Silicon catheters

In Vivo Test of the Infusion Device. Before the infusion device was used to deliver micro-volume of a heparin solution, the amount of the anticoagulant required to delay the normal clotting time from 1.02 min to > 15 min was determined. An intraperitoneal silicone catheter was inserted by way of a trocar needle into an anesthetized Wistar rat, and the external catheter end was connected to the flow rate testing assembly. With a glass hollow fibre flow moderator having a flow rate of 50 plitre/hr at 48 kPa driving pressure, it was found to require about 25 IU/kg/hr to obtain a Lee-White... 

Central venous catheters are reluctantly used as blood access for hemodialysis because of safety concerns and frequent complications, for example sepsis, thrombosis, and vessel stenosis. Nevertheless, 20% or more of all patients rely on atrial catheters for chronic dialysis because of lack of other access. Potentially fatal risks related to central venous catheters include air embolism (1), severe blood loss (2), and electric shock (3). These specific risks have been substantially eliminated by the inherent design and implantation of Dialock (Biolink Corporation, USA). Dialock is a subcutaneous device consisting of a titanium housing with two passages with integrated valves connected to two silicone catheters. The system is implanted subcutaneously below the clavicle. The tips of the catheters are placed in the right atrium. The port is accessed percutaneously with needle cannulas. 

Urethritis has been described in patients with urinary catheters containing latex (3). In 100 men, the incidence of urethritis with latex catheters was 22% compared with 2% in patients managed with silicone catheters. In all cases, symptoms developed within 12 hours of use and urine specimens were sterile. 

Nacey JN, Tulloch AG, Ferguson AF. Catheter-induced urethritis a comparison between latex and silicone catheters in a prospective clinical trial. Br J Urol 1985 57(3) 325-8. 

In the HBMs described above, enhanced stability derives from multivalent inter-molecular interactions among linear lipo-polymers in the outer monolayer, relative to the fewer number of interactions expected per monomer in an unpolymerized HBM. An alternative strategy is to link covalently the lipid tail(s) to the inner monolayer, as described by Krishna et al. [60], They used a four-step approach to create poly(acrylatePC) coatings on silicone catheters (Fig. 3) (1) plasma polymerization of allyl alcohol on the catheter surface (2) reaction with acryloyl chloride (3) vesicle fusion of monoacryloyl-terminated lipids on the acryloyl functionalized... 

Fig. 3 Schematic illustration of the procedure for chemically grafting a polymerized lipid mono-layer onto a silicon catheter surface. Reprinted with permission from [60]. Copyright 2005,...

Subcutaneous implantable devices are composed of a reservoir component made of stainless steel, titanium, or plastic connected to a polyurethane or silicone catheter (Fig. 6.3). The reservoirs are implanted into the subcutaneous tissues in the chest wall, upper arm, or forearm (Jaques et al. 1992 Foley 1995 Kaufman et al. 1996). The stainless steel ports produce significant artifacts on computed tomography (CT) and magnetic resonance imaging (MRl), and are not often used in the chest wall location. Titanium ports cause only local MRI degradation and plastic ports result in minimal CT... 

Fig. 6.2. Tunneled chest wall catheters. Outer, single lumen silicone catheter with end hole middle, dual lumen silicone catheter with end holes inner, dual lumen catheter with valved-tip. Arrows mark location of cuff that is placed within the subcutaneous tunnel for stabilization. (Published with permission of Lippincott, Williams and Wilkins)...

The prototype non-tunneled small-bore intermediate-term catheter is the Hohn catheter (Bard Access Systems, Salt Lake City, Utah). This is a non-tapered silicone catheter available in 5-F single lumen and 7-F dual lumen varieties. It is designed for intermediate term use generally from 4-8 weeks (Hicks et al. 1994). The catheter is secured by suture. In many institutions, the PICC has largely replaced the Hohn. 

Another hydrophilic polymer studied as antifouling coating is poly-A-vinylpyrrolidone (Hydromer ). PU catheters coated with Hydromer significantly reduced the adhesion of five strains of S. epidermidis and one strain of S. aureusMore recently, a PVP coating was applied to PU for application as urinary tract biomaterial. While enaustation was less on the PVP-coated PU than on the uncoated PU and silicone catheters, E. coli and E. faecalis adhesion was similar on the coated and uncoated PUs. 

Boswald, M., Girisch, M., GreU, J., Spies, T., Stehr, K., Krall, T., Guggenbichler, J.-P., 1995. Antimicrobial activity and biocompatibUity of polyurethane and silicone catheters containing low concentrations of silver a new perspective in prevention of polymer-associated foreign-hody-infections. Zentralhlatt fiir Bakteriologie 283,187-200. 

Catheter Type The type of catheter being used is receiving much greater attention. The silicone catheter, which is flexible, and does not require the persistence of a sharp bevelled needle around the outside, appears to be an advance. Our own trials with this catheter are promising. Debate has continued about the importance of the dimensions and length of the indwelling catheter some (50) believe it to be influential while others do not (10). 

A device with shape memory technology and osmotic delivery has been developed to treat patients who suffer from a painful bladder condition known as interstitial cystitis/bladder pain syndrome (TARIS Biomedical Inc., MA). The device was made of a dual-lumen silicone catheter with one lumen loaded with lidocaine, which continuously leached out as contacted with urine. The second lumen of the device contains superelastic nitinol wire in a predefined form, which provides the... 

Whereas no reactions of polyurethane catheters to either of the aforementioned disinfectants are reported in the literature, PVI may adversely affect silicone tubing. Therefore, its compatibility with silicone catheters should be verified according to the manufacturer s recommendations prior to use. 

Hron P. Hydrophilisation of silicone rubber for medical applications. Polym Int, 2003, 52, 1531-1539. Tcholakian RK and Raad. Durability of anti-infective effect of long term silicone sheath catheters impregnated with antimicrobial agents. Antimicrob Agents Chemother, 2001, 45(7), 1990-1993. 

CATHETER URETHRAL FOLEY 24FR ROUND TIP SILICONIZED RBBR DISP 12S 6515001049006 BX 25 65 ... 

In 1978, on the basis of a few measurements of urine calcium and phosphate excretion as well as an awareness of the previously mentioned work regarding the amounts of calcium and phosphate normally accreted in utero and postnatally, it became apparent that the demineralization, fractures and rickets we were seeing in our infants were caused by calcium deficiency. Consequently we increased the amount of calcium added to the parenteral alimentation solutions. If more than 12.5 mM of the calcium were added to a liter of hyperalimentation solution, gross precipitation would occur in the feeding solution. If 10 mM of calcium were added per liter, crystalline precipitated began to build up on the inside of our barium-impregnated silicone rubber central venous catheters. This crystalline precipitate resulted in gradual occlusion and functional loss of these lines. After several false starts and six lost catheters, chemical and crystal analysis showed that the precipitate inside these catheters was CaHPO. ... 

One useful blend currently being employed as a very effective silicone solvent on an industrial scale is a mixture of 80 vol % hydrocarbon heptane and 20 vol % perfluoropentane, called 1.-12808 (see Table 6.7). 1.-12808 is useful for applying silicone lubricants to numerous medical devices, such as needles, IV spikes, blood filters, and catheters. This mixture shows no flash point and no explosion limits in air. The presence of the more volatile PFC, relative to the HC,... 

The authors of the above-discussed results consider the constant rate of heparin elution to be absolutely necessary for a successful functioning of the implant. Catheters made of these copolymers are much better, in respect of their thromboresistant properties, than the commercially available poly(tetrafluoroethylene) polyethylene, and plasticized polyvinyl chloride catheters (Table 8). The tested catheters were clotted in 9 cases of 81 (11 %), whereas usual silicone rubber catheters were clotted in 5 cases of 8 (63 %)70). 

Self-sterilizing Hospital Tiles to cover the floor and walls of operating rooms, silicone rubber for medical catheters and hospital garments and uniforms... 

Silicon micropumps offer major advantages in terms of system miniaturization and control over low flow rates with a stroke volume 160 nL.14 The micropump has the characteristics of very small in size, implantability in the human body, low flow rates (in the range of 10 pL/min), moderate pressure generation from the microactuator to move the drug, biocompatibility, and most important, a reliable design for safe operation. The implantable device is particularly suitable (over the injectable drug delivery systems) for patients with Parkinson s disease, Alzhiemer s disease, diabetes, and cancer, as well as chronically ill patients, because the catheter that is attached to the device can transport drug to the required site. 

In parallel to catheter-based delivery, stent-based approaches, such as passive stent coatings (diamond-like carbon, phosphorylcholine, and silicon carbide coatings) and immobilized drug coatings (heparin-coated stents), were evaluated for their ability to inhibit restenosis. Although animal studies demonstrated some promise, none of these technologies were clinically successful for restenosis prevention. The failure of these surface modification technologies further added to the need for the development of DES based on the principles of sustained CDD,... 

Silicone rubbers are used as a basis for various pipes used for the transfusion of blood and other physiological solutions, as well as in the production of catheters, probes, vessel prostheses, etc. E.g., multichannel catheters based on silicone rubbers can be easily inserted into vascular beds they can be used for simultaneous registration of blood pressure, injection of medicine and making tests. 

Fig. 4.15 (a) Silicon carbide varistors, and (b) zinc oxide varistors. (Courtesy of P.D. Devices Ltd. UK.) (c) PTC thermistors for motor protection and (d) NTC thermistors inset, catheter fitted with biomedical NTC thermistor for measuring blood temperature. (Courtesy of Thermometries.)... 

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