External Stress-Free Reversible Multiple Shape Memory Polymers.

The present work is focused on developing external stress-free two-way triple shape memory polymers (SMPs). Accordingly, a series of innovative approaches are proposed for the material design and preparation. Polyurethane prepolymers carrying crystalline polytetrahydrofuran (PTMEG) and poly(ε-caprolactone) (PCL) as the switching phases are respectively synthesized in advance and then cross-linked to produce the target material. The stepwise method is believed to be conducive to manipulation of the relative contribution of PCL and PTMEG. Moreover, the chain extender, 2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol (UPy), is incorporated to establish hydrogen bonds among the macromolecules. By straightforward stretching treatment at different temperatures, the hydrogen bond networks are successfully converted into an internal stress provider, which overcomes the challenge of stress relaxation of the melted low melting temperature polymer (i.e., PTMEG) and increases the efficiency of stress transfer. Meanwhile, the contraction force of the switching phases is tuned to match the internal tensile stress. As a result, the internal stress provider can closely collaborate with melting/recrystallization of the crystalline domains, leading to the repeated multiple shape memory effects. The cross-linked polyurethane is thus able to reversibly morph among three shapes and displays its potentials as soft robot and actuator. The strategy reported here has the advantages of easily accessible raw materials, simple reaction, and facile programing/deprograming/reprograming, so that it possesses wide applicability.

[Comparative study on specific chromatograms and main active components of wild and cultivated rhizomes of Paris polyphylla var. yunnanensis].

The present study is to compare specific chromatograms and main acitive components between wild and cultivated rhizomes of Paris polyphylla var. yunnanensis by HPLC. HPLC analysis was performed on a Waters XSelect HSS T3 C18 clumn (4.6 mm×250 mm, 5 µm), with a mobile phase consisting of acetonitrile (A)-water (B) at a flow rate of 1 mL•min⁻¹ (0-50 min,30%-50%A;50-80 min,50% A,80-85 min,50%-30%A;85-100 min,30% A). The detection wavelength was 203 nm and the column temperature was controlled at 30 ℃, and the injection volume was 10 µL. HPLC specific chromatograms of wild and cultivated rhizomes of P. polyphylla var. yunnanensis were established and nine steroidal saponins were simultaneously determined by the above method. The mean contents of paris saponin Ⅶ, paris saponin H and total average contents of four pennogenyl saponins in Rhizomes of wild samples were significantly higher than those of cultivated ones. However, this result is opposite from the average content of paris saponin Ⅰ and total average contents of five dioscins in the wild and cultivated samples. Because the significant differences occurred for the specific chromatograms and main active components between the wild and cultivated P. polyphylla var. yunnanensis, much more pharmacological and clinical researches are therefore necessary.