**2.5 Smart polymers with photo responsiveness**

Photo-sensitive polymeric materials are useful in that they could transport bioactive substances in reaction to light, including drug release happening nearly instantly and with excellent precision due to photo-induced restructuring in nano-carriers [48]. Three primary strategies were used to do this: This noninvasive form of drug administration reacts to the lighting of a certain wavelength and depends on either a single or multiple on-off drug release patterns [49]: (1) photo-generated change of hydrophobic nature to hydrophilic nature, (2) photo splitting reaction, and (3) photo-induced warming. Whilst also electromagnetic radiations with wavelengths in the range from 250 to 380 nm (ultraviolet region) and 700–900 nm (near-infrared region) are being used to stimulate photosensitive responses, light with wavelengths greater than 900 nm is inappropriate for delivery of drugs to certain parts of the human body, including the posterior section of the ocular system, because it cannot permeate the ocular soft tissue. Despite the fact that various polymers have been explored for ocular administration, several have been ruled out owing to chromophore intolerance and tissue destruction from photostimulation [50]. In order to establish an osmolality of a gel system, UV-responsiveness polymeric materials have been used in the eye to trigger an ionization process in the exposed to UV light, culminating in drug release through an inflow of solvent [51]. In another study, Viger et al. [52] used light thermally release of drugs to show the liberation of aqueous nano-platforms from watered poly(lactic-co-glycolic acid) (PLGA) micro-particulate system. Whenever moisture was subjected to NIR light with a wavelength of 980 nm, the photo-energy was quickly converted into thermal energy. The PLGA changed to a rubbery condition as a result of the warming, allowing the Nile red or Nile blue to be released from the micro-particulate system more easily. When compared with untreated particulates, the substantial release was achieved, which was also shown in vitro [52].

At the minimum one aqueous soluble area, at minimum one biodegradable part, as well as at least minimum of two free radical polymerizable portions are included in the macromers. Free radical activators polymerize macromers in presence of UV irradiation, visible light stimulation, or heat energy. Poly (vinyl alcohol), PEG, polysaccharides like hyaluronan, or peptides like albumin can make up the core aqueous soluble area. Polymers consisting of polyglycolic acid, polylactic acid, poly(anhydrides), polylactones, and poly(amino acids), may be used in the biodegradable zones. Acrylates, methacrylates, diacrylates, and other physiologically acceptable polymerizable units are favored polymerizable areas. Ethyl eosin,

camphorquinone, and acetophenone analogs, are examples of promoters that can be employed to generate free radicals [53].
