Bioprinting Cellularized Constructs Using a Tissue-specific Hydrogel Bioink

3D bioprinting of liver models: A systematic scoping review of methods, bioinks, and reporting quality

Background

Effective communication is crucial for broad acceptance and applicability of alternative methods in 3R biomedical research and preclinical testing. 3D bioprinting is used to construct intricate biological structures towards functional liver models, specifically engineered for deployment as alternative models in drug screening, toxicological investigations, and tissue engineering. Despite a growing number of reviews in this emerging field, a comprehensive study, systematically assessing practices and reporting quality for bioprinted liver models is missing.

Methods

In this systematic scoping review we systematically searched MEDLINE (Ovid), EMBASE (Ovid) and BioRxiv for studies published prior to June 2nd, 2022. We extracted data on methodological conduct, applied bioinks, the composition of the printed model, performed experiments and model applications. Records were screened for eligibility and data were extracted from included articles by two independent reviewers from a panel of seven domain experts specializing in bioprinting and liver biology. We used RAYYAN for the screening process and SyRF for data extraction. We used R for data analysis, and R and Graphpad PRISM for visualization.

Results

Through our systematic database search we identified 1042 records, from which 63 met the eligibility criteria for inclusion in this systematic scoping review. Our findings revealed that extrusion-based printing, in conjunction with bioinks composed of natural components, emerged as the predominant printing technique in the bioprinting of liver models. Notably, the HepG2 hepatoma cell line was the most frequently employed liver cell type, despite acknowledged limitations. Furthermore, 51% of the printed models featured co-cultures with non-parenchymal cells to enhance their complexity. The included studies offered a variety of techniques for characterizing these liver models, with their primary application predominantly focused on toxicity testing. Among the frequently analyzed liver markers, albumin and urea stood out. Additionally, Cytochrome P450 (CYP) isoforms, primarily CYP3A and CYP1A, were assessed, and select studies employed nuclear receptor agonists to induce CYP activity.

Conclusion

Our systematic scoping review offers an evidence-based overview and evaluation of the current state of research on bioprinted liver models, representing a promising and innovative technology for creating alternative organ models. We conducted a thorough examination of both the methodological and technical facets of model development and scrutinized the reporting quality within the realm of bioprinted liver models. This systematic scoping review can serve as a valuable template for systematically evaluating the progress of organ model development in various other domains. The transparently derived evidence presented here can provide essential support to the research community, facilitating the adaptation of technological advancements, the establishment of standards, and the enhancement of model robustness. This is particularly crucial as we work toward the long-term objective of establishing new approach methods as reliable alternatives to animal testing, with extensive and versatile applications.

Reproducible generation of human liver organoids (HLOs) on a pillar plate platform via microarray 3D bioprinting

Human liver organoids (HLOs) hold significant potential for recapitulating the architecture and function of liver tissues in vivo. However, conventional culture methods of HLOs, forming Matrigel domes in 6-/24-well plates, have technical limitations such as high cost and low throughput in organoid-based assays for predictive assessment of compounds in clinical and pharmacological lab settings. To address these issues, we have developed a unique microarray 3D bioprinting protocol of progenitor cells in biomimetic hydrogels on a pillar plate with sidewalls and slits, coupled with a clear bottom, 384-deep well plate for scale-up production of HLOs. Microarray 3D bioprinting, a droplet-based printing technology, was used to generate a large number of small organoids on the pillar plate for predictive hepatotoxicity assays. Foregut cells, differentiated from human iPSCs, were mixed with Matrigel and then printed on the pillar plate rapidly and uniformly, resulting in coefficient of variation (CV) values in the range of 15 - 18%, without any detrimental effect on cell viability. Despite utilizing 10 - 50-fold smaller cell culture volume compared to their counterparts in Matrigel domes in 6-/24-well plates, HLOs differentiated on the pillar plate exhibited similar morphology and superior function, potentially due to rapid diffusion of nutrients and oxygen at the small scale. Day 25 HLOs were robust and functional on the pillar plate in terms of their viability, albumin secretion, CYP3A4 activity, and drug toxicity testing, all with low CV values. From three independent trials of in situ assessment, the IC50 values calculated for sorafenib and tamoxifen were 6.2 ± 1.6 μM and 25.4 ± 8.3 μM, respectively. Therefore, our unique 3D bioprinting and miniature organoid culture on the pillar plate could be used for scale-up, reproducible generation of HLOs with minimal manual intervention for high-throughput assessment of compound hepatotoxicity.

Immersion bioprinting of hyaluronan and collagen bioink-supported 3D patient-derived brain tumor organoids

Organoids, and in particular patient-derived organoids, have emerged as crucial tools for cancer research. Our organoid platform, which has supported patient-derived tumor organoids (PTOs) from a variety of tumor types, has been based on the use of hyaluronic acid (HA) and collagen, or gelatin, hydrogel bioinks. One hurdle to high throughput PTO biofabrication is that as high-throughput multi-well plates, bioprinted volumes have increased risk of contacting the sides of wells. When this happens, surface tension causes bioinks to fall flat, resulting in 2D cultures. To address this problem, we developed an organoid immersion bioprinting method-inspired by the FRESH printing method-in which organoids are bioprinted into support baths in well plates. The bath-in this case an HA solution-shields organoids from the well walls, preventing deformation. Here we describe an improvement to our approach, based on rheological assessment of previous gelatin baths versus newer HA support baths, combined with morphological assessment of immersion bioprinted organoids. HA print baths enabled more consistent organoid volumes and geometries. We optimized the printing parameters of this approach using a cell line. Finally, we deployed our optimized immersion bioprinting approach into a drug screening application, using PTOs derived from glioma biospecimens, and a lung adenocarcinoma brain metastasis. In these studies, we showed a general dose dependent response to an experimental p53 activator compound and temozolomide (TMZ), the drug most commonly given to brain tumor patients. Responses to the p53 activator compound were effective across all PTO sets, while TMZ responses were observed, but less pronounced, potentially explained by genetic and epigenetic states of the originating tumors. The studies presented herein showcase a bioprinting methodology that we hope can be used in increased throughput settings to help automate biofabrication of PTOs for drug development-based screening studies and precision medicine applications.

Exploiting maleimide-functionalized hyaluronan hydrogels to test cellular responses to physical and biochemical stimuli

Currentin vitrothree-dimensional (3D) models of liver tissue have been limited by the inability to study the effects of specific extracellular matrix (ECM) components on cell phenotypes. This is in part due to limitations in the availability of chemical modifications appropriate for this purpose. For example, hyaluronic acid (HA), which is a natural ECM component within the liver, lacks key ECM motifs (e.g. arginine-glycine-aspartic acid (RGD) peptides) that support cell adhesion. However, the addition of maleimide (Mal) groups to HA could facilitate the conjugation of ECM biomimetic peptides with thiol-containing end groups. In this study, we characterized a new crosslinkable hydrogel (i.e. HA-Mal) that yielded a simplified ECM-mimicking microenvironment supportive of 3D liver cell culture. We then performed a series of experiments to assess the impact of physical and biochemical signaling in the form of RGD peptide incorporation and transforming growth factorß(TGF-ß) supplementation, respectively, on hepatic functionality. Hepatic stellate cells (i.e. LX-2) exhibited increased cell-matrix interactions in the form of cell spreading and elongation within HA-Mal matrices containing RGD peptides, enabling physical adhesions, whereas hepatocyte-like cells (HepG2) had reduced albumin and urea production. We further exposed the encapsulated cells to soluble TGF-ßto elicit a fibrosis-like state. In the presence of TGF-ßbiochemical signals, LX-2 cells became activated and HepG2 functionality significantly decreased in both RGD-containing and RGD-free hydrogels. Altogether, in this study we have developed a hydrogel biomaterial platform that allows for discrete manipulation of specific ECM motifs within the hydrogel to better understand the roles of cell-matrix interactions on cell phenotype and overall liver functionality.

Towards organoid culture without Matrigel

Organoids-cellular aggregates derived from stem or progenitor cells that recapitulate organ function in miniature-are of growing interest in developmental biology and medicine. Organoids have been developed for organs and tissues such as the liver, gut, brain, and pancreas; they are used as organ surrogates to study a wide range of questions in basic and developmental biology, genetic disorders, and therapies. However, many organoids reported to date have been cultured in Matrigel, which is prepared from the secretion of Engelbreth-Holm-Swarm mouse sarcoma cells; Matrigel is complex and poorly defined. This complexity makes it difficult to elucidate Matrigel-specific factors governing organoid development. In this review, we discuss promising Matrigel-free methods for the generation and maintenance of organoids that use decellularized extracellular matrix (ECM), synthetic hydrogels, or gel-forming recombinant proteins.

Bletilla striata polysaccharide cryogel scaffold for spatial control of foreign-body reaction

BACKGROUND

Implantation of a biomaterial may induce the foreign-body reaction to the host tissue that determines the outcome of the integration and the biological performance of the implants. The foreign-body reaction can be modulated by control of the material properties of the implants.

METHODS

First, we synthesized methacrylated Bletilla striata Polysaccharide (BSP-MA) and constructed a series of open porous cryogels utilizing this material via the freezing-thawing treatment of solvent-precursors systems. Second, Pore size and modulus were measured to characterize the properties of BSP cryogels. Live/dead staining of cells and CCK-8 were performed to test the cytocompatibility of the scaffolds. In addition, the Real-Time qPCR experiments were carried for the tests. Finally, the BSP scaffolds were implanted subcutaneously to verify the foreign-body reaction between host tissue and materials.

RESULTS

Our data demonstrated that cryogels with different pore sizes and modulus can be fabricated by just adjusting the concentration. Besides, the cryogels showed well cytocompatibility in the in vitro experiments and exhibited upregulated expression levels of pro-inflammation-related genes (Tnfa and Il1b) with the increase of pore size. In vivo experiments further proved that with the increase of pore size, more immune cells infiltrated into the inner zone of materials. The foreign-body reaction and the distribution of immune-regulatory cells could be modulated by tuning the material microstructure.

CONCLUSIONS

Collectively, our findings revealed Bletilla striata polysaccharide cryogel scaffold with different pore sizes can spatially control foreign-body reaction. The microstructure of cryogels could differentially guide the distribution of inflammatory cells, affect the formation of blood vessels and fibrous capsules, which eventually influence the material-tissue integration. This work demonstrates a practical strategy to regulate foreign body reaction and promote the performance of medical devices.

3D bioprinting: current status and trends—a guide to the literature and industrial practice

The multidisciplinary research field of bioprinting combines additive manufacturing, biology and material sciences to create bioconstructs with three-dimensional architectures mimicking natural living tissues. The high interest in the possibility of reproducing biological tissues and organs is further boosted by the ever-increasing need for personalized medicine, thus allowing bioprinting to establish itself in the field of biomedical research, and attracting extensive research efforts from companies, universities, and research institutes alike. In this context, this paper proposes a scientometric analysis and critical review of the current literature and the industrial landscape of bioprinting to provide a clear overview of its fast-changing and complex position. The scientific literature and patenting results for 2000–2020 are reviewed and critically analyzed by retrieving 9314 scientific papers and 309 international patents in order to draw a picture of the scientific and industrial landscape in terms of top research countries, institutions, journals, authors and topics, and identifying the technology hubs worldwide. This review paper thus offers a guide to researchers interested in this field or to those who simply want to understand the emerging trends in additive manufacturing and 3D bioprinting.

Graphic abstract

Bioengineering Approaches for the Advanced Organoid Research

Recent advances in 3D cell culture technology have enabled scientists to generate stem cell derived organoids that recapitulate the structural and functional characteristics of native organs. Current organoid technologies have been striding toward identifying the essential factors for controlling the processes involved in organoid development, including physical cues and biochemical signaling. There is a growing demand for engineering dynamic niches characterized by conditions that resemble in vivo organogenesis to generate reproducible and reliable organoids for various applications. Innovative biomaterial-based and advanced engineering-based approaches have been incorporated into conventional organoid culture methods to facilitate the development of organoid research. The recent advances in organoid engineering, including extracellular matrices and genetic modulation, are comprehensively summarized to pinpoint the parameters critical for organ-specific patterning. Moreover, perspective trends in developing tunable organoids in response to exogenous and endogenous cues are discussed for next-generation developmental studies, disease modeling, and therapeutics.

3D bioprinting of molecularly engineered PEG-based hydrogels utilizing gelatin fragments

Three-dimensional (3D) bioprinting is an additive manufacturing process in which the combination of biomaterials and living cells, referred to as a bioink, is deposited layer-by-layer to form biologically active 3D tissue constructs. Recent advancements in the field show that the success of this technology requires the development of novel biomaterials or the improvement of existing bioinks. Polyethylene glycol (PEG) is one of the well-known synthetic biomaterials and has been commonly used as a photocrosslinkable bioink for bioprinting; however, other types of cell-friendly crosslinking mechanisms to form PEG hydrogels need to be explored for bioprinting and tissue engineering. In this work, we proposed micro-capillary based bioprinting of a novel molecularly engineered PEG-based bioink that transiently incorporates low molecular weight gelatin (LMWG) fragments. The rheological properties and release profile of the LMWG fragments were characterized, and their presence during hydrogel formation had no effect on the swelling ratio or sol fraction when compared to PEG hydrogels formed without the LMWG fragments. For bioprinting, PEG was first functionalized with cell-adhesive RGD ligands and was then crosslinked using protease-sensitive peptides via a Michael-type addition reaction inside the micro-capillary. The printability was assessed by the analysis of extrudability, shape fidelity, and printing accuracy of the hydrogel filaments after the optimization of the gelation conditions of the PEG-based bioink. The LMWG fragments supplemented into the bioink allowed the extrusion of smooth and uniform cylindrical strands of the hydrogel and improved shape fidelity and printing accuracy. Encapsulated cells in both bioprinted and non-bioprinted PEG-based hydrogels showed high viability and continued to proliferate over time in culture with a well-defined cell morphology depending on the presence of the cell adhesive peptide RGD. The presented micro-capillary based bioprinting process for a novel PEG-based bioink can be promising to construct complex 3D structures with micro-scale range and spatiotemporal variations without using any cytotoxic photoinitiator, UV light, or polymer support.

Developments and Opportunities for 3D Bioprinted Organoids

Organoids developed from pluripotent stem cells or adult stem cells are three-dimensional cell cultures possessing certain key characteristics of their organ counterparts, and they can mimic certain biological developmental processes of organs in vitro. Therefore, they have promising applications in drug screening, disease modeling, and regenerative repair of tissues and organs. However, the construction of organoids currently faces numerous challenges, such as breakthroughs in scale size, vascularization, better reproducibility, and precise architecture in time and space. Recently, the application of bioprinting has accelerated the process of organoid construction. In this review, we present current bioprinting techniques and the application of bioinks and summarize examples of successful organoid bioprinting. In the future, a multidisciplinary combination of developmental biology, disease pathology, cell biology, and materials science will aid in overcoming the obstacles pertaining to the bioprinting of organoids. The combination of bioprinting and organoids with a focus on structure and function can facilitate further development of real organs.

Recapitulating Tumorigenesis in vitro: Opportunities and Challenges of 3D Bioprinting

Cancer is considered one of the most predominant diseases in the world and one of the principal causes of mortality per year. The cellular and molecular mechanisms involved in the development and establishment of solid tumors can be defined as tumorigenesis. Recent technological advances in the 3D cell culture field have enabled the recapitulation of tumorigenesis in vitro, including the complexity of stromal microenvironment. The establishment of these 3D solid tumor models has a crucial role in personalized medicine and drug discovery. Recently, spheroids and organoids are being largely explored as 3D solid tumor models for recreating tumorigenesis in vitro. In spheroids, the solid tumor can be recreated from cancer cells, cancer stem cells, stromal and immune cell lineages. Organoids must be derived from tumor biopsies, including cancer and cancer stem cells. Both models are considered as a suitable model for drug assessment and high-throughput screening. The main advantages of 3D bioprinting are its ability to engineer complex and controllable 3D tissue models in a higher resolution. Although 3D bioprinting represents a promising technology, main challenges need to be addressed to improve the results in cancer research. The aim of this review is to explore (1) the principal cell components and extracellular matrix composition of solid tumor microenvironment; (2) the recapitulation of tumorigenesis in vitro using spheroids and organoids as 3D culture models; and (3) the opportunities, challenges, and applications of 3D bioprinting in this area.

Multi-Domain Photopatterned 3D Tumor Constructs in a Micro-Physiological System for Analysis, Quantification, and Isolation of Infiltrating Cells

Cancer cell motility plays a central role in metastasis and tumor invasion but can be difficult to study accurately in vitro. A simple approach to address this challenge through the production of monolithic, photopatterned 3D tumor constructs in situ in a microfluidic device is described here. Through step-wise fabrication of adjoining hydrogel regions with and without incorporated cells, multidomain structures with defined boundaries are produced. By imaging cells over time, cellular activity with arbitrary control over medium conditions, including drug concentration and flow rate, is studied. First, malignant human colon carcinoma cells (HCT116) are studied for 10 days, comparing invasion dynamics and viability of cells in normal media to those exposed to two independent chemotherapeutic drugs: anti-proliferative 5-fluorouracil and anti-migratory Marimastat. Cytotoxicity is measured and significant differences are observed in cellular dynamics (migrating cell count, distance traveled, and rate) that correlate with the mechanism of each drug. Then, the platform is applied to the selective isolation of infiltrated cells through the photopatterning and subsequent dissolution of cleavable hydrogel domains. As a demonstration, the preferential collection of highly migratory cells (HCT116) over a comparable cell line with low malignancy and migratory potential (Caco-2) is shown.

Drug compound screening in single and integrated multi-organoid body-on-a-chip systems

Current practices in drug development have led to therapeutic compounds being approved for widespread use in humans, only to be later withdrawn due to unanticipated toxicity. These occurrences are largely the result of erroneous data generated by in vivo and in vitro preclinical models that do not accurately recapitulate human physiology. Herein, a human primary cell- and stem cell-derived 3D organoid technology is employed to screen a panel of drugs that were recalled from market by the FDA. The platform is comprised of multiple tissue organoid types that remain viable for at least 28 days, in vitro. For many of these compounds, the 3D organoid system was able to demonstrate toxicity. Furthermore, organoids exposed to non-toxic compounds remained viable at clinically relevant doses. Additional experiments were performed on integrated multi-organoid systems containing liver, cardiac, lung, vascular, testis, colon, and brain. These integrated systems proved to maintain viability and expressed functional biomarkers, long-term. Examples are provided that demonstrate how multi-organoid 'body-on-a-chip' systems may be used to model the interdependent metabolism and downstream effects of drugs across multiple tissues in a single platform. Such 3D in vitro systems represent a more physiologically relevant model for drug screening and will likely reduce the cost and failure rate associated with the approval of new drugs.

Immersion Bioprinting of Tumor Organoids in Multi-Well Plates for Increasing Chemotherapy Screening Throughput

The current drug development pipeline takes approximately fifteen years and $2.6 billion to get a new drug to market. Typically, drugs are tested on two-dimensional (2D) cell cultures and animal models to estimate their efficacy before reaching human trials. However, these models are often not representative of the human body. The 2D culture changes the morphology and physiology of cells, and animal models often have a vastly different anatomy and physiology than humans. The use of bioengineered human cell-based organoids may increase the probability of success during human trials by providing human-specific preclinical data. They could also be deployed for personalized medicine diagnostics to optimize therapies in diseases such as cancer. However, one limitation in employing organoids in drug screening has been the difficulty in creating large numbers of homogeneous organoids in form factors compatible with high-throughput screening (e.g., 96- and 384-well plates). Bioprinting can be used to scale up deposition of such organoids and tissue constructs. Unfortunately, it has been challenging to 3D print hydrogel bioinks into small-sized wells due to well-bioink interactions that can result in bioinks spreading out and wetting the well surface instead of maintaining a spherical form. Here, we demonstrate an immersion printing technique to bioprint tissue organoids in 96-well plates to increase the throughput of 3D drug screening. A hydrogel bioink comprised of hyaluronic acid and collagen is bioprinted into a viscous gelatin bath, which blocks the bioink from interacting with the well walls and provides support to maintain a spherical form. This method was validated using several cancerous cell lines, and then applied to patient-derived glioblastoma (GBM) and sarcoma biospecimens for drug screening.

Deconstructed Microfluidic Bone Marrow On-A-Chip to Study Normal and Malignant Hemopoietic Cell-Niche Interactions

Human hematopoietic niches are complex specialized microenvironments that maintain and regulate hematopoietic stem and progenitor cells (HSPC). Thus far, most of the studies performed investigating alterations of HSPC-niche dynamic interactions are conducted in animal models. Herein, organ microengineering with microfluidics is combined to develop a human bone marrow (BM)-on-a-chip with an integrated recirculating perfusion system that consolidates a variety of important parameters such as 3D architecture, cell-cell/cell-matrix interactions, and circulation, allowing a better mimicry of in vivo conditions. The complex BM environment is deconvoluted to 4 major distinct, but integrated, tissue-engineered 3D niche constructs housed within a single, closed, recirculating microfluidic device system, and equipped with cell tracking technology. It is shown that this technology successfully enables the identification and quantification of preferential interactions-homing and retention-of circulating normal and malignant HSPC with distinct niches.

[Current concepts and new developments of 3D printing in trauma surgery]

The use of 3D printing (synonyms "rapid prototyping" and "additive manufacturing") has played an increasing role in the industry for many years and finds more and more interest and application in musculoskeletal surgery, especially orthopedic trauma surgery.In this article the current literature is systematically reviewed, presented and evaluated in a condensed and comprehensive way according to anatomical (upper and lower extremities) and functional aspects. As many of the publications analyzed were feasibility studies, the degree of evidence is low and methodological weaknesses are obvious and numerous; however, this pioneering work is extremely stimulating and important for further development because the technical, medical and economic potential of this technology is huge and interesting for all those involved in the treatment of musculoskeletal problems.

Conductive collagen/polypyrrole-b-polycaprolactone hydrogel for bioprinting of neural tissue constructs

Bioprinting is increasingly being used for fabrication of engineered tissues for regenerative medicine, drug testing, and other biomedical applications. The success of this technology lies with the development of suitable bioinks and hydrogels that are specific to the intended tissue application. For applications such as neural tissue engineering, conductivity plays an important role in determining the neural differentiation and neural tissue regeneration. Although several conductive hydrogels based on metal nanoparticles (NPs) such as gold and silver, carbon-based materials such as graphene and carbon nanotubes and conducting polymers such as polypyrrole (PPy) and polyaniline were used, they possess several disadvantages. The long-term cytotoxicity of metal nanoparticles (NPs) and carbon-based materials restricts their use in regenerative medicine. The conductive polymers, on the other hand, are non-biodegradable and possess weak mechanical properties limiting their printability into three-dimensional constructs. The aim of this study is to develop a biodegradable, conductive, and printable hydrogel based on collagen and a block copolymer of PPy and polycaprolactone (PCL) (PPy-block-poly(caprolactone) [PPy-b-PCL]) for bioprinting of neural tissue constructs. The printability, including the influence of the printing speed and material flow rate on the printed fiber width; rheological properties; and cytotoxicity of these hydrogels were studied. The results prove that the collagen/PPy-b-PCL hydrogels possessed better printability and biocompatibility. Thus, the collagen/PPy-b-PCL hydrogels reported this study has the potential to be used in the bioprinting of neural tissue constructs for the repair of damaged neural tissues and drug testing or precision medicine applications.

Generation of Cost-Effective Paper-Based Tissue Models through Matrix-Assisted Sacrificial 3D Printing

Due to the combined advantages of cellulose and nanoscale (diameter 20-60 nm), bacterial cellulose possesses a series of attractive features including its natural origin, moderate biosynthesis process, good biocompatibility, and cost-effectiveness. Moreover, bacterial cellulose nanofibers can be conveniently processed into three-dimensional (3D) intertwined structures and form stable paper devices after simple drying. These advantages make it suitable as the material for construction of organ-on-a-chip devices using matrix-assisted sacrificial 3D printing. We successfully fabricated various microchannel structures embedded in the bulk bacterial cellulose hydrogels and retained their integrity after the drying process. Interestingly, these paper-based devices containing hollow microchannels could be rehydrated and populated with relevant cells to form vascularized tissue models. As a proof-of-concept demonstration, we seeded human umbilical vein endothelial cells (HUVECs) into the microchannels to obtain the vasculature and inoculated the MCF-7 cells onto the surrounding matrix of the paper device to build a 3D paper-based vascularized breast tumor model. The results showed that the microchannels were perfusable, and both HUVECs and MCF-7 cells exhibited favorable proliferation behaviors. This study may provide a new strategy for constructing simple and low-cost in vitro tissue models, which may find potential applications in drug screening and personalized medicine.

Current Biomedical Applications of 3D Printing and Additive Manufacturing

Additive manufacturing (AM) has emerged over the past four decades as a cost-effective, on-demand modality for fabrication of geometrically complex objects. The ability to design and print virtually any object shape using a diverse array of materials, such as metals, polymers, ceramics and bioinks, has allowed for the adoption of this technology for biomedical applications in both research and clinical settings. Current advancements in tissue engineering and regeneration, therapeutic delivery, medical device fabrication and operative management planning ensure that AM will continue to play an increasingly important role in the future of healthcare. In this review, we outline current biomedical applications of common AM techniques and materials.

3D bioprinting for high-throughput screening: Drug screening, disease modeling, and precision medicine applications

High-throughput technologies have become essential in many fields of pharmaceutical and biological development and production. Such technologies were initially developed with compatibility with liquid handling-based cell culture techniques to produce large-scale 2D cell culture experiments for the compound analysis of candidate drug compounds. Over the past two decades, tools for creating 3D cell cultures, organoids, and other 3D in vitro models, such as cell supportive biomaterials and 3D bioprinting, have rapidly advanced. Concurrently, a significant body of evidence has accumulated which speaks to the many benefits that 3D model systems have over traditional 2D cell cultures. Specifically, 3D cellular models better mimic aspects such as diffusion kinetics, cell-cell interactions, cell-matrix interactions, inclusion of stroma, and other features native to in vivo tissue and as such have become an integral part of academic research. However, most high throughput assays were not developed to specifically support 3D systems. Here, we describe the need for improved compatibility and relevant advances toward deployment and adoption of high throughput 3D models to improve disease modeling, drug efficacy testing, and precision medicine applications.

A multi-site metastasis-on-a-chip microphysiological system for assessing metastatic preference of cancer cells

Metastatic disease remains one of the primary reasons for cancer-related deaths, yet the majority of in vitro cancer models focus on the primary tumor sites. Here, we describe a metastasis-on-a-chip device that houses multiple bioengineered three-dimensional (3D) organoids, established by a 3D photopatterning technique employing extracellular matrix-derived hydrogel biomaterials. Specifically, cancer cells begin in colorectal cancer (CRC) organoid, which resides in a single microfluidic chamber connected to multiple downstream chambers in which liver, lung, and endothelial constructs are housed. Under recirculating fluid flow, tumor cells grow in the primary site, eventually enter circulation, and can be tracked via fluorescent imaging. Importantly, we describe that in the current version of this platform, HCT116 CRC cells preferentially home to the liver and lung constructs; the corresponding organs of which CRC metastases arise the most in human patients. We believe that in subsequent studies this platform can be implemented to better understand the mechanisms underlying metastasis, perhaps resulting in the identification of targets for intervention.

Natural Polymers for Organ 3D Bioprinting

Three-dimensional (3D) bioprinting, known as a promising technology for bioartificial organ manufacturing, has provided unprecedented versatility to manipulate cells and other biomaterials with precise control their locations in space. Over the last decade, a number of 3D bioprinting technologies have been explored. Natural polymers have played a central role in supporting the cellular and biomolecular activities before, during and after the 3D bioprinting processes. These polymers have been widely used as effective cell-loading hydrogels for homogeneous/heterogeneous tissue/organ formation, hierarchical vascular/neural/lymphatic network construction, as well as multiple biological/biochemial/physiological/biomedical/pathological functionality realization. This review aims to cover recent progress in natural polymers for bioartificial organ 3D bioprinting. It is structured as introducing the important properties of 3D printable natural polymers, successful models of 3D tissue/organ construction and typical technologies for bioartificial organ 3D bioprinting.

Applications of Bioengineered 3D Tissue and Tumor Organoids in Drug Development and Precision Medicine: Current and Future

Over the past decade, advances in biomedical and tissue engineering technologies, such as cell culture techniques, biomaterials, and biofabrication, have driven increasingly widespread use of three-dimensional (3D) cell culture platforms and, subsequently, the use of organoids in a variety of research endeavors. Given the 3D nature of these organoid systems, and the frequent inclusion of extracellular matrix components, these constructs typically have more physiologically accurate cell-cell and cell-matrix interactions than traditional 2D cell cultures. As a result, 3D organoids can serve as better model systems than their 2D counterparts. Moreover, as organoids can be biofabricated from highly functional human cells, they have certain advantages over animal models, being human in nature and more easily manipulated in the laboratory. In this review, we describe such organoid technologies and their deployment in drug development and precision medicine efforts. Organoid technologies are rapidly being developed for these applications and now represent a wide variety of tissue types and diseases. Evidence is emerging that organoids are poised for widespread adoption, not only in academia but also in the pharmaceutical industry and in clinical diagnostic applications, positioning them as indispensable tools in medicine.

Environmental Toxin Screening Using Human-Derived 3D Bioengineered Liver and Cardiac Organoids

INTRODUCTION

Environmental toxins, such as lead and other heavy metals, pesticides, and other compounds, represent a significant health concern within the USA and around the world. Even in the twenty-first century, a plethora of cities and towns in the U.S. have suffered from exposures to lead in drinking water or other heavy metals in food or the earth, while there is a high possibility of further places to suffer such exposures in the near future.

METHODS

We employed bioengineered 3D human liver and cardiac organoids to screen a panel of environmental toxins (lead, mercury, thallium, and glyphosate), and charted the response of the organoids to these compounds. Liver and cardiac organoids were exposed to lead (10 µM-10 mM), mercury (200 nM-200 µM), thallium (10 nM-10 µM), or glyphosate (25 µM-25 mM) for a duration of 48 h. The impacts of toxin exposure were then assessed by LIVE/DEAD viability and cytotoxicity staining, measuring ATP activity and determining IC50 values, and determining changes in cardiac organoid beating activity.

RESULTS

As expected, all of the toxins induced toxicity in the organoids. Both ATP and LIVE/DEAD assays showed toxicity in both liver and cardiac organoids. In particular, thallium was the most toxic, with IC50 values of 13.5 and 1.35 µM in liver and cardiac organoids, respectively. Conversely, glyphosate was the least toxic of the four compounds, with IC50 values of 10.53 and 10.85 mM in liver and cardiac organoids, respectively. Additionally, toxins had a negative influence on cardiac organoid beating activity as well. Thallium resulting in the most significant decreases in beating rate, followed by mercury, then glyphosate, and finally, lead. These results suggest that the 3D organoids have significant utility to be deployed in additional toxicity screening applications, and future development of treatments to mitigate exposures.

CONCLUSION

3D organoids have significant utility to be deployed in additional toxicity screening applications, such as future development of treatments to mitigate exposures, drug screening, and environmental toxin detection.

In vitro patient-derived 3D mesothelioma tumor organoids facilitate patient-centric therapeutic screening

Variability in patient response to anti-cancer drugs is currently addressed by relating genetic mutations to chemotherapy through precision medicine. However, practical benefits of precision medicine to therapy design are less clear. Even after identification of mutations, oncologists are often left with several drug options, and for some patients there is no definitive treatment solution. There is a need for model systems to help predict personalized responses to chemotherapeutics. We have microengineered 3D tumor organoids directly from fresh tumor biopsies to provide patient-specific models with which treatment optimization can be performed before initiation of therapy. We demonstrate the initial implementation of this platform using tumor biospecimens surgically removed from two mesothelioma patients. First, we show the ability to biofabricate and maintain viable 3D tumor constructs within a tumor-on-a-chip microfluidic device. Second, we demonstrate that results of on-chip chemotherapy screening mimic those observed in subjects themselves. Finally, we demonstrate mutation-specific drug testing by considering the results of precision medicine genetic screening and confirming the effectiveness of the non-standard compound 3-deazaneplanocin A for an identified mutation. This patient-derived tumor organoid strategy is adaptable to a wide variety of cancers and may provide a framework with which to improve efforts in precision medicine oncology.

Polymeric 3D Printed Structures for Soft-Tissue Engineering

3D printing, or rapid prototyping, is a fabrication technique that is used for various engineering applications with advantages such as mass production and fine tuning of spatial-dimensional properties. Recently, this fabrication method has been adopted for tissue engineering applications due to its ability to finely tune porosity and create precise, uniform, and repeatable structures. This review aims to introduce 3D printing applications in soft tissue engineering and regenerative medicine including state-of-the-art scaffolds and key future challenges. Furthermore, 3D printing of individual cells, an evolution of traditional 3D printing technology which represents a cutting-edge technique for the creation of cell seeded scaffolds in vitro, is discussed. Key advances demonstrate the advantages of 3D printing, while also highlighting potential shortcomings to improve upon. It is clear that as 3D printing technology continues to develop, it will serve as a truly revolutionary means for fabrication of structures and materials for regenerative applications.

Multi-tissue interactions in an integrated three-tissue organ-on-a-chip platform

Many drugs have progressed through preclinical and clinical trials and have been available - for years in some cases - before being recalled by the FDA for unanticipated toxicity in humans. One reason for such poor translation from drug candidate to successful use is a lack of model systems that accurately recapitulate normal tissue function of human organs and their response to drug compounds. Moreover, tissues in the body do not exist in isolation, but reside in a highly integrated and dynamically interactive environment, in which actions in one tissue can affect other downstream tissues. Few engineered model systems, including the growing variety of organoid and organ-on-a-chip platforms, have so far reflected the interactive nature of the human body. To address this challenge, we have developed an assortment of bioengineered tissue organoids and tissue constructs that are integrated in a closed circulatory perfusion system, facilitating inter-organ responses. We describe a three-tissue organ-on-a-chip system, comprised of liver, heart, and lung, and highlight examples of inter-organ responses to drug administration. We observe drug responses that depend on inter-tissue interaction, illustrating the value of multiple tissue integration for in vitro study of both the efficacy of and side effects associated with candidate drugs.

Exploration of Dynamic Elastic Modulus Changes on Glioblastoma Cell Populations with Aberrant EGFR Expression as a Potential Therapeutic Intervention Using a Tunable Hyaluronic Acid Hydrogel Platform

Glioblastoma (GBM) is one of most aggressive forms of brain cancer, with a median survival time of 14.6 months following diagnosis. This low survival rate could in part be attributed to the lack of model systems of this type of cancer that faithfully recapitulate the tumor architecture and microenvironment seen in vivo in humans. Therapeutic studies would provide results that could be translated to the clinic efficiently. Here, we assess the role of the tumor microenvironment physical parameters on the tumor, and its potential use as a biomarker using a hyaluronic acid hydrogel system capable of elastic modulus tuning and dynamic elastic moduli changes. Experiments were conducted to assess the sensitivity of glioblastoma cell populations with different mutations to varying elastic moduli. Cells with aberrant epithelial growth factor receptor (EGFR) expression have a predilection for a stiffer environment, sensing these parameters through focal adhesion kinase (FAK). Importantly, the inhibition of FAK or EGFR generally resulted in reversed elastic modulus preference. Lastly, we explore the concept of therapeutically targeting the elastic modulus and dynamically reducing it via chemical or enzymatic degradation, both showing the capability to reduce or stunt proliferation rates of these GBM populations.

Mesenchymal stem cells support growth and organization of host-liver colorectal-tumor organoids and possibly resistance to chemotherapy

Despite having yielded extensive breakthroughs in cancer research, traditional 2D cell cultures have limitations in studying cancer progression and metastasis and screening therapeutic candidates. 3D systems can allow cells to grow, migrate, and interact with each other and the surrounding matrix, resulting in more realistic constructs. Furthermore, interactions between host tissue and developing tumors influence the susceptibility of tumors to drug treatments. Host-liver colorectal-tumor spheroids composed of primary human hepatocytes, mesenchymal stem cells (MSC) and colon carcinoma HCT116 cells were created in simulated microgravity rotating wall vessel (RWV) bioreactors. The cells were seeded on hyaluronic acid-based microcarriers, loaded with liver-specific growth factors and ECM components. Only in the presence of MSC, large tumor foci rapidly formed inside the spheroids and increased in size steadily over time, while not greatly impacting albumin secretion from hepatocytes. The presence of MSC appeared to drive self-organization and formation of a stroma-like tissue surrounding the tumor foci and hepatocytes. Exposure to a commonly used chemotherapeutic 5-FU showed a dose-dependent cytotoxicity. However, if tumor organoids were allowed to mature in the RWV, they were less sensitive to the drug treatment. These data demonstrate the potential utility of liver tumor organoids for cancer progression and drug response modeling.

Bioprinting the Cancer Microenvironment

Cancer is intrinsically complex, comprising both heterogeneous cellular compositions and microenvironmental cues. During the various stages of cancer initiation, development, and metastasis, cell-cell interactions (involving vascular and immune cells besides cancerous cells) as well as cell-extracellular matrix (ECM) interactions (e.g., alteration in stiffness and composition of the surrounding matrix) play major roles. Conventional cancer models both two- and three-dimensional (2D and 3D) present numerous limitations as they lack good vascularization and cannot mimic the complexity of tumors, thereby restricting their use as biomimetic models for applications such as drug screening and fundamental cancer biology studies. Bioprinting as an emerging biofabrication platform enables the creation of high-resolution 3D structures and has been extensively used in the past decade to model multiple organs and diseases. More recently, this versatile technique has further found its application in studying cancer genesis, growth, metastasis, and drug responses through creation of accurate models that recreate the complexity of the cancer microenvironment. In this review we will focus first on cancer biology and limitations with current cancer models. We then detail the current bioprinting strategies including the selection of bioinks for capturing the properties of the tumor matrices, after which we discuss bioprinting of vascular structures that are critical toward construction of complex 3D cancer organoids. We finally conclude with current literature on bioprinted cancer models and propose future perspectives.

Cell sources for in vitro human liver cell culture models

In vitro liver cell culture models are gaining increasing importance in pharmacological and toxicological research. The source of cells used is critical for the relevance and the predictive value of such models. Primary human hepatocytes (PHH) are currently considered to be the gold standard for hepatic in vitro culture models, since they directly reflect the specific metabolism and functionality of the human liver; however, the scarcity and difficult logistics of PHH have driven researchers to explore alternative cell sources, including liver cell lines and pluripotent stem cells. Liver cell lines generated from hepatomas or by genetic manipulation are widely used due to their good availability, but they are generally altered in certain metabolic functions. For the past few years, adult and pluripotent stem cells have been attracting increasing attention, due their ability to proliferate and to differentiate into hepatocyte-like cells in vitro However, controlling the differentiation of these cells is still a challenge. This review gives an overview of the major human cell sources under investigation for in vitro liver cell culture models, including primary human liver cells, liver cell lines, and stem cells. The promises and challenges of different cell types are discussed with a focus on the complex 2D and 3D culture approaches under investigation for improving liver cell functionality in vitro Finally, the specific application options of individual cell sources in pharmacological research or disease modeling are described.