## 3 Results
### Synthesis and Characterization of Nanogel-Embedded Contact Lenses  
To serve as an ophthalmic drug delivery platform, the drug-loaded PSBMA nanogels were incorporated into a poly(hydroxyethyl methacrylate) (pHEMA) hydrogel matrix (Scheme 1). Briefly, the required quantity of each drug-loaded PSBMA nanogel was dispersed by ultrasonication in a premonomer mixture of HEMA and NVP, a commonly used comonomer in the manufacture of hydrogel contact lenses to boost water content [40]. Then, EGDMA as a crosslinker and AIBN as an initiator were added, and the contact lenses were fabricated by the cast molding method. The formulas for the prepared four batches of nanogel-embedded contact lenses are shown in Table 2, only with the ratio of drug-loaded nanogels varied. pHEMA lenses without nanogels were prepared as a control. The ATR-FTIR spectroscopy of pHEMA contact lens presented in Figure 1b showed typical stretching absorption bands at 1153 cm\({}^{-1}\) (-C-O-C), 1708 cm\({}^{-1}\) (-C=O), 2949 cm\({}^{-1}\) (CH\({}_{2}\)) and a wide absorption band in 3100\(-\)3600 cm\({}^{-1}\) region relating to the -OH group. The microstructure for the fabricated nanogel-embedded contact lens was investigated via SEM. The top surface of the freeze-dried pHEMA/LEV-2 contact lens exhibited an interconnecting pore with pore size around 5-25 um (Figure 3c). The uniform pore size distribution in the microstructure facilitates the diffusion of water molecules across the gel structure. A small number of nanoparticles with spherical shape could be clearly seen in the hydrogel matrix at the given scale, with the diameter around 200 nm (Figure 3d), indicating the successful incorporation of PSBMA nanogels. In addition, data demonstrated that the nanogels were stable and did not break or aggregate during the polymerization process. The optical clarity of the nanogel-embedded contact lenses was characterized by measuring the light transmittance in the range from 400 nm to 800 nm in a UV spectrophotometer. The pHEMA contact lenses exhibited about 96.9% of transmittance at 630 nm [41]. The transmittances of nanogel-embedded contact lenses decreased as nanogel content increased, and were approximately 94.5%, 92.8%, 90.0% and 88.5% for pHEMA/LEV-1, pHEMA/LEV-2, pHEMA/LEV-3 and pHEMA/LEV-4 at 630 nm, respectively (Figure 6a). The light transparency slightly decreased because of the incorporation of PSBMA nanogels. Similar results were also observed by [PERSON] et al. [27] and [PERSON] et al. [28] in that the transmittance of contact lenses decreased when nanoparticles were loaded. The Chinese characters  
Figure 5: The size distribution (**a**) and zeta potential (**b**) of PSBMA-4 nanogels before and after drug loading. (#means: eyes) under the series of contact lenses show that optical properties were not affected (Figure 6b), because the incorporated nanogels were monodispersed and were nano-sized (as can be seen from SEM results), which was not likely to significantly affect visual clarity. The water content of hydrogel contact lenses is a key determinant of their in situ performance and oxygen permeability [42]. In this regard, the EWC was measured by weighting the contact lenses before and after swelling, and the WCA was measured immediately after placing a 5-\(\upmu\)L water droplet on the nanogel-embedded contact lenses and on the control pHEMA contact lens surface. Figure 7a shows the EWC (%) values for the series of nanogel-embedded contact lenses and the control pHEMA contact lens. The water content of the pHEMA contact lens was about 70.5%. The very high EWC may be due to the presence of comonomer NVP, which favors the water retention. The EWCs of the series of nanogel-embedded contact lenses were decreased with the increasing nanogel weight ratio, with the approximate results of 69.3%, 65.5%, 52.2% and 51.5%, respectively. The highest incorporation amount with PSBMA nanogels still showed EWC above 50%, higher than many conventional pHEMA-based hydrogels (<50%) [43].