Improving the dynamic properties of silk particles by co-spray drying with L-leucine

Abstract

In this work, we describe a novel approach to engineer silk into composite micro-sized particles by a combination of wet milling and homogenization followed by co-spray drying of the silk micro-particle suspension with L-leucine. We report the first example of the formation of a discrete L-leucine layer onto a composite micro-powder via co-spray drying of the milled suspension. We used milled silk suspension with or without subsequent high-pressure homogenisation. High pressure homogenization was done to further reduce particle size and to understand if the change in size could change the interaction with L-leucine during spray drying. Powder rheometric results revealed that the co-spray dried silk powder (both unhomogenised and homogenised samples) has substantially modified the dynamic bulk properties compared to untreated powder, and the bulk behaviour has varied with the level of L-leucine addition. The silk powder without L-leucine exhibited higher compressibility (35%) than the L-leucine-added samples (25%) at 1 kPa pressure. Overall, the outcomes from this study revealed that L-leucine co-spray drying has reduced the cohesiveness and improved the stability and flowability of the silk powders irrespective of the final step of homogenization was performed or not. There were no substantial changes in particle size in the presence of L-leucine, based on laser size distribution measurements. These improved properties are expected to aid and enable further formulation processing and applications of silk protein powder in diverse fields such as cosmetics, composites, biomedical, and others.