The epoxy resin and hardener (CP362 A/B, Oriental Option Sdn Bhd, Penang, Malaysia) were prepared at a ratio of 2:1 (w/w) and poured into the paper mold to be cured overnight at the room temperature (25 ◦C). PDMS pre-polymer (Sylgard 184, Dow Corning, Midland, MI, USA) ...