Isolation and manipulation of living adherent cells by micromolded magnetic rafts

A new strategy for magnetically manipulating and isolating adherent cells with extremely high post-collection purity and viability is reported. Micromolded magnetic elements (termed microrafts) were fabricated in an array format and used as culture surfaces and carriers for living, adherent cells. A poly(styrene-co-acrylic acid) polymer containing well dispersed magnetic nanoparticles was developed for creating the microstructures by molding. Nanoparticles of γFe(2)O(3) at concentrations up to 1% wt.∕wt. could be used to fabricate microrafts that were optically transparent, highly magnetic, biocompatible, and minimally fluorescent. To prevent cellular uptake of nanoparticles from the magnetic polymer, a poly(styrene-co-acrylic acid) layer lacking γFe(2)O(3) nanoparticles was placed over the initial magnetic microraft layer to prevent cellular uptake of the γFe(2)O(3) during culture. The microraft surface geometry and physical properties were altered by varying the polymer concentration or layering different polymers during fabrication. Cells plated on the magnetic microrafts were visualized using standard imaging techniques including brightfield, epifluorescence, and confocal microscopy. Magnetic microrafts possessing cells of interest were dislodged from the array and efficiently collected with an external magnet. To demonstrate the feasibility of cell isolation using the magnetic microrafts, a mixed population of wild-type cells and cells stably transfected with a fluorescent protein was plated onto an array. Microrafts possessing single, fluorescent cells were released from the array and magnetically collected. A post-sorting single-cell cloning rate of 92% and a purity of 100% were attained.     

The Social Embeddedness of Transactions: Evidence from the Residential Real-Estate Industry

Information and communications technologies (ICT) are becoming pervasive in the residential real-estate industry and their usage is affecting the work lives of real-estate agents. Drawing on data from a regional study of the residential real-estate industry in the United States, we focus on the disintermediation or, more accurately, the reintermediation of real-estate agents in the sales process. Using data collected from interviews, direct observation, and archival records, we examine how real-estate agents are (1) taking advantage of new ICT in their work, and (2) protecting themselves from others wishing to displace their position in the real-estate value chain. Our analysis of this activity draws on two contrasting theoretical perspectives to illuminate the roles of residential real-estate agents: transaction cost and social capital. The results of this study provide insights into the ways in which ICT are used to build and draw on the social relationships that underpin the actual transactions, to help guide the process of buying/selling a house, and to invoke expertise as needed.     

Use of a virtual wall valve in polydimethylsiloxane microfluidic devices for bioanalytical applications

A simple method for micromanipulation of liquids and∕or small groups of cells is presented in this study. Microfabricated sieving structures composed of PDMS (polydimethylsiloxane) were used to segregate aqueous solutions. This microfluidic valving scheme was an application of Cassie-Baxter wetting and was termed "virtual walls" as a nonsolid barrier exists at an air∕water interface. The manipulation of the virtual-air-wall valve was accomplished by controlling the strength of surface-tension and hydrostatic-pressure forces. Virtual walls with a range of feature sizes were designed and characterized by monitoring air and water displacement in response to hydrostatic pressure. Thresholds for the virtual-air-wall valves to be turned on or off were quantified. The walls could also be formed or dissipated by the focused microbeam of a pulsed laser. As an illustration of the virtual wall utility, a series of microfluidic applications were demonstrated. First, the capability of virtual walls to temporarily segregate liquids was integrated into a device utilized to establish a chemical gradient. In a second application, the arraying of nonadherent cells within individual aqueous cavities created by the virtual walls was demonstrated. Individual cells were also released from the cavities on demand using a focused microbeam. The virtual walls were simple and easy-to-fabricate without the requirement for surface treatment or precision alignment, and should find usage in bioanalytical applications.     

The Social Embeddedness of Transactions: Evidence from the Residential Real-Estate Industry

Information and communications technologies (ICT) are becoming pervasive in the residential real-estate industry and their usage is affecting the work lives of real-estate agents. Drawing on data from a regional study of the residential real-estate industry in the United States, we focus on the disintermediation or, more accurately, the reintermediation of real-estate agents in the sales process. Using data collected from interviews, direct observation, and archival records, we examine how real-estate agents are (1) taking advantage of new ICT in their work, and (2) protecting themselves from others wishing to displace their position in the real-estate value chain. Our analysis of this activity draws on two contrasting theoretical perspectives to illuminate the roles of residential real-estate agents: transaction cost and social capital. The results of this study provide insights into the ways in which ICT are used to build and draw on the social relationships that underpin the actual transactions, to help guide the process of buying/selling a house, and to invoke expertise as needed.