Tissue Engineering

ii. Cell Types

An organism such as a mammal starts as a single, fertilized cell. All the different types of cells (nerve, muscle, etc.) that make up the tissues in the organism ultimately come from this one cell.

In the early stage of development of an embryo, a ball shaped mass of cells called a blastocyst is eventually formed. The interior layer of cells is termed the ‘inner cell mass’, and the cells in this structure are what ultimately form all the tissues in the body.

Figure: The development of an embryo from fertilized egg to blastocyst as it progresses down the fallopian tube, into the uterine cavity and eventually implants in the uterine lining. Stages:a. fertilization,b. zygote (2-cell), c. morula, d. blastocyst where the blue area at the top of the cavity indicates the inner cell mass.

The inner cell mass has three distinct layers of cells, called the germ cell layers (the ectoderm , the mesoderm, and the endoderm). All of the tissues in the full grown organism come from these layers.

Figure: The graphic above shows the three germ cell layers (from top to bottom: enctoderm, mesoderm, and endoderm) formed within the inner cell mass. The respiratory system, digestive system, and lymphatic system form from the endoderm; the cardiovascular system, reproductive system, muscles and ligaments from the mesoderm; and the nervous system and special sense organs from the ectoderm.

Since we are trying to create a blood vessel, we would like to use a cell type that is found in blood vessels. In this case we will use endothelial cells.

In order to have a pure cell culture, it is necessary to obtain the primary endothelial cells in an isolated and sterile form. To do this, we must get tissue that contains them, disaggregate the tissue (i.e. turn it into a collection of individual cells), grow a sufficient quantity of the cells, and cultivate the cells into a 3D tissue. These steps should be done under sterile conditions.

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