A novel multiple soaking temperature (MST) method to prepare polylactic acid foams with bi-modal open-pore structure and their potential in tissue engineering applications

• Polylactic acid foams having bi-modal open-pores structure were prepared.
• Multiple soaking temperature method was used for batch foaming.
• Large pores were caused by aggregation of CO2.
• Open-pores were created by optimizing foaming temperature.
• Fibroblast cells adhered and proliferated well on the foams.

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 μm and 8 μm, respectively. The biocompatibility of the PLA open-pore foams was verified by 3T3 fibroblast cell culture.

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