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Silk began to serve as a [[biomedicine|biomedical]] material for sutures in surgeries as early as the second century CE.<ref>{{cite journal |last1=Muffly |first1=Tyler |last2=Tizzano |first2=Anthony |last3=Walters |first3=Mark |title=The history and evolution of sutures in pelvic surgery. |journal=Journal of the Royal Society of Medicine |date=March 2011 |volume=104 |issue=3 |pages=107–12 |doi=10.1258/jrsm.2010.100243 |pmid=21357979 |pmc=3046193 |language=en |quote=Galen also recommended using silk suture when available.}}</ref> In the past 30 years, it has been widely studied and used as a [[biomaterial]] due to its [[strength of materials|mechanical strength]], [[biocompatibility]], tunable degradation rate, ease to load cellular growth factors (for example, BMP-2), and its ability to be processed into several other formats such as films, gels, particles, and scaffolds.<ref name="Rockwood-2011">{{cite journal |last1=Rockwood|first1=Danielle N|last2=Preda|first2=Rucsanda C|last3=Yücel|first3=Tuna|last4=Wang|first4=Xiaoqin|last5=Lovett|first5=Michael L|last6=Kaplan|first6=David L|title=Materials fabrication from ''Bombyx mori'' silk fibroin|journal=Nature Protocols|volume=6|issue=10|pages=1612–1631|doi=10.1038/nprot.2011.379|pmc=3808976|pmid=21959241|year=2011}}</ref> Silks from ''Bombyx mori'', a kind of cultivated silkworm, are the most widely investigated silks.<ref>{{cite journal |last1=Altman|first1=Gregory H|last2=Diaz|first2=Frank|last3=Jakuba|first3=Caroline|last4=Calabro|first4=Tara|last5=Horan|first5=Rebecca L|last6=Chen|first6=Jingsong|last7=Lu|first7=Helen|last8=Richmond|first8=John|last9=Kaplan|first9=David L|date=1 February 2003|title=Silk-based biomaterials|journal=Biomaterials|volume=24|issue=3|pages=401–416|doi=10.1016/S0142-9612(02)00353-8|pmid=12423595|citeseerx=10.1.1.625.3644}}</ref>
Silks derived from ''Bombyx mori'' are generally made of two parts: the [[silk fibroin]] fiber which contains a light chain of 25 kDa and a heavy chain of 350 kDa (or 390 kDa<ref>{{cite journal|author2-link=David L. Kaplan (engineer)|last1=Vepari|first1=Charu|last2=Kaplan|first2=David L.|date=2007-08-01|title=Silk as a biomaterial|journal=Progress in Polymer Science|series=Polymers in Biomedical Applications|volume=32|issue=8–9|pages=991–1007|doi=10.1016/j.progpolymsci.2007.05.013|pmc=2699289|pmid=19543442}}</ref>) linked by a single disulfide bond<ref>{{cite journal |last1=Zhou|first1=Cong-Zhao|last2=Confalonieri|first2=Fabrice|last3=Medina|first3=Nadine|last4=Zivanovic|first4=Yvan|last5=Esnault|first5=Catherine|last6=Yang|first6=Tie|last7=Jacquet|first7=Michel|last8=Janin|first8=Joel|last9=Duguet|first9=Michel|date=2000-06-15|title=Fine organization of ''Bombyx mori'' fibroin heavy chain gene|journal=Nucleic Acids Research|volume=28|issue=12|pages=2413–2419|pmc=102737|pmid=10871375|doi=10.1093/nar/28.12.2413}}</ref> and a glue-like protein, [[sericin]], comprising 25 to 30 percentage by weight. Silk fibroin contains hydrophobic [[beta sheet]] blocks, interrupted by small hydrophilic groups.
Most products fabricated from regenerated silk are weak and brittle, with only ≈1–2% of the mechanical strength of native silk fibers due to the absence of appropriate secondary and hierarchical structure,
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