Design Principles in Biomaterials and Scaffolds

This chapter focuses on recent developments in fabricating biomimetic, extracellular matrix (ECM)-like porous scaffolds useful for tissue engineering. Fabrication methods are critical for designing biological scaffolds; for example, for tissue regeneration, highly open-porous polymeric scaffolds are often required for high-density cell seeding and efficient nutrient and oxygen transport. The solvent casting/salt-leaching technique is widely used for fabricating scaffolds for tissue engineering. Polyglycolic acid (PLGA) dissolved in an organic solvent with salt particles is placed in a mold to produce a polymer/salt mixture, which is immersed in water to remove the salt particles and generate open-pore structures. The scaffolds prepared often show a dense surface layer and poor interconnectivity between the macropores, which reduces cell seeding into the scaffolds in vitro and causes nonuniform distribution of the seeded cells. The biodegradable scaffolds can be utilized as a gene carrier for sustained release of plasmid DNA, oligodeoxyribonucleotides (ODN), and siRNA. By delivering growth factor and other cytokine-related genes, transfected cells can be genetically controlled and used in tissue repair. Transfected cells could trigger neighboring cells to proliferate and differentiate to cells with specific phenotypes for specific tissue engineering applications. Conventional gene delivery carriers usually express highly positive charges such that the charge-charge interaction between negatively charged DNA molecules and the carriers can form a tight ionic complex. The excess use of highly positive polymer species such as polyethyleneimine (PEI), poly(L-lysine) (PLL), and positively charged fatty acids can cause severe cytotoxicity and reduces the biocompatibility of gene carriers.