Activation of ice recrystallization inhibition activity of poly(vinyl alcohol) using a supramolecular trigger

Antifreeze (glyco)proteins (AF(G)Ps) have potent ice recrystallisation inhibition (IRI) activity – a desirable phenomenon in applications such as cryopreservation, frozen food and more. In Nature AF(G)P activity is regulated by protein expression levels in response to an environmental stimulus; temperature. However, this level of regulation is not possible in synthetic systems. Here, a synthetic macromolecular mimic is introduced, using supramolecular assembly to regulate activity. Catechol-terminated poly(vinyl alcohol) was synthesised by RAFT polymerization. Upon addition of Fe3+, larger supramolecular star polymers form by assembly with two or three catechols. This increase in molecular weight effectively ‘switches on’ the IRI activity and is the first example of external control over the function of AFP mimetics. This provides a simple but elegant solution to the challenge of external control of AFP-mimetic function

Synthesis of star-branched poly(vinyl alcohol) and ice recrystallization inhibition activity

Antifreeze proteins are potent inhibitors of ice crystal growth (recrystallization), which is a highly desirable property for cryopreservation and other low temperature applications. It has emerged that relatively simple polymers based on poly(vinyl alcohol) can mimic this activity, but the link between architecture and activity is not known. Here, a trifunctional xanthate was designed and synthesized to prepare star-branched poly(vinyl alcohols) by RAFT/Xanthate mediated polymerization, and their ice growth inhibition activity probed for the first time. The trifunctional agent design affords the formation of well-defined star polymers, with no evidence of star-star linking, even at high conversions, and narrow molecular weight dispersity. It is observed that three-arm stars have identical activity to two-armed (i.e. linear) equivalents, suggesting that the total hydrodynamic size of the polymer (diameter three-arm ~ two-arm) rather than total valence of the functional groups is the key descriptor of activit

Thermoresponsive, well-defined, poly(vinyl alcohol) co-polymers

Thermoresponsive polymers have attracted huge interest as adaptable biomaterials based on their reversible solubility behaviour which can be exploited for controlled drug delivery or cellular uptake. The most famous and successful of these is poly(ethylene glycol) (PEG), but the thermal transition temperatures that are practically accessible are not physiologically useful. There are some notable examples of synthetic, responsive, polymers that are highly tunable over a physiologically relevant range, but there is still a need for these to be clinically validated in terms of toxicology and immunogenity for in vivo usage, in addition to their widely used in vitro applications. Poly(vinyl alcohol), PVA, is an appealing biocompatible polymer which is already used for a huge range of biomedical applications. Here, PVA is shown to be a highly tunable, thermoresponsive polymer scaffold. RAFT/MADIX polymerization is used to obtain a library of well-defined polymers between 8 and 50 kDa. Selective alkanoylation of the obtained PVA enabled the effect of side-chains, end-groups and molecular weight on the observable transition temperatures to be studied by turbidimetry. It was found that increasingly hydrophobic side chains (acetyl, propanoyl, butanoyl), or increasing their density led to corresponding decreases in cloud point. PVA with just 10 mol% butanoylation was shown to have a thermal transition temperature close to physiological temperatures (37 °C), compared to 70 mol% for acetylation, with temperatures in between accessible by controlling both the relative degree of functionalization, or by altering the chain length. Finally, a secondary response to esterase enzymes was demonstrated as a route to ‘turn off’ the responsive behaviour on demand. This study suggests that PVA-derived polymers may be a useful platform for responsive biomaterials

Electric utility acid fuel cell stack technology advancement

The principal effort under this program was directed at the fuel cell stack technology required to accomplish the initial feasibility demonstrations of increased cell stack operating pressures and temperatures, increased cell active area, incorporation of the ribbed substrate cell configuration at the bove conditions, and the introduction of higher performance electrocatalysts. The program results were successful with the primary accomplishments being: (1) fabrication of 10 sq ft ribbed substrate, cell components including higher performing electrocatalysts; (2) assembly of a 10 sq ft, 30-cell short stack; and (3) initial test of this stack at 120 psia and 405 F. These accomplishments demonstrate the feasibility of fabricating and handling large area cells using materials and processes that are oriented to low cost manufacture. An additional accomplishment under the program was the testing of two 3.7 sq ft short stacks at 12 psia/405 F to 5400 and 4500 hours respectively. These tests demonstrate the durability of the components and the cell stack configuration to a nominal 5000 hours at the higher pressure and temperature condition planned for the next electric utility power plant

Gold nanoparticle aggregation as a probe of antifreeze (glyco) protein-inspired ice recrystallization inhibition and identification of new IRI active macromolecules

Antifreeze (glyco)proteins are found in polar fish species and act to slow the rate of growth of ice crystals; a property known as ice recrystallization inhibition. The ability to slow ice growth is of huge technological importance especially in the cryopreservation of donor cells and tissue, but native antifreeze proteins are often not suitable, nor easily available. Therefore, the search for new materials that mimic this function is important, but currently limited by the low-throughout assays associated with the antifreeze properties. Here 30 nm gold nanoparticles are demonstrated to be useful colorimetric probes for ice recrystallization inhibition, giving a visible optical response and is compatible with 96 well plates for high-throughout studies. This method is faster, requires less infrastructure, and has easier interpretation than the currently used ‘splat’ methods. Using this method, a series of serum proteins were identified to have weak, but specific ice recrystallization inhibition activity, which was removed upon denaturation. It is hoped that high-throughput tools such as this will accelerate the discovery of new antifreeze mimics

Enhancement of macromolecular ice recrystallization inhibition activity by exploiting depletion forces

Antifreeze (glyco) proteins (AF(G)Ps) are potent inhibitors of ice recrystallization and may have biotechnological applications. The most potent AF(G)Ps function at concentrations a thousand times lower than synthetic mimics such as poly(vinyl alcohol), PVA. Here, we demonstrate that PVA’s ice recrystallization activity can be rescued at concentrations where it does not normally function, by the addition of noninteracting polymeric depletants, due to PVA forming colloids in the concentrated saline environment present between ice crystals. These depletants shift the equilibrium toward ice binding and, hence, enable PVA to inhibit ice growth at lower concentrations. Using theory and experiments, we show this effect requires polymeric depletants, not small molecules, to enhance activity. These results increase our understanding of how to design new ice growth inhibitors, but also offer opportunities to enhance activity by exploiting depletion forces, without re-engineering ice-binding materials. It also shows that when screening for IRI activity that polymer contaminants in buffers may give rise to false positive results

Polyurea microcapsules from isocyanatoethyl methacrylate copolymers

The synthesis of two types of isocyanate side chain containing copolymers, poly(methyl methacrylate-co-isocyanatoethyl methacrylate) (P(MMA-co-IEM)) and poly(benzyl methacrylate-co-isocyanatoethyl methacrylate) (P(BnMA-co-IEM)), which were synthesized by Cu(0)-mediated radical polymerization, is reported. Polymerization proceeded to high conversion giving polymers of relatively narrow molar mass distributions. The incorporation of the bulky aromatic groups in the latter copolymer rendered it sufficiently stable toward hydrolysis and enabled the isolation of the product and its characterization by 1 H and 13C NMR, and FTIR spectroscopy and SEC. Both P(MMA-co-IEM) and P(BnMA-co-IEM) were functionalized with dibutylamine, octylamine, and (R)-(1)-a-methylbenzyl-amine, which further proved the successful incorporation of the isocyanate groups. Furthermore, P(BnMA-co-IEM) was used for the fabrication of liquid core microcapsules via oil-in-water interfacial polymerization with diethylenetriamine as crosslinker. The particles obtained were in the size range of 10–90 mm in diameter independent of the composition of copolyme

Circulating markers of arterial thrombosis and late-stage age-related macular degeneration: a case-control study.

PURPOSE: The aim of this study was to examine the relation of late-stage age-related macular degeneration (AMD) with markers of systemic atherothrombosis. METHODS: A hospital-based case-control study of AMD was undertaken in London, UK. Cases of AMD (n=81) and controls (n=77) were group matched for age and sex. Standard protocols were used for colour fundus photography and to classify AMD; physical examination included height, weight, history of or treatment for vascular-related diseases and smoking status. Blood samples were taken for measurement of fibrinogen, factor VIIc (FVIIc), factor VIIIc, prothrombin fragment F1.2 (F1.2), tissue plasminogen activator, and von Willebrand factor. Odds ratios from logistic regression analyses of each atherothrombotic marker with AMD were adjusted for age, sex, and established cardiovascular disease risk factors, including smoking, blood pressure, body mass index, and total cholesterol. RESULTS: After adjustment FVIIc and possibly F1.2 were inversely associated with the risk of AMD; per 1 standard deviation increase in these markers the odds ratio were, respectively, 0.62 (95% confidence interval 0.40, 0.95) and 0.71 (0.46, 1.09). None of the other atherothrombotic risk factors appeared to be related to AMD status. There was weak evidence that aspirin is associated with a lower risk of AMD. CONCLUSIONS: This study does not provide strong evidence of associations between AMD and systematic markers of arterial thrombosis, but the potential effects of FVIIc, and F1.2 are worthy of further investigation

Bayes linear kinematics in the analysis of failure rates and failure time distributions

Collections of related Poisson or binomial counts arise, for example, from a number of different failures in similar machines or neighbouring time periods. A conventional Bayesian analysis requires a rather indirect prior specification and intensive numerical methods for posterior evaluations. An alternative approach using Bayes linear kinematics in which simple conjugate specifications for individual counts are linked through a Bayes linear belief structure is presented. Intensive numerical methods are not required. The use of transformations of the binomial and Poisson parameters is proposed. The approach is illustrated in two examples, one involving a Poisson count of failures, the other involving a binomial count in an analysis of failure times