Clean bioprinting - Fabrication of 3D organ models devoid of animal components

Bioprinting is a rapidly developing technology that enables the exact positioning of living cells embedded in bio-materials in precise spatial arrangements to fabricate engineered tissues and organs. While the ultimate goal of bio­printing approaches is to produce organs for transplantation purposes, bioprinted organ models also hold great potential for research purposes to serve as alternatives to animal experiments. By using human cells, humanized organ models can be generated that may produce more relevant results for human (patho-)physiology than animal models. However, standard bioprinting procedures currently use numerous hidden animal components. Virtually all studies published in the field to date make use of cells grown in media with fetal bovine serum (FBS). In addition, Matrigel, the extracellular matrix (ECM) harvested from Engelbreth-Holm-Swarm sarcoma grown in mice, is widely employed to cultivate stem cells and 3D organ models. Finally, most bioinks currently in use contain gelatin or comparable animal components to improve cell viability and adhesion. The present review will give an introduction to the potential of bioprinting to fabricate 3D models that may be substituted for animal experiments and will go on to describe strategies to replace animal components cur­rently included in standard procedures of bioprinting. These approaches comprise the adaptation of cells to FBS-free media, the use of bioinks composed of synthetic or plant material, and the replacement of animal ingredients by materials of human origin. We propose denoting bioprinting strategies devoid of animal components as clean bioprinting.