Cell-based therapies and tissue engineering

Tissue engineering involves the restoration of tissue structure or function through the use of living cells [1]. The specific applications may include direct injection of cells, combination of cells with a biomaterial scaffold in vitro or in situ, or implantation of a biomaterial scaffold alone that can induce surrounding cells into tissue restoration. The basic concept of tissue engineering is summarized in Fig. 1. This general process consists of cell isolation and expansion followed by a reimplantation procedure that may include cells and a scaffold material or, more likely, a combination of the two. From an otolaryngologic perspective, most head and neck applications would probably involve chondrocytes (cartilage cells) and osteoblasts (boneproducing cells) along with some type of scaffold material because of the importance of initial shape and support. At first glance, tissue engineering seems to be a simple concept, but a number of major challenges must be addressed before it will become a widely approved and accepted method for tissue replacement. A basic summary and classification of some of the major challenges are presented in Table 1. Some of these challenges are cellular; they range from identifying an appropriate cell source to devising ways to expand the cells and make sure that they function appropriately once they are being depended on to produce new tissue. Many engineering challenges also exist. For example, the properties of the scaffold material can have a major impact on the viability of cells and the quality of tissue created. In addition, engineered neotissues must overcome clinical challenges, including adhesion and integration into defect sites that may be poorly vascularized.