ResearchPad - Surfaces and Interfaces Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Synthetic Mimics of Bacterial Lipid A Trigger Optical Transitions in Liquid Crystal Microdroplets at Ultralow Picogram-per-Milliliter Concentrations]]>


We report synthetic six-tailed mimics of the bacterial glycolipid Lipid A that trigger changes in the internal ordering of water-dispersed liquid crystal (LC) microdroplets at ultralow (picogram-per-milliliter) concentrations. These molecules represent the first class of synthetic amphiphiles to mimic the ability of Lipid A and bacterial endotoxins to trigger optical responses in LC droplets at these ultralow concentrations. This behavior stands in contrast to all previously reported synthetic surfactants and lipids, which require near-complete monolayer coverage at the LC droplet surface to trigger ordering transitions. Surface-pressure measurements and SAXS experiments reveal these six-tailed synthetic amphiphiles to mimic key aspects of the self-assembly of Lipid A at aqueous interfaces and in solution. These and other results suggest that these amphiphiles trigger orientational transitions at ultralow concentrations through a unique mechanism that is similar to that of Lipid A and involves formation of inverted self-associated nanostructures at topological defects in the LC droplets.

<![CDATA[A Structure–Property Relationship Study of the Well-Defined Telodendrimers to Improve Hemocompatibility of Nanocarriers for Anticancer Drug Delivery]]>


A series of telodendrimer (a linear polyethyelene glycol-block-dendritic oligo-cholic acid) have been synthesized via a bottom-up approach to optimize the hemocompatibility of the nanocarrier. Numbers of hydrophilic glycerol groups were introduced onto the polar surface of cholic acid to reduce the plasma membrane lytic activity of telodendrimers. An interesting result was observed: only an optimum number of glycerol introduced could reduce the hemolytic properties of the nanocarrier; on the contrary, more glycerols or the amino-glycerol substitution onto cholic acid significantly increased the hemolytic properties of the nanocarriers. To further elucidate the structure–property relationship, the molecular dynamic approach was used to simulate the conformation of the subunits of telodendrimers with different glycerol substitution, and the binding energies and the polar surface areas of the hairpin conformations were calculated to explain the membrane activities of nanocarriers. In addition, these telodendrimer subunits were synthesized and their membrane activities were tested directly, which validated the computational prediction and correlated with the observed hemolytic activity of nanocarriers. The glycerol substitution sustained the facial amphiphilicity of cholic acid, maintaining the superior drug loading capacity (paclitaxel and doxorubicin), stability, cell uptake, and anticancer efficacy of payloads. The in vivo optical imaging study indicated that the optimized nanocarriers can specifically deliver drug molecules to the tumor sites more efficiently than free drug administration, which is essential for the enhanced cancer treatment.

<![CDATA[Sandwich Antibody Arrays Using Recombinant Antibody-Binding Protein L]]>


Antibody arrays are a useful for detecting antigens and other antibodies. This technique typically requires a uniform and well-defined orientation of antibodies attached to a surface for optimal performance. A uniform orientation can be achieved by modification of antibodies to include a single site for attachment. Thus, uniformly oriented antibody arrays require a bioengineered modification for the antibodies directly immobilization on the solid surface. In this study, we describe a “sandwich-type” antibody array where unmodified antibodies are oriented through binding with regioselectively immobilized recombinant antibody-binding protein L. Recombinant proL-CVIA bearing C-terminal CVIA motif is post-translationally modified with an alkyne group by protein farnesyltransferase (PFTase) at the cysteine residue in the CVIA sequence to give proL-CVIApf, which is covalently attached to an azido-modified glass slide by a Huisgen [3 + 2] cycloaddition reaction. Slides bearing antibodies bound to slides coated with regioselectively immobilized proL-CVIApf gave stronger fluorescence outputs and those where the antibody-binding protein was immobilized in random orientations on an epoxy-modified slide. Properly selected capture and detection antibodies did not cross-react with immobilized proL-CVIApf in sandwich arrays, and the proL-CVIApf slides can be used for multiple cycles of detected over a period of several months.

<![CDATA[Multiphase Water-in-Oil Emulsion Droplets for Cell-Free Transcription–Translation]]>


The construction of genetically encoded cellular mimics in compartments containing organized synthetic cytosols is desirable for the development of artificial cells. Phase separated aqueous domains were placed within water-in-oil emulsion droplets in a manner compatible with transcription and translation machinery. Aqueous two-phase and three-phase systems (ATPS and A3PS) were assembled with dextran, poly(ethylene glycol), and Ficoll. Aqueous two-phase systems were capable of supporting the cell-free expression of protein within water droplets, whereas the aqueous three-phase-based system did not give rise to detectable protein synthesis. The expressed protein preferentially partitioned to the dextran-enriched phase. The system could serve as a foundation for building cellular mimics with liquid organelles.

<![CDATA[Mechanically and Chemically Tunable Cell Culture System for Studying the Myofibroblast Phenotype]]>


Cell culture systems for studying the combined effects of matrix proteins and mechanical forces on the behavior of soft tissue cells have not been well developed. Here, we describe a new biomimetic cell culture system that allows for the study of mixtures of matrix proteins while controlling mechanical stiffness in a range that is physiological for soft tissues. This system consists of layer-by-layer (LbL)-assembled films of native matrix proteins atop mechanically tunable soft supports. We used hepatic stellate cells, which differentiate to myofibroblasts in liver fibrosis, for proof-of-concept studies. By culturing cells on collagen and lumican LbL-modified hydrogels, we demonstrate that this system is noncytotoxic and offers a valid control substrate, that the hydrogel determines the overall system mechanics, and that the addition of lumican to collagen influences the stellate cell phenotype. LbL-modified hydrogels offer the potential to study the influence of complex environmental factors on soft-tissue cells in culture.

<![CDATA[β Sheets Not Required: Combined Experimental and Computational Studies of Self-Assembly and Gelation of the Ester-Containing Analogue of an Fmoc-Dipeptide Hydrogelator]]>


In our work toward developing ester-containing self-assembling peptides as soft biomaterials, we have found that a fluorenylmethoxycarbonyl (Fmoc)-conjugated alanine-lactic acid (Ala-Lac) sequence self-assembles into nanostructures that gel in water. This process occurs despite Fmoc-Ala-Lac’s inability to interact with other Fmoc-Ala-Lac molecules via β-sheet-like amide–amide hydrogen bonding, a condition previously thought to be crucial to the self-assembly of Fmoc-conjugated peptides. Experimental comparisons of Fmoc-Ala-Lac to its self-assembling peptide sequence analogue Fmoc-Ala-Ala using a variety of microscopic, spectroscopic, and bulk characterization techniques demonstrate distinct features of the two systems and show that while angstrom-scale self-assembled structures are similar, their nanometer-scale size and morphological properties diverge and give rise to different bulk mechanical properties. Molecular dynamics simulations were performed to gain more insight into the differences between the two systems. An analysis of the hydrogen-bonding and solvent-surface interface properties of the simulated fibrils revealed that Fmoc-Ala-Lac fibrils are stronger and less hydrophilic than Fmoc-Ala-Ala fibrils. We propose that this difference in fibril amphiphilicity gives rise to differences in the higher-order assembly of fibrils into nanostructures seen in TEM. Importantly, we confirm experimentally that β-sheet-type hydrogen bonding is not crucial to the self-assembly of short, conjugated peptides, and we demonstrate computationally that the amide bond in such systems may act mainly to mediate the solvation of the self-assembled single fibrils and therefore regulate a more extensive higher-order aggregation of fibrils. This work provides a basic understanding for future research in designing highly degradable self-assembling materials with peptide-like bioactivity for biomedical applications.

<![CDATA[Modeling Persistence in Mesenchymal Cell Motility Using Explicit Fibers]]>


Cell motility is central to a variety of fundamental processes ranging from cancer metastasis to immune responses, but it is still poorly understood in realistic native environments. Previous theoretical work has tended to focus on intracellular mechanisms or on small pieces of interaction with the environment. In this article, we present a simulation which accounts for mesenchymal movement in a 3D environment with explicit collagen fibers and show that this representation highlights the importance of both the concentration and alignment of fibers. We show good agreement with experimental results regarding cell motility and persistence in 3D environments and predict a specific effect on average instantaneous cell speed and persistence. Importantly, we show that a significant part of persistence in 3D is directly dependent on the physical environment, instead of indirectly dependent on the environment through the biochemical feedback that occurs in cell motility. Thus, new models of motility in three dimensions will need to account for the effects of explicit individual fibers on cells. This model can also be used to analyze cellular persistence in both mesenchymal and nonmesenchymal motility in complex three-dimensional environments to provide insights into mechanisms of cell motion seen in various cancer cell types in vivo.

<![CDATA[Spatial Control over Cross-Linking Dictates the pH-Responsive Behavior of Poly(2-(tert-butylamino)ethyl methacrylate) Brushes]]>


Surface-initiated atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) produced pH-responsive secondary amine-functionalized polymer brushes with dry thicknesses ranging from 4 to 28 nm, as determined by ellipsometry. At low pH, linear PTBAEMA brushes became protonated and highly swollen; brush collapse occurred when the solution pH was increased to ca. 7.7 due to deprotonation. PTBAEMA brushes were subsequently cross-linked using tolylene-2,4-diisocyanate-terminated poly(propylene glycol) (PPG-TGI) in either THF (a good solvent for PTBAEMA) or n-hexane (a poor solvent). The intensity of the C–C–O component (286.5 eV) in the C1s X-ray photoelectron spectrum increased after reaction with PPG-TDI, suggesting that cross-linking was successful in both solvents. Ellipsometry studies indicated that the pH-responsive behavior of these cross-linked brushes is dictated by the spatial location of the PPG-TDI cross-linker. Thus, uniformly cross-linked brushes prepared in THF became appreciably less swollen at a given (low) pH than surface-cross-linked brushes prepared in n-hexane. Micro- and nanopatterned PTBAEMA brushes were prepared via UV irradiation and interference lithography, respectively, and characterized by atomic force microscopy. The change in brush height was determined as a function of pH, and these AFM observations correlated closely with the ellipsometric studies.

<![CDATA[On the Role of Specific Interactions in the Diffusion of Nanoparticles in Aqueous Polymer Solutions]]>


Understanding nanoparticle diffusion within non-Newtonian biological and synthetic fluids is essential in designing novel formulations (e.g., nanomedicines for drug delivery, shampoos, lotions, coatings, paints, etc.), but is presently poorly defined. This study reports the diffusion of thiolated and PEGylated silica nanoparticles, characterized by small-angle neutron scattering, in solutions of various water-soluble polymers such as poly(acrylic acid) (PAA), poly(N-vinylpyrrolidone) (PVP), poly(ethylene oxide) (PEO), and hydroxyethylcellulose (HEC) probed using NanoSight nanoparticle tracking analysis. Results show that the diffusivity of nanoparticles is affected by their dimensions, medium viscosity, and, in particular, the specific interactions between nanoparticles and the macromolecules in solution; strong attractive interactions such as hydrogen bonding hamper diffusion. The water-soluble polymers retarded the diffusion of thiolated particles in the order PEO > PVP > PAA > HEC whereas for PEGylated silica particles retardation followed the order PAA > PVP = HEC > PEO. In the absence of specific interactions with the medium, PEGylated nanoparticles exhibit enhanced mobility compared to their thiolated counterparts despite some increase in their dimensions.

<![CDATA[Topical application of L-arginine blocks advanced glycation by ascorbic acid in the lens of hSVCT2 transgenic mice]]>


Previous experiments from our laboratory showed that the oral intake of selected guanidino compounds could block the formation of crystallin-bound advanced ascorbylation products. Here we tested whether these were also active when applied as eye drops.


Two month old hSVCT2 transgenic mice (n=10) were treated twice daily with one drop of 0.1% L-arginine, γ-guanidinobutyric acid (GBA), penicillamine (PA) or N-acetylcysteine (NAC) in one eye and vehicle only in the other eye. After seven months, lens crystallins were isolated, dialyzed, and proteolytically digested to determine the protein-bound fluorescence at 335/385 and 370/440 nm excitation/emission and the advanced glycation/ascorbylation endproducts carboxymethyl-lysine (CML), carboxyethyl-lysine (CEL), glucosepane, glyoxal, and methylglyoxal hydroimidazolones G-H1 and MG-H1. The topical uptake of L-arginine and NAC was also evaluated in vitro and in vivo in rabbit lens.


In hSVCT2 mice, L-arginine decreased 335/385 and 370/440 nm fluorescence by 40% (p<0.001), CML, CEL, and glucosepane crystallin crosslinks by 35% (p<0.05), 30% (p<0.05), and 37% (p<0.05), respectively, without affecting MG-H1 and G-H1. NAC decreased 335/385 nm fluorescence by 50% (p<0.001) but, like PA and GBA, had no effect on other modifications. L-Arginine uptake into rabbit eyes treated topically reached identical lenticular plateau levels (~400 nmol/g wet weight) at 0.5% and 2.0% but levels remained three times higher at 5 h at 2% versus 0.5% concentration, respectively. In vitro studies showed a 100 fold higher L-arginine level than NAC levels, implicating high affinity uptake of the former.


L-Arginine when applied both orally and topically is a potent and broad suppressor of advanced ascorbylation in the lens. Its uptake in rabbit lens upon topical application suggests transcorneal uptake into the human lens should be feasible for testing its potential anticataract properties in clinical trials.