Preparation, Characterization, and Mechanism for Biodegradable and Biocompatible Polyurethane Shape Memory Elastomers

Thermally induced shape memory is an attractive feature of certain functional materials. Among the shape memory polymers, shape memory elastomers (SMEs) especially those with biodegradability have great potential in the biomedical field. In this study, we prepared waterborne biodegradable polyurethane SME based on poly­(ε-caprolactone) (PCL) oligodiol and poly­(l-lactic acid) (PLLA) oligodiol as the mixed soft segments. The ratio of the soft segments in polyurethanes was optimized for shape memory behavior. The thermally induced shape memory mechanism of the series of polyurethanes was clarified using differential scanning calorimeter (DSC), X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). In particular, the in situ SAXS measurements combined with shape deformation processes were employed to examine the stretch-induced (oriented) crystalline structure of the polyurethanes and to elucidate the unique mechanism for shape memory properties. The polyurethane with optimized PLLA crystalline segments showed a diamond-shape two-dimensional SAXS pattern after being stretched, which gave rise to better shape fixing and shape recovery. The shape memory behavior was further tested in 37 °C water. The biodegradable polyurethane comprising 38 wt % PCL segments and 25 wt % PLLA segments and synthesized at a relatively lower temperature by the waterborne procedure showed ∼100% shape recovery in 37 °C water. The biodegradable polyurethane SME also demonstrated good endothelial cell viability as well as low platelet adhesion/activation. We conclude that the waterborne biodegradable polyurethane SME possesses a unique thermally induced shape memory mechanism and may have potential applications in making shape memory biodegradable stents or scaffolds

Shape and Confinement Effects of Various Terminal Siloxane Groups on Supramolecular Interactions of Hydrogen-Bonded Bent-Core Liquid Crystals

To investigate the shape and confinement effects of the terminal siloxane groups on the self-assembled behavior of molecular arrangements in hydrogen-bonded (H-bonded) bent-core complexes, four H-bonded bent-core complexes <b>S1</b>, <b>P1</b>, <b>C4</b>, and <b>P8</b> with string-, ring-, and cage-like siloxane termini (i.e., linear siloxane unit −Si–O–Si–O–Si–, cyclic siloxane unit (Si–O)₄, and silsesquioxane unit POSS, respectively) were synthesized and investigated. By X-ray diffraction measurements, different types of SmCG (B8) phases and leaning angles were controlled by the shape effect of the string- and cage-like siloxane termini for <b>S1</b> and <b>P1</b> (with only one arm of H-bonded bent-core), respectively. In addition, the confinement effect of <b>P1</b>, <b>C4</b>, and <b>P8</b> (accompanied by increasing the numbers of attached H-bonded bent-core arms) resulted in higher transition temperatures and the diminishing of mesophasic ranges (even the disappearance of mesophase in <b>P8</b>). Moreover, AFM images showed the bilayer smectic CG phases of <b>S1</b> and <b>P1</b> were aligned to reveal highly ordered thread-like structures by a DC field. By spontaneous polarization measurements within the mesophasic ranges, <b>S1</b> and <b>P1</b> showed ferroelectric transitions but <b>C4</b> displayed antiferroelectricity. Finally, the electro-optical performance of B8 phases could be optimized through binary mixtures of <b>S1</b> and <b>P1</b>, and a well aligned modulated ribbon phase could be formed via specific molar ratios of the binary mixtures

Broad Ranges and Fast Responses of Single-Component Blue-Phase Liquid Crystals Containing Banana-Shaped 1,3,4-Oxadiazole Cores

In this study, we synthesized two novel 1,3,4-oxadiazole-based bent-core liquid crystals (<b>OXD7*</b>, <b>OXD5B7F*</b>) containing a chiral tail that display broad ranges of the blue phase III (34 and 7 K, respectively); we characterized them using polarized optical microscopy, differential scanning calorimetry, and circular dichroism. The electro-optical responses of both of these liquid crystals are much faster than those of previously reported single-component blue-phase liquid crystals. To optimize its electro-optical performance, we mixed <b>OXD7*</b> (the blue-phase range of which is broader than that of <b>OXD5B7F*</b>) with its analogue <b>OXD6</b> (at weight ratios of 6:4 and 4:6). We also performed molecular modeling of single-component BPLCs (<b>OXD7*</b> and <b>OXD5B7F*</b>) to analyze the possible parameters affecting their blue phase ranges

Multiscale mechanisms of nutritionally induced property variation in spider silks

<div><p>Variability in spider major ampullate (MA) silk properties at different scales has proven difficult to determine and remains an obstacle to the development of synthetic fibers mimicking MA silk performance. A multitude of techniques may be used to measure multiscale aspects of silk properties. Here we fed five species of Araneoid spider solutions that either contained protein or were protein deprived and performed silk tensile tests, small and wide-angle X-ray scattering (SAXS/WAXS), amino acid composition analyses, and silk gene expression analyses, to resolve persistent questions about how nutrient deprivation induces variations in MA silk mechanical properties across scales. Our analyses found that the properties of each spider’s silk varied differently in response to variations in their protein intake. We found changes in the crystalline and non-crystalline nanostructures to play specific roles in inducing the property variations we found. Across treatment <i>MaSp</i> expression patterns differed in each of the five species. We found that in most species <i>MaSp</i> expression and amino acid composition variations did not conform with our predictions based on a traditional <i>MaSp</i> expression model. In general, changes to the silk’s alanine and proline compositions influenced the alignment of the proteins within the silk’s amorphous region, which influenced silk extensibility and toughness. Variations in structural alignment in the crystalline and non-crystalline regions influenced ultimate strength independent of genetic expression. Our study provides the deepest insights thus far into the mechanisms of how MA silk properties vary from gene expression to nanostructure formations to fiber mechanics. Such knowledge is imperative for promoting the production of synthetic silk fibers.</p></div

Flow diagram of the methods implemented to examine the consequences of protein deprivation on MA silk gene expression, protein nanostructures, and mechanical properties for five species of spiders.

<p>Flow diagram of the methods implemented to examine the consequences of protein deprivation on MA silk gene expression, protein nanostructures, and mechanical properties for five species of spiders.</p

SAXS derived intensity <i>vs</i> waveband parameter (<i>q</i>) plots for the MA silks each of the 5 species’ MA silk.

<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p

Comparisons of the expressions of the MaSp1 genes previously isolated from the <i>Argiope trifasciata</i> (MaSp1a) and <i>Latrodectus hesperus</i> (MaSp1b), and the MaSp2 genes from <i>Argiope trifasciata</i> (MaSp2a) and <i>Latrodectus hesperus</i> (MaSp2b), across treatments for each of the five spiders.

<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p

WAXS derived intensity <i>vs</i> 2<i>θ</i> plots for MA silks of each species.

<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p

WAXS images derived for MA silks of each species of spider.

<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p

Summary of the consequences of protein deprivation on silk properties for the five species examined.

<p>Summary of the consequences of protein deprivation on silk properties for the five species examined.</p