Ionic Transport Through Single Solid‐State Nanopores Controlled with Thermally Nanoactuated Macromolecular Gates

Poly(N-isopropylacrylamide) (PNIPAAM) exhibits a lower critical solubility temperature (LCST) of 32°C. Using thin films of this compound as a model system, the potential of ‘smart polymers’ as biofouling-release agents was examined. PNIPAAM-coated glass slides were incubated in artificial sea water containing the marine bacterium Halomonas marina or in natural bay water at a temperature above the LCST. Upon rinsing of the biofouled samples with artificial sea water below the LCST, the dissolution of the coating released over 90% of the attached fouling material, a significant increase over the release obtained for glass controls. These experiments demonstrate the potential of PNIPAAM and similar polymers as possible fouling-release agents, and suggest that tethered PNIPAAM (or similar polymers) may be useful as regenerable fouling-release surfaces.

Thermodynamic properties of polyolefin solutions at high temperature: 2. Lower critical solubility temperatures for polybutene-1, polypentene-1 and poly(4-methylpentene-1) in hydrocarbon solvents and determination of the polymer-solvent interaction parameter for PB1 and one ethylene-propylene copolymer

Polyelectrolyte complex (PEC) micelles are formed by mixing a block copolymer composed of a neutral block and a charged block, with an oppositely charged polymer. The micelles formed have a PEC core, capable of encapsulating charged molecules like nucleic acids or proteins, while the neutral block(s) forms the corona that offers protection that can prevent cargo from being degraded under physiological conditions. This work explores using a thermosensitive polymer, poly(N-isopropyl acrylamide) (pNIPAM), as the primary corona-forming block and how that can be leveraged in the context of drug delivery. pNIPAM has a lower critical solubility temperature (LCST), above which a hydrophilic to hydrophobic transition occurs. We are characterizing micelles formed using a diblock copolymer of pNIPAM-b-poly(acrylic acid) with (1) poly(lysine) and (2) poly(ethylene glycol)-b-poly(lysine) using dynamic light scattering, small angle X-ray scattering, absorbance and fluorescence spectroscopy, and transmission electron microscopy. Our results indicate that mixing pNIPAM-b-poly(acrylic acid) and poly(lysine) creates worm-like micelles, while mixing the same diblock with poly(ethylene glycol)-b-poly(lysine) forms spherical micelles. At temperatures above 35 °C, the transition temperature of pNIPAM-b-poly(acrylic acid), the worm-like micelles lose their structure, while the spherical micelles retain their structure, but both aggregate into larger assemblies. Lastly, we evaluate the ability of these micelles to encapsulate and release model charged therapeutics, using a cationic monoion, methylene blue and a cationic polyion, polylysine conjugated rhodamine. We find that methylene blue is not encapsulated by the micelle, and instead exhibits counterion-like behaviour upon polyelectrolyte complex formation. Conversely, fluorescence measurements of rhodamine-labelled polylysine show fluorescence quenching indicating that the polyion is encapsulated. By mixing quenched and unlabelled micelles, we show that both systems are immune to molecular exchange with their environment and instead the cargo remains trapped in the quenched micellar cores. Measurement of the micelle fluorescence above the LCST, decreases indicating no substantial release for either system. However, the increase in micelle quenching above the LCST and its persistence after cooling may offer an additional protective environment for cargo that can be triggered by temperature.

In this paper, the positive effect of a gold layer on cell viability is demonstrated by examining the results given by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfop henyl)-2H-tetrazolium (MTS) assay and two-color cell fluorescence viability (TCCV) assay. These cytotoxicity tests were performed with human cervical adenocarcinoma cells (HeLa cell line) and transformed African green monkey kidney fibroblast cells (Cos-7 cell line). To fabricate the nanostructures as drug vehicles, first, poly(l,l-lactide-co-ethylene glycol) (PLLA-PEG) and poly(N-isopropylacrylamide-co-D,D-lactide) (PNIPAAm-PDLA) were synthesized, and then two kinds of thermosensitive nanospheres comprising "shell-in-shell" structures without a gold layer (PLLA-PEG@PNIPAAm-PDLA) and with a gold layer (Au@PLLA-PEG@PNIPAAm-PDLA) were constructed by a modified double-emulsion method (MDEM). Both of them displayed a unique thermosensitive character exhibiting the lower critical solubility temperature (LCST) at 36.7 degrees C which was confirmed by UV-vis spectroscopy and differential scanning calorimetry (DSC). The release profiles of entrapped bovine serum albumin (BSA) were monitored at 22 and 37 degrees C, respectively, to reveal the thermal dependence on the release rate. In cell viability tests, both PLLA-PEG@PNIPAAm-PDLA and Au@PLLA-PEG@PNIPAAm-PDLA showed excellent cell viability, and furthermore, Au@PLLA-PEG@PNIPAAm-PDLA, particularly at high doses, exhibited more enhanced cell viability than PLLA-PEG@PNIPAAm-PDLA. This effect is mainly attributed to the gold layer which binds the protein molecules first and consequently facilitates transmembrane uptake of essential nutrients in the cell media, resulting in favorable cell proliferation.

Novel amphiphilic conetworks (APCN) consisting of thermoresponsive poly(N-isoproplyacrylamide) (PNiPAAm) cross-linked by hydrophobic methacrylate-telechelic polyisobutylene (MA-PIB-MA) were successfully synthesized in a broad composition range. The resulting PNiPAAm-l-PIB conetworks (“l” stands for “linked by”) were obtained by radical copolymerization of NiPAAm with MA-PIB-MA in tetrahydrofuran, a cosolvent for all the components. Low amounts of extractables substantiated efficient network formation. The composition dependent two glass transition temperatures (Tg) by DSC analysis indicate microphase separation of the cross-linked components without mixed phases. It was found that the PNiPAAm-l-PIB conetworks are uniformly swellable in both water and n-hexane; i.e., these new materials behave either as hydrogels or as hydrophobic gels in aqueous or nonpolar media, respectively. The uniform swelling in both polar and nonpolar solutes indicates cocontinuous (bicontinuous) phase morphology. The equilibrium swelling degrees (R) depend on composition, that is, the higher the PIB content, the lower the R in water and the higher in n-hexane. The PNiPAAm phase keeps its thermoresponsive behavior in the conetworks as shown by significant decrease of the swelling degree in water between 20 and 35 °C. The lower critical solubility temperature (LCST) values determined by DSC are found to decrease from 34.1 °C (for the pure PNiPAAm homopolymer) to the range of 25–28 °C in the conetworks, and the extent of the LCST decrease is proportional with the PIB content. Deswelling-swelling, i.e., heating–cooling, cycle indicates insignificant hysteresis in these new thermoresponsive materials. This indicates that PNiPAAm-l-PIB conetworks with predetermined and thermoresponsive swelling behavior can be designed and utilized in several advanced applications on the basis of results obtained in the course of this study.

Formation of helices with controllable chirality in gel-fiber composites

In recent years, polymers with stimuli-responsive properties have been increasingly reported on due to their diverse applications. However, most of the studies have only focused on the performance of polymers under specific scenarios. The laws of changes in the properties in response to various external stimuli have been less systematically and quantitatively studied. In this paper, we prepared an amphiphilic polymer (PadaMX and PAdaM3QA−X) with temperature-, pH-, ion-, and β-cyclodextrin (β-CD)-responsive properties. According to the cloud point tested by the UV-Vis method, the lower critical soluble temperature (LCST) of PAdaM3QA−10% was more sensitive to a change in pH and less sensitive to a change in ions compared with PadaM3 due to quaternized side chains with a stronger intramolecular mutual repulsion. We then fabricated the coatings with responsive properties by immobilizing the adamantyl groups on β-CD-modified surfaces. The hydrophilicity of the coatings was improved after quaternization, as proven by the water contact angle (WCA) measurement. The antifouling and antibacterial performance was further evaluated via the fluorescence intensity of bovine serum albumin (BSA) adsorbed on the surfaces and the spread plate method. A 78.4% BSA desorption rate and a 96.8% sterilization rate were achieved by the PAdaM3QA−10% coating. In summary, this work prepared a multiple-stimuli-responsive amphiphilic copolymer for antifouling and antibacterial functionality via a “resistance–kill–release” mechanism.

Seventy pregnant sows and gilts in gestation crates with unbedded concrete-slat floors and partitions in common (which permitted contact by neighbors) in a closed house with air temperature 10 to 12 degrees C during cold weather were studied for 3 wk. The animals' lower critical temperature and thermoregulatory heat and feed requirements were estimated from measured variables, including ME intake, body weight and its change and body surface temperature, and other calculated values and assumptions. Estimates for a 165-kg sow or gilt in such an environment were: lower critical temperature = 15 degrees C; thermoregulatory heat requirement = 126 to 161 kcal/d per 1 C degree of coldness (higher as pregnancy progresses); and thermoregulatory feed requirement = 42 to 54 g/d per 1 C degree of coldness (assuming 3 kcal ME/g of diet). The sow's lower critical temperature was affected by state of pregnancy; in late pregnancy it was 1.6 to 2.6 C degrees lower than in early pregnancy. These estimates of the pregnant sow's thermoregulatory heat and feed requirements at effective environmental temperatures below the lower critical temperature accord well with those published before. But this estimate of the pregnant sow's lower critical temperature is approximately 5 C degrees lower than several made in laboratory settings on animals held individually, with no opportunity to huddle. The fact that every sow and gilt in this experiment could make mechanical contact with at least one neighbor at all times, and sometimes two, might account for much of the difference in lower critical temperature estimates.

Dynamic light scattering, or DLS, is commonly used to determine the lower critical transition temperature (LCST) of a temperature induced stimuli-responsive polymer. By applying a temperature sweep, the coacervation or agglomeration of stimuli-responsive polymers can be observed. For materials, such as Poly(N-isopropylacrylamide), or pNIPAM, which have a reverse LCST, the polymers are soluble at lower temperatures and condense or precipitate out of solution at higher temperatures. The transition temperature is the transition between this soluble and condensed state.Our lab has developed a protocol to look at changes in the LCST behavior in the presence of an applied potential. By lining the DLS cuvette with a conductive tape, we can apply the potential across the 1 cm light path. After a certain voltage threshold, changes in the observed LCST behavior is found with pNIPAM. To the best of our knowledge, this result has never been recorded. Typically, the LCST of pNIPAM is not adjustable, but using this technique, we can observe the effect with an applied potential. We share this protocol for other groups to use to investigate the effect of applied potential on the coacervation of stimuli-responsive polymers. We intend to report details of our protocol and initially observed results of the observed behavior in the presence of an applied potential. Acknowledgements: The authors would like to acknowledge the financial support from NIH (P20 GM113131), NSF (CBET 1638896), the Collaborative Research Excellence Initiative Pilot Research Program at the University of New Hampshire, and the Hamel Center of Undergraduate Research at the University of New Hampshire. The authors also would like to acknowledge the assistance of Dr. Balog’s laboratory and Dr. Halpern’s laboratory.

1. Oxygen consumption, body temperature, respiratory frequency and respiratory water loss of White Leghorn x Rhode Island hens were measured for short periods at six air temperatures between 2 and 32 degrees C. The hens were kept between tests in an open shed. The experiments were carried out over 3 years. 2. The upper critical temperature (Tcu) was estimated by the air temperature at which: 1, respiratory frequency increased above 60 respirations/min and 2, body temperature increased by 0.3 degrees C above that at the lower critical temperature. These responses to the test temperatures were examined as a function of the acclimatisation temperature (Ta) represented by the mean daily temperature during experimental periods. 3. A seasonal change in Tcu was observed, which correlated with Ta(r = 0.836). The seasonal 10 degrees C change in the Ta brought about a 3 degrees C change in Tcu, compared with an 8.5 degrees C change in the lower critical temperature. 4. Thermoneutral temperature zone decreased with increasing Ta; the two critical temperatures tended to merge at a Ta of 32 degrees C. The latter probably represents an upper limit for acclimatisation to heat.

The translocation of small molecules and polymers is an integral process for the functioning of living cells. Many of the basic physical, chemical, and biological interactions have not yet been studied because they are not directly experimentally accessible. We have shown that a combination of optical tweezers, single solid-state nanopores, and electrophysiological ionic current detection enable deeper insight into the behavior of polymers in confinement. Here we describe the experimental procedures that are necessary to manipulate single biopolymers in a single nanopore, not only by electrical fields, but also through mechanical forces using optical tweezers.

The translocation of long-chain molecules, such as DNA or peptides, through membranes is an integral process for the function of living cells. During the translocation process, a number of interactions of electrostatic or hydrophobic nature govern the translocation velocity. Most of these interactions remain largely unexplored on the single-molecule level due to a lack of suitable instrumentation. We have shown that a combination of optical tweezers, single solid-state nanopores, and electrophysiological ionic current detection can provide further insight into the behavior of polymers in confinement. Here, we describe the experimental procedures necessary for manipulation of single biopolymers in a single nanopore not only by electrical fields, but also through mechanical forces using optical tweezers.

The effects of ambient temperature on the body temperature, oxygen consumption, heart rate, breathing rate, evaporative water loss, and behavior of Heterohyrax brucei from the vicinity of Nairobi, Kenya, were studied. The mean rectal temperature of animals at rest in the absence of heat stress was 36.4° C, and telemetered abdominal temperatures of a normally active individual in an outdoor inclosure ranged from slightly below 35 to almost 37°. No periods of profound nocturnal hypothermia were observed. However, body temperature was labile and markedly affected by ambient temperatures, especially above 30°. Following exposures of 60 to 90 minutes to temperatures from 0 to 42.5°, the upper and lower limits of observed body temperatures were separated by 7 to 8°. Exposure to direct sunlight produced marked hyperthermia, increased rate and amplitude of breathing (mean resting rate, 37 per minute), sweating on the soles of the feet, and a marked decrease in tonus of skeletal muscles. The lower critical temperature was near 25°, but because of an anomalous decline in oxygen consumption at temperatures above 35°, no upper critical temperature was apparent. The standard metabolic rate was 0.52 milliliter O2 (gram hour)−1, which is about 20 per cent below the level predicted on the basis of body weight. Mean minimal total thermal conductance was 0.184 calories (gram hour ¼)−1. Above 25°, evaporative water loss increased directly with Ta. At an ambient temperature of 42.5° and a water vapor pressure of 12 millimeters Hg, the hyraxes evaporated enough water to dissipate all their metabolic heat production. About 22 per cent of the water was evaporated from the feet, which sweated profusely during heat stress. The mean minimum heart rate of 118 per minute occurred between ambient temperatures of 24 and 35°. This rate is about 52 per cent of that predicted on the basis of size. Heart rate increased at both higher and lower temperatures. Despite their labile body temperatures, low metabolic rate, and high thermal conductance rock hyraxes maintain body temperatures in the usual mammalian range with a minimum expenditure of energy. Thermoregulation is facilitated by the equable climate in which they live and by their use of patterns of behavior which contribute to control of body temperature. These include diurnality, basking, restricted periods of surface activity, gregarious fossorial habits, and huddling.

Critical composition in organized surfactant solutions

Mechanism of Sterility and Breeding Strategies for Photoperiod/Thermo-Sensitive Genic Male Sterile Rice