Engineered in vitro models: mimicking in vivo physiology

Human tissues are all characterized by an intrinsic complexity, rendering them difficult to model. Animal models often do not resemble human characteristics and involve strict ethical regulation for their use in research. For these and many other reasons, there is an increasing need for preclinical in vitro models to replace and reduce the use of animals in research and to study human cellular and tissue functionality. Current bioengineering strategies aim to advance three-dimensional (3D) in vitro models and mimic in vivo complexity as well as to study functional and systemic responses. Advancements in 3D in vitro technologies will provide the opportunity to study biological processes, additionally enabling high-throughput drugs testing and efficacy. This chapter focuses on bioengineering tools that define tissue microenvironment and functionality, with an emphasis on their inclusion as established emerging in vitro technologies. The chapter further illustrates the development of different in vitro models and compares a variety of strategies used to achieve in vivo–like functionalities. Last, it explores current regulations for validation of in vitro models and harmonization of practices for their use, providing insightful guidelines for future research.