Engineering Large Airways

A key issue facing trachea replacement attempts has been the discrepancy of the mechanical properties between the native tracheal tissue and that of the replacement construct; this difference is often one of the major causes for implant failure in vivo and within clinical efforts. The trachea is composed of distinct structural regions, with each component fulfilling a different role in maintaining overall tracheal stability. The trachea's horseshoe-shaped hyaline cartilage rings, smooth muscle and annular ligament collectively produce an anisotropic tissue that allows for longitudinal extensibility and lateral rigidity. Therefore, any tracheal substitute must be mechanically robust in order to withstand intra-thoracic pressure changes that occur during respiration. Conversely, they must also be able to deform radially to allow for changes in the cross-sectional area during coughing and swallowing. These complicated native tissue characteristics, coupled with a lack of standardised protocols to accurately quantify tracheal biomechanics as guidance for implant design, constitute a significant hurdle for tracheal biomaterial scaffold fabrication. This chapter aims to highlight the pressure forces exerted on the trachea and how they can influence tracheal construct design and also the biomechanical properties of the three main components of the trachea and how to mechanically assess them.