*5.1.3 CD-based polyester NSs*

CD-based Ester NSs synthesized with pyromellitic dianhydride (PMDA) are well known for delivering, enhancing solubility, and preventing the degradation of various drugs such as Curcumin [76], Insulin [20], Resveratrol [77], Erlotinib hydrochloride [78], among others. Ethylenediaminetetraacetic dianhydride (EDTA) is another cross-linker to synthesize ester CD NSs. Based on HRMAS probe-heads in a high-resolution NMR spectrometer on the transport properties of Ibuprofen sodium salt (IP), it was found that these NSs can be utilized for the rational design of smart systems for drug delivery and controlled release [79]. The various applications of CD-based polyester NSs ranging from the environment to pharmacy, chemistry, agriculture, gene delivery, cosmetics, biocatalysis, brought to a detailed study on their cross-linking density. Being a very challenging task, it presented the effect of cross-linking density on β-CD NSs physicochemical properties. Flory-Rehner theory and rheology enabled the authors to understand the correlation between the structural features of NSs and their physicochemical properties, which is a key requirement for future applications [34].
