Influence of extracellular matrix proteins and substratum topography on corneal epithelial cell alignment and migration

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Three-Dimensional Printed Design of Antibiotic-Releasing Esophageal Patches for Antimicrobial Activity Prevention

Pharyngoesophageal defects can cause exposure to various bacterial flora and severe inflammation. We fabricated a biodegradable polycaprolactone (PCL) patch composed of both thin film and three-dimensional (3D) printed lattice, and then investigated the efficacy of pharyngoesophageal reconstruction by using 3D printed antibiotic-releasing PCL patches that inhibited early inflammation by sustained tetracycline (TCN) release from both thin PCL films and printed rods implanted in esophageal partial defects. PCL was 3D printed in lattice form on a presolution casted PCL thin film at ∼100 μm resolution. TCN was loaded onto the PCL-printed patches by 3D printing a mixture of TCN and PCL particles melted at 100°C. TCN exhibited sustained release in vitro for over 1 month. After loading TCN, the patches showed decreased tensile strength and Young's modulus, and less than 20% TCN was slowly released from the 2.5% TCN-loaded PCL patches over 150 days. Cytotoxicity tests of extract solutions from patch samples demonstrated excellent in vitro cell compatibility. Antibiotic-releasing PCL patches were then transplanted into partial esophageal defects in rats. Microcomputed tomography analysis revealed no leak of orally injected contrast agent in the entire esophagus. Tissue remodeling was examined through histological responses of M1 and M2 macrophages. In particular, the 1% and 3% TCN patch groups exhibited significant muscle layer regeneration by desmin immunostaining. Further histological and immunofluorescence analyses revealed that the 1% and 3% TCN patch groups exhibited the best esophageal regeneration according to reepithelialization, neovascularization, and elastin texture around the implanted sites. Our antibiotic-releasing patch successfully consolidates the regenerative potential of esophageal muscle and mucosa and the antibacterial activity of TCN for 3D esophageal reconstruction. Impact statement Anastomosis site leakage and necrosis after pharyngoesophageal transplantation inevitably causes mortality because the mediastinum and neck compartments become contaminated. Herein, we present antibiotic-releasing pharyngoesophageal patch that prevents saliva leakage and has an antimicrobial effect. We have demonstrated antibiotic release profile and mechanical properties for esophageal transplantation. Upon esophageal transplantation of antibiotic-releasing polycaprolactone patches, antimicrobial effects and muscle regeneration around the graft sites were clearly identified in the group containing 1% and 3% of tetracycline. The esophageal graft led to the remarkable recovery throughout reepithelialization, neovascularization, and elastin texture of around the implanted sites. We believe that current system is capable of various applications that require antibacterial in vivo.

Transduction of cell and matrix geometric cues by the actin cytoskeleton

Engineered culture substrates have proven invaluable for investigating the role of cell and extracellular matrix geometry in governing cell behavior. While the mechanisms relating geometry to phenotype are complex, it is clear that the actin cytoskeleton plays a key role in integrating geometric inputs and transducing these cues into intracellular signals that drive downstream biology. Here, we review recent progress in elucidating the role of the cell and matrix geometry in regulating actin cytoskeletal architecture and mechanics. We address new developments in traditional two-dimensional culture paradigms and discuss efforts to extend these advances to three-dimensional systems, ranging from nanotextured surfaces to microtopographical systems (e.g. channels) to fully three-dimensional matrices.

Engineering topography: Effects on corneal cell behavior and integration into corneal tissue engineering

Cell-material interactions are important to tissue engineering. Inspired by the natural topographic structures on the extracellular matrix, a growing number of studies have integrated engineering topography into investigations of cell behavior on biomaterials. Engineering topography has a significant influence on cell behaviors. These cell-topography interactions play an important role in regenerative medicine and tissue engineering. Similarly, cell-topography interactions are important to corneal reconstruction and regeneration. In this review, we primarily summarized the effects of topographic cues on the behaviors of corneal cells, including cell morphology, adhesion, migration, and proliferation. Furthermore, the integration of engineering surface topography into corneal tissue engineering was also discussed.

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.

Biomaterials for corneal bioengineering

Corneal transplantation is an important surgical treatment for many common corneal diseases. However, a worldwide shortage of tissue from suitable corneal donors has meant that many people are not able to receive sight-restoring operations. In addition, rejection is a major cause of corneal transplant failure. Bioengineering corneal tissue has recently gained widespread attention. In order to facilitate corneal regeneration, a range of materials is currently being investigated. The ideal substrate requires sufficient tectonic durability, biocompatibility with cultured cellular elements, transparency, and perhaps biodegradability and clinical compliance. This review considers the anatomy and function of the native cornea as a precursor to evaluating a variety of biomaterials for corneal regeneration including key characteristics for optimal material form and function. The integration of appropriate cells with the most appropriate biomaterials is also discussed. Taken together, the information provided offers insight into the requirements for fabricating synthetic and semisynthetic corneas for in vitro modeling of tissue development and disease, pharmaceutical screening, and in vivo application for regenerative medicine.

Engineering Approaches to Study Cellular Decision Making

In their native environment, cells are immersed in a complex milieu of biochemical and biophysical cues. These cues may include growth factors, the extracellular matrix, cell-cell contacts, stiffness, and topography, and they are responsible for regulating cellular behaviors such as adhesion, proliferation, migration, apoptosis, and differentiation. The decision-making process used to convert these extracellular inputs into actions is highly complex and sensitive to changes both in the type of individual cue (e.g., growth factor dose/level, timing) and in how these individual cues are combined (e.g., homotypic/heterotypic combinations). In this review, we highlight recent advances in the development of engineering-based approaches to study the cellular decision-making process. Specifically, we discuss the use of biomaterial platforms that enable controlled and tailored delivery of individual and combined cues, as well as the application of computational modeling to analyses of the complex cellular decision-making networks.

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.

Biomechanical relationships between the corneal endothelium and Descemet's membrane

The posterior face of the cornea consists of the corneal endothelium, a monolayer of cuboidal cells that secrete and attach to Descemet's membrane, an exaggerated basement membrane. Dysfunction of the endothelium compromises the barrier and pump functions of this layer that maintain corneal deturgesence. A large number of corneal endothelial dystrophies feature irregularities in Descemet's membrane, suggesting that cells create and respond to the biophysical signals offered by their underlying matrix. This review provides an overview of the bidirectional relationship between Descemet's membrane and the corneal endothelium. Several experimental methods have characterized a richly topographic and compliant biophysical microenvironment presented by the posterior surface of Descemet's membrane, as well as the ultrastructure and composition of the membrane as it builds during a lifetime. We highlight the signaling pathways involved in the mechanotransduction of biophysical cues that influence cell behavior. We present the specific example of Fuchs' corneal endothelial dystrophy as a condition in which a dysregulated Descemet's membrane may influence the progression of disease. Finally, we discuss some disease models and regenerative strategies that may facilitate improved treatments for corneal dystrophies.

Patterning Biomaterials for the Spatiotemporal Delivery of Bioactive Molecules

The aim of tissue engineering is to promote the repair of functional tissues. For decades, the combined use of biomaterials, growth factors (GFs), and stem cells has been the base of several regeneration strategies. Among these, biomimicry emerged as a robust strategy to efficiently address this clinical challenge. Biomimetic materials, able to recapitulate the composition and architecture of the extracellular matrix, are the materials of choice, for their biocompatibility and higher rate of efficacy. In addition, it has become increasingly clear that restoring the complex biochemical environment of the target tissue is crucial for its regeneration. Toward this aim, the combination of scaffolds and GFs is required. The advent of nanotechnology significantly impacted the field of tissue engineering by providing new ways to reproduce the complex spatial and temporal biochemical patterns of tissues. This review will present the most recent approaches to finely control the spatiotemporal release of bioactive molecules for various tissue engineering applications.

Effect of Stratification on Surface Properties of Corneal Epithelial Cells

PURPOSE

The purpose of this study was to determine the influence of mucin expression in an immortalized human corneal epithelial cell line (hTCEpi) on the surface properties of cells, such as wettability, contact angle, and surface heterogeneity.

METHODS

hTCEpi cells were cultured to confluence in serum-free medium. The medium was then replaced by stratification medium to induce mucin biosynthesis. The mucin expression profile was analyzed using quantitative PCR and Western blotting. Contact angles were measured using a two-immiscible liquid method, and contact angle hysteresis was evaluated by tilting the apparatus and recording advancing and receding contact angles. The spatial distribution of mucins was evaluated with fluorescently labeled lectin.

RESULTS

hTCEpi cells expressed the three main ocular mucins (MUC1, MUC4, and MUC16) with a maximum between days 1 and 3 of the stratification process. Upon stratification, cells caused a very significant increase in contact angle hysteresis, suggesting the development of spatially discrete and heterogeneously distributed surface features, defined by topography and/or chemical functionality. Although atomic force microscopy measurements showed no formation of appreciable topographic features on the surface of the cells, we observed a significant increase in surface chemical heterogeneity.

CONCLUSIONS

The surface chemical heterogeneity of the corneal epithelium may influence the dynamic behavior of tear film by "pinning" the contact line between the cellular surface and aqueous tear film. Engineering the surface properties of corneal epithelium could potentially lead to novel treatments in dry eye disease.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Cell response on the biomimetic scaffold of silicon nano- and micro-topography

Silicon scaffolds were synthesized in a low-pressure furnace via a vapor–liquid–solid (VLS) mechanism.

Biomimetic stochastic topography and electric fields synergistically enhance directional migration of corneal epithelial cells in a MMP-3-dependent manner

Directed migration of corneal epithelial cells (CECs) is critical for maintenance of corneal homeostasis as well as wound healing. Soluble cytoactive factors and the intrinsic chemical attributes of the underlying extracellular matrix (ECM) participate in stimulating and directing migration. The central importance of the intrinsic biophysical attributes of the microenvironment of the cell in modulating an array of fundamental epithelial behaviors including migration has been widely documented. Among the best measures of these attributes are the intrinsic topography and stiffness of the ECM and electric fields (EFs). How cells integrate these multiple simultaneous inputs is not well understood. Here, we present a method that combines the use of (i) topographically patterned substrates (mean pore diameter 800nm) possessing features that approximate those found in the native corneal basement membrane; and (ii) EFs (0-150mVmm(-1)) mimicking those at corneal epithelial wounds that the cells experience in vivo. We found that topographic cues and EFs synergistically regulated directional migration of human CECs and that this was associated with upregulation of matrix metalloproteinase-3 (MMP3). MMP3 expression and activity were significantly elevated with 150mVmm(-1) applied-EF while MMP2/9 remained unaltered. MMP3 expression was elevated in cells cultured on patterned surfaces against planar surfaces. The highest single-cell migration rate was observed with 150mVmm(-1) applied EF on patterned and planar surfaces. When cultured as a confluent sheet, EFs induced collective cell migration on stochastically patterned surfaces compared with dissociated single-cell migration on planar surfaces. These results suggest significant interaction of biophysical cues in regulating cell behaviors and will help define design parameters for corneal prosthetics and help to better understand corneal wound healing.

Strategies for faster detachment of corneal cell sheet using micropatterned thermoresponsive matrices

Direct write assembly of parallel patterns of gelatin–poly(N-isopropylacrylamide) hybrids serve as suitable thermoresponsive material to develop patterned cell sheets of functional keratocytes for constructing a bioequivalent of corneal stroma.

Involvement of YAP, TAZ and HSP90 in contact guidance and intercellular junction formation in corneal epithelial cells

The extracellular environment possesses a rich milieu of biophysical and biochemical signaling cues that are simultaneously integrated by cells and influence cellular phenotype. Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (WWTR1; TAZ), two important signaling molecules of the Hippo pathway, have been recently implicated as nuclear relays of cytoskeletal changes mediated by substratum rigidity and topography. These proteins intersect with other important intracellular signaling pathways (e.g. Wnt and TGFβ). In the cornea, epithelial cells adhere to the stroma through a 3-dimensional topography-rich basement membrane, with features in the nano-submicron size-scale that are capable of profoundly modulating a wide range of fundamental cell behaviors. The influences of substratum-topography, YAP/TAZ knockdown, and HSP90 inhibition on cell morphology, YAP/TAZ localization, and the expression of TGFβ2 and CTGF, were investigated. The results demonstrate (a) that knockdown of TAZ enhances contact guidance in a YAP dependent manner, (b) that CTGF is predominantly regulated by YAP and not TAZ, and (c) that TGFβ2 is regulated by both YAP and TAZ in these cells. Additionally, inhibition of HSP90 resulted in nuclear localization and subsequent transcriptional-activation of YAP, formation of cell-cell junctions and co-localization of E-cadherin and β-catenin at adherens junctions. Results presented in this study reflect the complexities underlying the molecular relationships between the cytoskeleton, growth factors, heat shock proteins, and co-activators of transcription that impact mechanotransduction. The data reveal the importance of YAP/TAZ on the cell behaviors, and gene and protein expression.

Mechanism of induction of fibroblast to corneal endothelial cell

OBJECTIVE

To explore mechanism of nduction of fibroblast to corneal endothelial cell.

METHODS

Rabbit conjunctiva fibroblasts were used as feeder cells, rabbit oral mucosa epithelial cells were used as seed cells, and human denuded amniotic membrane was used as carrier to establish tissue engineering corneal endothelium. The transformation effect was observed.

RESULTS

As concentration of mitomycin C increased, cell survival rate gradually decreased, cell proliferation was obviously inhibited when concentration≥25 μg/mL; 5 days after being treated by 5 μg/mL mitomycin C, cell body was enlarged and extended without cell fusion, however after being treated by 0.5 μg/mL mitomycin C, cell body was significantly proliferated and gradually fused; after 3 weeks of culture, stratified epithelium appeared on rabbit oral mucosa epithelial cells, differentiation layers were 4-5 and were well differentiated, the morphology was similar to corneal endothelial cells; Under electron microscope, surface layer of cells were polygonal, tightly connected to another with microvilli on the border, there was hemidesmosome between basal cells and human denuded amniotic membrane.

CONCLUSIONS

Fibroblast cells have the potential of multi-directional differentiation, effective induction can promote emergence of intercellular desmosomes between seed cells and emergence of epithelial surface microvilli, and differentiate to the corneal endothelial cell. However, clinical application still needs more research and safety evaluation.

Regulation of tissue fibrosis by the biomechanical environment

The biomechanical environment plays a fundamental role in embryonic development, tissue maintenance, and pathogenesis. Mechanical forces play particularly important roles in the regulation of connective tissues including not only bone and cartilage but also the interstitial tissues of most organs. In vivo studies have correlated changes in mechanical load to modulation of the extracellular matrix and have indicated that increased mechanical force contributes to the enhanced expression and deposition of extracellular matrix components or fibrosis. Pathological fibrosis contributes to dysfunction of many organ systems. A variety of in vitro models have been utilized to evaluate the effects of mechanical force on extracellular matrix-producing cells. In general, application of mechanical stretch, fluid flow, and compression results in increased expression of extracellular matrix components. More recent studies have indicated that tissue rigidity also provides profibrotic signals to cells. The mechanisms whereby cells detect mechanical signals and transduce them into biochemical responses have received considerable attention. Cell surface receptors for extracellular matrix components and intracellular signaling pathways are instrumental in the mechanotransduction process. Understanding how mechanical signals are transmitted from the microenvironment will identify novel therapeutic targets for fibrosis and other pathological conditions.