Smart Bioinks for the Printing of Human Tissue Models

The influence of viscosity of hydrogels on the spreading and migration of cells in 3D bioprinted skin cancer models

Various in vitro three-dimensional (3D) tissue culture models of human and diseased skin exist. Nevertheless, there is still room for the development and improvement of 3D bioprinted skin cancer models. The need for reproducible bioprinting methods, cell samples, biomaterial inks, and bioinks is becoming increasingly important. The influence of the viscosity of hydrogels on the spreading and migration of most types of cancer cells is well studied. There are however limited studies on the influence of viscosity on the spreading and migration of cells in 3D bioprinted skin cancer models. In this review, we will outline the importance of studying the various types of skin cancers by using 3D cell culture models. We will provide an overview of the advantages and disadvantages of the various 3D bioprinting technologies. We will emphasize how the viscosity of hydrogels relates to the spreading and migration of cancer cells. Lastly, we will give an overview of the specific studies on cell migration and spreading in 3D bioprinted skin cancer models.

Molecular mechanisms of cellular dysfunction in testes from men with non-obstructive azoospermia

Male factor infertility affects 50% of infertile couples worldwide; the most severe form, non-obstructive azoospermia (NOA), affects 10-15% of infertile males. Treatment for individuals with NOA is limited to microsurgical sperm extraction paired with in vitro fertilization intracytoplasmic sperm injection. Unfortunately, spermatozoa are only retrieved in ~50% of patients, resulting in live birth rates of 21-46%. Regenerative therapies could provide a solution; however, understanding the cell-type-specific mechanisms of cellular dysfunction is a fundamental necessity to develop precision medicine strategies that could overcome these abnormalities and promote regeneration of spermatogenesis. A number of mechanisms of cellular dysfunction have been elucidated in NOA testicular cells. These mechanisms include abnormalities in both somatic cells and germ cells in NOA testes, such as somatic cell immaturity, aberrant growth factor signalling, increased inflammation, increased apoptosis and abnormal extracellular matrix regulation. Future cell-type-specific investigations in identifying modulators of cellular transcription and translation will be key to understanding upstream dysregulation, and these studies will require development of in vitro models to functionally interrogate spermatogenic niche dysfunction in both somatic and germ cells.

The Art of Building Living Tissues: Exploring the Frontiers of Biofabrication with 3D Bioprinting

The scope of three-dimensional printing is expanding rapidly, with innovative approaches resulting in the evolution of state-of-the-art 3D bioprinting (3DbioP) techniques for solving issues in bioengineering and biopharmaceutical research. The methods and tools in 3DbioP emphasize the extrusion process, bioink formulation, and stability of the bioprinted scaffold. Thus, 3DbioP technology augments 3DP in the biological world by providing technical support to regenerative therapy, drug delivery, bioengineering of prosthetics, and drug kinetics research. Besides the above, drug delivery and dosage control have been achieved using 3D bioprinted microcarriers and capsules. Developing a stable, biocompatible, and versatile bioink is a primary requisite in biofabrication. The 3DbioP research is breaking the technical barriers at a breakneck speed. Numerous techniques and biomaterial advancements have helped to overcome current 3DbioP issues related to printability, stability, and bioink formulation. Therefore, this Review aims to provide an insight into the technical challenges of bioprinting, novel biomaterials for bioink formulation, and recently developed 3D bioprinting methods driving future applications in biofabrication research.

Sustainable Biomass Lignin-Based Hydrogels: A Review on Properties, Formulation, and Biomedical Applications

Different techniques have been developed to overcome the recalcitrant nature of lignocellulosic biomass and extract lignin biopolymer. Lignin has gained considerable interest owing to its attractive properties. These properties may be more beneficial when including lignin in the preparation of highly desired value-added products, including hydrogels. Lignin biopolymer, as one of the three major components of lignocellulosic biomaterials, has attracted significant interest in the biomedical field due to its biocompatibility, biodegradability, and antioxidant and antimicrobial activities. Its valorization by developing new hydrogels has increased in recent years. Furthermore, lignin-based hydrogels have shown great potential for various biomedical applications, and their copolymerization with other polymers and biopolymers further expands their possibilities. In this regard, lignin-based hydrogels can be synthesized by a variety of methods, including but not limited to interpenetrating polymer networks and polymerization, crosslinking copolymerization, crosslinking grafted lignin and monomers, atom transfer radical polymerization, and reversible addition-fragmentation transfer polymerization. As an example, the crosslinking mechanism of lignin-chitosan-poly(vinyl alcohol) (PVA) hydrogel involves active groups of lignin such as hydroxyl, carboxyl, and sulfonic groups that can form hydrogen bonds (with groups in the chemical structures of chitosan and/or PVA) and ionic bonds (with groups in the chemical structures of chitosan and/or PVA). The aim of this review paper is to provide a comprehensive overview of lignin-based hydrogels and their applications, focusing on the preparation and properties of lignin-based hydrogels and the biomedical applications of these hydrogels. In addition, we explore their potential in wound healing, drug delivery systems, and 3D bioprinting, showcasing the unique properties of lignin-based hydrogels that enable their successful utilization in these areas. Finally, we discuss future trends in the field and draw conclusions based on the findings presented.

Research Progress of Cordyceps sinensis and Its Fermented Mycelium Products on Ameliorating Renal Fibrosis by Reducing Epithelial-to-Mesenchymal Transition

Renal fibrosis is a hallmark and common outcome of various chronic kidney diseases (CKDs) and manifests pathologically as accumulation and deposition of extracellular matrix (ECM) in the kidney. Epithelial-to-mesenchymal transition (EMT) has been shown to be an important mechanism involved in renal fibrosis. Cordyceps sinensis, a traditional Chinese medicine, has long been used for the treatment of renal fibrosis. As research on the mycelium of C. sinensis progressed, a variety of medicines developed from fermented mycelium were used to treat CKD. However, their efficacies and mechanisms have not been fully summarized. In this review, five medicines developed from fermented mycelium of C. sinensis are presented. The pharmacodynamic effects of C. sinensis on different animal models of renal fibrosis are summarized. The in vitro studies and related mechanisms of C. sinensis on renal cells are detailed. Finally, the application and efficacy of these five commercial medicines that meet national standards in different types of CKD are summarized. From this review, it can be concluded that C. sinensis can alleviate various causes of renal fibrosis to some extent, and its mechanism is related to TGF-β1 dependent signaling, inhibition of inflammation, and improvement of renal function. Further research on rigorously designed, large-sample, clinically randomized controlled trial studies and detailed mechanisms should be conducted.

Efficient dual crosslinking of protein-in-polysaccharide bioink for biofabrication of cardiac tissue constructs

Myocardial infarction (MI) is a lethal cardiac disease that causes most of the mortality across the world. MI is a consequence of plaque in the arterial walls of heart, which eventually result in occlusion and ischemia to the myocardial tissues due to inadequate nutrient and oxygen supply. As an efficient alternative to the existing treatment strategies for MI, 3D bioprinting has evolved as an advanced tissue fabrication technique where the cell-laden bioinks are printed layer-by-layer to create functional cardiac patches. In this study, a dual crosslinking strategy has been utilized towards 3D bioprinting of myocardial constructs by using a combination of alginate and fibrinogen. Herein, pre-crosslinking of the physically blended alginate-fibrinogen bioinks with CaCl₂ enhanced the shape fidelity and printability of the printed structures. Physicochemical properties of the bioinks such as rheology, fibrin distribution, swelling ratio and degradation behaviour, were determined post-printing for only ionically crosslinked & dual crosslinked constructs and found to be ideal for bioprinting of cardiac constructs. Human ventricular cardiomyocytes (AC 16) exhibited a significant increase in cell proliferation on day 7 and 14 in AF-DMEM-20 mM CaCl₂ bioink when compared to A-DMEM-20 mM CaCl₂ (p < 0.05). Furthermore, myocardial patches containing neonatal ventricular rat myocytes (NVRM) showed >80 % viability and also expressed sarcomeric alpha actinin & connexin 43. These results indicate that the dual crosslinking strategy was cytocompatible and also possess the potential to be used for biofabrication of thick myocardial constructs for regenerative medicine applications.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

Human in vitro spermatogenesis as a regenerative therapy - where do we stand?

Spermatogenesis involves precise temporal and spatial gene expression and cell signalling to reach a coordinated balance between self-renewal and differentiation of spermatogonial stem cells through various germ cell states including mitosis, and meiosis I and II, which result in the generation of haploid cells with a unique genetic identity. Subsequently, these round spermatids undergo a series of morphological changes to shed excess cytoplast, develop a midpiece and tail, and undergo DNA repackaging to eventually form millions of spermatozoa. The goal of recreating this process in vitro has been pursued since the 1920s as a tool to treat male factor infertility in patients with azoospermia. Continued advances in reproductive bioengineering led to successful generation of mature, functional sperm in mice and, in the past 3 years, in humans. Multiple approaches to study human in vitro spermatogenesis have been proposed, but technical and ethical obstacles have limited the ability to complete spermiogenesis, and further work is needed to establish a robust culture system for clinical application.

Advances in Stimuli-responsive Hydrogels for Tissue Engineering and Regenerative Medicine Applications: A Review Towards Improving Structural Design for 3D Printing

The physicochemical properties of polymeric hydrogels render them attractive for the development of 3D printed prototypes for tissue engineering in regenerative medicine. Significant effort has been made to design hydrogels with desirable attributes that facilitate 3D printability. In addition, there is significant interest in exploring stimuli-responsive hydrogels to support automated 3D printing into more structurally organised prototypes such as customizable bio-scaffolds for regenerative medicine applications. Synthesizing stimuli-responsive hydrogels is dependent on the type of design and modulation of various polymeric materials to open novel opportunities for applications in biomedicine and bio-engineering. In this review, the salient advances made in the design of stimuli-responsive polymeric hydrogels for 3D printing in tissue engineering are discussed with a specific focus on the different methods of manipulation to develop 3D printed stimuli-responsive polymeric hydrogels. Polymeric functionalisation, nano-enabling and crosslinking are amongst the most common manipulative attributes that affect the assembly and structure of 3D printed bio-scaffolds and their stimuli- responsiveness. The review also provides a concise incursion into the various applications of stimuli to enhance the automated production of structurally organized 3D printed medical prototypes.

Three-dimensional printing of smart constructs using stimuli-responsive biomaterials: A future direction of precision medicine

Three-dimensional (3D) printing, which is a valuable technique for the fabrication of tissue-engineered constructs and biomedical devices with complex architectures, has brought about considerable progress in regenerative medicine, drug delivery, and diagnosis of diseases. However, because of the static and inanimate properties of conventional 3D-printed structures, it is difficult to use them in therapies for active and precise medicine, such as improved tissue regeneration, targeted or controlled drug delivery, and advanced pathophysiological monitoring. The integration of stimuli-responsive biomaterials into 3D printing provides a potential strategy for designing and building smart constructs that exhibit programmed functions and controllable changes in properties in response to exogenous and autogenous stimuli. These features make 3D-printed smart constructs the next generation of tissue-engineered products. In this review, we introduce the prevalent 3D printing techniques (with an emphasis on the differences between 3D printing and bioprinting, and biomaterials and bioink), the working principle of each technique, and the advantages of using 3D printing for the fabrication of smart constructs. Stimuli-responsive biomaterials that are widely used for 3D printing of smart constructs are categorized, followed by a summary of their applications in tissue regeneration, drug delivery, and biosensors. Finally, the challenges and future perspectives of 3D-printed smart constructs are discussed.

Emerging Bioactive Agent Delivery-Based Regenerative Therapies for Lower Genitourinary Tissues

Injury to lower genitourinary (GU) tissues, which may result in either infertility and/or organ dysfunctions, threatens the overall health of humans. Bioactive agent-based regenerative therapy is a promising therapeutic method. However, strategies for spatiotemporal delivery of bioactive agents with optimal stability, activity, and tunable delivery for effective sustained disease management are still in need and present challenges. In this review, we present the advancements of the pivotal components in delivery systems, including biomedical innovations, system fabrication methods, and loading strategies, which may improve the performance of delivery systems for better regenerative effects. We also review the most recent developments in the application of these technologies, and the potential for delivery-based regenerative therapies to treat lower GU injuries. Recent progress suggests that the use of advanced strategies have not only made it possible to develop better and more diverse functionalities, but also more precise, and smarter bioactive agent delivery systems for regenerative therapy. Their application in lower GU injury treatment has achieved certain effects in both patients with lower genitourinary injuries and/or in model animals. The continuous evolution of biomaterials and therapeutic agents, advances in three-dimensional printing, as well as emerging techniques all show a promising future for the treatment of lower GU-related disorders and dysfunctions.

Smart biomaterials: From 3D printing to 4D bioprinting

This century is blessed with enhanced medical facilities on the grounds of the development of smart biomaterials. The rise of the four-dimensional (4D) bioprinting technology is a shining example. Using inert biomaterials as the bioinks for the three-dimensional (3D) printing process, static objects that might not be able to mimic the dynamic nature of tissues would be fabricated; by contrast, 4D bioprinting can be used for the fabrication of stimuli-responsive cell-laden structures that can evolve with time and enable engineered tissues to undergo morphological changes in a pre-planned way. For all the aptitude of 4D bioprinting technology in tissue engineering, it is imperative to select suitable stimuli-responsive biomaterials with cell-supporting functionalities and responsiveness; as a result, in this article, recent advances and challenges in smart biomaterials for 4D bioprinting are briefly discussed. An overview perspective concerning the latest developments in 4D-bioprinting is also provided.

Using clinically derived human tissue to 3-dimensionally bioprint personalized testicular tubules for in vitro culturing: first report

OBJECTIVE

To study the feasibility and spermatogenic potential of 3-dimensional (3D) bioprinting personalized human testicular cells derived from a patient with nonobstructive azoospermia (NOA).

DESIGN

A human testicular biopsy from a single donor with NOA was dissociated into single cells, expanded in vitro, and 3D bioprinted into tubular structures akin to the seminiferous tubule using AGC-10 bioink and an RX1 bioprinter with a CENTRA coaxial microfluidic printhead from Aspect Biosystems. Three-dimensional organoid cultures were used as a nonbioprinted in vitro control.

SETTING

Academic medical center.

PATIENT(S)

A 31-year-old man with NOA with testis biopsy demonstrating Sertoli cell-only syndrome.

INTERVENTION(S)

Three-dimensional bioprinting and in vitro culturing of patient-derived testis cells.

MAIN OUTCOME MEASURE(S)

Cellular viability after printing was determined, along with the expression of phenotypic and spermatogenic functional genetic markers after 12 days of in vitro culture.

RESULT(S)

Testicular cultures were expandable in vitro and generated sufficiently large numbers for 3D bioprinting at 35 million cells per mL of bioink. Viability 24 hours after printing was determined to be 93.4% ± 2.4%. Immunofluorescence staining for the phenotype markers SRY-Box transcription factor 9, insulin-like 3, actin alpha 2 smooth muscle, and synaptonemal complex protein 3 after 12 days was positive, confirming the presence of Sertoli, Leydig, peritubular myoid, and meiotic germ cells. Reverse transcription qualitative polymerase chain reaction analysis showed that after 12 days in spermatogenic media, the bioprints substantially up-regulated spermatogenic gene expression on par with nonbioprinted controls and showed a particularly significant improvement in genes involved in spermatogonial stem cell maintenance: inhibitor of deoxyribonucleic acid binding 4 by 365-fold; fibroblast growth factor 3 by 94,152-fold; stem cell growth factor receptor KIT by twofold; stimulated by retinoic acid 8 by 125-fold; deleted in azoospermia-like by 114-fold; synaptonemal complex protein 3 by sevenfold; zona pellucida binding protein by twofold; transition protein 1 by 2,908-fold; and protamine 2 by 11-fold.

CONCLUSION(S)

This study demonstrates for the first time the feasibility of 3D bioprinting adult human testicular cells. We show that the bioprinting process is compatible with high testicular cell viability and without loss of the main somatic phenotypes within the testis tissue. We demonstrate an increase in germ cell markers in the 3D bioprinted tubules after 12 days of in vitro culture. This platform may carry future potential for disease modeling and regenerative opportunities in a personalized medicine framework.