Fig. 2. Present and future in vitro models for PD.

a Existing approaches to model PD using iPSC-derived neurons/brain organoids. b Future prospect can combine several organoids (gut & brain organoids) to make an assembloid system where microbiota derived metabolites could be injected and thus it can mimic the gut brain axis in PD. c Further usage of the organ on chip system (the magnified view depicts the layout of organ on chip system) could mimic the gut brain axis where the sophisticated fluidics system can establish a connection between two on chip organs. In one chip it is possible to create intestine and brain in the other. The microfuidic system would establish the connection between the two and there would be an injection site for bacterial metabolites as depicted in the image. These approaches will improve the PD modeling and can be used to study disease progression or it can help in bulk drug screening.