, particularly those of the oral cavity. The characteristics and properties of each biomaterial currently available will be presented, as well as their potential applicability in the reconstruction of areas affected by neoplasia damaged after surgery. In addition, this study aims to examine the current limitations and challenges and to analyze the future prospects of this technology in maxillofacial surgery.

Advancement of 3D biofabrication in repairing and regeneration of cartilage defects

Three-dimensional (3D) bioprinting, an additive manufacturing technology, fabricates biomimetic tissues that possess natural structure and function. It involves precise deposition of bioinks, including cells, and bioactive factors, on basis of computer-aided 3D models. Articular cartilage injuries, a common orthopedic issue. Current repair methods, for instance microfracture procedure (MF), autologous chondrocyte implantation (ACI), and osteochondral autologous transfer surgery have been applied in clinical practice. However, each procedure has inherent limitation. For instance, MF surgery associates with increased subchondral cyst formation and brittle subchondral bone. ACI procedure involves two surgeries, and associate with potential risks infection and delamination of the regenerated cartilage. In addition, chondrocyte implantation's efficacy depends on the patient's weight, joint pathology, gender-related histological changes of cartilage, and hormonal influences that affect treatment and prognosis. So far, it is a still a grand challenge for achieving a clinical satisfactory in repairing and regeneration of cartilage defects using conditional strategies. 3D biofabrication provide a potential to fabricate biomimetic articular cartilage construct that has shown promise in specific cartilage repair and regeneration of patients. This review reported the techniques of 3D bioprinting applied for cartilage repair, and analyzed their respective merits and demerits, and limitations in clinical application. A summary of commonly used bioinks has been provided, along with an outlook on the challenges and prospects faced by 3D bioprinting in the application of cartilage tissue repair. It provided an overall review of current development and promising application of 3D biofabrication technology in articular cartilage repair.

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.

Rheological Characterization and Printability of Sodium Alginate-Gelatin Hydrogel for 3D Cultures and Bioprinting

The development of biocompatible hydrogels for 3D bioprinting is essential for creating functional tissue models and advancing preclinical drug testing. This study investigates the formulation, printability, mechanical properties, and biocompatibility of a novel Alg-Gel hydrogel blend (alginate and gelatin) for use in extrusion-based 3D bioprinting. A range of hydrogel compositions were evaluated for their rheological behavior, including shear-thinning properties, storage modulus, and compressive modulus, which are crucial for maintaining structural integrity during printing and supporting cell viability. The printability assessment of the 7% alginate-8% gelatin hydrogel demonstrated that the 27T tapered needle achieved the highest normalized Printability Index (POInormalized = 1), offering the narrowest strand width (0.56 ± 0.02 mm) and the highest printing accuracy (97.2%) at the lowest printing pressure (30 psi). In contrast, the 30R needle, with the smallest inner diameter (0.152 mm) and highest printing pressure (80 psi), resulted in the widest strand width (0.70 ± 0.01 mm) and the lowest accuracy (88.8%), resulting in a POInormalized of 0.274. The 30T and 27R needles demonstrated moderate performance, with POInormalized values of 0.758 and 0.558, respectively. The optimized 7% alginate and 8% gelatin blend demonstrated favorable printability, mechanical strength, and cell compatibility with MDA-MB-213 breast cancer cells, exhibiting high cell proliferation rates and minimal cytotoxicity over a 2-week culture period. This formulation offers a balanced approach, providing sufficient viscosity for precision printing while minimizing shear stress to preserve cell health. This work lays the groundwork for future advancements in bioprinted cancer models, contributing to the development of more effective tools for drug screening and personalized medicine.

Advances in 3D printing combined with tissue engineering for nerve regeneration and repair

The repair of nerve damage has long posed a challenge owing to limited self-repair capacity and the highly differentiated nature of nerves. While new therapeutic and pharmacologic interventions have emerged in neurology, their regenerative efficacy remains limited. Tissue engineering offers a promising avenue for overcoming the limitations of conventional treatments and increasing the outcomes of regenerative repair. By implanting scaffolds into damaged nerve tissue sites, the repair and functional reconstruction of nerve injuries can be significantly facilitated. The integration of three-dimensional (3D) printing technology introduces a novel approach for accurate simulation and scalably fabricating neural tissue structures. Tissue-engineered scaffolds developed through 3D printing technology are expected to be a viable therapeutic option for nerve injuries, with broad applicability and continued development. This review systematically examines recent advances in 3D printing and tissue engineering for nerve regeneration and repair. It details the basic principles and construction strategies of neural tissue engineering and explores the crucial role of 3D printing technology. Additionally, it elucidates specific applications and technical challenges associated with this integrated approach, thereby providing valuable insights into innovative strategies and pragmatic implementation within this field.

Human mesenchymal stromal cells-laden crosslinked hyaluronic acid-alginate bioink for 3D bioprinting applications in tissue engineering

Three-dimensional (3D) bioprinting is considered one of the most advanced tools to build up materials for tissue engineering. The aim of this work was the design, development and characterization of a bioink composed of human mesenchymal stromal cells (hMSC) for extrusion through nozzles to create these 3D structures that might potentially be apply to replace the function of damaged natural tissue. In this study, we focused on the advantages and the wide potential of biocompatible biomaterials, such as hyaluronic acid and alginate for the inclusion of hMSC. The bioink was characterized for its physical (pH, osmolality, degradation, swelling, porosity, surface electrical properties, conductivity, and surface structure), mechanical (rheology and printability) and biological (viability and proliferation) properties. The developed bioink showed high porosity and high swelling capacity, while the degradation rate was dependent on the temperature. The bioink also showed negative electrical surface and appropriate rheological properties required for bioprinting. Moreover, stress-stability studies did not show any sign of physical instability. The developed bioink provided an excellent environment for the promotion of the viability and growth of hMSC cells. Our work reports the first-time study of the effect of storage temperature on the cell viability of bioinks, besides showing that our bioink promoted a high cell viability after being extruded by the bioprinter. These results support the suggestion that the developed hMSC-composed bioink fulfills all the requirements for tissue engineering and can be proposed as a biological tool with potential applications in regenerative medicine and tissue engineering.

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.

Engineering with Biomedical Sciences Changing the Horizon of Healthcare-A Review

In the dynamic realm of healthcare, the convergence of engineering and biomedical sciences has emerged as a pivotal frontier. In this review we go into specific areas of innovation, including medical imaging and diagnosis, developments in biomedical sensors, and drug delivery systems. Wearable biosensors, non-wearable biosensors, and biochips, which include gene chips, protein chips, and cell chips, are all included in the scope of the topic that pertains to biomedical sensors. Extensive research is conducted on drug delivery systems, spanning topics such as the integration of computer modeling, the optimization of drug formulations, and the design of delivery devices. Furthermore, the paper investigates intelligent drug delivery methods, which encompass stimuli-responsive systems such as temperature, redox, pH, light, enzyme, and magnetic responsive systems. In addition to that, the review goes into topics such as tissue engineering, regenerative medicine, biomedical robotics, automation, biomechanics, and the utilization of green biomaterials. The purpose of this analysis is to provide insights that will enhance continuing research and development efforts in engineering-driven biomedical breakthroughs, ultimately contributing to the improvement of healthcare. These insights will be provided by addressing difficulties and highlighting future prospects.

Advances and Functional Integration of Hydrogel Composites as Drug Delivery Systems in Contemporary Dentistry

This study explores the recent advances of and functional insights into hydrogel composites, materials that have gained significant attention for their versatile applications across various fields, including contemporary dentistry. Hydrogels, known for their high water content and biocompatibility, are inherently soft but often limited by mechanical fragility. Key areas of focus include the customization of hydrogel composites for biomedical applications, such as drug delivery systems, wound dressings, and tissue engineering scaffolds, where improved mechanical properties and bioactivity are critical. In dentistry, hydrogels are utilized for drug delivery systems targeting oral diseases, dental adhesives, and periodontal therapies due to their ability to adhere to the mucosa, provide localized treatment, and support tissue regeneration. Their unique properties, such as mucoadhesion, controlled drug release, and stimuli responsiveness, make them ideal candidates for treating oral conditions. This review highlights both experimental breakthroughs and theoretical insights into the structure-property relationships within hydrogel composites, aiming to guide future developments in the design and application of these multifunctional materials in dentistry. Ultimately, hydrogel composites represent a promising frontier for advancing materials science with far-reaching implications in healthcare, environmental technology, and beyond.

Advancements in Hydrogels for Corneal Healing and Tissue Engineering

Hydrogels have garnered significant attention for their versatile applications across various fields, including biomedical engineering. This review delves into the fundamentals of hydrogels, exploring their definition, properties, and classification. Hydrogels, as three-dimensional networks of crosslinked polymers, possess tunable properties such as biocompatibility, mechanical strength, and hydrophilicity, making them ideal for medical applications. Uniquely, this article offers original insights into the application of hydrogels specifically for corneal tissue engineering, bridging a gap in current research. The review further examines the anatomical and functional complexities of the cornea, highlighting the challenges associated with corneal pathologies and the current reliance on donor corneas for transplantation. Considering the global shortage of donor corneas, this review discusses the potential of hydrogel-based materials in corneal tissue engineering. Emphasis is placed on the synthesis processes, including physical and chemical crosslinking, and the integration of bioactive molecules. Stimuli-responsive hydrogels, which react to environmental triggers, are identified as promising tools for drug delivery and tissue repair. Additionally, clinical applications of hydrogels in corneal pathologies are explored, showcasing their efficacy in various trials. Finally, the review addresses the challenges of regulatory approval and the need for further research to fully realize the potential of hydrogels in corneal tissue engineering, offering a promising outlook for future developments in this field.

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.

Tailoring biomaterials for skin anti-aging

Skin aging is the phenomenon of degenerative changes in the structure and function of skin tissues over time and is manifested by a gradual loss of skin elasticity and firmness, an increased number of wrinkles, and hyperpigmentation. Skin anti-aging refers to a reduction in the skin aging phenomenon through medical cosmetic technologies. In recent years, new biomaterials have been continuously developed for improving the appearance of the skin through mechanical tissue filling, regulating collagen synthesis and degradation, inhibiting pigmentation, and repairing the skin barrier. This review summarizes the mechanisms associated with skin aging, describes the biomaterials that are commonly used in medical aesthetics and their possible modes of action, and discusses the application strategies of biomaterials in this area. Moreover, the synergistic effects of such biomaterials and other active ingredients, such as stem cells, exosomes, growth factors, and antioxidants, on tissue regeneration and anti-aging are evaluated. Finally, the possible challenges and development prospects of biomaterials in the field of anti-aging are discussed, and novel ideas for future innovations in this area are summarized.

Ethics of Organ Donation and Transplantation: Toward Self-Sufficiency

Organ donation, intersecting medical necessity and ethical responsibility, calls for policies respecting individual autonomy while aiming for societal selfsufficiency. This article evaluates various government policies, emphasizing the ethical use of nudges in decision-making and the potential impact on autonomy. We argue that, while some policies might be coercive, others may inadvertently disrespect autonomy through subtle influences on decisionmaking. To reach self sufficiency in organ donation and transplantation and to keep adherent to medical ethics, especially informed consent, and gift of life campaigns, governments must determine the legal procedures by which their residents are registered, or can register, as organ donors. Provided that governments recognize that people have a right to determine what happens to their organs after they die, there are 4 feasible options to choose from: optin, opt-out, mandated active choice, and voluntary active choice. This article investigated the ethics of these policies' use of nudges and pokes to affect organ donor registration ways, rules, and rates. We argue that the use of nudges in this context is morally problematic. It is disrespectful of people's autonomy to take advantage of their cognitive biases since doing so involves bypassing, not engaging, their rational capacities. We conclude that, although mandated active choice policies are not problem free, they are coercive; after all, voluntary active choice, opt-in, and opt-out policies are potentially less respectful of people's autonomy since their use of nudges could significantly affect people's decision making.

Design considerations and biomaterials selection in embedded extrusion 3D bioprinting

In embedded extrusion 3D bioprinting, a temporary matrix preserves a paste-like filament ejecting from a narrow nozzle. For granular sacrificial matrices, the methodology is known as the freeform reversible embedding of suspended hydrogels (FRESH). Embedded extrusion 3D bioprinting methods result in more rapid and controlled manufacturing of cell-laden tissue constructs, particularly vascular and multi-component structures. This report focuses on the working principles and bioink design criteria for implementing conventional embedded extrusion and FRESH 3D bioprinting strategies. We also present a set of experimental data as a guideline for selecting the support bath or matrix. We discuss the advantages of embedded extrusion methods over conventional biomanufacturing methods. This work provides a short recipe for selecting inks and printing parameters for desired shapes in embedded extrusion and FRESH 3D bioprinting methods.

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.

Pneumatic extrusion bioprinting-based high throughput fabrication of a melanoma 3D cell culture model for anti-cancer drug screening

The high incidence of malignant melanoma highlights the need forin vitromodels that accurately represent the tumour microenvironment, enabling developments in melanoma therapy and drug screening. Despite several advancements in 3D cell culture models, appropriate melanoma models for evaluating drug efficacy are still in high demand. The 3D pneumatic extrusion-based bioprinting technology offers numerous benefits, including the ability to achieve high-throughput capabilities. However, there is a lack of research that combines pneumatic extrusion-based bioprinting with analytical assays to enable efficient drug screening in 3D melanoma models. To address this gap, this study developed a simple and highly reproducible approach to fabricate a 3D A375 melanoma cell culture model using the pneumatic extrusion-based bioprinting technology. To optimise this method, the bioprinting parameters for producing 3D cell cultures in a 96-well plate were adjusted to improve reproducibility while maintaining the desired droplet size and a cell viability of 92.13 ± 6.02%. The cross-linking method was optimised by evaluating cell viability and proliferation of the 3D bioprinted cells in three different concentrations of calcium chloride. The lower concentration of 50 mM resulted in higher cell viability and increased cell proliferation after 9 d of incubation. The A375 cells exhibited a steadier proliferation rate in the 3D bioprinted cell cultures, and tended to aggregate into spheroids, whereas the 2D cell cultures generally formed monolayered cell sheets. In addition, we evaluated the drug responses of four different anti-cancer drugs on the A375 cells in both the 2D and 3D cell cultures. The 3D cell cultures exhibited higher levels of drug resistance in all four tested anti-cancer drugs. This method presents a simple and cost-effective method of producing and analysing 3D cell culture models that do not add additional complexity to current assays and shows considerable potential for advancing 3D cell culture models' drug efficacy evaluations.

Exploring Synergistic Effects of Bioprinted Extracellular Vesicles for Skin Regeneration

Regenerative medicine represents a paradigm shift in healthcare, aiming to restore tissue and organ function through innovative therapeutic strategies. Among these, bioprinting and extracellular vesicles (EVs) have emerged as promising techniques for tissue rejuvenation. EVs are small lipid membrane particles secreted by cells, known for their role as potent mediators of intercellular communication through the exchange of proteins, genetic material, and other biological components. The integration of 3D bioprinting technology with EVs offers a novel approach to tissue engineering, enabling the precise deposition of EV-loaded bioinks to construct complex three-dimensional (3D) tissue architectures. Unlike traditional cell-based approaches, bioprinted EVs eliminate the need for live cells, thereby mitigating regulatory and financial obstacles associated with cell therapy. By leveraging the synergistic effects of EVs and bioprinting, researchers aim to enhance the therapeutic outcomes of skin regeneration while addressing current limitations in conventional treatments. This review explores the evolving landscape of bioprinted EVs as a transformative approach for skin regeneration. Furthermore, it discusses the challenges and future directions in harnessing this innovative therapy for clinical applications, emphasizing the need for interdisciplinary collaboration and continued scientific inquiry to unlock its full therapeutic potential.

Nanomaterials-Based Hybrid Bioink Platforms in Advancing 3D Bioprinting Technologies for Regenerative Medicine

3D bioprinting is recognized as the ultimate additive biomanufacturing technology in tissue engineering and regeneration, augmented with intelligent bioinks and bioprinters to construct tissues or organs, thereby eliminating the stipulation for artificial organs. For 3D bioprinting of soft tissues, such as kidneys, hearts, and other human body parts, formulations of bioink with enhanced bioinspired rheological and mechanical properties were essential. Nanomaterials-based hybrid bioinks have the potential to overcome the above-mentioned problem and require much attention among researchers. Natural and synthetic nanomaterials such as carbon nanotubes, graphene oxides, titanium oxides, nanosilicates, nanoclay, nanocellulose, etc. and their blended have been used in various 3D bioprinters as bioinks and benefitted enhanced bioprintability, biocompatibility, and biodegradability. A limited number of articles were published, and the above-mentioned requirement pushed us to write this review. We reviewed, explored, and discussed the nanomaterials and nanocomposite-based hybrid bioinks for the 3D bioprinting technology, 3D bioprinters properties, natural, synthetic, and nanomaterial-based hybrid bioinks, including applications with challenges, limitations, ethical considerations, potential solution for future perspective, and technological advancement of efficient and cost-effective 3D bioprinting methods in tissue regeneration and healthcare.

Molecular and cellular signalling pathways for promoting neural tissue growth - A tissue engineering approach

Neural tissue engineering is a sub-field of tissue engineering that develops neural tissue. Damaged central and peripheral nervous tissue can be fabricated with a suitable scaffold printed with biomaterials. These scaffolds promote cell growth, development, and migration, yet they vary according to the biomaterial and scaffold printing technique, which determine the physical and biochemical properties. The physical and biochemical properties of scaffolds stimulate diverse signalling pathways, such as Wnt, NOTCH, Hedgehog, and ion channels- mediated pathways to promote neuron migration, elongation and migration. However, neurotransmitters like dopamine, acetylcholine, gamma amino butyric acid, and other signalling molecules are critical in neural tissue engineering to tissue fabrication. Thus, this review focuses on neural tissue regeneration with a tissue engineering approach highlighting the signalling pathways. Further, it explores the interaction of the scaffolds with the signalling pathways for generating neural tissue.

Micro/nanoengineered agricultural by-products for biomedical and environmental applications

Agriculturally derived by-products generated during the growth cycles of living organisms as secondary products have attracted increasing interest due to their wide range of biomedical and environmental applications. These by-products are considered promising candidates because of their unique characteristics including chemical stability, profound biocompatibility and offering a green approach by producing the least impact on the environment. Recently, micro/nanoengineering based techniques play a significant role in upgrading their utility, by controlling their structural integrity and promoting their functions at a micro and nano scale. Specifically, they can be used for biomedical applications such as tissue regeneration, drug delivery, disease diagnosis, as well as environmental applications such as filtration, bioenergy production, and the detection of environmental pollutants. This review highlights the diverse role of micro/nano-engineering techniques when applied on agricultural by-products with intriguing properties and upscaling their wide range of applications across the biomedical and environmental fields. Finally, we outline the future prospects and remarkable potential that these agricultural by-products hold in establishing a new era in the realms of biomedical science and environmental research.

Advancements in tissue engineering for cardiovascular health: a biomedical engineering perspective

Myocardial infarction (MI) stands as a prominent contributor to global cardiovascular disease (CVD) mortality rates. Acute MI (AMI) can result in the loss of a large number of cardiomyocytes (CMs), which the adult heart struggles to replenish due to its limited regenerative capacity. Consequently, this deficit in CMs often precipitates severe complications such as heart failure (HF), with whole heart transplantation remaining the sole definitive treatment option, albeit constrained by inherent limitations. In response to these challenges, the integration of bio-functional materials within cardiac tissue engineering has emerged as a groundbreaking approach with significant potential for cardiac tissue replacement. Bioengineering strategies entail fortifying or substituting biological tissues through the orchestrated interplay of cells, engineering methodologies, and innovative materials. Biomaterial scaffolds, crucial in this paradigm, provide the essential microenvironment conducive to the assembly of functional cardiac tissue by encapsulating contracting cells. Indeed, the field of cardiac tissue engineering has witnessed remarkable strides, largely owing to the application of biomaterial scaffolds. However, inherent complexities persist, necessitating further exploration and innovation. This review delves into the pivotal role of biomaterial scaffolds in cardiac tissue engineering, shedding light on their utilization, challenges encountered, and promising avenues for future advancement. By critically examining the current landscape, we aim to catalyze progress toward more effective solutions for cardiac tissue regeneration and ultimately, improved outcomes for patients grappling with cardiovascular ailments.

Advances in 3D bioprinting for urethral tissue reconstruction

Urethral conditions affect children and adults, increasing the risk of urinary tract infections, voiding and sexual dysfunction, and renal failure. Current tissue replacements differ from healthy urethral tissues in structural and mechanical characteristics, causing high risk of postoperative complications. 3D bioprinting can overcome these limitations through the creation of complex, layered architectures using materials with location-specific biomechanical properties. This review highlights prior research and describes the potential for these emerging technologies to address ongoing challenges in urethral tissue engineering, including biomechanical and structural mismatch, lack of individualized repair solutions, and inadequate wound healing and vascularization. In the future, the integration of 3D bioprinting technology with advanced biomaterials, computational modeling, and 3D imaging could transform personalized urethral surgical procedures.

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

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

3D printed arrowroot starch-gellan scaffolds for wound healing applications

Skin, the largest organ in the body, blocks the entry of environmental pollutants into the system. Any injury to this organ allows infections and other harmful substances into the body. 3D bioprinting, a state-of-the-art technique, is suitable for fabricating cell culture scaffolds to heal chronic wounds rapidly. This study uses starch extracted from Maranta arundinacea (Arrowroot plant) (AS) and gellan gum (GG) to develop a bioink for 3D printing a scaffold capable of hosting animal cells. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction analysis (XRD) prove that the isolated AS is analogous to commercial starch. The cell culture scaffolds developed are superior to the existing monolayer culture. Infrared microscopy shows the AS-GG interaction and elucidates the mechanism of hydrogel formation. The physicochemical properties of the 3D-printed scaffold are analyzed to check the cell adhesion and growth; SEM images have confirmed that the AS-GG printed scaffold can support cell growth and proliferation, and the MTT assay shows good cell viability. Cell behavioral and migration studies reveal that cells are healthy. Since the scaffold is biocompatible, it can be 3D printed to any shape and structure and will biodegrade in the requisite time.

Advancements in Regenerative Hydrogels in Skin Wound Treatment: A Comprehensive Review

This state-of-the-art review explores the emerging field of regenerative hydrogels and their profound impact on the treatment of skin wounds. Regenerative hydrogels, composed mainly of water-absorbing polymers, have garnered attention in wound healing, particularly for skin wounds. Their unique properties make them well suited for tissue regeneration. Notable benefits include excellent water retention, creating a crucially moist wound environment for optimal healing, and facilitating cell migration, and proliferation. Biocompatibility is a key feature, minimizing adverse reactions and promoting the natural healing process. Acting as a supportive scaffold for cell growth, hydrogels mimic the extracellular matrix, aiding the attachment and proliferation of cells like fibroblasts and keratinocytes. Engineered for controlled drug release, hydrogels enhance wound healing by promoting angiogenesis, reducing inflammation, and preventing infection. The demonstrated acceleration of the wound healing process, particularly beneficial for chronic or impaired healing wounds, adds to their appeal. Easy application and conformity to various wound shapes make hydrogels practical, including in irregular or challenging areas. Scar minimization through tissue regeneration is crucial, especially in cosmetic and functional regions. Hydrogels contribute to pain management by creating a protective barrier, reducing friction, and fostering a soothing environment. Some hydrogels, with inherent antimicrobial properties, aid in infection prevention, which is a crucial aspect of successful wound healing. Their flexibility and ability to conform to wound contours ensure optimal tissue contact, enhancing overall treatment effectiveness. In summary, regenerative hydrogels present a promising approach for improving skin wound healing outcomes across diverse clinical scenarios. This review provides a comprehensive analysis of the benefits, mechanisms, and challenges associated with the use of regenerative hydrogels in the treatment of skin wounds. In this review, the authors likely delve into the application of rational design principles to enhance the efficacy and performance of hydrogels in promoting wound healing. Through an exploration of various methodologies and approaches, this paper is poised to highlight how these principles have been instrumental in refining the design of hydrogels, potentially revolutionizing their therapeutic potential in addressing skin wounds. By synthesizing current knowledge and highlighting potential avenues for future research, this review aims to contribute to the advancement of regenerative medicine and ultimately improve clinical outcomes for patients with skin wounds.

Extracellular Vesicles and Hydrogels: An Innovative Approach to Tissue Regeneration

Extracellular vesicles have emerged as promising tools in regenerative medicine due to their inherent ability to facilitate intercellular communication and modulate cellular functions. These nanosized vesicles transport bioactive molecules, such as proteins, lipids, and nucleic acids, which can affect the behavior of recipient cells and promote tissue regeneration. However, the therapeutic application of these vesicles is frequently constrained by their rapid clearance from the body and inability to maintain a sustained presence at the injury site. In order to overcome these obstacles, hydrogels have been used as extracellular vesicle delivery vehicles, providing a localized and controlled release system that improves their therapeutic efficacy. This Review will examine the role of extracellular vesicle-loaded hydrogels in tissue regeneration, discussing potential applications, current challenges, and future directions. We will investigate the origins, composition, and characterization techniques of extracellular vesicles, focusing on recent advances in exosome profiling and the role of machine learning in this field. In addition, we will investigate the properties of hydrogels that make them ideal extracellular vesicle carriers. Recent studies utilizing this combination for tissue regeneration will be highlighted, providing a comprehensive overview of the current research landscape and potential future directions.

Fabrication Method for Shape-Controlled 3D Tissue Using High-Porosity Porous Structure

Shape-controlled 3D tissues resemble natural living tissues in human and animal bodies and are essential materials for developing and improving technologies in regenerative medicine, drug discovery, and biological robotics. In previous studies, shape-controlled 3D tissues were fabricated using scaffold structures or 3D bioprinting techniques. However, controlling the shape of 3D tissues without leaving non-natural materials inside the 3D tissue and efficiently fabricating them remains challenging. In this paper, we propose a novel method for fabricating shape-controlled 3D tissues free of non-natural materials using a flexible high-porosity porous structure (HPPS). The HPPS consisted of a micromesh with pore sizes of 14.87 ± 1.83 μm, lattice widths of 2.24 ± 0.10 μm, thicknesses of 9.96 ± 0.92 μm, porosity of 69.06 ± 3.30%, and an I-shaped microchamber of depth 555.26 ± 11.17 μm. U-87 human glioma cells were cultured in an I-shaped HPPS microchamber for 48 h. After cultivation, the 3D tissue was released within a few seconds while maintaining its I-shape. Specific chemicals, such as proteolytic enzymes, were not used. Moreover, the viability of the released cells composed of shape-controlled 3D tissues free of non-natural materials was above 90%. Therefore, the proposed fabrication method is recommended for shape-controlled 3D tissues free of non-natural materials without applying significant stresses to the cells.

The Long Road to Develop Custom-built Livers: Current Status of 3D Liver Bioprinting

Although liver transplantation is the gold-standard therapy for end-stage liver disease, the shortage of suitable organs results in only 25% of waitlisted patients undergoing transplants. Three-dimensional (3D) bioprinting is an emerging technology and a potential solution for personalized medicine applications. This review highlights existing 3D bioprinting technologies of liver tissues, current anatomical and physiological limitations to 3D bioprinting of a whole liver, and recent progress bringing this innovation closer to clinical use. We reviewed updated literature across multiple facets in 3D bioprinting, comparing laser, inkjet, and extrusion-based printing modalities, scaffolded versus scaffold-free systems, development of an oxygenated bioreactor, and challenges in establishing long-term viability of hepatic parenchyma and incorporating structurally and functionally robust vasculature and biliary systems. Advancements in liver organoid models have also increased their complexity and utility for liver disease modeling, pharmacologic testing, and regenerative medicine. Recent developments in 3D bioprinting techniques have improved the speed, anatomical, and physiological accuracy, and viability of 3D-bioprinted liver tissues. Optimization focusing on 3D bioprinting of the vascular system and bile duct has improved both the structural and functional accuracy of these models, which will be critical in the successful expansion of 3D-bioprinted liver tissues toward transplantable organs. With further dedicated research, patients with end-stage liver disease may soon be recipients of customized 3D-bioprinted livers, reducing or eliminating the need for immunosuppressive regimens.

A biologically functional bioink based on extracellular matrix derived collagen for 3D printing of skin

Over the past few years, several advancements have been made to develop artificial skin that mimics human skin. Artificial skin manufactured using 3D printing technology that includes all epidermal and dermal components, such as collagen, may offer a viable solution. The skin-specific bioink was derived from digested chicken skin and incorporated into PVA (polyvinyl alcohol) and gelatin. The prepared bioink was further analyzed for its structure, stability, biocompatibility, and wound healing potential in in vitro, in ovo, and in vivo models. The 3D-printed skin showed excellent mechanical properties. In vitro scratch assays showed the proliferation and migration of cells within 24 h. In an in ovo assay, the 3D-printed skin facilitated the attachment of cells to the scaffolds. In the animal study, the quick cellular recruitment at the injury site accelerated wound healing. Further, hydroxyproline content was estimated to be 0.9-1.2 mg/ml, and collagen content was 7.5 %, which confirmed the epithelization. The relative expressions of MMP-9, COMP, TNF-α, and IL-6 genes were found to be increased compared to the control. These results demonstrate that 3D bioprinting represents a suitable technology to generate bioengineered skin for therapeutic and industrial applications in an automated manner.

Aloe vera-based biomaterial ink for 3D bioprinting of wound dressing constructs

This study emphasizes the development of a multifunctional biomaterial ink for wound healing constructs. The biomaterial ink benefits from Aloe vera's intrinsic biocompatible, biodegradable, antioxidant, antimicrobial, anti-inflammatory, and immunomodulatory attributes, thus alleviating the need for supplementary substances employed to combat infections and stimulate tissue regeneration. Moreover, this biomaterial ink seeks to address the scarcity of standardized printable materials possessing adequate biocompatibility and physicochemical properties, which hinder its widespread clinical adoption. The biomaterial ink was synthesized via ionic crosslinking to enhance its rheological and mechanical characteristics. The findings revealed that Aloe vera substantially boosted the hydrogel's viscoelastic behavior, enabling superior compressive modulus and the extrusion of fine filaments. The bioprinted constructs exhibited desirable resolution and mechanical strength while displaying a porous microstructure analogous to the native extracellular matrix. Biological response demonstrated no detrimental impact on stem cell viability upon exposure to the biomaterial ink, as confirmed by live/dead assays. These outcomes validate the potential of the developed biomaterial ink as a resource for the bioprinting of wound dressings that effectively foster cellular proliferation, thereby promoting enhanced wound healing by leveraging Aloe vera's inherent properties.

Tailored chitosan/glycerol micropatterned composite dressings by 3D printing for improved wound healing

Wound infection control is a primary clinical concern nowadays. Various innovative solutions have been developed to fabricate adaptable wound dressings with better control of infected wound healing. This work presents a facile approach by leveraging 3D printing to fabricate chitosan/glycerol into composite dressings with tailored micropatterns to improve wound healing. The bioinks of chitosan/glycerol were investigated as suitable for 3D printing. Then, three tailored micropatterns (i.e., sheet, strip, and mesh) with precise geometry control were 3D printed onto a commercial dressing to fabricate the micropatterned composite dressings. In vitro and in vivo studies indicate that these micropatterned dressings could speed up wound healing due to their increased water uptake capacity (up to ca. 16-fold@2 min), benign cytotoxicity (76.7 % to 90.4 % of cell viability), minor hemolytic activity (<1 %), faster blood coagulation effects (within 76.3 s), low blood coagulation index (14.5 % to 18.7 % @ 6 min), enhanced antibacterial properties (81.0 % to 86.1 % against S. aureus, 83.7 % to 96.5 % against E. coli), and effective inhibition of wound inflammation factors of IL-1β and TNF-α. Such tailored micropatterned composite dressing is facile to obtain, highly reproducible, and cost-efficient, making it a promising implication for improved and personalized contaminated wound healing.

3D printed scaffolds based on hyaluronic acid bioinks for tissue engineering: a review

Hyaluronic acid (HA) is widely distributed in human connective tissue, and its unique biological and physicochemical properties and ability to facilitate biological structure repair make it a promising candidate for three-dimensional (3D) bioprinting in the field of tissue regeneration and biomedical engineering. Moreover, HA is an ideal raw material for bioinks in tissue engineering because of its histocompatibility, non-immunogenicity, biodegradability, anti-inflammatory properties, anti-angiogenic properties, and modifiability. Tissue engineering is a multidisciplinary field focusing on in vitro reconstructions of mammalian tissues, such as cartilage tissue engineering, neural tissue engineering, skin tissue engineering, and other areas that require further clinical applications. In this review, we first describe the modification methods, cross-linking methods, and bioprinting strategies for HA and its derivatives as bioinks and then critically discuss the strengths, shortcomings, and feasibility of each method. Subsequently, we reviewed the practical clinical applications and outcomes of HA bioink in 3D bioprinting. Finally, we describe the challenges and opportunities in the development of HA bioink to provide further research references and insights.

Microscale tissue engineering of liver lobule models: advancements and applications

The liver, as the body's primary organ for maintaining internal balance, is composed of numerous hexagonal liver lobules, each sharing a uniform architectural framework. These liver lobules serve as the basic structural and functional units of the liver, comprised of central veins, hepatic plates, hepatic sinusoids, and minute bile ducts. Meanwhile, within liver lobules, distinct regions of hepatocytes carry out diverse functions. The in vitro construction of liver lobule models, faithfully replicating their structure and function, holds paramount significance for research in liver development and diseases. Presently, two primary technologies for constructing liver lobule models dominate the field: 3D bioprinting and microfluidic techniques. 3D bioprinting enables precise deposition of cells and biomaterials, while microfluidics facilitates targeted transport of cells or other culture materials to specified locations, effectively managing culture media input and output through micro-pump control, enabling dynamic simulations of liver lobules. In this comprehensive review, we provide an overview of the biomaterials, cells, and manufacturing methods employed by recent researchers in constructing liver lobule models. Our aim is to explore strategies and technologies that closely emulate the authentic structure and function of liver lobules, offering invaluable insights for research into liver diseases, drug screening, drug toxicity assessment, and cell replacement therapy.

Tissue Bioprinting: Promise and Challenges

In recent years, we have witnessed remarkable progress in the field of regenerative medicine, in large part fuelled by developments in advanced biofabrication technologies such as three-dimensional (3D) bioprinting [...].

Investigation of Biomaterial Ink Viscosity Properties and Optimization of the Printing Process Based on Pattern Path Planning

Extruded bioprinting is widely used for the biomanufacturing of personalized, complex tissue structures, which requires biomaterial inks with a certain viscosity to enable printing. However, there is still a lack of discussion on the controllable preparation and printability of biomaterial inks with different viscosities. In this paper, biomaterial inks composed of gelatin, sodium alginate, and methylcellulose were utablesed to investigate the feasibility of adjustment of rheological properties, thereby analyzing the effects of different rheological properties on the printing process. Based on the response surface methodology, the relationship between the material components and the rheological properties of biomaterial inks was discussed, followed by the prediction of the rheological properties of biomaterial inks. The prediction accuracies of the power-law index and consistency coefficient could reach 96% and 79%, respectively. The material group can be used to prepare biomaterial inks with different viscosity properties in a wide range. Latin hypercube sampling and computational fluid dynamics were used to analyze the effects of different rheological properties and extrusion pressure on the flow rate at the nozzle. The relationship between the rheological properties of the biomaterial ink and the flow rate was established, and the simulation results showed that the changes in the rheological properties of the biomaterial ink in the high-viscosity region resulted in slight fluctuations in the flow rate, implying that the printing process for high-viscosity biomaterial inks may have better versatility. In addition, based on the characteristics of biomaterial inks, the printing process was optimized from the planning of the print pattern to improve the location accuracy of the starting point, and the length accuracy of filaments can reach 99%. The effect of the overlap between the fill pattern and outer frame on the print quality was investigated to improve the surface quality of complex structures. Furthermore, low- and high-viscosity biomaterial inks were tested, and various printing protocols were discussed for improving printing efficiency or maintaining cell activity. This study provides feasible printing concepts for a wider range of biomaterials to meet the biological requirements of cell culture and tissue engineering.

Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

Biomaterials / bioinks and extrusion bioprinting

Bioinks are formulations of biomaterials and living cells, sometimes with growth factors or other biomolecules, while extrusion bioprinting is an emerging technique to apply or deposit these bioinks or biomaterial solutions to create three-dimensional (3D) constructs with architectures and mechanical/biological properties that mimic those of native human tissue or organs. Printed constructs have found wide applications in tissue engineering for repairing or treating tissue/organ injuries, as well as in vitro tissue modelling for testing or validating newly developed therapeutics and vaccines prior to their use in humans. Successful printing of constructs and their subsequent applications rely on the properties of the formulated bioinks, including the rheological, mechanical, and biological properties, as well as the printing process. This article critically reviews the latest developments in bioinks and biomaterial solutions for extrusion bioprinting, focusing on bioink synthesis and characterization, as well as the influence of bioink properties on the printing process. Key issues and challenges are also discussed along with recommendations for future research.

Trends in Photopolymerizable Bioinks for 3D Bioprinting of Tumor Models

Three-dimensional (3D) bioprinting technologies involving photopolymerizable bioinks (PBs) have attracted enormous attention in recent times owing to their ability to recreate complex structures with high resolution, mechanical stability, and favorable printing conditions that are suited for encapsulating cells. 3D bioprinted tissue constructs involving PBs can offer better insights into the tumor microenvironment and offer platforms for drug screening to advance cancer research. These bioinks enable the incorporation of physiologically relevant cell densities, tissue-mimetic stiffness, and vascularized channels and biochemical gradients in the 3D tumor models, unlike conventional two-dimensional (2D) cultures or other 3D scaffold fabrication technologies. In this perspective, we present the emerging techniques of 3D bioprinting using PBs in the context of cancer research, with a specific focus on the efforts to recapitulate the complexity of the tumor microenvironment. We describe printing approaches and various PB formulations compatible with these techniques along with recent attempts to bioprint 3D tumor models for studying migration and metastasis, cell-cell interactions, cell-extracellular matrix interactions, and drug screening relevant to cancer. We discuss the limitations and identify unexplored opportunities in this field for clinical and commercial translation of these emerging technologies.

Development and Optimisation of Hydrogel Scaffolds for Microvascular Network Formation

Traumatic injuries are a major cause of morbidity and mortality worldwide; however, there is limited research on microvascular traumatic injuries. To address this gap, this research aims to develop and optimise an in vitro construct for traumatic injury research at the microvascular level. Tissue engineering constructs were created using a range of polymers (collagen, fibrin, and gelatine), solvents (PBS, serum-free endothelial media, and MES/NaCl buffer), and concentrations (1-5% w/v). Constructs created from these hydrogels and HUVECs were evaluated to identify the optimal composition in terms of cell proliferation, adhesion, migration rate, viability, hydrogel consistency and shape retention, and tube formation. Gelatine hydrogels were associated with a lower cell adhesion, whereas fibrin and collagen ones displayed similar or better results than the control, and collagen hydrogels exhibited poor shape retention; fibrin scaffolds, particularly at high concentrations, displayed good hydrogel consistency. Based on the multipronged evaluation, fibrin hydrogels in serum-free media at 3 and 5% w/v were selected for further experimental work and enabled the formation of interconnected capillary-like networks. The networks formed in both hydrogels displayed a similar architecture in terms of the number of segments (10.3 ± 3.21 vs. 9.6 ± 3.51) and diameter (8.6446 ± 3.0792 μm vs. 7.8599 ± 2.3794 μm).