Abstract:
The present invention provides a deflectable catheter whose puller member connections are accomplished with minimal, if any, surface deformation which could otherwise accelerate breakage under tension. The catheter includes a molded member that encases an end of a puller member to enable connection of the end to a fixed or movable structure in the control handle without significant surface deformation in the puller member. The molded member is of a thermoplastic material that encases a preformed end of the puller member, which may be a puller wire or a high modulus fiber material. 
     The molded member may be configured as desired, for example, as a screw that is fastened to a structure in the control handle. Alternatively, the preformed end of the puller member, for example, a puller wire, can be directly connected to and jointly encased in the molded member with another preformed end of a second puller member, for example, a high modulus fiber material. Such a connected puller member whose distal portion is the puller wire and whose proximal portion is the high modulus fiber material can be well suited for control handle that employs pulleys for increased throw capacity.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to deflectable catheters, and more particularly to catheters with tensile members to effectuate deflection. 
       BACKGROUND OF INVENTION 
       [0002]    Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is. 
         [0003]    Deflectable catheters have been designed to provide deflection in at least one direction by a puller wire, if not also deflection in an opposite direction by a second puller wire. In such a construction, the puller wires extend into opposing off-axis lumens within a distal section of the catheter. For example, U.S. Pat. No. 6,210,407, the disclosure of which is incorporated herein by reference, is directed to a bi-directional catheter comprising two puller wires and a control handle having at least two moveable members longitudinally movable between first and second positions. The proximal end of each puller wire is connected to an associated movable member of the control handle. Proximal movement of a movable member relative to the catheter body results in proximal movement of the puller wire associated with that movable member relative to the catheter body, and thus deflection of the tip section in the direction of the lumen in which that puller wire extends. 
         [0004]    While the aforementioned catheter provides bi-directional steering, the mechanical efficiencies of the steering and the deflection mechanism of the control handle can be improved upon. For example, the use of pulleys in the control handle can increase the throw capacity of the catheter. However, the repeated bending and straightening of the puller wires trained around the pulleys during deflection operations can significantly reduce the life span of the puller wires due to fatigue failure. If a different tensile material is trained around the pulleys, means for connecting this different material to a puller wire can pose additional challenges. 
         [0005]    Current means for attaching puller wire ends typically involve mechanical crimping utilizing a stainless steel ferrule crimped on the puller wire end. The stainless to stainless steel crimping process may cause puller wire surface deformation (nicks or notches) that change the wire section modulus thus creating localized stress raisers that have a propensity to initiate crack propagation during puller wire tensile force cycling that occurs during catheter handle actuation. Due to limited space in the catheter shaft, the puller wire is designed to be as small as possible thus it is subjected to high tensile stresses during catheter handle operation. Any changes in the puller wire&#39;s cross sectional area in tension could result in puller wire failure during catheter operation. Hence, there is a desire for a deflectable catheter whose puller wire connections avoid such surface deformations. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a deflectable catheter whose puller member connections are accomplished with minimal, if any, surface deformation which could otherwise accelerate breakage under tension. The deflectable catheter comprises an elongated catheter body, a deflectable section distal the catheter body, a control handle proximal the catheter body, and a puller member responsive to the control handle to deflect the deflectable section. Advantageously, the catheter includes a molded member that encases an end of the puller member to enable connection of the end to a fixed or movable structure in the control handle, such as a wall for anchoring, a spring for tension adjustment, or even to another puller member, without any surface deformation or cross sectional area changes in the puller member. In accordance with a feature of the present invention, the molded member consists of a thermoplastic material that encases a preformed end of the puller member, which may be a puller wire or a high modulus (resistance to creep under load) and tensile strength fiber material. 
         [0007]    To better hold the end of the puller member in the molded member, the end of the puller member is preformed with a knot, a loop or a coil. The molded member may be configured as desired, for example, as a screw that is fastened to a structure in the control handle as a means to anchor the puller member to the control handle. Alternatively, the preformed end of the puller member, for example, a puller wire, can be directly connected to and jointly encased in the molded member with another preformed end of a second puller member, for example, a high modulus fiber material. Such a connected puller member whose distal portion is the puller wire and whose proximal portion is the high modulus fiber material can be well suited for control handle that employs pulleys for increased throw capacity. In one embodiment, the connected puller member is positioned in the control handle while the distal puller wire extends distally from the control handle. As such, it is the proximal high modulus fiber material, and not the puller wire, that interacts with the deflection mechanism and bears the repetitions of bending and straightening around a pulley during catheter handle deflection operations. 
         [0008]    In a more detailed embodiment, the molded member is translucent or transparent so that the encased end(s) can be inspected. It is also contemplated that the molded member be visible through a window provided in the control handle housing, as a visual indication of deflection and degree of deflection. To that end, the molded member can bear indicia and/or contain phosphors so that the movement and position of the molded member within the control handle can be readily assessed by a user in low ambient light. In yet another detailed embodiment, the control handle housing is configured with a track along which the molded member moves during deflection for quieter and smoother operation. 
         [0009]    The present invention is also directed to a method of securing a puller member in a control handle for a deflectable catheter, comprising preforming an end of the puller member, placing the preformed end in an insert mold, filling the insert mold with thermoplastic material to form a molded member, and positioning the molded member encasing the end of the puller member in a control handle. 
         [0010]    The method may also include shaping the thermoplastic material into a screw configuration and fastening the molded member to a wall in the control handle. The method may further include joining the end of the puller member with an end of a second puller member, and placing joined ends of the puller members in the insert mold. 
         [0011]    In an embodiment, a joined connection between two puller members comprises a loop formed in the end of one puller member, and a knot formed in the end of the other puller member, wherein the one puller member is a puller wire and the other puller member is a high modulus fiber material. Alternatively, the joined connection comprises a coil formed in the end of one puller member, and a knot formed in the end of the other puller member, wherein the one puller member is a puller wire and the other puller member is a high modulus fiber material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0013]      FIG. 1  is a side view of an embodiment of the catheter of the invention. 
           [0014]      FIG. 1   a  is an exploded top view of a control handle of the catheter of  FIG. 1 . 
           [0015]      FIG. 2  is a top plan view of an embodiment of a deflection assembly within a housing half of a control handle. 
           [0016]      FIG. 3  is a side view of a first embodiment of a molded member securing two puller members to each other. 
           [0017]      FIG. 4  is a side view of a second embodiment of a molded member securing two puller members to each other. 
           [0018]      FIG. 5  is a side view of a third embodiment of a molded member securing two puller members to each other. 
           [0019]      FIG. 6 . is a side view of a fourth embodiment of a molded member securing two puller members to each other 
           [0020]      FIG. 7  is a longitudinal cross-sectional view of the control handle housing half of  FIG. 2  taken along line  7 — 7 . 
           [0021]      FIG. 8  is a longitudinal cross-sectional view of the control handle housing half of  FIG. 2  taken along line  8 — 8 . 
           [0022]      FIG. 9  is a top view of the control handle housing half of  FIG. 2  assembled with the other control handle housing half. 
           [0023]      FIG. 10  is an alternative embodiment of a deflection assembly and control handle housing half. 
           [0024]      FIG. 11  is a longitudinal cross-sectional view of the control handle housing half of  FIG. 10  taken along line  11 — 11 . 
           [0025]      FIG. 12  is a longitudinal cross-sectional view of the control handle housing half of  FIG. 10  taken along line  12 — 12 . 
           [0026]      FIG. 13  is a detailed side cross-sectional view of an alternative embodiment of a track in locking engagement with a molded member. 
           [0027]      FIG. 14  is side cross-sectional view of an alternative embodiment of a catheter control handle. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The present invention provides deflectable catheter puller wire joint connections and terminations with improved durability against material fatigue and breakage due to stresses borne during deflection operations. As shown in  FIG. 1 , the catheter  10  comprises an elongated catheter body  12  having proximal and distal ends, a deflectable section  14  distal the catheter body  12 , and a control handle  16  at the proximal end of the catheter body  12 . Description of suitable construction of the catheter body  12  and the deflectable section  14  can be found in U.S. Pat. Nos. 6,602,242 and 6,120,476, the entire disclosures of which are hereby incorporated by reference. 
         [0029]    For deflecting the deflectable section  14 , the catheter  10  has puller members  32  that extend from the control handle through the catheter body  12  to the deflectable section  14 . Distal ends of the puller members  32  are anchored in the deflectable section  14  and their proximal ends are anchored in the control handle. Longitudinal movement of the puller members  32  relative to the catheter body  12 , which results in deflection of the tip section  14 , is accomplished by manipulation of a deflection knob  18  on the control handle  16 . A suitable bidirectional control handle is generally described in U.S. application Ser. No. 10/871,691, filed Jun. 15, 2004, the entire disclosure of which is hereby incorporated by reference. 
         [0030]    With reference to  FIG. 1   a , the control handle  16  comprises a generally elongated handle housing  40 , which can be made of any suitable rigid material. In the illustrated embodiment, the housing  40  has two opposing halves  42 ,  44  that are joined by glue, sonic welding or other suitable means. The control handle  16  employs means for deflection that is responsive to an operator in deflecting the catheter. With reference to  FIG. 2 , the illustrated embodiment of the control handle  16  employs a steering or deflection assembly  48  having a lever structure  50  carrying a pair of coordinated pulleys  52  that act on the puller members  32  to deflect the section  14 . The deflection knob  18  and the lever structure  50  are rotationally coupled such that rotation of the deflection knob by a user rotates the lever structure which draws the puller members  32  to deflect the distal section  14 . There are also a pair of stops  56  that help effectuate deflection by applying tension on the puller elements, and a pair of constant force springs  54  attached to the proximal ends of the puller members to take up slack. As described below in further detail, the placement of the stops  56  is adjustable to vary the tension on the puller members. 
         [0031]    The control handle  16  is configured such that while the pulleys  52  of the steering assembly  48  increase the throw capacity of the catheter  10 , the puller members are not exposed to an increased risk of fatigue or breakage attributable to the pulleys. In accordance with the present invention, each puller member  32  may be a connected or segmented puller member having multiple puller members that are joined in series. In the illustrated embodiment, the puller member  32  has a distal puller wire portion  33  and a proximal tensile fiber portion  35  such that the puller wire portion  33  extends from the control handle  16  to the deflectable section  14  and the proximal tensile fiber  35  engages the pulley with in the control handle. In this manner, the more flexible tensile fiber portion  35  interacts with the pulley and it, as opposed to the puller wire  33 , undergoes repeated bending and straightening during deflection operations. The tensile fibers  35  therefore saves the puller wires  33  from bending stress imposed fatigue failure caused by the pulleys  52 . 
         [0032]    Each puller wire portion or puller wire  33  is made of any suitable metal, such as stainless steel or Nitinol. Preferably each puller wire  33  has a low friction coating, such as a coating of Teflon® or the like. Each puller wire  33  has a diameter preferably ranging from about 0.006 inch to about 0.012 inch. Preferably both of the puller wires  33  have the same diameter. 
         [0033]    Each tensile fiber portion or tensile fiber  35  may be of a high modulus fiber material, preferably having an ultimate tensile strength substantially in the range of 412-463 ksi (2480-3200 Mpa) such as High Molecular Density Polyethylene (e.g., Spectra™ or Dyneema™), a spun para-aramid fiber polymer (e.g., Kevlar™) or a melt spun liquid crystal polymer fiber rope (e.g., Vectran™), or a high strength ceramic fiber (e.g., Nextel™). The term fiber is used herein interchangeably with the term fibers in that the tensile fiber may be of a woven or braided construction. In any case, these materials tend to be flexible, providing suitable durability when used in wrapped engagement with the pulleys  52  and the like for greater throw in the control handle  16  for deflecting the catheter tip. Further, they are substantially non-stretching, which increases the responsiveness to the manipulation of the control handle, and nonmagnetic so that they generally appear transparent to an MRI. The low density of the material causes it to be generally transparent to an x-ray machine. The materials can also be nonconductive to avoid shorting. Vectran™, for example, has high strength, high abrasion resistance, is an electrical insulator, nonmagnetic, is polymeric, and has low elongation under sustained loading conditions. 
         [0034]    In accordance with the present invention, the puller wire  33  and the tensile fiber  35  are connected or secured to each other by a molded member  60  that encases preformed/preshaped adjacent ends  63 ,  65  within a thermoplastic material that is formed by insert molding. Referring to  FIGS. 3-6 , the molded member  60  provides an advantageously small interconnection volume for a space-limited control handle, that secures the puller wire  33  and the tensile fiber  35  to each other and the thermoplastic material is generally self-dampening so there is little if any perceptible noise generated in the control handle during catheter deflection. Moreover, the thermoplastic material can be translucent, if not transparent, allowing passage of light, so that after formation of the molded member  60  the adjacent ends  63 ,  65  and interior of the molded member  60  can be visibly inspected. Significantly, the molded member  60  allows the puller wire  33  and the tensile member  35  to be connected in a manner that minimizes deformations or changes in cross-sectional area of the puller wire end  63  that can create localized stress raisers that are attributed to breakage and deflection failure. It is understood by one of ordinary skill in the art that the preshaping of the puller wire ends can be a manual process and/or an automated process. 
         [0035]    With reference to  FIG. 3 , an embodiment of a molded member  60   a  is shown as encasing interconnected preformed ends  63  of the puller wire  33  and  65  of the tensile fiber  35 . The proximal end of the puller wire  33  is turned back on itself to form a loop  67  and wound about a more distal portion  69  that remains linear, with at least ten turns. The distal end of the tensile fiber  35  is inserted through the loop  67 , turned back on itself and tied with a more distal portion to form a knot  70 . The two ends are placed centrally in an insert mold  71   a  that is filled with thermoplastic material to encapsulate the joined two ends and portions distal and proximal thereof. 
         [0036]    In this configuration, the puller wire  33  and the tensile fiber  35  are generally linearly aligned with each other and there is relatively low residual stress in the preformed end of the puller wire  33  that is subjected to alternative tensile forces. This embodiment can provide favorable tensile force versus elongation curves during cyclic tensile loading conditions at 500 cycles, which in turn can afford a connection with a greater average tensile force at breakage. Additionally, this embodiment of the molded member  60  can tolerate a smaller molded volume. 
         [0037]    With reference to  FIG. 4 , another embodiment of a molded member  60   b  is shown as encasing interconnected preformed end  63  of the puller wire  33  and the preformed end  65  of the tensile fiber  35 . The proximal end of the puller wire is turned back on itself to form the loop  67  and twisted together with the more distal portion  69 , with at least ten turns, preferably at least 12 turns. The distal end  65  of the tensile fiber  35  is inserted through the loop  67  and tied to form a knot  72  that is larger than the loop  67  and prevents the distal end  35  from slipping out of the loop. The two ends are placed centrally in an insert mold  71   b  that is filled with thermoplastic material to encapsulate the joined two ends and portions distal and proximal thereof. 
         [0038]    In this configuration, the puller wire  33  may be subjected to a bending moment and tensile forces during deflection and thus have a lower tensile force at puller wire failure than the above embodiment of  FIG. 3 . Due to the greater number of turns in the puller wire  33 , the molded member  60   b  may have a greater insert molded length than the molded member  60   a . However, the molded member  60   b  still provides favorable tensile force versus elongation curves during cyclic tensile loading conditions at 500 cycles. 
         [0039]    With reference to  FIG. 5 , yet another embodiment of a molded member  60   c  is shown as encasing interconnected preformed ends  63  and  65 . The proximal end  63  of the puller wire  33  is shaped with a coil  74  with at least four windings to form a channel  76  through which the distal end  65  of the tensile fiber  35  is inserted, turned back and tied with a more distal portion of the tensile fiber to form a knot  78 . The two ends are placed centrally in an insert mold  71   c  that is filled with thermoplastic material to encapsulate the joined two ends and portions distal and proximal thereof. 
         [0040]    In this configuration, the puller wire  33  can be subjected to tensile and bending moment forces during cyclic tensile testing; thus, the force at puller wire failure can be lower than either of the aforementioned embodiments. The molded member  60   c  may provide less favorable tensile force versus elongation curves during cyclic tensile loading conditions when compared to the molded members  60   a  and  60   b . Due to the size of the coil and number of windings, the molded member  60   c  can have a insert molded volume greater than the aforementioned embodiments. 
         [0041]    With reference to  FIG. 6 , a further embodiment of a molded member  60   d  is shown as encasing adjacent but free preformed ends  63  and  65 . The end  63  and  65  can be preformed in any of the aforementioned manners, and the puller wire  33  and tensile fiber  35  are in linear alignment with each other. The two ends are placed centrally in an insert mold  71   d  that is filled with thermoplastic material to encapsulate the two ends and portions distal and proximal thereof. 
         [0042]    Referring back to  FIG. 2 , the puller members  32  are generally parallel as they enter the control handle  16  at its distal end. In the embodiment illustrated, the control handle is configured such that the puller members  32  diverge as they approach the pulleys  52  of the steering mechanism  48 , with a divider  80  facilitating this divergence. Regardless of its configuration, the molded member  60  connecting a respective puller wire  33  and tensile fiber  35  is situated between a pulley  52  and the distal end of the divider  80  (or at least sufficiently distal of the pulley  52 ) so that the puller wire  33  does not interact with the pulley and the molded member  60  does not interfere the deflection mechanism  48 . In the illustrated embodiment of  FIG. 2 , the molded members  60  may be of any shape or volume so long as they can move freely in their designated pathways within the control handle  16 . 
         [0043]    Extending proximally from the molded member  60 , the tensile fiber  35  is trained around a pulley  52 . Each proximal end  65  of the tensile fiber continues to extend between a channel  84  defined by a pair of racks  86   a  and  86   b  and is connected to a free end of a spring  54  proximal the channel  84 . In the illustrated embodiment, the springs are flat coil springs that exert a constant force to take up slack in the puller members  32  as they undergo cycles of distal and proximal movement with deflection operation of the catheter  10 . In fact, if suitable, the springs can be connected or secured to the tensile fibers  35  by a molded member  60 ′ in accordance with the foregoing embodiments and description of the molded member  60  with reference to  FIGS. 3-6 . 
         [0044]    The molded member  60 ′ connecting the tensile fibers  35  and the springs  88  are situated between the respective pairs of racks  86   a  and  86   b  so that they can interact with stops  56 . As better shown in  FIGS. 7 and 8 , the puller member (being the tensile fiber  35  in  FIG. 7 ) passes between the racks  86   a  and  86   b  and under the stop  90 , but the molded member  60  is formed with sufficient size or at least height (see  FIG. 8 ) to encounter and abut with the stop (see  FIG. 2 ). Thus, during assembly of the control handle  16  before the two halves  42  and  44  of the housing are joined, the stops  56  are selectively positioned between the racks to achieve a desirable tension in each puller member. As means for adjusting tension setting of the puller members, the stops  56  and the racks  86   a  and  896   b  are configured for selective locking engagement at a selected position along the racks  86   a  and  896   b . In the illustrated embodiment, the stops and the racks are each configured with notches  92  that engage with each other so the stops can interlock with the racks at a plurality of different positions along the racks. Once inserted between the racks, the stops  90  are fixedly positioned to abut the proximal end of the molded members  60 ′ and prevent their proximal movement beyond the distal end of the stops  90 . 
         [0045]    As a further feature of the present invention, the molded members  60  between the puller wires  33  and tensile fibers  65  can be adapted to provide visual indication of the deflection and the degree of deflection of the catheter  10 . With reference to  FIGS. 2 and 9 , the molded members  60  may comprise a marking or indicia  100  (e.g., a band) that is visible to an operator through a window  102  provided in the opposing half  44  after the control handle is assembled. An outer surface of the housing half  44  may also have marking or indicia  101 , e.g., alphanumeric symbols indicating degree of deflection. Viewing the relative positions of the indicia  100  through the window  102 , the operator can assess whether the catheter  10  is straight or deflected, the direction of deflection and/or degree of deflection. Moreover, the thermoplastic material of the molded members  60  may have glow in the dark properties, that is, by containing phosphors or other substances that radiate visible light, so that the molded members and/or markings are visible even in low light environment. 
         [0046]    In an alternative embodiment of the control handle as illustrated in  FIGS. 10 ,  11  and  12 , the molded members  60  are each configured to slide within tracks  110  formed between the divider  80  and each adjacent rack  86   a  in the housing half  42 . The molded members  60  each have a T-shaped cross-section where a leg of the T-shape rides in the track. This embodiment may offer a smoother operation and a quieter deflection control handle. It is understood by one of ordinary skill in the art that the configuration of the tracks  110  and the molded members  60  may be varied as desired or appropriate. For example, an interlocking configuration as shown in  FIG. 13  may be desired. 
         [0047]    Catheters may also be deflectable in a single direction as effectuated by a single puller member  32  whether it comprises a puller wire  33  for its entire length or has a proximal portion that is a tensile fiber  35 . Such single deflection catheters may have a control handle  16 , as shown in  FIG. 14 , that comprises a piston  54  with a thumb control  56  for manipulating the puller member  32 . Such a control handle is described in U.S. Pat. No. 6,120,476, the entire disclosure of which is hereby incorporated by reference. 
         [0048]    With reference to  FIGS. 14 and 15 , the puller member  32  extends through the piston  54  and its proximal end terminates at a distal end of a molded member  60 ″ that serves to anchor or secure the proximal end of the puller member to a transverse wall  122  toward the proximal end of the control handle  16 . In the illustrated embodiment, the molded member is configured as a screw that is inserted through hole  124  and fastened by a nut  126  that allows adjustment of the tension on the puller member  32  (which in the illustrated embodiment is a puller wire  33 ). In accordance with a feature of the present invention, the molded member  60 ″ is of a similar construction as the aforementioned molded members  60  and  60 ′ such that the preformed proximal end of the puller member is encased within a thermoplastic material. As such, the anchoring of a puller wire to a structure in the control handle is accomplished without significant deformations or changes in cross-sectional area of the puller wire that can cause earlier failure and breakage. 
         [0049]    As used herein, insert molding refers to an injection molding process whereby plastic (including thermoplastic) is injected into a cavity and around an insert piece placed into the same cavity just prior to molding, thus the term insert molding. Here, the insert piece(s) are the preformed ends of a puller wire, a tensile fiber, a spring, or the like, that are encapsulated by the plastic. 
         [0050]    Moreover, as used herein, thermoplastic material refers to materials that is plastic or deformable, melts to a liquid when heated and freezes to a crystalline or amorphous state when cooled sufficiently. Amorphous plastic polymer chain orientations are random and these types of plastics have high impact strengths and toughness. Crystalline plastic polymer chains are orderly, densely packed arrangements and these polymers in general have lower impact strengths and toughness. Most thermoplastics are high molecular weight polymers whose chains associate through weak van der Waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting polymers (Bakelite; vulcanized rubber) which once formed and cured, can never be remelted and remolded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene. 
         [0051]    Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name. Thermoplastics as used herein include the following: Acrylonitrile butadiene styrene (ABS), Acrylic, Ethylene-Vinyl Acetate (EVA), Ethylene vinyl alcohol (EVAL), Fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), Ionomers, Liquid Crystal Polymer (LCP), Polyacetal (POM or Acetal), Polyacrylates (Acrylic), Polyacrylonitrile (PAN or Acrylonitrile), Polyamide (PA or Nylon), Polyamide-imide (PAI), Polyaryletherketone (PAEK or Ketone), Polybutadiene (PBD), Polybutylene (PB), Polybutylene terephthalate (PBT), Polyethylene terephthalate (PET), Polyurethane (TPU), Polycarbonate (PC), Polyketone (PK), Polyester, Polyethylene/Polythene/Polyethene, Polyetherimide (PEI), Polyethylenechlorinates (PEC), Polyimide (PI), Polylactic acid (PLA), Polymethylpentene (PMP), Polyphenylene oxide (PPO), Polyphenylene sulfide (PPS), Polyphthalamide (PPA), Polypropylene (PP), Polystyrene (PS), Polysulfone (PSU), Polyvinyl chloride (PVC), Spectralon, and combinations thereof. 
         [0052]    The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. 
         [0053]    Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.