preparation-monodomain-liquid-crystal-elastomers-liquid-crystal

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

Rice University

Access to fresh produce and other healthy foods differs between poor ethnic and wealthier non-ethnic neighborhoods. Given the need to improve access, emergency food organizations, such as food pantries, can provide assistance. Food pantry clients, many living in poor ethnic neighborhoods, are at highest risk for inadequate intake of fruits and vegetables as emergency food assistance often does not include a supply of fresh produce. This study examines the extent to which food pantry clients live within reasonable walking distance of stores carrying fresh produce, and it proposes a strategy to increase accessibility of produce to those clients.

Disparities in access to fresh produce in low-income neighborhoods in Los Angeles.

Giant splenic artery aneurysms are extremely rare entities that have important clinical implications. The size and the natural history pose unique challenges in the management of these lesions. We present one such case that was associated with a primary arteriovenous malformation in the splenic hilum. This is the third largest aneurysm reported in literature so far and the characteristic feature is that this is the first case of a hilar arteriovenous fistula complicated by formation of a giant aneurysm and another smaller aneurysm. In our opinion the hilar malformation was congenital in origin and responsible for the formation of the two aneurysms. We also present an up to date review of literature on this subject.

Giant splenic artery aneurysm associated with arteriovenous malformation.

This study compares the efficacy of 0.01% rh-PDGF-BB with standard wound care in 20 patients with diabetes mellitus with neuropathic large plantar ulcers off-loaded with modified total contact cast. The incidence, duration and rate of healing were compared. An accelerated rate of healing in rhPDGF group was observed.

Which is the better option: recombinant human PDGF-BB 0.01% gel or standard wound care, in diabetic neuropathic large plantar ulcers off-loaded by a customized contact cast?

There are conflicting reports about the effectiveness of perfluorocarbons used in the two-layer method (TLM) of pancreas preservation for human islet transplantation. The mechanism of action is unclear and the optimal role of this method uncertain. The study design was a meta-analysis of the evidence that TLM improves islet isolation outcomes. Pubmed, CENTRAL, EMBASE, Science Citation Index, and BIOSIS were searched electronically in January 2008. After selecting the relevant human trials for meta-analysis data relating to donor variables, study design, primary and secondary islet isolation outcomes were extracted. Electronic searches identified eight unique citations, describing 11 human studies that were eligible for the meta-analysis. When comparing TLM with preservation in University of Wisconsin (UW) solution, there was a statistically significant higher islet yield [WMD 711.55, 95% confidence interval (CI) 140.03-1283.07] in the TLM group. The proportion of transplantable preparations obtained was not significantly different (OR 1.30, 95% CI 0.89-1.88) between the two groups. The rate of successful islet isolations for marginal organs was higher in the TLM group (OR 6.69, 95% CI 1.80-24.87). Improved oxygenation and preservation of cellular bioengertics is thought to be the main underlying mechanism, although no single mechanism has yet been confirmed. There is currently no clear evidence that the TLM is beneficial in human islet transplantation. It may improve the preservation of marginal organs.

A meta-analysis of the impact of the two-layer method of preservation on human pancreatic islet transplantation.

The mechanism of the two-layer method (TLM) of pancreas preservation is unclear. Facilitating oxygen diffusion into preserved pancreas has been suggested, but direct measurements of tissue pO(2) have yielded conflicting results. The degree of penetration of perfluorocarbon (PFC) into the pancreas during TLM storage is unknown. Segments of porcine pancreas (7.5 cm in length) were preserved either in University of Wisconsin solution (UW) alone (n = 6) or in TLM for 24 h (n = 6). Pancreatic samples were analyzed using Varian INOVA 9.4 T MR scanner. External PFC standard was introduced for quantification. Four consecutive transverse images of 4 mm thickness were obtained using a spin-echo sequence. (19)Fluorine magnetic resonance spectroscopy ((19)F MRS) was performed with the same parameters except with more averages. MR data were confirmed by headspace chromatography. PFC standard was readily detected in (19)F MR images. There was no signal from pancreas in (19)F MR images following either UW or TLM storage. (19)F MR spectra typical of PFC were not obtained from either UW- or TLM-preserved pancreas with nonlocalized (19)F MRS. Mean concentration of PFC in TLM pancreas measured by head space chromatography was 0.011 nl/g (SD ± 0.006), not significantly different from background concentration (0.012 nl/g, SD ± 0.006) in UW pancreas (p = 0.42). There was no evidence of penetration of PFC into pancreas tissues investigated either by MR or chromatography in organs preserved at hypothermia by TLM, and mechanisms of TLM remain speculative.

Limited penetration of perfluorocarbon in porcine pancreas preserved by two-layer method with (19)fluorine magnetic resonance spectroscopy and headspace gas chromatography.

Biological tissues have the remarkable ability to remodel and repair in response to disease, injury and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials that respond to external stresses through a permanent increase in stiffness are uncommon. Here we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a mobile nematic director, which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement.

Dynamic self-stiffening in liquid crystal elastomers.

Les tissus biologiques ont la capacit&eacute; remarquable de remodeler et de r&eacute;parer en r&eacute;ponse &agrave; la maladie, les blessures et les sollicitations m&eacute;caniques. Les mati&egrave;res synth&eacute;tiques n&#39;ont pas la complexit&eacute; des tissus biologiques, et des mat&eacute;riaux synth&eacute;tiques qui r&eacute;pondent aux sollicitations ext&eacute;rieures gr&acirc;ce &agrave; une augmentation permanente de la rigidit&eacute; sont rares. Nous rapportons ici que polydomain n&eacute;matique le cristal liquide &eacute;lastom&egrave;res augmentent rigidit&eacute; jusqu&#39;&agrave; 90 % lorsqu&#39;il est soumis &agrave; une faible amplitude (5 %), compression (dynamique) r&eacute;p&eacute;titif. Raidissement de l&#39;&eacute;lastom&egrave;re est influenc&eacute;e par le contenu de cristaux liquides, la pr&eacute;sence d&#39;une phase de cristaux liquides n&eacute;matiques et l&#39;utilisation d&#39;une dynamique par opposition &agrave; une d&eacute;formation statique. Par rh&eacute;ologiques et mesures de diffraction des rayons x, des raidisseurs peuvent &ecirc;tre attribu&eacute;s &agrave; un directeur n&eacute;matique mobile, qui tourne &agrave; la suite de la compression dynamique. Renfort sous compression dynamique n&#39;a pas &eacute;t&eacute; observ&eacute;e auparavant dans les cristaux liquides &eacute;lastom&egrave;res et peut &ecirc;tre utile pour le d&eacute;veloppement de l&#39;autor&eacute;paration des mat&eacute;riaux ou pour le d&eacute;veloppement de mat&eacute;riaux biocompatibles, adaptatifs pour le remplacement des tissus.

Dynamique self-stiffening dans les cristaux liquides &eacute;lastom&egrave;res.

Tessuti biologici hanno la capacit&agrave; notevole di ritoccare e riparare in risposta alla malattia, infortunio e sollecitazioni meccaniche. Materiali sintetici mancano la complessit&agrave; dei tessuti biologici e materiali artificiali che rispondono alle sollecitazioni esterne attraverso un aumento permanente di rigidit&agrave; sono infrequenti. Qui riportiamo quello polydomain nematic liquid crystal elastomeri aumentano della rigidit&agrave; fino al 90% quando &egrave; sottoposto a una bassa ampiezza (5%), compressione ripetitiva (dinamica). Irrigidimento di elastomero &egrave; influenzata dal contenuto di cristalli liquidi, la presenza di una fase di nematic liquid crystal e l&#39;uso di una dinamica rispetto a deformazione statica. Attraverso reologiche e le misure di diffrazione a raggi x, di rinforzo possono essere attribuite a un direttore nematic mobile, che ruota in risposta a compressione dinamica. Irrigidimento sotto compressione dinamica non &egrave; stata osservata in precedenza in elastomeri di cristalli liquidi e pu&ograve; essere utile per lo sviluppo di materiali di auto-guarigione o per lo sviluppo di materiali biocompatibili, adattivi per la sostituzione di tessuto.

Dinamica self-stiffening in elastomeri di cristalli liquidi.

Monodomain liquid crystal elastomers (LCEs) are shape-responsive materials, but shape changes are typically limited to simple uniaxial extensions or contractions. Here, we demonstrate that complex surface patterns and shape changes, including patterned wrinkles, helical twisting, and reversible folding, can be achieved in LCE-polystyrene (PS) bilayers. LCE-PS bilayer shape changes are achieved in response to simple temperature changes and can be controlled through various material parameters including overall aspect ratio and LCE and polystyrene film thicknesses. Deposition of a patterned PS film on top of an LCE enables the preparation of an elastomer that reversibly twists and a folding leaf-like elastomer, which opens and closes in response to temperature changes. The phenomena are captured through finite element simulations, in quantitative agreement with experiments.

Shape-responsive liquid crystal elastomer bilayers.

We explore the phase behaviour, solution conformation, and interfacial properties of bottlebrush polymers with side-chains comprised of poly(N-isopropylacrylamide) (PNIPAAM), a thermally responsive polymer that exhibits a lower critical solution temperature (LCST) in water. PNIPAAM bottlebrush polymers with controlled side-chain length and side-chain end-group structure are prepared using a "grafting-through" technique. Due to reduced flexibility of bottlebrush polymer side-chains, side-chain end-groups have a disproportionate effect on bottlebrush polymer solubility and phase behaviour. Bottlebrush polymers with a hydrophobic end-group have poor water solubilities and depressed LCSTs, whereas bottlebrush polymers with thiol-terminated side-chains are fully water-soluble and exhibit an LCST greater than that of PNIPAAM homopolymers. The temperature-dependent solution conformation of PNIPAAM bottlebrush polymers in D2O is analyzed by small-angle neutron scattering (SANS), and data analysis using the Guinier-Porod model shows that the bottlebrush polymer radius decreases as the temperature increases towards the LCST for PNIPAAM bottlebrush polymers with relatively long 9 kg mol(-1) side-chains. Above the LCST, PNIPAAM bottlebrush polymers can form a lyotropic liquid crystal phase in water. Interfacial tension measurements show that bottlebrush polymers reduce the interfacial tension between chloroform and water to levels comparable to PNIPAAM homopolymers without the formation of microemulsions, suggesting that bottlebrush polymers are unable to stabilize highly curved interfaces. These results demonstrate that bottlebrush polymer side-chain length and flexibility impact phase behavior, solubility, and interfacial properties.

Thermoresponsive PNIPAAM bottlebrush polymers with tailored side-chain length and end-group structure.

Laparoscopic right hepatectomy has become a standard procedure for laparoscopic resection in specialized centers;1-6 however, tumor involvement of the inferior vena cava (IVC) is still considered a contraindication. Here, we describe a safe technique of totally laparoscopic extended right hepatectomy to segment 1 combined with IVC resection using an anterior approach.

Totally laparoscopic right hepatectomy combined with resection of the inferior vena cava by anterior approach.

The Pringle maneuver is widely used in liver surgery to reduce intraoperative blood loss. However, total vascular inflow occlusion is frequently associated with ischemia reperfusion injury leading to postoperative liver dysfunction and impaired recovery. We describe herein an original procedure of modified Pringle maneuver (MPM) during laparoscopic liver resection with selective clamping of hepatic arterial inflow.

Aditya Agrawal

Chemical and Biomolecular Engineering

Rice University

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

Aditya Agrawal

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Chemical and Biomolecular Engineering

Rice University

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

Chemical and Biomolecular Engineering