The vascular system including the cardiovascular system, liver, lungs, etc. can provide a range of primary cells that are particularly used in research applications. The most popular types of primary cells used in in vitro research applications are endothelial cells, fibroblasts, keratinocytes, melanocytes, etc. These are the heterogenous population that is being maintained in vitro for a limited period of time. These cells are highly in demand for in vitro applications due to their minimized ethical concerns over animal use and ability to represent the most relevant results as compared to alternative cell lines.