A composition comprising a pure silk fibroin-based protein fragment substantially lacking sericin, having an average weight average molecular weight in the range of about 17 kDa to about 38 kDa, and about 1.5 to about 3.0 Disclosed are compositions having a polydispersity in the range of, substantially uniform, comprising from 0 ppm to about 500 ppm inorganic residues and from 0 ppm to about 500 ppm organic residues. [Selection] Fig. 79セリシンを実質的に欠いている純粋な絹フィブロインベースのタンパク質断片を含む組成物であって、約17kDa~約38kDaの範囲の平均の重量平均分子量を有し、約1.5~約3.0の範囲の多分散性を有し、実質的に均一であり、0ppm~約500ppmの無機残渣を含み、0ppm~約500ppmの有機残渣を含む組成物を開示する。【選択図】図79