**5. New vocal fold wound closure device – Bioabsorbable microclips**

A large part of our work is focused on the development of bioabsorable surgical microclips for vocal fold wound closure. Based on combining the ease and efficiency of using fibrin glue with the precision of microsutures, such surgical microclips have the potential to reduce vocal fold scar and procedure time, cumulating in cost savings and reduced morbidity for patients.

Surgical clips have been used in various areas of the body but have not been described previously for use on the vocal folds. This may be due to challenges facing the design of a surgical clip for application in this area, including the need for extremely small size, ability to withstand high vibration frequencies and shearing stresses during phonation, and the need for bio-absorbability. A number of materials have been studied in the design of surgical clips in other areas. Stainless steel clips and materials such as titanium and tantalum have been used for example to ligate the cystic duct and artery in laparoscopic cholecystectomy (Charara, Dion et al. 1994) However, some limitations of these materials include significant foreign body reaction, poor holding power and significant interference with roentgenologic studies like computerized tomography (CT) and magnetic resonance imaging (Klein, Jessup et al. 1994; Min Tan and Okada 1999; Pietak, Staiger et al. 2006; Rosalbino, De Negri et al. 2010). The

Using stroboscopy, Choo et al observed vibratory dynamics in their mechanically driven model similar to that of the mucosal wave in human vocal folds. After simulating a microflap and then subjecting the vocal fold phantom to vibration, cracks were found propagating radially outwards. Both these features suggested that the setup had potential

Fig. 2. Mechanical larynx setup courtesy of Choo et al (Choo, Lau et al. 2010).

**5. New vocal fold wound closure device – Bioabsorbable microclips** 

A large part of our work is focused on the development of bioabsorable surgical microclips for vocal fold wound closure. Based on combining the ease and efficiency of using fibrin glue with the precision of microsutures, such surgical microclips have the potential to reduce vocal fold scar and procedure time, cumulating in cost savings and reduced

Surgical clips have been used in various areas of the body but have not been described previously for use on the vocal folds. This may be due to challenges facing the design of a surgical clip for application in this area, including the need for extremely small size, ability to withstand high vibration frequencies and shearing stresses during phonation, and the need for bio-absorbability. A number of materials have been studied in the design of surgical clips in other areas. Stainless steel clips and materials such as titanium and tantalum have been used for example to ligate the cystic duct and artery in laparoscopic cholecystectomy (Charara, Dion et al. 1994) However, some limitations of these materials include significant foreign body reaction, poor holding power and significant interference with roentgenologic studies like computerized tomography (CT) and magnetic resonance imaging (Klein, Jessup et al. 1994; Min Tan and Okada 1999; Pietak, Staiger et al. 2006; Rosalbino, De Negri et al. 2010). The

for surgical experimentation.

morbidity for patients.

introduction of ligating clips manufactured from novel polymers such as polydioxanone in laparoscopic cholecystectomy helped to address these limitations. These clips are completely absorbed in the process of ester bond hydrolysis over a period of 180 days and the by-products are excreted by urine. Moreover, these clips produce minimal tissue reactivity with good adhesion and are radiolucent (Klein, Jessup et al. 1994).

Earlier investigations using clips constructed from such polymers proved unsuitable for our requirements, as they could not provide adequate structural strength due to the minute size of the clips. As such, we are investigating the potential of using magnesium as the main bioabsorbable material to construct such microclips.

There are many reviews on the potential and viability of magnesium as a biomaterial (Pietak, Staiger et al. 2006; Witte, Hort et al. 2008; Zeng, Dietzel et al. 2008). Most of these studies focused on the use of magnesium in orthopaedic implants and bio-absorbable vascular stents, concentrating on improving its mechanical properties by alloying with various elements. Zhang et al. (Zhang and Yang 2008) reported significant improvement of both biocompatibility and mechanical properties with use of Zn as an additional alloying element to Mg-Si. Gu et al. (Gu, Zheng et al. 2009) reported good biocompatibility of magnesium with various alloying elements, recommending Al and Y for stents and Al, Ca, Zn, Sn, Si and Mn for orthopaedic implants. Drynda et al. (Drynda, Hassel et al. 2010) developed and evaluated fluoride coated Mg-Ca alloys for cardiovascular stents, reporting good biocompatibility and better degradation behaviour. However, as pure magnesium has been found to corrode too quickly in the low pH environment of physiological systems, much effort has also been placed into developing alloys or coatings to limit its degradation behaviour (Zeng, Dietzel et al. 2008). Rosalbino et al. (Rosalbino, De Negri et al. 2010) reported improved corrosion behaviour of Mg-Zn-Mn alloys for orthopaedic implants. Kannan et al. (Kannan and Raman 2008) studied the corrosion of AZ series (Al and Zn) magnesium alloys with the further addition of Ca, reporting significantly improved corrosion resistance with a reduction in mechanical properties (15% ultimate tensile strength and 20% elongation before fracture). Zhang et al. (Zhang, Zhang et al. 2009) reported the use of dual layer coatings of hydroxyapatite to considerably slow down the degradation of 99.9% pure magnesium substrates without heat treatment.

Based on the good biocompatibility and healing results demonstrated by these previous studies, we hypothesized that a bio-absorbable magnesium clip will be able to hold the wound site more securely and facilitate better healing as compared to surgical glue adhesives. Furthermore, with a design specifically aimed to reduce technical complexity in achieving apposition of epithelial flaps, a specifically designed prototype applicator could improve the ease of handling and speed of insertion, possibly translating to improved surgical outcomes. Due to the difficulty of simulating the vocal fold environment for both mechanical and bioabsorbability studies, in-vivo experiments were carried out to evaluate the feasibility of the clips in accordance to an approved protocol.

#### **5.1 In-vivo evaluation of microclips**

A 30-40 kg pig has upper airway dimensions that provide reasonable approximation to that of an adult human. Using this in-vivo model we were able to approach the larynx

Investigation of Experimental Wound Closure Techniques in Voice Microsurgery 125

We have given an overview of the current techniques used clinically for vocal fold wound closure and an update on the potential of some microsurgical techniques proposed in current literature. Animal and artificial models have been discussed, highlighting the complexities of selecting appropriate experimental models and methods for evaluation of vocal fold microsurgery. We shared our experience in experimental microsurgery with respect to wound closure, specifically addressing the vocal fold microclip, which is a new wound closure device. The methods for testing the integrity and bio-absorption properties of such devices in vivo and the technical challenges of applying such devices accurately

Alipour, F. and S. Jaiswal (2008). "Phonatory characteristics of excised pig, sheep, and cow

Alipour, F., S. Jaiswal, et al. (2011). "Vocal Fold Elasticity in the Pig, Sheep, and Cow

Alipour, J. and S. Jaiswal (2007). "Glottal airflow resistance in excised pig, sheep and cow

Benninger, M. S. (2000). "Microdissection or Microspot CO2 Laser for Limited Vocal Fold Benign Lesions: A Prospective Randomized Trial." *The Laryngoscope* 110 (S92): 1-1. Benninger, M. S., D. Alessi, et al. (1996). "Vocal fold scarring: Current concepts and management." *Otolaryngology - Head and Neck Surgery* 115 (5): 474-482. Blakeslee, D. B., R. E. Banks, et al. (1995). "Analysis of Vocal Fold Function in the Miniswine

Bleach, N., C. Milford, et al., Eds. (1997). *Operative Otorhinolaryngology*, Blackwell Science

Bless, D. and N. Welham. (2010). "Characterization of vocal fold scar formation, prophylaxis,

Branski, R. C., C. A. Rosen, et al. (2005). "Acute vocal fold wound healing in a rabbit model."

Branski, R. C., K. Verdolini, et al. (2006). "Vocal Fold Wound Healing: A Review for

Burns, J. A., R. E. Hillman, et al. (2009). "Phonomicrosurgical treatment of intracordal vocal-

Campagnolo, A. M., D. H. Tsuji, et al. (2010). "Histologic study of acute vocal fold wound

Carneiro, C. d. G. and F. Scapini (2009). "The Rabbit as an Experimental Model in

Charara, J., Y. M. Dion, et al. (1994). "Mechanical characterization of endoscopic surgical

healing after corticosteroid injection in a rabbit model." *Ann Otol Rhinol Laryngol*

staples during an experimental hernia repair." *Clinical Materials* 16 (Compendex):

and treatment using animal models." 6. Retrieved 9417024, 18, from http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=reference&D=ovftl&NEWS=N

during microsurgery in the larynx were also discussed.

larynges." *J Acoust Soc Am* 123 (6): 4572-4581.

Model." *Journal of Investigative Surgery* 8 (6): 409-424.

Larynges." *Journal of Voice* 25 (2): 130-136.

larynges." *Journal of Voice*.

&AN=00020840-201012000-00003.

*Ann Otol Rhinol Laryngol* 114 (1 Pt 1): 19-24.

Clinicians." *Journal of Voice* 20 (3): 432-442.

fold cysts in singers." *The Laryngoscope* 119 (2): 419-422.

Laryngology." *Arq. Int. Otorrinolaringol.* 13 (2): 146-150.

**6. Conclusion** 

**7. References** 

Ltd.

119 (2): 133-139.

81-89.

using a standard adult operating laryngoscope (Promed 222mm operating laryngoscope, Tuttlingen, Germany). To simulate endoscopic laryngeal microsurgery, the pig was positioned supine with the cervical spine slightly flexed. The laryngoscope was passed trans-orally following intubation with a size 5 endotracheal tube. As in most mammals, the epiglottis is intra-nasal and must therefore be drawn down into the oropharynx in order to access the vocal folds during laryngoscopy; if per-oral intubation is performed, this is usually accomplished during intubation. The laryngoscope was suspended on a custom made frame that enabled adjustments to be made to the position of the scope's tip, so as to optimize visualization of the vocal folds. By combining this with a 400mm focallength binocular microscope, the setup as seen in Figure 3 was close to that expected during surgery in an adult human.

Fig. 3. Setup for endoscopic laryngeal microsurgery in the anaesthetized pig. (a) Operating laryngoscope. (b) Suspension device. (c) Binocular microscope.

A longitudinal incision was made on one or both vocal folds using a sickle knife. An epithelial flap was elevated using micro-forceps and a dissector. The flap was then replaced and secured with either micro-clips (3-6 clips on one side), microsuture or fibrin glue. The animal was monitored daily until the end of the three weeks study, after which the animal was sacrificed and its vocal fold excised for histological evaluation.

Feedback on the surgical procedure for the microclips was generally positive. Implantation time was found to be less than a minute per microclip due to the straightforward nature of the application technique. Due to the limited workspace within the laryngoscope, microsuturing was found to be more complex than applying the microclips, which greatly simplified approximation of the vocal fold wound edges. From preliminary results of the excised vocal folds after sacrificing the pigs, there was no damage found on the contralateral vocal folds, demonstrating the safety of the microclips. We are still awaiting histological results, but scar formation is comparable to that of using sutures based on visual inspection.

## **6. Conclusion**

124 Otolaryngology

using a standard adult operating laryngoscope (Promed 222mm operating laryngoscope, Tuttlingen, Germany). To simulate endoscopic laryngeal microsurgery, the pig was positioned supine with the cervical spine slightly flexed. The laryngoscope was passed trans-orally following intubation with a size 5 endotracheal tube. As in most mammals, the epiglottis is intra-nasal and must therefore be drawn down into the oropharynx in order to access the vocal folds during laryngoscopy; if per-oral intubation is performed, this is usually accomplished during intubation. The laryngoscope was suspended on a custom made frame that enabled adjustments to be made to the position of the scope's tip, so as to optimize visualization of the vocal folds. By combining this with a 400mm focallength binocular microscope, the setup as seen in Figure 3 was close to that expected

b

Fig. 3. Setup for endoscopic laryngeal microsurgery in the anaesthetized pig. (a) Operating

a

A longitudinal incision was made on one or both vocal folds using a sickle knife. An epithelial flap was elevated using micro-forceps and a dissector. The flap was then replaced and secured with either micro-clips (3-6 clips on one side), microsuture or fibrin glue. The animal was monitored daily until the end of the three weeks study, after which the animal

Feedback on the surgical procedure for the microclips was generally positive. Implantation time was found to be less than a minute per microclip due to the straightforward nature of the application technique. Due to the limited workspace within the laryngoscope, microsuturing was found to be more complex than applying the microclips, which greatly simplified approximation of the vocal fold wound edges. From preliminary results of the excised vocal folds after sacrificing the pigs, there was no damage found on the contralateral vocal folds, demonstrating the safety of the microclips. We are still awaiting histological results, but scar formation is comparable to that of using sutures based on visual

laryngoscope. (b) Suspension device. (c) Binocular microscope.

was sacrificed and its vocal fold excised for histological evaluation.

during surgery in an adult human.

c

inspection.

We have given an overview of the current techniques used clinically for vocal fold wound closure and an update on the potential of some microsurgical techniques proposed in current literature. Animal and artificial models have been discussed, highlighting the complexities of selecting appropriate experimental models and methods for evaluation of vocal fold microsurgery. We shared our experience in experimental microsurgery with respect to wound closure, specifically addressing the vocal fold microclip, which is a new wound closure device. The methods for testing the integrity and bio-absorption properties of such devices in vivo and the technical challenges of applying such devices accurately during microsurgery in the larynx were also discussed.
