Pyloromyotomy through circumbilical incision with fascial extension.

Extending the fascial incision underlying the circumbilical approach to the shape of an 'inverted T' permits easy delivery of the pyloric tumour for Ramstedt's pyloromyotomy. This modification was used in 51 consecutive infants (42 male, 9 female) with a mean age of 4.7 weeks. Extension of the skin incision or conversion to the right hypochondrium approach was not necessary in any patient and the mean operating time was 31.4 min. Mild wound infection occurred in two infants (3.9%) that resolved with antibiotic treatment. Follow-up at 3 months did not detect any incisional hernia. This modification allows delivery of small or large pyloric tumours, is associated with a low rate of wound infection and does not alter the excellent cosmetic finish.

Endothelial, cardiac muscle and skeletal muscle exhibit different viscous and elastic properties as determined by atomic force microscopy.

This study evaluated the hypothesis that, due to functional and structural differences, the apparent elastic modulus and viscous behavior of cardiac and skeletal muscle and vascular endothelium would differ. To accurately determine the elastic modulus, the contribution of probe velocity, indentation depth, and the assumed shape of the probe were examined. Hysteresis was observed at high indentation velocities arising from viscous effects. Irreversible deformation was not observed for endothelial cells and hysteresis was negligible below 1 microm/s. For skeletal muscle and cardiac muscle cells, hysteresis was negligible below 0.25 microm/s. Viscous dissipation for endothelial and cardiac muscle cells was higher than for skeletal muscle cells. The calculated elastic modulus was most sensitive to the assumed probe geometry for the first 60 nm of indentation for the three cell types. Modeling the probe as a blunt cone-spherical cap resulted in variation in elastic modulus with indentation depth that was less than that calculated by treating the probe as a conical tip. Substrate contributions were negligible since the elastic modulus reached a steady value for indentations above 60 nm and the probe never indented more than 10% of the cell thickness. Cardiac cells were the stiffest (100.3+/-10.7 kPa), the skeletal muscle cells were intermediate (24.7+/-3.5 kPa), and the endothelial cells were the softest with a range of elastic moduli (1.4+/-0.1 to 6.8+/-0.4 kPa) depending on the location of the cell surface tested. Cardiac and skeletal muscle exhibited nonlinear elastic behavior. These passive mechanical properties are generally consistent with the function of these different cell types.

Total internal reflection microscopy and atomic force microscopy (TIRFM-AFM) to study stress transduction mechanisms in endothelial cells.

The cytoskeleton plays a key role in providing strength and structure to the cell. A force balance exists between the cytoskeleton and the extracellular matrix/substratum via the focal contact regions. The purpose of this study is to integrate atomic force microscopy (AFM) and total internal reflection fluorescence microscopy (TIRFM) data to determine the effect of localized force application over the cell surface on the cell's focal contacts size and position. TIRFM gives detailed information on the cell-substrate contact regions and AFM is a tool for elasticity measurements, force application, and topographic surface mapping of the cell. TIRFM data were calibrated by varying the intensity of the evanescent wave to change the interfacial angle at the glass-cell interface. The individual focal contact intensity was found to decrease with increasing interfacial angles from 66 degrees to 80 degrees as the depth of penetration varied from 150 to 66 nm. A measure of cellular mechanical properties was obtained by collecting a set of force curves over the entire cell using the Bioscope AFM. The nuclear region appears to be stiffer than the cell body. Preliminary results of the nanonewtons force application to the cell surface indicate that the cell-substrate contacts rearrange to offset the force. It is evident that the stress applied to the surface is transmitted to the cell-substrate contact region.

Atomic force and total internal reflection fluorescence microscopy for the study of force transmission in endothelial cells.

This paper describes the combined use of atomic force microscopy (AFM) and total internal reflection fluorescence microscopy (TIRFM) to examine the transmission of force from the apical cell membrane to the basal cell membrane. A Bioscope AFM was mounted on an inverted microscope, the stage of which was configured for TIRFM imaging of fluorescently labeled human umbilical vein endothelial cells (HUVECs). Variable-angle TIRFM experiments were conducted to calibrate the coupling angle with the depth of penetration of the evanescent wave. A measure of cellular mechanical properties was obtained by collecting a set of force curves over the entire apical cell surface. A linear regression fit of the force-indentation curves to an elastic model yields an elastic modulus of 7.22 +/- 0. 46 kPa over the nucleus, 2.97 +/- 0.79 kPa over the cell body in proximity to the nucleus, and 1.27 +/- 0.36 kPa on the cell body near the edge. Stress transmission was investigated by imaging the response of the basal surface to localized force application over the apical surface. The focal contacts changed in position and contact area when forces of 0.3-0.5 nN were applied. There was a significant increase in focal contact area when the force was removed (p < 0.01) from the nucleus as compared to the contact area before force application. There was no significant change in focal contact coverage area before and after force application over the edge. The results suggest that cells transfer localized stress from the apical to the basal surface globally, resulting in rearrangement of contacts on the basal surface.

In vivo biocompatibility and biostability of modified polyurethanes.

Modified segmented polyurethanes were examined for biostability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS endcapped polyether polyurethane (SPU-S), and two polycarbonate polyurethanes (SPU-PCU and SPU-C) were investigated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress-strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively describe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC densities and cell coverage on SPU-S were attributed to the hydrophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attributed to hydrolysis of the carbonate linkage.