Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Beyond 2D: Novel biomaterial approaches for modeling the placenta

This review considers fully three-dimensional biomaterial environments of varying complexity as these pertain to research on the placenta. The developments in placental cell sources are first considered, along with the corresponding maternal cells with which the trophoblast interact. We consider biomaterial sources, including hybrid and composite biomaterials. Properties and characterization of biomaterials are discussed in the context of material design for specific placental applications. The development of increasingly complicated three-dimensional structures includes examples of advanced fabrication methods such as microfluidic device fabrication and 3D bioprinting, as utilized in a placenta context. The review finishes with a discussion of the potential for in vitro, three-dimensional placenta research to address health disparities and sexual dimorphism, especially in light of the exciting recent changes in the regulatory environment for in vitro devices.

Revolutionizing the female reproductive system research using microfluidic chip platform

Comprehensively understanding the female reproductive system is crucial for safeguarding fertility and preventing diseases concerning women's health. With the capacity to simulate the intricate physio- and patho-conditions, and provide diagnostic platforms, microfluidic chips have fundamentally transformed the knowledge and management of female reproductive health, which will ultimately promote the development of more effective assisted reproductive technologies, treatments, and drug screening approaches. This review elucidates diverse microfluidic systems in mimicking the ovary, fallopian tube, uterus, placenta and cervix, and we delve into the culture of follicles and oocytes, gametes' manipulation, cryopreservation, and permeability especially. We investigate the role of microfluidics in endometriosis and hysteromyoma, and explore their applications in ovarian cancer, endometrial cancer and cervical cancer. At last, the current status of assisted reproductive technology and integrated microfluidic devices are introduced briefly. Through delineating the multifarious advantages and challenges of the microfluidic technology, we chart a definitive course for future research in the woman health field. As the microfluidic technology continues to evolve and advance, it holds great promise for revolutionizing the diagnosis and treatment of female reproductive health issues, thus propelling us into a future where we can ultimately optimize the overall wellbeing and health of women everywhere.

3D microfluidics-assisted modeling of glucose transport in placental malaria

The human placenta is a critical organ, mediating the exchange of nutrients, oxygen, and waste products between fetus and mother. Placental malaria (PM) resulted from Plasmodium falciparum infections causes up to 200 thousand newborn deaths annually, mainly due to low birth weight, as well as 10 thousand mother deaths. In this work, a placenta-on-a-chip model is developed to mimic the nutrient exchange between the fetus and mother under the influence of PM. In this model, trophoblasts cells (facing infected or uninfected blood simulating maternal blood and termed “trophoblast side”) and human umbilical vein endothelial cells (facing uninfected blood simulating fetal blood and termed “endothelial” side) are cultured on the opposite sides of an extracellular matrix gel in a compartmental microfluidic system, forming a physiological barrier between the co-flow tubular structure to mimic a simplified maternal–fetal interface in placental villi. The influences of infected erythrocytes (IEs) sequestration through cytoadhesion to chondroitin sulfate A (CSA) expressed on the surface of trophoblast cells, a critical feature of PM, on glucose transfer efficiency across the placental barrier was studied. To create glucose gradients across the barrier, uninfected erythrocyte or IE suspension with a higher glucose concentration was introduced into the “trophoblast side” and a culture medium with lower glucose concentration was introduced into the “endothelial side”. The glucose levels in the endothelial channel in response to CSA-adherent erythrocytes infected with CS2 line of parasites in trophoblast channel under flow conditions was monitored. Uninfected erythrocytes served as a negative control. The results demonstrated that CSA-binding IEs added resistance to the simulated placental barrier for glucose perfusion and decreased the glucose transfer across this barrier. The results of this study can be used for better understanding of PM pathology and development of models useful in studying potential treatment of PM.

Recycled Bifunctional Heterostructure Material: g-GaN/SnS for Photocatalytic Decomposition of Water and Efficient Detection of NO2

Recently, the energy crisis and environmental pollution problems have become increasingly severe. There is an urgent need to develop a class of multifunctional materials that can both produce clean energy and detect harmful gases. Herein, we propose a g-GaN/SnS heterostructure and explored its dual-optimal performance in photocatalytic hydrogen production and gas detection. Our results demonstrated that the g-GaN/SnS heterostructure has a suitable type II band alignment and excellent absorption in the visible range, which both indicate its potential application in photocatalysis. Furthermore, when the g-GaN/SnS heterostructure acted as a gas detection material, it was consistently susceptible to NO₂ gas molecules, according to charge transfer. Additionally, it has a very suitable material recovery time (∼0.5 h) when used for NO₂ detection, illustrating the recyclability of the material. Interestingly, the applied electric field of -0.4 V/Å can greatly increase the absorption coefficient in the visible range to 150% of the original. Also, the applied electric field of 0.6 V/Å can substantially enhance the gas detection sensitivity by 27% compared to the case without the electric field. Thus, the g-GaN/SnS heterostructure we proposed not only has the advantage of being bifunctional but also has the potential to be recycled.

Microfluidic Invasion Chemotaxis Platform for 3D Neurovascular Co-Culture

Advances in microfabrication and biomaterials have enabled the development of microfluidic chips for studying tissue and organ models. While these platforms have been developed primarily for modeling human diseases, they are also used to uncover cellular and molecular mechanisms through in vitro studies, especially in the neurovascular system, where physiological mechanisms and three-dimensional (3D) architecture are difficult to reconstruct via conventional assays. An extracellular matrix (ECM) model with a stable structure possessing the ability to mimic the natural extracellular environment of the cell efficiently is useful for tissue engineering applications. Conventionally used techniques for this purpose, for example, Matrigels, have drawbacks of owning complex fabrication procedures, in some cases not efficient enough in terms of functionality and expenses. Here, we proposed a fabrication protocol for a GelMA hydrogel, which has shown structural stability and the ability to imitate the natural environment of the cell accurately, inside a microfluidic chip utilizing co-culturing of two human cell lines. The chemical composition of the synthesized GelMA was identified by Fourier transform infrared spectrophotometry (FTIR), its surface morphology was observed by field emission electron microscopy (FESEM), and the structural properties were analyzed by atomic force microscopy (AFM). The swelling behavior of the hydrogel in the microfluidic chip was imaged, and its porosity was examined for 72 h by tracking cell localization using immunofluorescence. GelMA exhibited the desired biomechanical properties, and the viability of cells in both platforms was more than 80% for seven days. Furthermore, GelMA was a viable platform for 3D cell culture studies and was structurally stable over long periods, even when prepared by photopolymerization in a microfluidic platform. This work demonstrated a viable strategy to conduct co-culturing experiments as well as modeling invasion and migration events. This microfluidic assay may have application in drug delivery and dosage optimization studies.

Developing G value as an indicator for assessing the molecular status of immobilized antibody

Antibody-functionalized nanoparticles (Ab-NPs) are widely used in bioassays due to their excellent affinity, specificity toward antigen, and ease of operation. However, the uncontrollable molecular status of antibodies on NPs severely limits their applications. This work aims at developing a simple method to evaluate the antigen-binding activity of Ab-NPs using two parameters, i.e., antibody adsorption amount and antigen-binding strength. Herein, we proposed a mathematical expression, G, to quantitively describe the amount and strength of Ab-NPs. G value could be used to assess the antigen-binding performance of NPs influenced by surface and solution factors. Seven types of polymers with different surface properties, including four positively and three negatively charged polymer brushes, were grown from silica NPs via surface-initiated atom transfer radical polymerization (SI-ATRP). A pair of antigen and antibody, human chorionic gonadotropin (hCG) and anti-hCG, were selected to screen the antibody immobilization property of polymer brushes. Among them, the G values of 2 polymer-NPs with opposite charges reached maximum, resulting in low detection limits for hCG, where pDMAEA-NP and pMMA-NP represent Poly[N,N-(dimethylamino)ethyl acrylate]-NP and poly(methyl methacrylate)-NP, respectively. The G value of Ab-NPs makes it feasible to estimate the molecular status of the adsorbed antibodies on surfaces, thus showing great potential for in vitro biosensing and bioseparation.

Current understanding in deciphering trophoblast cell differentiation during human placentation

The placenta is a unique organ that forms during gestation and supports fetus survival and communication with the mother. However, of such an arguably essential organ for a successful pregnancy, our knowledge is limited. New progress has been made for human placenta study in recent years. We herein summarize the current understanding of human placental trophoblast differentiation and the molecules that govern trophoblast cell lineage specification. More importantly, the powerful tools for placental studies are also explained, such as human trophoblast stem cells (hTSCs), 3-dimensional (3D) trophoblast organoids, engineering-based placental devices, and single-cell RNA sequencing (sc-RNAseq). These advances have brought us new insights into placental development and provided multiple investigation strategies for deciphering molecular mechanisms.

3D Printed Microfluidic Spiral Separation Device for Continuous, Pulsation-Free and Controllable CHO Cell Retention

The development of continuous bioprocesses-which require cell retention systems in order to enable longer cultivation durations-is a primary focus in the field of modern process development. The flow environment of microfluidic systems enables the granular manipulation of particles (to allow for greater focusing in specific channel regions), which in turn facilitates the development of small continuous cell separation systems. However, previously published systems did not allow for separation control. Additionally, the focusing effect of these systems requires constant, pulsation-free flow for optimal operation, which cannot be achieved using ordinary peristaltic pumps. As described in this paper, a 3D printed cell separation spiral for CHO-K1 (Chinese hamster ovary) cells was developed and evaluated optically and with cell experiments. It demonstrated a high separation efficiency of over 95% at up to 20 × 10⁶ cells mL^-1. Control over inlet and outlet flow rates allowed the operator to adjust the separation efficiency of the device while in use-thereby enabling fine control over cell concentration in the attached bioreactors. In addition, miniaturized 3D printed buffer devices were developed that can be easily attached directly to the separation unit for usage with peristaltic pumps while simultaneously almost eradicating pump pulsations. These custom pulsation dampeners were closely integrated with the separator spiral lowering the overall dead volume of the system. The entire device can be flexibly connected directly to bioreactors, allowing continuous, pulsation-free cell retention and process operation.

Modelling the Human Placental Interface In Vitro-A Review

Acting as the primary link between mother and fetus, the placenta is involved in regulating nutrient, oxygen, and waste exchange; thus, healthy placental development is crucial for a successful pregnancy. In line with the increasing demands of the fetus, the placenta evolves throughout pregnancy, making it a particularly difficult organ to study. Research into placental development and dysfunction poses a unique scientific challenge due to ethical constraints and the differences in morphology and function that exist between species. Recently, there have been increased efforts towards generating in vitro models of the human placenta. Advancements in the differentiation of human induced pluripotent stem cells (hiPSCs), microfluidics, and bioprinting have each contributed to the development of new models, which can be designed to closely match physiological in vivo conditions. By including relevant placental cell types and control over the microenvironment, these new in vitro models promise to reveal clues to the pathogenesis of placental dysfunction and facilitate drug testing across the maternal-fetal interface. In this minireview, we aim to highlight current in vitro placental models and their applications in the study of disease and discuss future avenues for these in vitro models.

Bioengineered Microphysiological Placental Models: Towards Improving Understanding of Pregnancy Health and Disease

Driven by a lack of appropriate human placenta models, recent years have seen the introduction of bioengineered in vitro models to better understand placental health and disease. Thus far, the focus has been on the maternal-foetal barrier. However, there are many other physiologically and pathologically significant aspects of the placenta that would benefit from state-of-the-art bioengineered models, in particular, integrating advanced culture systems with contemporary biological concepts such as organoids. This critical review defines and discusses the key parameters required for the development of physiologically relevant in vitro models of the placenta. Specifically, it highlights the importance of cell type, mechanical forces, and culture microenvironment towards the use of physiologically relevant models to improve the understanding of human placental function and dysfunction.

Liquid-Liquid Flows with Non-Newtonian Dispersed Phase in a T-Junction Microchannel

Immiscible liquid–liquid flows in microchannels are used extensively in various chemical and biological lab-on-a-chip systems when it is very important to predict the expected flow pattern for a variety of fluids and channel geometries. Commonly, biological and other complex liquids express non-Newtonian properties in a dispersed phase. Features and behavior of such systems are not clear to date. In this paper, immiscible liquid–liquid flow in a T-shaped microchannel was studied by means of high-speed visualization, with an aim to reveal the shear-thinning effect on the flow patterns and slug-flow features. Three shear-thinning and three Newtonian fluids were used as dispersed phases, while Newtonian castor oil was a continuous phase. For the first time, the influence of the non-Newtonian dispersed phase on the transition from segmented to continuous flow is shown and quantitatively described. Flow-pattern maps were constructed using nondimensional complex We^0.4·Oh^0.6 depicting similarity in the continuous-to-segmented flow transition line. Using available experimental data, the proposed nondimensional complex is shown to be effectively applied for flow-pattern map construction when the continuous phase exhibits non-Newtonian properties as well. The models to evaluate an effective dynamic viscosity of a shear-thinning fluid are discussed. The most appropriate model of average-shear-rate estimation based on bulk velocity was chosen and applied to evaluate an effective dynamic viscosity of a shear-thinning fluid. For a slug flow, it was found that in the case of shear-thinning dispersed phase at low flow rates of both phases, a jetting regime of slug formation was established, leading to a dramatic increase in slug length.

Bioengineering Approaches for Placental Research

Research into the human placenta's complex functioning is complicated by a lack of suitable physiological in vivo models. Two complementary approaches have emerged recently to address these gaps in understanding, computational in silico techniques, including multi-scale modeling of placental blood flow and oxygen transport, and cellular in vitro approaches, including organoids, tissue engineering, and organ-on-a-chip models. Following a brief introduction to the placenta's structure and function and its influence on the substantial clinical problem of preterm birth, these different bioengineering approaches are reviewed. The cellular techniques allow for investigation of early first-trimester implantation and placental development, including critical biological processes such as trophoblast invasion and trophoblast fusion, that are otherwise very difficult to study. Similarly, computational models of the placenta and the pregnant pelvis at later-term gestation allow for investigations relevant to complications that occur when the placenta has fully developed. To fully understand clinical conditions associated with the placenta, including those with roots in early processes but that only manifest clinically at full-term, a holistic approach to the study of this fascinating, temporary but critical organ is required.

Development of an Organ-on-a-Chip-Device for Study of Placental Pathologies

The human placenta plays a key role in reproduction and serves as a major interface for maternofetal exchange of nutrients. Study of human placenta pathology presents a great experimental challenge because it is not easily accessible. In this paper, a 3D placenta-on-a-chip model is developed by bioengineering techniques to simulate the placental interface between maternal and fetal blood in vitro. In this model, trophoblasts cells and human umbilical vein endothelial cells are cultured on the opposite sides of a porous polycarbonate membrane, which is sandwiched between two microfluidic channels. Glucose diffusion across this barrier is analyzed under shear flow conditions. Meanwhile, a numerical model of the 3D placenta-on-a-chip model is developed. Numerical results of concentration distributions and the convection-diffusion mass transport is compared to the results obtained from the experiments for validation. Finally, effects of flow rate and membrane porosity on glucose diffusion across the placental barrier are studied using the validated numerical model. The placental model developed here provides a potentially helpful tool to study a variety of other processes at the maternal-fetal interface, for example, effects of drugs or infections like malaria on transport of various substances across the placental barrier.

Biosensors: A novel approach to and recent discovery in detection of cytokines

Cytokines in tissues and physiological fluids can function as potentially suitable biomarkers. Cytokines are involved in stimulating different body responses including inflammatory response to external pathogens, regulating cell-to-cell communication, and maintaining tissue homeostasis. Consequently, cytokines are extensively used to monitor and predict disease progression and to track the outcome of patient treatment. The critical diagnosis of cytokine and chemokine biomarkers has been the focus of attention and it has been continuously directing the trajectory of related research to developing a novel sensing platform. Given the major challenges and constraints of the older identification methods including their high costs, low sensitivity, and high specificity, the development of biosensor technology as a simple and inexpensive tool with high sensitivity is quite attractive and interesting. The fundamental aim of this study is to present the state-of-the-art biosensor systems in order to detect different types of cytokines and to emphasize the role of these systems in the prevention, monitoring, and treatment of various cytokine-associated diseases.