Matrix transformation of lunar regolith and its use as a feedstock for additive manufacturing.

Building a sustainable human habitat on the Moon requires advances in excavation, paving, and additive manufacturing to construct landing pads, surface transportation arteries, resilient shelters, and scientific outposts. Construction of infrastructure elements on the lunar surface necessitates exploration of the interfacial reactivity of locally sourced regolith and the adaptation of Earth-based construction techniques. Various crosslinking frameworks and sintering methods have been proposed as a means of consolidating lunar regolith into load-bearing structures but each have challenges related to incomplete understanding of reaction chemistry, excessive thermal budgets, and lack of universal applicability to different mineral components of regolith. We describe here a versatile experimental and computational study of the consolidation of a regolith simulant through formation of siloxane networks enmeshing mineral particles by surface dissolution-precipitation and polycondensation reactions. Furthermore, by tailoring the rheological properties of the formulation an additive manufacturing feedstock can be developed for the construction of lunar infrastructure.

Generating multiple optical vortices in orange beams induced by selectively pumped frequency-doubled solid-state Raman lasers with mode conversion.

We employ a selectively pumped solid-state laser with stimulated Raman scattering and second-harmonic generation to generate frequency-doubled lasing modes (FDLMs) at 588 nm. The FDLMs are transformed by using an external cylindrical mode converter to generate various structured beams with multiple optical vortices. Theoretical analyses clearly reveal the relationship between the mode components in the laser emission and the transverse displacement of the off-center pumping. We further verify that the experimental results for the transformed FDLMs can be numerically reconstructed with a theoretical model. By analyzing the phase structures of the converted beams, it can be demonstrated that the number of vortices rises from 2 to 19 with increasing off-center displacement.

Characterizing α-helical peptide aggregation on supported lipid membranes using microcantilevers.

We report the use of lipid membrane-coated microcantilevers to probe the interactions between phospholipid membranes and membrane-active peptides. This sensing method integrates two well-developed techniques: solid-supported lipid bilayers (SLBs) and microcantilever sensors. SLBs are prepared on the silicon dioxide surface of the microcantilevers using a vesicle fusion method. As molecules adsorb onto the surface of the microcantilever, the microcantilever bends due to the induced compressive or tensile stresses, which result from the surface free energy change. Real-time surface stress changes in the SLB due to interactions with small molecules can be detected by monitoring the deflection of the microcantilever. We investigate the mechanism for the interaction between SLBs and PEP1, a synthetic amphipathic peptide resembling a segment of the nonstructural protein (NS5A) of the hepatitis C virus. Initially, the PEP1 peptides adsorb onto the lipid membranes, and then at a critical concentration, the peptides begin to aggregate and form pores; finally, the peptides destabilize and induce solubilization of the supported membranes. The membrane-coated microcantilever sensor is capable of characterizing the kinetics and dynamics of this process with great sensitivity.

Lipid bilayer phase transformations detected using microcantilevers.

We report the use of microcantilevers to measure the phase transition temperature (T(m)) of supported lipid bilayers or lipid monolayers. During the solid-liquid phase transition, a supported lipid bilayer or monolayer undergoes a conformational change in which the lipid acyl chains transition from an ordered state to a disordered state. This process is accompanied by a free energy change, which is coupled to changes in the surface stress in the underlying solid support layer. These surface stress changes can be readily detected using microcantilevers. The surface stress of the solid-like phase of 1-myristoyl-2-palmitoyl-sn-glycero-3-phosphocholine (MPPC) decreases linearly as the temperature increases and abruptly jumps at the main phase transition temperature. This phase transition temperature corresponds well with that found for free membranes. For an MPPC monolayer, this phase transition temperature is shifted, indicating that the existence of the solid support affects the monolayer structure. The addition of cholesterol into the bilayer decreases the phase transition temperature by ~0.38 °C per mol % of cholesterol. Differences in MPPC stability when it is either a bilayer or a monolayer can be detected through these sensitive surface stress measurements.

Stimuli-responsive color films of poly(4-vinylpyridine)-b-poly(ε-caprolactone) complexed with cyano-capped chromophores.

Here, we develop a method to fabricate stimuli-responsive color films using block copolymer, poly(4-vinylpyridine)-b-poly(ε-caprolactone) (P4VP-PCL), as a template complexed with functionalized chromophores. The P4VP block in the P4VP-PCL can be associated with a cyano end-capped chromophore via charge transfer, which is a noncovalent interaction that can be conveniently manipulated by external stimuli, giving a specific color. The color of the film can be switched by tuning the charge transfer interaction between the chromophore and P4VP with controlled environmental conditions, such as pH, temperature, and moisture, while maintaining high transmittance for visible light due to the formation of the nanostructure of chromophore/P4VP-PCL complex. However, the association/dissociation process between chromophore and P4VP is diffusion-dominated, which may limit the kinetic response time for color change. A way to create quick and reversible color switching can be achieved by a combination of stimuli. The contrasting color change of the responsive chromophore/P4VP-PCL thin films which exhibit RGB primary colors can provide a sensor film that is flexible, fast-responsive, and convenient.

De novo motif discovery facilitates identification of interactions between transcription factors in Saccharomyces cerevisiae.

MOTIVATION: Gene regulation involves complicated mechanisms such as cooperativity between a set of transcription factors (TFs). Previous studies have used target genes shared by two TFs as a clue to infer TF-TF interactions. However, this task remains challenging because the target genes with low binding affinity are frequently omitted by experimental data, especially when a single strict threshold is employed. This article aims at improving the accuracy of inferring TF-TF interactions by incorporating motif discovery as a fundamental step when detecting overlapping targets of TFs based on ChIP-chip data. RESULTS: The proposed method, simTFBS, outperforms three naïve methods that adopt fixed thresholds when inferring TF-TF interactions based on ChIP-chip data. In addition, simTFBS is compared with two advanced methods and demonstrates its advantages in predicting TF-TF interactions. By comparing simTFBS with predictions based on the set of available annotated yeast TF binding motifs, we demonstrate that the good performance of simTFBS is indeed coming from the additional motifs found by the proposed procedures. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Probing insertion and solubilization effects of lysolipids on supported lipid bilayers using microcantilevers.

The interaction of surfactants with lipid membranes can result in composition change, area expansion, solubilization, or the formation of protrusion features of the membranes. Amphipathic surfactant molecules are simplified analogues to membrane-active drugs and peptides which are known for inserting into lipid bilayers; however, the effect of these amphipathic molecules on supported membranes is not well characterized. In this paper we explore the use of microcantilever sensors to quantify surfactants' effects on lipid membranes. We use microcantilevers which are coated with lipid membranes to probe the interactions between lysolipids and supported lipid bilayers (SLBs). In particular, we investigate the effects of four zwitterionic surfactants similar to phospholipids: lysolipids of different aliphatic chain lengths (lysophosphocholines, lysoPCs, 12:0, 14:0, 16:0, and 18:0) on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine-supported lipid bilayers. By monitoring the deflection of the microcantilevers, real-time free energy changes in the SLBs upon the addition of lysolipids can be detected. Additionally, the bending direction reveals whether the lysoPCs incorporate into or solubilize the SLB. When the bulk lysoPC concentration is less than its critical micelle concentration (CMC), we observe a compressive bending of the microcantilever, indicating adsorption to the SLB. Additionally, the change in surface stress is found to be proportional to the amount of membrane-bound lysoPCs. For bulk concentrations greater than the CMC, lysoPCs 12:0 and 14:0, there is tensile bending, indicating that the lysoPCs begin to solubilize and destroy the SLBs. Interestingly, this is not observed for lysoPCs with longer chain lengths. This new method of using microcantilevers for detecting and quantifying the surfactant insertion and solubilization of SLBs offers additional insights into the interactions between small amphipathic molecules and lipid membranes.

Monitoring DNA binding to Escherichia coli lactose repressor using quartz crystal microbalance with dissipation.

Lactose repressor protein (LacI) functions as a negative transcription regulator in Escherichia coli by binding to the operator DNA sequence. Our understanding of the immobilized LacI function and the effect of ligand binding on the conformation of LacI-DNA complexes remains poorly understood. Here, we have examined the difference in functionality of wild-type and mutant LacI binding to the target DNA using quartz crystal microbalance with dissipation (QCM-D). To direct the orientation of LacI binding to the gold surface, residue 334 was substituted with cysteine (T334C) to generate a sulfur-gold linkage. Position 334 is located on the surface opposite the DNA-binding domain and remote from the site for inducer binding. With T334C immobilized on the gold surface, our sensors successfully detect operator binding as well as the release of the operator DNA from the repressor in the presence of inducer isopropyl-ß-D-thiogalactoside (IPTG). Besides the natural operator DNA sequence (O(1)), a symmetric high-affinity DNA sequence (O(sym)), and a non-specific DNA (O(ns)) sequence with low affinity were also used. In addition, the impact of anti-inducer o-nitrophenyl-beta-d-fucoside (ONPF), which stabilizes LacI operator binding, was examined. The results from immobilized mutant LacI are in good agreement with known solution parameters for LacI-ligand interactions, demonstrating that QCM-D provides a rapid and efficient measurement of DNA binding and impact of ligands upon binding for this complex oligomeric protein.

Using microcantilevers to study the interactions of lipid bilayers with solid surfaces.

We report the use of free-standing microcantilever beams, which have been used as an ultrasensitive method for measuring the surface free energy changes on a substrate induced by the adsorption of thin films, to probe the interactions between a solid surface and a phospholipid bilayer. We relate the observed deflection of a cantilever to the changes in the surface free energy of the solid surface which supports the phospholipid bilayer. We observe that the deflection is influenced by electrostatic and intermolecular interactions of the bilayer with the substrate. Increasing the surface charge density in the supported lipid bilayer (SLB), by increasing the ratio of cationic to zwitterionic lipids in bilayer, resulted in an increase in cantilever deflection. The surface free energy changes due to lipid transfer between anionic unilamellar vesicles and a cationic supported bilayer were also observed using microcantilevers. Finally, the adsorption free energy of a mixed lipid and cholesterol bilayer was measured demonstrating a detectable decrease in affinity between the phospholipid bilayer and the solid surface as a result of the addition of cholesterol. Our results reveal a new technique to probe the adsorption free energy of a SLB system as a function of the interactions governing the structure of supported lipid membranes.