15502-m-pleumeekers

INTRODUCTION Cartilage plays a key role with respect to form and function of facial features. When cartilage of the nose or ear is damaged by injury it does not have the capacity to regenerate. This means that an ear or nose remains mutilated once its cartilage structure is disrupted. A reconstructive procedure is then necessary to create a new framework with a good three-dimensional (3D) structure capable of withstanding normal mechanical forces. Practically, the reconstruction of the ala nasi or minor ear defects is most often performed using auricular or septal cartilage grafts. [181, 182] In more extensive cases costal cartilage can be used, offering more material for harvest and providing a more rigid support. Ear, septal or costal cartilage can be used for reconstruction but the availability of material for transplantation is generally limited and donor site morbidity remains a risk. This is especially the case in burn patients who often suffer from extensive damage to the nose and ears due to their protruded position and thin skin coverage. [181, 183, 184] As such, regenerative medicine offers exciting possibilities to overcome these problems. New developments in the field of tissue engineering have already found their way to the clinic. Yanaga and colleagues for example performed several clinical experiments in which newly developed cartilage from autologous chondrocytes isolated from the ear was used for ear framework reconstruction. [182, 185] With increased attention for tissue engineered alternatives we need structural information on the tissues we are seeking to replicate. However, there is little data in literature on the mechanical characteristics and differences in composition and structure between the various facial cartilage types, in particular the ear, alar and septal cartilage. Although they share a common embryonic origin, facial cartilage soon differentiates into distinct cartilage subtypes according to their specific structural function. In the early stage of developing vertebrates, the embryonic region that is to become the head and neck is transiently divided into segments known as the pharyngeal arcs (PA’s). The ear has a combined origin and is derived from PA1 and PA2 that form the hillocks of His at six weeks development. Eventually these six hillocks fuse together to form the outer ear. [186, 187] PA1 grows further outwards to form the lower mandibular process and upper maxillary process. The latter later forms the frontal prominence and the medial and lateral nasal processes which will form into the alar nasi and after final fusion into the septum. [188] Mature ear cartilage consists of an intricate network of elastin fibers and collagen bundles surrounded by a layer of perichondrium. This high elastin content makes it unique among the various cartilage subtypes in the facial region. The anatomy of the human nose on the other hand consists of several separate structural elements. A major part is the septum providing support for the bridge of the nose and on either side the septolateral and lobular cartilages to support the ala nasi. The lateral area further comprises of several sesamoid cartilages and accessory cartilages. In contrast with ear cartilage, the nasal structures are all made of hyaline cartilage. Hyaline cartilage consists mainly of collagen, in particular type II and is divided into several zones. [189] The extracellular matrix (ECM) structure and its biochemical composition are essential to the mechanical function of cartilage. Standard biochemistry assays can be used to determine the concentration of the main tissue components. In order to visualise the 3D 45 FACIAL CARTILAGE CHARACTERISTICS 3