Micropatterned dynamically adhesive substrates for cell migration

We present a novel approach to examine cell migration using dynamically adhesive substrates consisting of three spatially and functionally distinct regions: the first is permanently nonadhesive to cells, the second is permanently adhesive, and the final region is electrochemically switched from nonadhesive to adhesive. We applied a double microcontact printing approach to pattern gold surfaces with carboxylic acid-terminated self-assembled monolayers (SAMs) that permit initial cell adhesion, with methyl-terminated SAMs that permit adsorption of a nonadhesive, and with tri(ethylene glycol)-terminated SAMs that can be electrochemically "switched" to permit cell migration from a prespecified pattern onto a new pattern. Using these substrates, we investigated the migration of epithelial cells from monolayers onto narrow, branching tracks of extracellular matrix in order to characterize how lead cells influence the direction of movement of followers. Time-lapse imaging revealed that, on average, five cells consistently chose one branch before other cells entered the second branch, providing evidence to suggest that intercellular communication plays an important role in guiding the cohesive movement of epithelial sheets. This platform may be of use in furthering our understanding of the mechanisms underlying cellular decision-making during migration in both individual and multicellular contexts.     

The development of a cellular automaton-finite volume model for dendritic growth

A cellular automaton to track the solid–liquid interface movement is linked to finite volume computations of solute diffusion to simulate the behavior of dendritic structures in binary alloys during solidification. A significant problem encountered in the CA formulation has been the presence of artificial anisotropy in growth kinetics introduced by a Cartesian CA grid. A new technique to track the interface movement is proposed to model dendritic growth in different crystallographic orientations while reducing the anisotropy due to grid orientation. The model stability with respect to the numerical parameters (cell size and time step) for various operating conditions is examined. A method for generating an operating window in Δt and Δx has been identified, in which the model gives a grid-independent set of results for calculated dendrite tip radius and tip undercooling. Finally, the model is compared to published experimental and analytical results for both directional and equiaxed growth conditions.     

Bioinspired vesicle restraint and mobilization using a biopolymer scaffold

Biology employs vesicles to package molecules (e.g., neurotransmitters) for their targeted delivery in response to specific spatiotemporal stimuli. Biology is also capable of employing localized stimuli to exert an additional control on vesicle trafficking; intact vesicles can be restrained (or mobilized) by association with (or release from) a cytoskeletal scaffold. We mimic these capabilities by tethering vesicles to a biopolymer scaffold that can undergo (i) stimuli-responsive network formation (for vesicle restraint) and (ii) enzyme-catalyzed network cleavage (for vesicle mobilization). Specifically, we use the aminopolysaccharide chitosan as our scaffold and graft a small number of hydrophobic moieties onto its backbone. These grafted hydrophobes can insert into the bilayer to tether vesicles to the scaffold. Under acidic conditions, the vesicles are not restrained by the hydrophobically modified chitosan (hm-chitosan) because this scaffold is soluble. Increasing the pH to neutral or basic conditions allows chitosan to form interpolymer associations that yield a strong, insoluble restraining network. Enzymatic hydrolysis of this scaffold by chitosanase cleaves the network and mobilizes intact vesicles. Potentially, this approach will provide a controllable means to store and liberate vesicle-based reagents/therapeutics for microfluidic/medical applications.     

Short stereoselective synthesis of alpha-substituted gamma-lactams

A concise, stereoselective synthesis of alpha-substituted gamma-lactams is reported. gamma-Lactam scaffolds 2 and 3, possessing an Evans' chiral auxiliary and two types of N substituents, were successfully alkylated with different electrophiles to give alpha-substituted gamma-lactams with reasonable diastereoselectivities. The use of a masked carboxymethyl function off the lactam nitrogen provided a convergent means to alpha-substituted gamma-lactam dipeptide isosteres.     

A new reverse wormlike micellar system: mixtures of bile salt and lecithin in organic liquids

We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.     

Collaboration in tool development and capacity investments in high technology manufacturing networks

The procurement of capital intensive tools for hi-tech industries is one of the most complex tasks. Astronomical amounts of capital are invested in the processing equipment. Further, there is a large effort from the original equipment manufacturer (OEM) in customizing the high capital intensive equipment to suit their production process. This problem has received little attention from the quantitative decision making literature. For the first time we analyze the problem of OEM deciding on collaborating with the tool supplier via a special type of contract which we refer as “collaboration options”. We show that there are benefits to both the OEM and the tool suppliers from the collaboration.     

The sulfinyl moiety as an internal nucleophile. 2. Stereoselective synthesis of (-)-galantinic acid via 1,3-asymmetric induction

A stereoselective synthesis of (-)-galantinic acid is disclosed. The key steps include hydrolytic kinetic resolution of a racemic epoxide and regio- and stereoselective heterofunctionalization of an olefin, using a pendant sulfinyl group as the nucleophile. The participation of the sulfinyl group was unambiguously proven by conducting the reaction in the presence of H(2)(18)O.     

Two-dimensional Monte Carlo simulations of ionic and nonionic silane self-assembly on hydrophilic surfaces

Aqueous chemistries have recently been shown to be useful for the deposition of hydrophobic films of nonionic and cationic silanes on hydrophilic substrates for the prevention of stiction in MEMS. The Monte Carlo method is used to simulate in two dimensions the self-assembly of silane films on a hydrophilic surface. We investigate the impact of charged group in cationic silane on the overall structure of the films. We characterize the film structure with spatial pair correlations at each molecular layer of the deposited films. The simulations reveal long-range correlations for the film of cationic silanes. Based on our two-dimensional simulations, we report an average "most probable" structure for the films of nonionic and cationic silanes.