Fig 1 showed the number of L929 mouse fibroblasts attached and proliferated on the blended F/S
films prepared from 2 types of silk fibroins at various sericin concentrations. For both types of silk
fibroin, we found the lower cell number attached and proliferated on the blended F/S films at all
sericin concentrations, compared to that on glass and pure fibroin. However, PDT calculated from
log phase of cell growth indicated that proliferation rate of cells cultured on the blended F/S films
was similar to that of cells cultured on glass and pure fibroin films. This implied that low number of
cells attached on the blended films could further proliferate on such films. From the results, heat
extracted sericin might show less biocompatibility to L929 cells. Thus, we further investigated the
compatibility of sericin extracted from other methods such as acid, alkali and urea treatments,
compared to that extracted from heat treatment. The results (Fig 2) showed the number of L929
mouse fibroblasts attached and proliferated on pure silk sericin films which were extracted by
different methods. For cell attachment test, heat and alkali extracted sericin films showed low
percentage of cell attachment at 48% and 53%, respectively, while high percentage of cell
attachment on acid and urea extracted sericin (92% and 88%, respectively) was found (Table 2).
However, after 48 h culture, number of cells proliferated on all sericin films was not significantly
different. This indicated that L929 cells had different proliferation rate when cultured on different
types of sericin films, as confirmed by PDT. The PDT of cells proliferated on urea extracted sericin
film (27 h) was similar to that on heat extracted sericin film (29 h). Furthermore, cells proliferated
on both pure heat and urea extracted sericin films showed significantly lower PDT than those
proliferated on the blended F/S films. This suggested that sericin extracted by urea treatment could
enhance cell proliferation rate which may be due to the suitability of its polypeptide chains.