Quantifying the dimensions of nanoscale organic surface layers in natural waters.

Nanoscale surface films are known to develop on surfaces exposed to natural waters and have potential impacts on many environmental processes. A new method using atomic force microscopy is presented which physically removes the developed film in a defined area and then quantifies the difference in height between the film and the area where the film has been removed. The difference gives the absolute thickness of the surface film, which has not previously been measured. Suwannee River humic acid was exposed to substrates, and the surface film thickness as a function of pH and exposure time was measured. Discrete and very small colloids in the range 1-5 nm were observed as expected, and these sat on a coherent surface film, notthe original mica substrate. Low pH values of 2 gave rise to relatively thick surface films of about3 nm, although these films were not continuous at higher pH values. At pH 4.8, the film thickness increased with exposure time up to about 5 h and did not subsequently increase. The maximum film thickness measured was about 1 nm at that pH. The method is applicable to the measurement of many environmental surfaces, although resolution will depend on the substrate and film roughness.

Characterization of freshwater natural aquatic colloids by atomic force microscopy (AFM).

Atomic force microscopy (AFM) has been used to image and quantify riverine colloids in a quantitative and relatively nonperturbing manner. Three main classes of material have been imaged including fibrils (about 10 nm in diameter and 100 nm or more in length), discrete, near-spherical, small colloids primarily below 30-50 nm in diameter, and a surface film, of at least several nanometers thickness, which coatsthe entire mica surface within 30 min of exposure to river water. Colloid structure was found to vary as a function of pH, particularly at high pH. Substantially different structures were observed at high pH values, with the loss of the near-spherical colloids possibly due to rearrangement and aggregation. In addition,film thicknesses of up to 100 nm were estimated on the silicon nitride AFM cantilever after 30 h of deposition in the same water (unperturbed and size fractionated). The observation of these surface films has important implications for understanding the mechanisms by which colloids might bind trace elements. In particular, development of surface coatings implies that binding of pollutants (at least initial surface binding) may be dominated by adsorbed surface layers.

Imaging and force-distance analysis of human fibroblasts in vitro by atomic force microscopy.

The structure of human fibroblasts have been characterised in vitro by atomic force microscopy (AFM) operated in the imaging or in the force versus distance (F-d) modes. The choice of cell substrate is important to ensure good adhesion. Of greater significance in the context of AFM analysis, is the observation that the substrate affects the imaging conditions for in vitro analysis of live cells. For instance, very rarely will glass coverslips lead to acceptable outcomes (i.e., resolved cytoskeletal structure). Activated tissue culture dishes, on the other hand, promote conditions that routinely result in good quality images. Those conditions are then unaffected by adoption of relatively high force loadings (more than 10 nN), large fields of view (100 x 100 microm2) and high scan speeds (up to ca. 200 microm/sec), all of which exceed values recommended in the literature. Plasma membranes are fragile in the context of AFM analysis (F-d analysis gives an equivalent Young's Modulus of ca. 5 kPa). However, the present work suggests that fragility per se need not be a problem, rather it is the adhesive interactions with the tip, which under some circumstances may exceed 20 nN, that are the source of poor imaging conditions. The present results, being supported by a qualitative model, suggest that the activated substrate acts as a preferential scavenger of cellular debris thus preventing the tip from biofouling, and will therefore promote low adhesion between tip and membrane. Good imaging conditions provide non-destructive in vitro information about cytoskeletal structure and dynamics, as shown in two examples concerned with cytochalasin treatment and with the MTT assay.

Transcondylar fractures of the distal humerus.

We classify transcondylar fractures of the distal humerus into four groups: undisplaced; simple displaced; T-type; and fracture dislocations (Posada's fracture). Our treatment of these fractures is based upon this classification. Undisplaced fractures are treated with immobilization. Displaced fractures are reduced and stabilized with internal fixation. Stabilization of these fractures is difficult because the distal fragments are small and a large portion of their surface is covered with articular cartilage. Transposition of the ulnar nerve allows us to use the cubital tunnel as a point for fixation. We found in our series of 11 patients that undisplaced fractures have the best prognosis. However, all of our patients lost elbow motion, particularly extension. Radiographic signs of post-traumatic arthritis were more pronounced in displaced fractures.

Isolated avulsion of a flexor digitorum superficialis tendon insertion.

A case of an avulsion of a flexor digitorum superficialis tendon insertion of a healthy white man is presented. Five months after the injury exploration showed that the chiasma of the superficialis had retracted to the region of the distal palmar crease. Excision of the distal portion of the superficialis tendon, the scar surrounding the palmar plate, and release of the palmar plate and collateral ligaments was done. Four months after the operation the active range of motion of the proximal interphalangeal joint ranged from 20 to 105 degrees.

Carpal tunnel syndrome in the adolescent.

Three cases of carpal tunnel syndrome in the adolescent age group are described. All were associated with an increase in the patient's athletic activities. After a trial of conservative treatment, all symptoms were successfully relieved by surgical release.