Table 1.
Comparison of the repetitive primary structural elements of natural adhesive polymers.
| Natural polymer | Amino acid motif/Chemical structure | Ecological purpose | Adhesion strength | References | |
|---|---|---|---|---|---|
| Sericin | (SSTGSSSNTDSNSNSVGSSTSGGSSTYGYSSNSRDGSV)n | Sticky outside coating |  |
4.1 ± 2 N | Ahn et al., 2001 |
| Silkworm firboin | GAGAGS, GXn, where X = A, Y, V | Core of silk fiber |  |
54 mN or 146.6 mN/cm2 | Jiang et al., 2006; Kundu et al., 2008a |
| Aggregate silk | Gly-rich (64-mer), XPGXG (36-mer,) GGX/NXNXN (33-mer) | Aqueous glue for web |  |
0.1–0.4 mN | Sahni et al., 2011; Vasanthavada et al., 2012; Opell et al., 2013 |
| Piriform silk | QQSSVA, PXPXP | Attachment cement |  |
39.8 ± 8.9 mN | Perry et al., 2010; Grawe et al., 2014; Wolff et al., 2015 |
| Caddisfly silk | O-phospho-ser cluster (SX)n where X = V, L, I, R; and n is 2–6 | Underwater cement for protective case |  |
32.7 ± 6.6 MPa (stress at fracture) | Ohkawa et al., 2013; Lane et al., 2015 |
| Chitosan |  |
Shellfish |  |
32.4 ± 14.5 mN 3.9–6.7 mN/cm2 | Bernkop-Schnürch and Freudl, 1999; Lehr et al., 1992 |
Note that the values for adhesion strength cannot be compared due to different techniques used to gather the data.