Collagen vitrigel: a novel scaffold that can facilitate a three-dimensional culture for reconstructing organoids

Functionalized Collagen I Membranes as a Bruch's Membrane Mimetic for Outer Retinal In Vitro Models

Physiologically relevant in vitro models of the human outer retina are required to better elucidate the complex interplay of retinal tissue layers and investigate their role in retinal degenerative disorders. Materials currently used to mimic the function of Bruch's membrane fail to replicate a range of important structural, mechanical, and biochemical properties. Here, we detail the fabrication of a surface-functionalized, fibrous collagen I membrane. We demonstrate its ability to better replicate a range of important material properties akin to the function of human Bruch's membrane when compared with a commonly utilized synthetic polyethylene terephthalate alternative. We further reveal the ability of this membrane to support the culture of the ARPE-19 cell line, as well as human pluripotent stem cell-derived RPE-like cells and human umbilical vein endothelial cells. This material could provide greater physiological relevance to the native Bruch's membrane than current synthetic materials and further improve the outcomes of in vitro outer retinal models.

Global Literature Analysis of Organoid and Organ-on-Chip Research

Organoids and cells in organ-on-chip platforms replicate higher-level anatomical, physiological, or pathological states of tissues and organs. These technologies are widely regarded by academia, the pharmacological industry and regulators as key biomedical developments. To map advances in this emerging field, a literature analysis of 16,000 article metadata based on a quality-controlled text-mining algorithm is performed. The analysis covers titles, keywords, and abstracts of categorized academic publications in the literature and preprint databases published after 2010. The algorithm identifies and tracks 149 and 107 organs or organ substructures modeled as organoids and organ-on-chip, respectively, stem cell sources, as well as 130 diseases, and 16 groups of organisms other than human and mouse in which organoid/organ-on-chip technology is applied. The analysis illustrates changing diversity and focus in organoid/organ-on-chip research and captures its geographical distribution. The downloadable dataset provided is a robust framework for researchers to interrogate with their own questions.

Tissue engineering RPE sheet derived from hiPSC-RPE cell spheroids supplemented with Y-27632 and RepSox

BACKGROUND

Retinal pigment epithelium (RPE) cell therapy is a promising way to treat many retinal diseases. However, obtaining transplantable RPE cells is time-consuming and less effective. This study aimed to develop novel strategies for generating engineered RPE patches with physiological characteristics.

RESULTS

Our findings revealed that RPE cells derived from human induced pluripotent stem cells (hiPSCs) successfully self-assembled into spheroids. The RPE spheroids treated with Y27632 and Repsox had increased expression of epithelial markers and RPE-specific genes, along with improved cell viability and barrier function. Transcriptome analysis indicated enhanced cell adhesion and extracellular matrix (ECM) organization in RPE spheroids. These RPE spheroids could be seeded and bioprinted on collagen vitrigel (CV) membranes to construct engineered RPE sheets. Circular RPE patches, obtained by trephining a specific section of the RPE sheet, exhibited abundant microvilli and pigment particles, as well as reduced proliferative capacity and enhanced maturation.

CONCLUSIONS

Our study suggests that the supplementation of small molecules and 3D spheroid culture, as well as the bioprinting technique, can be effective methods to promote RPE cultivation and construct engineered RPE sheets, which may support future clinical RPE cell therapy and the development of RPE models for research applications.

Ultra-thin and ultra-porous nanofiber networks as a basement-membrane mimic

Current basement membrane (BM) mimics used for modeling endothelial and epithelial barriers in vitro do not faithfully recapitulate key in vivo physiological properties such as BM thickness, porosity, stiffness, and fibrous composition. Here, we use networks of precisely arranged nanofibers to form ultra-thin (∼3 μm thick) and ultra-porous (∼90%) BM mimics for blood-brain barrier modeling. We show that these nanofiber networks enable close contact between endothelial monolayers and pericytes across the membrane, which are known to regulate barrier tightness. Cytoskeletal staining and transendothelial electrical resistance (TEER) measurements reveal barrier formation on nanofiber membranes integrated within microfluidic devices and transwell inserts. Further, significantly higher TEER values indicate a biological benefit for co-cultures formed on the ultra-thin nanofiber membranes. Our BM mimic overcomes critical technological challenges in forming co-cultures that are in proximity and facilitate cell-cell contact, while still being constrained to their respective sides. We anticipate that our nanofiber networks will find applications in drug discovery, cell migration, and barrier dysfunction studies.

Biomaterials used for tissue engineering of barrier-forming cell monolayers in the eye

Cell monolayers that form a barrier between two structures play an important role for the maintenance of tissue functionality. In the anterior portion of the eye, the corneal endothelium forms a barrier that controls fluid exchange between the aqueous humor of the anterior chamber and the corneal stroma. This monolayer is central in the pathogenesis of Fuchs endothelial corneal dystrophy (FECD). FECD is a common corneal disease, in which corneal endothelial cells deposit extracellular matrix that increases the thickness of its basal membrane (Descemet's membrane), and forms excrescences (guttae). With time, there is a decrease in endothelial cell density that generates vision loss. Transplantation of a monolayer of healthy corneal endothelial cells on a Descemet membrane substitute could become an interesting alternative for the treatment of this pathology. In the back of the eye, the retinal pigment epithelium (RPE) forms the blood-retinal barrier, controlling fluid exchange between the choriocapillaris and the photoreceptors of the outer retina. In the retinal disease dry age-related macular degeneration (dry AMD), deposits (drusen) form between the RPE and its basal membrane (Bruch's membrane). These deposits hinder fluid exchange, resulting in progressive RPE cell death, which in turn generates photoreceptor cell death, and vision loss. Transplantation of a RPE monolayer on a Bruch's membrane/choroidal stromal substitute to replace the RPE before photoreceptor cell death could become a treatment alternative for this eye disease. This review will present the different biomaterials that are proposed for the engineering of a monolayer of corneal endothelium for the treatment of FECD, and a RPE monolayer for the treatment of dry AMD.

Alginate-Based 3D A549 Cell Culture Model to Study Paracoccidioides Infection

A three-dimensional (3D) lung aggregate model based on sodium alginate scaffolds was developed to study the interactions between Paracoccidioides brasiliensis (Pb) and lung epithelial cells. The suitability of the 3D aggregate as an infection model was examined using cell viability (cytotoxicity), metabolic activity, and proliferation assays. Several studies exemplify the similarity between 3D cell cultures and living organisms, which can generate complementary data due to the greater complexity observed in these designed models, compared to 2D cell cultures. A 3D cell culture system of human A549 lung cell line plus sodium alginate was used to create the scaffolds that were infected with Pb18. Our results showed low cytotoxicity, evidence of increased cell density (indicative of cell proliferation), and the maintenance of cell viability for seven days. The confocal analysis revealed viable yeast within the 3D scaffold, as demonstrated in the solid BHI Agar medium cultivation. Moreover, when ECM proteins were added to the alginate scaffolds, the number of retrieved fungi was significantly higher. Our results highlight that this 3D model may be promising for in vitro studies of host-pathogen interactions.

Pharmacological Functions, Synthesis, and Delivery Progress for Collagen as Biodrug and Biomaterial

Collagen has been widely applied as a functional biomaterial in regulating tissue regeneration and drug delivery by participating in cell proliferation, differentiation, migration, intercellular signal transmission, tissue formation, and blood coagulation. However, traditional extraction of collagen from animals potentially induces immunogenicity and requires complicated material treatment and purification steps. Although semi-synthesis strategies such as utilizing recombinant E. coli or yeast expression systems have been explored as alternative methods, the influence of unwanted by-products, foreign substances, and immature synthetic processes have limited its industrial production and clinical applications. Meanwhile, macromolecule collagen products encounter a bottleneck in delivery and absorption by conventional oral and injection vehicles, which promotes the studies of transdermal and topical delivery strategies and implant methods. This review illustrates the physiological and therapeutic effects, synthesis strategies, and delivery technologies of collagen to provide a reference and outlook for the research and development of collagen as a biodrug and biomaterial.

Cryopreservation of Cell Sheets for Regenerative Therapy: Application of Vitrified Hydrogel Membranes

Organ transplantation is the first and most effective treatment for missing or damaged tissues or organs. However, there is a need to establish an alternative treatment method for organ transplantation due to the shortage of donors and viral infections. Rheinwald and Green et al. established epidermal cell culture technology and successfully transplanted human-cultured skin into severely diseased patients. Eventually, artificial cell sheets of cultured skin were created, targeting various tissues and organs, including epithelial sheets, chondrocyte sheets, and myoblast cell sheets. These sheets have been successfully used for clinical applications. Extracellular matrix hydrogels (collagen, elastin, fibronectin, and laminin), thermoresponsive polymers, and vitrified hydrogel membranes have been used as scaffold materials to prepare cell sheets. Collagen is a major structural component of basement membranes and tissue scaffold proteins. Collagen hydrogel membranes (collagen vitrigel), created from collagen hydrogels through a vitrification process, are composed of high-density collagen fibers and are expected to be used as carriers for transplantation. In this review, the essential technologies for cell sheet implantation are described, including cell sheets, vitrified hydrogel membranes, and their cryopreservation applications in regenerative medicine.

Regulation of the Keratocyte Phenotype and Cell Behavior Derived from Human Induced Pluripotent Stem Cells by Substrate Stiffness

Substrate stiffness has been indicated as an important factor to control stem cell fate, including proliferation and differentiation. To optimize the stiffness for the differentiation process from h-iPSCs (human induced pluripotent stem cells) into h-iCSCs (human corneal stromal cells derived from h-iPSCs) and the phenotypic maintenance of h-iCSCs in vitro, h-iPSCs were cultured on matrigel-coated tissue culture plate (TCP) (10⁶ kPa), matrigel-coated polydimethylsiloxane (PDMS) 184 (1250 kPa), and matrigel-coated PDMS 527 (4 kPa) before they were differentiated to h-iCSCs. Immunofluorescence staining, quantitative real-time polymerase chain reaction (RT-qPCR), and western blot demonstrated that the stiffer substrate TCP promoted the h-iCSCs' differentiation from h-iPSCs. On the contrary, softer PDMS 527 was more effective to maintain the phenotype of h-iCSCs cultured in vitro. Finally, we cultured h-iCSCs on PDMS 527 until P3 and seeded them on a biomimetic collagen membrane to form the single-layer and multiple-layer bioengineered corneal stroma with high transparency properties and cell survival rate. In conclusion, the study is helpful for differentiating h-iPSCs to h-iCSCs and corneal tissue engineering by manipulating stiffness mechanobiology.

Microfluidic cell engineering on high-density microelectrode arrays for assessing structure-function relationships in living neuronal networks

Neuronal networks in dissociated culture combined with cell engineering technology offer a pivotal platform to constructively explore the relationship between structure and function in living neuronal networks. Here, we fabricated defined neuronal networks possessing a modular architecture on high-density microelectrode arrays (HD-MEAs), a state-of-the-art electrophysiological tool for recording neural activity with high spatial and temporal resolutions. We first established a surface coating protocol using a cell-permissive hydrogel to stably attach a polydimethylsiloxane microfluidic film on the HD-MEA. We then recorded the spontaneous neural activity of the engineered neuronal network, which revealed an important portrait of the engineered neuronal network-modular architecture enhances functional complexity by reducing the excessive neural correlation between spatially segregated modules. The results of this study highlight the impact of HD-MEA recordings combined with cell engineering technologies as a novel tool in neuroscience to constructively assess the structure-function relationships in neuronal networks.

[Methods of surgical reconstruction of the conjunctiva]

Reconstruction of the conjunctiva is required for restoration of damaged ocular surface and is an essential part of that process. Traumas, chemical and thermal burns, multiple surgical intervention can seriously damage the integrity of conjunctival tissue and promote the growth of fibrous tissue, scarring of contractures and their shortening, as well as other complications such as trichiasis, erosion and ulcers on the cornea. When a larger area is affected, there may not be enough donor tissue to replace the defect, in which case the tissue grafts are required to be large enough. Modern modifications of surgical techniques and the continued development of tissue engineering, as well as advancements in stem cell research offer promising novel alternatives for solution of those problems. This article reviews the existing surgical methods of conjunctival reconstruction.

The progress in techniques for culturing human limbal epithelial stem cells

In vitro culture of human limbal epithelial stem cells (hLESCs) is crucial to cell therapy in the treatment of limbal stem cell deficiency, a potentially vision-threatening disease that is characterized by persistent corneal epithelial defects and corneal epithelium conjunctivalization. Traditionally, hLESCs are cultivated based on either limbal tissue explants or single-cell suspensions in culture media containing xenogenous components, such as fetal bovine serum and murine 3T3 feeder cells. Plastic culture dishes and human amniotic membranes are classical growth substrates used in conventional hLESC culture systems. The past few decades have witnessed considerable progress and innovations in hLESC culture techniques to ensure a higher level of biosafety and lower immunogenicity for further cell treatment, including complete removal of xenogenous components from culture media, the application of human-derived feeder cells, and the development of novel scaffolds. Three-dimensional artificial niches and three-dimensional culture techniques have also been established to simulate the real microenvironment of limbal crypts for better cell outgrowth and proliferation. All these progresses ensure that in vitro cultured hLESCs are more adaptable to translational stem cell therapy for limbal stem cell deficiency.

Generation of Lens Progenitor Cells and Lentoid Bodies from Pluripotent Stem Cells: Novel Tools for Human Lens Development and Ocular Disease Etiology

In vitro differentiation of human pluripotent stem cells (hPSCs) into specialized tissues and organs represents a powerful approach to gain insight into those cellular and molecular mechanisms regulating human development. Although normal embryonic eye development is a complex process, generation of ocular organoids and specific ocular tissues from pluripotent stem cells has provided invaluable insights into the formation of lineage-committed progenitor cell populations, signal transduction pathways, and self-organization principles. This review provides a comprehensive summary of recent advances in generation of adenohypophyseal, olfactory, and lens placodes, lens progenitor cells and three-dimensional (3D) primitive lenses, "lentoid bodies", and "micro-lenses". These cells are produced alone or "community-grown" with other ocular tissues. Lentoid bodies/micro-lenses generated from human patients carrying mutations in crystallin genes demonstrate proof-of-principle that these cells are suitable for mechanistic studies of cataractogenesis. Taken together, current and emerging advanced in vitro differentiation methods pave the road to understand molecular mechanisms of cataract formation caused by the entire spectrum of mutations in DNA-binding regulatory genes, such as PAX6, SOX2, FOXE3, MAF, PITX3, and HSF4, individual crystallins, and other genes such as BFSP1, BFSP2, EPHA2, GJA3, GJA8, LIM2, MIP, and TDRD7 represented in human cataract patients.

Functional Evaluation of 3D Liver Models Labeled with Polysaccharide Functionalized Magnetic Nanoparticles

Establishing a rapid in vitro evaluation system for drug screening is essential for the development of new drugs. To reproduce tissues/organs with functions closer to living organisms, in vitro three-dimensional (3D) culture evaluation using microfabrication technology has been reported in recent years. Culture on patterned substrates with controlled hydrophilic and hydrophobic regions (Cell-able^TM) can create 3D liver models (miniature livers) with liver-specific Disse luminal structures and functions. MRI contrast agents are widely used as safe and minimally invasive diagnostic methods. We focused on anionic polysaccharide magnetic iron oxide nanoparticles (Resovist^®) and synthesized the four types of nanoparticle derivatives with different properties. Cationic nanoparticles (TMADM) can be used to label target cells in a short time and have been successfully visualized in vivo. In this study, we examined the morphology of various nanoparticles. The morphology of various nanoparticles showed relatively smooth-edged spherical shapes. As 3D liver models, we prepared primary hepatocyte-endothelial cell heterospheroids. The toxicity, CYP3A, and albumin secretory capacity were evaluated in the heterospheroids labeled with various nanoparticles. As the culture period progressed, the heterospheroids labeled with anionic and cationic nanoparticles showed lower liver function than non-labeled heterospheroids. In the future, there is a need to improve the method of creation of artificial 3D liver or to design a low-invasive MRI contrast agent to label the artificial 3D liver.

Applications of human organoids in the personalized treatment for digestive diseases

Digestive system diseases arise primarily through the interplay of genetic and environmental influences; there is an urgent need in elucidating the pathogenic mechanisms of these diseases and deploy personalized treatments. Traditional and long-established model systems rarely reproduce either tissue complexity or human physiology faithfully; these shortcomings underscore the need for better models. Organoids represent a promising research model, helping us gain a more profound understanding of the digestive organs; this model can also be used to provide patients with precise and individualized treatment and to build rapid in vitro test models for drug screening or gene/cell therapy, linking basic research with clinical treatment. Over the past few decades, the use of organoids has led to an advanced understanding of the composition of each digestive organ and has facilitated disease modeling, chemotherapy dose prediction, CRISPR-Cas9 genetic intervention, high-throughput drug screening, and identification of SARS-CoV-2 targets, pathogenic infection. However, the existing organoids of the digestive system mainly include the epithelial system. In order to reveal the pathogenic mechanism of digestive diseases, it is necessary to establish a completer and more physiological organoid model. Combining organoids and advanced techniques to test individualized treatments of different formulations is a promising approach that requires further exploration. This review highlights the advancements in the field of organoid technology from the perspectives of disease modeling and personalized therapy.

Customizable Collagen Vitrigel Membranes and Preliminary Results in Corneal Engineering

Corneal opacities are a leading cause of visual impairment that affect 4.2 million people annually. The current treatment is corneal transplantation, which is limited by tissue donor shortages. Corneal engineering aims to develop membranes that function as scaffolds in corneal cell transplantation. Here, we describe a method for producing transplantable corneal constructs based on a collagen vitrigel (CVM) membrane and corneal endothelial cells (CECs). The CVMs were produced using increasing volumes of collagen type I: 1X (2.8 μL/mm²), 2X, and 3X. The vitrification process was performed at 40% relative humidity (RH) and 40 °C using a matryoshka-like system consisting of a shaking-oven harboring a desiccator with a saturated K₂CO₃ solution. The CVMs were characterized via SEM microscopy, cell adherence, FTIR, and manipulation in an ex vivo model. A pilot transplantation of the CECs/CVM construct in rabbits was also carried out. The thickness of the CVMs was 3.65–7.2 µm. The transparency was superior to a human cornea (92.6% = 1X; 94% = 2X; 89.21% = 3X). SEM microscopy showed a homogenous surface and laminar organization. The cell concentration seeded over the CVM increased threefold with no significant difference between 1X, 2X, and 3X (p = 0.323). The 2X-CVM was suitable for surgical manipulation in the ex vivo model. Constructs using the CECs/2X-CVM promoted corneal transparency restoration.

Functional analysis of human brain endothelium using a microfluidic device integrating a cell culture insert

The blood-brain barrier (BBB) is a specialized brain endothelial barrier structure that regulates the highly selective transport of molecules under continuous blood flow. Recently, various types of BBB-on-chip models have been developed to mimic the microenvironmental cues that regulate the human BBB drug transport. However, technical difficulties in complex microfluidic systems limit their accessibility. Here, we propose a simple and easy-to-handle microfluidic device integrated with a cell culture insert to investigate the functional regulation of the human BBB endothelium in response to fluid shear stress (FSS). Using currently established immortalized human brain microvascular endothelial cells (HBMEC/ci18), we formed a BBB endothelial barrier without the substantial loss of barrier tightness under the relatively low range of FSS (0.1-1 dyn/cm2). Expression levels of key BBB transporters and receptors in the HBMEC/ci18 cells were dynamically changed in response to the FSS, and the effect of FSS reached a plateau around 1 dyn/cm2. Similar responses were observed in the primary HBMECs. Taking advantage of the detachable cell culture insert from the device, the drug efflux activity of P-glycoprotein (P-gp) was analyzed by the bidirectional permeability assay after the perfusion culture of cells. The data revealed that the FSS-stimulated BBB endothelium exhibited the 1.9-fold higher P-gp activity than that of the static culture control. Our microfluidic system coupling with the transwell model provides a functional human BBB endothelium with secured transporter activity, which is useful to investigate the bidirectional transport of drugs and its regulation by FSS.

HepG2-NIAS cells, a new subline of HepG2 cells that can enhance not only CYP3A4 activity but also expression of drug transporters and form bile canaliculus-like networks by the oxygenation culture via a collagen vitrigel membrane

We reported the enhanced liver-specific function and structure of HepG2 cells by the oxygenation culture via a collagen vitrigel membrane (CVM). The cells were conditioned in our laboratory for a long period, so their characteristics may change from the original HepG2 cells registered in RIKEN cell bank (RCB) with the number of 1648 (HepG2-RCB1648 cells). We named the conditioned HepG2-RCB1648 cells in our laboratory as HepG2-NIAS cells. Here, we clarified the features of HepG2 cells with three different culture histories by analyzing their morphology and viability, CYP3A4 activity, the potential to form bile canaliculus-like structures, and the expression of drug transporters. On plastic, HepG2-NIAS cells grew as a monolayer without the formation of large aggregates involving dead cells that were observed in HepG2-RCB1648 cells and HepG2-RCB1886 cells. In the oxygenation culture via a CVM, the CYP3A4 activity of HepG2-NIAS cells increased to almost half level in direct comparison to that of differentiated HepaRG cells cultured on a collagen-coated plate; however, that of HepG2-RCB1648 cells and HepG2-RCB1886 cells was almost not detected. HepG2-NIAS cells formed bile canaliculus-like networks in which fluorescein was accumulated after the exposure of fluorescein diacetate, although HepG2-RCB1648 cells and HepG2-RCB1886 cells did not possess the potential. Also, immunohistological observations revealed that HepG2-NIAS cells remarkably enhanced the expression of drug transporters, NTCP, OATP1B1, OATP1B3, BSEP, MDR1, MRP2, and BCRP. These results suggest that HepG2-NIAS cells are a new subline of HepG2 cells useful for drug development studies. HepG2-NIAS cells were registered in RCB with the number of 4679.

Towards organoid culture without Matrigel

Organoids-cellular aggregates derived from stem or progenitor cells that recapitulate organ function in miniature-are of growing interest in developmental biology and medicine. Organoids have been developed for organs and tissues such as the liver, gut, brain, and pancreas; they are used as organ surrogates to study a wide range of questions in basic and developmental biology, genetic disorders, and therapies. However, many organoids reported to date have been cultured in Matrigel, which is prepared from the secretion of Engelbreth-Holm-Swarm mouse sarcoma cells; Matrigel is complex and poorly defined. This complexity makes it difficult to elucidate Matrigel-specific factors governing organoid development. In this review, we discuss promising Matrigel-free methods for the generation and maintenance of organoids that use decellularized extracellular matrix (ECM), synthetic hydrogels, or gel-forming recombinant proteins.

Transplantation of human iPS cell-derived airway cells on vitrigel membrane into rat nasal cavity

The nasal mucosa functions as a frontline biological defense against various foreign substances and pathogens. Maintaining homeostasis of the nasal epithelium is necessary to promote good health. Nasal epithelia are constantly replaced under normal conditions. However, hereditary diseases, including primary ciliary dyskinesia and cystic fibrosis, can result in intractable dysfunction of the nasal mucosa. Since there is no treatment for this underlying condition, extrinsic manipulation is necessary to recover and maintain nasal epithelia in cases of hereditary diseases. In this study, we explored the use of airway epithelial cells (AECs), including multi-ciliated airway cells (MCACs), derived from human induced pluripotent stem cells (hiPSCs) on porcine atelocollagen vitrigel membranes, as a candidate of a therapeutic method for irreversible nasal epithelial disorders. To confirm the regenerative capacity of iPSC-derived AECs, we transplanted them into nasal cavities of nude rats. Although the transplanted cells were found within cysts isolated from the recipient nasal respiratory epithelia, they survived in some rats. Furthermore, the surviving cells were composed of multiple cell types similar to the human airway epithelia. The results could contribute to the development of novel transplantation-related technologies for the treatment of severe irreversible nasal epithelial disorders.

Bioengineering Approaches for the Advanced Organoid Research

Recent advances in 3D cell culture technology have enabled scientists to generate stem cell derived organoids that recapitulate the structural and functional characteristics of native organs. Current organoid technologies have been striding toward identifying the essential factors for controlling the processes involved in organoid development, including physical cues and biochemical signaling. There is a growing demand for engineering dynamic niches characterized by conditions that resemble in vivo organogenesis to generate reproducible and reliable organoids for various applications. Innovative biomaterial-based and advanced engineering-based approaches have been incorporated into conventional organoid culture methods to facilitate the development of organoid research. The recent advances in organoid engineering, including extracellular matrices and genetic modulation, are comprehensively summarized to pinpoint the parameters critical for organ-specific patterning. Moreover, perspective trends in developing tunable organoids in response to exogenous and endogenous cues are discussed for next-generation developmental studies, disease modeling, and therapeutics.

An overview of current alternative models in the context of ocular surface toxicity

The 21st century has seen a steadily increasing social awareness of animal suffering, with increased attention to ethical considerations. Developing new integrated approaches to testing and assessment (IATA) strategies is an Organisation for Economic Co-operation and Development (OECD) goal to reduce animal testing. Currently, there is a lack of alternative models to test for ocular surface toxicity (aside from irritation) in lieu of the Draize eye irritation test (OECD guideline No. 405) performed in rabbits. Five alternative in vitro or ex vivo methods have been validated to replace this reference test, but only in combination. However, pathologies like Toxicity-Induced Dry Eye (TIDE), cataract, glaucoma, and neuropathic pain can occur after exposure to a pharmaceutical product or chemical and therefore need to be anticipated. To do so, new models of lacrimal glands, lens, and neurons innervating epithelia are required. These models must take into account real-life exposure (dose, time, and tear film clearance). The scientific community is working hard to develop new, robust, alternative, in silico, and in vitro models, while attempting to balance ethics and availability of biological materials. This review provides a broad overview of the validated methods for analyzing ocular irritation and those still used by some industries, as well as promising models that need to be optimized according to the OECD. Finally, we give an overview of recently developed innovative models, which could become new tools in the evaluation of ocular surface toxicity within the scope of IATAs.

Generation of Tetrafluoroethylene-Propylene Elastomer-Based Microfluidic Devices for Drug Toxicity and Metabolism Studies

Polydimethylsiloxane (PDMS) is widely used to fabricate microfluidic organs-on-chips. Using these devices (PDMS-based devices), the mechanical microenvironment of living tissues, such as pulmonary respiration and intestinal peristalsis, can be reproduced in vitro. However, the use of PDMS-based devices in drug discovery research is limited because of their extensive absorption of drugs. In this study, we investigated the feasibility of the tetrafluoroethylene-propylene (FEPM) elastomer to fabricate a hepatocyte-on-a-chip (FEPM-based hepatocyte chip) with lower drug absorption. The FEPM-based hepatocyte chip expressed drug-metabolizing enzymes, drug-conjugating enzymes, and drug transporters. Also, it could produce human albumin. Although the metabolites of midazolam and bufuralol were hardly detected in the PDMS-based hepatocyte chip, they were detected abundantly in the FEPM-based hepatocyte chip. Finally, coumarin-induced hepatocyte cytotoxicity was less severe in the PDMS-based hepatocyte chip than in the FEPM-based hepatocyte chip, reflecting the different drug absorptions of the two chips. In conclusion, the FEPM-based hepatocyte chip could be a useful tool in drug discovery research, including drug metabolism and toxicity studies.

Condensed ECM-based nanofilms on highly permeable PET membranes for robust cell-to-cell communications with improved optical clarity

The properties of a semipermeable porous membrane, including pore size, pore density, and thickness, play a crucial role in creating a tissue interface in a microphysiological system (MPS) because it dictates multicellular interactions between different compartments. The small pore-sized membrane has been preferentially used in an MPS for stable cell adhesion and the formation of tissue barriers on the membrane. However, it limited the applicability of the MPS because of the hindered cell transmigration via sparse through-holes and the optical translucence caused by light scattering through pores. Thus, there remain unmet challenges to construct a compartmentalized MPS without those drawbacks. Here we report a submicrometer-thickness (∼500 nm) fibrous extracellular matrix (ECM) film selectively condensed on a large pore-sized track-etched (TE) membrane (10µm-pores) in an MPS device, which enables the generation of functional tissue barriers simultaneously achieving optical transparency, intercellular interactions, and transmigration of cells across the membrane. The condensed ECM fibers uniformly covering the surface and 10µm-pores of the TE membrane permitted sufficient surface areas where a monolayer of the human induced pluripotent stem cell-derived brain endothelial cells is formed in the MPS device. The functional maturation of the blood-brain barrier (BBB) was proficiently achieved due to astrocytic endfeet sheathing the brain endothelial cells through 10µm pores of the condensed-ECM-coated TE (cECMTE) membrane. We also demonstrated the extravasation of human metastatic breast tumor cells through the human BBB on the cECMTE membrane. Thus, the cECMTE membrane integrated with an MPS can be used as a versatile platform for studying various intercellular communications and migration, mimicking the physiological barriers of an organ compartment.

Application of Collagen I and IV in Bioengineering Transparent Ocular Tissues

Collagens represent a major group of structural proteins expressed in different tissues and display distinct and variable properties. Whilst collagens are non-transparent in the skin, they confer transparency in the cornea and crystalline lens of the eye. There are 28 types of collagen that all share a common triple helix structure yet differ in the composition of their α-chains leading to their different properties. The different organization of collagen fibers also contributes to the variable tissue morphology. The important ability of collagen to form different tissues has led to the exploration and application of collagen as a biomaterial. Collagen type I (Col-I) and collagen type IV (Col-IV) are the two primary collagens found in corneal and lens tissues. Both collagens provide structure and transparency, essential for a clear vision. This review explores the application of these two collagen types as novel biomaterials in bioengineering unique tissue that could be used to treat a variety of ocular diseases leading to blindness.

Growth factor delivery using extracellular matrix-mimicking substrates for musculoskeletal tissue engineering and repair

Therapeutic approaches for musculoskeletal tissue regeneration commonly employ growth factors (GFs) to influence neighboring cells and promote migration, proliferation, or differentiation. Despite promising results in preclinical models, the use of inductive biomacromolecules has achieved limited success in translation to the clinic. The field has yet to sufficiently overcome substantial hurdles such as poor spatiotemporal control and supraphysiological dosages, which commonly result in detrimental side effects. Physiological presentation and retention of biomacromolecules is regulated by the extracellular matrix (ECM), which acts as a reservoir for GFs via electrostatic interactions. Advances in the manipulation of extracellular proteins, decellularized tissues, and synthetic ECM-mimetic applications across a range of biomaterials have increased the ability to direct the presentation of GFs. Successful application of biomaterial technologies utilizing ECM mimetics increases tissue regeneration without the reliance on supraphysiological doses of inductive biomacromolecules. This review describes recent strategies to manage GF presentation using ECM-mimetic substrates for the regeneration of bone, cartilage, and muscle.

Collagen Vitrigel Membrane-Coated Nylon Line Prevents Stenosis After Conization of the Cervix Uteri

Cervical stenosis is a postoperative complication of conization for uterine cervical malignancy, but a standard method of preventing this complication has yet to be established. Collagen vitrigel is a collagen-based biomaterial that has antifibrotic and epithelization promoting actions. We evaluated the antistenotic effect of an indwelling collagen vitrigel membrane-coated nylon line (CVNL) after cervical conization in rabbits. In one group of rabbits, a CVNL was placed in the cervical canal after conization. In another group, a nylon line without a collagen coating was placed in the cervical canal after conization. The control group underwent cervical conization without placement of a device. The control (conization alone) and nylon (conization plus indwelling nylon line) groups exhibited cervical swelling. Rabbits in the CVNL group (cervical conization plus indwelling CVNL in the xerogel state) had a normal cervical surface. The cervical canal in the control group was enlarged and showed cystic changes attributed to cervical stenosis. The nylon group exhibited a trend toward cervical canal dilatation. In the CVNL group, the cervical canal was normal and did not show cystic dilatation. Fibrosis occurred to a lesser degree in the nylon group than in the control group, and the CVNL group exhibited minimal interstitial fibrosis. The control and nylon groups showed increased numbers of myofibroblasts in the regenerated cervix, but few myofibroblasts were observed in the CVNL group. Abundant collagen type III was observed in regenerated cervical tissue in the control and nylon groups but not in the CVNL group. The number of proliferative mesenchymal cells in the regenerated cervix was lowest in the CVNL group. The expressions of connective tissue growth factor (CTGF, a regulator of fibroblast growth and extracellular matrix secretion), extracellular signal-regulated protein kinases 1 and 2, and c-Jun N-terminal kinase (which are involved in the induction of CTGF by transforming growth factor-β) were lower in the CVNL group than in the control or nylon groups. This study describes an indwelling CVNL that prevents cervical stenosis and cystic changes after conization. These effects were likely mediated by inhibition of fibrosis, myofibroblast emergence, CTGF expression, and collagen type III deposition in regenerating cervix. Impact statement Collagen vitrigel is a high-density collagen material that promotes epithelization, inhibits fibrosis, and suppresses inflammation in regenerating tissue. We evaluated whether a collagen vitrigel membrane-coated nylon line would prevent cervical stenosis after conization in the rabbit. We found that an indwelling collagen vitrigel membrane-coated nylon line prevented cervical canal stenosis and cystic changes after cervical conization by inhibiting fibrosis, myofibroblast emergence, connective tissue growth factor expression, and collagen type III deposition in the regenerating cervix. Our device has potential as a new method of preventing cervical canal fibrosis and stenosis after conization for cervical cancer.

A new collagen scaffold for the improvement of corneal biomechanical properties in a rabbit model

Although collagen based materials are widely used in corneal tissue engineering with promising results. The usage of such materials for the improvement of corneal biomechanical properties is still unclear. In this study, we aimed to investigate a new Viscoll collagen-based membrane for the improvement of corneal biomechanical characteristics.The right eyes of 15 Chinchilla rabbits were implanted with the membrane via an intrastromal pocket, with the contralateral intact eyes as controls. At 7, 30, 90, and 180 days post-surgery, the rabbits underwent anterior segment optical coherence topography, clinical examination, and slit-lamp microscopy. Additionally, the corneal samples also underwent histological examination followed by the assessment of the biomechanical characteristics of four treated and non-treated corneas at 30, 90, and 180 days, including keratometry at 180 days, post operation. Data are presented as means ± confidence intervals with a 95% confidence level. All the operated corneas retained their transparency throughout the study. Implantation approximately doubled the central corneal thickness. Corneas became stronger by approximately 87% between 1 and 6 months after surgery (maximum fracture load, 13.3 ± 0.8 and 24.9 ± 1.4 N, respectively), and their elasticity increased by approximately 27% over the same time frame (maximum slope of the elastic region of the stress-strain curve, 11.5 ± 0.2 and 14.6 ± 1.4 N/mm respectively). We have thus proposed a new method to increase corneal thickness and strengthen the corneal tissues while preserving their transparency and demonstrated its safety and efficacy in a rabbit model over 6 months. This may be a suitable alternative to the existing corneal collagen crosslinking procedure.

Collagen I Based Enzymatically Degradable Membranes for Organ-on-a-Chip Barrier Models

Organs-on-chips are microphysiological in vitro models of human organs and tissues that rely on culturing cells in a well-controlled microenvironment that has been engineered to include key physical and biochemical parameters. Some systems contain a single perfused microfluidic channel or a patterned hydrogel, whereas more complex devices typically employ two or more microchannels that are separated by a porous membrane, simulating the tissue interface found in many organ subunits. The membranes are typically made of synthetic and biologically inert materials that are then coated with extracellular matrix (ECM) molecules to enhance cell attachment. However, the majority of the material remains foreign and fails to recapitulate the native microenvironment of the barrier tissue. Here, we study microfluidic devices that integrate a vitrified membrane made of collagen-I hydrogel (VC). The biocompatibility of this membrane was confirmed by growing a healthy population of stem cell derived endothelial cells (iPSC-EC) and immortalized retinal pigment epithelium (ARPE-19) on it and assessing morphology by fluorescence microscopy. Moreover, VC membranes were subjected to biochemical degradation using collagenase II. The effects of this biochemical degradation were characterized by the permeability changes to fluorescein. Topographical changes on the VC membrane after enzymatic degradation were also analyzed using scanning electron microscopy. Altogether, we present a dynamically bioresponsive membrane integrated in an organ-on-chip device with which disease-related ECM remodeling can be studied.

Second-generation lung-on-a-chip with an array of stretchable alveoli made with a biological membrane

The air-blood barrier with its complex architecture and dynamic environment is difficult to mimic in vitro. Lung-on-a-chips enable mimicking the breathing movements using a thin, stretchable PDMS membrane. However, they fail to reproduce the characteristic alveoli network as well as the biochemical and physical properties of the alveolar basal membrane. Here, we present a lung-on-a-chip, based on a biological, stretchable and biodegradable membrane made of collagen and elastin, that emulates an array of tiny alveoli with in vivo-like dimensions. This membrane outperforms PDMS in many ways: it does not absorb rhodamine-B, is biodegradable, is created by a simple method, and can easily be tuned to modify its thickness, composition and stiffness. The air-blood barrier is reconstituted using primary lung alveolar epithelial cells from patients and primary lung endothelial cells. Typical alveolar epithelial cell markers are expressed, while the barrier properties are preserved for up to 3 weeks.

Three-Dimensional in vitro Models of Healthy and Tumor Brain Microvasculature for Drug and Toxicity Screening

Tissue vascularization is essential for its oxygenation and the homogenous diffusion of nutrients. Cutting-edge studies are focusing on the vascularization of three-dimensional (3D) in vitro models of human tissues. The reproduction of the brain vasculature is particularly challenging as numerous cell types are involved. Moreover, the blood-brain barrier, which acts as a selective filter between the vascular system and the brain, is a complex structure to replicate. Nevertheless, tremendous advances have been made in recent years, and several works have proposed promising 3D in vitro models of the brain microvasculature. They incorporate cell co-cultures organized in 3D scaffolds, often consisting of components of the native extracellular matrix (ECM), to obtain a micro-environment similar to the in vivo physiological state. These models are particularly useful for studying adverse effects on the healthy brain vasculature. They provide insights into the molecular and cellular events involved in the pathological evolutions of this vasculature, such as those supporting the appearance of brain cancers. Glioblastoma multiform (GBM) is the most common form of brain cancer and one of the most vascularized solid tumors. It is characterized by a high aggressiveness and therapy resistance. Current conventional therapies are unable to prevent the high risk of recurrence of the disease. Most of the new drug candidates fail to pass clinical trials, despite the promising results shown in vitro. The conventional in vitro models are unable to efficiently reproduce the specific features of GBM tumors. Recent studies have indeed suggested a high heterogeneity of the tumor brain vasculature, with the coexistence of intact and leaky regions resulting from the constant remodeling of the ECM by glioma cells. In this review paper, after summarizing the advances in 3D in vitro brain vasculature models, we focus on the latest achievements in vascularized GBM modeling, and the potential applications for both healthy and pathological models as platforms for drug screening and toxicological assays. Particular attention will be paid to discuss the relevance of these models in terms of cell-cell, cell-ECM interactions, vascularization and permeability properties, which are crucial parameters for improving in vitro testing accuracy.

Exploiting CRISPR Cas9 in Three-Dimensional Stem Cell Cultures to Model Disease

Three-dimensional (3D) cell culture methods have been widely used on a range of cell types, including stem cells to modulate precisely the cellular biophysical and biochemical microenvironment and control various cell signaling cues. As a result, more in vivo-like microenvironments are recapitulated, particularly through the formation of multicellular spheroids and organoids, which may yield more valid mechanisms of disease. Recently, genome-engineering tools such as CRISPR Cas9 have expanded the repertoire of techniques to control gene expression, which complements external signaling cues with intracellular control elements. As a result, the combination of CRISPR Cas9 and 3D cell culture methods enhance our understanding of the molecular mechanisms underpinning several disease phenotypes and may lead to developing new therapeutics that may advance more quickly and effectively into clinical candidates. In addition, using CRISPR Cas9 tools to rescue genes brings us one step closer to its use as a gene therapy tool for various degenerative diseases. Herein, we provide an overview of bridging of CRISPR Cas9 genome editing with 3D spheroid and organoid cell culture to better understand disease progression in both patient and non-patient derived cells, and we address potential remaining gaps that must be overcome to gain widespread use.

Multifunctional synthetic Bowman's membrane-stromal biomimetic for corneal reconstruction

As the outermost layer of the eye, the cornea is vulnerable to physical and chemical trauma, which can result in loss of transparency and lead to corneal blindness. Given the global corneal donor shortage, there is an unmet need for biocompatible corneal substitutes that have high transparency, mechanical integrity and regenerative potentials. Herein we engineered a dual-layered collagen vitrigel containing biomimetic synthetic Bowman's membrane (sBM) and stromal layer (sSL). The sBM supported rapid epithelial cell migration, maturation and multilayer formation, and the sSL containing tissue-derived extracellular matrix (ECM) microparticles presented a biomimetic lamellar ultrastructure mimicking the native corneal stroma. The incorporation of tissue-derived microparticles in sSL layer significantly enhanced the mechanical properties and suturability of the implant without compromising the transparency after vitrification. In vivo performance of the vitrigel in a rabbit anterior lamellar keratoplasty model showed full re-epithelialization within 14 days and integration of the vitrigel with the host tissue stroma by day 30. The migrated epithelial cells formed functional multilayer with limbal stem cell marker p63 K14 expressed in the lower layer, epithelial marker K3 and K12 expressed through the layers and tight junction protein ZO-1 expressed by the multilayers. Corneal fibroblasts migrated into the implants to facilitate host/implant integration and corneal stromal regeneration. In summary, these results suggest that the multi-functional layers of this novel collagen vitrigel exhibited significantly improved biological performance as corneal substitute by harnessing a fast re-epithelialization and stromal regeneration potential.

Multi-laboratory Validation Study of the Vitrigel-Eye Irritancy Test Method as an Alternative to In Vivo Eye Irritation Testing

Collagen vitrigel membranes (CVMs) comprising high-density collagen fibrils equivalent to in vivo connective tissues have been widely used in cell culture applications. A human corneal epithelium (hCE) model was previously developed by the Takezawa group, by culturing HCE-T cells (derived from hCE cells) on a CVM scaffold in a chamber that provided an air–liquid interface culture system. This hCE model was used to establish a new test method, known as the Vitrigel-Eye Irritancy Test (Vitrigel-EIT) method, which can be used to estimate the ocular irritation potential of test chemicals by analysing relative changes in transepithelial electrical resistance (TEER) over time. The current study was conducted in order to assess the reliability and relevance of the Vitrigel-EIT method at three participating laboratories by determining the method’s within-laboratory reproducibility and between-laboratory reproducibility, as well as its capacity for distinguishing non-irritants from irritants in a bottom-up approach. The initial test sample size was found to be too low to evaluate the predictive capacity of the test method, and so it was evaluated with additional in-house data for a total of 93 test chemicals. The results showed 80–100% within-laboratory reproducibility and an excellent between-laboratory reproducibility that met the acceptance criteria of 80%. However, the method’s predictive capacity for distinguishing non-irritants (test chemicals not requiring classification and labelling for eye irritation or serious eye damage, i.e. United Nations Globally Harmonised System of Classification and Labelling of Chemicals (GHS) No Category) from irritants (GHS Categories 1 and 2) in a bottom-up approach was unacceptable because of false negative rates as high as 16.7%. After considerable review of the data with a view to using the method for regulatory purposes, it was determined that a more defined applicability domain, excluding test chemical solutions with a pH of 5 or less and solid test chemicals, improved the false negative rate to 4.2%. These results suggested that, within this carefully defined applicability domain, the Vitrigel-EIT method could be a useful alternative for distinguishing test chemicals that are ocular non-irritants from those that are irritants as part of a bottom-up approach.

Establishment of a multilayered 3D cellular model of the retinal-blood barrier

Retinal disorders are leading causes of blindness. Still, treatment strategies are limited and the challenging anatomical barriers of the eye limit the evaluation and development of new therapeutics. Among these layers of barriers is the blood-retinal barrier, which separates the retina from the choroid by the Bruch's membrane. This work aimed to establish a 3D cellular model that recapitulates barrier properties of the BRB and diffusion through the vitreous, the main barriers encountered upon intravitreal injection. Several parameters were evaluated namely co-culture time of ARPE-19 and HUVECs and different biomaterial compositions of hydrogels to better mimic the human vitreous. The developed vitreous mimic has viscoelastic properties similar to human vitreous. Co-culture of human retinal and endothelial cells showed increased transepithelial resistance with longer co-culture times concomitant with reduced permeability to FITC-dextran 40 kDa. The proposed models lay the foundation of a platform for faster assessment of a large number of samples and without the use of animals.

Adipose-derived stromal/stem cells improve epidermal homeostasis

Wound healing is regulated by complex interactions between the keratinocytes and other cell types including fibroblasts. Recently, adipose-derived mesenchymal stromal/stem cells (ASCs) have been reported to influence wound healing positively via paracrine involvement. However, their roles in keratinocytes are still obscure. Therefore, investigation of the precise effects of ASCs on keratinocytes in an in vitro culture system is required. Our recent data indicate that the epidermal equivalents became thicker on a collagen vitrigel membrane co-cultured with human ASCs (hASCs). Co-culturing the human primary epidermal keratinocytes (HPEK) with hASCs on a collagen vitrigel membrane enhanced their abilities for cell proliferation and adhesion to the membrane but suppressed their differentiation suggesting that hASCs could maintain the undifferentiated status of HPEK. Contrarily, the effects of co-culture using polyethylene terephthalate or polycarbonate membranes for HPEK were completely opposite. These differences may depend on the protein permeability and/or structure of the membrane. Taken together, our data demonstrate that hASCs could be used as a substitute for fibroblasts in skin wound repair, aesthetic medicine, or tissue engineering. It is also important to note that a co-culture system using the collagen vitrigel membrane allows better understanding of the interactions between the keratinocytes and ASCs.

Engineered materials for organoid systems

Organoids are 3D cell culture systems that mimic some of the structural and functional characteristics of an organ. Organoid cultures provide the opportunity to study organ-level biology in models that mimic human physiology more closely than 2D cell culture systems or non-primate animal models. Many organoid cultures rely on decellularized extracellular matrices as scaffolds, which are often poorly chemically defined and allow only limited tunability and reproducibility. By contrast, the biochemical and biophysical properties of engineered matrices can be tuned and optimized to support the development and maturation of organoid cultures. In this Review, we highlight how key cell-matrix interactions guiding stem-cell decisions can inform the design of biomaterials for the reproducible generation and control of organoid cultures. We survey natural, synthetic and protein-engineered hydrogels for their applicability to different organoid systems and discuss biochemical and mechanical material properties relevant for organoid formation. Finally, dynamic and cell-responsive material systems are investigated for their future use in organoid research.

Transplantation of multiciliated airway cells derived from human iPS cells using an artificial tracheal patch into rat trachea

Tracheal resection is often performed for malignant tumours, congenital anomalies, inflammatory lesions, and traumatic injuries. There is no consensus on the best approach for the restoration of tracheal functionality in patients with tracheal defects. Artificial grafts made of polypropylene and collagen sponge have been clinically used by our group. However, 2 months are required to achieve adequate epithelialization of the grafts in humans. This study aimed to investigate the feasibility of transplantation therapy using an artificial trachea with human-induced pluripotent stem cell (hiPSC)-derived multiciliated airway cells (hiPSC-MCACs). Collagen vitrigel membrane, a biocompatible and absorbable material, was used as a scaffold to cover the artificial trachea with hiPSC-MCACs. Analyses of hiPSC-MCACs on collagen vitrigel membrane were performed by immunocytochemistry and electron microscopy and by assessing ciliary beat frequency. Along with the artificial trachea, hiPSC-MCACs were transplanted into surgically created tracheal defects of immunodeficient rats. The survival of transplanted cells was histologically evaluated at 1 and 2 weeks after the transplantation. The hiPSC-MCACs exhibited motile cilia on collagen vitrigel membrane. The surviving hiPSC-MCACs were observed in the endotracheal epithelium of the tracheal defect at 1 and 2 weeks after transplantation. These results suggest that hiPSC-MCAC is a useful candidate for tracheal reconstruction.

A high-density collagen xerogel thread prevents the progression of peritoneal fibrosis

An inserted high-density collagen xerogel thread prevents pathological fibrosis through the inhibition of inflammation and stromal cell proliferation in the peritoneum.

In vivo characterization of connective tissue remodeling using infrared photoacoustic spectra

Premature cervical remodeling is a critical precursor of spontaneous preterm birth, and the remodeling process is characterized by an increase in tissue hydration. Nevertheless, current clinical measurements of cervical remodeling are subjective and detect only late events, such as cervical effacement and dilation. Here, we present a photoacoustic endoscope that can quantify tissue hydration by measuring near-infrared cervical spectra. We quantify the water contents of tissue-mimicking hydrogel phantoms as an analog of cervical connective tissue. Applying this method to pregnant women in vivo, we observed an increase in the water content of the cervix throughout pregnancy. The application of this technique in maternal healthcare may advance our understanding of cervical remodeling and provide a sensitive method for predicting preterm birth.

Cyclodextrin Modulated Type I Collagen Self-Assembly to Engineer Biomimetic Cornea Implants

Collagen-rich tissues in the cornea exhibit unique and highly organized extracellular matrix ultrastructures, which contribute to its high load-bearing capacity and light transmittance. Corneal collagen fibrils are controlled during development by small leucine-rich proteoglycans (SLRPs) that regulate the fibril diameter and spacing in order to achieve the unique optical transparency. Cyclodextrins (CDs) of varying size and chemical functionality for their ability to regulate collagen assembly during vitrification process are screened in order to create biosynthetic materials that mimic the native cornea structure. Addition of βCD to collagen vitrigels produces materials with aligned fibers and lamellae similar to native cornea, resulting in mechanically robust and transparent materials. Biochemistry analysis revealed that CD interacts with hydrophobic amino acids in collagen to influence assembly and fibril organization. To translate the self-assembled collagen materials for cornea reconstruction, custom molds for gelation and vitrification are engineered to create βCD/Col implants with curvature matching that of the cornea. Acellular βCD/Col materials are implanted in a rabbit partial keratoplasty model with interrupted sutures. The implants demonstrate tissue integration and support re-epithelialization. Therefore, the addition of CD molecules regulates collagen self-assembly and provides a simple process to engineer corneal mimetic substitutes with advanced structural and functional properties.

A Cell Culture Approach to Optimized Human Corneal Endothelial Cell Function

Purpose

Cell-based therapies to replace corneal endothelium depend on culture methods to optimize human corneal endothelial cell (HCEC) function and minimize endothelial-mesenchymal transition (EnMT). Here we explore contribution of low-mitogenic media on stabilization of phenotypes in vitro that mimic those of HCECs in vivo.

Methods

HCECs were isolated from cadaveric donor corneas and expanded in vitro, comparing continuous presence of exogenous growth factors (“proliferative media”) to media without those factors (“stabilizing media”). Identity based on canonical morphology and expression of surface marker CD56, and function based on formation of tight junction barriers measured by trans-endothelial electrical resistance assays (TEER) were assessed.

Results

Primary HCECs cultured in proliferative media underwent EnMT after three to four passages, becoming increasingly fibroblastic. Stabilizing the cells before each passage by switching them to a media low in mitogenic growth factors and serum preserved canonical morphology and yielded a higher number of cells. HCECs cultured in stabilizing media increased both expression of the identity marker CD56 and also tight junction monolayer integrity compared to cells cultured without stabilization.

Conclusions

HCECs isolated from donor corneas and expanded in vitro with a low-mitogenic media stabilizing step before each passage demonstrate more canonical structural and functional features and defer EnMT, increasing the number of passages and total canonical cell yield. This approach may facilitate development of HCEC-based cell therapies.

Tissue-Engineered Neo-Urinary Conduit from Decellularized Trachea

Decellularized tissues have been increasingly popular for constructing scaffolds for tissue engineering applications due to their beneficial biological compositions and mechanical properties. It is therefore natural to consider decellularized trachea for construction of tissue-engineered trachea, as well as other tubular organs. A Neo-Urinary Conduit (NUC) is such a tubular organ that works as a passage for urine removal in bladder cancer patients who need a urinary diversion after their diseased bladder is removed. In this study, we report our findings on the feasibility of using a decellularized trachea for NUC applications. As a NUC scaffold, decellularized trachea provides benefits of having not only naturally occurring biological components but also having sufficient mechanical properties and structural integrity. We, therefore, decellularized rabbit trachea, evaluated its mechanical performance, and investigated its ability to support in vitro growth of human smooth muscle cells (hSMCs) and human urothelial cells (hUCs). The decellularized trachea had appropriate biomechanical properties with ultimate tensile strength of ∼0.34 MPa in longitudinal direction and ∼1.0 MPa in circumferential direction and resisted a radial burst pressure of >155 mm Hg. Cell morphology study by scanning electron microscopy further showed that hUCs grown on decellularized trachea adopted a typical flatten and interconnected network structure in the lumen of the scaffold, while they formed a round spherical shape and did not spread on the outer surfaces. SMCs, on the other hand, spread well throughout the scaffold. The gene expression analysis by real time quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence studies further confirmed scaffold's ability to support long-term growth of hSMCs. Since uroepithelium has been shown to regenerate itself over time in vivo, these findings suggest that it is possible to construct a NUC from decellularized trachea without any preseeding of UCs. In future, we plan to translate decellularized trachea in a preclinical animal model and evaluate its biological performance.

Fabrication of a Corneal Model Composed of Corneal Epithelial and Endothelial Cells via a Collagen Vitrigel Membrane Functioned as an Acellular Stroma and Its Application to the Corneal Permeability Test of Chemicals

A collagen vitrigel membrane (CVM) we developed can function as both a scaffold for cells and a pathway for chemicals. To extrapolate the corneal permeability of chemicals in vivo, we proposed six corneal models using the CVM. Thin and thick CVMs were used as models for Bowman's membrane (BM) and an acellular stroma (AS), respectively. Models for a corneal epithelium (CEpi), a CEpi-AS, a CEpi-endothelium (Endo), and a CEpi-AS-Endo were fabricated by culturing corneal epithelial cells and/or corneal endothelial cells on the surface of CVMs. Subsequently, the permeability coefficient (P_app) value of each model was calculated using five chemicals with different molecular radii; cyanocobalamin and four fluorescein isothiocyanate-dextrans (FD) (FD-4, FD-10, FD-20, and FD-40). The slopes of P_app versus molecular radii of those chemicals in the both BM and AS models were almost similar to data using an excised rabbit corneal stroma. The ratios of P_app values in models for BM, CEpi, and CEpi-Endo against those in data using an excised rabbit cornea were calculated as 75.4-fold, 6.4-fold, and 4.5-fold for FD-4, and 38.7-fold, 10.0-fold, and 4.2-fold for FD-10, respectively. Similarly, those in models for AS, CEpi-AS, and CEpi-AS-Endo were calculated as 26.1-fold, 2.5-fold, and 0.6-fold for FD-4, and 26.1-fold, 1.5-fold, and 0.6-fold for FD-10, respectively. These results suggest that the CEpi-AS-Endo model with both the barrier function of corneal cell layers and the diffusion capacity of chemicals in thick CVM is most appropriate for extrapolating the corneal permeability of chemicals in vivo.

Engineered basement membranes: from in vivo considerations to cell-based assays

Engineered basement membranes are required to mimic in vivo properties within cell-based assays.