Today, the need for vascular grafts is growing in importance, this is owed to the increasing number of patients requiring artificial vessel implantations because of cardiovascular diseases, hemodialysis treatments, etc.
Downsides of Existing Synthetic Blood Vessels
Various laborious methods are used by tissue engineers to produce synthetic blood vessels. Woven or knitted vascular grafts of polyurethane (PU), polyethylene terephthalate (PET), and polytetrafluorethylene (ePTFE) are successfully employed in large diameters (> 6 mm). Yet, small diameter woven or knitted vascular grafts (< 6 mm) do not give good results due to intimal hyperplasia, early thrombosis formation, aneurysm etc. Consequently, there is still room at the small diameter level for further improvements and research.
Ideally, a vascular graft should perform all the functions of native vessels. Including structural, morphological, mechanical and biological features. So, very similar to native vessels, nanofibrous vascular grafts are comprised of layers with different functions, therefore multilayered designs of the artificial grafts are better than single layer designs. The design parameters are determined with respect to the mission and the structure of the building layers of the native vessels.
Benefits of Electrospun Vascular Grafts
Electrospun vascular grafts have many advantages over the other varieties of tissue engineered artificial vessels. Among various applications for building artificial vessels to provide all these qualities by using multiple effortful techniques; electrospinning is a unique method that permits the design of all the layers at once.
Firstly, nanotopography of the electrospun mesh resembles ECM (extra cellular matrix) i.e. high surface area and interconnected pores provide endothelium formation and so hinder arterial thrombosis. Modifications like protein lining, heparin incorporation, or polymer surface chemistry on the inner surface of the small diameter electrospun grafts allow spiral flow of blood just like in the native vessels which minimize related complications.
To grow, migrate, multiply and attach deep within the structure with controllable pore size and porosity of the assembly, it is possible to maintain the design for SMC (smooth muscle cells). Electrospinning technology permits vascular graft construction with required features by supplying broad material options, flexibility in production parameters and adjustable morphology and composition.
The rotating mills are made up of titanium to make it easy to remove the stand-alone tubular coating. The NS24 model electrospinning device was utilized to construct the artificial blood vessels. Shown in the images below in figure 1, the specially designed mill collector with different diameter options has been assembled to the system and a continuous electrospun web has been coated on the rotating mill in a tubular form. A homogenous, uniform structure was gained by the reciprocal movement of the collector mechanism.
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Figure 1: The electrospun TPU vascular graft with a diameter of 3 mm.
Image Credit: Inovenso
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Figure 2: The set-up of rotating shaft collector assembled to the system.
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Figure 3: The process of construction with a 3-nozzle feeding unit.
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SEM images taken from the outer surface of an electrospun artificial vessel.
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Image Credit: Inovenso
SEM images of the inner surface of an electrospun nanofibrous artificial graft:
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Image Credit: Inovenso
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Image Credit: Inovenso
SEM images of the cross-section indicating different densities mimicking the multilayer structure:
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Image Credit: Inovenso
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Image Credit: Inovenso
This information has been sourced, reviewed and adapted from materials provided by Inovenso.
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