A three-dimensional in vitro ovarian cancer coculture model using a high-throughput cell patterning platform

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.

The Adoption of Three-Dimensional Additive Manufacturing from Biomedical Material Design to 3D Organ Printing

Three-dimensional (3D) bioprinting promises to change future lifestyle and the way we think about aging, the field of medicine, and the way clinicians treat ailing patients. In this brief review, we attempt to give a glimpse into how recent developments in 3D bioprinting are going to impact vast research ranging from complex and functional organ transplant to future toxicology studies and printed organ-like 3D spheroids. The techniques were successfully applied to reconstructed complex 3D functional tissue for implantation, application-based high-throughput (HTP) platforms for absorption, distribution, metabolism, and excretion (ADME) profiling to understand the cellular basis of toxicity. We also provide an overview of merits/demerits of various bioprinting techniques and the physicochemical basis of bioink for tissue engineering. We briefly discuss the importance of universal bioink technology, and of time as the fourth dimension. Some examples of bioprinted tissue are shown, followed by a brief discussion on future biomedical applications.

Modeling Tumor Phenotypes In Vitro with Three-Dimensional Bioprinting

The tumor microenvironment plays a critical role in tumor growth, progression, and therapeutic resistance, but interrogating the role of specific tumor-stromal interactions on tumorigenic phenotypes is challenging within in vivo tissues. Here, we tested whether three-dimensional (3D) bioprinting could improve in vitro models by incorporating multiple cell types into scaffold-free tumor tissues with defined architecture. We generated tumor tissues from distinct subtypes of breast or pancreatic cancer in relevant microenvironments and demonstrate that this technique can model patient-specific tumors by using primary patient tissue. We assess intrinsic, extrinsic, and spatial tumorigenic phenotypes in bioprinted tissues and find that cellular proliferation, extracellular matrix deposition, and cellular migration are altered in response to extrinsic signals or therapies. Together, this work demonstrates that multi-cell-type bioprinted tissues can recapitulate aspects of in vivo neoplastic tissues and provide a manipulable system for the interrogation of multiple tumorigenic endpoints in the context of distinct tumor microenvironments.

Modeling Epidermal Growth Factor Inhibitor-mediated Enhancement of Photodynamic Therapy Efficacy Using 3D Mesothelioma Cell Culture

We have demonstrated that lung-sparing surgery with intraoperative photodynamic therapy (PDT) achieves remarkably extended survival for patients with malignant pleural mesothelioma (MPM). Nevertheless, most patients treated using this approach experience local recurrence, so it is essential to identify ways to enhance tumor response. We previously reported that PDT transiently activates EGFR/STAT3 in lung and ovarian cancer cells and inhibiting EGFR via erlotinib can increase PDT sensitivity. Additionally, we have seen higher EGFR expression associating with worse outcomes after Photofrin-mediated PDT for MPM, and the extensive desmoplastic reaction associated with MPM influences tumor phenotype and therapeutic response. Since extracellular matrix (ECM) proteins accrued during stroma development can alter EGF signaling within tumors, we have characterized novel 3D models of MPM to determine their response to erlotinib combined with Photofrin-PDT. Our MPM cell lines formed a range of acinar phenotypes when grown on ECM gels, recapitulating the locally invasive phenotype of MPM in pleura and endothoracic fascia. Using these models, we confirmed that EGFR inhibition increases PDT cytotoxicity. Together with emerging evidence that EGFR inhibition may improve survival of lung cancer patients through immunologic and direct cell killing mechanisms, these results suggest erlotinib-enhanced PDT may significantly improve outcomes for MPM patients.

Three-dimensional printing biotechnology for the regeneration of the tooth and tooth-supporting tissues

The tooth and its supporting tissues are organized with complex three-dimensional (3D) architecture, including the dental pulp with a blood supply and nerve tissues, complex multilayer periodontium, and highly aligned periodontal ligament (PDL). Mimicking such 3D complexity and the multicellular interactions naturally existing in dental structures represents great challenges in dental regeneration. Attempts to construct the complex system of the tooth and tooth-supporting apparatus (i.e., the PDL, alveolar bone, and cementum) have made certain progress owing to 3D printing biotechnology. Recent advances have enabled the 3D printing of biocompatible materials, seed cells, and supporting components into complex 3D functional living tissue. Furthermore, 3D bioprinting is driving major innovations in regenerative medicine, giving the field of regenerative dentistry a boost. The fabrication of scaffolds via 3D printing is already being performed extensively at the laboratory bench and in clinical trials; however, printing living cells and matrix materials together to produce tissue constructs by 3D bioprinting remains limited to the regeneration of dental pulp and the tooth germ. This review summarizes the application of scaffolds for cell seeding and biofabricated tissues via 3D printing and bioprinting, respectively, in the tooth and its supporting tissues. Additionally, the key advantages and prospects of 3D bioprinting in regenerative dentistry are highlighted, providing new ideas for dental regeneration.

Developments with 3D bioprinting for novel drug discovery

Introduction: Although there have been significant contributions from the pharmaceutical industry to clinical practice, several diseases remain unconquered, with the discovery of new drugs remaining a paramount objective. The actual process of drug discovery involves many steps including pre-clinical and clinical testing, which are highly time- and resource-consuming, driving researchers to improve the process efficiency. The shift of modelling technology from two-dimensions (2D) to three-dimensions (3D) is one of such advancements. 3D Models allow for close mimicry of cellular interactions and tissue microenvironments thereby improving the accuracy of results. The advent of bioprinting for fabrication of tissues has shown potential to improve 3D culture models. Areas covered: The present review provides a comprehensive update on a wide range of bioprinted tissue models and appraise them for their potential use in drug discovery research. Expert opinion: Efficiency, reproducibility, and standardization are some impediments of the bioprinted models. Vascularization of the constructs has to be addressed in the near future. While much progress has already been made with several seminal works, the next milestone will be the commercialization of these models after due regulatory approval.

Epithelial-to-Mesenchymal Transition (EMT) and Drug Response in Dynamic Bioengineered Lung Cancer Microenvironment

Tumor microenvironment and the interplay of physical and mechanical forces are key determinants of cancer initiation, progression, and response to drug treatment. However, the impact of tumor microenvironment on cancer progression is poorly understood, in large due to the lack of in vitro models that recapitulate the physical aspects of tumor microenvironment. Herein, a simple, dynamic 3D nonsmall cell lung carcinoma culture using a multichannel microfluidic model platform is developed for evaluating the contribution of flow-induced hydrodynamic shear stress on epithelial-to-mesenchymal transition (EMT). It is found that flow induces changes in cellular morphology and EMT in 2D and 3D when lung cancer A549 cells are cultured on a microfluidic chip under laminar flow for 4-5 days compared to traditional static cultures. The role of dynamic cell culture on chemotherapeutic effects is monitored. Drug response with an existing anti-cancer drug, e.g., erlotinib and an investigational drug (NSC-750212), shows distinct cytotoxic effects in flow compared to static cultures, suggesting a potential influence of flow on drug efficacy in 2D and 3D models. The platform demonstrates the ability to create a dynamic microscale tumor model, which could be explored as a tool for early drug screening and treatment monitoring in cancer and other diseases.

Pharmaceutical Additive Manufacturing: a Novel Tool for Complex and Personalized Drug Delivery Systems

Inter-individual variability is always an issue when treating patients of different races, genders, ages, pharmacogenetics, and pharmacokinetic characteristics. However, the development of novel dosage forms is limited by the huge investments required for production line modifications and dosages diversity. Additive manufacturing (AM) or 3D printing can be a novel alternative solution for the development of controlled release dosages because it can produce personalized or unique dosage forms and more complex drug-release profiles. The primary objective of this manuscript is to review the 3D printing processes that have been used in the pharmaceutical area, including their general aspects, materials, and the operation of each AM technique. Advantages and shortcomings of the technologies are discussed with respect to practice and practical applications. Thus, this review will provide an overview and discussion on advanced pharmaceutical AM technologies, which can be used to produce unique controlled drug delivery systems and personalized dosages for the future of personalized medicine.

Addressing Unmet Clinical Needs with 3D Printing Technologies

Recent advances in 3D printing have enabled the creation of novel 3D constructs and devices with an unprecedented level of complexity, properties, and functionalities. In contrast to manufacturing techniques developed for mass production, 3D printing encompasses a broad class of fabrication technologies that can enable 1) the creation of highly customized and optimized 3D physical architectures from digital designs; 2) the synergistic integration of properties and functionalities of distinct classes of materials to create novel hybrid devices; and 3) a biocompatible fabrication approach that facilitates the creation and cointegration of biological constructs and systems. This progress report describes how these capabilities can potentially address a myriad of unmet clinical needs. First, the creation of 3D-printed prosthetics to regain lost functionalities by providing structural support for skeletal and tubular organs is highlighted. Second, novel drug delivery strategies aided by 3D-printed devices are described. Third, the advancement of medical research heralded by 3D-printed tissue/organ-on-chips systems is discussed. Fourth, the developments of 3D-printed tissue and organ regeneration are explored. Finally, the potential for seamless integration of engineered organs with active devices by leveraging the versatility of multimaterial 3D printing is envisioned.

Coaxial extrusion bioprinted shell-core hydrogel microfibers mimic glioma microenvironment and enhance the drug resistance of cancer cells

Glioblastoma (GBM) is the most common primary malignant central nervous system tumor. The current treatment is mainly surgical resection combined with radiotherapy, chemotherapy and other comprehensive treatment methods. However, the treatment effect is unsatisfactory, the resistance of cancer cells to alkylating agent is the major reason for the recurrence of GBM. It is necessary to develop an ideal in vitro model to investigate the drug resistance of glioma cells. In this study, shell-glioma stem cell GSC23/core-glioma cell line U118 (G/U) hydrogel microfibers with high cell viability were constructed by coaxial extrusion bioprinting. It was found that core-U118 cells gradually proliferated to form fiber-like cell aggregates and the interactions between cell-cell and cell-extracellular matrix (ECM) were increased. Furthermore, compared with shell/core-U118 (U) hydrogel microfibers, the expressions of matrix metalloproteinase-2 (MMP2), MMP9, vascular endothelial growth factor receptor-2 (VEGFR2) and O6-methylguanine-DNA methyltransferase (MGMT) which are related to tumor invasion and drug resistance were significantly enhanced in G/U hydrogel microfibers. Moreover, U118 cells derived from G/U microfibers had greater drug resistance in vitro and the level of MGMT promoter methylation in G/U cultured U118 cells was significantly lower than that of U cultured cells. In summary, coaxial extrusion bioprinted G/U hydrogel microfiber is a preferable platform for mimicking glioma microenvironment, as well as for drug development and screening.

Alteration of microRNA profiling in sphere-cultured ovarian carcinoma cells

Ovarian cancer is an aggressive and lethal cancer, which in part, can be attributed to complications in the effective detection of this disease during early stages of progression. Frequently, epithelial ovarian cancer is disseminated to the abdominal cavity and forms multicellular aggregates. This unique early metastatic event, and formation of the multicellular aggregate is implicated to provide a basis for understanding the underlying molecular mechanisms of metastasis in ovarian cancer. Therefore, a 3-dimensional (3D) sphere culture system was established in the present study to mimic the later stages of ovarian cancer. The aim of the present study was to investigate whether microRNAs (miRNAs), which have functions in metastasis and chemoresistance in various cancer models, are altered in ovarian cancer cells by 3-dimensional (3D) culture. A multicellular aggregate of SKOV3ip1 ovarian carcinoma cells was generated using a 3D sphere culture system. Cell viability analysis demonstrated that the sphere-cultured SKOV3ip1 cells exhibited chemoresistance compared with those in a conventional 2-dimensional (2D) monolayer cultured SKOV3ip1 system. Under the same experimental conditions, 71 upregulated miRNAs and 63 downregulated miRNAs were identified in the 3D sphere-cultured SKOV3ip1 cells. The predicted targets of the 3D sphere-culture specific miRNAs were further identified using PITA, microRNAorg and TargetScan. Compared with the target gene pool and Kyoto Encyclopedia of Genes and Genomes pathway, the present study provides evidence that the 3D sphere culture-specific miRNAs regulated sphere formation and chemoresistance in 3D sphere-cultured SKOV3ip1 cells. Overall, the results of the present study demonstrated that miRNA-mediated regulation is implicated to provoke features of SKOV3ip1 multicellular aggregation, including sphere formation and chemoresistance.

Design of spherically structured 3D in vitro tumor models -Advances and prospects

Three-dimensional multicellular tumor models are receiving an ever-growing focus as preclinical drug-screening platforms due to their potential to recapitulate major physiological features of human tumors in vitro. In line with this momentum, the technologies for assembly of 3D microtumors are rapidly evolving towards a comprehensive inclusion of tumor microenvironment elements. Customized spherically structured platforms, including microparticles and microcapsules, provide a robust and scalable technology to imprint unique biomolecular tumor microenvironment hallmarks into 3D in vitro models. Herein, a comprehensive overview of novel advances on the integration of tumor-ECM components and biomechanical cues into 3D in vitro models assembled in spherical shaped platforms is provided. Future improvements regarding spatiotemporal/mechanical adaptability, and degradability, during microtumors in vitro 3D culture are also critically discussed considering the realistic potential of these platforms to mimic the dynamic tumor microenvironment. From a global perspective, the production of 3D multicellular spheroids with tumor ECM components included in spherical models will unlock their potential to be used in high-throughput screening of therapeutic compounds. It is envisioned, in a near future, that a combination of spherically structured 3D microtumor models with other advanced microfluidic technologies will properly recapitulate the flow dynamics of human tumors in vitro.

STATEMENT OF SIGNIFICANCE

The ability to correctly mimic the complexity of the tumor microenvironment in vitro is a key aspect for the development of evermore realistic in vitro models for drug-screening and fundamental cancer biology studies. In this regard, conventional spheroid-based 3D tumor models, combined with spherically structured biomaterials, opens the opportunity to precisely recapitulate complex cell-extracellular matrix interactions and tumor compartmentalization. This review provides an in-depth focus on current developments regarding spherically structured scaffolds engineered into in vitro 3D tumor models, and discusses future advances toward all-encompassing platforms that may provide an improved in vitro/in vivo correlation in a foreseeable future.

3D bioprinting of functional tissue models for personalized drug screening and in vitro disease modeling

3D bioprinting is emerging as a promising technology for fabricating complex tissue constructs with tailored biological components and mechanical properties. Recent advances have enabled scientists to precisely position materials and cells to build functional tissue models for in vitro drug screening and disease modeling. This review presents state-of-the-art 3D bioprinting techniques and discusses the choice of cell source and biomaterials for building functional tissue models that can be used for personalized drug screening and disease modeling. In particular, we focus on 3D-bioprinted liver models, cardiac tissues, vascularized constructs, and cancer models for their promising applications in medical research, drug discovery, toxicology, and other pre-clinical studies.

Applications of 3D printing in cancer

The tumor heterogeneity and interindividual variability is a major problem when treating cancer as every patient responds in a different way to the current drug therapies. 3D printing is a tool that can hamper the issues faced in cancer patients allowing for individualization of treatment by the production of in vitro models with microenvironments mimicking more closely real cancer conditions facilitating complex therapies. Further improvements are required, for example the development of biocompatible bioinks or need for vascularization. The journey from bench to bedside is challenging from the regulatory point of view where the establishment of manufacturing guidelines, quality systems and safety of use and administration of personalized medicines remains unclear. This review will provide an insight into the major applications of 3D printing in cancer both in the development of in vitro cancer models as well as personalized medicines for cancer patients focused on hydrogels and therapeutic implants.

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3D printed drug delivery and testing systems - a passing fad or the future?

The US Food and Drug Administration approval of the first 3D printed tablet in 2015 has ignited growing interest in 3D printing, or additive manufacturing (AM), for drug delivery and testing systems. Beyond just a novel method for rapid prototyping, AM provides key advantages over traditional manufacturing of drug delivery and testing systems. These includes the ability to fabricate complex geometries to achieve variable drug release kinetics; ease of personalising pharmacotherapy for patient and lowering the cost for fabricating personalised dosages. Furthermore, AM allows fabrication of complex and micron-sized tissue scaffolds and models for drug testing systems that closely resemble in vivo conditions. However, there are several limitations such as regulatory concerns that may impede the progression to market. Here, we provide an overview of the advantages of AM drug delivery and testing, as compared to traditional manufacturing techniques. Also, we discuss the key challenges and future directions for AM enabled pharmaceutical applications.

3D bioprinting of tissues and organs for regenerative medicine

3D bioprinting is a pioneering technology that enables fabrication of biomimetic, multiscale, multi-cellular tissues with highly complex tissue microenvironment, intricate cytoarchitecture, structure-function hierarchy, and tissue-specific compositional and mechanical heterogeneity. Given the huge demand for organ transplantation, coupled with limited organ donors, bioprinting is a potential technology that could solve this crisis of organ shortage by fabrication of fully-functional whole organs. Though organ bioprinting is a far-fetched goal, there has been a considerable and commendable progress in the field of bioprinting that could be used as transplantable tissues in regenerative medicine. This paper presents a first-time review of 3D bioprinting in regenerative medicine, where the current status and contemporary issues of 3D bioprinting pertaining to the eleven organ systems of the human body including skeletal, muscular, nervous, lymphatic, endocrine, reproductive, integumentary, respiratory, digestive, urinary, and circulatory systems were critically reviewed. The implications of 3D bioprinting in drug discovery, development, and delivery systems are also briefly discussed, in terms of in vitro drug testing models, and personalized medicine. While there is a substantial progress in the field of bioprinting in the recent past, there is still a long way to go to fully realize the translational potential of this technology. Computational studies for study of tissue growth or tissue fusion post-printing, improving the scalability of this technology to fabricate human-scale tissues, development of hybrid systems with integration of different bioprinting modalities, formulation of new bioinks with tuneable mechanical and rheological properties, mechanobiological studies on cell-bioink interaction, 4D bioprinting with smart (stimuli-responsive) hydrogels, and addressing the ethical, social, and regulatory issues concerning bioprinting are potential futuristic focus areas that would aid in successful clinical translation of this technology.

Advanced Cell and Tissue Biomanufacturing

This position paper assesses state-of-the-art advanced biomanufacturing and identifies paths forward to advance this emerging field in biotechnology and biomedical engineering, including new research opportunities and translational and corporate activities. The vision for the field is to see advanced biomanufacturing emerge as a discipline in academic and industrial communities as well as a technological opportunity to spur research and industry growth. To navigate this vision, the paths to move forward and to identify major barriers were a focal point of discussions at a National Science Foundation-sponsored workshop focused on the topic. Some of the major needs include but are not limited to the integration of specific scientific and engineering disciplines and guidance from regulatory agencies, infrastructure requirements, and strategies for reliable systems integration. Some of the recommendations, major targets, and opportunities were also outlined, including some "grand challenges" to spur interest and progress in the field based on the participants at the workshop. Many of these recommendations have been expanded, materialized, and adopted by the field. For instance, the formation of an initial collaboration network in the community was established. This report provides suggestions for the opportunities and challenges to help move the field of advanced biomanufacturing forward. The field is in the early stages of effecting science and technology in biomanufacturing with a bright and important future impact evident based on the rapid scientific advances in recent years and industry progress.

Engineering Breast Cancer Microenvironments and 3D Bioprinting

The extracellular matrix (ECM) is a critical cue to direct tumorigenesis and metastasis. Although two-dimensional (2D) culture models have been widely employed to understand breast cancer microenvironments over the past several decades, the 2D models still exhibit limited success. Overwhelming evidence supports that three dimensional (3D), physiologically relevant culture models are required to better understand cancer progression and develop more effective treatment. Such platforms should include cancer-specific architectures, relevant physicochemical signals, stromal-cancer cell interactions, immune components, vascular components, and cell-ECM interactions found in patient tumors. This review briefly summarizes how cancer microenvironments (stromal component, cell-ECM interactions, and molecular modulators) are defined and what emerging technologies (perfusable scaffold, tumor stiffness, supporting cells within tumors and complex patterning) can be utilized to better mimic native-like breast cancer microenvironments. Furthermore, this review emphasizes biophysical properties that differ between primary tumor ECM and tissue sites of metastatic lesions with a focus on matrix modulation of cancer stem cells, providing a rationale for investigation of underexplored ECM proteins that could alter patient prognosis. To engineer breast cancer microenvironments, we categorized technologies into two groups: (1) biochemical factors modulating breast cancer cell-ECM interactions and (2) 3D bioprinting methods and its applications to model breast cancer microenvironments. Biochemical factors include matrix-associated proteins, soluble factors, ECMs, and synthetic biomaterials. For the application of 3D bioprinting, we discuss the transition of 2D patterning to 3D scaffolding with various bioprinting technologies to implement biophysical cues to model breast cancer microenvironments.

Engineering a 3D-Bioprinted Model of Human Heart Valve Disease Using Nanoindentation-Based Biomechanics

In calcific aortic valve disease (CAVD), microcalcifications originating from nanoscale calcifying vesicles disrupt the aortic valve (AV) leaflets, which consist of three (biomechanically) distinct layers: the fibrosa, spongiosa, and ventricularis. CAVD has no pharmacotherapy and lacks in vitro models as a result of complex valvular biomechanical features surrounding resident mechanosensitive valvular interstitial cells (VICs). We measured layer-specific mechanical properties of the human AV and engineered a three-dimensional (3D)-bioprinted CAVD model that recapitulates leaflet layer biomechanics for the first time. Human AV leaflet layers were separated by microdissection, and nanoindentation determined layer-specific Young’s moduli. Methacrylated gelatin (GelMA)/methacrylated hyaluronic acid (HAMA) hydrogels were tuned to duplicate layer-specific mechanical characteristics, followed by 3D-printing with encapsulated human VICs. Hydrogels were exposed to osteogenic media (OM) to induce microcalcification, and VIC pathogenesis was assessed by near infrared or immunofluorescence microscopy. Median Young’s moduli of the AV layers were 37.1, 15.4, and 26.9 kPa (fibrosa/spongiosa/ventricularis, respectively). The fibrosa and spongiosa Young’s moduli matched the 3D 5% GelMa/1% HAMA UV-crosslinked hydrogels. OM stimulation of VIC-laden bioprinted hydrogels induced microcalcification without apoptosis. We report the first layer-specific measurements of human AV moduli and a novel 3D-bioprinted CAVD model that potentiates microcalcification by mimicking the native AV mechanical environment. This work sheds light on valvular mechanobiology and could facilitate high-throughput drug-screening in CAVD.

Biofabrication strategies for 3D in vitro models and regenerative medicine

Organs are complex systems composed of different cells, proteins and signalling molecules that are arranged in a highly ordered structure to orchestrate a myriad of functions in our body. Biofabrication strategies can be applied to engineer 3D tissue models in vitro by mimicking the structure and function of native tissue through the precise deposition and assembly of materials and cells. This approach allows the spatiotemporal control over cell-cell and cell-extracellular matrix communication and thus the recreation of tissue-like structures. In this Review, we examine biofabrication strategies for the construction of functional tissue replacements and organ models, focusing on the development of biomaterials, such as supramolecular and photosensitive materials, that can be processed using biofabrication techniques. We highlight bioprinted and bioassembled tissue models and survey biofabrication techniques for their potential to recreate complex tissue properties, such as shape, vasculature and specific functionalities. Finally, we discuss challenges, such as scalability and the foreign body response, and opportunities in the field and provide an outlook to the future of biofabrication in regenerative medicine.

Engineering 3D approaches to model the dynamic microenvironments of cancer bone metastasis

Cancer metastasis to bone is a three-dimensional (3D), multistep, dynamic process that requires the sequential involvement of three microenvironments, namely, the primary tumour microenvironment, the circulation microenvironment and the bone microenvironment. Engineered 3D approaches allow for a vivid recapitulation of in vivo cancerous microenvironments in vitro, in which the biological behaviours of cancer cells can be assessed under different metastatic conditions. Therefore, modelling bone metastasis microenvironments with 3D cultures is imperative for advancing cancer research and anti-cancer treatment strategies. In this review, multicellular tumour spheroids and bioreactors, tissue engineering constructs and scaffolds, microfluidic systems and 3D bioprinting technology are discussed to explore the progression of the 3D engineering approaches used to model the three microenvironments of bone metastasis. We aim to provide new insights into cancer biology and advance the translation of new therapies for bone metastasis.

Enabling personalized implant and controllable biosystem development through 3D printing

The impact of additive manufacturing in our lives has been increasing constantly. One of the frontiers in this change is the medical devices. 3D printing technologies not only enable the personalization of implantable devices with respect to patient-specific anatomy, pathology and biomechanical properties but they also provide new opportunities in related areas such as surgical education, minimally invasive diagnosis, medical research and disease models. In this review, we cover the recent clinical applications of 3D printing with a particular focus on implantable devices. The current technical bottlenecks in 3D printing in view of the needs in clinical applications are explained and recent advances to overcome these challenges are presented. 3D printing with cells (bioprinting); an exciting subfield of 3D printing, is covered in the context of tissue engineering and regenerative medicine and current developments in bioinks are discussed. Also emerging applications of bioprinting beyond health, such as biorobotics and soft robotics, are introduced. As the technical challenges related to printing rate, precision and cost are steadily being solved, it can be envisioned that 3D printers will become common on-site instruments in medical practice with the possibility of custom-made, on-demand implants and, eventually, tissue engineered organs with active parts developed with biorobotics techniques.

Organ-on-a-Chip Systems for Women's Health Applications

Biomedical research, for a long time, has paid little attention to the influence of sex in many areas of study, ranging from molecular and cellular biology to animal models and clinical studies on human subjects. Many studies solely rely on male cells/tissues/animals/humans, although there are profound differences in male and female physiology, which can significantly impact disease mechanisms, toxicity of compounds, and efficacy of pharmaceuticals. In vitro systems have been traditionally very limited in their capacity to recapitulate female-specific physiology and anatomy such as dynamic sex-hormone levels and the complex interdependencies of female reproductive tract organs. However, the advent of microphysiological organ-on-a-chip systems, which attempt to recreate the 3D structure and function of human organs, now gives researchers the opportunity to integrate cells and tissues from a variety of individuals. Moreover, adding a dynamic flow environment allows mimicking endocrine signaling during the menstrual cycle and pregnancy, as well as providing a controlled microfluidic environment for pharmacokinetic modeling. This review gives an introduction into preclinical and clinical research on women's health and discusses where organ-on-a-chip systems are already utilized or have the potential to deliver new insights and enable entirely new types of studies.

3D Miniaturization of Human Organs for Drug Discovery

"Engineered human organs" hold promises for predicting the effectiveness and accuracy of drug responses while reducing cost, time, and failure rates in clinical trials. Multiorgan human models utilize many aspects of currently available technologies including self-organized spherical 3D human organoids, microfabricated 3D human organ chips, and 3D bioprinted human organ constructs to mimic key structural and functional properties of human organs. They enable precise control of multicellular activities, extracellular matrix (ECM) compositions, spatial distributions of cells, architectural organizations of ECM, and environmental cues. Thus, engineered human organs can provide the microstructures and biological functions of target organs and advantageously substitute multiscaled drug-testing platforms including the current in vitro molecular assays, cell platforms, and in vivo models. This review provides an overview of advanced innovative designs based on the three main technologies used for organ construction leading to single and multiorgan systems useable for drug development. Current technological challenges and future perspectives are also discussed.

Laser-fabricated cell patterning stencil for single cell analysis

Precise spatial positioning and isolation of mammalian cells is a critical component of many single cell experimental methods and biological engineering applications. Although a variety of cell patterning methods have been demonstrated, many of these methods subject cells to high stress environments, discriminate against certain phenotypes, or are a challenge to implement. Here, we demonstrate a rapid, simple, indiscriminate, and minimally perturbing cell patterning method using a laser fabricated polymer stencil. The stencil fabrication process requires no stencil-substrate alignment, and is readily adaptable to various substrate geometries and experiments.

Assessing multiparametric drug response in tissue engineered tumor microenvironment models

The tumor microenvironment is important in promoting treatment resistance of tumor cells via multiple mechanisms. However, studying this interaction often proves difficult. In vivo animal models are costly, time-consuming, and often fail to adequately predict human response to treatment. Conversely, testing drug response on human tumor cells in vitro in 2D cell culture excludes the important contribution of stromal cells and biophysical forces seen in the in vivo tumor microenvironment. Here, we present tissue-engineered models of both human brain and breast tumor microenvironments incorporating key stromal cell populations for assessing multiple mechanisms of therapeutic response using flow cytometry. We show our physiologically-relevant systems used to interrogate a variety of parameters associated with chemotherapeutic efficacy, including cell death, proliferation, drug uptake, and invasion of cancer and stromal cell populations. The use of flow cytometry allows for single cell, quantitative, and fast assessments of multiple outcomes affecting anti-tumor therapy failure. Our system can be modified to add and remove cellular components with ease, thereby enabling the study of individual cellular contributions in the tumor microenvironment. Together, our models and analysis methods illustrate the importance of developing fast, cost-effective, and reproducible methods to model complex human systems in a physiologically-relevant manner that may prove useful for drug screening efforts in the future.

In Situ Printing-then-Mixing for Biological Structure Fabrication Using Intersecting Jets

Although traditional three-dimensional bioprinting technology is suitable for many tissue engineering applications, various biomaterials and constructs call for bioprinting innovations. There is a need for the fabrication of complex structures from reactive biomaterials as well as heterogeneous structures with controlled material compositions. In particular, during reactive material printing, reactive solutions/suspensions that undergo changes in rheological properties or cytocompatibility are not printable using traditional bioprinting approaches that require all components of bioinks to be mixed before deposition. The objective of this study is to develop and implement an intersecting jets-based inkjet bioprinting approach, which enables voxel-resolution printing-then-mixing for the fabrication of biological structures using reactive materials as well as structures having a compositional gradient. Inkjetting is implemented herein as a versatile technique to simultaneously deposit droplets of disparate materials at controlled locations where active collision, mixing, and coalescence occur. For reactive material printing, neural stem cell (NSC) spheres are fabricated from reactive PuraMatrix hydrogel solution and physiological cell suspension, and cell-laden alginate structures are also printed in air directly from reactive sodium alginate and calcium chloride solutions. For heterogeneous structure printing, collagen sheets with a hydroxyapatite (HAP) content gradient are fabricated to demonstrate the unique online control of material composition throughout a structure. It is demonstrated that the proposed bioprinting approach is feasible for applications that utilize reactive materials or require heterogeneous compositions.

3D bioprinting for drug discovery and development in pharmaceutics

Successful launch of a commercial drug requires significant investment of time and financial resources wherein late-stage failures become a reason for catastrophic failures in drug discovery. This calls for infusing constant innovations in technologies, which can give reliable prediction of efficacy, and more importantly, toxicology of the compound early in the drug discovery process before clinical trials. Though computational advances have resulted in more rationale in silico designing, in vitro experimental studies still require gaining industry confidence and improving in vitro-in vivo correlations. In this quest, due to their ability to mimic the spatial and chemical attributes of native tissues, three-dimensional (3D) tissue models have now proven to provide better results for drug screening compared to traditional two-dimensional (2D) models. However, in vitro fabrication of living tissues has remained a bottleneck in realizing the full potential of 3D models. Recent advances in bioprinting provide a valuable tool to fabricate biomimetic constructs, which can be applied in different stages of drug discovery research. This paper presents the first comprehensive review of bioprinting techniques applied for fabrication of 3D tissue models for pharmaceutical studies. A comparative evaluation of different bioprinting modalities is performed to assess the performance and ability of fabricating 3D tissue models for pharmaceutical use as the critical selection of bioprinting modalities indeed plays a crucial role in efficacy and toxicology testing of drugs and accelerates the drug development cycle. In addition, limitations with current tissue models are discussed thoroughly and future prospects of the role of bioprinting in pharmaceutics are provided to the reader.

STATEMENT OF SIGNIFICANCE

Present advances in tissue biofabrication have crucial role to play in aiding the pharmaceutical development process achieve its objectives. Advent of three-dimensional (3D) models, in particular, is viewed with immense interest by the community due to their ability to mimic in vivo hierarchical tissue architecture and heterogeneous composition. Successful realization of 3D models will not only provide greater in vitro-in vivo correlation compared to the two-dimensional (2D) models, but also eventually replace pre-clinical animal testing, which has their own shortcomings. Amongst all fabrication techniques, bioprinting- comprising all the different modalities (extrusion-, droplet- and laser-based bioprinting), is emerging as the most viable fabrication technique to create the biomimetic tissue constructs. Notwithstanding the interest in bioprinting by the pharmaceutical development researchers, it can be seen that there is a limited availability of comparative literature which can guide the proper selection of bioprinting processes and associated considerations, such as the bioink selection for a particular pharmaceutical study. Thus, this work emphasizes these aspects of bioprinting and presents them in perspective of differential requirements of different pharmaceutical studies like in vitro predictive toxicology, high-throughput screening, drug delivery and tissue-specific efficacies. Moreover, since bioprinting techniques are mostly applied in regenerative medicine and tissue engineering, a comparative analysis of similarities and differences are also expounded to help researchers make informed decisions based on contemporary literature.

Directing the Self-assembly of Tumour Spheroids by Bioprinting Cellular Heterogeneous Models within Alginate/Gelatin Hydrogels

Human tumour progression is a dynamic process involving diverse biological and biochemical events such as genetic mutation and selection in addition to physical, chemical, and mechanical events occurring between cells and the tumour microenvironment. Using 3D bioprinting we have developed a method to embed MDA-MB-231 triple negative breast cancer cells, and IMR-90 fibroblast cells, within a cross-linked alginate/gelatin matrix at specific initial locations relative to each other. After 7 days of co-culture the MDA-MB-231 cells begin to form multicellular tumour spheroids (MCTS) that increase in size and frequency over time. After ~15 days the IMR-90 stromal fibroblast cells migrate through a non-cellularized region of the hydrogel matrix and infiltrate the MDA-MB-231 spheroids creating mixed MDA-MB-231/IMR-90 MCTS. This study provides a proof-of-concept that biomimetic in vitro tissue co-culture models bioprinted with both breast cancer cells and fibroblasts will result in MCTS that can be maintained for durations of several weeks.

Current and emerging applications of 3D printing in medicine

Three-dimensional (3D) printing enables the production of anatomically matched and patient-specific devices and constructs with high tunability and complexity. It also allows on-demand fabrication with high productivity in a cost-effective manner. As a result, 3D printing has become a leading manufacturing technique in healthcare and medicine for a wide range of applications including dentistry, tissue engineering and regenerative medicine, engineered tissue models, medical devices, anatomical models and drug formulation. Today, 3D printing is widely adopted by the healthcare industry and academia. It provides commercially available medical products and a platform for emerging research areas including tissue and organ printing. In this review, our goal is to discuss the current and emerging applications of 3D printing in medicine. A brief summary on additive manufacturing technologies and available printable materials is also given. The technological and regulatory barriers that are slowing down the full implementation of 3D printing in the medical field are also discussed.

Microfluidic on-chip biomimicry for 3D cell culture: a fit-for-purpose investigation from the end user standpoint

A plethora of 3D and microfluidics-based culture models have been demonstrated in the recent years with the ultimate aim to facilitate predictive in vitro models for pharmaceutical development. This article summarizes to date the progress in the microfluidics-based tissue culture models, including organ-on-a-chip and vasculature-on-a-chip. Specific focus is placed on addressing the question of what kinds of 3D culture and system complexities are deemed desirable by the biological and biomedical community. This question is addressed through analysis of a research survey to evaluate the potential use of microfluidic cell culture models among the end users. Our results showed a willingness to adopt 3D culture technology among biomedical researchers, although a significant gap still exists between the desired systems and existing 3D culture options. With these results, key challenges and future directions are highlighted.

Cancer drug discovery: recent innovative approaches to tumor modeling

INTRODUCTION

Cell culture models have been at the heart of anti-cancer drug discovery programs for over half a century. Advancements in cell culture techniques have seen the rapid evolution of more complex in vitro cell culture models investigated for use in drug discovery. Three-dimensional (3D) cell culture research has become a strong focal point, as this technique permits the recapitulation of the tumor microenvironment. Biologically relevant 3D cellular models have demonstrated significant promise in advancing cancer drug discovery, and will continue to play an increasing role in the future.

AREAS COVERED

In this review, recent advances in 3D cell culture techniques and their application in tumor modeling and anti-cancer drug discovery programs are discussed. The topics include selection of cancer cells, 3D cell culture assays (associated endpoint measurements and analysis), 3D microfluidic systems and 3D bio-printing.

EXPERT OPINION

Although advanced cancer cell culture models and techniques are becoming commonplace in many research groups, the use of these approaches has yet to be fully embraced in anti-cancer drug applications. Furthermore, limitations associated with analyzing information-rich biological data remain unaddressed.

Bioprinting technologies for disease modeling

There is a great need for the development of biomimetic human tissue models that allow elucidation of the pathophysiological conditions involved in disease initiation and progression. Conventional two-dimensional (2D) in vitro assays and animal models have been unable to fully recapitulate the critical characteristics of human physiology. Alternatively, three-dimensional (3D) tissue models are often developed in a low-throughput manner and lack crucial native-like architecture. The recent emergence of bioprinting technologies has enabled creating 3D tissue models that address the critical challenges of conventional in vitro assays through the development of custom bioinks and patient derived cells coupled with well-defined arrangements of biomaterials. Here, we provide an overview on the technological aspects of 3D bioprinting technique and discuss how the development of bioprinted tissue models have propelled our understanding of diseases' characteristics (i.e. initiation and progression). The future perspectives on the use of bioprinted 3D tissue models for drug discovery application are also highlighted.

Coaxial 3D bioprinting of self-assembled multicellular heterogeneous tumor fibers

Three-dimensional (3D) bioprinting of living structures with cell-laden biomaterials has been achieved in vitro, however, some cell-cell interactions are limited by the existing hydrogel. To better mimic tumor microenvironment, self-assembled multicellular heterogeneous brain tumor fibers have been fabricated by a custom-made coaxial extrusion 3D bioprinting system, with high viability, proliferative activity and efficient tumor-stromal interactions. Therein, in order to further verify the sufficient interactions between tumor cells and stroma MSCs, CRE-LOXP switch gene system which contained GSCs transfected with "LOXP-STOP-LOXP-RFP" genes and MSCs transfected with "CRE recombinase" gene was used. Results showed that tumor-stroma cells interacted with each other and fused, the transcription of RFP was higher than that of 2D culture model and control group with cells mixed directly into alginate, respectively. RFP expression was observed only in the cell fibers but not in the control group under confocal microscope. In conclusion, coaxial 3D bioprinted multicellular self-assembled heterogeneous tumor tissue-like fibers provided preferable 3D models for studying tumor microenvironment in vitro, especially for tumor-stromal interactions.

Emerging Biofabrication Strategies for Engineering Complex Tissue Constructs

The demand for organ transplantation and repair, coupled with a shortage of available donors, poses an urgent clinical need for the development of innovative treatment strategies for long-term repair and regeneration of injured or diseased tissues and organs. Bioengineering organs, by growing patient-derived cells in biomaterial scaffolds in the presence of pertinent physicochemical signals, provides a promising solution to meet this demand. However, recapitulating the structural and cytoarchitectural complexities of native tissues in vitro remains a significant challenge to be addressed. Through tremendous efforts over the past decade, several innovative biofabrication strategies have been developed to overcome these challenges. This review highlights recent work on emerging three-dimensional bioprinting and textile techniques, compares the advantages and shortcomings of these approaches, outlines the use of common biomaterials and advanced hybrid scaffolds, and describes several design considerations including the structural, physical, biological, and economical parameters that are crucial for the fabrication of functional, complex, engineered tissues. Finally, the applications of these biofabrication strategies in neural, skin, connective, and muscle tissue engineering are explored.

[3D bioprinting in regenerative medicine and tissue engineering]

Additive manufacturing covers a number of fashionable technologies that attract the interest of researchers in biomaterials and tissue engineering. Additive manufacturing applied to regenerative medicine covers two main areas: 3D printing and biofabrication. If 3D printing has penetrated the world of regenerative medicine, bioassembly and bioimprinting are still in their infancy. The objective of this paper is to make a non-exhaustive review of these different complementary aspects of additive manufacturing in restorative and regenerative medicine or for tissue engineering.

3D Printing of Tissue Engineered Constructs for In Vitro Modeling of Disease Progression and Drug Screening

2D cell culture and preclinical animal models have traditionally been implemented for investigating the underlying cellular mechanisms of human disease progression. However, the increasing significance of 3D vs. 2D cell culture has initiated a new era in cell culture research in which 3D in vitro models are emerging as a bridge between traditional 2D cell culture and in vivo animal models. Additive manufacturing (AM, also known as 3D printing), defined as the layer-by-layer fabrication of parts directed by digital information from a 3D computer-aided design file, offers the advantages of simultaneous rapid prototyping and biofunctionalization as well as the precise placement of cells and extracellular matrix with high resolution. In this review, we highlight recent advances in 3D printing of tissue engineered constructs that recapitulate the physical and cellular properties of the tissue microenvironment for investigating mechanisms of disease progression and for screening drugs.

Bio-inks for 3D bioprinting: recent advances and future prospects

In the last decade, interest in the field of three-dimensional (3D) bioprinting has increased enormously. This review describes all the currently used bio-printing inks, including polymeric hydrogels, polymer bead microcarriers, cell aggregates and extracellular matrix proteins.

Three-dimensional cell-based bioprinting for soft tissue regeneration

Three-dimensional (3D) bioprinting technologies have been developed to offer construction of biological tissue constructs that mimic the anatomical and functional features of native tissues or organs. These cutting-edge technologies could make it possible to precisely place multiple cell types and biomaterials in a single 3D tissue construct. Hence, 3D bioprinting is one of the most attractive and powerful tools to provide more anatomical and functional similarity of human tissues or organs in tissue engineering and regenerative medicine. In recent years, this 3D bioprinting continually shows promise for building complex soft tissue constructs through placement of cell-laden hydrogel-based bioinks in a layer-by-layer fashion. This review will discuss bioprinting technologies and their applications in soft tissue regeneration.

Drug screening in 3D in vitro tumor models: overcoming current pitfalls of efficacy read-outs

There is cumulating evidence that in vitro 3D tumor models with increased physiological relevance can improve the predictive value of pre-clinical research and ultimately contribute to achieve decisions earlier during the development of cancer-targeted therapies. Due to the role of tumor microenvironment in the response of tumor cells to therapeutics, the incorporation of different elements of the tumor niche on cell model design is expected to contribute to the establishment of more predictive in vitro tumor models. This review is focused on the several challenges and adjustments that the field of oncology research is facing to translate these advanced tumor cells models to drug discovery, taking advantage of the progress on culture technologies, imaging platforms, high throughput and automated systems. The choice of 3D cell model, the experimental design, choice of read-outs and interpretation of data obtained from 3D cell models are critical aspects when considering their implementation in drug discovery. In this review, we foresee some of these aspects and depict the potential directions of pre-clinical oncology drug discovery towards improved prediction of drug efficacy.