Section 4 Plastic and Reconstructive Problems

Tissue Engineering in Otorhinolaryngology

stituted by biocompatible and re-absorbable material that promote adhesion, proliferation and cell differentiation, in order to allow a successful restoration of the extracellular matrix. 5,15 A wide range of materials has been used, such as hydrogels based on hyaluronic acid (Carbylan-SX and Carbylan-GSX). 12 These biomaterials, when applied to an injured vocal fold (such as a deep biopsy), modulate scar for- mation and consequently preserve the vocal fold viscoelastic properties. 9 Acellular biological scaffolds have also been used as an alternative to hydrogels. These structures are derived from porcine intestinal mucosa, lamina propria of bovine vocal folds or human umbilical vein. They are then submitted to decellularization procedures based on the immune response triggered by contact with human vocal fold fibroblasts. 16 Kishimoto et al. 17 conducted a study in 6 patients with a vocal fold scar or sulcus, who were submitted to the place- ment of such scaffolds in a subepithelial bag after excision of scar tissue. In the 6 months following surgery, a significant restoration of the extracellular matrix was observed, with improvement of acoustic parameters, and total degradation of the scaffold material. Therefore, it is a promising medical device. Cell therapy in laryngology is based on the injection of cells that will produce extracellular matrix elements, resul- ting in the reconstruction of the vocal fold microstructure. These cells are generally fibroblasts, 18 bone marrow or adi- pose tissue stem cells 19 (which are capable of producing, in vitro , all the elements of the vocal fold), 20 and embry- onic stem cells. 21 In all cell therapy-based studies, a clear improvement of vocal fold fibroelastic properties has been observed. 18--21 However, the potential risk for neoplastic transformation of targeted tissues 3,5 and many ethical issues concerning the manipulation of embryonic cells have limited its use. Many head and neck surgical procedures, such as rhinoplasty, septoplasty, correction of septal perforation, or pinna recon- struction involve the use of autologous cartilage which is collected from the nasal septum, ribs, or concha. 2 Despite being a limited resource concerning its finite extension and particular geometrical configuration, septal cartilage has been the most commonly used, due to its structural features and accessibility. 22,23 Tissue engineering may, therefore, provide an alternative, with the possibility of originating a higher amount of cartilage with the desired shape. The first and most popular work in this area was published in 1997 by Cao et al. 24 The production of an ear-shaped car- tilage matrix for treating a 3-year-old child was described, using bovine chondrocytes added to a previously molded polyglycolic acid matrix (scaffold). These elements were implanted in the back of a laboratory mouse, and new repli- cating chondrocytes were observed within 12 weeks. More recently, Yanaga et al. 25 published a series of 4 cases in which the surgical technique for reconstruction of Cells Plastic and Reconstructive Surgery

cal and microbiological aggression. 5 Fibroblasts are the main cell type in the lamina propria. These cells are produced and embedded in an extracellular matrix. The extracellu- lar matrix supports all tissue cells and plays an important role in the regulation of cell migration, proliferation and differentiation. 6,7 Hyaluronic acid abounds particularly in the superficial layer of the lamina propria, hydrating the vocal folds and making them compressible. The remaining layers are mainly composed of collagen and elastin, which are responsible, respectively, for tensile and elastic resis- tance of the vocal folds. 5,6 When the ultrastructure of the extracellular matrix is altered, either by surgical interventions or factors such as infection, trauma, or radiation, a disruption of the vibrating function of the vocal folds may result. 6,8,9 In these situa- tions there is usually an aberrant healing process that favors collagen deposition and decreased production of hyaluronic acid and elastin fibers, which ultimately, leads to scar for- mation, responsible for dysphonia. A number of therapeutic interventions have been described to prevent and/or treat vocal fold scars or atrophy, invariably with limited success due to the difficulty of restoring the mucosal wave. Thus, the goal of regenerative medicine concerning vocal folds is restoring the vibratory and respiratory functions of the larynx through the reconstruction of the lamina propria’s extracellular matrix using the elements described below. Growth factors are the only elements that, to date, have been successfully applied in vocal fold bioengineering. 5,10 Within these, fibroblast growth factor assumes a prominent position since it has an important role in the regulation of scar formation. Hirano showed that fibroblast growth factor enhanced the production of hyaluronic acid by fibrob- lasts of the vocal folds, while inhibiting local deposition of collagen. 11,12 He described a clinical case in which fibrob- last growth factor was used in the treatment of atrophic vocal folds of a 63-year-old male, with clear improvement of acoustic parameters only 1 week after surgery. 12 Another cytokine that has been increasingly studied in the treatment of vocal scars is the hepatocyte growth factor, mainly due to its anti-fibrotic and angiogenic properties. 5 Similar to the fibroblast growth factor, hepatocyte growth factor also stimulates the production of hyaluronic acid and elastin and inhibits collagen synthesis. 13,14 Hirano made another experience where he injected hydrogel impreg- nated with hepatocyte growth factor in a previously injured canine vocal fold. Here, a structural regeneration of the vocal fold with improvement of the mucosal wave was observed. 3,5 Despite the promising results, the safety profile of these newly used growth factors has not been completely defined, and the risk of malignant transformation has been consid- ered as a major limitation to their clinical application. 5 Regulators/Growth Factors

Scaffolds

Any scaffolds used in laryngology should have structural features, chemical composition and mechanical properties similar to those of the lamina propria. These should be con-