Examining the Thermostability of Silk Fibroin Micro- and Nano- Particles

Biopolymeric micro- and nano- particles made from naturally derived materials have been utilized for encapsulation and controlled release of bioactive molecules. Formation of these particles from silk fibroin is useful due to the stabilization properties of the biopolymer and its degradation into small, soluble peptides and amino acids in vivo. This work aims to further investigate the stability of silk fibroin particles to advance the potential for translation when used in the design of controlled delivery systems. We investigated the thermostability of particles stored at 23 and 37°C to evaluate the potential of silk particle formulations to bypass the need for strict cold-chain storage. The particles used for these experiments will be compared relative to a control batch of particles stored at 4°C, which express hydrodynamic diameters of ~200-1000 nm. The silk fibroin is initially isolated from Bombyx mori cocoons, and the particles are formed by phase separation with polyvinyl alcohol (PVA), which is induced via probe sonication. The amplitude of sonication, silk processing conditions, and relative concentrations of silk and PVA contribute to the final particle characteristics. In our group, previous work determined a set of parameters that result in desired particles sizes. For our sonicating conditions, we utilized a sonication amplitude of 25% for 30 seconds prior to casting the film and a sonication amplitude of 15% for 15 seconds after resuspension, using silk degummed for 60 minutes. Weekly samples were imaged via a Keyence BZ-X800 microscope in bright field to observe and confirm the absence of any bacterial contamination. Weekly samples were also analyzed via dynamic light scattering (DLS) to assess changes in average hydrodynamic particle diameter (Z_avg) and particle size distribution (PDI). Additionally, scanning electron microscopy (SEM) was used to evaluate morphology and confirm physical size. No changes were measured in the Z_avg and the PDI values remained consistent over time compared to the control. Future work aims to explore the thermostability of silk fibroin particles loaded with therapeutic agents and oxygen carriers.