**1. Introduction**

Stem cells represent an unlimited cell source because of their property of self-renewal, and they can also differentiate into almost all adult cell types thanks to their pluripotency characteristic [1]. One of the main problems of stem cell research was the invasively harvesting techniques, such as through bone marrow, adipose tissue extraction by liposuction, or blood apheresis [2]. In 2006, the discovery that adult somatic cells can be reprogrammed into the so-called induced pluripotent stem cells (iPSCs) has allowed to generate stem cell lines with minimally

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

invasive techniques, like skin biopsy or, more recently, blood withdrawal [3]. These recent findings has led to an outstanding increase in disease mechanisms and drug screening studies involving stem cells, in particular for neurodegenerative diseases because of the impossibility to obtain neural cells from patients. The ability to reprogram patient-specific cells also opens new opportunities for the personalized medicine approach of drug discovery. Moreover, the development of 3D bioprinting provided a useful tool to generate innovative cell cultures, permitting to have a 3D model in which cells can be disposed with a controlled manner and where they can grow in a tissue-like structures [4]. Obviously, 3D bioprinting opened new possibilities in the field of tissue engineering, but it can be helpful also for disease modeling. In fact, the generation of a 3D scaffold that can resemble the human tissues will permit to study neurodegenerative diseases in the so-called brain in dish. Finally, the combination of 3D bioprinting technique with iPSC technology will permit to develop one of the most realistic and reliable in vitro cell cultures, permitting to study organoids with patients' differentiated cells, leading to a personalized medicine approach in drug testing.

induced pluripotent stem cells (iPSCs) from adult human cells and to reprogram cells from several tissues [15]. Moreover, it is now possible to generate iPS cells by different transduction methods (**Figure 1**), using different viral and nonviral constructs, as well as integrative and non-integrative system approaches [17]. The best methods to reprogram cells are the non-integrative methods, and the four main groups are available: non-integrative viral delivery, episomal delivery, RNA delivery, and protein delivery [18]. The establishment of human iPS cells has led to have an unlimited source of stem cells overcoming the ethical limit of hES cells. Moreover, iPSCs can be reprogrammed from any somatic cell line of the patients providing a way to study diseases' mechanisms potentially for each patient, opening to the so-called personalized medicine (**Figure 1**). Actually, many iPSCs' lines have been generated from patients with neurodegenerative disease, like Alzheimer's disease (AD) [19], Parkinson's disease (PD) [20], amyotrophic lateral sclerosis (ALS) [21], and Huntington's

From Neuronal Differentiation of iPSCs to 3D Neural Organoids: Modeling…

http://dx.doi.org/10.5772/intechopen.80055

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**Figure 1.** An overview of iPSC technology. Somatic cells can be taken from several sources, like the skin, blood, and urine. There are many reprogramming strategies, and the best ones are the non-integrative strategies. iPSCs can be differentiated into diverse cell lines that can be used for disease modeling, for drug discovery, and for cell replacement

therapy (the image was taken from Sharma [23]).

disease (HD) [22].
