Discuss about the Biomaterial and Medical Devices.
Contact lens is an optical medical device that rests on the corneal surface of the eye and functions to bend light rays so that the image gets properly focused on the retina at the back of the eye. It is made out of high grade plastic polymers and is mainly used to correct vision deficiencies and is termed as cosmetic lens as far as this application is concerned (He and Benson 2014). On the other hand, another type of lens, the therapeutic or bandage lens is used to treat certain eye disorders. Contact lens is used as an effective alternative to glasses. Depending on the needs and preferences of the individual, different categories of lenses such as that of soft and hard lens are broadly available that renders adequate flexibility and convenience. Correction of a variety of vision disorders such as that of myopia, hyperopia, astigmatism, presbyopia are made possible through wearing of contact lens. Suitability of contact lens is normally determined by virtue of an eye examination. Assessment pertinent to the health of the eye is conducted normally through refraction for detecting the accurate power of the lens (Caló and Khutoryanskiy 2015).
Material used in Construction
Contact lens is available in two or more options whereby daily disposable lens or frequent replacement lens are the commonest types. Hard lens is composed of a transparent rigid polymer named poly(methylmethacrylate) (PMMA) that is now obsolete owing to its disadvantage in use because of less permeability of oxygen. Soft lens is made of polyacrylamide that is capable of absorbing water and is considered hydrophilic. Water containing plastics called hydrogels constitutes the soft lens and has successfully replaced the hard lens. Further, silicone hydrogel lens is an advanced type of contact lens and is more porous compared to other lens thereby allowing more oxygen permeability (Farandos et al. 2015). Gas permeable or rigid gas permeable lens is considered as rigid lens that account for greater permeability of oxygen due to greater porosity. This property has rendered advantage over the non-porous PMMA lens and hence has successfully replaced them and helps in provision of sharper optics. Soft lens has polymer that has 3-dimensional amorphous network with crosslinks that remains above its glass transition temperature and produced out of cast molding or spin cast method, less commonly from lath cutting process (Liu and Etzkorn 2015).
Contribution of material to function of device
The soft type of contact lens that is commonly in use is made up of a polymer called polyacrylamide that contains nitrogen in its structure which upon cross linking adds to the absorption of more water. Water content with respect to soft contact lens generally varies between 38% and 79% crucial to maintain the softness and flexibility of the lens. However, despite its advantages the high water contact makes the lens more prone to be fragile by means of reducing the clarity of vision that is further reflected in providing less protection to cornea. The hydrogel component of the soft lens mainly due to its aqueous phase adds to the oxygen permeability. Soft lens is responsible for adhering to the cornea by means of a tear film of only capillary thickness between the lens and the corneal surface. The thinner shape of the soft lens accounts for conferring greater oxygen transfer capacity and reducing the corneal issues of the eyes. The hydrogel soft contact lens adds to supply of greater oxygen to the corneal tissue and thereby rendering better clarity of vision for the wearer (Kirschner and Anseth 2013).
Alternative material that might have been considered
The limitations of the hydrogel soft lens have paved the path for more advanced and novel types of lens such as that of the rigid gas permeable lens (RGP). RGP lens is composed of a combination of materials that include silicone, PMMA and fluoropolymer. This combination acts in favor of passing the oxygen directly through the lens to the eye adding to the comfort of the wearer. Further the rigidity of RGP also contributes to rendering clearer vision in comparison to soft lens. Astigmatism and bifocal disorders are also better corrected by this lens than other soft lens may offer. Comfort in wearing and provision for crystal clear optics is provided through the RPG lens. The central zone of this lens is occupied by rigid gas permeable area that remains surrounded by a region consisting of hydrogel or silicon hydrogel material. The incorporation of the fluoride doped side chains has been assigned to crease the permeability of the lens. Resistance to lipid deposits is also provided by virtue of coupling fluorine with siloxane. Moreover, greater ductility in addition to good handling characteristics and easier care system compared to soft lens contributes to advantage for RPG lens (Piñero et al. 2014).
Caló, E. and Khutoryanskiy, V.V., 2015. Biomedical applications of hydrogels: A review of patents and commercial products. European Polymer Journal, 65, pp.252-267.
Farandos, N.M., Yetisen, A.K., Monteiro, M.J., Lowe, C.R. and Yun, S.H., 2015. Contact lens sensors in ocular diagnostics. Advanced healthcare materials, 4(6), pp.792-810.
He, W. and Benson, R., 2014. Polymeric biomaterials (pp. 55-76). William Andrew Publishing: Oxford.
Kirschner, C.M. and Anseth, K.S., 2013. Hydrogels in healthcare: from static to dynamic material microenvironments. Acta materialia, 61(3), pp.931-944.
Liu, Z. and Etzkorn, J., Verily Life Sciences Llc, 2016. In-situ tear sample collection and testing using a contact lens. U.S. Patent 9,320,460.
Piñero, D.P., Pérez-Cambrodí, R.J., Ruiz-Fortes, P. and Blanes-Mompó, F.J., 2014. New-generation hybrid contact lens for the management of extreme irregularity in a thin cornea after unsuccessful excimer laser refractive surgery. Eye & contact lens, 40(3), pp.e16-e20.