2.3. Surface modification of TPU

The purchased TPU was cut into sheets (circle, d = 1 cm) and prepared according to the literature [54]. The TPU sheets were cleaned with 2% Tween-20 (98% deionized water) under sonication for 15 min followed by deionized water and anhydrous ethanol twice for 15 min each time. Next, the TPU sheets were dried under a gentle N₂ flow. Then the surface of the cleaned TPU sheets was activated using a plasma irradiator. Specifically, the sheets were set into the cavity and irradiated with a plasma irradiator at 70 W for 5 min on each side under an O₂ flow (0.3–0.4 MPa). After irradiation, these sheets were immersed into the functionalization reagent containing 1 : 10 bromoform: toluene (v/v) for 7–8 h to functionalize the activated TPU surfaces with brominated groups. The bromoform modified TPU sheets were washed with toluene, CH₂Cl₂, and ethanol. They were then kept in a vacuum vessel for overnight drying. The dried bromoform-modified TPU surface was incubated in an 80 μL solution of peptide polymer (DLL: BLG = 90 : 10) (1 mg/mL) in 1X degassed PBS buffer (pH 7.4, supplemented with 10% glycerol v/v) for 9–10 h. Later, an aliquot of 10 μL thioglycerol solution at 100 mg/mL in 1X degassed PBS buffer (pH 7.4, supplemented with 10% glycerol v/v) was added, and the whole mixture was incubated for another 3–4 h at room temperature. Finally, the peptide polymer-modified TPU surface (TPU-P) was cleaned by deionized water and dried under a gentle N₂ flow.