Airway-On-A-Chip: Designs and Applications for Lung Repair and Disease.

The lungs are affected by illnesses including asthma, chronic obstructive pulmonary disease, and infections such as influenza and SARS-CoV-2. Physiologically relevant models for respiratory conditions will be essential for new drug development. The composition and structure of the lung extracellular matrix (ECM) plays a major role in the function of the lung tissue and cells. Lung-on-chip models have been developed to address some of the limitations of current two-dimensional in vitro models. In this review, we describe various ECM substitutes utilized for modeling the respiratory system. We explore the application of lung-on-chip models to the study of cigarette smoke and electronic cigarette vapor. We discuss the challenges and opportunities related to model characterization with an emphasis on in situ characterization methods, both established and emerging. We discuss how further advancements in the field, through the incorporation of interstitial cells and ECM, have the potential to provide an effective tool for interrogating lung biology and disease, especially the mechanisms that involve the interstitial elements.

Progressive stretch enhances growth and maturation of 3D stem-cell-derived myocardium.

Bio-engineered myocardium has great potential to substitute damaged myocardium and for studies of myocardial physiology and disease, but structural and functional immaturity still implies limitations. Current protocols of engineered heart tissue (EHT) generation fall short of simulating the conditions of postnatal myocardial growth, which are characterized by tissue expansion and increased mechanical load. To investigate whether these two parameters can improve EHT maturation, we developed a new approach for the generation of cardiac tissues based on biomimetic stimulation under application of continuously increasing stretch. Methods: EHTs were generated by assembling cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CM) at high cell density in a low collagen hydrogel. Maturation and growth of the EHTs were induced in a custom-made biomimetic tissue culture system that provided continuous electrical stimulation and medium agitation along with progressive stretch at four different increments. Tissues were characterized after a three week conditioning period. Results: The highest rate of stretch (S3 = 0.32 mm/day) increased force development by 5.1-fold compared to tissue with a fixed length, reaching contractility of 11.28 mN/mm². Importantly, intensely stretched EHTs developed physiological length-dependencies of active and passive forces (systolic/diastolic ratio = 9.47 ± 0.84), and a positive force-frequency relationship (1.25-fold contractility at 180 min-1). Functional markers of stretch-dependent maturation included enhanced and more rapid Ca2+ transients, higher amplitude and upstroke velocity of action potentials, and pronounced adrenergic responses. Stretch conditioned hiPSC-CMs displayed structural improvements in cellular volume, linear alignment, and sarcomere length (2.19 ± 0.1 µm), and an overall upregulation of genes that are specifically expressed in adult cardiomyocytes. Conclusions: With the intention to simulate postnatal heart development, we have established techniques of tissue assembly and biomimetic culture that avoid tissue shrinkage and yield muscle fibers with contractility and compliance approaching the properties of adult myocardium. This study demonstrates that cultivation under progressive stretch is a feasible way to induce growth and maturation of stem cell-derived myocardium. The novel tissue-engineering approach fulfills important requirements of disease modelling and therapeutic tissue replacement.

Cyclic uniaxial cell stretching in tissue culture using a LEGO®-based mechanical stretcher and a polydimethylsiloxane stretchable vessel.

Mechanical signals are essential for the regulation of many biological processes. Therefore, it has become paramount to account for these mechanical parameters when exploring biological processes. Here, we describe a protocol to apply cyclic uniaxial stretch on cells in culture using a LEGO®-based mechanical stretcher and a flexible custom-made polydimethylsiloxane culture vessel as well as validated downstream applications. While this system offers an out-of-the-box limited type of simulation, it provides a reliable and low-cost opportunity to perform cell stretching. For complete details on the use and execution of this protocol, please refer to Boulter et al. (2020).

In vitro three-dimensional organotypic culture models of the oral mucosa.

Three-dimensional, organotypic models of the oral mucosa have been developed to study a wide variety of phenomena occurring in the oral cavity. Although a number of models have been developed in academic research labs, only a few models have been commercialized. Models from academic groups offer a broader range of phenotypes while the commercial models are more focused on the oral and gingival mucosa. The commercialized models are manufactured under highly controlled conditions and meet the requirements of quality standards, which leads to high levels of reproducibility. These in vitro models have been used to evaluate the irritancy of oral care products such as toothpastes, mouthwashes, and mucoadhesives. The effects of cigarette smoke on oral cavity tissues have been studied and compared to those of e-cigarettes. Oral tissue models have facilitated investigation of the mechanisms of oral mucositis and oral candidiasis and have been used to examine transbuccal drug delivery rates and the absorption of nanoparticles. Infection studies have investigated the effects of HIV-1 along with the effects of commensal and pathogenic bacteria. More recently, a differentiated oral tissue model has been shown to express the ACE2 receptor, which is known to be important for the receptor-mediated entry of the SARS-CoV-2 coronavirus into human cells and tissues. Hence, oral mucosal models may find application in determining whether viral infection of the oral mucosa is possible and whether such infection has implications vis-a-vis the current COVID-19 pandemic. As is apparent, these models are used in a broad variety of applications and often offer advantages versus animal models in terms of reproducibility, avoiding species extrapolation, and the ethical concerns related to human and animal experimentation. The goals of this paper are to review commercially available models of the human buccal and gingival mucosa and highlight their use to gain a better understanding of a broad range of phenomena affecting tissues in the oral cavity.

In vitro modeling of solid tumor interactions with perfused blood vessels.

Molecular crosstalk between intra-tumor blood vessels and tumor cells plays many critical roles in tumorigenesis and cancer metastasis. However, it has been very difficult to investigate the biochemical mechanisms underlying the overlapping, multifactorial processes that occur at the tumor-vascular interface using conventional murine models alone. Moreover, traditional two-dimensional (2D) culture models used in cancer research do not recapitulate aspects of the 3D tumor microenvironment. In the present study, we introduce a microfluidic model of the solid tumor-vascular interface composed of a human umbilical vein endothelial cell (HUVEC)-lined, perfusable, bioengineered blood vessel and tumor spheroids embedded in an extracellular matrix (ECM). We sought to optimize our model by varying the composition of the tumor spheroids (MDA-MB-231 breast tumor cells + mesenchymal stem cells (MSCs)/human lung fibroblasts (HLFs)/HUVECs) and the extracellular matrix (ECM: collagen, Matrigel, and fibrin gels with or without free HLFs) that we used. Our results indicate that culturing tumor spheroids containing MDA-MB-231 cells + HUVECs in an HLF-laden, fibrin-based ECM within our microfluidic device optimally (1) enhances the sprouting and migration of tumor spheroids, (2) promotes angiogenesis, (3) facilitates vascular invasion, and (4) preserves the structural integrity and functionality of HUVEC-lined microfluidic channels. This model may provide a platform for drug screening and mechanism studies on solid tumor interactions with functional blood vessels.

Intestinal Organoid Culture in Polymer Film-Based Microwell Arrays.

As organoids offer a promising tool to study cell biology and model diseases, organoid technology has rapidly evolved over the last few years. Even though intestinal organoids are one of the most well-established organoid systems, they currently rely on the embedding into an excess amount of poorly defined, tumor-derived extracellular matrix. Here, a novel suspension method is suggested to grow mouse intestinal organoids inside thermoformed microwell arrays. This platform promotes the controlled growth of organoids under matrix-reduced conditions, with Matrigel only used as medium supplement. Hence, this system provides numerous advantages over the previously established methods. Based on the findings, viable and functional mouse intestinal organoids can be preserved for longer periods than in traditional Matrigel domes. Additionally, this microwell-based technique renders a novel organoid culture system in which the heterogeneity of the organoids is significantly reduced. The method paves the way toward more controlled organoid culture systems that can also be beneficial for further downstream applications, such as automated imaging techniques and micromanipulations, which constitute valuable tools for high-throughput applications and translational studies.

Engineering slit-like channels for studying the growth of epithelial tissues in 3D-confined spaces.

The development of epithelial lumens in ducts is essential to the functioning of various organs and in organogenesis. Ductal elongation requires the collective migration of cell cohorts in three-dimensional (3D) confined spaces, while maintaining their epithelial integrity. Epithelial lumens generally adopt circular morphologies, however abnormalities in complex physiological environments can lead to the narrowing of glandular spaces that adopt elongated and slit-like morphologies. Here, we describe a simple method to form epithelial tissues in microchannels of various widths (100-300 µm) with a constant height of 25 µm that mimic elongated geometries of glandular spaces. The significance of this biomimetic platform has been evidenced by studying the migration of epithelial cell sheets inside these narrow slits of varying dimensions. We show that the growth of epithelial tissues in 3D-confined slits leads to a gradient of cell density along the slit axis and that the migration cell velocity depends on the extent of the spatial confinement. Our findings indicate that nuclear orientation is higher for leader cells and depends on the slit width, whereas YAP protein was predominantly localized in the nucleus of leader cells. This method will pave the way to studies aiming at understanding how 3D-confined spaces, which are reminiscent of in vivo pathological conditions, can affect the growth and the homeostasis of epithelial tissues.

Microwell-based pancreas-on-chip model enhances genes expression and functionality of rat islets of Langerhans.

Organ-on-chip technology is a promising tool for investigating physiological in vitro responses in drug screening development, and in advanced disease models. Within this framework, we investigated the behavior of rat islets of Langerhans in an organ-on-chip model. The islets were trapped by sedimentation in a biochip with a microstructure based on microwells, and perfused for 5 days of culture. The live/dead assay confirmed the high viability of the islets in the biochip cultures. The microfluidic culture leads to upregulation of mRNA levels of important pancreatic islet genes: Ins1, App, Insr, Gcgr, Reg3a and Neurod. Furthermore, insulin and glucagon secretion were higher in the biochips compared to the Petri conditions after 5 days of culture. We also confirmed glucose-induced insulin secretion in biochips via high and low glucose stimulations leading to high/low insulin secretion. The high responsiveness of the pancreatic islets to glucagon-like peptide 1 (GLP-1) stimulation in the biochips was reflected by the upregulation of mRNA levels of Gcgr, Reg3a, Neurog3, Ins1, Ins2, Stt and Glp-1r and by increased insulin secretion. The results obtained highlighted the functionality of the islets in the biochips and illustrated the potential of our pancreas-on-chip model for future pancreatic disease modeling and anti-diabetic drugs screening.

The new biocompatible material for mouse ovarian follicle development in three-dimensional in vitro culture systems.

To establish a protocol of optimized three-dimensional (3D) culture of ovarian follicles, various biomaterials have been investigated with regard to their properties and functions on in vitro follicle growth. The present study aims to compare the new biomaterial, extracellular matrix-derived soft hydrogel (ES-hydrogel) and alginate, and evaluate the effects of biomaterials on further in vitro 3D culture growth of ovarian follicle and oocyte maturation. The isolated follicles from mouse ovaries were randomly divided into two-dimensional (2D) culture, alginate and ES-hydrogel, and just seeded on culture wells (2D culture) or encapsulated with alginate or ES-hydrogel (3D culture). Culture media from each group were collected on days 4, 8 and 10 or 11 for 17ß-oestradiol (E2) and progesterone (P4) measurement. On day 10 of in vitro culture, follicular survival and pseudo-antrum formation rate were examined, and oocyte maturation was induced by adding human chorionic gonadotropin and epidermal growth factor. After 17 h, ovulated mature oocytes collected and analyzed for oocyte diameter, normal spindle and chromosome alignment configuration, reactive oxygen species (ROS) level, and mitochondrial membrane potential level. To compare mechanical properties of two biomaterials, storage modulus was measured with the advanced rheometric expansion system. Our results showed that follicles cultured in ES-hydrogel, were significantly superior to those cultured 2D or alginate in the pseudo-antrum formation rate, cumulus-oocyte complexes (COCs) rate, MII oocyte rate, normal spindle rate, and E2 production. The ES-hydrogel and alginate groups were not significantly different in follicle survival rate, oocyte diameter, P4 production, ROS, and mitochondrial membrane potential levels. The storage modulus of ES-hydrogel was lower than that of alginate, suggesting that the improved follicular physiology and oocyte maturation in the ES-hydrogel group was due to better hormone exchange through a less stiff encapsulating material. This study shows that 3D culture system using ES-hydrogel effectively improve the outcome of in vitro ovarian follicle culture, supporting follicle morphology and growth and enhancing oocyte maturation. It means one of the most important factors for 3D culture of ovarian follicle was the selection of appropriate and effective biomaterial that can preserve the structure and morphology of ovarian follicle and facilitate nutrition and hormone exchange.

Development of A 3D Tissue Slice Culture Model for the Study of Human Endometrial Repair and Regeneration.

The human endometrium undergoes sequential phases of shedding of the upper functionalis zone during menstruation, followed by regeneration of the functionalis zone from the remaining basalis zone cells, and secretory differentiation under the influence of the ovarian steroid hormones estradiol (E2) and progesterone (P4). This massive tissue regeneration after menstruation is believed to arise from endometrial stromal and epithelial stem cells residing in the basal layer of the endometrium. Although many endometrial pathologies are thought to be associated with defects in these stem cells, studies on their identification and regulation are limited, primarily due to lack of easily accessible animal models, as these processes are unique to primates. Here we describe a robust new method to study endometrial regeneration and differentiation processes using human endometrial tissue slice cultures incorporating an air-liquid interface into a 3D matrix scaffold of type I collagen gel, allowing sustained tissue viability over three weeks. The 3D collagen gel-embedded endometrial tissue slices in a double-dish culture system responded to ovarian steroid hormones, mimicking the endometrial changes that occur in vivo during the menstrual cycle. These changes included the E2-induced upregulation of Ki-67, estrogen receptor (ER), and progesterone receptor (PR) in all endometrial compartments and were markedly suppressed by both P4 and E2 plus P4 treatments. There were also distinct changes in endometrial morphology after E2 and P4 treatments, including subnuclear vacuolation and luminal secretions in glands as well as decidualization of stromal cells, typical characteristics of a progestational endometrium in vivo. This long-term slice culture method provides a unique in vivo-like microenvironment for the study of human endometrial functions and remodeling during early pregnancy and experiments on stem cell populations involved in endometrial regeneration and remodeling. Furthermore, this model has the potential to enable studies on several endometrial diseases, including endometrial cancers and pregnancy complications associated with defects in endometrial remodeling.

A multi-chamber tissue culture device for load-dependent parallel evaluation of tendon explants.

BACKGROUND: Injuries in the musculoskeletal system, such as tendon and ligament ruptures, are challenging to manage and often require surgical reconstructions with limited long-term success. Thus, characterizations of these tissues are urgently needed to better understand cellular mechanisms that regulate tissue homeostasis and healing. Explant culturing systems allow for ex vivo analysis of tissues in an environment that mimics the native microenvironment in vivo. METHODS: Collaborative efforts within our institution facilitated the establishment of a novel explant culturing system. Tissue specimens cultured in single wells, with individual applied loading and/or biological environment, allowed characterization of tissue cultured under a variety of biological loading conditions. Quantitative PCR analysis for selected gene markers was our primary outcome. RESULTS: Data were stratified for analysis by either culture environment or loading condition. Our gene expression results show that specimens clustered by culture condition may differ in molecular markers related to ECM production (e.g., Col1a1, Adamts4) and/or organization (e.g., Tnc, Dnc). In contrast, loading condition did significantly alter the median gene expression levels of tissues in comparison to unloaded control samples, although gene expression values related to ECM degradation (e.g., Mmp1, Mmp10) were altered in tendons cultured under tension in the device. CONCLUSION: Our study demonstrates promising utility of a novel explant culturing system for further characterization of musculoskeletal tissues such as native tendons and ligaments, as well as pathologic fibrotic tissues resulting from arthrofibrosis or Dupuytren's disease.

Rolling-sliding load decreases the loss of chondrocyte viability and the mechanical properties of cartilage explants preserved in vitro.

The viability of cartilage explants preserved in vitro decreases with time, which limits its use for transplantation. The effect of mechanical stimulation to cartilage explants in vitro is unknown. In this study, we observed the effects of mechanical stimulation on chondrocyte viability and the mechanical properties of cartilage explants preserved in vitro using a rolling-sliding loading device designed by us, and the optimal stimulation protocol was established. A cylindrical osteochondral mass drilled on the femoral condyle of a healthy pig was divided into two groups (loading group and control group), and changes in the chondrocyte survival rate, matrix composition and cartilage biomechanical properties was observed at different time points. Additionally, the mRNA expression of the apoptosis-related proteins caspase-3/Bax/Bcl-2, the cytoskeletal proteins actin/vimentin, and the matrix-related protein MMP13 were detected. The loading group exhibited delayed collagen and aggrecan degeneration and improved chondrocyte viability for three days. Protein and mRNA detection showed that apoptotic factors such as caspase-3 and Bax decreased rapidly in cartilage tissue after loading. The cytoskeletal proteins actin and vimentin showed no significant changes in mRNA expression in the control group, but was significantly higher in the loading group. MMP-13 mRNA expression was significantly higher in both the control group and loading group. Overall, this study suggests that suitable mechanical stimulation decreases the loss of chondrocyte viability and the mechanical properties of cartilage explants in vitro and improves cartilage preservation.

A Microfluidic Platform Based on Robust Gas and Liquid Exchange for Long-term Culturing of Explanted Tissues.

Microfluidic devices are important platforms to culture and observe biological tissues. Compared with conventional setups, microfluidic devices have advantages in perfusion, including an enhanced delivery of nutrients and gases to tissues. However, explanted tissues can maintain their functions for only hours to days in microfluidic devices, although their observations are desired for weeks. The suprachiasmatic nucleus (SCN) is a brain region composed of heterogeneous cells to control the biological clock system through synchronizing individual cells in this region. The synchronized and complicated cell-cell interactions of SCN cells are difficult to reproduce from seeded cells. Thus, the viability of explanted SCN contributes to the study of SCN functions. In this paper, we propose a new perfusion platform combining a PDMS microfluidic device with a porous membrane to culture an explanted SCN for 25 days. We expect that this platform will provide a universal interface for microfluidic manipulation of tissue explants.

Non-physiologic Bioreactor Processing Conditions for Heart Valve Tissue Engineering.

PURPOSE: Conventional methods of seeding decellularized heart valves for heart valve tissue engineering have led to inconsistent results in interstitial cellular repopulation, particularly of the distal valve leaflet, and notably distinct from documented re-endothelialization. The use of bioreactor conditioning mimicking physiologic parameters has been well explored but cellular infiltration remains challenging. Non-characteristic, non-physiologic conditioning parameters within a bioreactor, such as hypoxia and cyclic chamber pressure, may be used to increase the cellular infiltration leading to increased recellularization. METHODS: To investigate the effects of novel and perhaps non-intuitive bioreactor conditioning parameters, ovine aortic heart valves were seeded with mesenchymal stem cells and cultured in one of four environments: hypoxia and high cyclic pressures (120 mmHg), normoxia and high cyclic pressures, hypoxia and negative cyclic pressures (- 20 mmHg), and normoxia and negative cyclic pressures. Analysis included measurements of cellular density, cell phenotype, and biochemical concentrations. RESULTS: The results revealed that the bioreactor conditioning parameters influenced the degree of recellularization. Groups that implemented hypoxic conditioning exhibited increased cellular infiltration into the valve leaflet tissue compared to normoxic conditioning, while pressure conditioning did not have a significant effect of recellularization. Protein expression across all groups was similar, exhibiting a stem cell and valve interstitial cell phenotype. Biochemical analysis of the extracellular matrix was similar between all groups. CONCLUSION: These results suggest the use of non-physiologic bioreactor conditioning parameters can increase in vitro recellularization of tissue engineered heart valve leaflets. Particularly, hypoxic culture was found to increase the cellular infiltration. Therefore, bioreactor conditioning of tissue engineered constructs need not always mimic physiologic conditions, and it is worth investigating novel or uncharacteristic culture conditions as they may benefit aspects of tissue culture.

Assembly and Application of a Three-Dimensional Human Corneal Tissue Model.

The cornea provides a functional barrier separating the outside environment from the intraocular environment, thereby protecting posterior segments of the eye from infection and damage. Pathological changes that compromise the structure or integrity of the cornea may occur as a result of injury or disease and can lead to debilitating effects on visual acuity. Over 10 million people worldwide are visually impaired or blind due to corneal opacity. Thus, physiologically relevant in vitro approaches to predict corneal toxicity of chemicals or effective treatments for disease prior to ocular exposure, as well as to study the corneal effects of systemic, chronic conditions, such as diabetes, are needed to reduce use of animal testing and accelerate therapeutic development. We have previously bioengineered an innervated corneal tissue model using silk protein scaffolds to recapitulate the structural and mechanical elements of the anterior cornea and to model the functional aspects of corneal sensation with the inclusion of epithelial, stromal, and neural components. The purpose of this unit is to provide a step-by-step guide for preparation, assembly, and application of this three-dimensional corneal tissue system to enable the study of corneal tissue biology. © 2019 by John Wiley & Sons, Inc.

Teburu-Open source 3D printable bioreactor for tissue slices as dynamic three-dimensional cell culture models.

Three-dimensional tissue cultures are important models for the study of cell-cell and cell-matrix interactions, as well as, to investigate tissue repair and reconstruction pathways. Therefore, we designed a reproducible and easy to handle printable bioreactor system (Teburu), that is applicable for different approaches of pathway investigation and targeted tissue repair using human tissue slices as a three-dimensional cell culture model. Here, we definitively describe Teburu as a controlled environment to reseed a 500-µm thick decellularized human liver slice using human mesenchymal stroma cells. During a cultivation period of eight days, Teburu, as a semi-open and low consumption system, was capable to maintain steady pH and oxygenation levels. Its combination with additional modules delivers an applicability for a wide range of tissue engineering approaches under optimal culture conditions.

Culture of periprosthetic tissue in blood culture bottles for diagnosing periprosthetic joint infection.

BACKGROUND: The purpose of this meta-analysis was to evaluate the diagnostic accuracy of periprosthetic tissue culture in blood culture bottles (BCB) for periprosthetic joint infection (PJI). METHODS: PubMed, Web of Science, and Embase were systematically searched for eligible studies evaluating the diagnostic performance of periprosthetic tissue culture in BCB for the diagnosis of PJI. The pooled data were analysed by Meta-Disc software. RESULTS: Four studies with a total of 1071 patients were included in this meta-analysis. The summarized estimates showed that periprosthetic tissue culture in BCB may be of great value in PJI diagnosis with a pooled sensitivity of 0.70 (95% confidence interval [CI]; 0.66-0.75), specificity of 0.97 (95% CI: 0.95-0.98); positive likelihood ratio (PLR) of 20.98 (95% CI: 11.52-38.2); negative likelihood ratio (NLR) of 0.28 (95% CI: 0.20-0.40); and diagnostic odds ratio (DOR) of 92.26 (95% CI: 43.93-193.78). CONCLUSIONS: The present meta-analysis showed that periprosthetic tissue in BCB improves the results of microorganism cultures, with a sensitivity of 70% and a specificity of 97%. However, more large-scale, well-performed studies are needed to verify our findings.

A Novel Technique Enables Quantifying the Molecular Interaction of Solvents with Biological Tissues.

The pharmaceutical industry uses various solvents to increase drug penetrability to tissues. The solvent's choice affects the efficacy of a drug. In this paper, we provide an unprecedented means of relating a solvent to a tissue quantitatively. We show that the solvents induce reorientation of the tissue surface molecules in a way that favors interaction and, therefore, penetrability of a solvent to a tissue. We provide, for the first time, a number for this tendency through a new physical property termed Interfacial Modulus (Gs). Gs, which so far was only predicted theoretically, is inversely proportional to such interactions. As model systems, we use HeLa and HaCaT tissue cultures with water and with an aqueous DMSO solution. The measurements are done using Centrifugal Adhesion Balance (CAB) when set to effective zero gravity. As expected, the addition of DMSO to water reduces Gs. This reduction in Gs is usually higher for HaCaT than for HeLa cells, which agrees with the common usage of DMSO in dermal medicine. We also varied the rigidities of the tissues. The tissue rigidity is not expected to relate to Gs, and indeed our results didn't show a correlation between these two physical properties.

Embryonic Midfacial Palatal Organ Culture Methods in Developmental Toxicology.

The morphogenesis of the secondary palate provides an interesting model for many of the processes involved in embryonic development. A number of in vitro models have been used to study craniofacial development, including whole embryo culture, palatal mesenchymal and micromass cell cultures, and Trowell-like palatal cultures in which dissected palates are cultured individually or as pairs in contact on a support above medium. This chapter presents a detailed protocol for the culture of maxillary midfacial tissues, including the palatal shelves, in suspension culture. This method involves isolation of the midfacial tissues (maxillary arch and palatal shelves) and suspension of the tissues in medium in flasks. On a rocker in an incubator, the palatal shelves elevate, grow, make contact, and fuse in a time span analogous to that occurring in the intact embryo in utero.