Establishing design principles for spray dried nanofibrillar supraparticles towards modular pulmonary drug delivery systems

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Amyloid nanofibrils (ANFs) were synthesized (few μm length, ~10 nm width) from whey protein (beta-lactoglobulin, βLG) and their influence on the morphology of spray-dried supraparticles (SPs) was analyzed quantitatively with scanning electron microscopy (SEM). Silica nanoparticles (SNPs; 10, 50, 100 nm diameter) or soft polysaccharide nanoparticles (phytoglycogen; ~50 nm diameter) and silver nanowires (SNWs) were used as the SP nanoparticle fraction. We found that ANFs enhance the morphological crumpling of SPs compared to βLG control, indicating faster onset of structural arrest during the SP consolidation due to the high aspect-ratio of ANFs. The crumpling transition could be further modulated by ultrasonic breakup of ANFs to shorter lengths (lower aspect-ratio). Crumpled SP shapes occurred at higher ANF content with increasing SNP size, while soft nanoparticles impeded crumpling at low ANF content. Hollow SP shapes were not observed likely due to crumpling being favored by large drying stresses and plasticity afforded by ANFs. Results on SNW-containing SPs are too preliminary to draw conclusions.Structural integrity of ANFs after spray drying remains unclear. Field-emission SEM could not discern ANFs on SP surfaces. Transmission electron microscopy of never-dried SPs were inconclusive on the presence of ANFs, while water-dispersed SPs displayed short ANF segments.These results have direct relevance to SP particle interactions, aerodynamic/drug release properties and clearance by illuminating the control of SP shape/surface area, and indirectly, their cohesiveness.