Bi-modal pore structures were obtained by stepwise depressurization in batch foaming method. In this study, a novel method was developed to produce polylactic acid (PLA) foam with bi-modal pore structure by using multiple soaking temperature (MST) method based on one-step pressure release. The effects of soaking time and temperatures on the formation of bi-modal pore structure were investigated in detail. The formation of macro pores was attributed to the synergistic effect of the supercritical carbon dioxide (SC-CO2) aggregation and the depressurization process. Moreover, bi-modal open-pore structures could be obtained at certain processing conditions. The PLA foams achieved porosity and open pore content as high as 87.9% and 82.4%, with average macro and micro pore size of 150 mu m and 8 mu m, respectively. The biocompatibility of the PLA open-pore foams was verified by 3T3 fibroblast cell culture. (C) 2015 Elsevier B.V. All rights reserved.