Mechanical properties of 2D and 3D braided textile composites

The purpose of this research was to determine the mechanical properties of 2D and 3D braided textile composite materials. Specifically, those designed for tension or shear loading were tested under static loading to failure to investigate the effects of braiding. The overall goal of the work was to provide a structural designer with an idea of how textile composites perform under typical loading conditions. From test results for unnotched tension, it was determined that the 2D is stronger, stiffer, and has higher elongation to failure than the 3D. It was also found that the polyetherether ketone (PEEK) resin system was stronger, stiffer, and had higher elongation at failure than the resin transfer molding (RTM) epoxy. Open hole tension tests showed that PEEK resin is more notch sensitive than RTM epoxy. Of greater significance, it was found that the 3D is less notch sensitive than the 2D. Unnotched compression tests indicated, as did the tension tests, that the 2D is stronger, stiffer, and has higher elongation at failure than the RTM epoxy. The most encouraging results were from compression after impact. The 3D braided composite showed a compression after impact failure stress equal to 92 percent of the unimpacted specimen. The 2D braided composite failed at about 67 percent of the unimpacted specimen. Higher damage tolerance is observed in textiles over conventional composite materials. This is observed in the results, especially in the 3D braided materials

Polylactic Acid (PLA) Scaffolds for Tissue Engineering Applications do not Biodegrade in Physiological Saline at Room Temperature

Three-dimensional (3D) printable scaffolds are advantageous for their ability to be custom made to fill hard tissue defects. In this approach, scaffolds are required to be osteoconductive such that cells (osteoblasts) can attach and proliferate on the scaffolds and subsequently go on to become bone. It is desirable for the scaffold to biodegrade while bone formation occurs. Biodegradation occurs through the process of polymer chains being broken down into smaller chains, resulting in eventual extinction of the polymer altogether. Knowledge of biodegradation rates is important for prediction of scaffold stiffness and strength used in engineering analysis. Polylactic acid, or PLA, is a popular filament used in 3D printing (3DP). Biodegradation of PLA occurs through the process of hydrolysis which utilizes water molecules to break down the polymer chain. In this study, PLA scaffolds were tested to determine their baseline degradation rates. Eight X-type scaffold specimens were selected for the assessment of PLA sustainability due to soaking in cell culture media held at room temperature (20° C). Specimens were weighted, measured, and mechanically tested at the onset of the protocol (t = 0 weeks) and at weeks 1-7, week 10, and week 32. Mechanical compression tests made between steel plates within the elastic limit. Following testing, the structural stiffness (slope of the load-displacement curve) was calculated within the linear elastic region. Statistical analysis using JMP (SAS institute, Cary, NC) was performed to detect degradation in weight and stiffness with soak time. A significant difference is indicated by