Figure 3. Energy usage and achievable dimensions in scaffold-free processes.

Scaffold-free processes differ with respect to the energy required for tissue formation and the dimensions that can be achieved. Spheroid or aggregate formation based on the methods of hanging drop, round or v-bottom well plates, or rotational culture requires minimal energy and forms aggregates of small dimensions. Pellet culture requires substantial energy in the form of centrifugation and similarly forms small-diameter cellular aggregates. Finally, self-assembly and larger self-organization techniques such as cell sheet engineering are able to generate sizeable constructs of clinically relevant dimensions.