Ultrafine silk powder from biocompatible surfactant-assisted milling

• Ultrafine and uniform silk particles with d(0.5) of around 200 nm were produced.
• Milling was conducted in the presence of a biocompatible surfactant (Tween 80).
• Effects of surfactant concentration and bead size were analyzed.

A method for producing silk nanoparticles was presented where a biocompatible surfactant, Tween 80, was used to assist milling. Initially, silk particles with a volume median particle size (d(0.5)) of ~ 7 μm were produced as a precursor, by attritor milling of silk snippets. The precursor particles were subsequently bead milled using 0.5-mm beads and Tween 80 of various concentrations. Silk particles with d(0.5) of ~ 200 nm having a narrow particle size distribution (d(0.9)–d(0.1) = 191 nm) were produced by employing 30% Tween 80 on the weight of powder (owp). Reducing bead size to 0.05 mm did not influence the final d(0.5) significantly. Recovering silk nanoparticles from slurries was carried out using spray drying and freeze drying. Spray drying resulted in particles with d(0.5) of 2–3 μm, regardless of the primary particle size in the slurry. Freeze drying induced a much higher level of particle aggregation than spray drying.

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