Damage to Polymer Coatings on Microguidewire Tips through Shaping and J-wiring for Optimizing Flow Diverter Deployment: A Scanning Electron Microscopy Study

Article information

Neurointervention. 2026;21(1):44-52

Publication date (electronic) : 2026 January 12

doi : https://doi.org/10.5469/neuroint.2025.01130

Rasmus Holmboe Dahl, MD¹, Esben Thormann, PhD², René Wugt Larsen, PhD², Goetz Benndorf, MD, PhD^,3

¹Department of Radiology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark

²Department of Chemistry, Technical University of Denmark, Kongens Lyngby, Denmark

³Department of Radiology, Baylor College of Medicine, Houston, TX, USA

Correspondence to: Goetz Benndorf, MD, PhD Department of Radiology, Baylor College of Medicine, 1 Baylor Plz, Houston, TX 77030, USA E-mail: benndorf@bcm.edu

This work was presented at the 21st Annual Meeting of the Society of Neurointerventional Surgery in Colorado Springs, CO, USA (July 2024).

Received 2025 November 29; Revised 2025 December 22; Accepted 2025 December 26.

Abstract

INTRODUCTION

Delayed onset of non-ischemic cerebral enhancing (NICE) lesions following endovascular procedures is a rare phenomenon with a distinctive MRI pattern, characterized by multiple punctate, annular, or nodular contrast enhancements in the brain parenchyma downstream from the vascular territory accessed during endovascular therapy (EVT) [1]. These enhancing foci usually have a cortical, subcortical, or leptomeningeal distribution and a perifocal edema [1]. They are thought to represent inflammatory foreign body reactions to cerebral emboli of polymer micro-fragments originating from polymer-coated endovascular devices [2].

In the literature, NICE lesions have mainly been reported following endovascular treatment of cerebral aneurysms [1,3-6]. While benchtop testing of endovascular devices has identified some causes of coating damage and micro-fragment generation [7-13], the range of mechanisms that can damage polymer-coated devices during aneurysm treatment is not fully understood. The so-called J-wiring technique is widely used in patients treated by flow diversion to improve flow diverter wall apposition [14]. However, this technique may potentially damage polymer coatings due to frictional interaction between (1) the shaping device and microguidewire tip when creating the 180° J-loop and (2) the interaction between the J-loop and flow diverter during J-wiring [15]. In this study, we examined 3 microguidewires for coating damage using scanning electron microscopy (SEM) after applying the J-wiring technique to optimize flow diverter wall apposition in an in vitro aneurysm model.

MATERIALS AND METHODS

Guidewire Testing

Three commonly used commercially available 0.014″ guidewires, including the Avigo^TM (Medtronic), Synchro^® (Stryker), and Traxcess^TM (Terumo Neuro), were tested. Four unused samples of each guidewire were obtained: (1) 1 of each guidewire served as a control and was neither shaped nor used for the J-wiring technique; (2) 1 of each guidewire was shaped into a J-loop, but not used for the J-wiring technique; and (3) 2 of each guidewire had their distal ends shaped to a J-loop and were used to simulate the J-wiring technique in the aneurysm model. All devices were used following the manufacturer’s instructions. The guidewire tips were shaped into a 180° curve (J-loop) using a standard metal shaping tool. The J-wiring technique was simulated by inserting the guidewire into the aneurysm model via the PhenomTM 27 and moving its tip back and forth 3 times inside the flow diverter under fluoroscopic guidance (Fig. 1). The shaped guidewire tips were moved over the full length of the flow diverter between its proximal and distal ends. The distal 10 mm of all guidewires was cut and stored in dry test tubes.

Fig. 1.

Radiograph of the silicone vascular model with a Pipeline^TM Vantage flow diverter (Medtronic) deployed in a curved segment with a 6-mm aneurysm. The J-wiring technique was performed by shaping the tips of the Avigo^TM (Medtronic) (shown), Synchro^® (Stryker), and Traxcess^TM (Terumo Neuro) guidewires into 180° J-loops and moving the J-loop back and forth 3 times inside the flow diverter. The curved arrow indicates the back-and-forth movement of the guidewire tips during the J-wiring technique. The guidewires were moved between the proximal and distal ends (full length) of the flow diverter. Guidewire tips were cut immediately after withdrawal from the model and subsequently imaged by scanning electron microscopy.

RESULTS

Avigo^TM Guidewire

Representative images are shown in Fig. 2. The control guidewire remained intact. J-shaping alone caused continuous coating damage to the inner and outer curves of the guidewire, leaving a rough and irregular surface. The J-wiring technique (including J-shaping) caused continuous coating damage to the inner and outer curves of both guidewires.

Fig. 2.

Scanning electron micrographs of the Avigo^TM (Medtronic) guidewire tip. (A, B) Unshaped control: intact coating with a few small irregularities. (C, D) J-shaping alone: continuous coating damage on both the inner and outer curves of the guidewire (arrows). (E, F) The J-wiring technique: continuous coating damage on both the inner and outer curves of the guidewire (arrows).

Synchro^® Guidewire

Representative images are shown in Fig. 3. The control guidewire remained intact. J-shaping alone did not cause any coating damage. The J-wiring technique (including J-shaping) resulted in minor coating damage to the inner and outer curves of both guidewires, spanning multiple consecutive levels between gaps in the hypotube, which exposed a slightly irregular surface. In one area, delamination of the probably deeper irregular surface led to a partially attached micro-fragment measuring 9 μm in length (Fig. 3D). The guidewires exhibited a few focal areas with different types of coating damage, including long, linear scratches (Fig. 3E) and localized areas where the coating was “dragged” along the hypotube (Fig. 3F). The latter type of damage was found on the inner curve of the J-loop and was caused by a force applied in the direction from proximal to distal (right to left in Fig. 3F), most likely during the shaping maneuver.

Fig. 3.

Scanning electron micrographs of the Synchro® (Stryker) guidewire tip (polymer-coated hypotube). (A, B) Unshaped control: the coating is intact. The guidewire was also intact after J-shaping alone (not shown). (C–F) The J-wiring technique: slight coating damage were found on both the outer (arrows in C and D) and inner (not shown) curves of the guidewire on multiple consecutive levels of the hypotube, exposing an irregular surface. A partially attached micro-fragment probably coming off the deeper irregular surface (arrowheads in D). Other types of coating damage that spanned multiple gaps in the hypotube include long, linear scratches (arrows in E) and focal areas of coating being dragged along the hypotube (arrows in F).

Traxcess^TM Guidewire

Representative images are shown in Fig. 4. The control wire had one focal area with coating damage, but was otherwise intact. J-shaping alone caused coating damage to the inner and outer curves of the guidewire, spanning multiple consecutive levels of the coiled wire, exposing longitudinal grooves in the wire surface, possibly from the wire drawing process. The J-wiring technique (including J-shaping) caused coating damage to the inner and outer curves of both guidewires, spanning multiple consecutive levels of the coiled wire, which seemed to be more extensive than after J-shaping alone. The coating was mostly damaged on the outer crest (central part) of the coiled wire, while it was intact in the valleys (gaps) between the coiled wire.

Fig. 4.

Scanning electron micrographs of the Traxcess^TM (Terumo Neuro) guidewire tip (polymer-coated coiled wire). (A, B) Unshaped control: the guidewire is intact apart from a single focal area of coating damage (arrows). A few irregularities in the coating in the gaps between the coiled wire are observed. (C, D) J-shaping alone: coating damage on both the inner and outer curves of the guidewire (arrows) on multiple consecutive levels of the coiled wire. (E, F) The J-wiring technique: coating damage on both the inner and outer curves of the guidewire (arrows) on multiple consecutive levels of the coiled wire, most extensive on the outer curve. A close-up of the coating damage in (F) shows multiple longitudinal grooves in the coiled wire. The coating damage mainly involves the central part of the coiled wire, while the coating in the gaps between the coiled wire remains intact.

DISCUSSION

NICE lesions are thought to be granulomatous foreign-body reactions to cerebral emboli of hydrophilic polymer micro-fragments. They represent a rare complication to neuroendovascular therapy that sometimes may require long-term immunosuppressive treatment. NICE lesions develop following 0.05–2.30% of procedures in patients undergoing EVT for cerebral aneurysms and have been reported after simple coiling, stent/balloon-assisted coiling, and flow diversion [1,3-6]. Polymer coatings may detach from endovascular devices either through time-dependent chemical degradation or mechanical damage [16]. The continuous degradation of polymer coatings in contact with saline or blood increases over time and may result in the shredding of polymer fragments within 15 minutes [8,9]. Mechanical damage to coatings occurs when polymer-coated devices forcefully interact with each other, the vasculature, or with tools used for endovascular procedures. This can result in the breakage of chemical bonds within the polymer coating or lead to the separation of the coating from the deeper structure of the device [16]. Avoiding mechanical coating damage seems the most feasible way to reduce the risk of NICE lesions during endovascular procedures.

In this small study, we show that J-shaping alone and the J-wiring technique (including J-shaping) cause considerable mechanical damage to polymer coatings on guidewire tips. Firstly, the manual shaping of the guidewire tip into a 180° J-loop caused damage to both the outer and inner curves of the J-loop in 2 of 3 guidewires. While some coating damage on the inner curve of the guidewire tip was expected after shaping due to the mechanical force from the metal shaping tool, we were surprised to find coating damage on the outer curve, which was only touched by the glove during the shaping maneuver. More tests are needed to determine whether coating damage occurs when ‘shapeable tips’ are curved to less than a 180° J-loop, which is commonly performed during various endovascular procedures. Guidewires are usually inserted directly after shaping, and may thus pose a potential risk of inadvertently introducing polymer micro-fragments into the cerebral circulation if shaping causes coating damage. Therefore, it seems advisable to consider using preshaped guidewires when possible or to flush guidewire tips with saline after a shaping maneuver to remove potential coating debris.

Secondly, the J-wiring technique (including J-shaping) to optimize flow diverter wall apposition caused damage to both the outer and inner curves of the J-loop on all 3 guidewires. Since J-shaping alone caused coating damage, we cannot establish to what degree the J-wiring step itself contributed to the overall damage. However, coating damage appeared more extensive after the J-wiring technique compared to J-shaping alone in 2 of 3 guidewires, suggesting that additional damage may be caused by the backand- forth movement of the J-loop within the flow diverter (J-wiring step). It is conceivable that a damaged coating integrity during the initial manual J-shaping increases the risk of further damage, thereby generating polymer micro-fragments during the J-wiring step. Importantly, this is of particular concern because this additional abrasion and shedding would migrate directly into the cerebral circulation. The contribution of the J-wiring step to coating damage could more precisely be explored in future studies by analyzing water samples drawn from the aneurysm model for micro-fragments.

The vulnerability of polymer-coated devices to coating damage can be attributed to both mechanical design and coating composition [17]. We observed differences in the overall pattern of damage among guidewires, primarily determined by the guidewire tip design. On the smooth cylindrical Avigo^TM tip, frictional stresses were distributed continuously along the surface, resulting in continuous abrasions. For the Synchro^® tip, the polymer coating is applied over a hypotube with small gaps that act as “stress-relief” points, so that damage appeared as short, segmented rather than continuous abrasions. For the Traxcess^TM tip with a coiled design, contact occurred mainly on the outer coil crests, concentrating damage in these regions while leaving the valleys largely intact. Therefore, the wire tip architecture determines where stresses build up during shaping and manipulation, which may also have implications for the size and shape of generated micro-fragments. While longer coating fragments could potentially peel off the Avigo^TM guidewire tip, the length of fragments coming off the Traxcess^TM and Synchro^® guidewire tips would probably be shorter than the diameter of the distal coiled wire (~65 μm) and the distance between gaps in the hypotube (~70 μm). Previous clinical and in vitro studies have reported a large variability in the size of micro-fragments [15,18]. Furthermore, we found indications of damage involving the superficial coating and probably also the deeper structure of the Synchro^® guidewire after the J-wiring technique, highlighting that micro-fragments of various materials may be generated from the same guidewire [15,19].

The chemistry of a polymer coating also influences how the material fails under stress. To our knowledge, the exact chemical composition of polymer coatings on the Avigo^TM, Traxcess^TM, and Synchro^® tips is not publicly disclosed. However, hydrophilic coatings, such as polyvinylpyrrolidone-based coatings, are soft and compliant, allowing them to deform and wear away gradually rather than fracture [20]. Polytetrafluoroethylene-based coatings are relatively brittle and exhibit low surface adhesion, so they tend to crack or flake when the interface with the metal substrate is weakened [21]. Polyurethane- or polyamide-based coatings are more elastic and resistant to crack propagation, so damage is confined to small torn regions at points of highest stress [22]. Thus, these commonly used polymer coatings differ in the energy required for a crack to propagate or for the coating to separate from the substrate, which may explain why some coatings fail by brittle flaking and others by gradual abrasion.

Our experiment provides evidence for a new mechanism contributing to coating damage on microguidewires during flow diversion, adding to the list of routinely performed procedural steps during EVT that may result in coating damage. Previously, backloading of microguidewires through insertion tools has been associated with coating damage and micro-fragmentation [15,19]. In addition, coaxial manipulation of combinations of microcatheters, catheters, and sheaths has been associated with coating damage in benchtop tests [10-12]. Tight-fitting catheter combinations [2], the withdrawal of microcatheters through rotating hemostatic valves [7,13], and friction in coaxial catheter systems due to tortuous vascular anatomy [12] have all been reported as mechanisms potentially causing coating damage. Recently, coil delivery during aneurysm treatment has been shown to damage the inner lining of microcatheters, which may contribute to thrombus formation within the microcatheter [23]. The effect of coating impairment on thrombogenicity and navigation capabilities of microguidewires remains to be determined.

Richter et al. [3] reported an increased incidence of NICE lesions associated with certain families of flow diverters in a retrospective, multicenter study involving 1,201 patients treated by flow diversion. However, insufficient data on catheters and guidewires did not allow for identification of the exact cause of this association. Rather than the flow diverter itself, it could be that a particular guiding catheter, microcatheter, guidewire, or microguidewire (or a specific combination of these devices) was responsible for causing NICE lesions. Our study emphasizes that data on all types of endovascular devices, including guidewires and microguidewires (often multiple per procedure), should be collected in future studies to better determine the relative contribution of each device to the risk of NICE lesions.

CONCLUSION

Damage to polymer coatings on guidewire tips can result from J-shaping and the J-wiring technique used to optimize flow diverter wall apposition. In our study, both steps damaged the outer and inner curves of the J-loop, with the most extensive changes seen after the J-wiring technique. Differences in the overall patterns of coating damage among guidewires were primarily determined by the guidewire tip design. These processes may generate polymer micro-fragments, increasing the risk of cerebral polymer emboli and the development of NICE lesions in patients treated for cerebral aneurysms with flow diverters. Damage caused by manual shaping of a guidewire tip might pose a risk of introducing micro-fragments into the cerebral circulation during insertion. Using pre-shaped guidewires or thoroughly flushing the guidewire after manual shaping may help reduce this risk. Future studies should examine a wider variety of guidewires under standardized conditions to compare their durability.

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