# Nanotechnology and Early Human Development
## 5 Ocular System  
The regeneration of damaged ocular parts resulting in vision loss is a complex and current issue, and engineering approaches are becoming increasingly tested. Potential targets are congenital and acquired diseases which may occur during childhood, including genetic retinal defects (i.e., retinitis pigmentosa) and retinopathy of prematurity (ROP), characterized by excessive vascular proliferation leading to retinal detachment [36]. Given that vascular endothelial growth factor (VEGF) plays a crucial role in the pathogenes of ROP and other retinal diseases, injection of anti-VEGF agents (i.e., bevacizumab) is effective in reverting retinal neovascularization while avoiding detrimental effects of other procedures (such as laser therapy). Some authors developed a nano-sized siRNA therapeutic delivery system loaded with VEGF receptor 2 and found that, in an animal model of ocular neovascularization, it was a safe and effective method of reducing vessel proliferation [37]. According to the International Classification of ROP, the instrumental fundus examination of the eye of premature infants allows the identification of five different stages of evolution of the disease. From stage 1 to stage 3, the retina is still adherent, while in stage 4, partial retinal detachment begins. In the presence of a partial detachment and increased vascular activity, the retina may further detach from the epithelial layer of the choroid to which it adheres physiologically. If vascular activity diminishes after medical treatment (ROP regression), it is advisable to employ a geometric-mechanical criterion to determine the onset of its further propagation, which also depends on many other pathogenic factors, for example myopia. It is necessary to adopt a fracture mechanics approach to this delamination problem. Many models regarding the mechanics of the eye have been proposed in the literature. To our knowledge, only one paper describes a mathematical model to study the mechanics of retinal detachment [38]. Based on an energy criterion, the problem of quasi-static and axisymmetric propagation of a detaching retina has been solved. The propagating boundary value problem has been reformulated in a variational form allowing variations of the boundary and deformation of the detaching retina. In our opinion, the model should be reformulated by using a more rigorous adhesion-delamination theory. In a later paper [39], the authors extended the model, taking into account the geometrical variations induced by the evolution of myopia. According to the clinical evidence, detachment propagation is initiated when the energy release rate exceeds the critical energy release rate reached at severe levels of myopia without other stress factors acting on the retina. Nanotechnology may be used to increase drug bioavailability in the intraocular tissues, thus reducing the need for repeated injections and complications [40]. The use of nanoparticulate systems--liposomes, nanoparticles, and nanoemulsions, with a size less than 1000 nm--has been explored as an appropriate alternative to conventional options. In particular, liposomes are composed of phospholipids and cholesterol, forming a layer capable of surrounding an aqueous compartment, thus allowing the encapsulation of drugs and protection from degradation; polymeric nanoparticles, either natural or synthetic, are polymeric colloidal particles, which adsorb, absorb, attach, or encapsulate drug molecules. Solid lipid nanoparticles consist of a nanosized lipidic core stabilized by a layer of surfactants. The nanostructured lipid carrier represents a novel system allowing greater drug loading and availability compared to older systems. Polymeric micelles are a nanosized (10 to 100 nm) self-assembly of amphiphilic block copolymers (hydrophobic core and hydrophilic shell). Nanoemulsions typically include droplets of a specific liquid stabilized by surfactants and dispersed in another liquid.