fig1 shows an enlarged side view of a guidewire made according to a very desirable variation of the inventive guidewire ( 100 ). the guidewire ( 100 ) is made up of the wire core formed of a flexible torqueable wire filament material , of the alloys described below , and has a total length typically between about 50 and 300 centimeters . the proximal section ( 102 ) preferably has a uniform diameter ( along its length ) of about 0 . 010 to 0 . 025 inches , preferably 0 . 010 to 0 . 018 inches . the relatively more flexible distal section ( 104 ) extends for 3 to 30 centimeters or more of the distal end of the guidewire ( 100 ). there may be a middle section ( 106 ) having a diameter intermediate between the diameter of the two portions of the wire adjoining the middle section . the middle section ( 106 ) may be continuously tapered , may have a number of tapered sections or sections of differing diameters , or may be of a uniform diameter along its length . if middle section ( 106 ) is of a generally uniform diameter , the guidewire core will neck down as is seen at ( 108 ). the distal section ( 104 ) of the guidewire ( 100 ) typically has an end cap ( 110 ), a fine wire coil ( 112 ), and a solder joint ( 114 ). the fine wire coil ( 112 ) may be radiopaque and made from materials including but not limited to platinum and its alloys . specific inventive variations of the distal section ( 104 ) are described below . the end cap ( 110 ) may be radiopaque to allow knowledge of the position of the coil ( 112 ) during the process of inserting the catheter and traversal of the guidewire through the vasculature . all or part of the guidewire proximal section ( 102 ) and middle section ( 106 ) and distal section ( 104 ) may be coated with a thin layer ( 116 ) of polymeric material to improve its lubricity without adversely affecting the flexibility or shapeability of the guidewire . fig2 shows a variation of the inventive guidewire which is a composite , e . g ., a distal portion of the guidewire core is produced of the specified alloy and the composite is of another material or configuration . in particular , the composite guidewire ( 140 ) is made up of a proximal section ( 142 ) that is a section of small diameter tubing of , e . g ., an appropriate stainless steel or high elasticity alloy such as those discussed elsewhere herein . the tubular proximal section ( 142 ) is attached by soldering or by gluing or by other joining method suitable for the materials involved at the joint ( 144 ) to a distal section ( 146 ) that extends to the distal end of the composite guidewire assembly ( 140 ). the distal tip ( 148 ) of the catheter assembly ( 140 ) may be of the same configuration as those otherwise described herein . the catheter assembly may be coated ( 150 ) with polymeric material , as desired . fig3 shows a partial cutaway of one embodiment of the distal section ( 104 ) and the distal end of the intermediate section ( 106 ). the metallic guidewire core is shown partially coated with polymer ( 116 ) and a malleable metal coating ( 118 ) on the tapered portion of the distal tip . the malleable metal may be selected from suitable radiopaque materials such as gold or other easily solderable materials such as silver , platinum , palladium , rhodium , and alloys of the above . the tip also includes a radiopaque coil ( 112 ) which is bounded on its proximal end by a solder joint ( 114 ) and is joined with the end of the guidewire at ( 110 ). the radiopaque coil ( 112 ) may be made of known suitable materials such as platinum , palladium , rhodium , silver , gold , and their alloys . preferred is an alloy containing platinum and a small amount of tungsten . the proximal and distal ends of coil ( 112 ) may be secured to the core wire by soldering . fig4 shows a partial cutaway of another embodiment of the distal section ( 104 ) of the inventive guidewire . in this embodiment , the metal guidewire core has a proximal tapered portion ( 120 ), a distal tapered section ( 122 ) with a solder joint ( 114 ) separating the two sections , and a constant diameter tip ( 124 ). the distal tip ( 124 ) may have constant diameter typically between about 0 . 002 and 0 . 005 inches , preferably about 0 . 003 inches . the distal tip ( 124 ) is preferably between about 1 and 5 cm in length , preferably about 2 cm but the portion of constant diameter extends for at least about 25 % of the distance between the solder joint ( 128 ) and the solder joint ( 114 ). this constant diameter section marginally stiffens the distal tip assembly for enhanced control . the entire distal section ( 104 ) desirably is between about 20 and 50 cm , preferably about 25 cm in length . the maximum diameter of the proximal tapered portion ( 120 ) of the guidewire core typically is between about 0 . 005 and 0 . 020 inches , preferably about 0 . 010 inches . the distal tapered portion ( 122 ) and distal tip ( 124 ) are again shown with a malleable metal coating ( 118 ) such that the distal tapered portion ( 122 ) and distal tip ( 124 ) stay bent upon forming by the physician . in this embodiment , the fine wire coil ( 112 ) is bounded on its proximal end by a solder joint ( 114 ) and on its distal end by an end cap ( 110 ). the end cap ( 110 ) is connected to the guidewire by means of a metallic ribbon ( 126 ). the ribbon ( 126 ) may be made of stainless steel , platinum , palladium , rhodium , silver , gold , tungsten , and their alloys or other materials which are plastic and that are easily soldered . the ribbon ( 126 ) is soldered to the fine wire coil ( 112 ) and to the distal tip ( 124 ) of the distal section ( 104 ) of the guidewire at a solder joint ( 128 ) such that the end cap ( 110 ) is secured against the fine wire coil ( 112 ). fig5 a and 5b show yet another inventive embodiment of the distal section ( 104 ) of the guidewire ( 100 ). fig5 a shows a side view , partial cutaway of the inventive guidewire . the fine wire coil ( 112 ) may be bounded by a polymer adhesive ( 136 ) that joins the coil ( 112 ) to the core wire and an end cap ( 110 ) and further secured to the guidewire core by a solder joint ( 128 ). in this embodiment , the distal section ( 104 ) of the guidewire again comprises a tapered portion ( 120 ) that is proximal to the polymer adhesive ( 136 ) and a tapered portion ( 122 ) that is distal to the polymer adhesive ( 136 ). the distal section ( 104 ) also comprises a smaller diameter portion ( 130 ) or &# 34 ; neck &# 34 ; that may be surrounded by optional inner coil ( 132 ). as may be seen from fig5 a , just distal of the neck ( 130 ) is a section which is larger in side view than is the neck . as may be seen from fig5 a , just distal of the neck ( 130 ) is a section which is larger in side view than is the neck . the inner coil ( 132 ) may be made of a suitable metallic material preferably that is easy to solder and preferably radiopaque . it is preferably platinum or stainless steel . one way to produce neck ( 130 ) is to flatten the distal portion of the guidewire ( 134 ) distal to the neck so that the resulting spade ( 134 ) is no longer of circular cross - section but rather is of rectangular shape . this may be more easily visualized in fig5 b since that figure shows a cutaway top view of the guidewire shown in fig5 a . as in above - described embodiments , the end cap ( 110 ) is secured to the guidewire by a metallic ribbon ( 126 ). the solder joint ( 128 ) secures the guidewire core to the inner helical coil ( 132 ) which secures the end cap ( 110 ) via the ribbon ( 126 ) and further secures the outer fine wire coil ( 112 ). this configuration is especially valuable for use with guidewire materials which are not easily solderable . the solder joint need not adhere to the guidewire and yet the inner coil ( 132 ), ribbon ( 126 ), and outer fine wire coil ( 112 ) all are maintained as a single integral unit and have no chance of slipping proximally or distally on the guidewire assembly . although the embodiment described with reference to fig5 a and 5b speaks generally of a guidewire made of a high elasticity alloy , materials for the guidewire and the ribbon such as stainless steel , platinum , palladium , rhodium and the like are suitable with that embodiment . fig6 is a partial side view of a midsection joint in the inventive guidewire . on many variations of the inventive guidewire , various sections of the core are joined by tapered sections such as seen at ( 160 ). this means that the guidewire core is significantly stiffer at the proximal end of the tapered joint ( 160 ). we have found that it is sometimes desirable to place grooves ( 162 ) in that proximal end to lower the overall stiffness of the guidewire at that junction and yet retain the columnar strength . this guidewire is typically used in a catheter which is made up of an elongate tubular member having proximal and distal ends . the catheter is ( again ) about 50 to 300 centimeters in length , typically between about 100 and 200 centimeters in length . often , the catheter tubular member has a relatively stiff proximal section which extends along a major portion of the catheter length and one or more relatively flexible distal sections which provide greater ability of the catheter to track the guidewire through sharp bends and turns encountered as the catheter is advanced through the torturous paths found in the vasculature . the construction of a suitable catheter assembly having differential flexibility along its length is described in u . s . pat . no . 4 , 739 , 768 . we have found that certain alloys , particularly ni - ti alloys , retain their super - elastic properties during traversal through the vasculature and yet are sufficiently pliable that they provide the physician using the guidewire with enhanced &# 34 ; feel &# 34 ; or feedback and yet do not &# 34 ; whip &# 34 ; during use . that is to say , as a guidewire is turned it stores energy during as a twist and releases it precipitously as it &# 34 ; whips &# 34 ; to quickly recover the stored stress . the preferred alloys do not incur significant unrecovered strain during use . we have also found that if the eccentricity of the wire , i . e ., the deviation of the cross - section of the guidewire from &# 34 ; roundness &# 34 ; ( particularly in the middle section ) is maintained at a very low value , the guidewire is much easier to steer or direct through the vasculature . the material used in the guidewires of this invention are of shape memory alloys which exhibit super - elastic / pseudo - elastic shape recovery characteristics . these alloys are known . see , for instance , u . s . pat . nos . 3 , 174 , 851 and 3 , 351 , 463 as well as 3 , 753 , 700 ; however , the &# 39 ; 700 patent describes a less desirable material because of the higher modulus of the material due to an increased iron content . these metals are characterized by their ability to be transformed from an austenitic crystal structure to a stress - induced martensitic ( sim ) structure at certain temperatures , and return elastically to the austenitic structure when the stress is removed . these alternating crystalline structures provide the alloy with its super - elastic properties . one such well - known alloy , nitinol , is a nickel - titanium alloy . it is readily commercially available and undergoes the austenite - sim - austenite transformation at a variety of temperature ranges between - 20 ° c . and 30 ° c . these alloys are especially suitable because of their capacity to elastically recover almost completely to the initial configuration once the stress is removed . typically there is little plastic deformation , even at relatively high strains . this allows the guidewire to undertake substantial bends as it passes through the body &# 39 ; s vasculature , and yet return to its original shape once the bend has been traversed without retaining any hint of a kink or a bend . however , the tips shown are often sufficiently plastic that the initial tip formation is retained . nevertheless , compared to similar stainless steel guidewires , less force need be exerted against the interior walls of the vessels to deform the guidewire of the invention along the desired path through the blood vessel thereby decreasing trauma to the interior of the blood vessel and reducing friction against the coaxial catheter . a guidewire , during its passage through the vasculature to its target site , may undertake numerous bends and loops . the desirably of enhancing the ease with which a guidewire may be twisted to allow the bent distal tip to enter a desired branch of the vasculature cannot be overstated . we have found that a major factor in enhancing such ease of use , that is , in enhancing the controllability of the guidewires is by controlling the eccentricity of the cross - section of the middle portion of the guidewire . we have found that by maintaining the middle portion of the guidewire ( 106 in fig1 ) to an eccentricity ratio of 1 ± 10 - 4 , the guidewire is significantly more controllable than those which fall outside this ratio . by &# 34 ; eccentricity &# 34 ;, we mean that at any point along the guidewire the ratio of the largest diameter at that cross - section to the smallest diameter of the wire at that cross - section . to achieve these results of high strength and enhanced control even while allowing feedback to the attending physician during use , we have found that the following physical parameters of the alloy are important . in a stress - strain test as shown on a stress - strain diagram such as that found in fig7 the stress found at the midpoint of the upper plateau ( up ) ( measured , e . g . at about 3 % strain when the test end point is about 6 % strain ) should be in the range of 75 ksi ( thousand pounds per square inch ) + 10 ksi and , preferably , in the range of 75 ksi ± 5 ksi . additionally , this material should exhibit a lower plateau ( lp ) of 25 ± 7 . 5 ksi , preferably 20 ± 2 . 5 ksi , measured at the midpoint of the lower plateau . the material preferably has no more than about 0 . 25 % residual strain ( rs ) ( when stressed to 6 % strain and allowed to return ) and preferably no more than about 0 . 15 % residual strain . the preferred material is nominally 50 . 6 %± 0 . 2 % ki and the remainder ti . the alloy should contain no more than about 500 parts per million of any of o , c , or n . typically such commercially available materials will be sequentially mixed , cast , formed , and separately co - worked to 30 - 40 %, annealed and stretched . by way of further explanation , fig7 shows a stylized stress - strain diagram showing the various parameters noted above and their measurement on that diagram . as stress is initially applied to a sample of the material , the strain is at first proportional ( a ) until the phase change from austentite to martensite begins at ( b ). at the upper plateau ( up ), the energy introduced with the applied stress is stored during the formation of the quasi - stable martensite phase or stress - induced - martensite ( sim ). upon substantial completion of the phase change , the stress - strained relationship again approaches a proportional relationship at ( c ). the stress is no longer applied when the strain reaches 6 %. the measured value ( up ) is found at the midpoint between zero and 6 % strain , i . e ., at 3 % strain . if another terminal condition of strain is chosen , e . g ., 7 %, the measured valued of ( up ) and ( lp ) would be found at 3 . 5 %. materials having high up values produce guidewires which are quite strong and allow exceptional torque transmission but cause a compromise in the resulting &# 34 ; straightness &# 34 ; of the guidewire . we have found that guidewires having high up values in conjunction with high lp values are not straight . these guidewires are difficult to use because of their tendency to &# 34 ; whip &# 34 ; as they are turned . again , that is to say , as a guidewire is turned it stores energy during as a twist and releases it quickly . the difficulty of using such a whipping guidewire should be apparent . materials having up values as noted above are suitable as guidewires . furthermore , materials having values of lp which are high , again , are not straight . lowering the value of lp compromises the ability of the guidewire to transmit torque but improves the ease with which a straight guidewire may be produced . lowering the lp value too far , however , results in a guidewire which , although round , has poor tactile response . it feels somewhat &# 34 ; vague &# 34 ; and &# 34 ; soupy &# 34 ; during its use . the lp values provided for above allow excellent torque transmission , straightness , and the valuable tactile response . the values of residual strain discussed above define a materials which do not kink or otherwise retain a &# 34 ; set &# 34 ; or configuration after stress during use as a guidewire . in each instance , the following procedure was used in producing the data displayed in the table which follows : commercial ni - ti alloy wires having a nominal composition of 50 . 6 % ni and the remainder ti , and diameters of 0 . 13 &# 34 ;, 0 . 16 &# 34 ;, or 0 . 18 &# 34 ; were stressed at room temperature . in each instance , values for transition temperature , ps , up , and lp were measured . additionally , several of the noted wires were introduced into a u - shaped tygon tube and spun to allow qualitative evaluation of the roundness and tactile response of the wires . comments on that response are also found in the following table . table______________________________________ comparative / invention up lp ps a * qualitative # ( c / i ) ( ksi ) ( ksi ) (%) t ° c . spin test______________________________________1 . sup . 1 i 74 . 48 31 . 45 0 . 06 - 11 smooth rotation , good feel2 . sup . 2 i 76 . 94 18 . 90 0 . 121 - 8 smooth rotation , good feel3 . sup . 3 i 71 . 92 24 . 06 0 . 10 13 . 5 smooth4 . sup . 4 c 78 . 24 58 . 82 0 . 20 - 9 very rough turning , whipped5 . sup . 5 c 63 . 80 13 . 25 0 . 2 12 . 5 smooth turning , mushy feel6 . sup . 6 c 58 . 30 13 . 31 0 . 0 - 12 turned roughly , mushy feel7 . sup . 7 c -- -- -- -- difficult to______________________________________ turn . sup . 1 commercially available from u . s . nitinol , inc . . sup . 2 commercially available from special metals , inc . . sup . 3 commercially available from shape metal alloys , inc . . sup . 4 commercially available as a plastic coated 0 . 13 &# 34 ; guidewire from fuji terumo , inc . . sup . 5 commercially available from iti . . sup . 6 commercially available from metal tek . sup . 7 stainless steel * measured at room temperature with no applied stress . these data describe both guidewires made according to the invention and comparative guidewires . additionally , they show that guidewire made from a typical stainless steel alloy is very difficult to turn using the qualitative test described above . as mentioned above , all or part of the guidewire core may be covered or coated with one or more layers of a polymeric material . the coating is applied typically to enhance the lubricity of the guidewire core during its traversal of the catheter lumen or the vascular walls . as noted above , at least a portion of the guidewire core may simply be coated by dipping or spraying or by similar process with such materials as polysulfones , polyfluorocarbons ( such as teflon ), polyolefins such as polyethylene , polypropylene , polyesters ( including polyamides such as the nylon &# 39 ; s ), and polyurethanes ; their blends and copolymers such as polyether block amides ( e . g ., pebax ). it is often desirable to utilize a coating such as discussed just above on the proximal portion of the guidewire and a coating such as discussed below on the more distal sections . any mixture of coatings placed variously on the guidewire is acceptable as chosen for the task at hand . the guidewire core may also be at least partially covered with other hydrophilic polymers including those made from monomers such as ethylene oxide and its higher homologs ; 2 - vinyl pyridine ; n - vinylpyrrolidone ; polyethylene glycol acrylates such as mono - alkoxy polyethylene glycol mono ( meth ) acrylates , including mono - methoxy triethylene glycol mono ( meth ) acrylate , mono - methoxy tetraethylene glycol mono ( meth ) acrylate , polyethylene glycol mono ( meth ) acrylate ; other hydrophilic acrylates such as 2 - hydroxyethylmethacrylate , glycerylmethacrylate ; acrylic acid and its salts ; acrylamide and acrylonitrile ; acrylamidomethylpropane sulfonic acid and its salts cellulose , cellulose derivatives such as methyl cellulose ethyl cellulose , carboxymethyl cellulose , cyanoethyl cellulose , cellulose acetate , polysaccharides such as amylose , pectin , amylopectin , alginic acid , and cross - linked heparin ; maleic anhydride ; aldehydes . these monomers may be formed into homopolymers or block or random copolymers . the use of oligomers of these monomers in coating the guidewire for further polymerization is also an alternative . preferred precursors include ethylene oxide ; 2 - vinyl pyridine ; n - vinylpyrrolidone and acrylic acid and its salts ; acrylamide and acrylonitrile polymerized ( with or without substantial crosslinking ) into homopolymers , or into random or block copolymers . additionally , hydrophobic monomers may be included in the coating polymeric material in an amount up to about 30 % by weight of the resulting copolymer so long as the hydrophilic nature of the resulting copolymer is not substantially compromised . suitable monomers include ethylene , propylene , styrene , styrene derivatives , alkylmethacrylates , vinylchloride , vinylidenechloride , methacrylonitrile , and vinyl acetate . preferred are ethylene , propylene , styrene , and styrene derivatives . the polymeric coating may be cross - linked using various techniques , e . g ., by light such as ultraviolet light , heat , or ionizing radiation , or by peroxides or azo compounds - such as acetyl peroxide , cumyl peroxide , propionyl peroxide , benzoyl peroxide , or the like . a polyfunctional monomer such as divinylbenzene , ethylene glycol dimethacrylate , trimethylolpropane , pentaerythritol di - ( or tri - or tetra -) methacrylate , diethylene glycol , or polyethylene glycol dimethacrylate , and similar multifunctional monomers capable of linking the monomers and polymers discussed above . polymers or oligomers applied using the procedure described below are activated or functionalized with photoactive or radiation - active groups to permit reaction of the polymers or oligomers with the underlying polymeric surface . suitable activation groups include benzophenone , thioxanthone , and the like ; acetophenone and its derivatives specified as : r 1 is h , r 2 is an alkoxy group including -- och 3 , -- oc 2 h 3 , r 3 is ph ; or r 1 = r 2 = an alkoxy group , r 3 is ph ; or r 1 = r 2 = an alkoxy group , r 3 is h ; or r 1 = r 2 = cl , r 3 is h or cl . the polymeric coating may then be linked 25 with the substrate using known and appropriate techniques selected on the basis of the chosen activators , e . g ., by ultraviolet light , heat , or ionizing radiation . crosslinking with the listed polymers or oligomers may be accomplished by use of peroxides or azo compounds such as acetyl peroxide , cumyl peroxide , propionyl peroxide , benzoyl peroxide , or the like . a polyfunctional monomer such as divinylbenzene , ethylene glycol dimethacrylate , trimethylolpropane , pentaerythritol di - ( or tri - or tetra -) methacrylate , diethylene glycol , or polyethylene glycol dimethacrylate , and similar multifunctional monomers capable of linking the polymers and oligomers discussed above is also appropriate for this invention . the polymeric coating may be applied to the guidewire by any of a variety of methods , e . g ., by spraying a solution or suspension of the polymers or of oligomers of the monomers onto the guidewire core or by dipping it into the solution or suspension . initiators may be included in the solution or applied in a separate step . the guidewire may be sequentially or simultaneously dried to remove solvent after application of the polymer or oligomer to the guidewire and crosslinked . the solution or suspension should be very dilute since only a very thin layer of polymer is to be applied . we have found that an amount of oligomer or polymer in a solvent of between 0 . 25 % and 5 . 0 % ( wt ), preferred is 0 . 5 to 2 . 0 % ( wt ), is excellent for thin and complete coverage of the resulting polymer . preferred solvents for this procedure when using the preferred polymers and procedure are water , low molecular weight alcohols , and ethers , especially methanol , propanol , isopropanol , ethanol , and their mixtures . other water miscible solvents , e . g ., tetrahydrofuran , methylene dichloride , methylethylketone , dimethylacetate , ethyl acetate , etc ., are suitable for the listed polymers and must be chosen according to the characteristics of the polymer ; they should be polar because of the hydrophilic nature of the polymers and oligomers but , because of the reactivity of the terminal groups of those materials , known quenching effects caused by oxygen , hydroxyl groups and the like must be recognized by the user of this process when choosing polymers and solvent systems . particularly preferred as a coating for the guidewire cores discussed herein are physical mixtures of homo - oligomers of at least one of polyethylene oxide ; poly - 2 - vinyl pyridine ; polyvinylpyrrolidone , polyacrylic acid , polyacrylamide , and polyacrylonitrile . the catheter bodies or substrates are preferably sprayed or dipped , dried , and irradiated to produce a polymerized and crosslinked polymeric skin of the noted oligomers . the lubricious hydrophilic coating is preferably produced using generally simultaneous solvent removal and crosslinking operations . the coating is applied at a rate allowing &# 34 ; sheeting &# 34 ; of the solution , e . g ., formation of a visibly smooth layer without &# 34 ; runs &# 34 ;. in a dipping operation for use with most polymeric substrates including those noted below , the optimum coating rates are found at a linear removal rate between 0 . 25 and 2 . 0 inches / sec , preferably 0 . 5 and 1 . 0 inches / sec . the solvent evaporation operations may be conducted using a heating chamber suitable for maintaining the surface at a temperature between 25 ° c . and the glass transition temperature ( t g ) of the underlying substrate . preferred temperatures are 50 ° c . to 125 ° c . most preferred for the noted and preferred solvent systems is the range of 75 ° to 110 ° c . ultraviolet light sources may be used to crosslink the polymer precursors onto the substrate . movement through an irradiation chamber having an ultraviolet light source at 90 - 375 nm ( preferably 300 - 350 nm ) having an irradiation density of 50 - 300 mw / cm 2 ( preferably 150 - 250 mw / cm 2 ) for a period of three to seven seconds is desired . passage of a guidewire core through the chamber at a rate of 0 . 25 to 2 . 0 inches / second ( 0 . 5 to 1 . 0 inches / second ) in a chamber having three to nine inches length is suitable . when using ionizing radiation , a radiation density of 1 to 100 krads / cm 2 ( preferably 20 to 50 krads / cm 2 ) may be applied to the solution or suspension on the polymeric substrate . exceptional durability of the resulting coating is produced by repetition of the dipping / solvent removal / irradiation steps up to five times . preferred are two to four repetitions . we have found that it is often desirable to incorporate a &# 34 ; tie &# 34 ; layer as a coating between the outer polymeric surface and the guidewire core to enhance the overall adhesion of the outer polymeric surface to the core . of course , these materials must be able to tolerate the various other solvents , cleaners , sterilization procedures , etc . to which the guidewire and its components are placed during other production steps . choice of materials for such tie layers is determined through their functionality . specifically , the materials are chosen for their affinity or tenacity to the outer polymeric lubricious or hydrophilic coating . clearly , the tie layer material must be flexible and strong . the material must be extrudable and preferably easily made into shrinkable tubing for mounting onto the guidewire through heating . we have found that various nylon &# 39 ; s , polyethylene , polystyrene , polyurethane , and preferably polyethylene terephthalate ( pet ) make excellent tie layers . these tubing materials may be also formulated to include radio opaque materials such as barium sulfate , bismuth trioxide , bismuth carbonate , tungsten , tantalum or the like . as noted above , one readily achievable manner of applying a tie layer is by heat - shrinking the tubing onto the guidewire . the guidewire core is simply inserted into a tubing of suitable size -- often with a small amount of a &# 34 ; caulking &# 34 ; it either end to seal the tubing from incursion of fluids or unsterile materials from beneath the tubing . the tubing is cut to length and heated until it is sufficiently small in size . the resulting tubing tie layer desirably is between about 0 . 0025 and 0 . 015 inches in thickness . the thinner layers are typically produced from polyurethane or pet . the layer of lubricious polymer is then placed on the outer surface of the shrunk tubing . another procedure for preparing or pretreating guidewires prior to receiving a subsequent coating of a polymer , preferably a polymer which is lubricious , biocompatible , and hydrophilic , is via the use of a plasma stream to deposit a hydrocarbon or fluorocarbon residue . the procedure is described as follows : the guidewire core is placed in a plasma chamber and cleaned with an oxygen plasma etch . the guidewire core is then exposed to a hydrocarbon plasma to deposit a plasma - polymerized tie layer on the guidewire core to complete the pretreatment . the hydrocarbon plasma may comprise a lower molecular weight ( or gaseous ) alkanes such as methane , ethane , propane , isobutane , butane or the like ; lower molecular weight alkenes such as ethene , propene , isobutene , butene or the like or ; gaseous fluorocarbons such as tetrafluoromethane , trichlorofluoromethane , dichlorodifluoromethane , trifluorochloromethane , tetrafluoroethylene , trichlorofluoroethylene , dichlorodifluoroethylene , trifluorochloroethylene and other such materials . mixtures of these materials are also acceptable . the tie layer apparently provides c -- c bonds for subsequent covalent bonding to the outer hydrophilic polymer coating . preferred flow rates for the hydrocarbon into the plasma chamber are in the range of 500 c . c ./ min . to 2000 c . c ./ min . and the residence - time of the guidewire in the chamber is in the range of 1 - 20 minutes , depending on the chosen hydrocarbon and the plasma chamber operating parameters . power settings for the plasma chamber are preferably in the range of 200 w to 1500 w . a tie layer of plasma - produced hydrocarbon residue having a thickness on the order of 10 å thick is disposed between core and coating . this process typically produces layers of hydrocarbon residue less than about 100 å in thickness , and more typically less than about 100å . tie layer effectively bonds the outer layer to the guidewire core while adding very little additional bulk to the guidewire . guidewires made according to this invention therefore avoid the size and maneuverability problems of prior art guidewires . the pretreated guidewire may be coated by a polymer using a procedure such as described above . for example , the pretreated guidewire may be dipped in a solution of a photoactive hydrophilic polymer system , i . e ., a latently photoreactive binder group covalently bonded to a hydrophilic polymer . after drying , the coated guidewire is cured by exposing it to uv light . the uv light activates the latently reactive group in the photoactive polymer system to form covalent bonds with crosslinked c -- c bonds in the hydrocarbon residue tie layer . the dipping and curing steps are preferably repeated often enough , typically twice , to achieve the appropriate thickness of the hydrophilic coating layer . one highly preferred variation of the invention involves a guidewire with metal core , preferably 0 . 010 to 0 . 025 &# 34 ; thick stainless steel or nitinol . the exterior surface of guidewire is a biocompatible coating of a polyacrylamide / polyvinylpyrrolidone mixture bonded to a photoactive binding agent . the preferred coating is made from a mixture of bio - metric systems pa03 and pv05 ( or pv01 ) binding systems according to the examples below . the photoactive hydrophilic polymer system of this preferred embodiment is a mixture of bio - metric systems pa03 polyacrylamide / binder system and bio - metric systems pv05 polyvinylpyrrolidone system . the polyacrylamide system provides lubricity , and the polyvinylpyrrolidone system provides both lubricity and binding for durability . the exact proportions of the two systems may be varied to suit the application . as an alternative , however , the hydrophilic biocompatible coating may be polyacrylamide alone , polyvinylpyrrolidone alone , polyethylene oxide , or any suitable coating known in the art . in addition , a coating of heparin , albumin or other proteins may deposited over the hydrophilic coating in a manner known in the art to provide additional biocompatibility features . the guidewire or other device may be cleaned by using an argon plasma etch in place of the oxygen plasma etch . the thickness of the plasma - polymerized tie layer may also vary without departing from the scope of this invention . the following examples are further illustrative of the articles and methods of this invention . the invention is not limited to these examples . a 0 . 016 &# 34 ; diameter nitinol guidewire was placed in a plasma etch mk ii plasma chamber and cleaned with an oxygen plasma for 10 minutes . methane flowing at a rate of 2000 c . c ./ min . was admitted into the chamber , and the chamber operated at a power setting of 400 w for 2 minutes to deposit a hydrocarbonaceous residue onto the surface of the wire . all but approximately six inches of the wire was dipped in a polyvinylpyrrolidone / polyacrylamide ( pvp / pa ) photocrosslinkable solution of a mixture of 67 % bsi pv01 and 33 % bsi pa03 . the coated guidewire was then dried and exposed to an ultraviolet light ( 325 nm .) for 8 seconds . the dipping , drying , and exposing steps were repeated twice . when wetted , the resulting wire felt lubricious and required less force to pull through an 0 . 018 &# 34 ; id catheter than an uncoated wire . a 0 . 016 &# 34 ; diameter nitinol guidewire was placed in a plasma etch mk ii plasma chamber and cleaned with an oxygen plasma for 10 minutes . methane flowing at a rate of 1500 c . c ./ min . was admitted into the chamber , and the chamber was operated at a power setting of 600 w for 5 minutes to plasma - treat the methane into a hydrocarbonaceous residue on the surface of the wire . all but approximately six inches of the wire was dipped in a polyvinylpyrrolidone / polyacrylamide ( pvp / pa ) photocrosslinkable solution consisting essentially a mixture of 50 % bsi pv01 and 50 % bsi pa03 . the coated guidewire was then dried and exposed to an ultraviolet light ( 325 nm .) for 8 seconds . the dipping , drying , and exposing steps were repeated . when wetted , the resulting wire felt lubricious and required less force to pull through an 0 . 018 &# 34 ; id catheter than an uncoated wire . a 0 . 016 &# 34 ; diameter nitinol guidewire was placed in a plasma etch mk ii plasma chamber and cleaned with an oxygen plasma for 10 minutes . ethane flowing at a rate of 900 c . c ./ min . was admitted into the chamber , and the chamber was operated at a power setting of 600 w for 10 minutes to deposit a hydrocarbon residue onto the surface of the wire . all but approximately six inches of the wire was dipped in a polyvinylpyrrolidone / polyacrylamide ( pvp / pa ) photocrosslinkable solution of a mixture of 33 % bsi pv01 and 67 % bsi pa03 . the coated guidewire was then dried and exposed to an ultraviolet light ( 325 nm .) for 8 seconds . the dipping , drying , and exposing steps were repeated twice . when wetted , the resulting wire felt lubricious and required less force to pull through an 0 . 01811 id catheter than an uncoated wire . although preferred embodiments of the present invention have been described , it should be understood that various changes , adaptations , and modifications may be made therein without departing from the spirit of the invention and the scope of the claims which follow .
this invention is a surgical device . it is a guidewire for use in a catheter and is used for accessing a targeted site in a lumen system of a patient &# 39 ; s body . the guidewire may be of a high elasticity metal alloy , preferably a ni - ti alloy , having specified physical parameters , and is especially useful for accessing peripheral or soft tissue targets . a special variation of the inventive guidewire includes the concept of coating the wire with a one or more lubricious polymers to enhance its suitability for use within catheters and with the interior of vascular lumen . the &# 34 ; necked &# 34 ; guidewire tip also forms a specific variant of the invention .