Observation of chemically protected polydimethylsiloxane: towards crack-free PDMS.

The current modification of polydimethylsiloxane (PDMS) substrates via oxygen plasma treatment causes surface cracks. Here, we demonstrate a method to prevent crack formation by chemical treatment. Chemical modification renders the surface hydrophilic for several days and is effective in preserving the elasticity of the PDMS surface at the nanoscale level.

Inkjet printing of UV-curable adhesive and dielectric inks for microfluidic devices.

Bonding of polymer-based microfluidics to polymer substrates still poses a challenge for Lab-On-a-Chip applications. Especially, when sensing elements are incorporated, patterned deposition of adhesives with curing at ambient conditions is required. Here, we demonstrate a fabrication method for fully printed microfluidic systems with sensing elements using inkjet and stereolithographic 3D-printing.

Nanostructured gold microelectrodes for extracellular recording from electrogenic cells.

We present a new biocompatible nanostructured microelectrode array for extracellular signal recording from electrogenic cells. Microfabrication techniques were combined with a template-assisted approach using nanoporous aluminum oxide to develop gold nanopillar electrodes. The nanopillars were approximately 300-400 nm high and had a diameter of 60 nm. Thus, they yielded a higher surface area of the electrodes resulting in a decreased impedance compared to planar electrodes. The interaction between the large-scale gold nanopillar arrays and cardiac muscle cells (HL-1) was investigated via focused ion beam milling. In the resulting cross-sections we observed a tight coupling between the HL-1 cells and the gold nanostructures. However, the cell membranes did not bend into the cleft between adjacent nanopillars due to the high pillar density. We performed extracellular potential recordings from HL-1 cells with the nanostructured microelectrode arrays. The maximal amplitudes recorded with the nanopillar electrodes were up to 100% higher than those recorded with planar gold electrodes. Increasing the aspect ratio of the gold nanopillars and changing the geometrical layout can further enhance the signal quality in the future.

Limitations of score-based daily outcome predictions in the individual intensive care patient. An example of the RIAHDH algorithm.

OBJECTIVE: The nature of score-based predictions is probabilistic, and their accuracy depends on the reliability and validity of the applied system. As an example, the present study investigates the accuracy of the RIP-algorithm (RIP = Riyadh Intensive Care Program) based on daily APACHE II scores, and compares it with published results of that algorithm from other investigators. DESIGN: Prospective observational study and review of the literature. PATIENTS AND METHODS: 1,986 consecutive admissions of 1,808 patients to a surgical intensive care unit were documented. Daily changes of score values were used to derive a risk of death estimation. Sensitivity and the rate of false predictions were calculated for score-based predictions. Health status one year after discharge was assessed in survivors predicted to die. RESULTS: Daily application of the algorithm identified 109 situations leading to death predictions in 56 patients. Five of these patients were discharged alive from the hospital (positive predictive value 91%). One year later 3 of these patients were still alive. The algorithm identified 51 of the non-survivors (sensitivity 19%), 110 died in the ICU without prediction. Altogether 270 patients died during their hospital stay. Among the 6 independent validation studies, similar results were found, but differences occurred due to the problematic assessment of consciousness. CONCLUSIONS: Sequential assessment of scores in intensive care could identify high risk patients, but with some degree of uncertainty. Therefore, the scores should only be used by those familiar with their limitations and risks.

Cell detachment method using shock-wave-induced cavitation.

The detachment of adherent HeLa cells from a substrate after the interaction with a shock wave is analyzed. Cavitation bubbles are formed in the trailing, negative pressure cycle following the shock front. We find that the regions of cell detachment are strongly correlated with spatial presence of cavitation bubbles. It is shown that the cavitation bubble collapse generates a transient high-speed flow along the substrate surface leading to rapid detachment of the cells. Flow trajectories are reconstructed from the video recordings using robust image-processing methods. From these trajectories, an estimate of the shear stress acting on the cells is obtained and the area of detachment is estimated with a kinetic model. Furthermore, it is suggested that the application of shock waves extends the known methods of cell detachment with the ability to control the process in space and time.

Luminescence of transient bubbles at elevated ambient pressures.

The light emission of transient laser-produced cavitation bubbles in water is investigated in a range of ambient pressures up to 5 bar and laser energies up to 30 mJ. At elevated pressures bubble luminescence can be increased more than two fold for bubbles created with the same laser energy, and up to almost an order of magnitude comparing bubbles of the same maximum radius. Both the conversion of large laser energies into mechanical energy of the bubble, and the conversion of mechanical energy into light are improved at higher pressure.