An Experimental Study into the Behaviour of Tube and Fitting Scaffold Structures under Cyclic Side and Vertical Loads

The United Kingdom and European codes for the analysis and design of tubular scaffold structures assume that the scaffolds are subjected primarily to vertical loads and to horizontal loads at right-angles to the scaffold. The effects of dynamic loading caused by large winds tend to be ignored and the code analyses often only require static loading on the structures to be considered. To investigate side loads, a scaffold frame built according to the UK standard was made and inserted into a testing rig. Five different load combinations were made to determine the behaviour of the scaffold under different side loads, which were varied cyclically to simulate different wind loads, especially when vertical loads were also applied. The results showed that cyclical loads affected scaffold behaviour, especially when the bases of the scaffold standards were not tied to the base at the bottom of the test rig. Changes should be made to the UK and European codes BS EN 74.1, BS 5975 and BS EN 128 11-1 for the design of scaffold structures to increase safety.

Engineering the Composition of Microfibers to Enhance the Remodeling of a Cell-Free Vascular Graft

The remodeling of vascular grafts is critical for blood vessel regeneration. However, most scaffold materials have limited cell infiltration. In this study, we designed and fabricated a scaffold that incorporates a fast-degrading polymer polydioxanone (PDO) into the microfibrous structure by means of electrospinning technology. Blending PDO with base polymer decreases the density of electrospun microfibers yet did not compromise the mechanical and structural properties of the scaffold, and effectively enhanced cell infiltration. We then used this technique to fabricate a tubular scaffold with heparin conjugated to the surface to suppress thrombosis, and the construct was implanted into the carotid artery as a vascular graft in animal studies. This graft significantly promoted cell infiltration, and the biochemical cues such as immobilized stromal cell-derived factor-1α further enhanced cell recruitment and the long-term patency of the grafts. This work provides an approach to optimize the microfeatures of vascular grafts, and will have broad applications in scaffold design and fabrication for regenerative engineering.

Fabrication and Properties of Electrospun Collagen Tubular Scaffold Crosslinked by Physical and Chemical Treatments

Tissue engineered scaffold was regarded as a promising approach instead of the autograft. In this study, small diameter electrospun collagen tubular scaffold with random continuous smooth nanofibers was successfully fabricated. However, the dissolution of collagen in concentrated aqueous (conc. aq.) acetic acid caused to the serious denaturation of collagen. A novel method ammonia treatment here was adopted which recovered the collagen triple helix structure according to the analysis of IR spectra. Further dehydrothermal (DHT) and glutaraldehyde (GTA) treatments were applied to introduce the crosslinks to improve the properties of collagen tube. The nanofibrous structure of collagen tube in a wet state was preserved by the crosslinking treatments. Swelling ratio and weight loss decreased by at least two times compared to those of the untreated collagen tube. Moreover, tensile strength was significantly enhanced by DHT treatment (about 0.0076 cN/dTex) and by GTA treatment (about 0.075 cN/dTex). In addition, the surface of crosslinked collagen tube kept the hydrophilic property. These results suggest that DHT and GTA treatments can be utilized to improve the properties of electrospun collagen tube which could become a suitable candidate for tissue engineered scaffold.

A novel polymeric fibrous microstructured biodegradable small-caliber tubular scaffold for cardiovascular tissue engineering

Increasing morbidity of cardiovascular diseases in modern society has made it crucial to develop artificial small-caliber cardiovascular grafts for surgical intervention of diseased natural arteries, as alternatives to the gold standard autologous implants. Synthetic small-caliber grafts are still not in use due to increased risk of restenosis, lack of lumen re-endothelialization and mechanical mismatch, leading sometimes either to graft failure or to unsuccessful remodeling and pathology of the distal parts of the anastomosed healthy vascular tissues. In this work, we aimed to synthesize small-caliber polymeric (polycaprolactone) tissue-engineered vascular scaffolds that mimic the structure and biomechanics of natural vessels. Electrospinning was implemented to prepare microstructured polymeric membranes with controlled axis-parallel fiber alignment. Consequently, we designed small-caliber multilayer anisotropic biodegradable nanofibrous tubular scaffolds, giving attention to their radial compliance. Polycaprolactone scaffold morphology and mechanical properties were assessed, quantified, and compared with those of native vessels and commercial synthetic grafts. Results showed a highly hydrophobic scaffold material with a three-layered tubular morphology, 4-mm internal diameter/0.25 ± 0.09-mm thickness, consisting of predominantly axially aligned thin (1.156 ± 0.447 μm), homogeneous and continuous microfibers, with adequate (17.702 ± 5.369 μm) pore size, potentially able to promote cell infiltration in vivo. In vitro accelerated degradation showed a 5% mass loss within 17–25 weeks. Mechanical anisotropy was attained as a result, almost one order of magnitude difference of the elastic modulus (18 ± 3 MPa axially/1 ± 0.3 MPa circumferentially), like that of natural arterial walls. Furthermore, a desirable radial compliance (5.04 ± 0.82%, within the physiological pressure range) as well as cyclic stability of the tubular scaffold was achieved. Finally, cytotoxicity evaluation of the polymeric scaffolds revealed that the materials were nontoxic and did not release substances harmful to living cells (over 80% cell viability achieved).

A biomimetic orthogonal-bilayer tubular scaffold for the co-culture of endothelial cells and smooth muscle cells

To mimic blood vessels, a polycaprolactone tubular scaffold was prepared via electrospinning and winding. Endothelial cells were cultured on the inner layer with axial nanofibers and smooth muscle cells were cultured on the outer layer with circumferential nanofibers.

Designing Biomimetic Triple-Layered Nanofibrous Vascular Grafts via Combinatorial Electrospinning Approach

Biomimetic vascular grafts with multi-layered nanostructures can mimic structure and function of native blood vessels, but it is often challenging. This study demonstrates the feasibility of using combinatorial electrospinning approach for designing triple-layered nanofibrous tubular scaffold with inner and outer layer made up of co-axial poly(lactic-co-glycolic acid) (PLGA)/gelatin nanofibers (PLGA-core/gelatin-shell) and the intermediate layer with PLGA nanofibers that mimics native vascular structure. The assessment of biomechanical and biological analysis showed enhanced mechanical strength, suture strength and biocompatibility when cultured with human umbilical vein endothelial cells (HUVECs). Altogether, the results suggest that the combinatorial electrospinning approach is potentially useful for the fabrication of biomimetic vascular grafts suitable for cardiovascular tissue engineering applications.