Cationic polysaccharides for gene delivery

Cationic polysaccharides were synthesized by conjugation of various oligoamines including monoquaternary ammonium oligoamines and spermine to oxidized dextran by reductive amination and tested for gene transfection. Monoquaternary ammonium polycations were expected to strongly complex DNA due to increased surface cationic charge of the carrier which may result in a higher transfection yield. However, the transfection yields were much lower compared to the parent vector, dextran–spermine conjugate, which was highly effective both in vitro and in vivo. Modification of dextran–spermine conjugate with increasing amounts of the oleic acid and MPEG resulted in high gene transfection in vivo.     

Cationic liposomes-polyallylamine-plasmid nanocomplexes for gene delivery

The aim of the present study was to prepare, characterise and evaluate the transfection efficiency of ternary complexes (lipopolyplexes) composed of cationic liposome, polyallylamine (PAA), plasmid DNA (pDNA). PAA was reacted with a varying amount of a linker, 6-bromohexanoic acid (6-bromo-HA), to prepare a series of modified polymers. Lipopolyplexes consisting of cationic liposome, PAA (or modified PAA), pDNA were prepared. The nanoparticles, so formed, were characterised by their size and zeta potential and were subsequently evaluated for their cytotoxicity and transfection ability on Neuro2A cells. Mean size of prepared complexes ranged from 170 to 280 nm. All lipopolylexes showed a positive zeta potential. Highest transfection efficiency was for lipopolyplex containing PAA 15 kDa-modified polymer and liposome at C/P ratio of 0.5. High molecular weight PAA was more toxic than PAA 15 kDa for Neuro2A cells especially in higher C/P ratio. The results indicate that using the hydrophobic modified PAA in the structure of lipopolyplexes is an effective strategy for improving transfection efficiency.     

New directions in liquid crystal science

While we are all familiar with liquid crystal displays, an industry currently worth more than US dollars 60 billion yr(-1) and growing rapidly, fewer people are aware of the breadth of the subject of liquid crystals--one that represents the study of the fourth state of matter. Liquid crystals are found as essential elements in biological systems, soaps and detergents, sensor technologies and in the manipulation of electromagnetic radiation of various wavelengths. This meeting was designed to highlight both the truly multidisciplinary nature of liquid crystal science and to feature those areas away from electro-optic displays; these issues are developed and summarized in more detail.     

Lyotropic liquid crystal polymers for engineering applications

Abstract

The use of lyotropic liquid crystal polymers such as Kevlar and Twaron in high tech engineering applications has been common for many years. These materials possess excellent temperature resistance and very good mechanical properties. These two materials are polyaramids, but the newer polybenzazoles are also of a liquid crystal nature when present in appropriate solvents. Their rigid rod structures make it possible for these materials to form composite structures with isotropic polymers, where the fibre reinforcement is on a molecular level. This is a unique and very interesting possibility which has yet to be fully developed.

MST/1254     

Thermotropic liquid crystal polymers for engineering applications

Abstract

It is relatively recently that thermotropic liquid crystal polymers for load bearing applications have become commercially available. These materials possess good mechanical properties and excellent processability and are intended for use at elevated temperatures in harsh chemical environments. In this paper, the phenomenon of liquid crystallinity is described and the way in which it improves the mechanical properties and processability of polymers is explained. The synthetic strategies involved in obtaining nematic mesophases in polyesters are discussed fully, particularly those involved in the synthesis of commercially available materials. The future of these new types of engineering thermoplastic will depend on cost and on the appropriate application of the unique properties they offer.

MST/875     

Kerr modulators based on polymer-dispersed liquid crystal complexes

We have demonstrated a possibility to design light modulator based on Kerr effect using borate La₂CaB₁₀O₁₉ (LCBO) nanocrystallites incorporated into two different polymer-dispersed liquid crystal composites (PDLC). For this reason we have used different amount of the LCBO nanocrystallites to find the optimal conditions for the Kerr modulators. It was established that for the both PDLC systems the borate nanocrystals may be used for effective operation by elecrooptical susceptibilities varying the content of the nanocrystals. At the same time the frequency shift of the Kerr coefficient seems to be sensitive only for the LCBO nanocrystals content about 5% by weight. The maximal value of the Kerr coefficients were varied within the 4 × 10⁻⁹ to 6 × 10⁻¹⁰ m V^−2.     

A liquid crystal phase grating for instrumentation applications

Abstract

A liquid crystal phase grating, suitable for instrumentation applications has been developed that utilizes refractive index matching to enable it to be switched from a diffracting to a non-diffracting state by application of an electric field. The effect of the non-uniform molecular alignment during switching is considered and compared with measured data for such a device. The observed switching potentially offers a device in which the mark/space ratio may be varied with the applied electric field.     

Study of the dynamic characteristics of polymer-dispersed liquid crystal compositions: Prospects for optoelectronic applications of fullerene complexes with phthalocyanine nanocrystals

The switching and modulation characteristics of fullerene-containing polymer-dispersed liquid crystal structures involving fullerene complexes with magnesium phthalocyanine nanocrystals are studied for the first time. It is established that these systems are characterized by small switching times of the electrooptical response to pulsed drive voltage under the conditions of cw He-Ne laser irradiation. It is suggested that effective charge carrier production in the structures doped with pure phthalocyanine leads to frustration of a homogeneous orientation of the liquid crystal mesophase, which is restored upon adding C₆₀and/or C₇₀ fullerenes. A possible reorientation mechanism is considered and it is shown that fullerene-containing polymer-dispersed liquid crystal systems with distributed orientation related to the presence of fullerene complexes with magnesium phthalocyanine can be used for the effective switching of electrooptical response and have good prospects for application in the systems of optical data processing and in display technologies.     

Tunable lasing from a cholesteric liquid crystal film embedded with a liquid crystal nanopore network

Continuous tuning of lasing wavelength is achieved in cholesteric liquid crystal lasers by embedding a network of nanopores with an average size of 10 nm filled with liquid crystals inside a polymerized matrix with helical order. The device possesses both high transparency and a fast response time because the tuning is driven by local reorientation of the liquid crystal molecules in the nanopores.     

Holographically formed polymer dispersed liquid crystal films for transmission mode spectrometer applications

We show proof of concept of a transmission-mode wavelength filtering device consisting of layered holographically formed polymer dispersed liquid crystal (H-PDLC) cells. H-PDLC cells were fabricated from a thiolene based polymer composite to have transmission notches in the near-IR wavelength range. Wavelength filtering was achieved by stacking four H-PDLC cells with transmission notches spaced at 10 nm intervals. Results show a broad transmission notch spanning the spectral width of the constituent cells. With bias applied to an individual cell within the stack, the transmission notch of the cell inverts and the overall transmission envelope changes shape. Using a transmitted energy sensing device and a lineshape mapping algorithm, spectral content can be determined to a resolution of 0.1 nm for narrow banded signals. Applications for this switchable wavelength filtering device include serial detection of spectral content for telecom data signals or chemical and biological sample identification through absorption or emission spectroscopy.     

Non-display applications and the next generation of liquid crystal over silicon technology

The next generation of applications for liquid crystal (LC) over silicon technology will be non-display oriented systems such as adaptive optical interconnects, optical switches and optical image processors. These new non-display applications have a different set of material parameters, which means that existing display-based materials are not entirely optimal. This is particularly the case when the application is driven by phase modulation at high frame rates (more than 1 kHz). An example of such a non-display application is in adaptive optical interconnects. Optical data transmission between printed circuit boards is becoming more and more important as the data rate in electronic systems increases into the gigahertz region. One way of avoiding the data bottlenecks in board to board interconnects is to use optical links to transmit the data. Recent research into free-space optical links has shown that a high level of manufacturing tolerance must be used to maintain the link. However, one way of avoiding these limitations is to use a reconfigurable LC phase hologram as a beam-steering element to compensate for movement between the boards and maintain the optical data path.     

Dual drug-loaded cubic liquid crystal gels for transdermal delivery: inner structure and percutaneous mechanism evaluations

Abstract

The goal of this paper was to develop and evaluate dual component-loaded with the hydrophilic sinomenine hydrochloride (SH) and lipophilic cinnamaldehyde (CA) cubic liquid crystal gels for transdermal delivery. The gels was prepared with a vortex method using phytantriol/water (70:30, w/w) and characterized by polarized light microscopy, small-angle X-ray scattering and rheology. The inner structure of the gels were Pn3m cubic phase and exhibited a pseudoplastic fluid behavior. Furthermore, the in vitro release profile showed that the release behavior of the two drugs from cubic liquid crystal gels conformed to Higuchi equation and were dominated by Fick’s diffusion (n?<?0.45). The ex vivo penetration experiment indicated that dual components-loaded liquid crystal gels can enhance and extend the skin permeation of these two drugs, especially the ratio of SH to CA is 1: 0.5. Finally, transdermal mechanisms were evaluated using laser scanning confocal microscopy and attenuated total reflectance-fourier transform infrared, hinting that hydrophilic and lipophilic drugs weaken each other’s transdermal velocity at the initial stage of penetration. In short, the dual drug-loaded liquid crystal gels was a promising strategy for transdermal applications in treatment of chronic disease.     

Formulation and characterization of liquid crystal systems containing azelaic acid for topical delivery

Purpose: The aim of this study is to prepare and characterize azelaic acid (AzA) containing liquid crystal (LC) drug delivery systems for topical use.

Methods: Two ternary phase diagrams, containing liquid paraffin as the oil component and a mixture of two nonionic surfactants (Brij 721P and Brij 72), were constructed. Formulations chosen from the phase diagrams were characterized by polarized light microscopy, rheological analyses, differential scanning calorimetry (DSC), and small angle x-ray scattering spectroscopy.

Results: Polarized light microscopy proved that except the oil/water emulsion (O/W E), other formulations showed lamellar LC structure. In vitro release studies indicated that the fastest release was achieved by the Lamellar LC (LLC) and O/W E systems, whereas slower release was obtained from the emulsion containing lamellar LC (E-LLC) and distorted lamellar LC (D-LLC) systems. Results of rheological measurements both supported the results of in vitro release studies and showed that the emulsion containing the LC (E-LLC) system had the most stable structure. The formulations and their effect on stratum corneum (SC) were evaluated by DSC studies. The lamellar LC (LLC), emulsion containing lamellar liquid crystal (E-LLC), and O/W E formulations had an effect on both lipid and protein components of SC, whereas distorted lamellar liquid crystal (D-LLC) system had an effect on only the lipid components of SC.

Conclusions: LLC systems could be considered promising for the topical delivery of AzA.     

Wavelength-dependent diffraction patterns from a liquid crystal display

Liquid crystal displays (LCDs) are invaluable for a variety of optical applications, including the encoding of programmable diffractive optical elements. The pixel structure in these devices produces a set of diffracted orders of which the central order is the strongest. In most devices that we have examined, the intensity distribution of the diffraction pattern is independent of the wavelength of the illuminating light. Recently we have been examining the performance of LCDs having very small pixel sizes. We compare results for two devices from the same manufacturer. One of them exhibits the normal behavior. For the other, we find surprisingly strong wavelength dependence. The diffraction pattern varies from having most of the energy in the zero order for long wavelengths to having the energy distributed among 50-60 orders as the wavelength decreases. We attribute this behavior to a phase structure over each pixel. We analyze this behavior using a simple two-dimensional model that qualitatively explains the phenomenon. These results can be viewed in two ways--on the positive side this behavior might lead to optical logic or fan-out applications. On the negative side, there is less intensity available in the normally used zero order.     

Improved hollow-core photonic crystal fiber design for delivery of nanosecond pulses in laser micromachining applications

We report the delivery of high-energy nanosecond pulses (approximately 65 ns pulse width) from a high-repetition-rate (up to 100 kHz) Q-switched Nd:YAG laser through the fundamental mode of a hollow-core photonic crystal fiber (HC-PCF) at 1064 nm. The guided mode in the HC-PCF has a low overlap with the glass, allowing delivery of pulses with energies above those attainable with other fibers. Energies greater than 0.5 mJ were delivered in a single spatial mode through the hollow-core fiber, providing the pulse energy and high beam quality required for micromachining of metals. Practical micromachining of a metal sheet by fiber delivery has been demonstrated.     

Optical properties of organo-soluble polyimide thin films and their applications in liquid crystal displays

Three organo-soluble polyimide powders have been synthesized. Their imidization was verified by Fourier transform infrared (FTIR) and thermal gravimetric analysis (TGA) techniques. The amorphous morphology of their thin films were confirmed by X-ray diffraction. Polyimide thin films were prepared by solution casting or spin coating. UV–visible transmission spectra of thin films revealed that they are almost transparent in the range of visible light. With in-plane orientation, revealed by FTIR spectra, negative birefringence (Δn) of thin films were observed, and refractive indices of the thin films along the film plane (n_TE) and normal to the plane (n_TM) were measured by a prism coupler. Because of negative birefringence of the thin films, they can be substituted for the compensation films for twisted nematic liquid crystal displays (TN-LCDs) to extend their viewing angles. In this paper, a 90°C TN-LCD and 120°C TN-LCD were taken as examples to show the compensation effect of thin films of a qualified polyimide.     

Ray matrix analysis of the fast Fresnel transform with applications towards liquid crystal displays

We reexamine a previously published algorithm for performing a fast Fresnel diffraction calculation that uses two Fourier transform operations and is computationally much faster than the conventional approach. We analyze this technique using a ray matrix analysis and find explicit expressions for the maximum and minimum distances over which this algorithm is accurate. These distances coincide with the experimental distances that are appropriate when patterns are encoded onto liquid crystal displays. We show two examples that confirm our ideas. We expect that these results will be very useful for computational comparison with experimental studies of a variety of diffraction phenomena.