Page 108 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 5
5.5 Selection of sca old material
In general, there a two groups of polymer materials to be considered for use in electrospinning to obtain a valve sca old: the naturally derived and the synthetic polymers. Natural polymers such as polysaccharides, gelatin, collagen,47 elastin,48 silk49 and fibrinogen50 were electrospun into sca olds for cardiovascular research. In contrast to synthetic polymers, these materials provide many of the natural instructive cues for cell attachment and proliferation. They are considered as biodegradable, though biosafety should be ensured prior to their use. On the other hand, the natural polymers demonstrate batch to batch variation and the electrospinning process is less versatile since there is a limited choice of solvents which do not compromise the integrity of the polymers.51,52 The latter also limits the control over the mechanical properties, the design and biodegradability of the resulting sca old. In contrast to these natural polymers many synthetic polymers can be dissolved and electrospun in a broader range of solvents as well as directly out of their molten state. This o ers more possibilities and design freedom to obtain a sca old tailored to the desired tissue requirements. The most commonly known and used synthetic polymers in tissue engineering are the poly(α-hydroxy acids), such as the lactic -and glycolic acids as well as poly(ε-caprolactone) (PCL) and their copolymers.53 In addition, there are man-made
polymeric systems, such as polyurethanes (PU),54,55 polyphosphazenes56 or supramolecular polymers,57 specifically designed to meet desired mechanical properties, cell responses and integration of functionalities, such as peptides or growth factors.
The poly(α-hydroxy acids), with poly(lactic acid-co-glycolic acid) (PLGA) as most investigated polymer due to its variable degradability,58 and PCL59 are representatives of biodegradable polymers. They degrade mainly by hydrolysis in a few weeks to several months, depending on the molecular structure, molecular weight, fiber morphology, etc.60 It is evident that the degradation products of the biodegradable polymers must be non-toxic and do not provoke any foreign body response.61
5.6 Sca old properties to meet tissue requirements
Electrospinning, which allows the creation of fibrous sca olds with control over 3D sca old architecture, is exploited for cardiovascular tissue engineering and heart valve tissue engineering in particular. Once familiar with the tissue requirements for the human semilunar heart valves, di erent electrospinning settings and modalities can be applied to meet these requirements on macro- to microscopic level. These include the valve geometry, degradation,
106