Cardiovascular diseases are the leading causes of mortality in Europe and worldwide. Currently, synthetic prostheses used in bypass vascular surgery are produced from polyethylene terephthalate and expanded polytetrafluoroethylene. Those materials show less than optimal, insufficient biocompatibility and durability properties, especially if used for small diameter blood vessels. Within the frame of ERC Advanced Grant “BIOSILICA” (From gene to biomineral: Biosynthesis and application of sponge biosilica; Grant No. 268476), we discovered that distinct natural, biodegradable and biofunctional polymers, including biosilica and inorganic polyphosphate (anionic), are not only bio-printable but also morphogenetically active. These biopolymers can be functionally processed by non-toxic and charged (cationic) linkers with growth/differentiation potencies, allowing the fabrication of a novel “Modular Small Diameter Vascular Graft (MSDVG)" which combines in an optimal way physical strength with physiological activities. In order to fabricate these synthetic vessels, an easy-to-handle extruder device has also been developed.
The aim of the ERC-PoC project was to provide the proof-of-concept of the MSDVG. These blood vessel implants should be brought to a (pre)demonstration stage by reaching the ISO standards.
In order to reach the objectives of this project, the following studies have been performed. The biomaterials used for the fabrication of the MSDVGs have been optimized. Besides of polyP, two biologically inert polyanions, alginate and a modified chitosan, have been included. The fabricated extrudable and printable hydrogel could be hardened in a controlled way, in dependence on the calcium concentration, the reaction time, as well as additional supplements. In addition, the biologically inert alginate-modified chitosan hydrogel has been functionalized with gelatin which exposes the RGD cell recognition signal. Besides of calcium ions, the three polyanions forming the biomaterial (polyP, alginate and modified chitosan) have been processed/hardened by addition of polycations, including poly-lysine and His/Gly-tagged RGD, which support the attachment of endothelial cells to the MSDVGs. The production process of the vascular graft biomaterial has been optimized and scaled-up. The structural, functional and biological properties of the MSDVGs optimized in this project have been determined, including their mechanical properties (hardness/elastic modulus) and burst pressure (pulsatile flow experiments). The biocompatibility of the vascular graft biomaterial has been studied using endothelial cells. In parallel to cell growth studies, the density of cells attached onto the MSDVG surface was determined. The expression of endothelial cell markers has been studied in RT-qPCR experiments. The biomaterial did not significantly affect clotting of human plasma. The antibacterial activity of the polyP component of the MSDVGs has been demonstrated using the filter paper disc assay. In vivo studies in sheep revealed no toxicity or other adverse side effects of the material. A market analysis has been performed and a Business Plan, including an analysis of relevant industry/competitors, risk factors, regulations, market entry barriers, stakeholders, and market segmentation, as well as a SWOT analysis has been prepared. Three dissemination events, both to experts and potential end-users, as well as to the broader public, have been performed.
The striking advantages of the MSDVG, making them superior to conventional vascular grafts, can be summarized as follows: (i) Their mechanical properties can be adapted to the needs of individual patients. (ii) They are able to prevent thrombosis. (iii) They can be produced with bi- or multi-layered walls of different hardness, porosity or permeability providing optimal growth conditions for endothelial cells. (iv) Their degradation rates are adjustable to the vascular regeneration rate. (v) They can be easily fabricated.
The socio-economic benefits of our new vascular grafts are considered as extremely high. Worldwide, the number of patients receiving prosthetic grafts for coronary and peripheral vessel reconstruction, repair of aneurysm, or for hemodialysis access is steadily increasing and expected to reach a number of >1.8 million/year. The expenses for those prosthetic vascular grafts in Europe have increased to >25 billion €/year. Besides of their economical value, our new type of artificial blood vessels will certainly improve the quality of life and well-being of patients who have cardiovascular disorders. In particular, they will contribute to an amelioration and treatment of atherosclerosis, a major biomedical challenge in our ageing society.
