Section 4 Plastic and Reconstructive Problems

L. Ribeiro et al.

Resultados y conclusiones: Hay posibilidades muy interesantes para futuros tratamientos en otorrinolaringología que aplican los conceptos de la ingeniería de tejidos. © 2014 Elsevier Espa˜na, S.L.U. and Sociedad Espa˜nola de Otorrinolaringología y Patología Cérvico-Facial. Todos los derechos reservados.

Introduction

row, adipose tissue or blood, 4 and are not totally pluripotent as they are positioned in a later stage of the differentiation line, having a finite capacity to multiply depending on the origin of the tissue. Adult cells can be obtained from a biopsy specimen of the tissue to be regenerated, and their replication is induced in vitro before transplantation. Being phylogenetically more advanced, adult cells do not have the ability to replicate endlessly or to transform into different cell types. These features, combined with the possibility of perpetuation of pre-existing pathological changes in the donor organ or tis- sue, represent important limitations in their use.

In the current era the paradigm of medicine is constantly changing, as new concepts and methods of life support and disease control arise. Tissue engineering is becoming one of the most promising weapons in medical practice. Based on highly advanced technological procedures, tis- sue and organ reconstruction may, within a short time, become gold-standard treatments for a rising number of medical conditions where classical pharmacological or surgi- cal interventions have limited effectiveness. In fact, recent developments in the area clearly show impressive results in the rehabilitation of functionally or structurally committed organs and tissues. 1 Otorhinolaryngology (ORL), as a medical specialty with a wide range of medical and surgical interventions, naturally assumes a position of leadership in the application of tissue engineering techniques. The aim of this review is the description of the fundamen- tals of regenerative medicine and its potential applications in ORL.

Regulators/Growth Factors

Growth factors are molecules that regulate proliferation, differentiation and cell function, and therefore may induce, accelerate or inhibit those cellular processes. They are an essential element in regenerative medicine. Depending on the technique used, these molecules can be included in a scaffold, which serves as a means for their controlled release, which will influence and control cell growth. 3

Fundamentals

Scaffolds

The main goal of tissue engineering is restoring functional or structural tissue by using living elements that will later be integrated in patients. 1 In this process, 3 basic components are generally present: cells, regulators/growth factors and scaffolds, which may or may not be used simultaneously. 2,3

Scaffolds are porous 3-dimensional structures that provide mechanical support and physical protection to cells and growth factors. 2 These should be composed of a biocom- patible and reabsorbable matrix, 1,2,5 allowing for complete tissue regeneration. Collagen and fibrin are among the most commonly used materials, and are generally obtained from natural sources; polyglycolic acid, a synthetic polymer, may also be used. 2

Cells

Most papers published within the past 20 years have focused mainly on cell therapy, 1 which consists in the deposit of selected living cells in an appropriate scaffold, that, when exposed to a specific microenvironment, will multiply and differentiate into the desired structure. Different cell sub- types may be used: stem cells and adult cells. 1--3 Stem cells are characterized not only by their ability of continuous and unlimited self-renewal, but also by the pos- sibility of differentiation into any cellular phenotype. 2 Stem cells are assumed as having the highest potential in regen- erative medicine, although their use is limited by ethical issues and the potential risk of neoplastic transformation. Stem cells can be obtained from embryonic or mature tis- sues. Embryonic stem cells are derived from blastocysts, and therefore can differentiate into any mature cell type of the 3 germ layers. 4 On the other hand, adult stem cells can be collected from certain niches in the body, namely bone mar-

Applications of Tissue Engineering in Otorhinolaryngology

Laryngology

The vocal folds are able to vibrate at a frequency up to 1000 Hz 3 , due to their microstructure consisting of epithe- lium, lamina propria and the vocal muscle. The lamina propria is composed by a superficial layer (Reinke space), an intermediate layer and a deeper layer, each of these having specific cellular components, which are ultimately related to the organ function. The stratified epithelium covers the entire surface of the vocal folds, and represents a barrier against physical, chemi-