Localized microjetting in the collapse of surface macrocavities.

This paper focuses on the multiscale mechanism of collapse of hemicylindrical annular surface macrocavities in steel caused by high-strain, high-strain rate plastic flow of copper. Experiments and simulations revealed that a two-stage process is responsible for the observed microjetting phenomena: the formation of lateral copper microjets from the localized shear flow in copper at the interface during the filling of the cavity, and their subsequent collision at the apex of the macrocavity generating two additional horizontal microjets. The lengths of these microjets were an order of magnitude smaller than the cavity size but linearly scaled with the cavity radius. This process of microjet development is sensitive to the cavity geometry and is unlike the previously observed jetting phenomena in cavitation, impact crater collapse, or shock-induced cavity collapse.

Occlusion of the vas deferens in dogs with a biocompatible hydrogel solution.

The surgically exposed vasa deferentia of 21 dogs were injected, under visual inspection, with Hypan N-90 acrylic hydrogel (50-150 microL). The hydrogel was deposited inside the vas lumen via a 22-gauge Teflon intercatheter. The solution gelled within 120 seconds. Semen was collected by manual collection and analyzed for volume, sperm count and viability. After occlusion with 150 microL of the polymer in the distal direction (direction of the testis), the volume of ejaculate (2.2 mL) did not change. Subsequent samples showed no viable or dead spermatozoa. The stained smears of the ejaculate showed the presence of cell debris, granulocytes and few epithelial cells. When the vas was injected with 50 microL of the polymer in either a distal or proximal direction, the occlusion effectiveness was 75% and 25%, respectively. In the proximal direction, granulomas were noticed in the vas wall where semen leaked through the injection port. Histology of successfully occluded vasa (with Hypan) showed no cellular reaction or fibrotic changes in the proximity of the polymer. For less than or equal to 20 weeks after vas occlusion, no evidence of abnormal morphology was found in the epididymal and testicular tissue. This highly biocompatible polymer solution, when gelled in contact with tissue fluid, offers safe and effective occlusion of the vas with the promise of reversibility.