A method of making a membrane, the method comprising: (a) casting a first polymer solution containing dissolvable silica nanoparticles onto a patterned substrate, said substrate providing a template of peaks and valleys, (a 1) casting a second polymer solution containing silica dissolvable nanoparticles onto the cast solution of (a); (b) carrying out phase inversion and obtaining a membrane comprising at least one patterned microporous surface; (c) dissolving the nanoparticles and obtaining a nanoparticle-depleted membrane comprising a single integral layer having(i) a first microporous surface;(ii) a second microporous surface;wherein at least the first microporous surface comprises a patterned surface comprising a plurality of peaks and valleys; the patterned surface comprising a plurality of first region surfaces comprising the peaks and a plurality of second region surfaces comprising the valleys;and,(iii) a porous bulk between the first microporous surface and the second microporous surface, the porous bulk comprising a plurality of first region bulks and a plurality of second region bulks;(a) the first region bulks extending from the respective first region surfaces toward the second microporous surface, the first region bulks comprising a first set of pores having outer rims, prepared by removing introduced dissolvable silica nanoparticles, the first set of pores having a first controlled pore size, and a second set of pores connecting the outer rims of the first set of pores, the second set of pores having a second controlled pore size, and a first polymer matrix supporting the first set of pores, wherein the first controlled pore size is greater than the second controlled pore size;(b) the second region bulks extending from the respective second region surfaces toward the second microporous surface, the second region bulks comprising a third set of pores having outer rims, prepared by removing introduced dissolvable silica nanoparticles, the third set of pores having a third controlled pore size, and a fourth set of pores connecting the outer rims of the third set of pores, the fourth set of pores having a fourth controlled pore size, and a second polymer matrix supporting the third set of pores, wherein the third controlled pore size is greater than the fourth controlled pore size; and wherein the pore size of the third set of pores is at least 20% larger or smaller than the pore size of the first pores and wherein said membrane comprises a hexagonal packing of said first and third set of pores, respectively, and a void fraction in the range from 66 vol.-% to 73 vol.-%; and, (d) washing the nanoparticle-depleted membrane. (a) casting a first polymer solution containing dissolvable silica nanoparticles onto a patterned substrate, said substrate providing a template of peaks and valleys, (a 1) casting a second polymer solution containing silica dissolvable nanoparticles onto the cast solution of (a); (b) carrying out phase inversion and obtaining a membrane comprising at least one patterned microporous surface; (c) dissolving the nanoparticles and obtaining a nanoparticle-depleted membrane comprising a single integral layer having(i) a first microporous surface;(ii) a second microporous surface;wherein at least the first microporous surface comprises a patterned surface comprising a plurality of peaks and valleys; the patterned surface comprising a plurality of first region surfaces comprising the peaks and a plurality of second region surfaces comprising the valleys;and,(iii) a porous bulk between the first microporous surface and the second microporous surface, the porous bulk comprising a plurality of first region bulks and a plurality of second region bulks;(a) the first region bulks extending from the respective first region surfaces toward the second microporous surface, the first region bulks comprising a first set of pores having outer rims, prepared by removing introduced dissolvable silica nanoparticles, the first set of pores having a first controlled pore size, and a second set of pores connecting the outer rims of the first set of pores, the second set of pores having a second controlled pore size, and a first polymer matrix supporting the first set of pores, wherein the first controlled pore size is greater than the second controlled pore size;(b) the second region bulks extending from the respective second region surfaces toward the second microporous surface, the second region bulks comprising a third set of pores having outer rims, prepared by removing introduced dissolvable silica nanoparticles, the third set of pores having a third controlled pore size, and a fourth set of pores connecting the outer rims of the third set of pores, the fourth set of pores having a fourth controlled pore size, and a second polymer matrix supporting the third set of pores, wherein the third controlled pore size is greater than the fourth controlled pore size; and wherein the pore size of the third set of pores is at least 20% larger or smaller than the pore size of the first pores and wherein said membrane comprises a hexagonal packing of said first and third set of pores, respectively, and a void fraction in the range from 66 vol.-% to 73 vol.-%; and, (d) washing the nanoparticle-depleted membrane.