There is a strong need for tissue engineering scaffolds that are mechanically robust, exhibit good biocompatibility, and can be made from readily available materials. To this end, blends of commercially available poly(ethylene glycol) diacrylate (PEGDA) with molecular weights of 400 and 3400 were UV-crosslinked at total polymer concentrations that varied systematically from 20 to 40 wt %. The compressive strength and cell viability were determined for each PEGDA mixture. The compressive modulus of the blends was maximized when the wt % ratio PEGDA3400/400 was about 40/60, with the compressive strength reaching 1.7 MPa. Cell viability results with a LIVE/DEAD fluorescence assay show an average viability of ~ 80% at a total PEGDA concentration of 20 wt %, for all blends. Increasing the total polymer concentration increased the compressive modulus of a polymer, but adversely affected cell viability for all the PEGDA blend compositions. The blend composition affected the mechanical behavior of the discs, where a higher degree of crosslinking was achieved by increasing the concentration of shorter chained PEGDA400, whereas elasticity was gained by incorporating longer chained PEGDA3400 into the blends. These results can be exploited for use in tissue engineering applications, where a mechanically robust scaffold is advantageous.

Multi-layered composites composed of mammalian cells arranged in a hydrogel have been prepared using an acoustic focusing technique. Acoustic focusing is a simple, non-chemical technique that allows for the fast arrangement of cells in matrices where the control of cell geometry is beneficial. Breast cancer cells (MDA-MB231), were dispersed in a 30 wt % solution of poly(ethylene glycol) diacrylate (PEGDA) of molecular weight 400 at a density of 5 × 10 6 cells per ml of PEGDA solution. An ultrasonic field was used to organize the cells into multiple layers prior to polymerization of PEGDA. Disk-shaped hydrogel composites, typically 1 cm in diameter and 2 mm thick were prepared based on a PEGDA solution volume of 130 uL. At an acoustic frequency of 2.32 MHz, composites were fabricated, where concentric rings/layers of cells were interspersed with cell-free hydrogel. The cells were located in annuli approximately 80 μm thick and about 300 μm apart. The structure and viability of the cells within these constructs were studied using a fluorescent LIVE/DEAD assay. The viability of the cells was on the order of 50%. Cell death was primarily attributed to exposure of cells to the PEGDA solution prior to polymerization, rather than adverse effects of polymerization or the sound field itself.

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Processes in the chemical jndustry and hydrogen generation were identified as potentia] users of heat from high temperature (9000C) gas cooled reactors and light water reactors operating at 3250C. There was no inherent technical or efficiency advantage in using nuclear power heat except for the Iack of greenhouse gas emissions.

The Westinghouse Sulfur Process is a member of the sulfur family of hydrogen generating thermochemical cycles being considered by the DOE for coupling with an HTGR. It has been proven experimentally and utilizes mature technology. Westinghouse has identified process improvements that increase the efficiency and reduce materials and HTGR-Hydrogen Process integration issues. Increasing the hydrogen plant operating pressure improves the thermal efficiency of the Westinghouse Sulfur Process from 40% to ∼55% (LHV basis) at H2SO4 concentrations of 40% to 80% by weight. The use of a directly heated decomposition reactor in conjunction with an HTGR allows higher decomposition reactor operating temperatures. This increases the per-pass percent conversion and increases overall efficiency. Other advantages are total separation of the coolant and process streams, the maturity of this technology (it has been used for over a century in the steel industry at temperatures up to 1,200°C), and the ready availability of materials.