Rational, yet simple, design and synthesis of an antifreeze-protein inspired polymer for cellular cryopreservation

Antifreeze (glyco) proteins AF(G)Ps are potent ice recrystallization inhibitors, which is a desirable property to enhance cryopreservation of donor tissue/cells. Here we present the rational synthesis of a new, biomimetic, ice-recrystallization inhibiting polymer derived from a cheap commodity polymer, based on an ampholyte structure. The polymer is used to enhance the cryopreservation of red blood cells, demonstrating a macromolecular solution to tissue storage

Equation of State of H2O Ice Using Melt-Recrystallization

The recent surge in exoplanet discoveries due to advancements in astrophysical technology and analysis has brought the reliability of early equation of state measurements into question as they are the limiting factor when modeling composition of these planets. H2O content is among the most important for the search of habitable planets as well as in understanding planetary dynamics and atmosphere formation. Over the last three decades the equation of state of H2O has been investigated with various techniques but, has suffered from anisotropic strain and poor powder statistics resulting in a large discrepancy in equation of state fits. At pressures within the interior of many planets, the hydrogen bonds in H2O gradually weaken and are replaced by ionic bonds in ice-X. By melt-recrystallization of ice via laser heating as it is compressed, we observe the transition from ice-VII to ice X at a pressure of 30.9 ± 2.9 GPa, evidenced by an abrupt 2.5-fold increase in bulk modulus, implying an increase in bond strength. This transition is preceded by a modified ice structure of tetragonal symmetry, ice-VIIt

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

The marginal shear stress of Ice Stream B, West Antarctica

To ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stress in its marginal shear zones (the "Snake" and the "Dragon"), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress meter. The observed marginal shear strain rate of 0.14 a^(-1) is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the Dragon, obtained by using a hot-water ice-coring drill. The test-specimen orientation relative to the stress axes in the tests is chosen on the basis of c-axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin. The resulting marginal shear stress is (2.2 ± 0.3) × 10^5 Pa. This implies that 63-100% of the ice stream's support against gravitational loading comes from the margins and only 37-0% from the base, so that the margins play an important role in controlling the ice-stream motion. The marginal shear-stress value is twice that given by the ice-stream model of Echelmeyer and others (1994} and the corresponding strain-rate enhancement factors differ greatly (E ≈ 1-2 vs 10-12.5). This large discrepancy could be explained by recrystallization of the ice during or shortly after coring. Estimates of the expected recrystallization time-scale bracket the ~1 h time-scale of coring and leave the likelihood of recrystallization uncertain. However, the observed two-maximum fabric type is not what is expected for annealing recrystallization from the sharp single-maximum fabric that would be expected in situ at the high shear strains involved (γ~20). Experimental data from Wilson (1982) suggest that, if the core did recrystallize, the prior fabric was a two-maximum fabric not substantially different from the observed one, which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation. These issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress

Two-step recrystallization of water in concentrated aqueous solution of poly(ethylene glycol).

Crystallization behavior of water in a concentrated aqueous solution of poly(ethylene glycol) (PEG) with a water content of 37.5 wt % was investigated by temperature variable mid-infrared (mid-IR) spectroscopy in a temperature range of 298-170 K. The mid-IR spectrum of water at 298 K showed that a large water cluster was not formed and that most of the water molecules were associated with the PEG chain. Ice formation, however, occurred as found in previous studies by differential scanning calorimetory. Ice formations were grouped into three types: crystallization at 231 K during cooling, that at 198 K during heating, and that at 210 K during heating. The latter two were just recrystallization. These ice formations were the direct transition from hydration species to ice without condensation regardless of crystallization or recrystallization. This means that the recrystallized water in the present system was not generated from low-density amorphous solid water. At a low cooling rate, nearly complete crystallization at 231 K during cooling and no recrystallization were observed. At a high cooling rate, no crystallization and two-step recrystallization at 198 and 210 K were observed. The former and latter recrystallizations were found to be generated from water associated with the PEG chains with ttg (the sequence -O-CH(2)-CH(2)-O- having a trans (t) conformation about the -C-O- bond and a gauche (g) conformation about the -C-C- bond) and random conformations, respectively. These results indicate that recrystallizable water does not have a single specific water structure

Influence of ISPs from a polar sea-ice microalga on whipped cream detected by cryo-Raman microscopy

The occurrence of recrystallization and large ice areas after storage of frozen food products makes the use of ice-structuring proteins (ISPs) in food products meaningful. Food products are frozen to extend shelf-life during long storage periods while preservation of the overall sensoric quality. Recrystallisation processes alter and, in the worst case, damage the structure of the food, resulting in an unsightly thawed e.g. cream cake or cream puff product. Freezing and freeze storage behaviour of various food products should be investigated in order to optimize the manufacturing of frozen products and to maintain the product quality with appropriate storage until the consumers usage. We present a study on the influence of ice-structuring proteins, isolated from the sea-ice microalgae Fragilariopsis cylindrus (fcISP), on frozen whipped cream. The individual phases of the frozen cream foam have been detected by cryo-Raman spectroscopy and visualized. The advantage of the unique cryo-Raman spectroscopy system available at the AWI is that the individual components can be detected not only qualitatively, but also localized in the frozen sample. We show that the fat and ice structure in frozen cream, and their temperature-induced changes, are well detectable by cryo-Raman spectroscopy. Furthermore, the effect of fcISPs on the microstructure shows an inhibition of ice recrystallization, leading to smaller grain aggregates and a finer fat distribution than without fcISPs. We therefore suggest that fcISPs are an effective mean in controlling recrystallization processes in frozen goods

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