Design and development of three-dimensional scaffolds for tissue engineering

Tissue engineering is a concept whereby cells are taken from a patient, their number expanded and seeded on a scaffold. The appropriate stimuli (chemical, biological, mechanical and electrical) are applied and over a relatively short time new tissue is formed. This new tissue is implanted to help restore function in the patient. The scaffold is a three-dimensional substrate and it serves as a template for tissue regeneration. The ideal scaffolds should have an appropriate surface chemistry and microstructures to facilitate cellular attachment, proliferation and differentiation. In addition, the scaffolds should possess adequate mechanical strength and biodegradation rate without any undesirable by-products. Research in this area has been intense over the past 10 years or so on biopolymer formulation and on scaffold fabrication. This paper summarized some important issues related to scaffold design and development from biodegradable polymers. The mechanical properties and bio-compatibility of commonly used biopolymers are reviewed. The scaffold design and fabrication techniques are overviewed, their advantages and manufacturing feasibility are compared. The scaffold architecture, including pore size and size distributions, and its effects on the cells' growth are discussed. The scaffold should offer a hierarchical structure that varies over length scales of 0.1 similar to 1 mm. Conventional processing techniques can not yet fabricate a scaffold with control over both architecture and surface chemistry. There is, however, an emerging scaffold fabricating technique using solid free form fabrication (SFF). It has shown to be highly effective in integrating structural architecture with changes in surface chemistry of the scaffolds, and integration of growth factors.