Tissue engineered vascular grafts
Different manufacturing techniques can be selected to produce a TEVG of this kind. To improve the properties of these grafts, autologous ECs and VSMCs obtained from differentiation of bone marrow-derived cells were seeded in decellularized matrices and then tested in ovine Tillman et al.
Overall, the main limitation of the technique is the time to produce the graft which, considering the duration between the formation of a confluent sheet and the fusion throughout the bioreactor conditioning, was assessed to be around 28 weeks L'Heureux et al.
What are vascular grafts made of
On the other hand, this strategy showed limitations in terms of sterility and its time-consuming nature. Nonetheless, at 7 days post-implantation, the grafts exhibited bleeding and detachment of the layers leading to the failure of the implant. Inner diameter of the grafts is 1. Cyclic deformation in addition to pulsatile flow conditioning improved mechanical properties of the graft Syedain et al. Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The aim of the present work was development of a method for producing vascular grafts with small diameter based on poly L-lactide PLLA microfibers, studies of their structure, strength and deformation properties, in vivo investigation of biological tissue formation on the obtained grafts, and analysis of bioresorption mechanism. L'Heureux's group further improved the production of an off-the-shelf graft attempting to define a procedure to store the graft after the manufacturing process. We focus on the techniques employed in the manufacturing process of the grafts and categorize the approaches as scaffold-based synthetic, natural, or hybrid or self-assembled cell-sheet, microtissue aggregation and bioprinting. Biodegradable TEVGs, cellularized or based on hybrid approach, shielding the scaffold lumen from the bloodstream, show a reduction in thrombus events. Surgical revascularization with implantation of conduits made of non-biodegradable polymers, including Polytetrafluoroethylene PTFE , Gore-Tex, and Dacron, prove to be effective when replacing large vessels. Angiographic Study Angiographic studies were carried out with the aid of a Philips Allura Xper FD 20 setup Netherlands after open puncture of rats abdominal aorta in the area above prosthesis zone. As described in this review, an extensive variety of cells have been tested, both to build the core of the graft in the case of a scaffold-free approach and to cellularize the scaffold in the pre-implantation stage. Furthermore, biodegradable polymers offer the possibility for the cells to colonialize the porous structure and thereby stimulate the production of ECM proteins. The surgical bypass grafting mostly involves the use of autologous vessels, such as the saphenous vein and internal thoracic artery.
As described in this review, an extensive variety of cells have been tested, both to build the core of the graft in the case of a scaffold-free approach and to cellularize the scaffold in the pre-implantation stage.
In this approach, a temperature—responsive poly N-isopropylacrylamide is used as culturing surface, allowing the easy detachment of the cell aggregate when the culture is confluent Asakawa et al.
Small diameter vascular grafts
Another approach sees the casting of a suspension of gel and cells into a mold to produce a tubular structure. Tissue Engineering Halfway through the twentieth century, the first autologous saphenous vein was used as a vascular graft in a clinical application by Kunlin A variety of polymers and copolymers have been tested. Furthermore, biodegradable polymers offer the possibility for the cells to colonialize the porous structure and thereby stimulate the production of ECM proteins. Computed tomography CT scan and ultrasonography showed no stenosis and structural integrity of the TEVG at 6 months follow-up Ju et al. Natural Materials ECM based grafts The lack of bio-activity of synthetic scaffolds prompted researchers to investigate natural polymers obtained from ECM as a possible alternative option. We focus on the techniques employed in the manufacturing process of the grafts and categorize the approaches as scaffold-based synthetic, natural, or hybrid or self-assembled cell-sheet, microtissue aggregation and bioprinting. The various approaches being explored to generate TEVGs are described, including scaffold-based methods using synthetic and natural polymers , the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted.
Low patency rates of the synthetic prostheses with diameter less than 5 mm are related, first of all, to development of neointimal hyperplasia at anastomosis sites and the absence of endothelial layer on the inner side of prostheses [ 1 — 4 ].
This consists of casting a mixture of the desired gel and cell suspension in a tubular mold made of a polypropylene tube.
Vascular graft polymers
The sheet is rolled around a mandrel and matured under dynamic conditions to develop vessel-like properties. Nonetheless, at 7 days post-implantation, the grafts exhibited bleeding and detachment of the layers leading to the failure of the implant. Self-assembled TEVGs are based on the concept that cells, placed in a 3D environment and with the right stimuli, would be able to organize themselves in a complex tissue. These grafts have shown satisfactory long-term results for replacement of large- and medium-diameter arteries, such as the carotid or common femoral artery, but have poor patency rates when applied to small-diameter vessels, such as coronary arteries and arteries below the knee. The technique consisted of peeling off a confluent culture of VSMCs and fibroblasts and carefully shaping the cell sheet with all the released ECM into a tubular structure Figure 2A. D The TEVG undergoes cellularization with the expanded autologous cells before moving to dynamic conditioning into bioreactor which allows the maturation of the structure. Various TEVG models fabricated with synthetic polymers have been assessed in preclinical small and large animal models. Maintaining the integrity of the environment during the assembling of the vascular tree is challenging, and a minimum of 7 days is required to allow for the fusion of the spheroids on to the tubular surface. To further improve the mechanical properties of the TEVG, a suspension of ovine dermal fibroblasts were added to the fibrin and the gelled structure was cultured for a total period of 5 weeks the first 2 in static conditions and the remaining 3 under pulsatile flow stimulation Syedain et al. A,B Tissues obtained from biopsies of patients are treated and cells are isolated and expanded in vitro. Common presentations are coronary heart disease, cerebrovascular disease, peripheral arterial disease, and deep vein thrombosis. This attempt led to the fabrication of a vessel-like structure with poor mechanical properties, that required a Dacron mesh to act as a structural support. No thrombosis was seen and implants remained patent, with the absence of occlusion or ischemia detected at the 1 month follow-up.
Another important quality requisite is the similarity of TEVG mechanical properties to the native tissue, with a recommended minimum burst pressure of mmHg Konig et al.
based on 118 review