## 3 Results and Discussion
### Chemical and Physical Analyses  
The chemical structures of the HPC-based hydrogels prepared by the simultaneous reactions of radiation crosslinking and polymerization were analyzed using Fourier transform infrared (FT-IR) spectroscopy. The FT-IR spectra of the hydrogels after washing and drying are shown in Figure 7. The HPC-based hydrogels displayed a prominent peak at 1050 cm\({}^{-1}\), which was attributed to C-O asymmetric stretching. The prominent band for confirming the ester on 23G and HEMA was observed at 1722 cm\({}^{-1}\) and was attributed to the stretching vibration of C = O. The peak at approximately 1722 cm\({}^{-1}\) was also observed in the HPC/23G/HEMA hydrogel, with a low gel fraction obtained at 10 kGy. Therefore, this indicated that 23G and HEMA were combined chemically or physically with HPC as the homopolymer and unreacted monomer were removed by washing before the measurement. Although there was almost no peak observed in the HPC/23G hydrogel spectrum, this could be due to the very low concentration of 23G. Clearly, 23G was present in the HPC/23G hydrogels because both the gel fraction and tensile strength increased compared to the HPC hydrogels prepared without 23G. The transmittances of the HPC/23G and HPC/23G/HEMA hydrogels are shown in Figure 8. Both HPC-based hydrogels were highly transparent and exhibited almost the same transparency as the HPC hydrogel without 23G and HEMA. Figure 6: (**a**) Gel fraction and (**b**) Sw of HPC/23G hydrogels as a function of dose. The HPC/23G/HEMA hydrogels were prepared by the irradiation to the mixed aqueous solutions, in which the concentrations of HPC, 23G, HEMA were (\(\Circinus\)) 20/0.2/0, (\(\Circinus\)) 20/0.2/1, (\(\square\)) 20/0.2/2, and (\(\Diamond\)) 20/0.2/4 wt.%. The mechanical properties of HPC-based hydrogels are shown in Figure 9. [PERSON]'s moduli of HPC-based hydrogels were evaluated and were almost the same at approximately 0.1 MPa. The elasticity of HPC-based hydrogels was comparable to that of a commercially available hydrogel for soft contact lenses [5]. In addition, it is important to have an appropriate balance between the tensile strength and elongation at break because the soft contact lenses are handled manually. The relationship between the tensile strength and elongation at break of the HPC-based hydrogels is shown in Figure 10. As previously described, the tensile strength and elongation at break of the hydrogels were improved by adding 23G to HPC. The elongation at break was further improved by adding HEMA to HPC/23G, which reached 125%. As a result, the HPC/23G/HEMA hydrogel obtained at 50 kGy had a good balance between the tensile strength and the elongation at break, which exhibited a tensile strength of 0.2 MPa and elongation at break of 125%. These values were about 2.0 and 1.8 times compared to the HPC hydrogel without 23G and HEMA, respectively. Therefore, the addition of the crosslinker 23G improved the tensile strength with an increase in the crosslinking density and increased the elongation at break of 125%. Figure 8: UV-vis spectra of HPC-based hydrogels obtained at the following concentration and dose. HPC/23G (20/0.2 wt.%, 30 kGy) and HPC/23G/HEMA (20/0.2/ 2 wt.%, 50 kGy). Figure 7: FT–IR ATR spectra of HPC-based hydrogels obtained at the following concentration and dose. HPC (20 wt.%, 50 kGy), HPC/23G (20/0.2 wt.%, 50 kGy), and HPC/23G/HEMA (20/0.2/ 2 wt.%, 10 kGy and 50 kGy). break by introducing a polyethylene glycol unit with high molecular mobility between the HPC composed of a rigid glucose ring. The introduction of poly (HEMA) in the network polymer increased the mobility of the network polymer, resulting in a further increase in the elongation at break of the hydrogels. The tensile strength of the HEMA-based contact lens materials is reported to be in the range of 0.1-0.6 MPa [30]. The mechanical properties of the HPC/23G/HEMA hydrogel are within the range of those of HEMA-based contact lens materials, so the HPC/23G/HEMA hydrogel could be used as a contact lens material.