Photo-patterned multi-domain multi-component hybrid hydrogels

This paper explores multi-component gelation systems containing two low-molecular-weight gelators and a polymer gelator. By controlled spatial and temporal application of different triggers – physical and chemical – it is possible to sequentially assemble gel networks, with a degree of self-sorting. A photo-patterned gel with four different domains was fabricated from a complex mixture of components, with the history of each domain programming the gel

Hybrid and Multi-Component Hydrogels

Low-molecular-weight gelators (LMWGs) form a network via non-covalent interactions to immobilise the surrounding bulk solvent and form a gel. Whilst such gels are highly responsive and dynamic, they are often mechanically weak. In order to enhance the mechanical strength of such networks, the LMWG network can be supplemented with a second network formed from stronger polymer gelators (PGs) to yield a multi-component, multi-functional material – a hybrid gel. By using this multi-functionality, hybrid gels were made that could demonstrate the following: a) robustness yet responsiveness, b) spatial control over the formation of one network in the presence of another, and c) temporal control over the formation of one network in the presence of another. For the first aim, a pH-responsive LMWG (1,3:2,4-dibenzylidene-D-sorbitol dicarboxylic acid, DBS-CO2H) was combined with the robust PG agarose. The assembly of DBS-CO2H in the presence and absence of agarose was investigated by NMR and CD spectroscopies, whilst materials properties were examined by rheology. DBS-CO2H was found to retain its pH-responsive character, as was demonstrated by cycling the pH within the gel – whilst the DBS-CO2H network could be switched “on” or “off”, the robust agarose network remained intact. Following this, DBS-CO2H was combined with the photo-inducible PG poly(ethylene glycol) dimethacrylate (PEGDM). Spectroscopic methods and electron microscopy showed that the kinetics and morphology of DBS-CO2H assembly were impacted by the presence of PEGDM. The application of a mask during photoirradiation allowed patterning of the PEGDM network to form a material with two distinct, spatially-resolved regions, defined as a “multidomain gel”, achieving the second aim. The different domains had different properties with regards to the diffusion and release of dyes. DBS-CO2H was then combined with another pH-responsive LMWG (1,3:2,4-dibenzylidene-D-sorbitol-dicarbonyl-glycine, DBS-Gly). The two gelators showed a good degree of kinetic self-sorting, their self-assembly being triggered at different pHs. It was possible to use two proton sources – the slow hydrolysis of glucono-δ-lactone, and the more rapid photoacid generator diphenyliodonium nitrate – to achieve a two-step process of network formation. As the second step was UV-initiated, photopatterned multi-component gels were produced; these materials were both spatially and temporally resolved, achieving the third aim. Finally, the combination of DBS-CO2H, DBS-Gly and PEGDM into a three-gelator, multi-component hybrid hydrogel was investigated

Evaluation of matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) for the Identification of Group B Streptococcus.

Objective Group B Streptococcus (GBS) is a leading cause of neonatal meningitis and sepsis worldwide. Intrapartum antibiotics given to women carrying GBS are an effective means of reducing disease in the first week of life. Rapid and reliable tests are needed to accurately identify GBS from these women for timely intrapartum antibiotic administration to prevent neonatal disease. Many laboratories now use matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) by direct plating or cell lysis for the identification of GBS isolates. The cell lysis step increases time to results for clinical samples and is more complex to perform. Therefore, we seek to evaluate the sensitivity and specificity of the quicker and more rapid direct plating method in identifying GBS. Results We directly compared swab isolates analysed by both direct plating and cell lysis method and demonstrated that direct plating has a sensitivity and specificity of 0.97 and 1, respectively, compared to an additional cell lysis step. We demonstrated that MALDI-TOF MS can be successfully used for batch processing by the direct plating method which saves time. These results are reassuring for laboratories worldwide who seek to identify GBS from swabs samples as quickly as possible

Photopatterned Multidomain Gels : Multi-Component Self-Assembled Hydrogels Based on Partially Self-Sorting 1,3:2,4-Dibenzylidene-d-sorbitol Derivatives

We report a multicomponent self-assembling system based on 1,3:2,4-dibenzyldene-d-sorbitol (DBS) derivatives which form gels as the pH is lowered in a controlled way. The two DBS gelators are functionalized with carboxylic acids: the first in the 4-position of the aromatic rings (DBS-CO2H), the second having glycine connected through an amide bond and displaying a terminal carboxylic acid (DBS-Gly). Importantly, these two self-assembling DBS-acids have different pKa values, and as such, their self-assembly is triggered at different pHs. Slowly lowering the pH of a mixture of gelators using glucono-d-lactone (GdL) initially triggers assembly of DBS-CO2H, followed by DBS-Gly; a good degree of kinetic self-sorting is achieved. Gel formation can also be triggered in the presence of diphenyliodonium nitrate (DPIN) as a photoacid under UV irradiation. Two-step acidification of a mixture of gelators using (a) GdL and (b) DPIN assembles the two networks sequentially. By combining this approach with a mask during step b, multidomain gels are formed, in which the network based on DBS-Gly is positively patterned into a pre-existing network based on DBS-CO2H. This innovative approach yields spatially resolved multidomain multicomponent gels based on programmable low-molecular-weight gelators, with one network being positively 'written' into another

Early Operations Flight Correlation of the Lunar Laser Communications Demonstration (LLCD) on the Lunar Atmosphere and Dust Environment Explorer (LADEE)

The Lunar Atmosphere and Dust Environment Explorer (LADEE) mission launched on September 7, 2013 with a one month cruise before lunar insertion. The LADEE spacecraft is a power limited, octagonal, composite bus structure with solar panels on all eight sides with four vertical segments per side and 2 panels dedicated to instruments. One of these panels has the Lunar Laser Communications Demonstration (LLCD), which represents a furthering of the laser communications technology demonstration proved out by the Lunar Reconnaissance Orbiter (LRO). LLCD increases the bandwidth of communication to and from the moon with less mass and power than LROs technology demonstrator. The LLCD Modem and Controller boxes are mounted to an internal cruciform composite panel and have no dedicated radiator. The thermal design relies on power cycling of the boxes and radiation of waste heat to the inside of the panels, which then reject the heat when facing cold space. The LADEE mission includes a slow roll and numerous attitudes to accommodate the challenging thermal requirements for all the instruments on board. During the cruise phase, the internal Modem and Controller avionics for LLCD were warmer than predicted by more than modeling uncertainty would suggest. This caused concern that if the boxes were considerably warmer than expected while off, they would also be warmer when operating and could limit the operational time when in lunar orbit. The thermal group at Goddard Space Flight Center evaluated the models and design for these critical avionics for LLCD. Upon receipt of the spacecraft models and audit was performed and data was collected from the flight telemetry to perform a sanity check of the models and to correlate to flight where possible. This paper describes the efforts to correlate the model to flight data and to predict the thermal performance when in lunar orbit and presents some lessons learned

Full stress tensor measurement using colour centres in diamond

Stress and strain are important factors in determining the mechanical, electronic, and optical properties of materials, relating to each other by the material's elasticity or stiffness. Both are represented by second rank field tensors with, in general, six independent components. Measurements of these quantities are usually achieved by measuring a property that depends on the translational symmetry and periodicity of the crystal lattice, such as optical phonon energies using Raman spectroscopy, the electronic band gap using cathodoluminescence, photoelasticity via the optical birefringence, or Electron Back Scattering Diffraction (EBSD). A reciprocal relationship therefore exists between the maximum sensitivity of the measurements and the spatial resolution. Furthermore, of these techniques, only EBSD and off-axis Raman spectroscopy allow measurement of all six components of the stress tensor, but neither is able to provide full 3D maps. Here we demonstrate a method for measuring the full stress tensor in diamond, using the spectral and optical polarization properties of the photoluminescence from individual nitrogen vacancy (NV) colour centres. We demonstrate a sensitivity of order 10 MPa, limited by local fluctuations in the stress in the sample, and corresponding to a strain of about 10^-5, comparable with the best sensitivity provided by other techniques. By using the colour centres as built-in local sensors, the technique overcomes the reciprocal relationship between spatial resolution and sensitivity and offers the potential for measuring strains as small as 10^-9 at spatial resolution of order 10 nm. Furthermore it provides a straightforward route to volumetric stress mapping. Aside from its value in understanding strain distributions in diamond, this new approach to stress and strain measurement could be adapted for use in micro or nanoscale sensors.Comment: 12 pages, 5 figures - supplementary informations included in appendi

P1_8 Escaping the Moons of Mars using a Pogo Stick

The objective of this paper was to investigate the gravitational field strengths of the Martian Moons; Deimos and Phobos’ effect on a pogo stick and it’s rider. It was hypothesised that spring required to escape Deimos would be smaller due to the gravitational field strength being lower. This hypothesis was tested using Hooke’s Law and the Newtonian Laws of gravity to calculate the spring size needed to propel the pogo stick and its rider to a point where it was no longer under the effects of the respective moons gravitational pull. We found this value for the spring decompression to be 1.56 m on Deimos and 5.1 m on Phobos. These values confirmed the hypothesis we made and therefore it would be possible to use a pogo stick to escape the Martian Moons’ gravity

P1_7 Solar-Powered Superhero: What’s Superman’s Power Consumption?

In this paper, we assess the viability of Superman being powered by solar energy. We do this by calculating the energy that he would be able to absorb in a day - 3 × 107J - and comparing it to the energy that he requires to carry out certain superhuman activities. We find that he could leap the Empire State Building 75 times using the energy he acquires in a day, but he requires 3 days worth of energy to match the energy output of a train for one second

P1_2 Using Trebuchets for Lunar Satellites

In this paper we investigated the possibility of launching a 10 kg satellite into lunar orbit from the surface of the Moon, using a trebuchet. We found that the mass of the counterweight required would be 330 tonnes. We also discussed how the kinetic energy required for the speed of the orbit and the gravitational energy needed to be overcome changed as a result of the orbital radius