A Facile and Scalable Hydrogel Patterning Method for Microfluidic 3D Cell Culture and Spheroid-in-Gel Culture Array

Open-Top Patterned Hydrogel-Laden 3D Glioma Cell Cultures for Creation of Dynamic Chemotactic Gradients to Direct Cell Migration

The laminar flow profiles in microfluidic systems coupled to rapid diffusion at flow streamlines have been widely utilized to create well-controlled chemical gradients in cell cultures for spatially directing cell migration. However, within hydrogel-based closed microfluidic systems of limited depth (≤0.1 mm), the biomechanical cues for the cell culture are dominated by cell interactions with channel surfaces rather than with the hydrogel microenvironment. Also, leaching of poly(dimethylsiloxane) (PDMS) constituents in closed systems and the adsorption of small molecules to PDMS alter chemotactic profiles. To address these limitations, we present the patterning and integration of a PDMS-free open fluidic system, wherein the cell-laden hydrogel directly adjoins longitudinal channels that are designed to create chemotactic gradients across the 3D culture width, while maintaining uniformity across its ∼1 mm depth to enhance cell-biomaterial interactions. This hydrogel-based open fluidic system is assessed for its ability to direct migration of U87 glioma cells using a hybrid hydrogel that includes hyaluronic acid (HA) to mimic the brain tumor microenvironment and gelatin methacrylate (GelMA) to offer the adhesion motifs for promoting cell migration. Chemotactic gradients to induce cell migration across the hydrogel width are assessed using the chemokine CXCL12, and its inhibition by AMD3100 is validated. This open-top hydrogel-based fluidic system to deliver chemoattractant cues over square-centimeter-scale areas and millimeter-scale depths can potentially serve as a robust screening platform to assess emerging glioma models and chemotherapeutic agents to eradicate them.

Cancer-on-chip models for metastasis: importance of the tumor microenvironment

Cancer-on-chip (CoC) models, based on microfluidic chips harboring chambers for 3D tumor-cell culture, enable us to create a controlled tumor microenvironment (TME). CoC models are therefore increasingly used to systematically study effects of the TME on the various steps in cancer metastasis. Moreover, CoC models have great potential for developing novel cancer therapies and for predicting patient-specific response to cancer treatments. We review recent developments in CoC models, focusing on three main TME components: (i) the anisotropic extracellular matrix (ECM) architectures, (ii) the vasculature, and (iii) the immune system. We aim to provide guidance to biologists to choose the best CoC approach for addressing questions about the role of the TME in metastasis, and to inspire engineers to develop novel CoC technologies.

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.

Engineered 3D ex vivo models to recapitulate the complex stromal and immune interactions within the tumor microenvironment

Cancer thrives in a complex environment where interactions between cellular and acellular components, surrounding the tumor, play a crucial role in disease development and progression. Despite significant progress in cancer research, the mechanism driving tumor growth and therapeutic outcomes remains elusive. Two-dimensional (2D) cell culture assays and in vivo animal models are commonly used in cancer research and therapeutic testing. However, these models suffer from numerous shortcomings including lack of key features of the tumor microenvironment (TME) & cellular composition, cost, and ethical clearance. To that end, there is an increased interest in incorporating and elucidating the influence of TME on cancer progression. Advancements in 3D-engineered ex vivo models, leveraging biomaterials and microengineering technologies, have provided an unprecedented ability to reconstruct native-like bioengineered cancer models to study the heterotypic interactions of TME with a spatiotemporal organization. These bioengineered cancer models have shown excellent capabilities to bridge the gap between oversimplified 2D systems and animal models. In this review article, we primarily provide an overview of the immune and stromal cellular components of the TME and then discuss the latest state-of-the-art 3D-engineered ex vivo platforms aiming to recapitulate the complex TME features. The engineered TME model, discussed herein, are categorized into three main sections according to the cellular interactions within TME: (i) Tumor-Stromal interactions, (ii) Tumor-Immune interactions, and (iii) Complex TME interactions. Finally, we will conclude the article with a perspective on how these models can be instrumental for cancer translational studies and therapeutic testing.

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.

Advances in tissue engineering of cancer microenvironment-from three-dimensional culture to three-dimensional printing

Cancer treatment development is a complex process, with tumor heterogeneity and inter-patient variations limiting the success of therapeutic intervention. Traditional two-dimensional cell culture has been used to study cancer metabolism, but it fails to capture physiologically relevant cell-cell and cell-environment interactions required to mimic tumor-specific architecture. Over the past three decades, research efforts in the field of 3D cancer model fabrication using tissue engineering have addressed this unmet need. The self-organized and scaffold-based model has shown potential to study the cancer microenvironment and eventually bridge the gap between 2D cell culture and animal models. Recently, three-dimensional (3D) bioprinting has emerged as an exciting and novel biofabrication strategy aimed at developing a 3D compartmentalized hierarchical organization with the precise positioning of biomolecules, including living cells. In this review, we discuss the advancements in 3D culture techniques for the fabrication of cancer models, as well as their benefits and limitations. We also highlight future directions associated with technological advances, detailed applicative research, patient compliance, and regulatory challenges to achieve a successful bed-to-bench transition.

Nanofabrication Technologies to Control Cell and Tissue Function in Three-Dimension

In the 2000s, advances in cellular micropatterning using microfabrication contributed to the development of cell-based biosensors for the functional evaluation of newly synthesized drugs, resulting in a revolutionary evolution in drug screening. To this end, it is essential to utilize cell patterning to control the morphology of adherent cells and to understand contact and paracrine-mediated interactions between heterogeneous cells. This suggests that the regulation of the cellular environment by means of microfabricated synthetic surfaces is not only a valuable endeavor for basic research in biology and histology, but is also highly useful to engineer artificial cell scaffolds for tissue regeneration. This review particularly focuses on surface engineering techniques for the cellular micropatterning of three-dimensional (3D) spheroids. To establish cell microarrays, composed of a cell adhesive region surrounded by a cell non-adherent surface, it is quite important to control a protein-repellent surface in the micro-scale. Thus, this review is focused on the surface chemistries of the biologically inspired micropatterning of two-dimensional non-fouling characters. As cells are formed into spheroids, their survival, functions, and engraftment in the transplanted site are significantly improved compared to single-cell transplantation. To improve the therapeutic effect of cell spheroids even further, various biomaterials (e.g., fibers and hydrogels) have been developed for spheroid engineering. These biomaterials not only can control the overall spheroid formation (e.g., size, shape, aggregation speed, and degree of compaction), but also can regulate cell-to-cell and cell-to-matrix interactions in spheroids. These important approaches to cell engineering result in their applications to tissue regeneration, where the cell-biomaterial composite is injected into diseased area. This approach allows the operating surgeon to implant the cell and polymer combinations with minimum invasiveness. The polymers utilized in hydrogels are structurally similar to components of the extracellular matrix in vivo, and are considered biocompatible. This review will provide an overview of the critical design to make hydrogels when used as cell scaffolds for tissue engineering. In addition, the new strategy of injectable hydrogel will be discussed as future directions.

Pump-less, recirculating organ-on-a-chip (rOoC) platform

We developed a novel, pump-less directional flow recirculating organ-on-a-chip (rOoC) platform that creates controlled unidirectional gravity-driven flow by a combination of a 3D-tilting system and an optimized microfluidic layout. The rOoC platform was assembled utilizing a layer-to-layer fabrication technology based on thermoplastic materials. It features two organoid compartments supported by two independent perfusion channels and separated by a hydrogel barrier. We developed a computational model to predict wall shear stress values and then measured the flow rate in the microfluidic channels with micro-Particle-Image-Velocimetry (μPIV). The suitability of the rOoC for functional culture of endothelial cells was tested using HUVECs seeded in the perfusion channels. HUVECs aligned in response to the directional flow, formed a barrier and were able to sprout into the organoid compartments. Next, we demonstrated the viability of human stem-cell derived liver organoids in the organoid compartments. Finally, we show the possibility to circulate immune cells in the microfluidic channels that retain viability without being trapped or activated. The rOoC platform allows growing and connecting of two or more tissue or organ representations on-chip with the possibility of applying gradients, endothelial barriers, microvasculature and circulating cells independent of external tubing and support systems.

Controlling Microenvironments with Organs-on-Chips for Osteoarthritis Modelling

Osteoarthritis (OA) remains a prevalent disease affecting more than 20% of the global population, resulting in morbidity and lower quality of life for patients. The study of OA pathophysiology remains predominantly in animal models due to the complexities of mimicking the physiological environment surrounding the joint tissue. Recent development in microfluidic organ-on-chip (OoC) systems have demonstrated various techniques to mimic and modulate tissue physiological environments. Adaptations of these techniques have demonstrated success in capturing a joint tissue's tissue physiology for studying the mechanism of OA. Adapting these techniques and strategies can help create human-specific in vitro models that recapitulate the cellular processes involved in OA. This review aims to comprehensively summarise various demonstrations of microfluidic platforms in mimicking joint microenvironments for future platform design iterations.

Recent Advances of Organ-on-a-Chip in Cancer Modeling Research

Although many studies have focused on oncology and therapeutics in cancer, cancer remains one of the leading causes of death worldwide. Due to the unclear molecular mechanism and complex in vivo microenvironment of tumors, it is challenging to reveal the nature of cancer and develop effective therapeutics. Therefore, the development of new methods to explore the role of heterogeneous TME in individual patients' cancer drug response is urgently needed and critical for the effective therapeutic management of cancer. The organ-on-chip (OoC) platform, which integrates the technology of 3D cell culture, tissue engineering, and microfluidics, is emerging as a new method to simulate the critical structures of the in vivo tumor microenvironment and functional characteristics. It overcomes the failure of traditional 2D/3D cell culture models and preclinical animal models to completely replicate the complex TME of human tumors. As a brand-new technology, OoC is of great significance for the realization of personalized treatment and the development of new drugs. This review discusses the recent advances of OoC in cancer biology studies. It focuses on the design principles of OoC devices and associated applications in cancer modeling. The challenges for the future development of this field are also summarized in this review. This review displays the broad applications of OoC technique and has reference value for oncology development.

A High-Throughput and Uniform Amplification Method for Cell Spheroids

Cell culture is an important life science technology. Compared with the traditional two-dimensional cell culture, three-dimensional cell culture can simulate the natural environment and structure specificity of cell growth in vivo. As such, it has become a research hotspot. The existing three-dimensional cell culture techniques include the hanging drop method, spinner flask method, etc., making it difficult to ensure uniform morphology of the obtained cell spheroids while performing high-throughput. Here, we report a method for amplifying cell spheroids with the advantages of quickly enlarging the culture scale and obtaining cell spheroids with uniform morphology and a survival rate of over 95%. Technically, it is easy to operate and convenient to change substances. These results indicate that this method has the potential to become a promising approach for cell-cell, cell-stroma, cell-organ mutual interaction research, tissue engineering, and anti-cancer drug screening.

Generation of 3D Spheroids Using a Thiol-Acrylate Hydrogel Scaffold to Study Endocrine Response in ER+ Breast Cancer

Culturing cancer cells in a three-dimensional (3D) environment better recapitulates in vivo conditions by mimicking cell-to-cell interactions and mass transfer limitations of metabolites, oxygen, and drugs. Recent drug studies have suggested that a high rate of preclinical and clinical failures results from mass transfer limitations associated with drug entry into solid tumors that 2D model systems cannot predict. Droplet microfluidic devices offer a promising alternative to grow 3D spheroids from a small number of cells to reduce intratumor heterogeneity, which is lacking in other approaches. Spheroids were generated by encapsulating cells in novel thiol–acrylate (TA) hydrogel scaffold droplets followed by on-chip isolation of single droplets in a 990- or 450-member trapping array. The TA hydrogel rapidly (∼35 min) polymerized on-chip to provide an initial scaffold to support spheroid development followed by a time-dependent degradation. Two trapping arrays were fabricated with 150 or 300 μm diameter traps to investigate the effect of droplet size and cell seeding density on spheroid formation and growth. Both trapping arrays were capable of ∼99% droplet trapping efficiency with ∼90% and 55% cellular encapsulation in trapping arrays containing 300 and 150 μm traps, respectively. The oil phase was replaced with media ∼1 h after droplet trapping to initiate long-term spheroid culturing. The growth and viability of MCF-7 3D spheroids were confirmed for 7 days under continuous media flow using a customized gravity-driven system to eliminate the need for syringe pumps. It was found that a minimum of 10 or more encapsulated cells are needed to generate a growing spheroid while fewer than 10 parent cells produced stagnant 3D spheroids. As a proof of concept, a drug susceptibility study was performed treating the spheroids with fulvestrant followed by interrogating the spheroids for proliferation in the presence of estrogen. Following fulvestrant exposure, the spheroids showed significantly less proliferation in the presence of estrogen, confirming drug efficacy.

Microfluidic harvesting of breast cancer tumor spheroid-derived extracellular vesicles from immobilized microgels for single-vesicle analysis

Investigating cellular and vesicular heterogeneity in breast cancer remains a challenge, which encourages the development of controllable in vitro systems that mimic the tumor microenvironment. Although three-dimensional cell culture better recapitulates the heterogeneity observed in tumor growth and extracellular vesicle (EV) biogenesis, the physiological relevance is often contrasted with the control offered by two-dimensional cell culture. Therefore, to challenge this misconception we developed a novel microfluidic system harboring highly tunable three-dimensional EV microbioreactors (^EVμBRs) to model micrometastatic EV release in breast cancer while capitalizing on the convenient, low-volume, and sterile interface provided by microfluidics. The diameter and cellular occupancy of the ^EVμBRs could be precisely tailored to various configurations, supporting the formation of breast cancer tumor spheroids. To immobilize the ^EVμBRs within a microchannel and facilitate EV extraction, oxygen inhibition in free-radical polymerization was repurposed to rapidly generate two-layer hydrodynamic traps in situ using a digital-micromirror device (DMD)-based ultraviolet (UV) projection system. Breast cancer tumor spheroid-derived EVs were harvested with as little as 20 μL from the microfluidic system and quantified by single-EV immunofluorescence for CD63 and CD81. Despite the low-volume extraction, differences in biomarker expression and coexpression of the tetraspanins on single EVs were observed. Furthermore, the ^EVμBRs were capable of recapitulating heterogeneity at a cellular and vesicular degree, indicating the utility and robustness of the microfluidic system to investigate physiologically relevant EVs in breast cancer and other disease models.