OoC Devices Research Articles

Barrier-on-a-Chip with a Modular Architecture and Integrated Sensors for Real-Time Measurement of Biological Barrier Function.

Biological barriers are essential for the maintenance of organ homeostasis and their dysfunction is responsible for many prevalent diseases. Advanced in vitro models of biological barriers have been developed through the combination of 3D cell culture techniques and organ-on-chip (OoC) technology. However, real-time monitoring of tissue function inside the OoC devices has been challenging, with most approaches relying on off-chip analysis and imaging techniques. In this study, we designed and fabricated a low-cost barrier-on-chip (BoC) device with integrated electrodes for the development and real-time monitoring of biological barriers. The integrated electrodes were used to measure transepithelial electrical resistance (TEER) during tissue culture, thereby quantitatively evaluating tissue barrier function. A finite element analysis was performed to study the sensitivity of the integrated electrodes and to compare them with conventional systems. As proof-of-concept, a full-thickness human skin model (FTSm) was grown on the developed BoC, and TEER was measured on-chip during the culture. After 14 days of culture, the barrier tissue was challenged with a benchmark irritant and its impact was evaluated on-chip through TEER measurements. The developed BoC with an integrated sensing capability represents a promising tool for real-time assessment of barrier function in the context of drug testing and disease modelling.

Rapid Manufacturing of Multilayered Microfluidic Devices for Organ on a Chip Applications.

Microfabrication and Polydimethylsiloxane (PDMS) soft-lithography techniques became popular for microfluidic prototyping at the lab, but even after protocol optimization, fabrication is yet a long, laborious process and partly user-dependent. Furthermore, the time and money required for the master fabrication process, necessary at any design upgrade, is still elevated. Digital Manufacturing (DM) and Rapid-Prototyping (RP) for microfluidics applications arise as a solution to this and other limitations of photo and soft-lithography fabrication techniques. Particularly for this paper, we will focus on the use of subtractive DM techniques for Organ-on-a-Chip (OoC) applications. Main available thermoplastics for microfluidics are suggested as material choices for device fabrication. The aim of this review is to explore DM and RP technologies for fabrication of an OoC with an embedded membrane after the evaluation of the main limitations of PDMS soft-lithography strategy. Different material options are also reviewed, as well as various bonding strategies. Finally, a new functional OoC device is showed, defining protocols for its fabrication in Cyclic Olefin Polymer (COP) using two different RP technologies. Different cells are seeded in both sides of the membrane as a proof of concept to test the optical and fluidic properties of the device.

Microfluidics and organ-on-a-chip technologies: A systematic review of the methods used to mimic bone marrow.

Bone marrow (BM) is an organ responsible for crucial processes in living organs, e. g., hematopoiesis. In recent years, Organ-on-a-Chip (OoC) devices have been used to satisfy the need for in vitro systems that better mimic the phenomena occurring in the BM microenvironment. Given the growing interest in these systems and the diversity of developed devices, an integrative systematic literature review is required. We have performed this review, following the PRISMA method aiming to identify the main characteristics and assess the effectiveness of the devices that were developed to represent the BM. A search was performed in the Scopus, PubMed, Web of Science and Science Direct databases using the keywords ((“bone marrow” OR “hematopoietic stem cells” OR “haematopoietic stem cells”) AND (“organ in a” OR “lab on a chip” OR “microfluidic” OR “microfluidic*” OR (“bioreactor” AND “microfluidic*”))). Original research articles published between 2009 and 2020 were included in the review, giving a total of 21 papers. The analysis of these papers showed that their main purpose was to study BM cells biology, mimic BM niches, model pathological BM, and run drug assays. Regarding the fabrication protocols, we have observed that polydimethylsiloxane (PDMS) material and soft lithography method were the most commonly used. To reproduce the microenvironment of BM, most devices used the type I collagen and alginate. Peristaltic and syringe pumps were mostly used for device perfusion. Regarding the advantages compared to conventional methods, there were identified three groups of OoC devices: perfused 3D BM; co-cultured 3D BM; and perfused co-cultured 3D BM. Cellular behavior and mimicking their processes and responses were the mostly commonly studied parameters. The results have demonstrated the effectiveness of OoC devices for research purposes compared to conventional cell cultures. Furthermore, the devices have a wide range of applicability and the potential to be explored.

Fabrication of a microfluidic device by using two-photon lithography on a positive photoresist

Organ-on-chip (OoC) devices are increasingly used for biomedical research and to speed up the process of bringing a medicinal drug from the lab to the market. The technology also addresses ethical issues linked to animal testing as it offers a reduction in animal experiments through its possibility to mimic the environment in the human body. Hence, it produces more relevant results than plain cell-culture experiments, while still sharing the possibility of high-throughput testing by simultaneously operating many devices in parallel. The main components of an OoC device are microfluidic channels and porous membranes. Current chips are often assembled from several parts. In the development phase a small change in design will cause a delay in the research because a new prototype has to be built again step-by-step. This research addresses this problem by targeting the fabrication of a microfluidic device in a single lithography and development step. A device consisting of two crossed channels at different heights separated by a membrane was chosen. The manufacturing method used was two-photon lithography (TPL) on positive photoresist AZ 4562. TPL exploits the fact that two-photon absorption non-linearly depends on the light intensity. The required intensity is only achieved in a small volume around the focal point, called the voxel. By positioning and moving this voxel inside the resist, 3D manufacturing is possible. Therefore the technique can be used for the single step fabrication of a closed channel. By vertically moving the voxel through the resist, pores can be manufactured. In literature an ellipsoidal voxel shape is assumed, leading to the assumption that the maximum voxel, and therefore pore diameter is found at the focal plane, i.e. at z = 0. However, this research shows that the voxel may also have an hourglass-shape for a high enough laser intensity. In this case the maximum voxel diameter is found at a distance z from the focal plane. For the production of pores, therefore the maximum voxel diameter instead of the diameter at the focal plane has to be taken into account. The smallest pores produced measured 250 nm - 290 nm. AZ 4562 was used as a stamp and a mold for the manufacturing of 3D topographical features on a PDMS surface. Finally the microfluidic device was successfully produced in a layer of 50 µm thick resist. The channel width was 100 µm and the height was 10 µm. The channels were separated by 10 µm in height. The sizes of the input and output holes were adapted to the diameter of the smallest available blunt needle, which is 210 µm.

Polylactic is a Sustainable, Low Absorption, Low Autofluorescence Alternative to Other Plastics for Microfluidic and Organ-on-Chip Applications.

Organ-on-chip (OOC) devices are miniaturized devices replacing animal models in drug discovery and toxicology studies. The majority of OOC devices are made from polydimethylsiloxane (PDMS), an elastomer widely used in microfluidic prototyping, but posing a number of challenges to experimentalists, including leaching of uncured oligomers and uncontrolled absorption of small compounds. Here we assess the suitability of polylactic acid (PLA) as a replacement material to PDMS for microfluidic cell culture and OOC applications. We changed the wettability of PLA substrates and demonstrated the functionalization method to be stable over a time period of at least 9 months. We successfully cultured human cells on PLA substrates and devices, without coating. We demonstrated that PLA does not absorb small molecules, is transparent (92% transparency), and has low autofluorescence. As a proof of concept of its manufacturability, biocompatibility, and transparency, we performed a cell tracking experiment of prostate cancer cells in a PLA device for advanced cell culture.

Microfluidic endothelium-on-a-chip development, from in vivo to in vitro experimental models.

In the last years, animal testing in medical research has been a controversial topic because of various reasons, such as ethical considerations and species differences. Therefore, more attention has been given to develop new technologies that can replace animal experiments and create in vitro models. Organ-on-a-chip (OOC) technology is a new and advanced technology based on microfluidic devices that can mimic the structure and function of entire organs and tissues as in vitro models. OOC models are miniature tissues and organs that assign characteristics for three-dimensional (3D) cell culture representation that resemble the original organs, together with their specific microenvironment microfluidic systems and specific biophysical processes, in order to mimic the normal physiological conditions and functionalities of the organs. Existing OOC models, such as liver, pancreas, heart, skin, brain, kidney, vessels, have been developed and designed for a specific function study. This review focuses on the main knowledge concerning OOC research and especially vascular endothelium-on-a-chip (EOC) model, developed in order to offer specific tools for studying vascular functions in physiological and pathological conditions. The field of OOC devices is still at the beginning, but in the future, this technology may have important roles in developing novel therapeutic approaches, offering new therapeutic molecules and providing the first step towards personalized medicine.

Methods of Delivering Mechanical Stimuli to Organ-on-a-Chip.

Recent advances in integrating microengineering and tissue engineering have enabled the creation of promising microengineered physiological models, known as organ-on-a-chip (OOC), for experimental medicine and pharmaceutical research. OOCs have been used to recapitulate the physiologically critical features of specific human tissues and organs and their interactions. Application of chemical and mechanical stimuli is critical for tissue development and behavior, and they were also applied to OOC systems. Mechanical stimuli applied to tissues and organs are quite complex in vivo, which have not adequately recapitulated in OOCs. Due to the recent advancement of microengineering, more complicated and physiologically relevant mechanical stimuli are being introduced to OOC systems, and this is the right time to assess the published literature on this topic, especially focusing on the technical details of device design and equipment used. We first discuss the different types of mechanical stimuli applied to OOC systems: shear flow, compression, and stretch/strain. This is followed by the examples of mechanical stimuli-incorporated OOC systems. Finally, we discuss the potential OOC systems where various types of mechanical stimuli can be applied to a single OOC device, as a better, physiologically relevant recapitulation model, towards studying and evaluating experimental medicine, human disease modeling, drug development, and toxicology.

Tunable Microstructured Membranes in Organs-on-Chips to Monitor Transendothelial Hydraulic Resistance.

Tissue engineering is an interdisciplinary field, wherein scientists from different backgrounds collaborate to address the challenge of replacing damaged tissues and organs through the in vitro fabrication of functional and transplantable biological structures. Because the development and optimization of tissue engineering strategies rely on the complex interaction of cells, materials, and the physical-chemical tissue microenvironment, there is a need for experimental models that allow controlled studies of these aspects. Organs-on-chips (OOCs) have recently emerged as in vitro models that capture the complexity of human tissues in a controlled manner, while including functional readouts related to human organ physiology. OOCs consist of multiple microfluidic cell culture compartments, which are interfaced by porous membranes or hydrogels in which human cells can be cultured, thereby providing a controlled culture environment that resembles the microenvironment of a certain organ, including mechanical, biochemical, and geometrical aspects. Because OOCs provide both a well-controlled microenvironment and functional readouts, they provide a unique opportunity to incorporate, evaluate, and optimize materials for tissue engineering. In this study, we introduce a polymeric blend membrane with a three-dimensional double-porous morphology prepared from a poly(ɛ-caprolactone)-chitosan blends (PCL-CHT) by a modified liquid-induced phase inversion technique. The membranes have different physicochemical, microstructural, and morphological properties depending on different PCL-CHT ratios. Big surface pores (macrovoids) provide a suitable microenvironment for the incorporation of cells or growth factors, whereas an interconnected small porous (macroporous) network allows transfer of essential nutrients, diffusion of oxygen, and removal of waste. Human umbilical vein endothelial cells were seeded on the blend membranes embedded inside an OOC device. The cellular hydraulic resistance was evaluated by perfusing culture medium at a realistic transendothelial pressure of 20 cmH2O or 2 kPa at 37°C after 1 and 3 days postseeding. By introducing and increasing CHT weight percentage, the resistance of the cellular barrier after 3 days was significantly improved. The high tuneability over the membrane physicochemical and architectural characteristics might potentially allow studies of cell-matrix interaction, cell transportation, and barrier function for optimization of vascular scaffolds using OOCs. Impact Statement Organs-on-chips (OOCs) offer interesting potential for progress in the treatment of diseases and injury in the growing field of tissue engineering and regenerative medicine. The article presents a new way to develop polymer membrane with a tunable microstructured morphology and to implement this biomaterial inside an OOC device. The reader should find measurements of the transendothelial hydraulic resistance in real time during endothelial cells culture: a simple and controlled way of mimicking human physiological condition for vascular tissue regeneration. This combination of novel biomaterial inside an OOC will explore innovative ideas in tissue engineering field.

Conceptual Design of Micro-Bioreactors and Organ-on-Chips for Studies of Cell Cultures.

Engineering design of microbioreactors (MBRs) and organ-on-chip (OoC) devices can take advantage of established design science theory, in which systematic evaluation of functional concepts and user requirements are analyzed. This is commonly referred to as a conceptual design. This review article compares how common conceptual design principles are applicable to MBR and OoC devices. The complexity of this design, which is exemplified by MBRs for scaled-down cell cultures in bioprocess development and drug testing in OoCs for heart and eye, is discussed and compared with previous design solutions of MBRs and OoCs, from the perspective of how similarities in understanding design from functionality and user purpose perspectives can more efficiently be exploited. The review can serve as a guideline and help the future design of MBR and OoC devices for cell culture studies.

Obstructive Sleep Apnea Devices for Out-Of-Center (OOC) Testing: Technology Evaluation

Guidance is needed to help clinicians decide which out-of-center (OOC) testing devices are appropriate for diagnosing obstructive sleep apnea (OSA). A new classification system that details the type of signals measured by these devices is presented. This proposed system categorizes OOC devices based on measurements of Sleep, Cardiovascular, Oximetry, Position, Effort, and Respiratory (SCOPER) parameters.Criteria for evaluating the devices are also presented, which were generated from chosen pre-test and post-test probabilities. These criteria state that in patients with a high pretest probability of having OSA, the OOC testing device has a positive likelihood ratio (LR+) of 5 or greater coinciding with an in-lab-polysomnography (PSG)-generated apnea hypopnea index (AHI) ≥ 5, and an adequate sensitivity (at least 0.825).Since oximetry is a mandatory signal for scoring AHI using PSG, devices that do not incorporate oximetry were excluded. English peer-reviewed literature on FDA-approved devices utilizing more than 1 signal was reviewed according to the above criteria for 6 questions. These questions specifically addressed the adequacy of different respiratory and effort sensors and combinations thereof to diagnose OSA. In summary, the literature is currently inadequate to state with confidence that a thermistor alone without any effort sensor is adequate to diagnose OSA; if a thermal sensing device is used as the only measure of respiration, 2 effort belts are required as part of the montage and piezoelectric belts are acceptable in this context; nasal pressure can be an adequate measurement of respiration with no effort measure with the caveat that this may be device specific; nasal pressure may be used in combination with either 2 piezoelectric or respiratory inductance plethysmographic (RIP) belts (but not 1 piezoelectric belt); and there is insufficient evidence to state that both nasal pressure and thermistor are required to adequately diagnose OSA. With respect to alternative devices for diagnosing OSA, the data indicate that peripheral arterial tonometry (PAT) devices are adequate for the proposed use; the device based on cardiac signals shows promise, but more study is required as it has not been tested in the home setting; for the device based on end-tidal CO(2) (ETCO(2)), it appears to be adequate for a hospital population; and for devices utilizing acoustic signals, the data are insufficient to determine whether the use of acoustic signals with other signals as a substitute for airflow is adequate to diagnose OSA.Standardized research is needed on OOC devices that report LR+ at the appropriate AHI (≥ 5) and scored according to the recommended definitions, while using appropriate research reporting and methodology to minimize bias.