Figure 1. Scaffold-free tissue engineering.

The tissue-engineering paradigm typically consists of cells, scaffolds, and signals. The benefits of scaffold-free approaches have motivated the use of only cells and signals. Depicted here are example modalities within this paradigm, using homogeneous or heterogeneous cell populations in concert with mechanical (e.g., compressive loading) and/or biochemical stimuli (e.g., TGF-β1 or sucrose) to enhance neotissue properties. Two distinct forms of scaffold-free tissue engineering exist, termed the self-assembling process (SAP) and the self-organization technique (SOT). While self-organization requires the exogenous input of energy, self-assembly occurs in a closed system.