Page 102 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 5
Only recently, the tissue engineering paradigm has become increasingly oriented towards a so called in-situ approach, using the body as bioreactor system for the tissue formation phase.22 This in- situ tissue engineering approach represents an economically attractive approach providing o - the-shelf availability, less risk of contamination as extensive in-vitro culturing is omitted and a cheaper and shorter production process. The shi from the in-vitro to the in-situ tissue engineering approach emphasizes the role of the sca old, not only as a template for the cells to form a tissue, but also to enable cell invasion and to maintain valve functionality whilst the tissue is developing. This may require the use of slower degrading sca old materials, such as poly(ε-caprolactone) (PCL) and the inclusion of bioactive compounds into the sca old to guide tissue development. To summarize, the valve sca old should provide a natural template for cell invasion and tissue formation. Further, it should mimic native valve functionality and, additionally, allow for insertion via a minimally invasive approach. The development of such a valve sca old represents a true challenge within the heart valve tissue engineering field and may be facilitated by electrospinning.
5.4 Specific tissue requirements as a blueprint for sca old properties
The sca old plays a pivotal role in both the in-vitro and in-situ heart valve tissue engineering approach as heart valves are geometrically, mechanically and functionally challenging structures. To be able to define sca old requirements, one should be acquainted with the tissue requirements of the semilunar human heart valve from the macro- to the microscopic level. Here, information is provided on geometry, function, structure, composition and cell- matrix interactions of human semilunar heart valves to serve as a blueprint for sca old properties.
5.4.1 Geometry and function of semilunar heart valves
The semilunar valves consist of three flexible leaflets, three sinuses and a root. The average aortic valve diameter is 23 mm and the average pulmonary valve diameter is 26 mm for adult men. The valve diameter is directly correlated to the body surface area.23 Due to their u-shaped attachment to the arterial wall, the leaflets form cusps that intimately fit together during closure of the valve. The average height of the aortic root from the bottom of leaflet attachment to the top of the commissures is 18 mm. An aortic leaflet measures on average 0.4-0.5 mm in thickness and 16 mm in length from attachment to the root to
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