Bio-engineering of blood vessels
Blood vessel prostheses work best when the biochemical and mechanical properties match reality as much as possible and when they are made of biodegradable material. To this end tissue technologists grow natural vascular wall cells, endothelial cells, in a biodegradable tube made of collagen. According to Professor István Vermes tissue technologists are overly concerned with developing stem cells, necessary to build blood vessels, and not enough with the development of the vascular skeleton or scaffold, serving as a framework for those stem cells. During his address on the acceptance of the office of professor in the Molecular Aspects of Cell and Tissue Technology (on 11 april 2002) Vermes gave his vision on the bio-engineering of blood vessels. Besides professor at the University of Twente (The Netherlands) Vermes is doctor-clinical chemist and educator in the regional hospital Medisch Spectrum Twente in Enschede, and special professor in Laboratory Medicine at the Semmelweis Medical University in Budapest.
According to Vermes the key to successful development of artificial human tissue and organs lies in the structure and composition of the porous framework on which cells grow. “The traditional method starts with the development of a prosthesis made of artificial materials. I am concerned with bio-engineering a blood vessel, with biological materials as starting point. To this end we have to imitate all the natural functions of a vessel, including those of the scaffold with all functional biological materials such as growth factors. The skeleton has many more functions than just attaching and keeping cells together. It contains information in the shape of growth factors, cytokines and surface-properties for the growth and development of cells. The chemistry, the shape and way in which it moves under the influence of stress are of vital importance to influencing the behaviour of cells. The skeleton emits signals that are passed on to the inside of the cell via receptors on the cell surface.“ The future of the stem cell, how it develops or dies because of apoptosis, is dependent on the information coming from the vascular skeleton.
A blood vessel is built up, from the inside out, of six different layers of successively endothelial cells, elastic layers of among them smooth muscle cells with around them connective tissue with lymph vessels and nerves. Vermes: “Endothelial cells are important in translating changes in the blood through the production of materials that in turn take care of the balance between blood and the surrounding tissue. To understand the function of these cells in the blood vessel and for the production of the artificial vessel, we study this process by directing ourselves towards cell division (proliferation) and cell death (apoptosis) of endothelial cells.” Vermes` strategy is to grow stem cells that differentiate themselves selectively to smooth muscle cells and endothelial cells, and developing a scaffold in the shape of a porous tube of biodegradable and flexible polymers. The stem cells are seeded in the skeleton in the presence of, among others, growth factors.
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