Microelectrophoresis in a laser trap: a platform for measuring electrokinetic interactions and flow properties within microstructures.

We describe a combination of microelectrophoresis and laser-trap methodology to accurately measure the electric force acting on a charged microsphere which is trapped in an optical tweezer. This field/trap apparatus allows measuring of the zeta potential with submillivolt accuracy and high temporal resolution. The combination with stop-flow techniques in principle provides a mean to observe adsorption or enzyme kinetics with single molecule sensitivity. We show that it is possible to accurately profile the position and frequency dependent hydrodynamic and electro-osmotic flow inside a microchannel structure of dimensions typically used in microfluidic applications without the need of fluorescent markers. We found good agreement to the theory of electrophoretic flow when retardation effects for rapidly alternating electric fields are included.

[Ultrasonographic evaluation of the rotator cuff after shoulder arthroplasty]. / Sonographie der Rotatorenmanschette nach Schulter-Endoprothese.

AIM: Ultrasonography of the rotator cuff tendons is a standard imaging technique. Although increasing numbers of shoulder arthroplasty are performed, there is no available data concerning the use of ultrasound after shoulder replacement. Our experimental study was performed to analyse the value of ultrasonography after shoulder arthroplasty a) in an ex-vivo-setting and b) in a retrospective analysis of our patients after shoulder hemiprothesis. METHOD: After defrosting, anatomic modular humeral head replacement was performed in four fresh-frozen specimens with intact rotator cuffs. The supraspinatus and subscapularis tendons of each specimen were either detached to simulate a cuff defect or reattached anatomically (four times per specimen). Two experienced examiners then performed ultrasonography to evaluate the two tendons to be either intact or deficient. In a retrospective study, 22 patients with 25 hemiprotheses of the shoulder underwent clinical and sonographic examination. For documentation of the clinical findings, the Constant score was used. RESULTS: In the cadaver study, the reliability of the method was slightly higher for the subscapularis tendon (13 correct, 3 false results) than for the supraspinatus tendon (12 correct, 4 false results). In our patients, rotator cuff defects and effusions around the biceps tendon and in the subdeltoid bursa could be detected. Normal sonograms correlated with good clinical results. CONCLUSION: In the cadaver study, we found a good reproducibility of in-vivo conditions. We believe that ultrasonography is beneficial in follow-up evaluation after shoulder arthroplasty.

The value of ultrasound after shoulder arthroplasty.

OBJECTIVE: This study was undertaken to evaluate whether sonography is a useful tool in the diagnosis of soft tissue disorders as a possible cause for discomfort and/or pain after shoulder arthroplasty. DESIGN AND PATIENTS: Static and dynamic ultrasound examinations were performed in the standard sectional planes on 22 patients with 25 hemiprostheses and the results were correlated with the clinical outcome. The stability was determined in the transverse and frontal planes and the clinical results were evaluated according to the Constant and Swanson scores. RESULTS: Several pathological changes were detected: rotator cuff lesions, subdeltoid bursitis, changes around the long biceps tendon as well as an increase in intra-articular volume due to effusion and/or synovitis. The correlation of sonographic and clinical results demonstrated that patients with an excellent clinical result showed no or only a few pathological findings on sonography compared with those with a moderate or poor result. CONCLUSION: Pathological changes of the periarticular tissue in the direct neighbourhood of the implant can be detected by sonography, which can be recommended as a valuable examination technique to evaluate the soft tissue in patients after shoulder arthroplasty.

Microelectrophoresis of a bilayer-coated silica bead in an optical trap: application to enzymology.

We describe an apparatus that combines microelectrophoresis and laser trap technologies to monitor the activity of phosphoinositide-specific phospholipase C-delta1 (PLC-delta) on a single bilayer-coated silica bead with a time resolution of approximately 1 s. A 1-microm-diameter bead was coated with a phospholipid bilayer composed of electrically neutral phosphatidylcholine (PC) and negatively charged phosphatidylinositol 4,5-bisphosphate (2% PIP2) and captured in a laser trap. When an AC field was applied (160 Hz, 20 V/cm), the electrophoretic force produced a displacement of the bead, Delta(x), from its equilibrium position in the trap; Delta(x), which was measured using a fast quadrant diode detector, is proportional to the zeta potential and thus to the number of PIP2 molecules on the outer leaflet (initially, approximately 10(5)). When a solution containing PLC-delta flows past the bead, the enzyme adsorbs to the surface and hydrolyzes PIP2 to form the neutral lipid diacylglycerol. We observed a nonexponential decay of PIP2 on the bead with time that is consistent with a model based on the known structural properties of PLC-delta.

Serum sperm agglutinating antibody formation in vasectomized men treated with dexamethasone.

The effect of immunosuppression with dexamethasone on sperm antibody formation following vasectomy in men was determined. Vasectomized men were treated with dexamethasone (4 mg) tablets starting two days prior to vasectomy and each day thereafter for a total of eight days for a total dose of 30 mg. There was no significant difference in serum sperm agglutinating antibody, cholesterol, triglycerides, or lipoproteins between the dexamethasone and placebo groups. The finding that immunosuppression at the time of vasectomy did not inhibit sperm antibody formation in man was surprising because in a similar study with Cynomoglus monkeys treatment at the time of vasectomy with dexamethasone inhibited sperm antibody development. The difference between the two studies may be that in monkeys sperm antigen presentation comes at the time of vasectomy and therefore immunosuppression at this time can prevent an immune response, but in man sperm antigen presentation comes at some later time following vasectomy. This species difference in sperm antigen presentation following vasectomy in man compared to monkeys may affect subsequent atherosclerosis development and explain why no cardiovascular disease is found in man following vasectomy.