*2.1. Materials*

N-Isopropylacrylamide (NiPAm, TCI, Tokyo, Japan), 2-hydroxyethyl methacrylate (HEMA, Aldrich, St. Louis, MO, USA), N,N'-methylenebis(acrylamide) (MBA, Aldrich, St. Louis, MO, USA), ammonium persulfate (APS, Aldrich, St. Louis, MO, USA), and sodium dodecyl sulfate (SDS, Aldrich, St. Louis, MO, USA) were purchased and used as received.

### *2.2. Synthesis of p(NiPAm-co-HEMA) Microgels*

Microgels of the different molar ratios of NiPAm and HEMA were synthesized by free radical precipitation polymerization. The constituent monomers, NiPAm and HEMA, and the crosslinker, MBA, were dissolved accordingly to the specified molar ratio while the amount of the initiator, APS, and the surfactant, SDS, were kept constant. Six batches of p(NiPAm-co-HEMA) were synthesized, namely, 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, denoting the molar ratio between NiPAm and HEMA. The detailed recipe of each batch is summarized in Table 1. The monomers, crosslinker, and surfactant were dissolved in 498 mL of water. The reaction mixture was transferred to a 1 L-size, three-neck, and double-jacket reactor equipped with a condenser, a nitrogen inlet, and a mechanical stirrer. The reaction mixture was stabilized at 70 ◦C while stirring at 360 rpm under a nitrogen atmosphere for an hour. Afterward, 0.342 g of APS was dissolved in 2 mL of water and added to the mixture to initiate the polymerization. The reaction time for each batch is specified in Table 1. The resultant microgel dispersion was washed with three successive centrifugations to remove unreacted monomers and the surfactant. Finally, the dispersion was freeze-dried to obtain a solid sample for future use.

**Table 1.** Reaction recipe for the synthesis of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (p(NiPAm-co-HEMA)) microgels.


### *2.3. Rheological Characterization of p(NiPAm-co-HEMA) Microgels*

The gelling behavior of the p(NiPAm-co-HEMA) microgels was characterized by small-amplitude oscillatory shear (SAOS) tests. We used a commercial rotational rheometer (AR-G2, TA Instruments, New Castle, DE, USA) equipped with a cone-and-plate geometry (1◦; diameter: 60 mm) to perform the linear viscoelasticity characterization. The storage and loss moduli (G and G") were monitored at the fixed frequency of 0.63 (rad/s) with increasing temperature starting from 20 ◦C with the increment rate at 1 ◦C/min.
