Prokaryotic expression system and methods of using the same

A composition comprising a synthetic major ampullate spidroin protein (MaSp)-based polymer in the form of particles having an average size in the range of 0.5 μm to 1.5 μm;

• wherein said MaSp-based polymer is a MaSp1 protein comprising a single N-terminal region, a single C-terminal region and a repetitive region comprising 10-20 repeats, wherein at least one of:
• (i) each of said repeats is between 5 and 60 amino acids long;
• and (ii) each of said repeats has at least 70% homology to a repetitive sequence derived from the repetitive region of Araneus diadematus fibroin 4 (ADF4) protein,
• wherein the repetitive region of the ADF4 protein comprises the amino acid sequence as set forth in SEQ ID NO:
• 1 (AAAAAAASGSGGYGPENQGPSGPVAYGPGGPVSSAAAAAAAGSGPGGYGPENQ GPSGPGGYGPGGSGSSAAAAAAAASGPGGYGPGSQGPSGPGGSGGYGPGSQGPSG PGASSAAAAAAAASGPGGYGPGSQGPSGPGAYGPGGPGSSAAASGPGGYGPGSQ GPSGPGGSGGYGPGSQGPSGPGGPGASAAAAAAAAASGPGGYGPGSQGPSGPGA YGPGGPGSSAAASGPGGYGPGSQGPSGPGAYGPGGPGSSAAAAAAAGSGPGGYG PGNQGPSGPGGYGPGGPGSSAAAAAAASGPGGYGPGSQGPSGPGVYGPGGPGSSA AAAAAAGSGPGGYGPGNQGPSGPGGYGPGGSGSSAAAAAAAASGPGGYGPGSQ GPSGPGGSGGYGPGSQGPSGPGASSAAAAAAAASGPGGYGPGSQGPSGPGAYGPG GPGSSAAASGPGGYGPGSQGPSGPGAYGPGGPGSSAAAAAAASGPGGYGPGSQGP SGPGGSRGYGPGSQGPGGPGASAAAAAAAAASGPGGYGPGSQGPSGPGYQGPSG PGAYGPSPSASAS).