The aim of this study was to mimic the native three layered architecture of the arterial wall. To accomplish this, electrospinning was employed with the use of a 3-1 (input-output) nozzle and blends of polycaprolactone, elastin, and collagen.
Throughout native artery, collagen and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery under pulsatile deformations. The goal of this study was to mimic the structure of native artery by fabricating a multi-layered electrospun conduit composed of poly(caprolactone) (PCL) with the addition of elastin and collagen with blends of 45-45-10, 55-35-10, and 65-25-10 PCL-ELAS-COL to demonstrate mechanical properties indicative of native arterial tissue, while remaining conducive to tissue regeneration. Whole grafts and individual layers were analyzed using uniaxial tensile testing, dynamic compliance, suture retention, and burst strength. Compliance results revealed that changes to the middle/medial layer changed overall graft behavior with whole graft compliance values ranging from 0.8 – 2.8 % / 100 mmHg, while uniaxial results demonstrated an average modulus range of 2.0 – 11.8 MPa. Both modulus and compliance data displayed values within the range of native artery. Mathematical modeling was implemented to show how changes in layer stiffness affect the overall circumferential wall stress, and as a design aid to achieve the best mechanical combination of materials. Overall, the results indicated that a graft can be designed to mimic a tri-layered structure by altering layer properties.
Representative Results
When the electrospinning protocols are carried out correctly, the end product should be a soft, seamless tube with no initial signs of delamination between the layers. When the uniaxial tensile tests, burst strength tests, suture retention tests, and compliance tests are performed, the results should indicate that as the medial layer stiffness is increased, with decreased amounts of elastin, the associated mechanical properties should demonstrate a stiffer tube.
The most critical portion of this study is the electrospinning process. When using a 3-1 input-output nozzle, arching and charge loss may occur. If this does occur, the voltage associated with the polymer that is spinning will decrease causing welded, “wet” fibers and creating delamination between each of the three layers. Therefore, consistent electric potentials are essential to obtain an ideal multi-layered tube.
Compliance mismatch is one of the main causes of graft occlusion at the small diameter level. Developing a multi-layered vascular graft provides the ability to tailor graft properties towards something that could mimic the natural biomechanics and architecture of native artery. As steps in processing a multi-layered vascular graft progress in the future, our lab will investigate possible limitations such as delamination of the layers while the scaffold undergoes degradation in addition to adequate pore size for cellular infiltration. To test this, both acellular and cellular in vitro degradation studies will be performed under static and dynamic culture. These tests will determine both the migratory capabilities of the scaffolds and how they will effectively degrade under physiological conditions.
The authors have nothing to disclose.
We would like to thank the American Heart Association Mid-Atlantic Affiliate (0555407U,GLB) for funding.
Material Name | Type | Company | Catalogue Number | Comment |
---|---|---|---|---|
Polycaprolactone | Sigma | |||
Elastin | Elastin Products Company | |||
Collagen | ||||
Acetic Acid | Fisher | |||
Sodium Chloride | Fisher | |||
TRIS | Fisher | |||
6 L Avanti J-HC Centrifuge | Beckman Coulter | |||
1,1,1,3,3,3 hexafluoro-2-propanol | TCI America | |||
3 ml Becton Dickinson Syringe | ||||
CZE1000R Rack Mount Power Supply | Spellman | |||
High-Pressure Syringe Pump | Cole Parmer | |||
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide | Pierce | |||
70 % ethanol | Sigma Aldrich | |||
ImageTool 3.0 software | Shareware provided by UTHSCSA | |||
Scanning Electron Microscope | Zeiss EV050 | |||
MTS Bionix 200 testing system | MTS Systems Corp. | |||
TestWorks version 4 | ||||
Intelligent Tissue Engineering via Mechanical Stimulation (ITEMS) Bioreactor | Tissue Growth Technologies |