Corneal transplantation is the treatment of choice for patients with advanced corneal diseases. However, the outcome may be affected by graft rejection, high associated costs, surgical expertise, and most importantly the worldwide donor shortage. In recent years, bioprinting has emerged as an alternative method for fabricating tissue equivalents using autologous cells with architecture resembling the native tissue. In this study, we propose a freeform and cell‐friendly drop‐on‐demand bioprinting strategy for creating corneal stromal 3D models as suitable implants. Corneal stromal keratocytes (CSK) were bioprinted in collagen‐based bioinks as 3D biomimetic models and the geometrical outcome as well as the functionality of the bioprinted specimens were evaluated after in vitro culture. We showed that our bioprinting method is feasible to fabricate translucent corneal stromal equivalents with optical properties similar to native corneal stromal tissue, as proved by optical coherence tomography. Moreover, the bioprinted CSK were viable after the bioprinting process and maintained their native keratocyte phenotypes after 7 days in in vitro culture, as shown by immunocytochemistry. The proposed bioprinted human 3D corneal models can potentially be used clinically for patients with corneal stromal diseases.

Endoplasmic reticulum (ER) stress due to accumulation of hepatoviral or misfolded proteins is increasingly recognized as an important step in the pathogenesis of inflammatory, toxic, and metabolic liver diseases. ER stress results in the activation of several intracellular signaling pathways including Jun N‐terminal kinase (JNK). The AP‐1 (activating protein 1) transcription factor c‐Jun is a prototypic JNK target and important regulator of hepatocyte survival, proliferation, and liver tumorigenesis. Because the functions of c‐Jun during the ER stress response are poorly understood, we addressed this issue in primary hepatocytes and livers of hepatocyte‐specific c‐Jun knockout mice. ER stress was induced pharmacologically in vitro and in vivo and resulted in a rapid and robust induction of c‐Jun protein expression. Interestingly, ER‐stressed hepatocytes lacking c‐Jun displayed massive cytoplasmic vacuolization due to ER distension. This phenotype correlated with exacerbated and sustained activation of canonical ER stress signaling pathways. Moreover, sustained ER stress in hepatocytes lacking c‐Jun resulted in increased cell damage and apoptosis. ER stress is also a strong inducer of macroautophagy, a cell‐protective mechanism of self‐degradation of cytoplasmic components and organelles. Interestingly, autophagosome numbers in response to ER stress were reduced in hepatocytes lacking c‐Jun. To further validate these findings, macroautophagy was inhibited chemically in ER‐stressed wildtype hepatocytes, which resulted in cytoplasmic vacuolization and increased cell damage closely resembling the phenotypes observed in c‐Jun‐deficient cells. Conclusion: Our findings indicate that c‐Jun protects hepatocytes against excessive activation of the ER stress response and subsequent cell death and provide evidence that c‐Jun functionally links ER stress responses and macroautophagy. (HEPATOLOGY 2012)

Corneal integrity is essential for visual function. Transplantation remains the most common treatment option for advanced corneal diseases. A global donor material shortage requires a search for alternative treatments. Different stem cell populations have been induced to express corneal cell characteristics in vitro and in animal models. Yet before their application to humans, scientific and ethical issues need to be solved. The in vitro propagation and implantation of primary corneal cells has been rapidly evolving with clinical practices of limbal epithelium transplantation and a clinical trial for endothelial cells in progress, implying cultivated ocular cells as a promising option for the future. This review reports on the latest developments in primary ocular cell and stem cell research for corneal therapy.

Laser refractive surgeries reshape corneal stroma to correct refractive errors, but unavoidably affect corneal nerves. Slow nerve regeneration and atypical neurite morphology cause desensitization and neuro-epitheliopathy. Following injury, surviving corneal stromal keratocytes (CSKs) are activated to stromal fibroblasts (SFs). How these two different cell types influence nerve regeneration is elusive. Our study evaluated the neuro-regulatory effects of human SFs versus CSKs derived from the same corneal stroma using an in vitro chick dorsal root ganglion model. The neurite growth was assessed by a validated concentric circle intersection count method. Serum-free conditioned media (CM) from SFs promoted neurite growth dose-dependently, compared to that from CSKs. We detected neurotrophic and pro-inflammatory factors (interleukin-8, interleukin-15, monocyte chemoattractant protein-1, eotaxin, RANTES) in SFCM by Bio-Plex Human Cytokine assay. More than 130 proteins in SFCM and 49 in CSKCM were identified by nanoLC-MS/MS. Proteins uniquely present in SFCM had reported neuro-regulatory activities and were predicted to regulate neurogenesis, focal adhesion and wound healing. Conclusively, this was the first study showing a physiological relationship between nerve growth and the metabolically active SFs versus quiescent CSKs from the same cornea source. The dose-dependent effect on neurite growth indicated that nerve regeneration could be influenced by SF density.

We demonstrated the safety, feasibility, and therapeutic efficacy of intrastromal CSK injection. The cultivated CSKs can be a reliable cell source for potential cell-based therapy for corneal opacities.

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Corneal transplantation remains the ultimate treatment option for advanced stromal and endothelial disorders. Corneal tissue engineering has gained increasing interest in recent years, as it can bypass many complications of conventional corneal transplantation. The human cornea is an ideal organ for tissue engineering, as it is avascular and immune-privileged. Mimicking the complex mechanical properties, the surface curvature, and stromal cytoarchitecure of the in vivo corneal tissue remains a great challenge for tissue engineering approaches. For this reason, automated biofabrication strategies, such as bioprinting, may offer additional spatial control during the manufacturing process to generate full-thickness cell-laden 3D corneal constructs. In this review, we discuss recent advances in bioprinting and biomaterials used for in vitro and ex vivo corneal tissue engineering, corneal cell-biomaterial interactions after bioprinting, and future directions of corneal bioprinting aiming at engineering a full-thickness human cornea in the lab.

The biodegradable PLGA and PCL electro-spun scaffolds resulted in equal biocompatibility, while PMMA showed cytotoxicity. Only PLGA preserved hCEC morphology and consequently seems to be a promising candidate for TEEG construction.