Complex in vitro models: do not complicate it

Abstract

In vitro complex models The physiologically relevant and mimetic in vitro 3D models of tissues and organs, the so-called complex in vitro models (CIVMs), can be grouped into extracellular matrix (ECM)-independent models and ECM-dependent models. The holy grail of in vitro models is to achieve the same degree of complexity of the tissues to be mimicked to increase its relevance, which does not necessarily mean to involve the development of a complicated model. Important achievements in the field include the development of highly controlled in vitro models for studies of neurodegenerative diseases. Such complex microphysiological systems allow investigation of systemic interactions, pathology mechanisms associated with the microbiome, and how genetic and environmental factors can contribute to the appearance/ progression of pathological states [1]. For several years now, CIVMs have been proposed for regenerative and personal-ized medicine [2]. Another important application of CIVMs includes drug development [3]. Several pharma companies are now increasingly investing in reliable technological platforms for boosting drug discovery and decreasing drug development costs. CIVMs need to be properly designed and optimized for each specific application. As a starting point, the in vitro systems should fit a specific research question to be addressed. Other important "Do" and "Don't" tips and features should be also considered, as follows: 1. Do • Select the cell types to be used alone or in co-culture. A good way to generate the model is to start with two types of cells. • Select the adequate biomaterials and supportive artificial extracellular matrices that best mimic the target tissue/organ. • Select adequate processing and fabrication methods (e.g., conventional or advanced methods such as bio-printing) to decrease fabrication time and enhance the model's reproducibility. • Select and optimize your culture media and optimize your technologies for dynamic culturing (e.g., micro-fluidics and bioreactors). • Select the characterization techniques and make the model compatible with different scientific equipment for data acquisition, preferably for real-time monitoring and high-throughput analysis. 2. Don't • Complicate your model, i.e., a simple and reproducible model can make the adoption by other researchers easier. • Start your experiments without a prior pilot study, i.e., a prior optimization of the model is the key for the success. • Run experiments without a solid experimental design and planning, and select the best "gold" standard in order to properly validate your model. • Forget the statistical power of your experimental design. • Run experiments without considering the culturing time and costs of your model. With respect to the type of cells to be chosen, induced Pluripotent Stem Cells (iPSCs) have attracted considerable attention in the field of in vitro modeling due to their ability to differentiate into almost every cell type,