*3.2. FT-IR*

Figure 4A presents the Fourier transform infrared spectroscopy of the NIPAM and PNIPAM powders ranging from 2000 cm<sup>−</sup><sup>1</sup> to 1000 cm<sup>−</sup>1. The disappearance of the 1622 cm<sup>−</sup><sup>1</sup> (–C=C–) peak showed the success of the synthesis of PNIPAM between NIPAM monomers (Figure 4A(a)). The 1652 cm<sup>−</sup><sup>1</sup> connected with the C=O, the 1549 cm<sup>−</sup><sup>1</sup> was related to the C–N stretching vibration and N–H flexural vibration, and the 1245 cm<sup>−</sup><sup>1</sup> corresponded to the C–N–H of PNIPAM [37]. FT-IR was employed to investigate the relationship between sericin/PNIPAM/PEO nanofibers and cotton fabric. The H–C=N– and H–C=C were formed by the crosslinking reaction between GA and sericin and cotton fabric, respectively.

From Figure 4B(e), it could be observed that the characteristic absorption bands at 3084 cm<sup>−</sup><sup>1</sup> could be contributing to the H–C=C group, which proved the cross-linking reaction between the –OH group on cotton and GA. The characteristic band at 1635 cm<sup>−</sup><sup>1</sup> corresponded to the H–C=N– stretching vibration of the modified cotton fabric. This suggested that the cross-linking reaction between the sericin and GA occurred. The –CHO produced a characteristic band at 1713 cm<sup>−</sup>1. As we know, there was no extra GA in the resulting modified cotton fabric. Thus, the GA could make the reaction with the cotton textiles and sericin, separably. It was indicated that the glutaraldehyde could be a "bridge" that can crosslink the cotton fabric and the nanofibers [33,38].

**Figure 4.** (**A**): The FT-IR spectra (2000–1000 cm<sup>−</sup>1) of (**a**) NIPAM powders; (**b**) PNIPAM powders; (**B**): The FT-IR spectra (4000–500 cm<sup>−</sup>1) of (**c**) Sericin/PNIPAM/PEO nanofibers; (**d**) Cotton fabric; (**e**) Functionalized cotton fabric.

#### *3.3. Thermosensitive Behavior*

Figure 5A shows the schematic illustration of PNIPAM involving the hydrophobic/hydrophilic transformation. PNIPAM interacted preferentially with water molecules and formed a hydrogen bond in the temperature range below LCST [39]. When increasing the temperature above LCST, PNIPAM molecules gradually turn into hydrogen bonds between polymer molecules. Thus, it was severely restricted for each molecule's mobility because of the hydrogen-bonded polymer network.

The surface wettability of functionalized cotton fabric was measured with different temperatures by using the static contact angle of water droplets (5 μL). Figure 5B exhibits that the static water contact angle of functionalized cotton fabrics increased apparently with the increasing temperature of the fabrics, demonstrating a hydrophilicity/hydrophobicity change of functionalized cotton fabrics. The wettability of functionalized cotton fabrics became a hydrophobic state and the contact angle increased up to the maximum at about 95 ± 1.5◦, with the temperature improved.

Figure 5C shows the differential scanning calorimetry (DSC) thermogram curves of modified cotton fabric and cotton fabric. The initial temperature was considered as the lower critical solution temperature (LCST) value that was estimated with the intersection points of the two tangents (see Figure 5). It could be seen that the LCST of nanofibers and modified cotton fabric is 32.03 ◦C and 34.47 ◦C, respectively. Additionally, there was no phase transition peak in common cotton fabric. It was shown that the LCST of modified cotton fabric is between 30 ◦C and 36 ◦C, close to human body temperature.

**Figure 5.** Representation of (**A**) the hydrophobic–hydrophilic phase transition of PNIPAM hydrogels; (**B**) Contact angle measurements of multifunctional cotton fabric at different temperatures; (**C**) Differential scanning calorimetry thermogram curves of modified cotton fabric and cotton fabric. (**a**) Cotton fabric; (**b**) Functionalized cotton fabric. (The final results of data are shown as mean ± standard deviation).

#### *3.4. pH-Responsive Swelling Behaviors*

In Figure 6, the images show that sericin/PNIPAM/PEO hydrogels had different swelling ratio changes according to the pH swelling medium at temperatures of 15 ◦C and 37 ◦C. From Figure 6, it was shown that all the hydrogels presented the same trends and temperature-sensitive property under the pH test range. The swelling ratio of hydrogels was much higher at 15 ◦C than at 37 ◦C, which showed a temperature-sensitive characteristic. This was largely due to the network shrinking of PNIPAM when the temperature of the solutions was above LCST (37 ◦C). The swelling ratio of sericin/PNIPAM/PEO (55/15/30) hydrogel decreased a little with a rise in temperature. The minimum swelling ratio of hydrogel appeared at about pH 4.0. This is due to the non-charged and hydrophobic form of sericin side chains. The increasing swelling ratios of sericin/PNIPAM/PEO (55/15/30) hydrogel appeared with reducing the pH buffer solutions down to 4.0 or increasing it above 4.0. This was because the –NH2 of sericin was protonated into –NH3+ and –COOH of sericin charged to –COO− and then enhanced the electrostatic repulsion of interpenetrating network hydrogels.

The results showed that the swelling ratio was lower in all the specimens at pH 4.0 and pH 8.0, no matter what the composition of the hydrogels was. Additionally, there were better swelling ratios under acid or alkaline conditions.

**Figure 6.** Swelling ratio of sericin/PNIPAM/PEO hydrogels in pH buffer solutions at (**A**) 15 ◦C and (**B**) 37 ◦C, the final results of data are shown as mean ± standard deviation.

With the increasing sericin concentration, the swelling ratios increased at 15 ◦C (Figure 6A), and the order of swelling ratios was a complete transformation at 37 ◦C (Figure 6B). Along with the increase in sericin content, the number of –COOH and –NH2 was increased and resulted in the enhancement of the electrostatic repulsion of hydrogel. As can be seen, the sericin/PNIPAM/PEO hydrogels showed simultaneous pH and temperature sensitivity. It was an effective way to adjust the equilibrium swelling ratio and the swelling property of the hydrogels by changing the mixed proportion of hydrogels.

#### *3.5. Antimicrobial Activity*

The antibacterial activity of samples was evaluated against Gram-positive bacteria and Gram-negative bacteria such as *Staphylococcus aureus* (ATCC 6538) and *Escherichia coli* (ATCC 8739). The antimicrobial capability of the untreated cotton fabric and functionalized cotton fabric is shown in Table 3. The functionalized cotton fabrics exhibited antimicrobial property against the above microorganisms. The sericin/PNIPAM/PEO nanofibers could inhibit the growth of bacteria. All functionalized cotton fabrics showed lower antibacterial efficiency against *E. coli* and higher antibacterial property against *S. aureus*. It was revealed that the antibacterial efficiency of the functionalized cotton fabrics exhibited the highest antibacterial efficiency up to 85% of *E. coli* and 90% of *S. aureus*. This may be due to the fact that the sericin could control the free movement of the bacteria, inhibited respiration and finally rose to the death of bacteria. The sericin molecules had the electrostatic attraction with cell membranes of bacteria. The electrostatic attraction would decrease bacterial conductivity, reduce cell membrane permeability and partially inhibit metabolism. As a result, the intracellular composition containing water and protein was discharged and finally led to the death of bacteria [40].


**Table 3.** Antibacterial characteristic of cotton fabrics against *S. aureus* and *E. coli* bacteria.
