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-Airway smooth muscle (ASM) cellular and molecular biology is typically studied with single-cell cultures grown on flat 2D substrates. However, cells in vivo exist as part of complex 3D structures, and it is well established in other cell types that altering substrate geometry exerts potent effects on phenotype and function. These factors may be especially relevant to asthma, a disease characterized by structural remodeling of the airway wall, and highlights a need for more physiologically relevant models of ASM function. We utilized a tissue engineering platform known as microfabricated tissue gauges to develop a 3D culture model of ASM featuring arrays of ϳ0.4 mm long, ϳ350 cell "microtissues" capable of simultaneous contractile force measurement and cell-level microscopy. ASM-only microtissues generated baseline tension, exhibited strong cellular organization, and developed actin stress fibers, but lost structural integrity and dissociated from the cantilevers within 3 days. Addition of 3T3-fibroblasts dramatically improved survival times without affecting tension development or morphology. ASM-3T3 microtissues contracted similarly to ex vivo ASM, exhibiting reproducible responses to a range of contractile and relaxant agents. Compared with 2D cultures, microtissues demonstrated identical responses to acetylcholine and KCl, but not histamine, forskolin, or cytochalasin D, suggesting that contractility is regulated by substrate geometry. Microtissues represent a novel model for studying ASM, incorporating a physiological 3D structure, realistic mechanical environment, coculture of multiple cells types, and comparable contractile properties to existing models. This new model allows for rapid screening of biochemical and mechanical factors to provide insight into ASM dysfunction in asthma. 3D culture; tissue engineering; asthma; airway smooth muscle; airway wall remodeling ASTHMA IS AN OBSTRUCTIVE AIRWAY disease characterized by increased airway resistance and hyperresponsiveness (AHR) to certain environmental stimuli. The primary cause of AHR is not clear but ultimately it is airway smooth muscle (ASM) contraction that is responsible for airway narrowing. Alterations in sensitivity, force generation, or shortening velocity of ASM in response to contractile agonists may be possible disease mechanisms. It is now also well established that asthma is characterized by airway wall remodeling, which includes thickening of the airway wall and increased ASM mass (52), altered extracellular matrix (ECM) composition (4, 19), infiltration of inflammatory cells (9), and epithelial dysfunction (33). Since airway wall remodeling may precede clinical symptoms (7), it is possible that a putative defect in ASM contractile function arises as a result of the remodeling process. Structural changes in the airway wall may manifest as altered mechanical loads that alter how ASM force development translates into airway narrowing. Such changes could also modulate ASM contractile phenotype through ECM signaling and mechanotransduction, b...

Contact resistance measurements are reported for radio frequency microelectromechanical system switches operating in an ultrahigh vacuum system equipped with in situ oxygen plasma cleaning capabilities. Ru-based contacts were prepared by means of standard sputtering techniques, sputtering followed by postdeposition oxidation, ͑surface RuO 2 ͒ or reactive sputtering in the presence of oxygen ͑bulk RuO 2 ͒. In situ oxygen plasma cleaning lowered the resistance of Ru contacts by two or more orders of magnitude but not lower than Au contacts, irrespective of whether the Au contacts were cleaned. The time dependence of the resistance was fit to power law extrapolations to infer contact creep properties and resistance values at t = ϱ. Time-dependent creep properties of mixed Au-Ru contacts were observed to be similar to those of Au-Au contacts, while the absolute value of the resistance of such contacts was more comparable to Ru-Ru contacts. Prior to, and for short oxygen plasma exposure times, bulk RuO 2 resistance values exhibited much larger variations than values measured for surface RuO 2 . For O 2 plasma exposure times exceeding about 5 min, the bulk and surface RuO 2 resistance values converged, at both t = 0 and t = ϱ, with the t = ϱ values falling within experimental error of theoretical values predicted for ideal surfaces. The data strongly support prior reports in the surface science literature of oxygen plasma induced thickening of oxide layers present on Ru surfaces. In addition, they demonstrate that vacuum alone is insufficient to remove contaminants from the contact surfaces and/or prevent such contaminants from reforming after oxygen plasma exposure.