The requirements of structures for tissue engineering

Natural extracellular matrices (ECMs) have been isolated and extracted from various tissues, such as smaU-intestine submucosa, skin (from cadavers), pancreas and breast (Badylak, 2(X)7). Althongh these purified ECMs certainly have useful apphcations, then-use is limited in scope owing to the need for well-defined microenvironments in tissne regeneration and stem-cell transplantation, in which animal by-products and contaminants mnst be limited. Moreover, it has been demonstrated that, besides the spatial framework, tissue-specific ECM cues, namely the constituents and their stractural organization, are 

Rarely one material provides all the requirements for a given biomedical application and, in regard to biomaterial/scaffold for tissue engineering of bone and cartilage, this statement is even more accurate. Nevertheless, a set of requirements must be fulfilled, namely adequate mechanical behavior, suitable morphology, and sttuctural/functional properties (Marimuthu and Kim, 2009). 

The mechanical performance is an essential requirement for any biomedical application. Two features must be considered the bulk properties should be compatible with, as much as possible, the host mechanical ones, and a proper interface should transfer load from the scaffold to the native tissue. Values of modulus and tensile/ compressive strength of the materials determine the final mechanical properties of the scaffolds. The analysis of Fig. 5.3 demonstrates the range of tensile modulus and strength values of biological materials (Mano et al., 2004), and that neither polymers alone, nor ceramics/metals by themselves, provide the necessary array of properties. 

Scaffolds are often porous three-dimensional (3D) structures made of degradable materials. The quantity of pores, their size and distribution, along with their interconnectivity, are crucial aspects to provide the environment for bone regeneration. The balance between mechanical support and interconnected porosity is difficult to achieve. The processing methods to obtain scaffolds and the later tune of properties should also be a concern. Once again, polymer composites are an excellent answer to these problems but why The next section will present arguments to this question. 

---