Pump-Less Platform Enables Long-Term Recirculating Perfusion of 3D Printed Tubular Tissues.

The direction and pattern of fluid flow affect vascular structure and function, in which vessel-lining endothelial cells exhibit variable cellular morphologies and vessel remodeling by mechanosensing. To recapitulate this microenvironment, some approaches have been reported to successfully apply unidirectional flow on endothelial cells in organ-on-a-chip systems. However, these platforms encounter drawbacks such as the dependency on pumps or confinement to closed microfluidic channels. These constraints impede their synergy with advanced biofabrication techniques like 3D bioprinting, thereby curtailing the potential to introduce greater complexity into engineered tissues. Herein, a pumpless recirculating platform (UniPlate) that enables unidirectional media recirculation through 3D printed tubular tissues, is demonstrated.The device is made of polystyrene via injection molding in combination with 3D printed sacrifical gelatin templates. Tubular blood vessels with unidirectional perfusion are firstly engineered. Then the design is expanded to incorporate duo-recirculating flow for culturing vascularized renal proximal tubules with glucose reabsorption function. In addition to media recirculation, human monocyte recirculation in engineered blood vessels is also demonstrated for over 24 h, with minimal loss of cells, cell viability, and inflammatory activation. UniPlate can be a valuable tool to more precisely control the cellular microenvironment of organ-on-a-chip systems for drug discovery.

Fabrication of succinate-alginate xerogel films for in vitro coupling of osteogenesis and neovascularization.

The osseointegration of metallic implants is reliant on a cascade of molecular interactions and the delivery of macromolecules to the implant environment that occurs before substantial bone formation. Early blood vessel formation is a requisite first step in the healing timeline for osteoid formation, where vascular development can be accelerated as a result of controlled hypoxic conditioning. In this study, alginate-derived xerogel films containing varied concentrations of disodium succinate salt which has been shown to induce pseudohypoxia (short-term hypoxic effects while maintaining an oxygenated environment) were developed. Xerogels were characterized for their morphology, succinate release over time and cellular response with osteoblast-mimicking Saos-2 and human umbilical vein endothelial cells (HUVEC). Scanning electron microscopy revealed a multiscale topography that may favour osseointegration and alamarBlue assays indicated no cytotoxic effects during in vitro proliferation of Saos-2 cells. pH measurements of eluted succinate reach 95 % of peak value after 7 h of immersion for all gels containing 10 mM of succinate or less, and 60 % within the first 40 min. In vitro exposure of HUVECs to succinate-conditioned media increased the net concentration of total proteins measured by bicinchoninic acid (BCA) assay and maintains stable vascular endothelial growth factor (VEGF) and extracellular platelet-derived growth factor (PDGF) for vessel formation through comparison of enzyme-linked immunosorbent assays (ELISAs) of the culture media and cell lysate. Tube formation assays also showed a sustained increase in tube diameter across the first 48 h of HUVEC culture when succinate concentrations of 1 and 10 µM in the xerogel. Overall, the succinate-alginate films serve as a prospective organic coating for bone-interfacing implant materials which may induce temporary pseudohypoxic conditions favourable for early angiogenesis and bone regeneration in vivo at succinate concentrations of 1 or 10 µM.

Subtractive manufacturing with swelling induced stochastic folding of sacrificial materials for fabricating complex perfusable tissues in multi-well plates.

Organ-on-a-chip systems that recapitulate tissue-level functions have been proposed to improve in vitro-in vivo correlation in drug development. Significant progress has been made to control the cellular microenvironment with mechanical stimulation and fluid flow. However, it has been challenging to introduce complex 3D tissue structures due to the physical constraints of microfluidic channels or membranes in organ-on-a-chip systems. Inspired by 4D bioprinting, we develop a subtractive manufacturing technique where a flexible sacrificial material can be patterned on a 2D surface, swell and shape change when exposed to aqueous hydrogel, and subsequently degrade to produce perfusable networks in a natural hydrogel matrix that can be populated with cells. The technique is applied to fabricate organ-specific vascular networks, vascularized kidney proximal tubules, and terminal lung alveoli in a customized 384-well plate and then further scaled to a 24-well plate format to make a large vascular network, vascularized liver tissues, and for integration with ultrasound imaging. This biofabrication method eliminates the physical constraints in organ-on-a-chip systems to incorporate complex ready-to-perfuse tissue structures in an open-well design.

From Model System to Therapy: Scalable Production of Perfusable Vascularized Liver Spheroids in "Open-Top" 384-Well Plate.

Vasculature is a key component of many biological tissues and helps to regulate a wide range of biological processes. Modeling vascular networks or the vascular interface in organ-on-a-chip systems is an essential aspect of this technology. In many organ-on-a-chip devices, however, the engineered vasculatures are usually designed to be encapsulated inside closed microfluidic channels, making it difficult to physically access or extract the tissues for downstream applications and analysis. One unexploited benefit of tissue extraction is the potential of vascularizing, perfusing, and maturing the tissue in well-controlled, organ-on-a-chip microenvironments and then subsequently extracting that product for in vivo therapeutic implantation. Moreover, for both modeling and therapeutic applications, the scalability of the tissue production process is important. Here we demonstrate the scalable production of perfusable and extractable vascularized tissues in an "open-top" 384-well plate (referred to as IFlowPlate), showing that this system could be used to examine nanoparticle delivery to targeted tissues through the microvascular network and to model vascular angiogenesis. Furthermore, tissue spheroids, such as hepatic spheroids, can be vascularized in a scalable manner and then subsequently extracted for in vivo implantation. This simple multiple-well plate platform could not only improve the experimental throughputs of organ-on-a-chip systems but could potentially help expand the application of model systems to regenerative therapy.

Correction: Deep-LUMEN assay - human lung epithelial spheroid classification from brightfield images using deep learning.

Correction for 'Deep-LUMEN assay - human lung epithelial spheroid classification from brightfield images using deep learning' by Lyan Abdul et al., Lab Chip, 2020, DOI: .

Deep-LUMEN assay - human lung epithelial spheroid classification from brightfield images using deep learning.

Three-dimensional (3D) tissue models such as epithelial spheroids or organoids have become popular for pre-clinical drug studies. In contrast to 2D monolayer culture, the characterization of 3D tissue models from non-invasive brightfield images is a significant challenge. To address this issue, here we report a deep-learning uncovered measurement of epithelial networks (Deep-LUMEN) assay. Deep-LUMEN is an object detection algorithm that has been fine-tuned to automatically uncover subtle differences in epithelial spheroid morphology from brightfield images. This algorithm can track changes in the luminal structure of tissue spheroids and distinguish between polarized and non-polarized lung epithelial spheroids. The Deep-LUMEN assay was validated by screening for changes in spheroid epithelial architecture in response to different extracellular matrices and drug treatments. Specifically, we found the dose-dependent toxicity of cyclosporin can be underestimated if the effect of the drug on tissue morphology is not considered. Hence, Deep-LUMEN could be used to assess drug effects and capture morphological changes in 3D spheroid models in a non-invasive manner.

IFlowPlate-A Customized 384-Well Plate for the Culture of Perfusable Vascularized Colon Organoids.

Despite the complexity and structural sophistication that 3D organoid models provide, their lack of vascularization and perfusion limit the capability of these models to recapitulate organ physiology effectively. A microfluidic platform named IFlowPlate is engineered, which can be used to culture up to 128 independently perfused and vascularized colon organoids in vitro. Unlike traditional microfluidic devices, the vascularized organoid-on-chip device with an "open-well" design does not require any external pumping systems and allows tissue extraction for downstream analyses, such as histochemistry or even in vivo transplantation. By optimizing both the extracellular matrix (ECM) and the culture media formulation, patient-derived colon organoids are co-cultured successfully within a self-assembled vascular network, and it is found that the colon organoids grow significantly better in the platform under constant perfusion versus conventional static condition. Furthermore, a colon inflammation model with an innate immune function where circulating monocytes can be recruited from the vasculature, differentiate into macrophage, and infiltrate the colon organoids in response to tumor necrosis factor (TNF)- inflammatory cytokine stimulation is developed using the platform. With the ability to grow vascularized colon organoids under intravascular perfusion, the IFlowPlate platform could unlock new possibilities for screening potential therapeutic targets or modeling relevant diseases.

Modeling organ-specific vasculature with organ-on-a-chip devices.

Organ-on-a-chip devices, also known as microphysiological systems, have gained significant attention in recent years. Recent advances in tissue engineering and microfabrication have enabled these devices to provide more precise control over cellular microenvironments to mimic the tissue-level or organ-level function of the human body. These more complex tissue models can provide either an improvement in the functional expression and maturation of cells or an avenue to probe biological events and function that would otherwise be difficult to visualize and mechanistically study. This high-value information, when complimented with the existing gold-standards of cell-based assays and animal models, could potentially lead to more informed decision-making in drug development. A prevalent biological component in many organ-on-a-chip devices is an engineered vascular interface that is present in almost all organs of the human body. The vasculature and the vascular interface are particularly susceptible to biomechanical forces, they function as the conduits for inter-cellular and inter-organ interactions, and regulate drug transport. In this review, we examine the various approaches taken to model the human vasculature with an emphasis on the engineering of organ-specific vasculatures, and discuss various challenges and opportunities ahead as the field advances.

Therapeutic luminal coating of the intestine.

The gastrointestinal tract is the site of most drug delivery and therapeutic interventions for the management and treatment of numerous diseases. However, selective access to its mucosa, especially in the small bowel, is challenging. Here we develop an orally administered gut-coating formulation that provides a transient coating of the bowel. Through a materials screening campaign, we identified a sucrose octasulfate aluminium complex and further engineered the pH-dependent material into a complex coacervate formulation linked via pH-independent electrostatic interaction, which allowed an effective transient physical coating on the gastrointestinal mucosa, independent of gastric acid exposure. We tested the therapeutic values of this technology in two settings. Oral administration of this gut-coating formulation modulated the nutrient contact with bowel mucosa, which lowered the glucose responses in rodent models indicating a potential therapeutic utility in diabetes. Furthermore, the formulation protected biological agents from gastric acid exposure and degradation, which enabled oral delivery to the small bowel mucosa.