Injectable Silk Protein Microparticle-based Fillers: A Novel Material for Potential Use in Glottic Insufficiency

Objectives and Hypothesis. A novel, silk protein-based injectable filler was engineered with the intention of vocal fold augmentation as its eventual intended use. This injectable filler leverages the unique properties of silk protein's superior biocompatibility, mechanical tunability, and slow in vivo degradation to one day better serve the needs of otolaryngologists. This paper intends to demonstrate the mechanical properties of the proposed novel injectable and to evaluate its longevity in animal models. Materials and Methods. Experimental. The mechanical properties of silk bulking agents were determined to characterize deformation resistance and recovery compared with commercially available calcium hydroxylapatite through rheologic testing. Fresh porcine vocal fold tissue was used for injectable placement to simulate the mechanical outcomes of native tissue after bulking procedures. In vivo subcutaneous rodent implantation examined immune response, particle migration, and volume retention. Results. Porous, elastomeric silk microparticles demonstrate high recovery (>90% original volume) from compressive strain and mimic the native storage modulus of soft tissues (1-3 kPa). Injectable silk causes only a slight increase in porcine vocal fold stiffness immediately after injection (20%), preserving the native mechanics of bulked tissue. In the subcutaneous rat model, silk demonstrated biocompatibility and slow degradation, thus enabling host cell integration and tissue deposition. Conclusions. The presented novel silk injectable material demonstrates favorable qualities for a vocal fold injection augmentation material. An in vivo long-term canine study is planned.