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There is an ongoing effort to advance methodologies for culturing functional photoreceptors in vitro for retinal regenerative strategies. To support the formation of functional photoreceptors, a scaffold should replicate the native environment. The aim of this study was to optimize a sodium alginate–gelatin (SA-G) bioink to mimic the retinal properties while ensuring the printing of constructs with high shape fidelity. The optimized bioink was thoroughly characterized in terms of its physical, mechanical, and rheological properties, printability assessment, and preliminary biocompatibility. The material showed a constant degradation rate, which is crucial for effective tissue regeneration as it provides support for cell differentiation and polarization while gradually degrading to allow cell proliferation and matrix deposition. The optimized bioink displayed stiffness comparable to the native photoreceptor layer, potentially providing appropriate mechanical cues for photoreceptor maturation. Additionally, it exhibited shear-thinning behavior, the presence of yield stress, and fast recovery kinetics, which are essential for successful extrusion. The high shape fidelity of 3D-printed constructs suggested the feasibility of printing complex patterns to drive photoreceptor polarization. The preliminary cell results demonstrated homogeneous cell distribution and sustained cell viability over time. Overall, these findings indicate that the optimized bioink can provide the mechanical and topographical cues necessary for cultivating photoreceptors in vitro for retinal regeneration. [ABSTRACT FROM AUTHOR]

The menisci of the knee are complex fibro-cartilaginous tissues that play important roles in load bearing, shock absorption, joint lubrication, and stabilization. The objective of this study was to evaluate the interaction between the different meniscal tissue components (i.e., the solid matrix constituents and the fluid phase) and the mechanical response according to the developmental stage of the tissue. Menisci derived from partially and fully developed pigs were analyzed. We carried out biochemical analyses to quantify glycosaminoglycan (GAG) and DNA content according to the developmental stage. These values were related to tissue mechanical properties that were measured in vitro by performing compression and tension tests on meniscal specimens. Both compression and tension protocols consisted of multi-ramp stress-relaxation tests comprised of increasing strains followed by stress-relaxation to equilibrium. To better understand the mechanical response to different directions of mechanical stimulus and to relate it to the tissue structural composition and development, we performed numerical simulations that implemented different constitutive models (poro-elasticity, viscoelasticity, transversal isotropy, or combinations of the above) using the commercial software COMSOL Multiphysics. The numerical models also allowed us to determine several mechanical parameters that cannot be directly measured by experimental tests. The results of our investigation showed that the meniscus is a non-linear, anisotropic, non-homogeneous material: mechanical parameters increase with strain, depend on the direction of load, and vary among regions (anterior, central, and posterior). Preliminary numerical results showed the predominant role of the different tissue components depending on the mechanical stimulus. The outcomes of biochemical analyses related to mechanical properties confirmed the findings of the numerical models, suggesting a specific response of meniscal cells to the regional mechanical stimuli in the knee joint. During maturation, the increase in compressive moduli could be explained by cell differentiation from fibroblasts to metabolically active chondrocytes, as indicated by the found increase in GAG/DNA ratio. The changes of tensile mechanical response during development could be related to collagen II accumulation during growth. This study provides new information on the changes of tissue structural components during maturation and the relationship between tissue composition and mechanical response. [ABSTRACT FROM AUTHOR]

Optic nerve and retinal diseases such as age-related macular degeneration and inherited retinal dystrophies (IRDs) often cause permanent sight loss. Currently, a limited number of retinal diseases can be treated. Hence, new strategies are needed. Regenerative medicine and especially tissue engineering have recently emerged as promising alternatives to repair retinal degeneration and recover vision. Here, we provide an overview of retinal anatomy and diseases and a comprehensive review of retinal regeneration approaches. In the first part of the review, we present scaffold-free approaches such as gene therapy and cell sheet technology while in the second part, we focus on fabrication techniques to produce a retinal scaffold with a particular emphasis on recent trends and advances in fabrication techniques. To this end, the use of electrospinning, 3D bioprinting and lithography in retinal regeneration was explored. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) is the leading cause of vision loss in the elderly worldwide. So far, the etiology and the progression of AMD are not well known. Animalmodels have been developed to study the mechanisms involved in AMD; however, according to the "Three Rs" principle, alternative methods have been investigated. Here we present a strategy to develop a "Three Rs" compliant retinal three-dimensional (3D) in vitro model, including a Bruch's membrane model and retina pigment epithelium (RPE) layer. First, tensile testing was performed on porcine retina to set a reference for the in vitro model. The results of tensile testing showed a short linear region followed by a plastic region with peaks. Then, Bruch's membrane (BrM) was fabricated via electrospinning by using Bombyx mori silk fibroin (BMSF) and polycaprolactone (PCL). The BrM properties and ARPE-19 cell responses to BrM substrates were investigated. The BrM model displayed a thickness of 44 m, with a high porosity and an average fiber diameter of 1217 101 nm. ARPE-19 cells adhered and spread on the BMSF/PCL electrospun membranes. In conclusion, we are developing a novel 3D in vitro retinal model towards the replacement of animal models in AMD studies. [ABSTRACT FROM AUTHOR]