Human stem cell-based retina on chip as new translational model for validation of AAV retinal gene therapy vectors.

Gene therapies using adeno-associated viruses (AAVs) are among the most promising strategies to treat or even cure hereditary and acquired retinal diseases. However, the development of new efficient AAV vectors is slow and costly, largely because of the lack of suitable non-clinical models. By faithfully recreating structure and function of human tissues, human induced pluripotent stem cell (iPSC)-derived retinal organoids could become an essential part of the test cascade addressing translational aspects. Organ-on-chip (OoC) technology further provides the capability to recapitulate microphysiological tissue environments as well as a precise control over structural and temporal parameters. By employing our recently developed retina on chip that merges organoid and OoC technology, we analyzed the efficacy, kinetics, and cell tropism of seven first- and second-generation AAV vectors. The presented data demonstrate the potential of iPSC-based OoC models as the next generation of screening platforms for future gene therapeutic studies.

Integration of Electrospun Membranes into Low-Absorption Thermoplastic Organ-on-Chip.

In recent years, organ-on-chip (OoC) systems have provoked increasing interest among researchers from different disciplines. OoCs enable the recreation of in vivo-like microenvironments and the generation of a wide range of different tissues or organs in a miniaturized way. Most commonly, OoC platforms are based on microfluidic modules made of polydimethylsiloxane (PDMS). While advantageous in terms of biocompatibility, oxygen permeability, and fast prototyping amenability, PDMS features a major limitation as it absorbs small hydrophobic molecules, including many types of test compounds, hormones, and cytokines. Another common feature of OoC systems is the integration of membranes (i) to separate different tissue compartments, (ii) to confine convective perfusion to media channels, and/or (iii) to provide mechanical support for cell monolayers. Typically, porous polymer membranes are microstructured using track-etching (e.g., polyethylene terephthalate; PET) or lithography (e.g., PDMS). Although membranes of different biomechanical properties (rigid PET to elastic PDMS) have been utilized, the membrane structure and material remain mostly artificial and do not resemble in vivo conditions (extracellular matrix). Here, we report a method for the reliable fabrication and integration of electrospun membranes in OoC modules, which are made of laser-structured poly(methyl methacrylate) (PMMA). The choice of PMMA as base material provides optical parameters and biocompatibility similar to PDMS while avoiding the absorption problem. Using electrospinning for the generation of 3D membranes, microenvironments resembling the native extracellular matrix (ECM) can be generated. We tested two different kinds of electrospun membranes and established processes for a tight integration into PMMA modules. Human (microvasculature) endothelial as well as (retinal pigment) epithelial cell layers could be successfully cultured inside the systems for up to 7 days, while being either directly exposed to (endothelial cells) or protected (epithelial cells) from the shear flow. Our novel method enables the versatile fabrication of OoC platforms that can be tailored to the native environment of tissues of interest and at the same time are applicable for the testing of compounds or chemicals without constraints.

Merging organoid and organ-on-a-chip technology to generate complex multi-layer tissue models in a human retina-on-a-chip platform.

The devastating effects and incurable nature of hereditary and sporadic retinal diseases such as Stargardt disease, age-related macular degeneration or retinitis pigmentosa urgently require the development of new therapeutic strategies. Additionally, a high prevalence of retinal toxicities is becoming more and more an issue of novel targeted therapeutic agents. Ophthalmologic drug development, to date, largely relies on animal models, which often do not provide results that are translatable to human patients. Hence, the establishment of sophisticated human tissue-based in vitro models is of upmost importance. The discovery of self-forming retinal organoids (ROs) derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) is a promising approach to model the complex stratified retinal tissue. Yet, ROs lack vascularization and cannot recapitulate the important physiological interactions of matured photoreceptors and the retinal pigment epithelium (RPE). In this study, we present the retina-on-a-chip (RoC), a novel microphysiological model of the human retina integrating more than seven different essential retinal cell types derived from hiPSCs. It provides vasculature-like perfusion and enables, for the first time, the recapitulation of the interaction of mature photoreceptor segments with RPE in vitro. We show that this interaction enhances the formation of outer segment-like structures and the establishment of in vivo-like physiological processes such as outer segment phagocytosis and calcium dynamics. In addition, we demonstrate the applicability of the RoC for drug testing, by reproducing the retinopathic side-effects of the anti-malaria drug chloroquine and the antibiotic gentamicin. The developed hiPSC-based RoC has the potential to promote drug development and provide new insights into the underlying pathology of retinal diseases.

Organ-on-a-chip technologies that can transform ophthalmic drug discovery and disease modeling.

INTRODUCTION: Disorders of the eye that lead to visual impairment are affecting millions of people worldwide. Nevertheless, for many of these disorders, there are still no effective treatment options available due to the lack of in vitro model systems that emulate the physiological in vivo structure and function of human eyes. Microphysiological organ-on-a-chip (OoC) technology represents a novel and powerful approach to overcome the limitations of conventional model systems and lead to a paradigm shift in ophthalmic research. Areas covered: This review provides an overview of the various tissues of interest in ophthalmology and summarizes existing model systems, including their applications and limitations. Additionally, novel OoC systems with applications in ophthalmology are described and the advantages of these systems compared to conventional models are highlighted. Expert opinion: The physiological relevance of the first ophthalmic OoC systems that mimic human ocular compartments, such as the cornea and retina, has been successfully demonstrated in recent years. There is a great potential for the application of these platforms for future pharmacological target identification, safety, and efficacy testing, as well as personalized medicine. Further improvements and the development of new systems are of upmost importance, especially to model complex disorders affecting several tissues.