Anisotropy Properties of Tissues: A Basis for Fabrication of Biomimetic Anisotropic Scaffolds for Tissue Engineering

Tissue engineering has been a subject of extensive scientific exploration in the last two decades making gradual inroads into clinical studies as well. Along with regenerative cells and growth factors, biomaterial scaffolds are integral to the development of a tissue engineered construct. It is now appreciated that scaffolds should mimic the target tissue properties intimately in order to provide a micro-environment milieu that allows the seeded cells to differentiate into the desired tissue. Even from a structural viewpoint, mismatch between scaffold and native matrix properties can cause cell necrosis through mechanisms such as stress shielding. One of the key properties of most body tissues is that they exhibit anisotropy. However, most fabrication methods generate isotropic scaffolds and require specific modifications to produce anisotropic scaffolds. In the last decade, the advent of additive manufacturing and bioprinting has provided facile tools to fabricate scaffolds with desired anisotropy. On the other hand, a biomimetic scaffold can be designed only when target tissue anisotropy is well known to the tissue engineer. This review presents an overview of the anisotropic properties of different tissues, which will be critical for developing biomimetic engineered constructs. The traditional anatomical records do not adequately present these properties from the perspective of designing tissue engineering scaffolds. Subsequently, present state-of-the art in development of anisotropic scaffolds as well as tissue constructs using different conventional and emerging fabrication techniques is discussed. It is expected that the readers will obtain a comprehensive reference on the research area by examining these two aspects juxtaposed to each other and gain key trends for fabrication of anisotropic scaffolds, plausibly with improved regenerative outcomes.