Recent advances in biomedical polyurethane biostability and biodegradation

This paper summarizes our recent efforts to better understand the effects of antioxidants, the effects of strain-state, mechanistic studies of soft segment cleavage by reactive oxygen radicals, and the effects of different soft segment chemistries on the biostability/biodegradation of polyether polyurethanes (PEUUs). In vivo cage implant system studies and in vitro cobalt ion/hydrogen peroxide studies have been carried out on PEUUs and the polymers have been analysed by attenuated total reflectance and Fourier transform infrared (ATR-FTIR) spectroscopy, and scanning electron microscopic (SEM) characterization of the PEUU surfaces. The natural antioxidant, vitamin E, has been shown to inhibit biodegradation and enhance biostability of PEUUs. Studies of the effect of stress state on PEUU biodegradation demonstrate that stress can inhibit biodegradation. While polyether soft segments may be cleaved by the presence of reactive oxygen radicals, the presence of oxygen has a profound effect in accelerating biodegradation. The biodegradation of polyurethanes may be inhibited by substituting different chemistries such as polydimethylsiloxanes, polycarbonates, and hydrocarbon soft segments for the polyether soft segments. To safely utilize polyurethanes in long-term biomedical devices, the biodegradation mechanisms of polyurethane elastomers must be fully understood and subsequently prevented. © 1998 SCI.     

Photo-Responsive Supramolecular Micelles for Controlled Drug Release and Improved Chemotherapy

Development of stimuli-responsive supramolecular micelles that enable high levels of well-controlled drug release in cancer cells remains a grand challenge. Here, we encapsulated the antitumor drug doxorubicin (DOX) and pro-photosensitizer 5-aminolevulinic acid (5-ALA) within adenine-functionalized supramolecular micelles (A-PPG), in order to achieve effective drug delivery combined with photo-chemotherapy. The resulting DOX/5-ALA-loaded micelles exhibited excellent light and pH-responsive behavior in aqueous solution and high drug-entrapment stability in serum-rich media. A short duration (1–2 min) of laser irradiation with visible light induced the dissociation of the DOX/5-ALA complexes within the micelles, which disrupted micellular stability and resulted in rapid, immediate release of the physically entrapped drug from the micelles. In addition, in vitro assays of cellular reactive oxygen species generation and cellular internalization confirmed the drug-loaded micelles exhibited significantly enhanced cellular uptake after visible light irradiation, and that the light-triggered disassembly of micellar structures rapidly increased the production of reactive oxygen species within the cells. Importantly, flow cytometric analysis demonstrated that laser irradiation of cancer cells incubated with DOX/5-ALA-loaded A-PPG micelles effectively induced apoptotic cell death via endocytosis. Thus, this newly developed supramolecular system may offer a potential route towards improving the efficacy of synergistic chemotherapeutic approaches for cancer.     

The study for dispatch decision of medical emergency resources with real-time spatial analysis

The Journal of Supercomputing - According to previous research, the most important factor for patient’s survival is based on the emergency treatment in the ambulance and the effective...     

Physicochemical properties,digestibility and expected glycaemic index of high amylose rice differing in length-width ratio in Sri Lanka

Gelatinization, pasting, digestibility and estimated glycaemic index of six high amylose rice varieties differing in length/width ratio were studied. Amylose content ranged narrowly (27.8–29.1%). Resistant starch content ranged from 0.44% to 1.4%. In contrast to gelatinisation enthalpy, gelatinisation temperature (GT) ranged narrowly (76.7–77.4 °C). For all rice varieties, melting temperature of amylose-lipid complex I and II was around 99 °C and 110 °C, respectively. The enthalpy of amylose-lipid complex I and II ranged between 0.18–0.87 and 0.23–0.55, respectively. Expected in vitro glycaemic index (GI) of all tested varieties was similar (88.2–92.4). The results showed that the size of the rice grain (length/width) and resistant starch content had no apparent impact on the GI of high amylose rice. The dominant factors determining the digestibility and glycaemic response of the tested high amylose rice varieties seemed to be amylose content and the GT. Besides the pasting temperature, other pasting properties varied significantly but were not correlated to starch digestibility and estimated GI among the six rice varieties. Thus, RVA pasting properties, except for pasting temperature, may not be good predictors for the GI of these high amylose rice.     

Integrating after CEN Excision (ICE) Plasmids: Combining the ease of yeast recombination cloning with the stability of genomic integration

Yeast recombination cloning is a straightforward and powerful method for recombining a plasmid backbone with a specific DNA fragment. However, the utility of yeast recombination cloning is limited by the requirement for the backbone to contain an CEN/ARS element, which allows for the recombined plasmids to propagate. Although yeast CEN/ARS plasmids are often suitable for further studies, we demonstrate here that they can vary considerably in copy number from cell to cell and from colony to colony. Variation in plasmid copy number can pose an unacceptable and often unacknowledged source of phenotypic variation. If expression levels are critical to experimentation, then constructs generated with yeast recombination cloning must be subcloned into integrating plasmids, a step that often abrogates the utility of recombination cloning. Accordingly, we have designed a vector that can be used for yeast recombination cloning but can be converted into the integrating version of the resulting vector without an additional subcloning. We call these “ICE” vectors, for “Integrating after CEN Excision.” The ICE series was created by introducing a “rare-cutter” NotI-flanked CEN/ARS element into the multiple cloning sites of the pRS series yeast integration plasmids. Upon recovery from yeast, the CEN/ARS is excised by NotI digest and subsequently religated without need for purification or transfer to new conditions. Excision by this approach takes ~3 hr, allowing this refinement in the same time frame as standard recombination cloning.     

Hibiscus sabdariffa L. extracts reduce serum uric acid levels in oxonate-induced rats

Elevated serum levels of uric acid are associated with an increased risk for hyperuricemia, gout, hypertension, cardiovascular disease, and renal failure. Recent attention has focused on the bioactive properties of edible plants in preventing disease. Hibiscus sabdariffa L., a local soft drink material and medicinal herb in Taiwan, is used effectively in native medicines against hypertension, pyrexia, and liver disorders. We investigated the effects of the Hibiscus sabdariffa extract (HSE) on oxonic acid (OA)-induced hyperuricemia in rats. The HSE affected serum uric acid levels and urate enzymes such as uricase and xanthine oxidase (XO). We treated rats intraperitoneally with normal saline and oxonate solution for 1 week and with or without feeding allopurinol (an XO inhibitor) or HSE (1%, 2%, and 5%) for 5 weeks. We observed that treatment with HSE inhibited OA-induced hyperuricemia, with a greater uric acid lowering effect than allopurinol treatment. Our results showed that HSE effectively inhibited OA-induced hyperuricemia by decreasing uric acid and increasing uricase activity, but not by affecting XO activity.     

Developing a novel tri-switch tactile probing structure and its measurement characteristics on micro-CMM

This paper describes a novel tri-switch tactile structure assembling process and its measurement characteristics on micro-CMM. After assembling micro-ruby ball-ended stylus tips on micro-EDM, the spherical stylus was glued onto the CMM’s probing head manually. A novel tri-switch contacting structure was proposed to trigger the electro signal while the stylus tip makes contact with a micro-object. The experimental results show that the uncertainty could be as small as 0.08 μm at same the point detected repeatedly in the vertical direction. The depth of micro-hole and the profile of spherical lens are also selectable by use of this tri-switch tactile structure. This novel low-cost tri-switch triggering system may have promising future use on micro-CMM probing heads to measure micro-products’ geometric profiles.     

Structure and photovoltaic properties of ZnO nanowire for dye-sensitized solar cells

Aligned ZnO nanowires with different lengths (1 to approximately 4 μm) have been deposited on indium titanium oxide-coated glass substrates by using the solution phase deposition method for application as a work electrode in dye-sensitized solar cells (DSSC). From the results, the increases in length of zinc oxide (ZnO) nanowires can increase adsorption of the N3 dye through ZnO nanowires to improve the short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc), respectively. However, the J_sc and V_oc values of DSSC with ZnO nanowires length of 4.0 μm (4.8 mA/cm² and 0.58 V) are smaller than those of DSSC with ZnO nanowires length of 3.0 μm (5.6 mA/cm² and 0.62 V). It could be due to the increased length of ZnO nanowires also resulted in a decrease in the transmittance of ZnO nanowires thus reducing the incident light intensity on the N3 dye. Optimum power conversion efficiency (η) of 1.49% was obtained in a DSSC with the ZnO nanowires length of 3 μm.