Chemical Conjugation of Iron Oxide Nanoparticles for the Development of Magnetically Directable Silk Particles

Magnetically directable materials containing iron oxide nanoparticles (IONPs) have been utilized for a variety of medical applications, including localized drug delivery. Regenerated silk fibroin (RSF) has also been used in numerous regenerative medicine and drug delivery applications, given its biocompatibility and tunable properties. In this work, we explored the hypothesis that chemically conjugating IONPs to RSF to anchor the IONPs to silk microparticles would provide better magnetic guidance than nonconjugated IONPs untethered to silk microparticles. IONPs were fabricated using a coprecipitation method and conjugated with glutathione (GSH) prior to mixing with RSF. IONPs incorporated into RSF were mixed with potassium phosphate buffer to fabricate microparticles. IONPs with and without GSH were characterized for particle size, shape, morphology, GSH conjugation efficiency, and composition. Silk iron microparticles (SIMPs) were also characterized for particle size, shape, and composition and tested for stability, degradation properties, magnetic movability, and cytotoxicity. IONPs demonstrated a uniform size distribution and spherical morphology. Conjugation of IONPs with GSH was verified through changes in the X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) spectra. IONPs and RSF were able to be chemically conjugated and fabricated into SIMPs, which demonstrated a spherical and porous morphology. FTIR revealed an increased β-sheet content in SIMPs, suggesting that the IONPs may be inducing conformational changes in the silk fibroin. SIMPs showed stability up to 4 weeks in ultrapure water and rapid enzymatic degradation within 24 h. SIMPs were able to be moved magnetically through solution and through a hydrogel and were not cytotoxic.