A series of segmented poly(epsilon-caprolactone) polyurethanes (PCLUs) were prepared from poly(epsilon-caprolactone) (PCL) diol, 2,4-toluene diisocyanate and ethylene glycol. The molecular weight (M(n)) of PCL was 500-10,000, and the soft-to-hard molar ratio was 1:2 to 1:6. Their shape-memory behaviors were investigated as a function of PCL molecular weight, PCLU composition, and thermal/mechanical history. When a deformation temperature 15-20 degrees C below T(m) was chosen, the lowest recovery temperature (LRT) was 15-18 degrees C below T(m), and the recovery ratio was 94-100% for tensile deformation of 300% and for compression of 2.7-fold. The reasons for this deformation-recovery procedure and the mechanism for this shape recovery below T(m) were discussed. The shape recovery was associated with the premelting of the crystals formed during the deformation and fixation, and, thus, it could be accomplished in the solid state. Its driving force was the inner stress stored in the deformed specimen during deformation and crystallization. Therefore, the LRT was a more practical temperature for shape-memory PCLU than T(m). It could be conveniently measured by means of thermal mechanical analysis. By adjusting the molecular weight of the PCL diol and the hard-to-soft ratio, the LRT of PCLU could be adjusted to the range of 37-42 degrees C, and reasonable rigidity could be retained after shape recovery, fulfilling the essential requirements of medical implantations.

The objectives of the present study were to investigate heavy metal accumulation in 22 vegetable species and to assess the human health risks of vegetable consumption. Six vegetable types were cultivated on farmland contaminated with heavy metals (Pb, Cd, Cu, Zn, and As). The target hazard quotient (THQ) method was used to assess the human health risks posed by heavy metals through vegetable consumption. Clear differences were found in the concentrations of heavy metals in edible parts of the different vegetables. The concentrations of heavy metals decreased in the sequence as leafy vegetables > stalk vegetables/root vegetables/solanaceous vegetables > legume vegetables/melon vegetables. The ability of leafy vegetables to uptake and accumulate heavy metals was the highest, and that of melon vegetables was the lowest. This indicated that the low accumulators (melon vegetables) were suitable for being planted on contaminated soil, while the high accumulators (leafy vegetables) were unsuitable. In Shizhuyuan area, China, the total THQ values of adults and children through consumption of vegetables were 4.12 and 5.41, respectively, suggesting that the residents may be facing health risks due to vegetable consumption, and that children were vulnerable to the adverse effects of heavy metal ingestion.

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