Strategies for improving the physiological relevance of human engineered tissues

• Enhance physiological relevance by using bioreactors, 3D co-cultures, and vascularization.
• Long-term culture may be required to generate stable, physiologically relevant tissues.
• Nondestructive datapoints are essential in long-term culture for monitoring the same tissue.

This review examines important robust methods for sustained, steady-state, in vitro culture. To achieve ‘physiologically relevant’ tissues in vitro additional complexity must be introduced to provide suitable transport, cell signaling, and matrix support for cells in 3D environments to achieve stable readouts of tissue function. Most tissue engineering systems draw conclusions on tissue functions such as responses to toxins, nutrition, or drugs based on short-term outcomes with in vitro cultures (2–14 days). However, short-term cultures limit insight with physiological relevance because the cells and tissues have not reached a steady-state.