Spray Drying of Regenerated Silk: Understanding and Controlling Particle Size and Solubility

This study demonstrates the use of spray drying as a versatile processing technique to produce regenerated silk powders with a controllable particle size and solubility. After overcoming silk's shear sensitivity and establishing a usable processing window, semicrystalline silk powders were produced. The impact of silk properties and spray drying conditions on powder properties was then explored. Spray drying produced spherical hollow or collapsed particles similar to other spray dried proteins; particle size could be controlled from a d(50) of less than 5 to almost 40 μm through altering feedstock concentration. Interestingly, the silk secondary structure, which typically dictates silk solubility, was resilient to changes in spray drying conditions: all powder samples ranged from 39 to 42% β-sheet content. Yet despite these findings, silk solubility could be controlled from less than 4% to nearly 60% purely by changing fibroin molecular weight and, to a lesser extent, concentration. Given the commercial viability of spray drying, this study demonstrates significant potential for the production of powders with controllable properties for a range of possible applications, from biomaterials to food or cosmetic applications.