The Functions of an Ideal Scaffold
In general, appropriate tissue engineering scaffolds should be able to guide cells to grow, provide enough structural support, assist the transport of essential nutrients and waste products, and facilitate the formation of functional tissues and organs . Firstly, the scaffolds should provide a satisfactory cell-adhesion substrate because the majority of mammalian cell types are anchorage-dependent and will die if no cell-adhesion substrate is available. Secondly, the scaffolds should be designed as a three-dimensional environment with appropriate structure and functions, where the tissue repair needed cells can grow well with high loading efficiency and cellular functions can be properly regulated. Thirdly, the scaffold can provide enough and stable structural support for the embedded cells to be active and for the new tissue to regenerate inside and grow into the required shape and size without the need for further treatment. The mechanical support can effectively resist against various forces in vivo such that the predefined three-dimensional structure of the scaffolds is maintained during tissue development. Fourthly, the scaffolds should possess special structure that could provide interconnected three-dimensional space and channels for essential nutrients to reach the cells and tissues and bring them indispensible living energy. Meanwhile, the structure can allow for the discharge of the metabolic waste products of the cells and tissues inside the scaffolds. Furthermore, based on their high performances of every aspect, the scaffolds should facilitate the formation of desired tissues. Especially for in vivo tissue engineering scaffolds, they can not only spontaneously recruit or attract the needed cells to attach well on them, but also act as a template to guide or support the organization of the cells, promote their proliferation, and induce them into the desired tissues directly or by adsorbing or interacting with appropriate bioactive substances in the human body (e.g. cell adhesion peptides, growth factors, etc.) .