A 3D printed microfluidic perfusion device for multicellular spheroid cultures

Patient-Derived Organoids as Therapy Screening Platforms in Cancer Patients

Patient-derived organoids (PDOs) developed ex vivo and in vitro are increasingly used for therapeutic screening. They provide a more physiologically relevant model for drug discovery and development compared to traditional cell lines. However, several challenges remain to be addressed to fully realize the potential of PDOs in therapeutic screening. This paper summarizes recent advancements in PDO development and the enhancement of PDO culture models. This is achieved by leveraging materials engineering and microfabrication technologies, including organs-on-a-chip and droplet microfluidics. Additionally, this work discusses the application of PDOs in therapy screening to meet diverse requirements and overcome bottlenecks in cancer treatment. Furthermore, this work introduces tools for data processing and analysis of organoids, along with their microenvironment. These tools aim to achieve enhanced readouts. Finally, this work explores the challenges and future perspectives of using PDOs in drug development and personalized screening for cancer patients.

Advancing Tissue Culture with Light-Driven 3D-Printed Microfluidic Devices

Three-dimensional (3D) printing presents a compelling alternative for fabricating microfluidic devices, circumventing certain limitations associated with traditional soft lithography methods. Microfluidics play a crucial role in the biomedical sciences, particularly in the creation of tissue spheroids and pharmaceutical research. Among the various 3D printing techniques, light-driven methods such as stereolithography (SLA), digital light processing (DLP), and photopolymer inkjet printing have gained prominence in microfluidics due to their rapid prototyping capabilities, high-resolution printing, and low processing temperatures. This review offers a comprehensive overview of light-driven 3D printing techniques used in the fabrication of advanced microfluidic devices. It explores biomedical applications for 3D-printed microfluidics and provides insights into their potential impact and functionality within the biomedical field. We further summarize three light-driven 3D printing strategies for producing biomedical microfluidic systems: direct construction of microfluidic devices for cell culture, PDMS-based microfluidic devices for tissue engineering, and a modular SLA-printed microfluidic chip to co-culture and monitor cells.

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

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

On-chip recapitulation of the tumor microenvironment: A decade of progress

One of the hurdles to the development of new anticancer therapies is the lack of in vitro models which faithfully reproduce the in vivo tumor microenvironment (TME). Understanding the dynamic relationships between the components of the TME in a controllable, scalable, and reliable setting would indeed support the discovery of biological targets impacting cancer diagnosis and therapy. Cancer research is increasingly shifting from traditional two-dimensional (2D) cell culture toward three-dimensional (3D) culture models, which have been demonstrated to increase the significance and predictive value of in vitro data. In this scenario, microphysiological systems (also known as organs-on-chip) have emerged as a relevant technological platform enabling more predictive investigation of cell-cell and cell-ECM interplay in cancer, attracting a significant research effort in the last years. This review illustrates one decade of progress in the field of tumor-microenvironment-on-chip (TMOC) approaches, exploiting either cell-laden microfluidic chambers or microfluidic confined tumor spheroids to model the TME. TMOCs have been designed to recapitulate several aspects of the TME, including tumor cells, the tumor-associated stroma, the immune system, and the vascular component. Significantly, the last aspect has emerged for its pivotal role in orchestrating cellular interactions and modulating drug pharmacokinetics on-chip. A further advancement has been represented by integration of TMOCs into multi-organ microphysiological systems, with the final aim to follow the metastatic cascade to target organs and to study the effects of chemotherapies at a systemic level. We highlight that the increased degree of complexity achieved by the most advanced TMOC models has enabled scientists to shed new light on the role of microenvironmental factors in tumor progression, metastatic cascade, and response to drugs.

Biocatalytic Performance of β-Glucosidase Immobilized on 3D-Printed Single- and Multi-Channel Polylactic Acid Microreactors

Microfluidic devices have attracted much attention in the current day owing to the unique advantages they provide. However, their application for industrial use is limited due to manufacturing limitations and high cost. Moreover, the scaling-up process of the microreactor has proven to be difficult. Three-dimensional (3D) printing technology is a promising solution for the above obstacles due to its ability to fabricate complex structures quickly and at a relatively low cost. Hence, combining the advantages of the microscale with 3D printing technology could enhance the applicability of microfluidic devices in the industrial sector. In the present work, a 3D-printed single-channel immobilized enzyme microreactor with a volume capacity of 30 μL was designed and created in one step via the fused deposition modeling (FDM) printing technique, using polylactic acid (PLA) as the printing material. The microreactor underwent surface modification with chitosan, and β-glucosidase from Thermotoga maritima was covalently immobilized. The immobilized biocatalyst retained almost 100% of its initial activity after incubation at different temperatures, while it could be effectively reused for up to 10 successful reaction cycles. Moreover, a multi-channel parallel microreactor incorporating 36 channels was developed, resulting in a significant increase in enzymatic productivity.

Surface Acoustic Wave-Based Microfluidic Device for Microparticles Manipulation: Effects of Microchannel Elasticity on the Device Performance

Size sorting, line focusing, and isolation of microparticles or cells are fundamental ingredients in the improvement of disease diagnostic tools adopted in biology and biomedicine. Microfluidic devices are exploited as a solution to transport and manipulate (bio)particles via a liquid flow. Use of acoustic waves traveling through the fluid provides non-contact solutions to the handling goal, by exploiting the acoustophoretic phenomenon. In this paper, a finite element model of a microfluidic surface acoustic wave-based device for the manipulation of microparticles is reported. Counter-propagating waves are designed to interfere inside a PDMS microchannel and generate a standing surface acoustic wave which is transmitted to the fluid as a standing pressure field. A model of the cross-section of the device is considered to perform a sensitivity analysis of such a standing pressure field to uncertainties related to the geometry of the microchannel, especially in terms of thickness and width of the fluid domain. To also assess the effects caused by possible secondary waves traveling in the microchannel, the PDMS is modeled as an elastic solid material. Remarkable effects and possible issues in microparticle actuation, as related to the size of the microchannel, are discussed by way of exemplary results.

4D Printed Shape-Memory Elastomer for Thermally Programmable Soft Actuators

Polymeric shape-memory elastomers can recover to a permeant shape from any programmed deformation under external stimuli. They are mostly cross-linked polymeric materials and can be shaped by three-dimensional (3D) printing. However, 3D printed shape-memory polymers so far only exhibit elasticity above their transition temperature, which results in their programmed shape being inelastic or brittle at lower temperatures. To date, 3D printed shape-memory elastomers with elasticity both below and above their transition temperature remain an elusive goal, which limits the application of shape-memory materials as elastic materials at low temperatures. In this paper, we printed, for the first time, a custom-developed shape-memory elastomer based on polyethylene glycol using digital light processing, which possesses elasticity and stretchability in a wide temperature range, below and above the transition temperature. Young's modulus in these two states can vary significantly, with a difference of up to 2 orders of magnitude. This marked difference in Young's modulus imparts excellent shape-memory properties to the material. The difference in Young's modulus at different temperatures allows for the programming of the pneumatic actuators by heating and softening specific areas. Consequently, a single actuator can exhibit distinct movement modes based on the programming process it undergoes.

Vat photopolymerization 3D printed microfluidic devices for organ-on-a-chip applications

Organs-on-a-chip, or OoCs, are microfluidic tissue culture devices with micro-scaled architectures that repeatedly achieve biomimicry of biological phenomena. They are well positioned to become the primary pre-clinical testing modality as they possess high translational value. Current methods of fabrication have facilitated the development of many custom OoCs that have generated promising results. However, the reliance on microfabrication and soft lithographic fabrication techniques has limited their prototyping turnover rate and scalability. Additive manufacturing, known commonly as 3D printing, shows promise to expedite this prototyping process, while also making fabrication easier and more reproducible. We briefly introduce common 3D printing modalities before identifying two sub-types of vat photopolymerization - stereolithography (SLA) and digital light processing (DLP) - as the most advantageous fabrication methods for the future of OoC development. We then outline the motivations for shifting to 3D printing, the requirements for 3D printed OoCs to be competitive with the current state of the art, and several considerations for achieving successful 3D printed OoC devices touching on design and fabrication techniques, including a survey of commercial and custom 3D printers and resins. In all, we aim to form a guide for the end-user to facilitate the in-house generation of 3D printed OoCs, along with the future translation of these important devices.

Translational Nanomedicines Across Human Reproductive Organs Modeling on Microfluidic Chips: State-of-the-Art and Future Prospects

Forecasting the consequence of nanoparticles (NPs) and therapeutically significant molecules before materializing for human clinical trials is a mainstay for drug delivery and screening processes. One of the noteworthy obstacles that has prevented the clinical translation of NP-based drug delivery systems and novel drugs is the lack of effective preclinical platforms. As a revolutionary technology, the organ-on-a-chip (OOC), a coalition of microfluidics and tissue engineering, has surfaced as an alternative to orthodox screening platforms. OOC technology recapitulates the structural and physiological features of human organs along with intercommunications between tissues on a chip. The current review discusses the concept of microfluidics and confers cutting-edge fabrication processes for chip designing. We also outlined the advantages of microfluidics in analyzing NPs in terms of characterization, transport, and degradation in biological systems. The review further elaborates the scope and research on translational nanomedicines in human reproductive organs (testis, placenta, uterus, and menstrual cycle) by taking the advantages offered by microfluidics and shedding light on their potential future implications. Finally, we accentuate the existing challenges for clinical translation and scale-up dynamics for microfluidics chips and emphasize its future perspectives.

Spheroids as a 3D Model of the Hypoxic Tumor Microenvironment

Spheroids enable the study of tumors and tumor hypoxia using a more representative model of the physiological environment compared to 2D cell culture. Spheroids can be grown in a cell suspension or when adhered to a solid scaffold. The spheroid formation method used is dependent on cell type. Here we describe the most common spheroid formation methods, including hanging drop, low adhesion plates, hydrogel, micropatterned plates, and microfluidics. After spheroids are formed, they can be used for drug treatment trials and analyzed using Western Blots, qPCR, and microscopy. Microscopy can then be used to measure the invasiveness of cells when a basement membrane is added to spheroids and for monitoring changes in the proliferation, quiescent, and necrotic zones of spheroids.

A comparative study of tumour-on-chip models with patient-derived xenografts for predicting chemotherapy efficacy in colorectal cancer patients

Inter-patient and intra-tumour heterogeneity (ITH) have prompted the need for a more personalised approach to cancer therapy. Although patient-derived xenograft (PDX) models can generate drug response specific to patients, they are not sustainable in terms of cost and time and have limited scalability. Tumour Organ-on-Chip (OoC) models are in vitro alternatives that can recapitulate some aspects of the 3D tumour microenvironment and can be scaled up for drug screening. While many tumour OoC systems have been developed to date, there have been limited validation studies to ascertain whether drug responses obtained from tumour OoCs are comparable to those predicted from patient-derived xenograft (PDX) models. In this study, we established a multiplexed tumour OoC device, that consists of an 8 × 4 array (32-plex) of culture chamber coupled to a concentration gradient generator. The device enabled perfusion culture of primary PDX-derived tumour spheroids to obtain dose-dependent response of 5 distinct standard-of-care (SOC) chemotherapeutic drugs for 3 colorectal cancer (CRC) patients. The in vitro efficacies of the chemotherapeutic drugs were rank-ordered for individual patients and compared to the in vivo efficacy obtained from matched PDX models. We show that quantitative correlation analysis between the drug efficacies predicted via the microfluidic perfusion culture is predictive of response in animal PDX models. This is a first study showing a comparative framework to quantitatively correlate the drug response predictions made by a microfluidic tumour organ-on-chip (OoC) model with that of PDX animal models.

Emerging 3D printing technologies and methodologies for microfluidic development

This review paper examines recent (mostly 2018 or later) advancements in 3D printed microfluidics. Microfluidic devices are widely applied in various fields such as drug delivery, point-of-care diagnosis, and bioanalytical research. In addition to soft lithography, 3D printing has become an appealing technology to develop microfluidics recently. In this work, three main 3D printing technologies, stereolithography, fused filament deposition, and polyjet, which are commonly used to fabricate microfluidic devices, are thoroughly discussed. The advantages, limitations, and recent microfluidic applications are analyzed. New technical advancements within these technology frameworks are also summarized, which are especially suitable for microfluidic development. Next, new emerging 3D-printing technologies are introduced, including the direct printing of polydimethylsiloxane (PDMS), glass, and biopolymers. Although limited microfluidic applications based on these technologies can be found in the literature, they show high potential to revolutionize the next generation of 3D-printed microfluidic apparatus.

Microfluidics for 3D Cell and Tissue Cultures: Microfabricative and Ethical Aspects Updates

The necessity to improve in vitro cell screening assays is becoming ever more important. Pharmaceutical companies, research laboratories and hospitals require technologies that help to speed up conventional screening and therapeutic procedures to produce more data in a short time in a realistic and reliable manner. The design of new solutions for test biomaterials and active molecules is one of the urgent problems of preclinical screening and the limited correlation between in vitro and in vivo data remains one of the major issues. The establishment of the most suitable in vitro model provides reduction in times, costs and, last but not least, in the number of animal experiments as recommended by the 3Rs (replace, reduce, refine) ethical guiding principles for testing involving animals. Although two-dimensional (2D) traditional cell screening assays are generally cheap and practical to manage, they have strong limitations, as cells, within the transition from the three-dimensional (3D) in vivo to the 2D in vitro growth conditions, do not properly mimic the real morphologies and physiology of their native tissues. In the study of human pathologies, especially, animal experiments provide data closer to what happens in the target organ or apparatus, but they imply slow and costly procedures and they generally do not fully accomplish the 3Rs recommendations, i.e., the amount of laboratory animals and the stress that they undergo must be minimized. Microfluidic devices seem to offer different advantages in relation to the mentioned issues. This review aims to describe the critical issues connected with the conventional cells culture and screening procedures, showing what happens in the in vivo physiological micro and nano environment also from a physical point of view. During the discussion, some microfluidic tools and their components are described to explain how these devices can circumvent the actual limitations described in the introduction.

Cell Aggregate Assembly through Microengineering for Functional Tissue Emergence

Compared to cell suspensions or monolayers, 3D cell aggregates provide cellular interactions organized in space and heterogeneity that better resume the real organization of native tissues. They represent powerful tools to narrow down the gap between in vitro and in vivo models, thanks to their self-evolving capabilities. Recent strategies have demonstrated their potential as building blocks to generate microtissues. Developing specific methodologies capable of organizing these cell aggregates into 3D architectures and environments has become essential to convert them into functional microtissues adapted for regenerative medicine or pharmaceutical screening purposes. Although the techniques for producing individual cell aggregates have been on the market for over a decade, the methodology for engineering functional tissues starting from them is still a young and quickly evolving field of research. In this review, we first present a panorama of emerging cell aggregates microfabrication and assembly technologies. We further discuss the perspectives opened in the establishment of functional tissues with a specific focus on controlled architecture and heterogeneity to favor cell differentiation and proliferation.

Culture of cancer spheroids and evaluation of anti-cancer drugs in 3D-printed miniaturized continuous stirred tank reactors (mCSTR)

Cancer continues to be a leading cause of mortality in modern societies; therefore, improved and more reliable in vitro cancer models are needed to expedite fundamental research and anti-cancer drug development. Here, we describe the use of a miniaturized continuous stirred tank reactor (mCSTR) to first fabricate and mature cancer spheroids (i.e, derived from MCF7 cells, DU145 cells, and a mix of MCF7 cells and fibroblasts), and then to conduct anti-cancer drug assays under continuous perfusion. This 3 mL mCSTR features an off-center agitation system that enables homogeneous chaotic laminar mixing at low speeds to support cell aggregation. We incubated cell suspensions for 3 days in ultra-low-adherence (ULA) plates to allow formation of discoid cell aggregates (~600 µm in diameter). These cell aggregates were then transferred into mCSTRs and continuously fed with culture medium. We characterized the spheroid morphology and the expression of relevant tumor biomarkers at different maturation times for up to 4 weeks. The spheroids progressively increased in size during the first 5 to 6 days of culture to reach a steady diameter between 600 and 800 µm. In proof-of-principle experiments, we demonstrated the use of this mCSTR in anti-cancer drug testing. Three drugs commonly used in breast cancer treatment (doxorubicin, docetaxel, and paclitaxel) were probed at different concentrations in MCF7 derived spheroids. In these experiments, we evaluated cell viability, glucose consumption, spheroid morphology, lactate dehydrogenase activity, and the expression of genes associated with drug resistance (ABCB1 and ABCC1) and anti-apoptosis (Bcl2). We envision the use of this agitated system as a tumor-on-a-chip platform to expedite efficacy and safety testing of novel anti-cancer drugs and possibly in personalized medicine applications.

Evaluation and optimization of PolyJet 3D-printed materials for cell culture studies

Use of 3D printing for microfluidics is a rapidly growing area, with applications involving cell culture in these devices also becoming of interest. 3D printing can be used to create custom-designed devices that have complex features and integrate different material types in one device; however, there are fewer studies studying the ability to culture cells on the various substrates that are available. This work describes the effect of PolyJet 3D-printing technology on cell culture of two cell lines, bovine pulmonary artery endothelial cells (BPAECs) and Madin-Darby Canine Kidney (MDCK) cells, on two different types of printed materials (VeroClear or MED610). It was found that untreated devices, when used for studies of 1 day or more, led to unsuccessful culture. A variety of device treatment methodologies were investigated, with the most success coming from the use of sodium hydroxide/sodium metasilicate solution. Devices treated with this cleaning step resulted in culture of BPAECs and MDCK cells that were more similar to what is obtained in traditional culture flasks (in terms of cell morphology, viability, and cell density). LC-MS/MS analysis (via Orbitrap MS) was used to determine potential leachates from untreated devices. Finally, the use of a fiber scaffold in the devices was utilized to further evaluate the treatment methodology and to also demonstrate the ability to perform 3D culture in such devices. This study will be of use for researchers wanting to utilize these or other cell types in PolyJet-based 3D-printed devices.

Recent Advances in Additive Manufacturing and 3D Bioprinting for Organs-On-A-Chip and Microphysiological Systems

The re-creation of physiological cellular microenvironments that truly resemble complex in vivo architectures is the key aspect in the development of advanced in vitro organotypic tissue constructs. Among others, organ-on-a-chip technology has been increasingly used in recent years to create improved models for organs and tissues in human health and disease, because of its ability to provide spatio-temporal control over soluble cues, biophysical signals and biomechanical forces necessary to maintain proper organotypic functions. While media supply and waste removal are controlled by microfluidic channel by a network the formation of tissue-like architectures in designated micro-structured hydrogel compartments is commonly achieved by cellular self-assembly and intrinsic biological reorganization mechanisms. The recent combination of organ-on-a-chip technology with three-dimensional (3D) bioprinting and additive manufacturing techniques allows for an unprecedented control over tissue structures with the ability to also generate anisotropic constructs as often seen in in vivo tissue architectures. This review highlights progress made in bioprinting applications for organ-on-a-chip technology, and discusses synergies and limitations between organ-on-a-chip technology and 3D bioprinting in the creation of next generation biomimetic in vitro tissue models.

Computational Modelling and Big Data Analysis of Flow and Drug Transport in Microfluidic Systems: A Spheroid-on-a-Chip Study

Microfluidic tumour spheroid-on-a-chip platforms enable control of spheroid size and their microenvironment and offer the capability of high-throughput drug screening, but drug supply to spheroids is a complex process that depends on a combination of mechanical, biochemical, and biophysical factors. To account for these coupled effects, many microfluidic device designs and operating conditions must be considered and optimized in a time- and labour-intensive trial-and-error process. Computational modelling facilitates a systematic exploration of a large design parameter space via in silico simulations, but the majority of in silico models apply only a small set of conditions or parametric levels. Novel approaches to computational modelling are needed to explore large parameter spaces and accelerate the optimization of spheroid-on-a-chip and other organ-on-a-chip designs. Here, we report an efficient computational approach for simulating fluid flow and transport of drugs in a high-throughput arrayed cancer spheroid-on-a-chip platform. Our strategy combines four key factors: i) governing physical equations; ii) parametric sweeping; iii) parallel computing; and iv) extensive dataset analysis, thereby enabling a complete “full-factorial” exploration of the design parameter space in combinatorial fashion. The simulations were conducted in a time-efficient manner without requiring massive computational time. As a case study, we simulated >15,000 microfluidic device designs and flow conditions for a representative multicellular spheroids-on-a-chip arrayed device, thus acquiring a single dataset consisting of ∼10 billion datapoints in ∼95 GBs. To validate our computational model, we performed physical experiments in a representative spheroid-on-a-chip device that showed excellent agreement between experimental and simulated data. This study offers a computational strategy to accelerate the optimization of microfluidic device designs and provide insight on the flow and drug transport in spheroid-on-a-chip and other biomicrofluidic platforms.

Application of Ovarian Cancer Organoids in Precision Medicine: Key Challenges and Current Opportunities

Ovarian cancer (OC) is the leading cause of death among gynecologic malignances. Over the past decades, human-derived models have advanced from monolayer cell cultures to three-dimensional (3D) organoids that could faithfully recapitulate biological characteristics and tumor heterogeneity of primary tissues. As a complement of previous studies based on cell lines or xenografts, organoids provide a 3D platform for mutation–carcinogenesis modeling, high-throughput drug screening, genetic engineering, and biobanking, which might fulfill the gap between basic research and clinical practice. Stepwise, cutting-edge bioengineering techniques of organoid-on-a-chip and 3D bioprinting might converge current challenges and contribute to personalized therapy. We comprehensively reviewed the advantages, challenges, and translational potential of OC organoids. Undeniably, organoids represent an excellent near-physiological platform for OC, paving the way for precision medicine implementation. Future efforts will doubtlessly bring this innovative technique from bench to bedside.

Technological Advances in Tumor-On-Chip Technology: From Bench to Bedside

Simple Summary

Various 3D in vitro tumor models are rapidly advancing cancer research. Unlike animal models, they can be produced quickly and are amenable to high-throughput studies. Growing tumor spheroids in microfluidic tumor-on-chip platforms has particularly elevated the capabilities of such models. Tumor-on-chip devices can mimic multiple aspects of the dynamic in vivo tumor microenvironment in a precisely controlled manner. Moreover, new technologies for the on- and off-chip analysis of these tumor mimics are continuously emerging. There is thus an urgent need to review the latest developments in this rapidly progressing field. Here, we present an overview of the technological advances in tumor-on-chip technology by reviewing state-of-the-art tools for on-chip analysis. In particular, we evaluate the potential for tumor-on-chip technology to guide personalized cancer therapies. We strive to appeal to cancer researchers and biomedical engineers alike, informing on current progress, while provoking thought on the outstanding developments needed to achieve clinical-stage research.

Abstract

Tumor-on-chip technology has cemented its importance as an in vitro tumor model for cancer research. Its ability to recapitulate different elements of the in vivo tumor microenvironment makes it promising for translational medicine, with potential application in enabling personalized anti-cancer therapies. Here, we provide an overview of the current technological advances for tumor-on-chip generation. To further elevate the functionalities of the technology, these approaches need to be coupled with effective analysis tools. This aspect of tumor-on-chip technology is often neglected in the current literature. We address this shortcoming by reviewing state-of-the-art on-chip analysis tools for microfluidic tumor models. Lastly, we focus on the current progress in tumor-on-chip devices using patient-derived samples and evaluate their potential for clinical research and personalized medicine applications.

Microfluidic Devices as Process Development Tools for Cellular Therapy Manufacturing

Cellular therapies are creating a paradigm shift in the biomanufacturing industry. Particularly for autologous therapies, small-scale processing methods are better suited than the large-scale approaches that are traditionally employed in the industry. Current small-scale methods for manufacturing personalized cell therapies, however, are labour-intensive and involve a number of 'open events'. To overcome these challenges, new cell manufacturing platforms following a GMP-in-a-box concept have recently come on the market (GMP: Good Manufacturing Practice). These are closed automated systems with built-in pumps for fluid handling and sensors for in-process monitoring. At a much smaller scale, microfluidic devices exhibit many of the same features as current GMP-in-a-box systems. They are closed systems, fluids can be processed and manipulated, and sensors integrated for real-time detection of process variables. Fabricated from polymers, they can be made disposable, i.e. single-use. Furthermore, microfluidics offers exquisite spatiotemporal control over the cellular microenvironment, promising both reproducibility and control of outcomes. In this chapter, we consider the challenges in cell manufacturing, highlight recent advances of microfluidic devices for each of the main process steps, and summarize our findings on the current state of the art. As microfluidic cell culture devices have been reported for both adherent and suspension cell cultures, we report on devices for the key process steps, or unit operations, of both stem cell therapies and cell-based immunotherapies.

Recent innovations in cost-effective polymer and paper hybrid microfluidic devices

Hybrid microfluidic systems that are composed of multiple different types of substrates have been recognized as a versatile and superior platform, which can draw benefits from different substrates while avoiding their limitations. This review article introduces the recent innovations of different types of low-cost hybrid microfluidic devices, particularly focusing on cost-effective polymer- and paper-based hybrid microfluidic devices. In this article, the fabrication of these hybrid microfluidic devices is briefly described and summarized. We then highlight various hybrid microfluidic systems, including polydimethylsiloxane (PDMS)-based, thermoplastic-based, paper/polymer hybrid systems, as well as other emerging hybrid systems (such as thread-based). The special benefits of using these hybrid systems have been summarized accordingly. A broad range of biological and biomedical applications using these hybrid microfluidic devices are discussed in detail, including nucleic acid analysis, protein analysis, cellular analysis, 3D cell culture, organ-on-a-chip, and tissue engineering. The perspective trends of hybrid microfluidic systems involving the improvement of fabrication techniques and broader applications are also discussed at the end of the review.

Raman Spectroscopy-Based 3D Analysis of Odontogenic Differentiation of Human Dental Pulp Stem Cell Spheroids

Numerous efforts have been made to establish three-dimensional (3D) cell cultures that mimic the structure, cell composition, and functions of actual tissues and organs in vitro; however, owing to its intrinsic complexity, precise characterization of 3D differentiation remains challenging and often results in high variations in the resulting differentiated spheroids. This study reports a 3D Raman mapping-based analytical method that helps us to identify the crucial factors responsible for inducing variability in differentiated stem cell spheroids. Human dental pulp stem cell spheroids were generated at various cell densities using the hanging drop (HD) and molded parafilm-based (MP) methods and were then further subjected to odontogenic differentiation. Thereafter, the 3D cellular differentiation in these spheroids was analyzed based on three different Raman peaks, namely, 960, 1156/1528, and 2935 cm^-1, which correspond to hydroxyapatite (HA, odontogenic differentiation marker), β-carotene (precursor of HA), and proteins/cellular components (cell reference). By correlating such cell differentiation-related peaks and water/medium peaks (3400 cm^-1), we discovered that the diffusion of the medium containing various nutrients and differentiation factors was crucial in determining the variations in 3D differentiation of stem cell spheroids. Odontogenic differentiation was majorly induced at the outer shell of HD spheroids (up to ∼20 μm), whereas odontogenic differentiation was markedly induced in MP spheroids (up to 40-50 μm). Considering the challenges associated with high variations in spheroid and organoid differentiation, we conclude that the proposed Raman-based 3D analysis plays a pivotal role in stem cell-based regenerative therapy and drug screening.

Computational and experimental studies of a cell-imprinted-based integrated microfluidic device for biomedical applications

It has been proved that cell-imprinted substrates molded from template cells can be used for the re-culture of that cell while preserving its normal behavior or to differentiate the cultured stem cells into the template cell. In this study, a microfluidic device was presented to modify the previous irregular cell-imprinted substrate and increase imprinting efficiency by regular and objective cell culture. First, a cell-imprinted substrate from template cells was prepared using a microfluidic chip in a regular pattern. Another microfluidic chip with the same pattern was then aligned on the cell-imprinted substrate to create a chondrocyte-imprinted-based integrated microfluidic device. Computational fluid dynamics (CFD) simulations were used to obtain suitable conditions for injecting cells into the microfluidic chip before performing experimental evaluations. In this simulation, the effect of input flow rate, number per unit volume, and size of injected cells in two different chip sizes were examined on exerted shear stress and cell trajectories. This numerical simulation was first validated with experiments with cell lines. Finally, chondrocyte was used as template cell to evaluate the chondrogenic differentiation of adipose-derived mesenchymal stem cells (ADSCs) in the chondrocyte-imprinted-based integrated microfluidic device. ADSCs were positioned precisely on the chondrocyte patterns, and without using any chemical growth factor, their fibroblast-like morphology was modified to the spherical morphology of chondrocytes after 14 days of culture. Both immunostaining and gene expression analysis showed improvement in chondrogenic differentiation compared to traditional imprinting methods. This study demonstrated the effectiveness of cell-imprinted-based integrated microfluidic devices for biomedical applications.

3D-printed micro bubble column reactor with integrated microsensors for biotechnological applications: From design to evaluation

With the technological advances in 3D printing technology, which are associated with ever-increasing printing resolution, additive manufacturing is now increasingly being used for rapid manufacturing of complex devices including microsystems development for laboratory applications. Personalized experimental devices or entire bioreactors of high complexity can be manufactured within few hours from start to finish. This study presents a customized 3D-printed micro bubble column reactor (3D-µBCR), which can be used for the cultivation of microorganisms (e.g., Saccharomyces cerevisiae) and allows online-monitoring of process parameters through integrated microsensor technology. The modular 3D-µBCR achieves rapid homogenization in less than 1 s and high oxygen transfer with k_La values up to 788 h⁻¹ and is able to monitor biomass, pH, and DOT in the fluid phase, as well as CO₂ and O₂ in the gas phase. By extensive comparison of different reactor designs, the influence of the geometry on the resulting hydrodynamics was investigated. In order to quantify local flow patterns in the fluid, a three-dimensional and transient multiphase Computational Fluid Dynamics model was successfully developed and applied. The presented 3D-µBCR shows enormous potential for experimental parallelization and enables a high level of flexibility in reactor design, which can support versatile process development.

Can 3D Printing Bring Droplet Microfluidics to Every Lab?-A Systematic Review

In recent years, additive manufacturing has steadily gained attention in both research and industry. Applications range from prototyping to small-scale production, with 3D printing offering reduced logistics overheads, better design flexibility and ease of use compared with traditional fabrication methods. In addition, printer and material costs have also decreased rapidly. These advantages make 3D printing attractive for application in microfluidic chip fabrication. However, 3D printing microfluidics is still a new area. Is the technology mature enough to print complex microchannel geometries, such as droplet microfluidics? Can 3D-printed droplet microfluidic chips be used in biological or chemical applications? Is 3D printing mature enough to be used in every research lab? These are the questions we will seek answers to in our systematic review. We will analyze (1) the key performance metrics of 3D-printed droplet microfluidics and (2) existing biological or chemical application areas. In addition, we evaluate (3) the potential of large-scale application of 3D printing microfluidics. Finally, (4) we discuss how 3D printing and digital design automation could trivialize microfluidic chip fabrication in the long term. Based on our analysis, we can conclude that today, 3D printers could already be used in every research lab. Printing droplet microfluidics is also a possibility, albeit with some challenges discussed in this review.

Class II biocompatible E-Shell 300 3D printing material causes severe developmental toxicity in Danio rerio embryos and reduced cell proliferation in vitro – implications for 3D printed microfluidics

Additive manufacturing is a new technology that represents a highly promising, cheap, and efficient solution for the production of various tools in the biomedicine field. In our study, the toxicity of the commercially available E-Shell 300 series photopolymer, which is used in the manufacture of hearing aids and other implants and which could be potentially exploited in microfluidic device fabrication, was tested using in vivo and in vitro biological models. We examined B14 cell proliferation in direct contact with the three-dimensional (3D)-printed material as well as in water extracts to evaluate in vitro cytotoxicity. Similarly, in vivo tests were performed using an OECD-standardized fish embryo acute toxicity (FET) test on Danio rerio embryos in direct contact with the material and in extracts as well. Despite E-Shell 300 3D-printed material being declared as class-IIa biocompatible, in the case of direct contact with both biological models, the results demonstrated a considerable negative impact on cell proliferation and severe developmental toxicity. In this study, up to 84% reduced cell proliferation in vitro and 79% mortality of in vivo models were observed. In contrast, a negligible toxic influence of E-Shell 300 water extracts was present. Four different post-processing treatments to reduce the toxicity were also tested. We observed that post-printing treatment of 3D-printed material in 96% ethanol can reduce embryonic mortality in the FET test by 71% and also completely eliminate negative effects on cell proliferation. We analyzed leachates from the polymeric structures by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy, and we discovered the presence of surfactant residues. In summary, our results indicate the importance of biocompatibility testing of the 3D printing photopolymer material in direct contact with the given biological model. On the other hand, the possibility of eliminating toxic effects by an appropriate post-processing strategy opens the door for broader applications of E-Shell 300 photopolymers in the development of complex microfluidic devices for various biological applications.

E-Shell 300 3D-printed material demonstrated a considerable negative impact on cell proliferation and severe developmental toxicity due to release of surfactant residues. Post-treatment with ethanol improved the biocompatibility of the material.

Multifunctional microfluidic chip for cancer diagnosis and treatment

Microfluidic chip is not a chip in the traditional sense. It is technologies that control fluids at the micro level. As a burgeoning biochip, microfluidic chips integrate multiple disciplines, including physiology, pathology, cell biology, biophysics, engineering mechanics, mechanical design, materials science, and so on. The application of microfluidic chip has shown tremendous promise in the field of cancer therapy in the past three decades. Various types of cell and tissue cultures, including 2D cell culture, 3D cell culture and tissue organoid culture could be performed on microfluidic chips. Patient-derived cancer cells and tissues can be cultured on microfluidic chips in a visible, controllable, and high-throughput manner, which greatly advances the process of personalized medicine. Moreover, the functionality of microfluidic chip is greatly expanding due to the customizable nature. In this review, we introduce its application in developing cancer preclinical models, detecting cancer biomarkers, screening anti-cancer drugs, exploring tumor heterogeneity and producing nano-drugs. We highlight the functions and recent development of microfluidic chip to provide references for advancing cancer diagnosis and treatment.

An integrated microfluidic device for stem cell differentiation based on cell-imprinted substrate designed for cartilage regeneration in a rabbit model

Separating cells from the body and cultivating them in vitro will alter the function of cells. Therefore, for optimal cell culture in the laboratory, conditions similar to those of their natural growth should be provided. In previous studies, it has been shown that the use of cellular shape at the culture surface can regulate cellular function. In this work, the efficiency of the imprinting method increased by using microfluidic chip design and fabrication. In this method, first, a cell-imprinted substrate of chondrocytes was made using a microfluidic chip. Afterwards, stem cells were cultured on a cell-imprinted substrate using a second microfluidic chip aligned with the substrate. Therefore, stem cells were precisely placed on the chondrocyte patterns on the substrate and their fibroblast-like morphology was changed to chondrocyte's spherical morphology after 14-days culture in the chip without using any chemical growth factor. After chondrogenic differentiation and in vitro assessments (real-time PCR and immunocytotoxicity), differentiated stem cells were transferred on a collagen-hyaluronic acid scaffold and transplanted in articular cartilage defect of the rabbit. After 6 months, the post-transplantation analysis showed that the articular cartilage defect had been successfully regenerated in differentiated stem cell groups in comparison with the controls. In conclusion, this study showed the potency of the imprinting method for inducing chondrogenicity in stem cells, which can be used in clinical trials due to the safety of the procedure.

Current Advances on 3D-Bioprinted Liver Tissue Models

The liver, the largest gland in the human body, plays a key role in metabolism, bile production, detoxification, and water and electrolyte regulation. The toxins or drugs that the gastrointestinal system absorbs reach the liver first before entering the bloodstream. Liver disease is one of the leading causes of death worldwide. Therefore, an in vitro liver tissue model that reproduces the main functions of the liver can be a reliable platform for investigating liver diseases and developing new drugs. In addition, the limitations in traditional, planar monolayer cell cultures and animal tests for evaluating the toxicity and efficacy of drug candidates can be overcome. Currently, the newly emerging 3D bioprinting technologies have the ability to construct in vitro liver tissue models both in static scaffolds and dynamic liver-on-chip manners. This review mainly focuses on the construction and applications of liver tissue models based on 3D bioprinting. Special attention is given to 3D bioprinting strategies and bioinks for constructing liver tissue models including the cell sources and hydrogel selection. In addition, the main advantages and limitations and the major challenges and future perspectives are discussed, paving the way for the next generation of in vitro liver tissue models.

Micro Three-Dimensional Neuronal Cultures Generate Developing Cortex-Like Activity Patterns

Studies aimed at neurological drug discovery have been carried out both in vitro and in vivo. In vitro cell culture models have showed potential as drug testing platforms characterized by high throughput, low cost, good reproducibility and ease of handling and observation. However, in vitro neuronal culture models are facing challenges in replicating in vivo-like activity patterns. This work reports an in vitro culture technique that is capable of producing micro three-dimensional (μ3D) cultures of only a few tens of neurons. The μ3D cultures generated by this method were uniform in size and density of neurons. These μ3D cultures had complex spontaneous synchronized neuronal activity patterns which were similar to those observed in the developing cortex and in much larger 3D cultures, but not in 2D cultures. Bursts could be reliably evoked by stimulation of single neurons. Synchronized bursts in μ3D cultures were abolished by inhibitors of glutamate receptors, while inhibitors of GABA_A receptors had a more complex effect. This pharmacological profile is similar to bursts in neonatal cortex. Since large numbers of reproducible μ3D cultures can be created and observed in parallel, this model of the developing cortex may find applications in high-throughput drug discovery experiments.

Hydrogel microfluidic-based liver-on-a-chip: Mimicking the mass transfer and structural features of liver

Liver is fed by nutrition via diffusion across the vascular wall from blood flow. However, hepatocytes in liver models are directly exposed to the perfusion culture medium, where the shear stress reduces the cell viability and liver-specific functions. By mimicking the mass transfer and structural features of hepatic lobule, we designed a microfluidic liver-on-a-chip based on the di-acrylated pluronic F127 hydrogel. In the hydrogel chip, hepatocellular carcinoma HepG2 and human hepatic stellate cell LX-2 were statically cultured inside the microwells on the outer channel. These hepatic cells were fed by the diffused medium from the adjacent but separated inner channel with endothelial cell monolayers, which was perfused by the medium with physiologically relevant shear stress. As found, the hepatic cells in the liver-on-a-chip rapidly formed spheroids within 1-day incubation and expressed about one to two-fold higher viability/liver-specific functions than the corresponding static culture for at least 8 days. Moreover, the presence of endothelial cells also contributed to the expression of liver-specific functions in the liver-on-a-chip. Therefore, the proposed liver-on-a-chip provides a new concept for construction of 3D liver models in vitro, and shows the potential value for a variety of applications including bio-artificial livers and drug toxicity screening.

3D-Printed Bubble-Free Perfusion Cartridge System for Live-Cell Imaging

The advent of 3D-printing technologies has had a significant effect on the development of medical and biological devices. Perfusion chambers are widely used for live-cell imaging in cell biology research; however, air-bubble invasion is a pervasive problem in perfusion systems. Although 3D printing allows the rapid fabrication of millifluidic and microfluidic devices with high resolution, little has been reported on 3D-printed fluidic devices with bubble trapping systems. Herein, we present a 3D-printed millifluidic cartridge system with bent and flat tapered flow channels for preventing air-bubble invasion, irrespective of bubble volume and without the need for additional bubble-removing devices. This system realizes bubble-free perfusion with a user-friendly interface and no-time-penalty manufacturing processes. We demonstrated the bubble removal capability of the cartridge by continually introducing air bubbles with different volumes during the calcium imaging of Sf21 cells expressing insect odorant receptors. Calcium imaging was conducted using a low-magnification objective lens to show the versatility of the cartridge for wide-area observation. We verified that the cartridge could be used as a chemical reaction chamber by conducting protein staining experiments. Our cartridge system is advantageous for a wide range of cell-based bioassays and bioanalytical studies, and can be easily integrated into portable biosensors.

Beyond Polydimethylsiloxane: Alternative Materials for Fabrication of Organ-on-a-Chip Devices and Microphysiological Systems

Polydimethylsiloxane (PDMS) is the predominant material used for organ-on-a-chip devices and microphysiological systems (MPSs) due to its ease-of-use, elasticity, optical transparency, and inexpensive microfabrication. However, the absorption of small hydrophobic molecules by PDMS and the limited capacity for high-throughput manufacturing of PDMS-laden devices severely limit the application of these systems in personalized medicine, drug discovery, in vitro pharmacokinetic/pharmacodynamic (PK/PD) modeling, and the investigation of cellular responses to drugs. Consequently, the relatively young field of organ-on-a-chip devices and MPSs is gradually beginning to make the transition to alternative, nonabsorptive materials for these crucial applications. This review examines some of the first steps that have been made in the development of organ-on-a-chip devices and MPSs composed of such alternative materials, including elastomers, hydrogels, thermoplastic polymers, and inorganic materials. It also provides an outlook on where PDMS-alternative devices are trending and the obstacles that must be overcome in the development of versatile devices based on alternative materials to PDMS.

3D-printed Bioreactors for In Vitro Modeling and Analysis

In recent years, three-dimensional (3D) printing has markedly enhanced the functionality of bioreactors by offering the capability of manufacturing intricate architectures, which changes the way of conducting in vitro biomodeling and bioanalysis. As 3D-printing technologies become increasingly mature, the architecture of 3D-printed bioreactors can be tailored to specific applications using different printing approaches to create an optimal environment for bioreactions. Multiple functional components have been combined into a single bioreactor fabricated by 3D-printing, and this fully functional integrated bioreactor outperforms traditional methods. Notably, several 3D-printed bioreactors systems have demonstrated improved performance in tissue engineering and drug screening due to their 3D cell culture microenvironment with precise spatial control and biological compatibility. Moreover, many microbial bioreactors have also been proposed to address the problems concerning pathogen detection, biofouling, and diagnosis of infectious diseases. This review offers a reasonably comprehensive review of 3D-printed bioreactors for in vitro biological applications. We compare the functions of bioreactors fabricated by various 3D-printing modalities and highlight the benefit of 3D-printed bioreactors compared to traditional methods.

Advanced Fabrication Techniques of Microengineered Physiological Systems

The field of organs-on-chips (OOCs) has experienced tremendous growth over the last decade. However, the current main limiting factor for further growth lies in the fabrication techniques utilized to reproducibly create multiscale and multifunctional devices. Conventional methods of photolithography and etching remain less useful to complex geometric conditions with high precision needed to manufacture the devices, while laser-induced methods have become an alternative for higher precision engineering yet remain costly. Meanwhile, soft lithography has become the foundation upon which OOCs are fabricated and newer methods including 3D printing and injection molding show great promise to innovate the way OOCs are fabricated. This review is focused on the advantages and disadvantages associated with the commonly used fabrication techniques applied to these microengineered physiological systems (MPS) and the obstacles that remain in the way of further innovation in the field.

Digital Manufacturing for Microfluidics

The microfluidics field is at a critical crossroads. The vast majority of microfluidic devices are presently manufactured using micromolding processes that work very well for a reduced set of biocompatible materials, but the time, cost, and design constraints of micromolding hinder the commercialization of many devices. As a result, the dissemination of microfluidic technology-and its impact on society-is in jeopardy. Digital manufacturing (DM) refers to a family of computer-centered processes that integrate digital three-dimensional (3D) designs, automated (additive or subtractive) fabrication, and device testing in order to increase fabrication efficiency. Importantly, DM enables the inexpensive realization of 3D designs that are impossible or very difficult to mold. The adoption of DM by microfluidic engineers has been slow, likely due to concerns over the resolution of the printers and the biocompatibility of the resins. In this article, we review and discuss the various printer types, resolution, biocompatibility issues, DM microfluidic designs, and the bright future ahead for this promising, fertile field.

Quantitative Image-Based Cell Viability (QuantICV) Assay for Microfluidic 3D Tissue Culture Applications

Microfluidic 3D tissue culture systems are attractive for in vitro drug testing applications due to the ability of these platforms to generate 3D tissue models and perform drug testing at a very small scale. However, the minute cell number and liquid volume impose significant technical challenges to perform quantitative cell viability measurements using conventional colorimetric or fluorometric assays, such as MTS or Alamar Blue. Similarly, live-dead staining approaches often utilize metabolic dyes that typically label the cytoplasm of live cells, which makes it difficult to segment and count individual cells in compact 3D tissue cultures. In this paper, we present a quantitative image-based cell viability (QuantICV) assay technique that circumvents current challenges of performing the quantitative cell viability assay in microfluidic 3D tissue cultures. A pair of cell-impermeant nuclear dyes (EthD-1 and DAPI) were used to sequentially label the nuclei of necrotic and total cell populations, respectively. Confocal microscopy and image processing algorithms were employed to visualize and quantify the cell nuclei in the 3D tissue volume. The QuantICV assay was validated and showed good concordance with the conventional bulk MTS assay in static 2D and 3D tumor cell cultures. Finally, the QuantICV assay was employed as an on-chip readout to determine the differential dose responses of parental and metastatic 3D oral squamous cell carcinoma (OSCC) to Gefitinib in a microfluidic 3D culture device. This proposed technique can be useful in microfluidic cell cultures as well as in a situation where conventional cell viability assays are not available.

Adhesive bonding strategies to fabricate high-strength and transparent 3D printed microfluidic device

Recently, the use of 3D printing technologies has become prevalent in microfluidic applications. Although these technologies enable low-cost, rapid, and easy fabrication of microfluidic devices, fabricated devices suffer from optical opaqueness that inhibits their use for microscopic imaging. This study investigates bonding strategies using polydimethylsiloxane (PDMS) and printer resin as interlayer materials to fabricate high-strength optically transparent 3D-printed microfluidic devices. First, we fabricated microfluidic structures using a stereolithography 3D printer. We placed 3D-printed structures on interlayer materials coated surfaces. Then, we either let these 3D-printed structures rest on the coated slides or transferred them to new glass slides. We achieved bonding between 3D-printed structures and glass substrates with UV exposure for resin and with elevated temperature for PDMS interlayer materials. Bonding strength was investigated for different interlayer material thicknesses. We also analyzed the bright-field and fluorescence imaging capability of microfluidic devices fabricated using different bonding strategies. We achieve up to twofold (9.1 bar) improved bonding strength and comparable fluorescence sensitivity with respect to microfluidic devices fabricated using the traditional plasma activated PDMS-glass bonding method. Although stereolithography 3D printer allows fabrication of enclosed channels having dimensions down to ∼600 μm, monolithic transparent microfluidic channels with 280 × 110 μm² cross section can be realized using adhesive interlayers. Furthermore, 3D-printed microfluidic chips can be integrated successfully with Protein-G modified substrates using resin interlayers for detection of fluorescent-labeled immunoglobulin down to ∼30 ng/ml. Hence, this strategy can be applied to fabricate high-strength and transparent microfluidic chips for various optical imaging applications including biosensing.

A 3D printed microfluidic flow-cell for microscopy analysis of in situ-grown biofilms

Biofilm phenomena ranging from metabolic processes to attachment, detachment and quorum sensing are influenced by the fluid flow across the biofilm. A number of commercially available flow-cells allow for microscopy analysis of laboratory biofilms under flow, but there is a lack of shear controlled microfluidic devices that accommodate biofilms grown in situ on carriers or tissue samples. Therefore, we developed a flow-cell with adjustable geometry for microscopy analysis of in situ-grown biofilm samples under shear-controlled flow. The flow-cells were designed as one-piece disposable models, 3D-printed in resin and sealed with a coverslip after insertion of the biofilm sample. As a proof of concept, we studied the impact of stimulated saliva flow on pH developments in in situ-grown dental biofilms exposed to sucrose. Under static conditions, pH dropped in the biofilms, with pronounced differences between individual biofilms, but also between different microscopic fields of view within one biofilm. pH in the top layer of the biofilms tended to be lower than pH in the bottom layer. Under conditions of stimulated saliva flow (5 mm/min), pH rose to neutral or slightly alkaline values in all biofilms, and the vertical gradients were reversed, with the biofilm bottom becoming more acidic than the top. Hence, the present work demonstrates the importance of flow for the study of pH in dental biofilms.

Microphysiological systems for ADME-related applications: current status and recommendations for system development and characterization

Over the last decade, progress has been made on the development of microphysiological systems (MPS) for absorption, distribution, metabolism, and excretion (ADME) applications. Central to this progress has been proof of concept data generated by academic and industrial institutions followed by broader characterization studies, which provide evidence for scalability and applicability to drug discovery and development. In this review, we describe some of the advances made for specific tissue MPS and outline the desired functionality for such systems, which are likely to make them applicable for practical use in the pharmaceutical industry. Single organ MPS platforms will be valuable for modelling tissue-specific functions. However, dynamic organ crosstalk, especially in the context of disease or toxicity, can only be obtained with the use of inter-linked MPS models which will enable scientists to address questions at the intersection of pharmacokinetics (PK) and efficacy, or PK and toxicity. In the future, successful application of MPS platforms that closely mimic human physiology may ultimately reduce the need for animal models to predict ADME outcomes and decrease the overall risk and cost associated with drug development.

3D spheroids generated on carbon nanotube-functionalized fibrous scaffolds for drug metabolism and toxicity screening

The mechanical and electrical stimuli have a profound effect on the cellular behavior and function. In this study, a series of conductive nanofibrous scaffolds are developed by blend electrospinning of poly(styrene-co-maleic acid) (PSMA) and multiwalled-carbon nanotubes (CNTs), followed by grafting galactose as cell adhesion cues. When the mass ratios of CNTs to PSMA increase up to 5%, the alignment, Young's modulus and conductivity of fibrous scaffolds increase, whereas the average diameter, pore size and elongation at break decrease. Primary hepatocytes cultured on the scaffolds are self-assembled into 3D spheroids, which restores the hepatocyte polarity and sufficient expression of drug metabolism enzymes over an extended period of time. Among these conductive scaffolds, hepatocytes cultured on fibers containing 3% of CNTs (F3) show the highest clearance rates of model drugs, offering a better prediction of the in vivo data with a high correlation value. Moreover, the drug metabolism capability is maintained over 15 days and is more sensitive towards the inducers and inhibitors of metabolizing enzymes, demonstrating the applicability for drug-drug interaction studies. Thus, this culture system has been demonstrated as a reliable in vitro model for high-throughput screening of metabolism and toxicity in the early phases of drug development.

Structure establishment of three-dimensional (3D) cell culture printing model for bladder cancer

Purpose

Two-dimensional (2D) cell culture is a valuable method for cell-based research but can provide unpredictable, misleading data about in vivo responses. In this study, we created a three-dimensional (3D) cell culture environment to mimic tumor characteristics and cell-cell interactions to better characterize the tumor formation response to chemotherapy.

Materials and methods

We fabricated the 3D cell culture samples using a 3D cell bio printer and the bladder cancer cell line 5637. T24 cells were used for 2D cell culture. Then, rapamycin and Bacillus Calmette-Guérin (BCG) were used to examine their cancer inhibition effects using the two bladder cancer cell lines. Cell-cell interaction was measured by measuring e-cadherin and n-cadherin secreted via the epithelial-mesenchymal transition (EMT).

Results

We constructed a 3D cell scaffold using gelatin methacryloyl (GelMA) and compared cell survival in 3D and 2D cell cultures. 3D cell cultures showed higher cancer cell proliferation rates than 2D cell cultures, and the 3D cell culture environment showed higher cell-to-cell interactions through the secretion of E-cadherin and N-cadherin. Assessment of the effects of drugs for bladder cancer such as rapamycin and BCG showed that the effect in the 2D cell culture environment was more exaggerated than that in the 3D cell culture environment.

Conclusions

We fabricated 3D scaffolds with bladder cancer cells using a 3D bio printer, and the 3D scaffolds were similar to bladder cancer tissue. This technique can be used to create a cancer cell-like environment for a drug screening platform.

The Tumor-on-Chip: Recent Advances in the Development of Microfluidic Systems to Recapitulate the Physiology of Solid Tumors

The ideal in vitro recreation of the micro-tumor niche-although much needed for a better understanding of cancer etiology and development of better anticancer therapies-is highly challenging. Tumors are complex three-dimensional (3D) tissues that establish a dynamic cross-talk with the surrounding tissues through complex chemical signaling. An extensive body of experimental evidence has established that 3D culture systems more closely recapitulate the architecture and the physiology of human solid tumors when compared with traditional 2D systems. Moreover, conventional 3D culture systems fail to recreate the dynamics of the tumor niche. Tumor-on-chip systems, which are microfluidic devices that aim to recreate relevant features of the tumor physiology, have recently emerged as powerful tools in cancer research. In tumor-on-chip systems, the use of microfluidics adds another dimension of physiological mimicry by allowing a continuous feed of nutrients (and pharmaceutical compounds). Here, we discuss recently published literature related to the culture of solid tumor-like tissues in microfluidic systems (tumor-on-chip devices). Our aim is to provide the readers with an overview of the state of the art on this particular theme and to illustrate the toolbox available today for engineering tumor-like structures (and their environments) in microfluidic devices. The suitability of tumor-on-chip devices is increasing in many areas of cancer research, including the study of the physiology of solid tumors, the screening of novel anticancer pharmaceutical compounds before resourcing to animal models, and the development of personalized treatments. In the years to come, additive manufacturing (3D bioprinting and 3D printing), computational fluid dynamics, and medium- to high-throughput omics will become powerful enablers of a new wave of more sophisticated and effective tumor-on-chip devices.