Hylan B Gel Restores Structure and Function to Laser-Ablated Canine Vocal Folds Babak Jahan-Parwar, MD; Dinesh K. Chhetri, MD; Ming Ye, MD; Steven Hart, MD; Gerald S. Berke, MD Objectives: We evaluated cross-linked hyaluronic acid (hylan B gel) as a scaffold for tissue regeneration and mucosal wave restoration in carbon dioxide laser–ablated canine vocal folds. Methods: Five beagles underwent stroboscopy before ablation of the left vocal fold with a carbon dioxide laser. Four weeks later, stroboscopy was repeated before and after submucosal injection of hylan B gel into the left vocal fold of 4 ani- mals and of saline solution in 1 animal. Stroboscopy was repeated 12 weeks later, and histologic analysis was performed. Results: Four weeks after laser ablation, all animals had soft tissue defects and absence of mucosal waves. Hylan B in- jection restored mucosal waves, and saline injection did not. Twelve weeks after injection, hylan B–injected larynges had tissue regeneration and mucosal waves, and the saline-injected larynx had neither. Histology showed regenerated lamina propria with residual foci of hylan B in the hylan B–injected larynges and dense submucosal scar in the saline-injected animal. Conclusions: Submucosal hylan B gel injection in laser-ablated canine vocal folds restored tissue volume and mucosal waves and facilitated functional tissue regeneration over 12 weeks. Hylan B gel may have utility as a soft tissue scaffold for rehabilitation of phonatory function in vocal folds with lamina propria defects. Key Words: hyaluronic acid, hylan B, lamina propria, larynx, laser, tissue engineering, voice. Annals of Otology, Rhinology & Laryngology 117(9):703-707. © 2008 Annals Publishing Company. All rights reserved. 703 From the Division of Head and Neck Surgery, University of California–Los Angeles Medical Center, Los Angeles, California. Dr Jahan-Parwar is currently at the Department of Head and Neck Surgery, Southern California Permanente Medical Group, Baldwin Park, California. Funding was provided by the Division of Head and Neck Surgery, University of California–Los Angeles Medical Center. This study was performed in accordance with the PHS Policy on Humane Care and Use of Laboratory Animals, the NIH Guide for the Care and Use of Laboratory Animals, and the Animal Welfare Act (7 U.S.C. et seq); the animal use protocol was approved by the Institutional Animal Care and Use Committee (IACUC) of the University of California–Los Angeles Medical Center. Presented at the meeting of the American Laryngological Association, Phoenix, Arizona, April 30–May 1, 2004. Correspondence: Gerald S. Berke, MD, Division of Head and Neck Surgery, 200 Medical Plaza, Suite 550, Los Angeles, CA 90095. INTRODUCTION Laryngologists are frequently called upon to treat diseases resulting from loss of vocal fold lamina propria. Lamina propria defects can be due to mul- tiple causes, including atrophy, trauma, scarring, and endoscopic laser resection for vocal fold carci- noma. An ideal method for reconstruction of lami- na propria would be an implant that has viscoelastic properties similar to those of native lamina propria, allows for ultimate replacement by natural lamina propria, and is nontoxic, immunologically inert, and easily placed. Hyaluronic acid is an integral extracellular ma- trix protein in both the human and canine vocal fold laminae propriae. It provides structural support and contributes to the viscoelastic properties of the vo- cal fold lamina propria. Hyaluronic acid has been shown to have viscoelastic properties similar to those of natural vocal fold lamina propria. 1 Rabbit studies show that hyaluronic acid injected into rab- bit vocal folds undergoes rapid degradation, how- ever. 2 Cross-linked hyaluronic acid (hylan B gel) is a derivative of natural hyaluronic acid that has en- hanced rheological properties, has resistance to deg- radation, and promotes connective tissue ingrowth into injected sites. Hylan B gel has been proposed as an augmentation material for vocal fold insuffi- ciency. 3 Large defects of the vocal fold, such as those fol- lowing endoscopic laser resection for glottic car- cinoma, involve multiple layers of lamina propria. The layers of the human and canine vocal fold lami- nae propriae have differing compositions of ground substance, collagen, and elastin, as well as differing predominances of cellular elements. 4,5 Regeneration of complete lamina propria defects requires hetero- geneous cellular infiltration and heterogeneous pro- duction of extracellular matrix, depending upon the depth from the mucosal surface. Vocal fold fibro- blasts have been shown to vary the type of extracel- lular matrix produced, depending upon their envi- ronment. 6 Provision of an artificial soft tissue scaf-