Relationship between the kink and the structure of the guidewire

The guidewire is a medical device which is used to wide range of vascular procedures. It is led to the target place to navigation the percutan coronary intervention devices. The fracture or breaking of the guidewire is about 0.1-0.8% during this procedures. The guidewires’ flexibility and kink resistance is different between the different guidewires and within the guidewire as well. It is influenced by the core material, the core diameter, and the tip style. In this study the core diameter, and the tip style was defined under stereo-, metallic microscope, and scanning electron microscope. The core material was same in the guidewire. The core diameter was significant lower in the distal end member (31.7 μm ±1.77 μm), than on the shaft portion (176-343 μm) (p < 0.001). The tip style was a Core-to-Tip. The helical coil made of a wire with about 76.35 μm diameters, and with about 25.6 μm gaps between the turns.


Introduction
Medical guidewire is used to wide range of coronary and peripheral vascular procedures, such as angioplasty, diagnostic, interventional, and percutaneous access procedures, or radiology and neuroradiology.The guidewire is entered to the body, and it reaches the target side through the various vascular branches following the tortuous vascular vessels by pushing and rotating the part of the guidewire which is outside of the patients.After the position of the guidewire medical devices may be delivered to the desired side by simply sliding over the guidewire [1-3, 20, 21].
The length of the guidewire is between 50-300 cm, and the outer diameter is 0.204-1.072mm.The guidewire has a shaft portion and a distal end which comprise a helical wound.The shaft portion consists of a core, on which may be a helical coil, furthermore a cover and/or coating which is on the core or on the helical coil (Fig. 1).The distal end has different structure, however the proximal end of the helical coil contain the flattened distal part of the core [2,4].
The guidewire has six parts, which can influence the performance characteristics and clinical relevance.It is the core material, the core diameter, the core taper, the tip style, the covers and coils, and the coating (Fig. 1 [4].The core material usually made of type 304 stainless steel or Nitionol.The high tensile strength stainless steel has good flexibility, but Nitinol has excellent flexibility, and it is a superelastic alloy designed for kink resistance [4,5].The smaller core diameter increases the flexibility, and enhanced the trackability.The larger diameter has more support and torque [4]. The taper influence the tracking and the support.Broad, gradual, or long tapers improve the tracking, but it has less support.Abrupt or short taper has greater support but greater tendency to prolapsed too [4,5].The tip style affects the steering and the softness.Two tip styles are distinguished: the Shaping-Ribbon (Fig. 2), and the Core-to-Tip style (Fig. 3).The Shaping Ribbon is softer and flexible, but the Core-to-Tip has precise steering and tip control [4,5].The coils affect the support, the steering, the tracking, the visibility and the tactile feedback.The coil is located only on the tip or reached out outer the tip [4,5].It made of material with 13 gramm/cm 3 density, such as platinum alloy [6].The cover is located on the distal end, and the distal end of the shaft portion.It made of polymer or plastic.It provide the lubricity [4,5].The coating increase the trackability and minimized the friction.The coating may be hydrophilic or hydrophobic.It is located on the shaft.The hydrophilic coating is not use with cover [4,5].
The fracture or breaking of vascular procures which is terminated cardiac surgery, is about 2%.The fracture or breaking of the guidewire is about 0.1-0.8%[7,8].The damage of the guidewire are caused by manufacturing fault [9][10][11][12] or resulting from use [7,13,14].The guidewires' flexibility and kink resistance is different between the different guidewires and within the guidewire as well.It is influenced by the core material, the core diameter, and the tip style [4-6] [15-18].
In one documented case of one type of the guidewire was significant different the kink resistance between the distal end and the shaft portion of the guidewire [17].In this article the explanation of this difference was aimed to find.We have shown that the core material, the core diameter, and the tip style influence the kink resistance [4-6], [15][16][17][18].The core material was same along the guidewire therefore it was not cause the difference of kink resistance along the guidewire [19].We have investigated the rest of the properties, the core diameter, and the tip style.

Materials and methods
The core material of the investigated guidewire made of 304 grade SS.The hidden structures were revealed by longitudinal section grinding.The cut distal end of guidewire was laid in resin (Spofadental Duracryl Plus).After its hardening the appropriate side was grinded and polished (Buehler Alpha).Micrometer (Mitutoyo was used to determine the diameter.The approximate size of the hidden structures was defined by reflected-light (metallic) microscope (Olympus PMG-3).The pictures were made by Nikon SMZ2T stereomicroscope with Olympus Camedia 5500 digital camera, reflected-light microscope (Olympus PMG-3), and scanning electron microscope (Philips XL-30) equipped with energy-dispersive X-ray spectroscope (EDAX).The measure of the diameter was made three replicates.The main measured points were: the tip, the center of the distal end member, the joint of the distal end member and shaft portion.The other parts of the guidewire were also measured but randomly.

Results
3.1 The core diameter 3.1.1Guidewire diameter The guidewire diameter was marked on the packing (360 µm).We have found that the diameter was changed along the guidewire (Fig. 4).Three transitions were found by between the joint of the distal end and shaft portion (4 cm), the phosphate coating transition (7 cm), and by 17 cm from the distal tip (Fig. 4).

Core diameter within the distal end
The core diameter was not change within the distal tip (Fig. 5).Approximately the average size of the core diameter is 31.7 µm 1.77 µm (Fig. 5).

Core diameter within the shaft portion
The diameter of the shaft portion without phosphate coating was same as the diameter of the guidewire, i.e. increasing steadily from 176 µm to 303 µm (Fig. 4).
The thickness of the phosphate coating was only some µm; it was removed, the core was shown (Fig. 6).The phosphate coating was damaged during the kink procedures.It was detached partially or completely from the core surface.The SEM-EDAX spectrum of the pop-up part under the damaged phosphate coating (Fig. 7a) was compared with the SEM-EDAX spectrum of the coating (Fig. 7b) and the core (Fig. 7c) to prevent the origin of the pop-up part.In the SEM-EDAX spectrum of the pop-up part there were the material of the coating and the core too.It is demonstrating that the core was laid under the coating.

The change of the core diameter along the guidewire
The average core diameter of the distal end was approximately 31.7 µm±1.77µm.The core diameter of the shaft portion was increasing steadily from 176 µm to 303 µm from 4 cm to 7 cm measured from the distal tip, 309 µm from 7 cm to 17 cm measured from the distal tip, and 343 µm from 17 cm measured from the distal tip (Fig. 8).The core diameter was highly significant lower than the shaft portion diameter (p 0.001, Mann-Whitney U test; two-tailed test).

Tip style
The tip style was defined by longitudinal section grinding (Fig. 9).The core was laid along in the distal end to the tip within the helical coil.This tip style called Core-to-Tip.

Further structural investigations 3.3.1 The solder
The length of the solder was approximately 771 µm, and it involved 7 spiral ring (Fig. 10a).The thickest diameter, which was the thickest part of the guidewire, was approximately 361 µm (Fig. 10b).The rest part of the solder was within the helical coil; its diameter did not exceed the 347 µm diameter.Gap between the turns: The average gap between the turns was approximately 25.6 µm 0.86 µm (Fig. 12).

Discussion and conclusions
In this study we have investigated what influenced the different kink resistance between the distal end and the shaft portion of the guidewire.They were caused by the core material, the core diameter, and the tip style.The core material was same, therefore the other two parameters were defined.First of all the core diameter was investigated.The guidewire has three diameter transitions (between the joint of the distal end and shaft portion, by the phosphate coating transition, and by 17 cm from the distal tip), so the guidewire diameter was changed between 176-343 µm.The core within the distal tip was made visible by longitudinal section grinding.The core diameter was 31.7 µm 1.77 µm here.This diameter is significant lower than the diameter of the shaft portion (p 0.001, Mann-Whitney U test; two-tailed test).
The tip style was Core-to-Tip which contained the core whit about 31.7 µm diameters and the helical coil, which made of  The used methods and measures are suitable for investigation of another guidewires.They are useful widely, so soon we can compare the different types of the guidewires.
The flexibility and the kink resistance of the guidewire with Nitinol core material will be determined and compared to the guidewire with 304 grade SS core material.We suppose that the guidewire with Nitinol core material will be more flexible and it will have better kink resistance than the guidewire with 304 grade SS core material.They structure will be different from the guidewire with 304 grade SS core material.

Fig. 4 .
Fig. 4. The change of the guidewire diameter in function the distance from the guidewire tip

Fig. 5 .
Fig. 5.The core diameter which are measured a) in the center of the helical coil, and b) in the solder, metallic microscopic photo

Fig. 6 .
Fig. 6.The damaged phosphate coating a) small and b) higher magnification, SEM photo

Fig. 7 .Fig. 8 .
Fig. 7.The SEM-EDAX spectrum and the material composition of a) the part of the shaft portion under the phosphate coating b) the phosphate coating c) the core

Fig. 11 .
Fig. 11.One-one measure point of the wire diameter a) on the center of the helical coil and b) in the solder, metallic microscopic photo

Fig. 12 .
Fig. 12. a) The gap and b) its size, metallic microscopy photo