ABSTRACT
The three key components believed to be essential for tissue regeneration are stem cells, scaffold, and morphogens or growth factors (as illustrated in Figure 23.1). The scaffold should provide a three-dimensional porous and fully interpenetrable space for tissue ingrowth, accelerate the formation of tissue structure, and ultimately be replaced by a new extracellular matrix (ECM) to form completely natural tissues (Hubbell 1995; Ma et al. 2008). The scaffold may be implanted alone or in combination with cells and growth factors. After implantation, the scaffold allows for cell migration and organization. Ideally, a scaffold should be porous (to allow for placement of cells and growth factors), biocompatible with the host tissues, biodegradable, leave no toxic by-products, and have the correct shape and form to allow for replacement of the lost tissues (Young et al. 2002; Murray et al. 2007; Prescott et al. 2008). The rate at which degradation occurs has to coincide as much as possible with the rate of tissue formation; this means that while cells are fabricating their own natural matrix structure around themselves, the scaffold is able to provide structural integrity within the body, and eventually break down, leaving a newly formed tissue that will take over the mechanical load (Freed et al. 1994). Currently, two types of scaffolds are available: synthetic or natural scaffolds. Synthetic scaffolds are made from polyester materials, such as polylactic acid (PLA), polyglycolic acid (PGA), and polycaprolactone (PCL) that degrade within the human body. Synthetic scaffolds offer improved control over the degradation rate along with the ability to support the growth of different stem cell types (Taylor et al. 1994; Sharma and Elisseeff 2004). However, the difculties in obtaining high porosity and regular pore size are the disadvantages of these scaffolds that have led researchers to concentrate their efforts on engineering scaffolds at the nanostructural level to modify cellular interactions with the scaffold (Tuzlakoglu et al. 2005). Natural scaffolds are made from collagen and polysaccharidic materials, such as chitosan or glycosaminoglycans (GAGs) (Griffon et al. 2005; Guo et al. 2006; Prescott et al. 2008).
