Temperature-sensitive Surface Research Articles

High-temperature characterization of interdigitated transducers on gallium arsenide and surface acoustic wave analysis via interdigitated transducer modeling

Interdigitated transducer devices may provide an advantageous platform to study stress-enhanced interfacial phenomena at elevated temperatures, and an appropriate device design requires a thorough understanding of temperature-dependent material properties. In this study, the scattering parameter response for a surface acoustic wave resonator is simulated using a frequency-domain finite element method from 20 to 177 °C. Experimental device measurements are taken for the interdigitated transducer device fabricated on semi-insulating GaAs 100 oriented in the 110 direction, and the results are in good agreement with the simulation. Surface acoustic wave analysis provides the magnitude of bulk stress values and surface displacement over the experimental temperature range produced by a standing surface acoustic wave. The computational analysis combined with experimental verification suggests that such devices, when optimized for the maximum magnitude, can produce strain levels that could influence chemical potential associated with crystalline growth, atomic diffusion, and catalytic reactions. The modeling results demonstrate an interdigitated transducer's potential as an experimental platform to study the impact of strain on temperature-sensitive surface and bulk phenomena in piezoelectric materials.

Spectroscopic Characterization of an Atmospheric Pressure Plasma Jet Used for Cold Plasma Spraying

Cold plasma spray, a powder deposition method by means of an atmospheric pressure plasma jet is a promising coating technology for use on temperature sensitive surfaces. For further improvement of this coating process, a deeper understanding of its thermokinetic properties is required. By means of optical emission spectroscopy, the plasma effluent of an atmospheric pressure nitrogen arc jet is characterized by different distances from the nozzle and different gas flow rates of 35 Lmin−1 and 45 Lmin−1. A Boltzmann plot of N2+(B-X) was used to determine rotational temperatures, which were found to be around 4000 K at the nozzle exit. Excitation temperatures, analyzed using atomic nitrogen lines, were around 6000 K for all distances. Stark broadening of the Hα-line was too weak for determination of electron density for both gas flow rates. Overall no influence on gas flow rate was found.

Preparation of poly(N-isopropylacrylamide) by interface-mediated dissociative electron transfer reversible addition–fragmentation chain transfer (IMDET-RAFT) polymerization technique

N-isopropylacrylamide was successfully polymerized on silicon disc surfaces at room temperature by interface-mediated dissociative electron transfer reversible addition–fragmentation chain transfer (IMDET-RAFT) polymerization. The IMDET-RAFT technique was used for the first time to synthesize polymer brushes with a new mechanism using inorganic sulfides without using metal at room temperature. The polymerization was well controlled and the PNIPAAm brushes were successfully grown on silicon disc surfaces. The presence of sulfur atoms at the chain end was demonstrated by XPS experiments to demonstrate the controlled nature of the polymerization. Polymer brushes synthesized by IMDET-RAFT technique have high grafting density and grafting density was found to be 0.76 chain/nm2. This study is thought to be an important alternative to the new generation controlled/living polymerization, especially for RAFT polymerization techniques used in polymer brush synthesis. PNIPAAm brushes synthesized with IMDET-RAFT technique are an important starting point for future studies in terms of the synthesis of polymer brushes with IMDET-RAFT technique using a wide range of monomers both at ambient temperature and metal free. It is believed that this technique has the potential to be used in the future, especially in the preparation of temperature sensitive surfaces, bio-application studies and many surface modifications. In this study, application of silicon disc surfaces IMDET-RAFT polymerization was used for the first time to afford preparation of well-defined poly (NIPAAm) brushes at ambient temperature.

Synthesis and functionalisation of mesoporous materials for transparent coatings and organic dye adsorption

The novel synthesis and functionalisation of mesoporous materials, which can be used to fabricate transparent hydrophobic coatings with temperature-sensitive surface properties, and also show excellent adsorption behavior to Rhodamine B dye in water.

Suitability of thermal plasmas for large-area bacteria inactivation on temperature-sensitive surfaces – first results with Geobacillus stearothermophilus spores

The application of thermal plasma for large-area bacteria inactivation on temperature-sensitive surfaces is not a common one. Nonetheless, there are thermal plasma generators which offer a high sheath homogeneity and have proven to be suitable for treatment of thermally sensitive materials in the past. To investigate the suitability of such plasmas, agar dishes plated with endospores of Geobacillus stearothermophilus have been treated with a long arc plasma generator called LARGE. The achieved results have been compared with a commercially available non-thermal plasma generator. A significant inactivation of the endospores could be observed only after 60 s of treatment with the thermal plasma source. This was not possible with the non-thermal generator. Moreover, no temperature damage or increase of the specimen could be detected. An attempt to determine the main agents responsible for the microbicidal effects have been made – the influence of plasma gas composition, discharge current and treatment time has been investigated. Significant improvements in the disinfection rates after adding small amounts of nitrogen to the plasma gas could be observed. A first discussion regarding the suitability of thermal plasmas for bacteria inactivation has been given.

Design of Bioresponsive Interfaces using Conformational Transitions of Calmodulin

Some proteins undergo major conformational changes upon ligand binding, such as calmodulin (CaM). When CaM binds trifluoperazine (TFP), there is a marked transition of CaM from an open to a collapsed conformation, as can be seen in the distance distribution function obtained by small-angle X-ray scattering (SAXS). This functionality is transferred to interfacial structures in this project. Aqueous-solid interfaces are modified by covalent binding of PEG chains to the solid phase, which are cross-linked with a CaM mutant. The main achievements of this project are the controlled build-up of such interfacial layers and the characterization of the CaM functionality in these layers. Using X-ray reflectometry, we have observed that a PEG-CaM layer is growing in thickness upon rinsing with a TFP/Ca2+ solution and decreasing in thickness upon rinsing with an EGTA solution, which binds Ca2+ from CaM. Furthermore, pressure has been applied to probe the strength of interactions between CaM and TFP in solution and in the PEG-CaM layer, which are expected to be mainly electrostatic in nature. By measuring the fluorescence resonance energy transfer (FRET), we see a pressure-induced transition of collapsed CaM-TFP to open CaM-TFP free in solution. However, this transition cannot be observed in the PEG-CaM-TFP layer suggesting a stabilization of the collapsed state. Overall, novel biochemically responsive interfacial structures are formed that can be switched reversibly under ambient conditions, in contrast to well-known pH or temperature sensitive surface modifications.

Dually functionalized dendrimers by temperature-sensitive surface modification and gold nanoparticle loading for biomedical application

Stimuli-sensitive dendrimers of a new type were developed through dual functionalization of polyamidoamine (PAMAM) dendrimers with temperature-sensitive surface modification using propoxy diethylene glycol (PDEG) and Au nanoparticle (AuNP) loading.

The Temperature-Sensitive Behaviors of SMPU/PNIPAM Semi-IPN Films

A semi-interpenetrating polymer network was fabricated from SMPU (Shape-Memory Polyureathan and PNIPAM (poly (N-isopropylacrylamide)) with the method of in-situ crosslinking polymerization. The temperature-sensitivity of the semi-IPN films was investigated and discussed. The morphology was achieved by extracting the SMPU phase. The influence of PNIPAM phase to the phase transition behavior of SMPU was studied with DSC, the results of which showing that the phase transition temperature is increased by PNIPAM. The introduction of PNIPAM also endows the semi-IPN films with a temperature-sensitive surface hydrophilicity, which was proved by water contact angle measurement at different temperatures. Finally, the water vapor permeability evaluation reveals the temperature-sensitive transportation property of the semi-IPN films, which is formed by the swelling and shrinking of PNIPAM phase according to the environmental temperature. These results shows that the semi-IPN material is a good candidate for the fabrication of intelligent breathable garments.

Cell sheet technology and its applications in corneal tissue engineering

Cell sheet technology (CST) is based on the use of poly (N-isopropylacrylamide, PNIPAAm), which can be exhibit reversible hydration and dehydration of its polymer chains in response to temperature changes across the lower critical solution temperature(LCST)of 32°C. By reducing the incubation temperature to 20°C, all cultured cells are harvested as intact sheets along with their deposited extracellular matrix (ECM) due to the conversion of the grafted PIPAAm from hydrophobic to hydrophilic, as ECM remains present on the basal surface of the cell sheets, they can maintain cell viability and function as well as directly transplanted to tissue beds or even layered to create three-dimensional (3D) tissue-like structures without any scaffolds or sutures. The temperature-sensitive surfaces' preparation approaches, density, thickness, membrane additive ingredients and so on, all affect cell adhesion and proliferation. It can maintain cell viability and improve function by accelerating cell sheet detachment through changing the membrane compositions, density as well as types of graft substrate. With CST, cultured autologous/allogeneic corneal seed cells in vitro used as transplant sources can overcome the problems of immunorejection of transplanted tissues as well as donor organ shortages. So far, the cell sheet of limbal epithelium and autologous oral mucosal epithelium obtained by the CST have been successfully used in clinical graft for ocular surface reconstruction. Finally, There is an overview of preparations of temperature-responsive surfaces, impacts of various factors that influenced cultured cells in vitro and clinical applications or clinically relevant animal experimentations of CST in corneal tissue engineering.

Use of a Temperature Sensitive Surface Gel to Reduce Fouling

Numerous surface modification strategies have been developed to improve the fouling resistance of filtration membranes. A novel approach in which a temperature sensitive polymer gel is deposited on the surface is reported. The gel switches from an expanded, lower permeability, fouling-resistant hydrophilic state to a collapsed, higher permeability, fouling-prone hydrophobic state as the temperature is increased. By alternating between these two states, it is hypothesized that fouling can be reduced while minimizing the permeability reduction due to the surface modification. The hypothesis was tested by depositing a hydroxypropyl cellulose (HPC) gel on the surface of the cellulose acetate ultrafiltration membranes (Osmonics SN32) using divinyl sulfone (DVS) as a crosslinker. Unmodified and modified membranes were used to filter yeast and the HPC suspensions. To induce the hydrophobic-hydrophilic transition, the feed was switched alternately between room temperature and 60°C solutions. The experimental results support the hypothesis. Unmodified membranes fouled severely when operated at room temperature, 60°C, or oscillating between the two temperatures. The modified membranes fouled severely at 60°C but little fouling occurred at room temperature or with temperature oscillation. The results suggest that permanent surface modification is not required to reduce the fouling rates. Transient fluctuations in the surface chemistry and the structure are equally effective. Moreover, one can achieve higher filtration rates in transient operation because pores possess a larger effective diameter/higher permeability in the collapsed state than the expanded state.

Thermosensitive surfaces fabricated by plasma polymerization of N, N-diethylacrylamide

We report on the preparation of temperature sensitive surfaces by plasma polymerization (pp) of N, N-diethylacrylamide (DEA). The chemical composition of the resulting ppDEA films was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A higher retention of monomer structure could be achieved by reducing the plasma input power. The temperature sensitivity of the ppDEA films was shown by atomic force microscopy and water contact angle measurements. Its phase transition temperature was found to lie between 38 and 41 °C.

Temperature sensitization of liposomes by use of N-isopropylacrylamide copolymers with varying transition endotherms.

Three kinds of copolymers of N-isopropylacrylamide (NIPAM) with the same conformational transition temperature and varying transition endotherms were synthesized with N-acryloylpyrrolidine (APr), N,N-dimethylacrylamide (DMAM), and N-isopropylmethacrylamide (NIPMAM) as the comonomers. Two dodecyl groups were incorporated into the termini of these copolymers as an anchor for the fixation to a liposomal membrane. Egg yolk phosphatidylcholine liposomes having these copolymers were prepared and their temperature-sensitive contents release and association properties were investigated. While these copolymer exhibited a conformational transition at ca. 40 degrees C, DeltaH for the transition increased in the order of poly(APr-co-NIPAM) < poly(DMAM-co-NIPAM) < poly(NIPMAM-co-NIPAM). The liposomes containing poly(NIPMAM-co-NIPAM) showed a drastic release enhancement of entrapped calcein above the transition temperature, whereas the liposomes with poly(DMAM-co-NIPAM) and those with poly(APr-co-NIPAM) exhibited moderate and slight enhancement of calcein release above that temperature, respectively. On the contrary, the liposomes containing poly(APr-co-NIPAM) showed significant aggregation above the transition temperature, but the aggregation was hardly observed for the liposomes having poly(NIPMAM-co-NIPAM), indicating that poly(APr-co-NIPAM) more efficiently made the liposome surface hydrophobic. Thus, we concluded that the copolymer with a large DeltaH is suitable for obtaining functional liposomes with a temperature-sensitive contents release property, whereas the copolymer with a small DeltaH is appropriate for preparing functional liposomes with a temperature-sensitive surface property.

Steady and oscillatory thermocapillary convection generated by a bubble

In this article, we study steady and oscillatory thermocapillary and natural convective flows generated by a bubble on a heated solid surface. The dynamic characteristics of the time-dependent convection are captured using a combined numerical-experimental approach. The index of refraction fringe distribution patterns constructed numerically by taking an inverse Abel transform of the computed temperature fields are compared directly to the experimental Wollaston prism (WP) interferograms for both steady-state and oscillatory convection. The agreement between numerical predictions and experimental measurements is excellent in all cases. It is shown that below the critical Marangoni number, steady-state conditions are attainable. With increasing Ma, there is a complete transition from steady state up to a final nonperiodic fluctuating flow regime through several complicated symmetric and asymmetric oscillatory states. The most prevalent oscillatory mode corresponds to a symmetric up and down fluctuation of the temperature and flow fields associated with an axially traveling wave. Careful examination of the numerical results reveals that the origin of this class of convective instability is closely related to an intricate temporal coupling between large-scale thermal structures which develop in the fluid in the form of the cold return flow and the temperature sensitive surface of the bubble. Gravity and natural convection play an important role in the formation of these thermal structures and the initiation of the oscillatory convection. Consequently, at low-g, the time evolution of the temperature and flow fields around the bubble are very different from their 1-g counterparts for all Marangoni numbers.

Temperature-Sensitive Surfaces Prepared by UV Photografting Reaction of Photosensitizer and N-Isopropylacrylamide

A thermal-sensitive surface was prepared on the surface of a silicone wafer (substrate) by an ultraviolet photografting reaction between a photosensitizer, (N,N‘-diethylamino)dithiocarbamoylpropyl(trimethoxy)silane, and N-isopropylacrylamide. Ellipsometery measurement revealed a thin grafting layer (∼44 Å) consisting of a single terminal poly(N-isopropylacrylamide) (PNIPAAm) chain on the surface of the silicone wafers. X-ray photoelectron spectroscopy confirmed that the grafting layer was composed of the PNIPAAm structure. The properties of the grafting layer can be adjusted and manipulated by varying the photopolymerization time and the concentration of the monomer. Increasing the photopolymerization time and the concentration of the monomer increases both the thickness of the grafting layer and the wettability of the surface. The characteristics of the temperature-sensitive surface were investigated by dynamic contact angle as a function of temperature. The remarkable change on advancing contact angle can be observed around 32 °C. Compared with the substrate grafted by PNIPAAm gel, the substrate with a signal-terminal PNIPAAm chain exhibited a lower transition temperature and a narrower change range of transition temperature. This can be attributed to the mobile PNIPAAm chain with a single-terminal mode, which increases the characteristics of faster response to the temperature change.

Surfaces with Reversible Hydrophilic/Hydrophobic Characteristics on Cross-linked Poly(N-isopropylacrylamide) Hydrogels

Temperature-sensitive surfaces were prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) hydrogel on the surface of silicone wafers. The silicone wafer substrates were modified by organosilane (vinyltriethoxylsilane). They were further reacted with N-isopropylacrylamide (NIPAAm), using N,N‘-methylenebisacrylamide as the cross-linking agent, to generate the cross-linked PNIPAAm layer on the surface of the substrate. The surfaces modified by the cross-linked PNIPAAm layer were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and attenuated total reflectance−Fourier transform infrared (FTIR) spectroscopy. The reversible hydrophilic/hydrophobic properties of the surface were evaluated by the dynamic contact angle. The morphology of the surface modified by a cross-linked PNIPAAm layer can be turned from “sea island” to “mountain valley” by changing the molar ratio of NIPAAm to BisAAm and by varying the polymerization time. A completely hydrophilic surface (advancing contac...

Active Diffusion of Adsorbed Mycoplasmal Virus L3 on Acholeplasma laidlawii Cell Membranes

Mycoplasmas are wall-less prokaryotes. Since tail structures of complex bacteriophages are assumed to function in the penetration of bacterial cell walls, the reported infection of mycoplasmal cells by tailed viruses is most interesting [1, 2]. One of these viruses, mycoplasmal virus L3 (MVL3), is a polyhedral particle ~60 nm in diameter; it has a short tail ~10 nm in diameter and 20 nm long and contains linear double-stranded DNA with a molecular weight of ~26 x 106 [3]. Tail fibers have been described, but their exact number and length are still unknown. Although infection with this virus is lethal for the host cell, the infectious cycle is nonlytic [3]. Studies by electron microscopy have shown several types of interaction between MVL3 and the cell membrane of the host, Acholeplasma laidlawii, during the infectious cycle [7]. (1) Adsorbed virions are found in caps or clusters on the mycoplasmal cell membrane. Such viral capping represents a temperature-sensitive surface redistribution of virus adsorbed to cell receptors. Viruses randomly adsorbed at 4 C redistribute into clusters when the temperature is raised to 37 C. (2) Progeny virions are aligned radially at the membrane with tails oriented towards the membrane. (3) Some extracellular virions are found in small vesicles, so that the particle appears to be enveloped. In addition, large vesicles that contain

Conditional surface structure mutants of Caulobacter crescentus temperature-sensitive flagella formation due to an altered flagellin monomer

Two classes of temperature-sensitive surface structure mutants of Caulobacter crescentus have been isolated. Mutants in one class were unable to form flagella at the restrictive temperature (37°C) and mutants in the second class were unable to form a stalk structure at 37°C. All of the mutants appeared normal at the permissive temperature (23°C). Analysis of the conditional flagella mutant revealed that the temperature-sensitive lesion resided in the structural flagellin monomer, since (1) extracts of mutant cells grown at the restrictive temperature contained material cross-reacting with anti-flagellin antibody although flagella were not assembled. (2) Mutant flagellin prepared from cells grown at the permissive temperature was heat-denatured to a different conformation than wild-type flagellin, as demonstrated by lateral shifts in microcomplement fixation assays. (3) Amino acid analysis showed the presence of tyrosine in the mutant flagellin, whereas none was detected in the wild-type control. (4) Chymotryptic peptide maps of mutant and wild-type flagellin showed the appearance of two new peptides in the former case. (5) A spontaneous revertant regained both motility and wild-type flagellin amino acid composition and chymotryptic peptide maps. An alteration in the primary structure of the mutant flagellin therefore results in a temperature-dependent alteration in flagellin conformation, perhaps accounting for the inability to assemble a flagellar structure at the cell surface. Comparison of immunoprecipitates of intracellular and extracellular mutant flagellin, as well as flagellin concentrations, further showed that the inability to assemble a flagellar structure interfered with the regulatory processes controlling both the amount and structural integrity of the intracellular flagellin at the restrictive temperature.

Retransformation of a thermosensitive BALB/c–3T3 transformant by murine sarcoma virus at the non-permissive temperature

CERTAIN fibroblast cell lines exhibit some of the properties of transformed cells at one temperature while retaining normal properties at a higher temperature. For example, the spontaneous transformants of BALB/C–3T3 cells isolated by W. Eckhart (unpublished results) can grow in soft agar at 32 °C (the permissive temperature) but not at 39 °C (the non-permissive temperature). They show transformed morphology at 32 °C but normal morphology at 39 °C (ref. 1). They have certain temperature-sensitive surface properties such as ability to grow in Agarose, loss of a transformation-sensitive iodinatable glycoprotein (LETS)2,3, increase in total cell proteolytic activity4 and loss of the growth promoting activity of fibroblast growth factor5. But they behave normally with respect to the regulation of intracellular events. Unlike transformed fibro-blasts, both at permissive and non-permissive temperatures, BALB/C–3T3 cells exhibit density-dependent growth inhibition5. They cease growing as a result of serum limitation and express the typical increases in protein synthesis, ribosomal RNA synthesis and DNA synthesis when growth is initiated1,6. The evidence therefore suggests that the trans-formants have lost their potential to express a transformed phenotype at the non-permissive temperature. I now show that this is not an irreversible loss by demonstrating that murine sarcoma virus (MSV) can transform the cells at the non-permissive temperature.

Low Temperature Silicon Thermometer and Bolometer

By simple diffusion and etching procedures low temperature sensitive surface layers can be prepared on otherwise insulating silicon substrates. Temperature coefficients of the resistance of these layers of the order of unity can be obtained at any temperatures below 20 K. The usefulness of this silicon device as a low temperature thermometer and bolometer is demonstrated.