Patent Application
20080051759
As used herein, a “catheter” is a medical device that includes a flexible shaft, which contains one (including annular shafts, i.e., tubes) or more lumens, and which may be inserted into the body for introduction of fluids, for removal of fluids, or both.
A catheter may further include various accessory components, for example, molded components, over-molded sub-assemblies, connecting fittings such as hubs, extension tubes, and so forth. Various catheter tips designs are known, including stepped tips, tapered tips, over-molded tips and split tips (for multilumen catheters), among others.
A “central venous access catheter” is a catheter that provides access to the central venous circulation system.
Central venous access may be achieved by direct puncture of the central venous circulation system, e.g., via the internal jugular vein, subclavian vein or femoral vein. Catheters of this type, known as “central catheters” or “central venous catheters,” are relatively short, and can generally remain in place for only a short time (e.g., generally less than 7 days).
Other catheters have also been developed which can be inserted into peripheral veins (e.g., the antecubital, basilica, or cephalic vein) and advanced to access the central venous system, with the tip commonly positioned in the superior vena cava or right atrium, thus allowing for rapid dilution of infused fluids. These devices avoid difficulties associated with the direct puncture of the central venous circulation system, and they allow for long term (e.g., 180 days or more) and repeated access to a patient's vascular system, thereby avoiding multiple injections and minimizing trauma and pain to the patient.
Specific examples of catheters of this type include so-called peripherally inserted central catheters (“PICCs”), midline catheters, and peripheral catheters. A typical PICC, midline, or peripheral catheter contains a thin, flexible shaft, which contains one or more lumens and which terminates at the proximal end with a suitable fitting, such as a hub or other fitting. The primary difference between these three devices is the length of the tubing, with the peripheral catheter being the shortest and the PICC being the longest. The rationale for different lengths is driven by the type and duration of the therapy a patient is to receive.
Hemodialysis catheters are another important class of central venous access catheters. Hemodialysis catheters are commonly multi-lumen catheters in which one lumen is used to carry blood from the body to a dialysis machine, and another lumen returns blood to the body. Central venous access may be attained by puncture of various major blood vessels, including the internal jugular vein, subclavian vein, or femoral vein.
Central venous access may also be provided via venous access ports. These specialized catheters typically have the three following components: (a) a catheter, (b) a reservoir, typically formed of a metal or polymer, which holds a small amount of liquid and which is connected to the catheter, and (c) a septum, which covers the reservoir and allows access to the reservoir upon insertion of a needle. The reservoir and covering septum are surgically placed under the skin of the chest or arm, and the catheter extends into a central vein.
Catheter shafts for central venous catheters such as those describe above, among others, are typically made from polymers. Suitable polymers are those that can be formed into tubing that is flexible enough to be routed through the vasculature without causing trauma to the patient. When formed into tubing, the polymer chosen should also provide strength sufficient to ensure that the lumen does not collapse in the vasculature, and should resist repeated flexure. Polyurethane-based polymers are commonly employed to meet these criteria.
In general, polyurethanes are a family of polymers that are synthesized from polyfunctional isocyanates (e.g., diisocyanates, including both aliphatic and aromatic diisocyanates) and polyols (also, referred to as macroglycols, e.g., macrodiols). Commonly employed macroglycols include polyester glycols, polyether glycols and polycarbonate glycols. Typically, aliphatic or aromatic diols are also employed as chain extenders, for example, to impart the useful physical properties described above. Examples of diol chain extenders include butane diol, pentane diol, hexane diol, heptane diol, benzene dimethanol, hydraquinone diethanol and ethylene glycol.
Polyurethanes are commonly classified based on the type of macroglycol employed, with those containing polyester glycols being referred to as polyester polyurethanes, those containing polyether glycols being referred to as polyether polyurethanes, and those containing polycarbonate glycols being referred to as polycarbonate polyurethanes. Polyurethanes are also commonly designated aromatic or aliphatic on the basis of the chemical nature of the diisocyanate component in their formulation.
Preferred polyurethanes for the practice of the present invention are polycarbonate polyurethanes. For example, U.S. Patent Appln. No. 2004/0131863 to Belliveau et al., describes aliphatic polycarbonate polyurethanes which are the reactions products of (a) a hydroxyl terminated polycarbonate, (b) an aliphatic diisocyanate and (c) a lower aliphatic chain extender. Hydroxyl terminated polycarbonate polyol may be prepared by reacting a glycol with a carbonate, as disclosed in U.S. Pat. No. 4,131,731. Suitable aliphatic diisocyanates include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethyl hexamethylene diisocyanate (TMHDI), dicyclohexyl methane diisocyanate (HMDI), and dimer acid diisocyanate (DDI), with HMDI said to be preferred. Suitable chain extenders include lower aliphatic glycols having from about 2 to about 10 carbon atoms, such as, for instance ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,3-butanediol, 1,5-pentanediol, 1,4-cyclohexanedimethanol hydroquinone di(hydroxyethyl) ether, neopentyglycol, and the like, with 1,4-butanediol said to be preferred.
Polycarbonate polyurethanes are strong, allowing catheters to be formed with thinner walls, regardless of whether the catheter shaft is a single lumen shaft or a multi-lumen shaft. Subsequently, catheters made from these materials may be formed with smaller ODs as compared, for example to other catheter materials such as silicone, or they may be formed having the same OD, but with a larger ID, and therefore having a greater flow rate. Wall thickness for polycarbonate polyurethane catheter shafts will vary with application and may range, for example, from 0.003″ to 0.005″ to 0.01″ to 0.015″, among other thicknesses.
Moreover, while being sufficiently flexible to avoid trauma to the patient, these materials are stiff as compared, for example, to silicone, which helps with insertion of the catheter.
These materials are also thermoplastics, meaning that a variety of thermoplastic processing techniques, such as extrusion, molding, and so forth, may be employed to form medical devices and medical device components, including catheter shafts, from the same.
Kink resistance (i.e., resistance to failure as a result of repeated kinking), is also an important property of catheter shaft materials. In general, the kink resistance of polycarbonate polyurethanes lessens as the walls of the catheter shaft become thinner and thinner. Moreover, kink resistance also lessens significantly upon exposure to certain materials such as alcohol (i.e., ethanol, isopropyl alcohol, etc.) and alcohol-containing materials such as Chloropre® (a product commonly used for skin preparation, which contains 2% chlorhexadine gluconate and 70% isopropyl alcohol), among other materials. Hence, kink resistance is particularly important for central venous access devices such as PICCs, which have thin catheter walls and which are subjected to repeated exposure to alcohol at the entrance site of the body.
The present inventors have unexpectedly found that by employing an extruded catheter shaft which comprises a polycarbonate polyurethane having a weight average molecular weight in excess of 90,000 g/mol. that superior kink resistance is obtained, even upon exposure to substantial amounts of alcohol. Weight average molecular weight may be within the range, for example, of 90,000 to 95,000 to 100,000 to 105,000 to 110,000 or more.
To be visible under x-ray (e.g., by x-ray fluoroscopy), the catheter shaft may be rendered more absorptive of x-rays than the surrounding tissue. Examples of radiopaque agents include metals, metal salts, metal oxides, and iodinated compounds. More specific examples of such contrast agents include gold, tungsten, platinum, tantalum, iridium, or other dense metal, barium sulfate, bismuth subcarbonate, bismuth trioxide, bismuth oxychloride, metrizamide, iopamidol, iothalamate sodium, iodomide sodium, and meglumine. For example, in certain embodiments, the catheter shaft will further contain from 30 to 50 wt % barium, more preferably about 40 wt % barium.
In certain embodiments, the catheter shaft catheter shaft has a durometer value ranging from 50 A to 100 A, more preferably 75 A to 85 A, among other values.
A PICC catheter shaft 100 (also referred to herein as an “extrusion”), formed from a polycarbonate polyurethane polycarbonate polyurethane having a molecular weight in excess of 90,000, is illustrated in
The shaft 100 includes a body section 100Bo, having length LBo. The body section 100Bo also has an outer diameter ODBO and an inner diameter (lumen diameter) IDBo at its proximal end. The shaft 100 further includes a tip section 100Ti. At its distal end, the tip section 100Ti has an outer diameter ODTi and an inner diameter (lumen diameter) IDTi. The shaft 100 further has a tapered section 100Ta, having length LTa. LTi is the combined length of the tip section 100Ti and the tapered section 100Ta. The overall length is LOv. Typical dimensions for some of these values are provided in Table 1 below:
In
Although the catheter shaft shown in
Catheter shafts (extrusions) are formed using a range of Carbothane® resins having molecular weights of 76,000, 87,000, 102,000 and 110,000 g/mol from Noveon, Inc., Cleveland, Ohio.
Extrusions of OD's ranging from 4 Fr. (French) to 7 Fr. were cut to approximately 2.75 inches in length for testing. Where the extrusion is tested in conjunction with an assembly, such as that described in
Samples are exposed to vapor in a sealed glass jar by placing them on aluminum blocks above a solution of 70% alcohol or Chloropre® for a designated time. Temperature is controlled by immersing the jar halfway in a water bath at 37±2° C.
Axial Cycling Tester (built in house) is used for kink resistance testing. The distance between the grippers is set in the up and down positions such that the sample kinks when in the down position and undergoes 25% elongation.
Where an extrusion is tested in conjunction with an assembly, ten kinks are formed at the suture wing prior to testing. Also a three minute kink at body temperature is performed prior to testing.
The speed controller is adjusted as necessary to ensure that it is operating at 200±5 cycles per minute. The machine is stopped every 1000 cycles and the sample is examined at both kink locations for cracks or holes or for any other sign of failure.
These data are also displayed in a bar-graft format in
Table 2 below shows maximum, minimum, and average cycles to failure, both before and after sterilization two times in ethylene oxide using standard protocol for the following: twenty-one 102,000 mol. wt. extrusions, twenty-two 110,000 mol. wt. extrusions, and twenty-two 87,000 mol. wt. extrusions. This table again illustrates the advantages of increasing molecular weight vis-a-vis kink resistance.
Although various embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and are within the purview of the appended claims without departing from the spirit and intended scope of the invention.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/839,949, filed Aug. 24, 2006, entitled “Polycarbonate Polyurethane Venous Access Devices”, which is incorporated by reference in its entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| 60839949 | Aug 2006 | US |
