Permanent volumetric compression with heat treatment (PVCT) method was employed in order to create a negative Poisson’s ratio to the scaffolds . For the experimental specimen, heat treatment was applied to the temperature above its Tg in a drying oven (DMC-122, DJDAEIL, Daejeon, Korea). The specimen was then compressed in three orthogonal directions at the same time. Firstly, heat treatment was applied to the specimens at 50 °C/5 min, 50 °C/10 min, 60 °C/5 min and 60 °C/10 min. Secondly, tri-axial compression was applied with 2.4:1 and 3.1:1 in volumetric ratio. The experimental specimens were compressed in three orthogonal directions by two Teflon molds up to 1.5 × 1.5 × 1.5 (cm3) in size and became the same size as that of control (see Fig. 1). The specimens were then cooled at room temperature and removed from the mold.Fig. 1Make same pore size to control specimens via permanent volumetric compression. Volumetric compression ratios are 2.4 and 3.1. 2 × 2 × 2 (cm3) to 1.5 × 1.5 × 1.5 (cm3) size is 2.4 : 1 and 2.2 × 2.2 × 2.2 (cm3) to 1.5 × 1.5 × 1.5 (cm3) size 3.1 : 1