2.7. Lap-Shear Bonding Strength

Lap-shear bonding strength was measured with the method of ASTM standard (ASTM 2005). Fresh porcine skin was cut into 5.08 cm × 2.54 cm pieces with a No. 15 Uniblade^TM surgical scalpel (AD Surgical, Sunnyvale, CA, USA). Two skin strips were adhered on two aluminum blocks with dermal side up with Gorilla^® super glue (The Gorilla Glue Company, Cincinnati, OH, USA). The test specimens were kept moist by wrapping with gauzes soaked with phosphate buffered saline (PBS) (Fisher Scientific, Fair Lawn, NJ, USA) and placed in an environmental chamber at 25 °C. About 80 μL of WPI solution and 20 μL of GTA solution were applied on the skin dermal side and mixed with a small steel spatula and then the two porcine skin strips were overlapped together by the fixture. The bonding area was 2.54 cm × 1.0 cm. Glued specimens were kept for 30 min and tested by an Instron 5566 machine (Instron Corporation, Norwood, MA, USA). Specimens were put tightly in the loading cell of the Instron and the test was started until the two porcine skin stripes separated. The maximum load (N) was recorded and the bonding strength (kPa) was calculated.