Researchers from Tufts University, Imperial College London, and the University of Michigan have developed a new way to turn natural silk into an ultra-strong solid material without dissolving the fibers or using synthetic additives. The resulting material rivals advanced composites in strength and toughness while remaining biocompatible and tunable for medical applications.<\/p>\n
Instead of breaking silk down into proteins and rebuilding it, the team fused aligned silk fibers directly using controlled heat and pressure. The process preserves much of silk\u2019s original molecular structure, allowing the final material to retain the natural strength of the fibers.<\/p>\n
The researchers said the fused silk outperformed materials like bone and wood in tensile toughness and came close to Kevlar. It also showed higher ballistic impact resistance than some carbon fiber reinforced polymer composites.<\/p>\n
\u201cThe process breaks down the natural fibers into the individual silk fibroin proteins before processing them into new shapes, so we lose a lot of the inherent strength of the original fibers,\u201d said Chunmei Li, research assistant professor at Tufts School of Engineering.<\/p>\n
\u201cWith this new method, there\u2019s no need to dissolve the silk\u2014we simply align the fibers and apply heat and pressure, and they fuse together in one step.\u201d<\/p>\n
Silk strength rebuilt<\/p>\n
The material starts with commercially available silk moth cocoon fibers used in textile manufacturing. Researchers first removed sericin, the sticky coating around the fibers, using a mild sodium carbonate solution. The fibers were then aligned and hot-pressed under carefully controlled temperatures and pressures.<\/p>\n
During heating, the more mobile parts of the silk protein structure softened enough to bond neighboring fibers together while preserving the crystalline regions responsible for strength and flexibility.<\/p>\n
\u201cThe silk is like a composite,\u201d said David Kaplan, Stern Family Endowed Professor of Engineering at Tufts. \u201cThere is a more mobile, amorphous phase of the fiber proteins, and there is the part of the protein chain that folds to form sheet-like surfaces that stack up into crystalline structures.\u201d<\/p>\n
Researchers found an optimal processing window between 257 and 419 degrees Fahrenheit and pressures ranging from 1,900 to 9,800 atmospheres. Too little heat or pressure created weaker structures, while excessive temperatures made the material brittle.<\/p>\n
The final structure resembles wood at a microscopic level, with aligned fiber bundles bonded together to distribute stress efficiently. According to the researchers, this hierarchical structure contributes to the material\u2019s unusual combination of toughness and durability.<\/p>\n
Tuned for human body<\/p>\n
The team also tested fused silk for biomedical applications. Animal studies showed the material triggered only mild immune <\/a>responses that reduced over time.<\/p>\n Researchers found they could tune how quickly the material degrades by adjusting processing conditions. Less densely fused versions allowed cells to infiltrate gradually, while denser forms resisted breakdown and remained stable for longer periods.<\/p>\n \u201cWe can control how fast the material degrades depending on the conditions we use,\u201d Li said.<\/p>\n