## 4 Discussion  
The obtained results indicated that release of _Aloe vera_ extract from the lens was different in the ionic and non-ionic lenses. These findings bear clinical relevance because therapeutic contact lenses are an option to treat ocular diseases due to their ability to release drugs for extended periods of time. Therefore, the critical properties of lenses, such as water content and ion and oxygen permeability for comfortable day and night wear contact, are important topics of research to enable their therapeutic uses. We evaluated the release of _Aloe vera_ extract for two different types of therapeutic lenses. The non-ionic hydrogel lens that was tested, with 75% water, is a type of lens in which the water content is suited to bandaging the corneal surface. The hydration of these materials is best performed in buffered saline with a pH of 6.8-7.3. The tested ionic hydrogel lens had a 72% water content and met the criteria for high-performance daily-wear lenses. We analyzed the release of _Aloe vera_ extracts at five different times, comparing ionic and non-ionic therapeutic lenses. In our experiment, we verified that the ionic hydrogel lens released a higher quantity of aloesin than the non-ionic hydrogel lens for all the analysis times considered (after 30 min, 60 min, 2 h, 6 h, and 24 h). Hydrogels have proven to be an extremely versatile class of materials with many potential applications in ophthalmology. A hydrogel material is porous and traps aloesin. Our hypothesis is that aloesin remained passively trapped in the non-ionic lens, and the release was therefore lesser and decreased over time. Conversely, in the ionic lens, the negative charge rejected the aloesin, thus making its release continuous possible and leading to a steadily increasing release to the outside in the medium. Therefore, the release was greater and more prolonged over time for the ionic lens compared to the non-ionic lens. However, there was no measure of how much aloesin was absorbed by each lens, so we do not know how much was remaining in each lens (although it was clear that the ionic lens released more). Ionic hydrogel lenses are high performance soft lens materials because they are able to stay completely hydrated and dimensionally stable, as well as extremely wettable, on the eye. Staying hydrated during wear means that a 54% water, high performance G-(Glycerol Methacrylate) material lens can provide an oxygen transmission of 20 Dk/T at an average lens thickness of 105 microns, and a 75% water content G-material lens can provide 20 Dk/T all the way to an average lens thickness300 microns. This means that virtually any lens design can be a high performance daily wear lens. These high performance lens properties are a function of the polymer's water compatibility [22]. For material comparison, it is useful to examine the percent change in the pure saline contact angle between each material rather than a particular angle. The contact angle is reduced by 24% in going from a poly-HEMA-based lens to a 54% GMA/HEMA copolymer lens. This amount of change in contact angle may be what is necessary for patients to consistently have a comfort preference between two materials. Thus, the \"spikiness\" of lenses may also influence adhesion by reducing adhesion to both hydrophilic and hydrophobic lenses. In turn, this effect could be especially relevant for hydrophilic lenses [23]. The results of the present study highlight the relevance of how the lens material is fundamental in conditioning the release of drugs from therapeutic lenses with reference to extracts of _Aloe vera_. The hydrogel non-ionic material had a lower water content than the ionic material. The amount of drug a contact lens can absorb, as well as the drug's release, is influenced by the lens' water content [24]. The dehydration of conventional hydrogel lenses significantly impacts the oxygen permeability or the transmissibility value of the lens [24; 25; 26; 27].