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Background: Minority race/ethnicity is generally associated with antiretroviral therapy nonadherence in US-based studies. Limitations of the existing literature include small samples, subjective adherence measures, and inadequate control for potential confounders such as mental health and substance use, which have been consistently associated with poorer adherence., Methods: Individual-level data were pooled from 13 US-based studies employing electronic drug monitoring to assess adherence. Adherence was operationalized as percent of prescribed doses taken from the first 12 (monthly) waves of data in each study. Depression symptoms were aggregated from several widely used assessments, and substance use was operationalized as any use of cocaine/stimulants, heroin/opiates, ecstasy, hallucinogens, or sedatives in the 30-365 days preceding baseline., Results: The final analytic sample of 1809 participants ranged in age from 18 to 72 years and was 67% male. Participants were 53% African American, 14% Latino, and 34% White. In a logistic regression adjusting for age, gender, income, education, and site, race/ethnicity was significantly associated with adherence (P < 0.001) and persisted in a model that also controlled for depression and substance use (P < 0.001), with African Americans having significantly lower adherence than Latinos [odds ratio (OR) = 0.72, P = 0.04] and whites (OR = 0.60, P < 0.001). Adherence did not differ between whites and Latinos (OR = 0.84, P = 0.27)., Conclusions: Racial/ethnic differences in demographics, depression, and substance abuse do not explain the lower level of antiretroviral therapy adherence in African Americans observed in our sample. Further research is needed to explain the persistent disparity and might examine factors such as mistrust of providers, health literacy, and inequities in the health care system.

Microscale engineering technologies provide unprecedented opportunities to create cell culture microenvironments that go beyond current three-dimensional in vitro models by recapitulating the critical tissue-tissue interfaces, spatiotemporal chemical gradients, and dynamic mechanical microenvironments of living organs. Here we review recent advances in this field made over the past two years that are focused on the development of 'Organs-on-Chips' in which living cells are cultured within microfluidic devices that have been microengineered to reconstitute tissue arrangements observed in living organs in order to study physiology in an organ-specific context and to develop specialized in vitro disease models. We discuss the potential of organs-on-chips as alternatives to conventional cell culture models and animal testing for pharmaceutical and toxicology applications. We also explore challenges that lie ahead if this field is to fulfil its promise to transform the future of drug development and chemical safety testing.

Development of an in vitro living cell-based model of the intestine that mimics the mechanical, structural, absorptive, transport and pathophysiological properties of the human gut along with its crucial microbial symbionts could accelerate pharmaceutical development, and potentially replace animal testing. Here, we describe a biomimetic 'human gut-on-a-chip' microdevice composed of two microfluidic channels separated by a porous flexible membrane coated with extracellular matrix (ECM) and lined by human intestinal epithelial (Caco-2) cells that mimics the complex structure and physiology of living intestine. The gut microenvironment is recreated by flowing fluid at a low rate (30 μL h(-1)) producing low shear stress (0.02 dyne cm(-2)) over the microchannels, and by exerting cyclic strain (10%; 0.15 Hz) that mimics physiological peristaltic motions. Under these conditions, a columnar epithelium develops that polarizes rapidly, spontaneously grows into folds that recapitulate the structure of intestinal villi, and forms a high integrity barrier to small molecules that better mimics whole intestine than cells in cultured in static Transwell models. In addition, a normal intestinal microbe (Lactobacillus rhamnosus GG) can be successfully co-cultured for extended periods (>1 week) on the luminal surface of the cultured epithelium without compromising epithelial cell viability, and this actually improves barrier function as previously observed in humans. Thus, this gut-on-a-chip recapitulates multiple dynamic physical and functional features of human intestine that are critical for its function within a controlled microfluidic environment that is amenable for transport, absorption, and toxicity studies, and hence it should have great value for drug testing as well as development of novel intestinal disease models.

Interventions aimed at improving HIV medication adherence could be dismissed as ineffective due to statistical methods that are not sufficiently sensitive. Cross-sectional techniques such as t tests are common to the field, but potentially inaccurate due to increased risk of chance findings and invalid assumptions of normal distribution. In a secondary analysis of a randomized controlled trial, two approaches using logistic generalized estimating equations (GEE)-planned contrasts and growth curves-were examined for evaluating percent adherence data. Results of the logistic GEE approaches were compared to classical analysis of variance (ANOVA). Robust and bootstrapped estimation was used to obtain empirical standard error estimates. Logistic GEE with either planned contrasts or growth curves in combination with robust standard error estimates was superior to classical ANOVA for detecting intervention effects. The choice of longitudinal model led to key differences in inference. Implications and recommendations for applied researchers are discussed.

Despite substantial increases in the prevalence of adolescent overweight and obesity documented in recent decades, few studies have prospectively tracked their development during the entire adolescent period. The aims of this study were to characterize developmental trends in prevalence, incidence, and remission of overweight and obesity using annual data collected from ages 12 to 19 for 496 adolescent females. Ethnic differences between African American (n = 37), Latina (n = 96), and European American (n = 348) adolescents were also compared. The prevalence of overweight decreased slightly across adolescence and remission rates exceeded incidence (onset). Obesity was more chronic, with increasing incidence accompanied by decreasing remission rates. Middle through late adolescence was the period of greatest risk for the transition from overweight to obesity. African American and Latina females had higher overweight and obesity prevalence than European American females throughout adolescence. Differences in prevalence were driven by higher onset rates for African American and Latina females, whereas remission rates were comparable across ethnic groups. Results suggest that adolescence is not a high-risk period for onset of obesity for European American adolescent females, but is for African American and Latina adolescent females.

3D cell-culture models have recently garnered great attention because they often promote levels of cell differentiation and tissue organization not possible in conventional 2D culture systems. We review new advances in 3D culture that leverage microfabrication technologies from the microchip industry and microfluidics approaches to create cell-culture microenvironments that both support tissue differentiation and recapitulate the tissue-tissue interfaces, spatiotemporal chemical gradients, and mechanical microenvironments of living organs. These 'organs-on-chips' permit the study of human physiology in an organ-specific context, enable development of novel in vitro disease models, and could potentially serve as replacements for animals used in drug development and toxin testing., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Antiretroviral therapy (ART) greatly reduces morbidity and mortality for people with HIV/AIDS. However, for optimal effectiveness patients must achieve strict adherence to dosing regimens, which is difficult to maintain over the long term. Interventions to improve adherence have shown promising results, but with small effects. One explanation for small overall effects is that some patient subgroups are less able to benefit from current interventions; however, this explanation lacks empirical support. This study used multilevel modeling of data from a randomized controlled trial in an exploratory analysis to assess whether patient factors moderated the impact of peer support and pager reminders on ART adherence and biological markers of HIV. According to 272 interaction models using an alpha-corrected significance criteria, none of 34 patient characteristics significantly moderated either intervention. Findings suggest that intervention research might more profitably focus on other ways of improving effects, like individual patient needs, rather than target subgroups.

Mesenchymal condensation is critical for organogenesis, yet little is known about how this process is controlled. Here we show that Fgf8 and Sema3f, produced by early dental epithelium, respectively, attract and repulse mesenchymal cells, which cause them to pack tightly together during mouse tooth development. Resulting mechanical compaction-induced changes in cell shape induce odontogenic transcription factors (Pax9, Msx1) and a chemical cue (BMP4), and mechanical compression of mesenchyme is sufficient to induce tooth-specific cell fate switching. The inductive effects of cell compaction are mediated by suppression of the mechanical signaling molecule RhoA, and its overexpression prevents odontogenic induction. Thus, the mesenchymal condensation that drives tooth formation is induced by antagonistic epithelial morphogens that manifest their pattern-generating actions mechanically via changes in mesenchymal cell shape and altered mechanotransduction., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Many RNAs, proteins, and organelles are present in such low numbers per cell that random segregation of individual copies causes large "partitioning errors" at cell division. Even symmetrically dividing cells can then by chance produce daughters with very different composition. The size of the errors depends on the segregation mechanism: Control systems can reduce low-abundance errors, but the segregation process can also be subject to upstream sources of randomness or spatial heterogeneities that create large errors despite high abundances. Here we mathematically demonstrate how partitioning errors arise for different types of segregation mechanisms and how errors can be greatly increased by upstream heterogeneity but remarkably hard to avoid through controlled partitioning. We also show that seemingly straightforward experiments cannot be straightforwardly interpreted because very different mechanisms produce identical fits and present an approach to deal with this problem by adding binomial counting noise and testing for convexity or concavity in the partitioning error as a function of the binomial thinning parameter. The results lay a conceptual groundwork for more effective studies of heterogeneity among growing and dividing cells, whether in microbes or in differentiating tissues.

We evaluated a nurse-delivered adherence intervention in a preliminary randomized controlled trial among 70 HIV-positive outpatients initiating antiretroviral therapy (ART) in Beijing, China. In both arms, participants received a 30-min educational session, a pillbox, and a referral to a peer support group. In the enhanced arm, participants could choose an electronic reminder device, three sessions of counseling either alone or with a treatment adherence partner, or both reminder and counseling. Survey assessments and blood draws occurred at baseline, post-intervention (13 weeks), and follow-up (25 weeks). Primary outcomes were 7-day and 30-day adherence assessed by self-report and electronic drug monitoring (EDM), and secondary outcomes were HIV-1 RNA viral load and CD4 count. The intervention was feasible and well received. It led to some improvement in self-reported and EDM-assessed adherence but not the biological outcomes. Providing counseling and facilitating the use of electronic reminders to patients initiating ART merits further investigation as a culturally viable means of promoting adherence in China.

The success of highly active antiretroviral therapy (HAART) among persons living with HIV is largely dependent on strict medication adherence. Recent research suggests that alcohol and other drug use (AOD) may be an important barrier to HAART adherence. In this study, we examined the impact of AOD on HAART adherence as well as the moderating effects of general and medication-specific social support. The data were collected as part of a longitudinal randomized control trial with 224 HIV-positive patients at an HIV primary care clinic in the northwestern United States. Findings indicated that AOD use was negatively associated with HAART adherence and that medication-specific (but not general) social support moderated the AOD-adherence association at 3 (but not at 6 or 9) months. Results indicate the importance of medication-specific social support to treat comorbid AOD use and HIV; implications for future research and intervention programs for HIV-positive AOD users are discussed.

Gene expression involves inherently probabilistic steps that create fluctuations in protein abundances. The results from many in-depth analyses and genome-scale surveys have suggested how such fluctuations arise and spread, often in ways consistent with stochastic models of transcription and translation. But fluctuations also arise during cell division when molecules are partitioned stochastically between the two daughters. Here we mathematically demonstrate how stochastic partitioning contributes to the non-genetic heterogeneity. Our results show that partitioning errors are hard to correct, and that the resulting noise profiles are remarkably difficult to separate from gene expression noise. By applying these results to common experimental strategies and distinguishing between creation versus transmission of noise, we hypothesize that much of the cell-to-cell heterogeneity that has been attributed to various aspects of gene expression instead comes from random segregation at cell division. We propose experiments to separate between these two types of fluctuations and discuss future directions.

Background: text-messaging systems have been used to promote a range of health behaviors, including medication adherence among human immunodeficiency virus-positive individuals. However, little is currently known about the specific characteristics of messaging systems that promote user engagement., Objective: using data from a randomized controlled trial involving a pager-based text messaging system, this study sought to examine the overall usability of the system, user evaluation of the system, demographic and psychosocial correlates of usability, and its performance as an adherence assessment tool., Materials and Methods: the messaging system consisted of an alphanumeric pager capable of sending and receiving individualized text messages and the software necessary to program and track communication. The system was evaluated using behavioral outcomes (pager message response rate), self-report survey responses, focus group discussions, and data from electronic medication monitoring pill bottles., Results: Although the majority of participants reported that the system was effective in reminding them to take medication doses, the overall response rate to system messages was relatively low (42.8%) and dropped significantly over the course of the 3-month intervention period. In addition, user engagement did not differ significantly by most demographic and psychosocial variables., Conclusions: the pager-based text messaging system was received well by participants and appears to be applicable to a broad population; however, the system did not actively engage all participants over the course of the trial. Future research should determine whether systems customized to personal preference in notification style, frequency, and user device can increase use and provide further assistance to achieve optimal medication adherence.

Here, we describe a biomimetic microsystem that reconstitutes the critical functional alveolar-capillary interface of the human lung. This bioinspired microdevice reproduces complex integrated organ-level responses to bacteria and inflammatory cytokines introduced into the alveolar space. In nanotoxicology studies, this lung mimic revealed that cyclic mechanical strain accentuates toxic and inflammatory responses of the lung to silica nanoparticles. Mechanical strain also enhances epithelial and endothelial uptake of nanoparticulates and stimulates their transport into the underlying microvascular channel. Similar effects of physiological breathing on nanoparticle absorption are observed in whole mouse lung. Mechanically active "organ-on-a-chip" microdevices that reconstitute tissue-tissue interfaces critical to organ function may therefore expand the capabilities of cell culture models and provide low-cost alternatives to animal and clinical studies for drug screening and toxicology applications.

A direct fabrication method capable of producing fully-reversible, tunable nanochannel arrays, without the use of a molding step, is described. It is based on tunnel cracking of a readily-prepared brittle layer constrained between elastomeric substrates. The resulting nanochannels have adjustable cross-sections that can be reversibly opened, closed, widened and narrowed merely by applying and removing tensile strains to the substrate. This permits reversible trapping and release of nanoparticles, and easy priming or unclogging of the nanochannels for user-friendly and robust operations. The ease of fabrication and operation required to open and close the nanochannels is superior to previous approaches.

We describe a bioinspired microfluidic system that resembles pulmonary airways and enables on-chip generation of airway occluding liquid plugs from a stratified air-liquid two-phase flow. User-defined changes in the air stream pressure facilitated by mechanical components and tuning the wettability of the microchannels enable generation of well-defined liquid plugs. Significant differences are observed in liquid plug generation and propagation when surfactant is added to the buffer. The plug flow patterns suggest a protective role of surfactant for airway epithelial cells against pathological flow-induced mechanical stresses. We discuss the implications of the findings for clinical settings. This approach and the described platform will enable systematic investigation of the effect of different degrees of fluid mechanical stresses on lung injury at the cellular level and administration of exogenous therapeutic surfactants.

Objective: To determine the relative efficacy of peer support and pager messaging strategies versus usual care to improve medication adherence and clinical outcomes among HIV-positive outpatients initiating or switching to a new highly active antiretroviral therapy regimen., Design: A 2 3 2 factorial randomized controlled trial of a 3-month intervention with computer-assisted self-interviews and blood draws administered at baseline, 3, 6, and 9 months., Methods: HIV-positive patients at a public HIV specialty clinic in Seattle,WA (N = 224) were randomly assigned to peer support, pager messaging, both strategies, or usual care. The main outcomes were adherence according to self-report and electronic drug monitoring, CD4 count, and HIV-1 RNA viral load., Results: Intent-to-treat analyses suggested the peer intervention was associated with greater self-reported adherence at immediate postintervention. However, these effects were not maintained at follow-up assessment; nor were there significant differences in biological outcomes. The pager intervention, on the other hand, was not associated with greater adherence but was associated with improved biological outcomes at postintervention that were sustained at follow-up., Conclusions: Analyses indicate the potential efficacy of peer support and pager messaging to promote antiretroviral adherence and biological outcomes, respectively. More potent strategies still are needed.

Angiogenesis is controlled by physical interactions between cells and extracellular matrix as well as soluble angiogenic factors, such as VEGF. However, the mechanism by which mechanical signals integrate with other microenvironmental cues to regulate neovascularization remains unknown. Here we show that the Rho inhibitor, p190RhoGAP (also known as GRLF1), controls capillary network formation in vitro in human microvascular endothelial cells and retinal angiogenesis in vivo by modulating the balance of activities between two antagonistic transcription factors, TFII-I (also known as GTF2I) and GATA2, that govern gene expression of the VEGF receptor VEGFR2 (also known as KDR). Moreover, this new angiogenesis signalling pathway is sensitive to extracellular matrix elasticity as well as soluble VEGF. This is, to our knowledge, the first known functional cross-antagonism between transcription factors that controls tissue morphogenesis, and that responds to both mechanical and chemical cues.

To perform nontrivial, real-time computations on a sensory input stream, biological systems must retain a short-term memory trace of their recent inputs. It has been proposed that generic high-dimensional dynamical systems could retain a memory trace for past inputs in their current state. This raises important questions about the fundamental limits of such memory traces and the properties required of dynamical systems to achieve these limits. We address these issues by applying Fisher information theory to dynamical systems driven by time-dependent signals corrupted by noise. We introduce the Fisher Memory Curve (FMC) as a measure of the signal-to-noise ratio (SNR) embedded in the dynamical state relative to the input SNR. The integrated FMC indicates the total memory capacity. We apply this theory to linear neuronal networks and show that the capacity of networks with normal connectivity matrices is exactly 1 and that of any network of N neurons is, at most, N. A nonnormal network achieving this bound is subject to stringent design constraints: It must have a hidden feedforward architecture that superlinearly amplifies its input for a time of order N, and the input connectivity must optimally match this architecture. The memory capacity of networks subject to saturating nonlinearities is further limited, and cannot exceed square root N. This limit can be realized by feedforward structures with divergent fan out that distributes the signal across neurons, thereby avoiding saturation. We illustrate the generality of the theory by showing that memory in fluid systems can be sustained by transient nonnormal amplification due to convective instability or the onset of turbulence.

Stretching DNA has emerged as a vital process for studying the physical and biological properties of these molecules. Over the past decade, there has been increasing research interest in utilizing nanoscale fluidic channels to confine and stretch single DNA molecules. Nanofabricated systems for linearizing DNA have revealed new and important insights into the conformation changes of DNA molecules. They also have emerged as innovative techniques for efficiently separating DNA molecules based on size and for physically mapping genetic information along the genome. This review describes physical theories of DNA linearization, current DNA stretching techniques based on nanofabricated channels, and breakthroughs resulting from the use of nanofluidic channels for DNA linearization.

Cell culture systems are often static and are therefore nonphysiological. In vivo, many cells are exposed to dynamic surroundings that stimulate cellular responses in a process known as mechanotransduction. To recreate this environment, stretchable cell culture substrate systems have been developed, however, these systems are limited by being macroscopic and low throughput. We have developed a device consisting of 24 miniature cell stretching chambers with flexible bottom membranes that are deformed using the computer-controlled, piezoelectrically actuated pins of a Braille display. We have also developed efficient image capture and analysis protocols to quantify morphological responses of the cells to applied strain. Human dermal microvascular endothelial cells (HDMECs) were found to show increasing degrees of alignment and elongation perpendicular to the radial strain in response to cyclic stretch at increasing frequencies of 0.2, 1, and 5 Hz, after 2, 4, and 12h. Mouse myogenic C2C12 cells were also found to align in response to the stretch, while A549 human lung adenocarcinoma epithelial cells did not respond to stretch.

We describe a microfabricated airway system integrated with computerized air-liquid two-phase microfluidics that enables on-chip engineering of human airway epithelia and precise reproduction of physiologic or pathologic liquid plug flows found in the respiratory system. Using this device, we demonstrate cellular-level lung injury under flow conditions that cause symptoms characteristic of a wide range of pulmonary diseases. Specifically, propagation and rupture of liquid plugs that simulate surfactant-deficient reopening of closed airways lead to significant injury of small airway epithelial cells by generating deleterious fluid mechanical stresses. We also show that the explosive pressure waves produced by plug rupture enable detection of the mechanical cellular injury as crackling sounds.

Fluidic transport through nanochannels offers new opportunities to probe fundamental nanoscale transport phenomena and to develop tools for manipulating DNA, proteins, small molecules and nanoparticles. The small size of nanofabricated devices and the accompanying increase in the effect of surface forces, however, pose challenges in designing and fabricating flexible nanofluidic systems that can dynamically adjust their transport characteristics according to the handling needs of various molecules and nanoparticles. Here, we describe the use of nanoscale fracturing of oxidized poly(dimethylsiloxane) to conveniently fabricate nanofluidic systems with arrays of nanochannels that can actively manipulate nanofluidic transport through dynamic modulation of the channel cross-section. We present the design parameters for engineering material properties and channel geometry to achieve reversible nanochannel deformation using remarkably small forces. We demonstrate the versatility of the elastomeric nanochannels through tuneable sieving and trapping of nanoparticles, dynamic manipulation of the conformation of single DNA molecules and in situ photofabrication of movable polymeric nanostructures.

The formation of spherical aggregates of cells called embryoid bodies (EBs) is an indispensable step in many protocols in which embryonic stem (ES) cells are differentiated to other cell types. Appropriate morphology and embryo size are critical for the sequential developmental stages of naturally conceived embryos. Likewise, regulating the size of EBs and the timing of their formation is crucial for controlling the differentiation of ES cells within the EB. Existing methods of formation of EBs, however, are tedious or provide heterogeneously-sized EBs. Here we describe a microfluidic system for straightforward synchronized formation of uniform-sized EBs, the size of which can be controlled by changing the cross-sectional size of microchannels in the microfluidic device. The device consists of two microchannels separated by a semi-porous polycarbonate membrane treated to be resistant to cell adhesion. ES cells introduced into the upper channel self-aggregate to form uniformly-sized EBs. The semi-porous membrane also allows subsequent treatment of the non-attached EBs with different reagents from the lower channel without the need for wash out because of the compartmentalization afforded by the membrane. This method provides a simple yet robust means to control the formation of EBs and the subsequent differentiation of ES cells in a format compatible for ES cell processing on a chip.

The integration of semiporous membranes into poly(dimethylsiloxane) (PDMS) microfluidic devices is useful for mass transport control. Several methods such as plasma oxidation and manual application of PDMS prepolymer exist to sandwich such membranes into simple channel structures, but these methods are difficult to implement with reliable sealing and no leakage or clogging for devices with intricate channel features. This paper describes a simple but robust strategy to bond semiporous polyester and polycarbonate membranes between layers of PDMS microchannel structures effectively without channel clogging. A thin layer of PDMS prepolymer, spin-coated on a glass slide, is transferred to PDMS substrates with channel features as well as to the edges of the semiporous membrane by stamping. This thin PDMS prepolymer serves as "mortar" to strongly bond the two PDMS layers and seal off the crevices generated from the thickness of the membranes. This bonding method enabled the fabrication of an 8x12 criss-crossing microfluidic channel array with 96 combinations of fluid interactions. The capability of this device for bioanalysis was demonstrated by measuring responses of cells to different color fluorescent reagents.

This paper describes a simple microfluidic sorting system that can perform size profiling and continuous mass-dependent separation of particles through combined use of gravity (1 g) and hydrodynamic flows capable of rapidly amplifying sedimentation-based separation between particles. Operation of the device relies on two microfluidic transport processes: (i) initial hydrodynamic focusing of particles in a microchannel oriented parallel to gravity and (ii) subsequent sample separation where positional difference between particles with different mass generated by sedimentation is further amplified by hydrodynamic flows whose streamlines gradually widen out due to the geometry of a widening microchannel oriented perpendicular to gravity. The microfluidic sorting device was fabricated in poly(dimethylsiloxane), and hydrodynamic flows in microchannels were driven by gravity without using external pumps. We conducted theoretical and experimental studies on fluid dynamic characteristics of laminar flows in widening microchannels and hydrodynamic amplification of particle separation. Direct trajectory monitoring, collection, and post-analysis of separated particles were performed using polystyrene microbeads with different sizes to demonstrate rapid (<1 min) and high-purity (>99.9%) separation. Finally, we demonstrated biomedical applications of our system by isolating small-sized (diameter <6 microm) perfluorocarbon liquid droplets from polydisperse droplet emulsions, which is crucial in preparing contrast agents for safe, reliable ultrasound medical imaging, tracers for magnetic resonance imaging, or transpulmonary droplets used in ultrasound-based occlusion therapy for cancer treatment. Our method enables straightforward, rapid, real-time size monitoring and continuous separation of particles in simple stand-alone microfabricated devices without the need for bulky and complex external power sources. We believe that this system will provide a useful tool to separate colloids and particles for various analytical and preparative applications and may hold potential for separation of cells or development of diagnostic tools requiring point-of-care sample preparation or testing.

This study tested the hypothesis that perceived parenting would show reciprocal relations with adolescents' problem behavior using longitudinal data from 496 adolescent girls. Results provided support for the assertion that female problem behavior has an adverse effect on parenting; elevated externalizing symptoms and substance abuse symptoms predicted future decreases in perceived parental support and control. There was less support for the assertion that parenting deficits foster adolescent problem behaviors; initially low parental control predicted future increases in substance abuse, but not externalizing symptoms, and low parental support did not predict future increases in externalizing or substance abuse symptoms. Results suggest that problem behavior is a more consistent predictor of parenting than parenting is of problem behavior, at least for girls during middle adolescence.

This review describes recent developments in microfabricated flow cytometers and related microfluidic devices that can detect, analyze, and sort cells or particles. The high-speed analytical capabilities of flow cytometry depend on the cooperative use of microfluidics, optics and electronics. Along with the improvement of other components, replacement of conventional glass capillary-based fluidics with microfluidic sample handling systems operating in microfabricated structures enables volume- and power-efficient, inexpensive and flexible analysis of particulate samples. In this review, we present various efforts that take advantage of novel microscale flow phenomena and microfabrication techniques to build microfluidic cell analysis systems.

This work is the first demonstration of electrical modulation of surface energy to reversibly switch dynamic high-speed gas-liquid two-phase microfluidic flow patterns. Manipulation of dynamic two-phase systems with continuous high-speed flows is complex and interesting due to the multiple types of forces that need to be considered. Here, distinct stable flow patterns are formed through a multipronged approach: both surface tension forces generated by surface chemistry modulation as well as viscous and inertial forces produced by fluid flows are employed. The novel fluidic actuation mechanism provides insights into better understanding microscale two-phase flow dynamics and offers new opportunities for the development of two-phase biochemical microsystems that are mechanically simple and operational at high speeds.

The emergence of multi-drug resistant gram-positive cocci such as methicillin-resistant (MR) staphylococci, vancomycin-resistant (VR) enterococci, and vancomycin-intermediate resistant S. aureus (VISA) has given new urgency to the development of new antimicrobial agents. One of these is quinupristin/dalfopristin (Q/D). We decided to determine the susceptibility of gram-positive cocci isolated at two university hospitals in Seoul to Q/D and compare the results with eight other antimicrobial agents. We investigated 120 isolates of S. aureus including 49 MRSAs and one VISA, 120 isolates of coagulase negative staphylococci (CNS), 64 E. faecalis and 56 E. faecium, including seven strains of VR E. faecium. Minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) for several antimicrobials, including vancomycin and Q/D, were determined by broth microdilution. All S. aureus including VISA were susceptible to Q/D. Q/D MIC90 for both methicillin-susceptible S. aureus (MSSA) and MRSA was 0.25 g/mL. 49 (87.5%) of 56 E. faecium including six of seven VR E. faecium were susceptible to Q/D. E. faecalis were not susceptible to Q/D (only 1.5% susceptible), but were inhibited by ampicillin (94% susceptible) or vancomycin (95%). CNS was susceptible to Q/D (96% susceptible) and vancomycin (100% susceptible). One of 38 staphylococci and two of 17 E. faecium were tolerant to Q/D. In conclusion, Q/D showed excellent activity against all species of gram-positive cocci including MRSA, VISA, and VR E. faecium except E. faecalis, and may provide a valuable option for the treatment of infections caused by these emerging nosocomial pathogens of gram-positive cocci.

We applied infrequent-restriction-site PCR (IRS-PCR) to the investigation of an outbreak caused by 23 isolates of Acinetobacter baumannii in an intensive care unit from November 1996 to May 1997 and a pseudoepidemic caused by 16 isolates of Serratia marcescens in a delivery room from May to September 1996. In the epidemiologic investigation of the outbreak caused by A. baumannii, environmental sampling and screening of all health care workers revealed the same species from the Y piece of a mechanical ventilator and the hands of two health care personnel. IRS-PCR showed that all outbreak-related strains were genotypically identical and that three strains from surveillance cultures were also identical to the outbreak-related strains. In a pseudoepidemic caused by S. marcescens, IRS-PCR identified two different genotypes, and among them one genotype was predominant (15 of 16 [93.8%] isolates). Extensive surveillance failed to find any source of S. marcescens. Validation of the result of IRS-PCR by comparison with that of field inversion gel electrophoresis (FIGE) showed that they were completely concordant. These results suggest that IRS-PCR is comparable to FIGE for molecular epidemiologic studies. In addition, IRS-PCR was less laborious and less time-consuming than FIGE. To our knowledge, this is the first report of the application of IRS-PCR to A. baumannii and S. marcescens.

The benefits of radio-chemotherapy in HIV-negative primary central nervous system (CNS) lymphomas were analyzed in 40 patients, who received radiotherapy to the brain or craniospinal axis with the total dose of 4460-5940 cGy to the primary tumor. Radiotherapy was followed by systemic chemotherapy, mainly with the cyclophosphamide, doxorubicin, vincristine and prednisolone (CHOP) regimen, in 16 of the patients. Follow-up ranged from four to 95 months with a median of 15 months. The relapse rate was 72.5%, and 83% of the relapses occurred within the radiation field. Median survival was 19 months and the two-year survival rate was 41%. Survival was significantly influenced by treatment method and radiation dose when measured by univariate analysis; median survival and the two-year survival rate was 29 months and 63% after radio-chemotherapy, while 13.5 month and 29% after radiotherapy alone (p= 0.027), and 22 months and 49% with doses of 50 Gy or more, but 12.5 months and 13% with doses less than 50 Gy (p=0.009). However, statistical significance was lost in multivariate analysis. These results might suggest the short-term efficacy of radio-chemotherapy, however, cautious observation is needed to confirm long-term effects.

We analyzed the fluoroquinolone resistance mechanism of 28 isolates of ciprofloxacin-resistant E. coli from patients who received ciprofloxacin as a regimen of a selective gut decontamination. Isolates distinctive by infrequent restriction site polymerase chain reaction (IRS-PCR) were subjected to Hinf I restriction fragment length polymorphism analysis, single-stranded conformation polymorphism (SSCP), and nucleotide sequencing of the quinolone resistance determining region (QRDR) in gyrA. Double mutations in QRDR of gyrA (Ser83 Leu and Asp87Asn) were found from most of the strains. Nucleotide sequencing of the marR locus showed that 18 out of 28 (64%) ciprofloxacin-resistant E. coli strains had three types of base change in marR loci: a double-base change at nucleotides 1628 and 1751, or 1629 and 1751: and a single-base change at 1751. However, all the mutated strains showed no tolerance to cyclohexane test, suggesting the mutation in the marR region had no influence on overexpression of the MarA protein. In conclusion, mutation in gyrA was the main mechanism of ciporfloxacin resistance in E. coli from patients with selective gut decontamination. Therefore, mutation in the mar region did not influence the levels of ciprofloxacin resistance in our isolates.

We analyzed an outbreak of Escherichia coli bacteremia in eight patients with leukemia in a hematology-oncology unit from July to September 1994. The antibiograms and genotypic patterns of the isolates were different, thus suggesting that the outbreak did not originate from a single clone. However, all the isolates were resistant to quinolones, which led us to examine the microbiological records from 1992 to 1994. The incidence of quinolone-resistant E. coli bacteremia in the hematology-oncology unit ranged from 81.8% to 94.6% during this period. We then analyzed 36 more isolates recovered from late 1994 to 1995. Field inversion gel electrophoresis patterns of these isolates were also different. Analysis of the quinolone resistance determining region in gyrA revealed that all the isolates had a double mutation in gyrA. In conclusion, quinolone-resistant E. coli could be an emerging threat to neutropenic patients with leukemia who receive a quinolone prophylactically, and attention must be paid to this trend of resistance.