# Polymers and Polymer Nanocomposites for Cancer Therapy +
## Polymer Hydrogels and Nanogels
Some other chemical modifications have gained interest for the preparation of a photopolymerizable CS derivative or improvements to CS solubility in water [50]. It is worth noting the application of pH-responsive hydrogels in ophthalmic cancer therapy. Ophthalmic drug delivery is an area that is seeing a significant impact in therapy from hydrogels [94]. The drug-releasing process of hydrogel membranes made of MWCNTs, PVA, PVP, and PEG, such as PVA/PVP/MWCNTs and PVA/PEG/MWCNTs, was investigated. A maximum degree of swelling was observed at pH 7, and the swelling degree increased with the amount of MWCNTs. All hydrogel membranes followed non-Fickian mechanisms, and drug release was controlled by varying the amount of filler [95]. Crosslinking methacrylic acid with itaconic acid through ethylene glycol dimethacrylate was carried out to synthesize robust hydrogels for oral administration and tune them for the targeted release of 5 FU and Leucovorin calcium in the colon. Swelling, drug loading, and drug release evaluations were carried out at two different pH levels. The hydrogels obtained were biocompatible and nontoxic as investigated in an oral toxicity study on rabbits [96]. Poly(\(\epsilon\)-caprolactone-co-polydioxane)-b-PEG-b(\(\epsilon\)-caprolactone-co-polydioxane) triblock copolymer hydrogel has a semisolid morphology, is well-suited for the sustained delivery of hydrophilic macromolecular drugs, and shows the longest release period for hydrophobic drugs. Small molecular hydrophilic drugs such as Mitomycin C mainly aggregate in the loose hydrophilic shell of micelles, and given their low fluid mechanic radius, are released quickly through pore diffusion. In contrast, human serum albumin is released much slower because of its high hydrodynamic volume [97]. A biodegradable sol gel drug carrier made of an HA-Ca-AA hydrogel combining a hyaluronic acid-calcium complex (HA-Ca) and sodium alginate (AA-Na) components for the local sustained delivery of the drug Cyclosporine A was developed. An HA-Ca complex with a very high degree of substitution was prepared through the acid-base reaction of HA and Ca acetate. Gelation was completed within 2 to 45 min without the external addition of Ca salts, indicating the high potential of the hydrogel system for drug delivery through injection in vivo [98]. Porous silicon-based nanocomposite hydrogels were produced through the gelation of PEG double acrylate (PEGDA) macromers due to the initiation of singlet oxygen photosensitized with porous nSi under near-infrared (NIR) light irradiation. Multifunctional nSi/PEGDA nanocomposite hydrogels showed strong fluorescence, excellent biodegradability, significant photothermal effects, and sustained drug release with high efficiency (>80%). The authors concluded that these types of hydrogels will have clinical significance in local clinical therapies in the future [99]. An application of a polyacrylamide-co-grafted-gum ghatti (a polysaccharide) copolymer for transdermal delivery of an antipsychotic drug (Quetiapine fumarate) triggered by electric stimulus was also explored [100]. Light-responsive hydrogels are promising potential applications in drug/gene delivery, microlenses, sensors, etc., due to the fact that the activation process via light can be remote and noninvasive. The hydrogel consists of a deoxycholic acid-modified \(\delta\)-cyclodextrin derivative and an azobenzene-branched-PAA copolymer and can be converted efficiently from gel to sol upon photoirradiation with light at a 355-nm wavelength. The hydrogel is able to recover from sol to gel upon photoirradiation with light at a 450-nm wavelength. The reversible transition of this hydrogel can be controlled under mild conditions, suggesting that this hydrogel may have a promising role in bioengineering applications for the release of molecular or cellular species. A novel light-responsive hydrogel was made from a poly(isopropyl acrylamide) nanocomposite incorporating glycidyl methacrylate-functionalized graphene oxide [101].