A voice as smooth as silk?
Reviewed by Chris Burgess

A number of materials currently exist for vocal fold injection medialisation. Popular options include calcium hydroxylapatite (CaHA), hyaluronic acid (HA) and polydimethylsiloxane (PDMS). The authors of this paper state that there is an unmet need for an injectable material that can sustain medialisation by enabling tissue regrowth within the injected vocal fold to give a permanent effect. A novel, silk protein-based injectable filler is described and assessed in this study, both in an in vitro and in vivo (animal) context, to help determine its potential suitability for use in injection laryngoplasty procedures. Fresh porcine vocal fold tissue was injected with both the silk filler and Prolaryn Plus (a commercially available CaHA-carboxymethylcellulose vocal fold filler) to assess their relative mechanical and rheological properties. Subcutaneous implantation was also performed with both substances in live rodents to assess immune response, particle migration and volume retention. It is reported that lower injection forces were required for the silk filler in comparison to Prolaryn Plus. Injection with silk filler also resulted in less stiffness of the injected vocal fold. Similar macrophage and fibrous tissue infiltration around the injected particles was noted for both materials in the rodent studies. Infiltration of cells into the particles themselves was only noted with silk. Biodegredation analysis suggested that the silk particles would be completely degraded 18 months after implantation. No significant hepatic migration was observed. This is an interesting pre-clinical study with promising initial results. What will be even more interesting will be the results of the proposed in vivo vocal fold implantation study in a canine model, in particular to see whether granuloma formation is an issue (as has been observed with silk sutures). It will also be helpful to compare the outcomes of silk injection to PDMS injection, which is already established as an essentially permanent injectable material.

Injectable Silk Protein Microparticle-based Fillers: A Novel Material for Potential Use in Glottic Insufficiency.
Brown JE, Gulka CP, Giordano JEM, et al.
JOURNAL OF VOICE
2019;33(5):773-80.