Silastic tubing

While the effective life of Norplant I is at least five years, most of the users have the implants removed at an earlier time. Norplant II was developed to have a shorter life-span, and is composed of only two rods. Levonorgestrel is dispersed in the silastic matrix which is then inserted into a thin silastic tubing. This product has an effective life-span of two to three years (36). Because it is composed of only two rods, Norplant II also is easier to implant and remove. 

ALZET Osmotic Pumps (Durect Corp., Cupertino, CA) Silastic tubing (Dow-Corning Corp., Midland, MI)... 

Silastic capsules, consisting of 10 mm silastic tubing packed with drug or hormone with sealed ends (insertion of 3 mm glass beads), can be implanted through a small incision over the dorsal thoracic midline into the subcutaneous fat (57, 58). A number of companies will formulate drugs into various pelleted implants and these companies can be found online (e.g., Brookwood Pharmaceuticals). 

Cannulas are made of silicon rubber. The proximal bile cannula, which will be inserted into the common bile duct in the direction to the liver, is 18 cm long (Silastic tubing, Dow Coming, no. 605-135 0.51 i.d. and 0.94 o.d.) and has one square cut and one bevelled end. Two silicon rings are wrapped around the cannula at 7 mm and 50 mm, respectively, from the bevelled end. 

Figure 35.9 Effect of solvent extraction on XPS spectra of plasma polymer of tetrafluoroethylene deposited on Silastic tube extracted with w-hexane for 3h under continuous flow.

None of the smooth surfaces prepared by the depositing of plasma polymer on the smooth surface of Silastic tubing showed detectable thrombus formation by gamma camera imaging. Therefore, they were evaluated by measurement of relative rates of platelet consumption. Table 35.7 shows the results obtained using the plasma polymers described previously [5]. 

Figure 6a. ESC A Cl s spectrum of the luminal surface of Silastic tubing.

Protein Adsorption. Since protein adsorption is the earliest event in the thrombotic response of the blood to polymers, the types of proteins adsorbed from plasma to polyacrylamide-Silastic and Silastic tubes were examined. As described in the Experimental section, plasma was recirculated through the tubes for 2 h at 37°C and rinsed away with buffer. The proteins adsorbed to the polymers were eluted with SDS, separated by SDS-polyacrylamide slab gel electrophoresis, and silver-stained using a new extremely sensitive method (19). Figure 10 shows the results of these assays. 

Table II shows the effect on platelet consumption of increasing lengths of the polyacrylamide-Silastic tubing. The acrylamide surface is much more destructive to platelets than is the Silastic surface. Table II also shows that platelet consumption increases linearly with shunt area for both the polyacrylamide-Silastic shunts.

The animals used in these studies were conditioned male dogs of mixed breed. Access to the animals circulatory systems was accomplished via an acute shunt surgically implanted in the neck of the dog. The shunt was constructed of Vie in. Silastic tubing anastomosed to the carotid artery and jugular vein. Blood flow through the shunt was on the order of 1 L/min. 

When clinical symptoms require weekly thoracenteses, pleurodesis by tube thoracostomy or video-assisted pleuroscopy should be considered. In patients with severe cardiomyopathy or hypotension who may not tolerate significant sedation or anesthesia required for a video-assisted procedure, placement of sterile silastic tubes (PleuRx tubes, Denver Biomaterials, Colorado, U.S.) are a viable alternative. 

Figure 6-8 Ratio of two-phase friction factor to single-phase friction factor as a function of bead feed rate for 25-Mm beads in silastic tube (Peters, 1971). Relative humidity = 25%, fm =...

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