S1 Supporting Information to Entrapment of Metal Nanoparticles in Polymer Stomatocytes Daniela A. Wilson*, Roeland J. M. Nolte, and Jan C. M. van Hest* Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands Stomatocyte, hybrid polymersomes, shape transformation, platinum nanoparticles, confinement, nucleation, template Content 1. Materials ....................................................................................................................................... S2 2. Instrumentation .......................................................................................................................... S2 3. Synthesis of amphiphilic block copolymers ........................................................................... S3 4. Shape transformations of polymersomes into stomatocytes ............................................... S3 5. Synthesis of platinum nanoparticles with tailored size & shape ........................................... S4 Platinum nanoparticles via sonication method......................................................... S4 Platinum nanoparticles via hydrogen reduction method .......................................... S4 6. Entrapment of platinum nanoparticles via in situ method ..................................................... S5 7. Entrapment of platinum nanoparticles during shape transformation.................................... S6 Supplementary Fig. S1-3. Detailed TEM images of stomatocytes ........................................ S7 Supplementary Fig. S4. UV-VIS spectra of platinum nanoparticles and stomatocytes ......... S8 Supplementary Fig. S5-16. Detailed TEM and SEM images of stomatocyte hybrids............ S9 Supplementary Fig. 17. TEM images and size distribution of platinum nanoparticles ........ S20