Fabrication and laser patterning of polystyrene optical oxygen sensor films for lab-on-a-chip applications.

We present a novel and simple method for patterning oxygen-sensitive polystyrene thin films and demonstrate its potential for integration with microfluidic lab-on-a-chip devices. Optical oxygen sensing films composed of polystyrene with an embedded luminescent oxygen-sensitive dye present a convenient option for the measurement of oxygen levels in microfluidic and lab-on-a-chip devices; however, patterning and integrating the films with poly(dimethylsiloxane) (PDMS) microfluidic devices has proven difficult due to a residue after dry etch patterning that inhibits subsequent PDMS bonding. Our new method uses mask-less laser ablation by a commercial laser ablation system to define the outline of the structures and subsequent bulk film removal by aqueous lift-off. Because the bulk film is peeled or lifted off of the substrate rather than etched, the process is compatible with standard PDMS plasma bonding. We used ToF-SIMS analysis to investigate how laser ablation facilitates this fabrication process as well as why dry etching polystyrene inhibits PDMS plasma bonding. The results of this analysis showed evidence of chemical species formed during the laser ablation and dry etching processes that can produce these effects. Our new method's mask-less nature, simplicity, speed, and compatibility with PDMS bonding make it ideally suited for single-use lab-on-a-chip applications. To demonstrate the method's compatibility with PDMS microfluidics, we also present a demonstration of the sensors' integration into a microfluidic oxygen gradient generator device.

Microfluidic system for controlled gelation of a thermally reversible hydrogel.

The integration of cell culture and characterization onto a miniaturized platform promises to benefit many applications such as tissue engineering, drug screening, and those involving small, precious cell populations. This paper presents the controlled on-chip gelation of a thermally-reversible hydrogel. Channel design and flowrate control are crucial in determining hydrogel geometry, while integrated temperature control triggers reversible gel formation. Formation of hydrogel droplets through shearing of immiscible flows is demonstrated with subsequent on-chip gelation. The temperature of phase transition occurs between 32degC-34degC, well within the range for mammalian cell encapsulation and culture.

Internal modification of poly(dimethylsiloxane) microchannels with a borosilicate glass coating.

We report on an original technique for the in situ coating of poly(dimethylsiloxane) (PDMS) microchannels with borosilicate glass, starting from an active nonaqueous and alkali-free precursor solution. By chemical reaction of this active solution inside the microchannel and subsequent thermal annealing, a protective and chemically inert glass borosilicate coating is bonded to the PDMS. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and nuclear magnetic resonance spectroscopy of the active solution show that it is composed of a silicon oxide network with boron connectivity. Thermal gravimetric analysis demonstrates the absence of organic content when curing is done above 150 degrees C. The borosilicate nature of the glass coating covalently bonded to the PDMS is demonstrated using ATR-FTIR spectroscopy and X-ray photoelectron spectroscopy. Atomic force microscopy and scanning electron microscopy show a smooth and crack-free coating. The latter is used as an efficient protective barrier against diffusion in PDMS of fluorescent rhodamine B dye that is dissolved either in water or in toluene. Moreover, the coating prevents swelling and consequent structural damage of the PDMS when the latter is exposed to harsh chemicals such as toluene.

Success of ERCP at a referral center after a previously unsuccessful attempt.

BACKGROUND: The diagnostic and therapeutic success of endoscopic retrograde cholangiopancreatography (ERCP) depends on a number of factors. When an attempt at ERCP fails, the physician must decide whether to repeat the procedure, rely on another imaging procedure (noninvasive or invasive), or refer to another endoscopist/center. Our aim in this prospective study was to determine the role of a second attempt at ERCP at a referral ERCP center. METHODS: Five hundred sixty-two patients were referred for ERCP after having undergone a previous unsuccessful attempt to visualize the clinically relevant duct(s). RESULTS: The overall success in visualizing the desired duct was 96.4% (542 of 562). Advanced techniques for cannulation were used in 41% (229 of 562). Anatomic abnormalities possibly contributing to the previous lack of success were present in 27% of cases. ERCP with or without manometry identified a cause or potential cause for the signs and symptoms in 86% of patients. Sixty complications occurred in 57 patients (10.1%). ERCP was unsuccessful in 20 patients (3.6%). CONCLUSIONS: The cannulation success rate and diagnostic yield of further ERCP with an acceptable complication rate warrant consideration of referral to centers with available resources and expertise.

Triple-tissue sampling at ERCP in malignant biliary obstruction.

BACKGROUND: Procurement of cytologic samples by brushing is common practice at endoscopic retrograde cholangiopancreatography (ERCP) but has low sensitivity for cancer detection. Limited data are available on other techniques, including endoluminal fine-needle aspiration and forceps biopsy. This series reviews the yield of these three stricture sampling methods. METHODS: In this prospective study, patients with biliary obstruction with a clinical suspicion of malignancy underwent triple-tissue sampling at one ERCP session. Final cancer diagnosis was based on all sampling methods plus surgery, autopsy, and clinical follow-up. Tissue specimens were reported as normal, atypia, or malignant. RESULTS: A total of 133 patients were evaluated: 104 had cancer and 29 had benign strictures. Tissue sampling sensitivity varied according to the type of cancer; the highest yield was seen in ampullary cancers (62% to 85%). The cumulative sensitivity of triple-tissue sampling in the cancer patients was as follows: sensitivity was 52% if atypia was considered benign and 77% if it was considered malignant. The addition of a second or third technique increased sensitivity rates in most instances. No serious complications occurred from the tissue sampling methods. CONCLUSIONS: Tissue sampling sensitivity varied according to the type of cancer. Combining a second or third method increased sensitivity; general use of at least two sampling methods is therefore recommended.