Preparation of bi-continuous macroporous polyamide copolymer membranes for cell culture

Skinless bi-continuous macroporous membranes with extremely high porosity, ∼80%, were prepared by the non-solvent induced phase separation (NIPS) process, from casting dopes composed of Elvamide (co-polymer of Nylon-6, -66, and -610), chitosan, and formic acid that were immersed in a water bath maintained at 10 °C. The Chitosan, while functioned as a pore former, migrated along with out-diffusing formic acid into the bath during the NIPS process, thereby, breaking the top gel-layer and the boundaries between cellular pores to yield a morphology featuring interpenetration networks of pores and polymer host. The amount of chitosan added to the dope affected significantly the pore size and porosity of the membranes formed, as revealed by SEM observations. At the highest chitosan/Elvamide ratio of 0.155, very large pore size (∼30 μm) and porosity (83%) were achieved, whereas at the lowest ratio of 0.1, the membrane became asymmetric, and the pore size was reduced to ∼15 μm. 1H NMR analyses indicated that chitosan was completely removed during the precipitation process. Furthermore, L929 cells were cultured on various porous membranes. It is interesting to find that this cell was able to dwell on the pore walls in the cross sectional region, although with a smaller proliferation than on a flat nonporous surface.