The Mechanical Performance of 3D Warp Knitted Spacer Scaffold Fabrics Using Uniaxial and Biaxial Measurements.

TANG, XIAOQI. The Mechanical Performance of 3D Warp Knitted Spacer Scaffold Fabrics Using Uniaxial and Biaxial Measurements. Three dimensional (3D) warp knitted spacer fabrics have a unique thick sandwich structure and superior elasticity and compressibility. The common applications for these particular fabrics include protective devices, seating and acoustic and/or thermal isolation. Seldom are these 3D fabrics considered suitable for tissue engineering (TE) scaffolds. But because there are vertical filament yarns that can serve as guides we believe there is merit in proposing their use as thick scaffold materials that can promote cell migration through the thickness. Therefore, the purpose of this study was to evaluate the dynamic mechanical properties of different bicomponent 3D warp knitted structures by using cyclic uniaxial and biaxial test methods. In addition we determined how closely they mimicked the mechanical behavior of a native muscle tendon junction (MTJ). The common uniaxial cyclic textile test method requires the fabric to be repeatedly stretched by 10% in the weft (horizontal) direction. The second biaxial cyclic test method was found to be better at mimicking the dynamic stretch performance for muscle tendon junction (MTJ) tissues. By repeatedly applying 10% strain in the weft (horizontal) direction, the other warp (vertical) direction was held in a fixed position by a second pair of clamps. Due to the limited capacity of the load cells, the thicker fabrics were measured at 5% strain, while the thinner fabrics were measured under both 5% and 10% levels of strain. Several independent variables were intentionally varied during the knitting process so as to determine which variables controlled the dynamic mechanical properties of the scaffolds. They included the take up speed (250% & 1000%), the number of guide bars (4GB & 6GB), and two different materials, namely resorbable poly(lactic acid) (PLA) and non-resorbable polyester or poly(ethylene terephthalate) (PET) commonly used to fabricate sutures, vascular prostheses and endovascular stent grafts. Three dependent variables were measured during cyclic testing. They included; the maximum stress at 10% strain, the loss of energy in the hysteresis calculated from the stretch-recovery hysteresis curves, and the four linear regions were defined in terms of the stretch and recovery moduli. By comparing these values it was found that the take up speed was the primary factor that controlled the mechanical performance of the scaffolds. Compared with PLA, the PET scaffolds had higher mechanical values. The greater number of guide bars is known to generate denser fabrics, which also have higher mechanical values. In order to validate these results, viable native porcine MTJ tissues were harvested and measured under biaxial testing, which provided a direct comparison with the knitted MTJ scaffolds. The results indicate that the PET scaffold had similar features and trends to the native tissue among the three muscle, tendon and interface zones, while the PLA structures had inherently lower mechanical properties © Copyright 2016 Xiaoqi Tang All Rights Reserved The Mechanical Performance of 3D Warp Knitted Spacer Scaffold Fabrics Using Uniaxial and Biaxial Measurements