Mechanism of cryoprotection by extracellular polymeric solutes.

To elucidate the means by which polymer solutions protect cells from freezing injury, we cooled human monocytes to -80 degrees C or below in the presence of various polymers. Differential scanning calorimetric studies showed that those polymers which protect cells best have a limiting glass transition temperature (T'g) of approximately -20 degrees C; those with a T'g significantly higher or lower did not protect. Freeze-etch electron micrographs indicated that intracellular ice crystals had formed during this freezing procedure, but remained smaller than approximately 300 nm in the same proportion of cells as survived rapid thawing. We propose that cryoprotection of slowly frozen monocytes by polymers is a consequence of a T'g of -20 degrees C in the extracellular solution. In our hypothesis, the initial concentration and viscosity of protective polymer solutions reduce the extent and rate of cell water loss to extracellular ice and limit the injurious osmotic stress, which cells face during freezing at moderate rates to -20 degrees C. Below -20 degrees C, glass formation prevents further osmotic stress by isolating cells from extracellular ice crystals, virtually eliminating cell water loss at lower temperatures. On the other hand, the protective polymer solutions will allow some diffusion of water away from cells at temperatures above T'g. If conditions are correct, cells will concentrate the cytoplasm sufficiently during the initial cooling to T'g to avoid lethal intracellular freezing between T'g and the intracellular Tg, which has been depressed to low temperatures by that concentration. Thus, when polymers are used as cryoprotective agents, cell survival is contingent upon maintenance of osmotic stress within narrow limits.     

Cryoprotection of mammalian cells in tissue culture with polymers; possible mechanisms

Studies were undertaken to more clearly define the mechanism of cryoprotection by polymers. Significant cryoprotection of Chinese hamster cells in tissue culture was found in the presence of hydroxyethyl starch (HES), polyvinylpyrrolidone (PVP), and dextran. The addition of PVP to the medium after thawing did not increase the survival of these cells. The presence of PVP in the medium was shown to have no effect on the transport mechanism for alanine in unfrozen cells. The source of freeze-thaw injury did not appear to be due to a direct effect on this transport mechanism. Several physical parameters of polymeric solutions were monitored at subzero temperatures. The freezing point depression was found to increase dramatically at higher polymer concentrations. Tests on the NaCl concentration in the liquid fraction of partially frozen solutions showed that the increase in salt concentration with decreasing temperature was similar in the presence of 10% PVP or 2.5% DMSO, two agents which gave similar cryoprotection at these concentrations. NMR studies showed that polymers could retain water in the liquid state at temperatures as low as −35° C, and that the remaining water was highly structured. The cryoprotective properties of polymers appear to reside in their ability to alter the physical properties of solutions during the freezing process rather than in direct effects on cell membranes.     

Numerical simulation of selective freezing of target biological tissues following injection of solutions with specific thermal properties

Recently, we proposed a method for controlling the extent of freezing during cryosurgery by percutaneously injecting some solutions with particular thermal properties into the target tissues. In order to better understand the mechanism of the enhancement of freezing by these injections, a new numerical algorithm was developed to simulate the corresponding heat transfer process that is involved. The three-dimensional phase change processes in biological tissues subjected to cryoprobe freezing, with or without injection, were compared numerically. Two specific cases were investigated to illustrate the selective freezing method: the injection of solutions with high thermal conductivity; the injection of solutions with low latent heat. It was found that the localized injection of such solutions could significantly enhance the freezing effect and decrease the lowest temperature in the target tissues. The result also suggests that the injection of these solutions may be a feasible and flexible way to control the size of the ice ball and its direction of growth during cryosurgery, which will help to optimize the treatment process.     

Fabrication of highly porous scaffolds for tissue engineering based on star-shaped functional poly(ε-caprolactone)

The potential of novel functional star‐shaped poly(ε‐caprolactone)s of controlled molecular weight and low molecular weight distribution bearing acrylate end groups as material for biomedical applications was demonstrated in this study. The polymers were functionalized via Michael‐type addition of amino acid esters containing amino or thiol groups showing the potential for immobilization of biomolecules. Furthermore, scaffolds of different geometries were prepared by uniaxial freezing of polymer solutions followed by freeze drying. Different solvents and polymer concentrations were investigated, resulting in scaffolds with porosities between 76 and 96%. Mechanical properties of the scaffolds were investigated and the morphology was determined via scanning electron microscopy. Scaffolds with interconnected channels were prepared using benzene, 1,2‐dichloroethane or dioxane as solvent. The tubular longitudinal pores in honeycomb arrangement extend throughout the full extent of the scaffolds (typical pore sizes: 20–100 µm). Biotechnol. Bioeng. 2011; 108:694–703. © 2010 Wiley Periodicals, Inc.     

Electro-Optical Properties Characterization of Fish Type III Antifreeze Protein

Antifreeze proteins (AFPs) are ice-binding proteins that depress the freezing point of water in a non-colligative manner without a significant modification of the melting point. Found in the blood and tissues of some organisms (such as fish, insects, plants, and soil bacteria), AFPs play an important role in subzero temperature survival. Fish Type III AFP is present in members of the subclass Zoarcoidei. AFPIII are small 7-kDa—or 14-kDa tandem—globular proteins. In the present work, we study the behavior of several physical properties, such as the low-frequency dielectric permittivity spectrum, circular dichroism, and electrical conductivity of Fish Type III AFP solutions measured at different concentrations. The combination of the information obtained from these measurements could be explained through the formation of AFP molecular aggregates or, alternatively, by the existence of some other type of interparticle interactions. Thermal stability and electro-optical behavior, when proteins are dissolved in deuterated water, were also investigated.     

Characterization of degradable polyelectrolyte multilayers fabricated using DNA and a fluorescently-labeled poly(β-amino ester): shedding light on the role of the cationic polymer in promoting surface-mediated gene delivery

Polyelectrolyte multilayers (PEMs) fabricated from cationic polymers and DNA have been investigated broadly as materials for surface-mediated DNA delivery. One attractive aspect of this "multilayered" approach is the potential to exploit the presence of cationic polymer "layers" in these films to deliver DNA to cells more effectively. Past studies demonstrate that these films can promote transgene expression in vitro and in vivo, but significant questions remain regarding roles that the cationic polymers could play in promoting the internalization and processing of DNA. Here, we report physicochemical and in vitro cell-based characterization of DNA-containing PEMs fabricated using fluorescently end-labeled derivatives of a degradable polycation (polymer 1) used in past studies of surface-mediated transfection. This approach permitted simultaneous characterization of polymer and DNA in solution and in cells using fluorescence-based techniques, and provided information about the locations and behaviors of polymer 1 that could not be obtained using other methods. LSCM and flow cytometry experiments revealed that polymer 1 and DNA released from film-coated objects were both internalized extensively by cells and that they were colocalized to a significant extent inside cells (e.g., ~58% of DNA was colocalized with polymer). Fluorescence anisotropy measurements of solutions containing partially eroded films were also consistent with the presence of aggregates of polymer 1 and DNA in solution (e.g., after release from surfaces, but prior to internalization by cells). Our results support the view that polymer 1, which is incorporated into these materials as "layers" rather than as part of optimized, preformed "polyplexes", can act to promote or enhance surface-mediated DNA delivery. More broadly, our results suggest opportunities to improve the delivery properties of DNA-containing PEMs by incorporation of additional "layers" of other conventional cationic polymers designed to address specific intracellular barriers to transfection, such as endosomal escape, more effectively.     

High pressure freezing of intact plant tissues. Evaluation and characterization of novel features of the endoplasmic reticulum and associated membrane systems

We have used plant root tips frozen under high pressure in conjunction with freeze-fracture electron microscopy a) to evaluate the quality of freezing of unfixed, non-cryoprotected tissues obtainable with this method, b) to examine the structure of cells frozen under high pressure, c) to evaluate the usefulness of high pressure freezing to preserve transient membrane events, and d) to look for artifacts caused by the high pressure. A single artifact of high pressure, possibly related to the collapse of air spaces during pressurization before freezing, manifested itself as long tears or folds in the plasma membrane. Excellent freezing, as evidenced by the smooth, turgid appearance of all membrane systems and the lack of aggregated cytosolic materials was observed in 10 to 20% of samples. In the best preserved specimens freezing was uniform throughout the sample volume and all organelles were readily identified. In the remaining ones, a gradient of ice crystal sizes was seen; cells within 50 to 100 microns of the surface being better preserved than those in the interior. Cortical microtubules appeared well preserved as were close associations of endoplasmic reticulum (ER) with nuclear, Golgi and plasma membranes. Junctions between the ER and nuclear membrane were constricted and much thinner (30 nm in diameter) than in chemically-fixed, thin-sectioned tissue, and although no continuities between the ER and Golgi membranes were observed, many Golgi stacks had an adjacent ER cisterna either at the cis or trans face. Both Golgi and ER cisternae exhibited distinct, round dilations indicative of vesicle blebbing or vesicle fusion events. Characteristic disc- and horseshoe-shaped infoldings of the plasma membrane corresponding to fused secretory vesicle and/or membrane recycling structures were also prominent in many cells. Short extensions of the cortical ER cisternae were regularly observed appressed against these plasma membrane infoldings suggesting a functional role for the ER in vesicle-mediated secretion and/or membrane recycling. Many lipid bodies were intimately associated with the ER, some with their surface monolayer fused with the cytoplasmic leaflet of the ER membrane. Our findings demonstrate that high pressure freezing can provide excellent morphological preservation of intact tissues and can preserve fast, transient membrane events such as those associated with vesicle fusion and vesicle blebbing. We conclude that this is the best available method for freezing relatively large (up to 0.6 mm thick) tissue samples for study by electron microscopy.     

Synthesis of beta-cyclodextrin and starch based polymers for sorption of azo dyes from aqueous solutions

Three beta-cyclodextrin (polymers 1-3) and a starch-based (polymer 4) polymers were synthesized using hexamethylene diisocyanate (HMDI) as a cross-linking agent in dry dimethylformamide and used as a sorbent for the removal of some selected azo dyes from aqueous solutions. The cross-linked polymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analysis. Results of sorption showed that cyclodextrin and starch based polymers can be effectively used as a sorbent for the removal of anionic azo dyes. The Influence of the amide groups and the chemical structure of azo dyes are also studied. Results of sorption experiments showed that these adsorbent exhibited high sorption capacities toward Direct Violent 51 (80% for polymer 1, 69% for polymer 2, 70% for polymer 3 and 78% for polymer 4). The sorption capacity of dyes on the polymers was dependent on the presence of sulfonate groups of the anionic dyes. In order to explain the results an adsorption mechanism mainly physical adsorption and interactions such as hydrogen bonding, ion-exchange due to the nature of the polymer network and the formation of an inclusion complex due to the beta-CD molecules through host-guest interaction is proposed.     

Novel polymer substrates for SFM investigations of living cells, biological membranes, and proteins.

Extended studies were performed to prepare substrates for scanning force microscopy of biological samples with a surface roughness below 1 nm rms over an area of 500 x 500 nm2. The substrate smoothness and the lack of tip obscuring material are indispensable in order to visualize detailed structures of membrane surfaces, particularly when scanning the lamellipodia of mechanically sensitive goldfish glial cells where peripheral lamellipodia are only 20-30 nm in thickness. Appropriate substrates are poly(vinyl phenyl ketone) or furan polymers with corrugations of 0.3 and 0.15 nm rms, respectively, to which the growth-promoting protein laminin adsorbs directly with an acceptably increased roughness. Cells show normal growth behavior on these substrates and stick to the substrates in a stable fashion during several scans. Thus details of the membrane's surface may be resolved and are not obscured by the substrate texture. The uncoated furan polymer substrates are suitable for immobilization of membrane preparations such as purified membrane fragments containing bacteriorhodopsin or Na, K-ATPase and protein preparations such as antibodies.     

Cryopreservation of cartilage cell and tissue for biobanking

Preservation of cell and tissue samples from endangered species is a part of biodiversity conservation strategy. Therefore, setting up proper cell and tissue cryopreservation methods is very important as these tissue samples and cells could be used to reintroduce the lost genes into the breeding pool by nuclear transfer. In this study, we investigated the effect of vitrification and slow freezing on cartilage cell and tissue viability for biobanking. Firstly, primary adult cartilage cells (ACCs) and fetal cartilage cells (FCC) were cryopreserved by vitrification and slow freezing. Cells were vitrified after a two-step equilibration in a solution composed of ethylene glycol (EG), Ficoll and sucrose. For slow freezing three different cooling rates (0.5, 1 and 2 °C/min) were tested in straws. Secondly, the tissues taken from articular cartilage were cryopreserved by vitrification and slow freezing (1 °C/min). The results revealed no significant difference between the viability ratios, proliferative activity and GAG synthesis of cartilage cells which were cryopreserved by using vitrification or slow freezing methods. Despite the significant decrease in the viability ratio of freeze–thawed cartilage tissues, cryopreservation did not prevent the establishment of primary cell cultures from cartilage tissues. The results revealed that the vitrification method could be recommended to cryopreserve cartilage tissue and cells from bovine to be used as alternative cell donor sources in nuclear transfer studies for biobanking as a part of biodiversity conservation strategy. Moreover, cartilage cell suspensions were successfully cryopreserved in straws by using a controlled-rate freezing machine in the present study.     

Preparation of solid dispersions of nonsteroidal anti-inflammatory drugs with acrylic polymers and studies on mechanisms of drug-polymer interactions

This work studied the mechanisms of interaction between Eudragit RS100 (RS) and RL100 (RL) polymers with 3 nonsteroidal anti-inflammatory drugs: diflunisal (DIF), flurbiprofen (FLU), and piroxicam (PIR). Solid dispersions of polymers and drugs at different weight ratios were prepared by coevaporation of their ethanol solutions. The resulting coevaporates were characterized in the solid state (Fourier-transformed infrared spectroscopy (FT-IR) IR, differential scanning calorimetry, powder-x-ray diffractometry) as well as by studying the in vitro drug release in a gastroenteric environment. Absorption tests from drug solutions to the solid polymers were also performed to better explain the mechanism of interactions between them. The preparative conditions did not induce changes in the crystalline state of the drugs (amorphization or polymorphic change). Drugs strongly interacted with the ammonium groups present in polymers, giving an electrostatic interaction that reinforced the mere physical dispersion of drug molecules within polymer networks. Such interactions are related to the chemical structure of the drugs and to their dissociated or undissociated state. The dispersion of drugs in the polymer matrices strongly influenced their dissolution rate, which appeared slower and more gradual than those of the pure drugs, when polymer ratios were increased. RL coevaporates usually displayed higher dissolution rates. The kinetic evaluation of the dissolution profile, however, suggested that both the drug solubility in the external medium and its diffusion capacity within the polymer network are involved. In the sorption experiments, RL showed a greater adsorptive capacity than RS, in relation to the greater number of quaternary ammonium functions, which behave as activity sites for the electrostatic interactions. In the presence of Tris-HCl buffer (pH 7.4), drug adsorption was reduced, as a consequence of the competition of the chloride ions with drug anions for the polymer binding sites. In general, DIF and FLU displayed a similar interaction with RS and RL active sites; PIR's was different. The different molecular structures of these agents can justify such findings. The presence of a carboxyl group (instead of another dissociable acidic moiety, like the hydroxy-enolic one in the PIR molecule) could help explain the strong interaction with RS and RL polymers' quaternary ammonium centers. Preliminary studies like ours are important in helping develop better forecasting and increasing the understanding of the incorporation/release behavior of drugs from particulate delivery systems that can be made from these polymers.     

Structural analysis of telechelic polymer solution using dissipative particle dynamics simulations

A telechelic polymer is an amphiphilic polymer that can form micellar structures when dissolved in water. A telechelic polymer solution shows viscoelastic behaviour owing to the formation of characteristic networks, i.e. loops, bridges and dangling chains. For industrial purposes, telechelic polymers have many applications as thickening agents, such as in paints and cosmetics. Thus, it is desirable to predict and control the rheological properties of telechelic polymers. However, detailed studies at the molecular level have not yet been performed. In this study, I use the dissipative particle dynamics (DPD) method to investigate the relationship between the characteristic structural properties and the molecular structure in telechelic polymer solutions. I show that the morphology of telechelic polymer solutions depends on the concentration and chain length, the distribution of the end-to-end distance, the mean square end-to-end distance, the mean square radius of gyration and the time-averaged mean square displacement. Although an effect of entanglement is important for properties of polymer melts, the polymer chain composed of DPD particles cannot reproduce it. Therefore, I compare telechelic polymer solutions with and without the segmental repulsive potential (SRP), which can simulate the effect of entanglement in DPD simulations. The results indicate that it is necessary to include the SRP in DPD simulations to correctly analyse the behaviour of telechelic polymer solutions.     

Preservation of immunoreactivity and fine structure of adult C. elegans tissues using high-pressure freezing.

The location of a protein labeled by immunogold techniques can be resolved under an electron beam to within nanometers of its epitope, a resolution that makes immunoelectron microscopy a valuable tool for studies of cell biology. However, tissues in the nematode Caenorhabditis elegans are difficult to preserve for immunoelectron microscopic studies. The animal's cuticle slows the diffusion of solutions into the animal and thus makes it difficult to preserve both immunoreactivity and cell morphology. Here we describe a protocol that circumvents these problems. Specifically, we instantly immobilized tissue in vitreous ice by freezing living adult animals under high pressure. Frozen specimens were then chemically fixed, dehydrated, and embedded at low temperatures. As a result, chemical diffusion across the cuticle could occur over an extended period without morphological deterioration. We show that this method is capable of preserving both cell morphology, including fine structures, and immunoreactivity. Therefore, it provides a means to characterize the localization of endogenous proteins and exogenous proteins, such as the green fluorescent protein (GFP), with respect to subcellular compartments in C. elegans tissues by using postembedding immunogold labeling.     

Osmotic properties of poly(ethylene glycols): quantitative features of brush and bulk scaling laws

From glycosylated cell surfaces to sterically stabilized liposomes, polymers attached to membranes attract biological and therapeutic interest. Can the scaling laws of polymer "brushes" describe the physical properties of these coats? We delineate conditions where the Alexander-de Gennes theory of polymer brushes successfully fits the intermembrane distance versus applied osmotic stress data of Kenworthy et al. for poly(ethylene glycol)-grafted multilamellar liposomes. We establish that the polymer density and size in the brush must be high enough that, in a bulk solution of equivalent monomer density, the polymer osmotic pressure is independent of polymer molecular weight (the des Cloizeaux semidilute regime of bulk polymer solutions). The condition that attached polymers behave as semidilute bulk solutions offers a rigorous criterion for brush scaling-law behavior. There is a deep connection between the behaviors of semidilute polymer solutions in bulk and polymers grafted to a surface at a density such that neighbors pack to form a uniform brush. In this regime, two-parameter unconstrained fits of the Alexander-de Gennes brush scaling laws to the Kenworthy et al. data yield effective monomer lengths of 3.3-3.6 A, which agree with structural predictions. The fitted distances between grafting sites are larger than expected from the nominal mole fraction of poly(ethylene glycol)-lipids; the chains apparently saturate the surface. Osmotic stress measurements can be used to estimate the actual densities of membrane-grafted polymers.     

Role of solvent properties of aqueous media in macromolecular crowding effects

Analysis of the macromolecular crowding effects in polymer solutions show that the excluded volume effect is not the only factor affecting the behavior of biomolecules in a crowded environment. The observed inconsistencies are commonly explained by the so-called soft interactions, such as electrostatic, hydrophobic, and van der Waals interactions, between the crowding agent and the protein, in addition to the hard nonspecific steric interactions. We suggest that the changes in the solvent properties of aqueous media induced by the crowding agents may be the root of these “soft” interactions. To check this hypothesis, the solvatochromic comparison method was used to determine the solvent dipolarity/polarizability, hydrogen-bond donor acidity, and hydrogen-bond acceptor basicity of aqueous solutions of different polymers (dextran, poly(ethylene glycol), Ficoll, Ucon, and polyvinylpyrrolidone) with the polymer concentration up to 40% typically used as crowding agents. Polymer-induced changes in these features were found to be polymer type and concentration specific, and, in case of polyethylene glycol (PEG), molecular mass specific. Similarly sized polymers PEG and Ucon producing different changes in the solvent properties of water in their solutions induced morphologically different α-synuclein aggregates. It is shown that the crowding effects of some polymers on protein refolding and stability reported in the literature can be quantitatively described in terms of the established solvent features of the media in these polymers solutions. These results indicate that the crowding agents do induce changes in solvent properties of aqueous media in crowded environment. Therefore, these changes should be taken into account for crowding effect analysis.     

Cryobanking the genetic diversity in the critically endangered Iberian lynx (Lynx pardinus) from skin biopsies. Investigating the cryopreservation and culture ability of highly valuable explants and cells

Cryobanking skin samples permit preserving a maximum of genetic representation from the population biodiversity. This is a relevant aspect for threatened species, potentially menaced by an epizooty and from which it is difficult to obtain gametes. As a first step for properly cryobanking skin samples of a given species, the optimal conditions of culture and freezing have to be studied by covering a broad range of possibilities. This paper presents, for the first time, a systematic study of such conditions for the Iberian lynx (Lynx pardinus). To that end, we have analyzed twenty different culture conditions and fifteen different freezing solutions for skin explants, as well as three freezing solutions for isolated cells derived from them. The culture conditions included both two different culture strategies and several combinations of nutritional supplements and mitotic agents. For the freezing solutions, we have considered different concentrations of the permeating cryoprotectant dimethyl sulfoxide (Me₂SO) either alone (5%, 7.5%, 10%, 12.5% and 15% v/v for explants, 10% for isolated cells) or along with the non-permeating cryoprotectant sucrose (0.1 or 0.2 M). Our results have been analyzed through several quantitative parameters and show that only thawed explants cryopreserved in Me₂SO (10%) either alone or with sucrose (0.2 M) presented similar properties to those in optimal fresh cultures. In addition, for these freezing conditions, isolated thawed cells also presented high survival rates (90%) and percentages of cellular functionality (85%). These results, focussed on the most endangered felid in the world, could be also useful for other threatened/endangered species.     

Design of mucoadhesive polymeric films based on blends of poly(acrylic acid) and (hydroxypropyl)cellulose

Mixing of aqueous solutions of poly(acrylic acid) and (hydroxypropyl)cellulose results in formation of hydrogen-bonded interpolymer complexes, which precipitate and do not allow preparation of homogeneous polymeric films by casting. In the present work the effect of pH on the complexation between poly(acrylic acid) and (hydroxypropyl)cellulose in solutions and miscibility of these polymers in solid state has been studied. The pH-induced complexation-miscibility-immiscibility transitions in the polymer mixtures have been observed. The optimal conditions for preparation of homogeneous polymeric films based on blends of these polymers have been found, and the possibility of radiation cross-linking of these materials has been demonstrated. Although the gamma-radiation treatment of solid polymeric blends was found to be inefficient, successful cross-linking was achieved by addition of N,N'-methylenebis(acrylamide). The mucoadhesive potential of both soluble and cross-linked films toward porcine buccal mucosa is evaluated. Soluble films adhered to mucosal tissues undergo dissolution within 30-110 min depending on the polymer ratio in the blend. Cross-linked films are retained on the mucosal surface for 10-40 min and then detach.     

Lateral packing of protofibrils in fibrin fibers and fibrinogen polymers

The distinctive transverse banding pattern of fibrin fibers clearly indicates ordering of molecules in the longitudinal direction. In this study we examined the fibers of fibrin clots, as well as two types of fibrinogen polymers, by thin-section electron microscopy. The fibrinogen polymers have a transverse banding pattern identical to that of fibrin fibers—clearly indicating a regular longitudinal repeat—but they are larger in diameter, and show little or no branching. We therefore expected their overall ordering to be better than that of fibrin fibers. Several different fixation protocols were used. We readily observed the typical transverse banding seen previously by negative stain and metal replication techniques. However, only very rarely was any regular lateral lattice seen in any of the samples. X-ray diffraction was used to examine unfixed specimens of the two fibrinogen polymers and, once again, although a longitudinal repeat was evident, only rarely was evidence for lateral crystallinity seen. The electron-microscope and x-ray results showed that the needles and pellet fibers of fibrinogen have essentially the same internal architecture as thick fibrin fibers, and that all three types of polymer, although clearly transversely banded, have almost no crystallinity in their lateral protofibril packing.     

Thermochemical study of amino acid imprinted polymer films

Molecularly imprinted polymers provide an alternative to traditional methods of amino acid analysis. The imprinted polymers are more robust and significantly less expensive than, for example, ELISA analysis. Amino acid imprinted nylon‐6 thin films were studied by differential scanning calorimetry and scanning electron microscopy. Endothermic peaks were observed for imprinted films at temperatures higher than that for pure nylon, indicating the formation of a more‐ordered, hydrogen bonded polymer. Removal of the amino acid from the imprinted film resulted in reversion to the peak observed for pure nylon‐6. Additives, β‐cyclodextrin and multiwalled carbon nanotubes, were added to the imprinted polymer solutions as a means to increase the porosity of the films. These studies resulted in alternative morphologies and calorimetric results that provide additional functionalities and applications for imprinted polymers. Copyright © 2015 John Wiley & Sons, Ltd.     

The surface activity of PVP and other polymers and their antihemolytic capacity

The polymeric cryoprotective agents polyvinylpyrrolidone, dextran, and hydroxyethyl starch do not penetrate the cell membrane and are not present in high osmotic concentrations. Thus, they can exert little of the "antifreeze" behavior generally attributed to glycerol or dimethyl sulfoxide, and must protect cells from freezing injury by some action external to the cell surface. Surface energy measurements of droplets of hemoglobin solution immersed in solutions of cryoprotective polymers indicate that these polymers lower the surface energy of the solution below that of the hemoglobin droplets and form a stable interface. In injured cells, these polymers will therefore hide membrane defects by forming an interface across which hemoglobin cannot easily pass. When freezing is slow, the polymers have little if any true cryoprotective effect but interfere with hemoglobin release as an assay of injury.