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.

A novel silk-based vocal fold augmentation material: 6-month evaluation in a canine model.

OBJECTIVES: Ideal long-term vocal fold augmentation materials should be biocompatible, easily administered, allow tissue integration for long-term effect, and remain at the site of injection. A novel silk protein particle suspended in hyaluronic acid (Silk-HA) has been developed specifically for vocal fold augmentation to address this unmet need. This article presents the 6-month, preclinical findings of a canine vocal fold injection trial for Silk-HA. METHODS: Twelve beagle dogs were injected transorally in the lateral/deep aspect of their right thyroarytenoid muscles with 0.3 cc of Silk-HA or calcium hydroxylapatite in carboxymethyl cellulose (CaHA-CMC). The Silk-HA particle injectable was delivered via a custom catheter, whereas CaHA-CMC was delivered through a commercially available malleable needle. The six dogs from each material group were sacrificed 6 months from the injection date for the evaluation of implant longevity, immune response, and material migration. RESULTS: Silk-HA provides immediate medialization of the right vocal fold, lasting for a minimum of 6 months in a canine model. Silk-HA and CaHA-CMC both demonstrate similar inflammatory responses. The Silk-HA was shown to remain without migration at the site of injection in all six canine subjects, whereas CaHA-CMC demonstrated migration in four of the six canines. In two canines implanted with CaHA-CMC, material was discovered to migrate to the retropharyngeal lymph nodes. CONCLUSION: In a canine subject model, the Silk-HA material compares favorably in terms of longevity and immune response to CaHA-CMC. The lack of migration of the Silk-HA material demonstrates a promising potential for vocal fold injection in the clinic. LEVEL OF EVIDENCE: NA Laryngoscope, 129:1856-1862, 2019.

Predicting rates of in vivo degradation of recombinant spider silk proteins.

Developing fundamental tools and insight into biomaterial designs for predictive functional outcomes remains critical for the field. Silk is a promising candidate as a biomaterial for tissue engineering scaffolds, particularly where high mechanical loads or slow rates of degradation are desirable. Although bioinspired synthetic spider silks are feasible biomaterials for this purpose, insight into how well the degradation rate can be programmed by fine tuning the sequence remains to be determined. Here we integrated experimental approaches and computational modelling to investigate the degradation of two bioengineered spider silk block copolymers, H(AB)2 and H(AB)12 , which were designed based on the consensus domains of Nephila clavipes dragline silk. The effect of protein chain length and secondary structure on degradation was analysed in vivo. The degradation rate of H(AB)12 , the silk with longer chain length/higher molecular weight, and higher crystallinity, was slower when compared to H(AB)2 . Using full atomistic modelling, it was determined that the faster degradation of H(AB)2 was due to the lower folded molecular structure of the silk and the greater accessibility to solvent. Comparison of the specific surface areas of proteins via modelling showed that higher exposure of random coil and lower exposure of ordered domains in H(AB)2 led to the more reactive silk with a higher degradation rate when compared with H(AB)12 , as validated by the experimental results. The study, based on two simple silk designs demonstrated that the control of sequence can lead to programmable degradation rates for these biomaterials, providing a suitable model system with which to study variables in protein polymer design to predict degradation rates in vivo. This approach should reduce the use of animal screening, while also accelerating translation of such biomaterials for repair and regenerative systems. Copyright © 2016 John Wiley & Sons, Ltd.