Supramolecular polyurethane ureas are expected to have superior mechanical properties primarily due to the reversible, noncovalent interactions such as hydrogen bonding interactions. We synthesized polyurethane prepolymers from small molecular weight of poly(tetramethylene ether)glycol and isophorone diisocyanates, which were end capped with propylamine to synthesize polyurethane ureas with high contents of urea and urethane groups for hydrogen-bonding formations to facilitate self-healing. The effects of polyurethane urea molecular weight (3000 M n 9000), crosslinking, and cutting direction were studied in terms of thermal, mechanical, and morphological properties with an emphasis on the selfhealing efficiency. It was found that the thermal self-healability was more pronounced as the molecular weight of polyurethane urea decreased, showing a maximum of more than 96% with 3000 M n when the sample was cut along the stretch direction.Recently, thermoresponsive self-healing PUs based on the Diels-Alder reaction between furan and maleimide moieties were reported, where the shape-memory effect was used to autonomously close the crack. 20,21
A microporous hydrogel scaffold was developed from hyperbranched poly(glycidol) (HPG) and poly(ethylene oxide) (PEO) using electron beam (e-beam) induced cross-linking for tissue engineering applications. In this study, HPG was synthesized from glycidol using trimethylol propane as a core initiator and cross-linked hydrogels were made using 0, 10, 20, and 30% HPG with respect to PEO. The effects of %-HPG on the swelling ratio, cross-linking density, mechanical properties, morphology, degradation, and cytotoxicity of the hydrogel scaffolds were then investigated. Increasing the HPG content increased the pore size of the hydrogel scaffold, as well as the porosity, elongation at break, degree of degradation and swelling ratio. In contrast, the presence of HPG decreased the cross-linking density of the hydrogel. There was no significant difference in compressive modulus and tensile strength of all compositions. The pore size of hydrogel scaffolds could be easily tailored by controlling the content of HPG in the polymer blend. Evaluation of the cytotoxicity demonstrated that HPG/PEO hydrogel scaffold has potential for use as a matrix for cellular attachment and proliferation. These results indicate that cross-linked HPG/PEO hydrogel can function as a potential material for tissue engineering scaffolds. Moreover, a facile method to prepare hydrogel microporous scaffolds for tissue engineering by e-beam irradiation was developed.
After producing crystalline Si (c-Si) solar module, the output power of the c-Si module was decreased compared to the total amount of c-Si cells' power due to the increase of series resistance and the light absorption of the cover glass and encapsulant. We define this power loss as cell to module (CTM) loss and the decreasing power rate as CTM conversion ratio (CR). The typical CTM CR in other groups has a value of about 94%. The CTM CR is typically decreased with increasing the efficiency of solar cell due to the increase of I 2 R loss. In this experiment, we have focused on the increase of CTM CR through detail analysis to each module component. As a result, the CTM CR in c-Si photovoltaic modules can be significantly increased by appropriately optimizing a module component. The maximum CTM CR in this experimental obtained about 97% using 19% efficiency cells, and it is 264.1 W power in 6 Â 10 string module. V C 2013 AIP Publishing LLC. [http://dx.
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