Experimental Study of a Newly Developed Prosthesis and Its Initial Clinical Use in Microvascular Decompression Surgery

Abstract

This study aimed to develop a new, refined, and easy-to-use microvascular decompression surgical prosthesis and report its processability, uniformity, stability, and clinical safety.

In an experimental study, the processing time required to create five slings and five balls from a prototype clump (0.010 ± 0.001 grams) was measured. Similarly, the processing time to form a clump (0.01 ± 0.001 grams) by plucking an equivalent amount of fibers from commercial polytetrafluoroethylene felt was measured. After approval from the Pharmaceuticals and Medical Devices Agency, the new prosthesis was used in 39 consecutive microvascular decompression surgeries.

The handling time to make slings and balls from the refined polytetrafluoroethylene material was shorter than that from polytetrafluoroethylene felt (60.5 ± 4.81 versus 155 ± 6.59 seconds, p-value < 0.001 and 84.0 ± 8.51 versus 141.1 ± 7.02 seconds, p-value < 0.001). The tensile study showed that the prototype was significantly stronger than the slings conventionally made from polytetrafluoroethylene felt (6.2 ± 2.12 Newtons versus 1.56 ± 0.647 Newtons, p-value = 0.012). The adhesion study showed an equivalent adhesive strength to the conventional one (0.137 ± 0.05 Newtons versus 0.108 ± 0.05 Newtons, p-value = 0.40). The 39 microvascular decompression surgeries (trigeminal neuralgia, 13 cases; hemifacial spasm, 26 cases) showed no adverse events related to the materials (follow-up period: 9 months-3 years 9 months, mean: 2 years 9 months).

The new Pharmaceuticals and Medical Devices Agency-approved, refined polytetrafluoroethylene material, which is easier to handle and less time-consuming, exhibited uniform characteristics, excellent manipulability, sufficient strength, and clinical reliability for prostheses. It may serve as a valuable additional option for prostheses in microvascular decompression surgery.

Introduction

Microvascular decompression (MVD) surgery was first introduced by Gardner¹⁾ and has since been established as a radical treatment for hemifacial spasm (HFS) and trigeminal neuralgia (TN).^2-4) Over the years, a variety of prosthetic materials for MVD have been reported, including absorbable autologous muscle or fascia^3-9) and absorbable and non-absorbable artificial and exogenous materials.^{1,3,5,6,9-17)}

An ideal prosthesis should be easy to manipulate intraoperatively, remain stable within the subarachnoid space, and achieve the surgical objective of permanent vascular decompression with a minimal volume to reduce the risk of granulomatous reactions.^18-22)

In Japan, our nationwide survey²³⁾ revealed that exogenous materials are used in 96.5% of MVD surgeries, with polytetrafluoroethylene (PTFE) felt accounting for more than 80% of cases. While PTFE felt is the predominant material, polyvinyl alcohol (PVA) sponge¹⁵⁾―including Ivalon^Ⓡ3,24-27)―has also been employed. Furthermore, in MVD, surgical outcomes using a PVA sponge (e.g., Ivalon^Ⓡ) as the prosthesis show no significant difference compared with PTFE felt.^25,26) Among them, the most commonly used forms are slings and balls of various sizes, which are empirically prepared from PTFE felt immediately before the decompression, according to the techniques described by Fukushima in 1984²⁸⁾ and Sindou in 2008.²⁹⁾ One of the major challenges, however, had been the absence of officially approved materials for MVD. Despite the widespread use of PTFE, standardized experimental data on its key properties, such as length, thickness, and tensile and adhesive strengths, were lacking. This lack of approval by the Pharmaceuticals and Medical Devices Agency (PMDA) had imposed significant limitations on neurosurgeons in selecting an optimal prosthetic material.

In this study, we aimed to address this gap by developing a refined PTFE prosthesis with improved processability, uniformity, and stability. We conducted a series of quantitative assessments to obtain data on the thickness, length, strength, and other properties of the material. Consequently, this material became the first PMDA-approved MVD prosthesis in Japan and has been successfully used for MVD procedures. Herein, we report a new PTFE cottonoid material with excellent processability, uniformity, stability, and clinical safety.

Materials and Methods

Study design

The study protocol was approved by our institutional review board and performed in accordance with the principles of the Declaration of Helsinki. Each of the experiments was repeated five times.

PTFE materials used

For the experimental study, we prepared two types of PTFEs. The first was a PTFE felt (Crown Jun Felt^Ⓡ, Kono Seisakusho Co.), which is usually used as a patch material in cardiac surgeries. In MVD surgeries, it is plucked into small fibers, and clusters of fine fibers that look like cotton are rolled into small balls or twisted to make slings for use as prostheses in MVD surgeries (Figure 1A and B). The other product was a prototype (Figure 1C, Kono Seisakusho Co.), as described.

Figure 1.

Photographs of commercially available polytetrafluoroethylene (PTFE) felt and a prototype, along with images of the tensile and adhesion testing processes.

A: Commercially available PTFE felt is typically plucked with forceps into a cotton-like clump. B: From these clumps, balls and slings are formed for the use in prosthesis during microvascular decompression surgery. C: A prototype clump of PTFE fibers. D: A ball (0.01 g) made from the prototype (inserted photo lower left corner) is disassembled again and reformed into fibers to demonstrate uniformity. The ball consists of 90 fibers, almost all of which are uniform in shape. Scale bars: 8 mm width. E, F: Photos of tensile strength test (E) and adhesive strength test (F).

Manufacturing process of the prototype

The prototype was developed using a multi-step process. Fine PTFE powders are converted into porous PTFE membranes through various manufacturing processes, including lubricant mixing, precompression, extrusion, stretching, and sintering. Fine vertical grooves were created on a strip with a height of 70 mm to separate the incisions into thin fibers. This process created a cluster of PTFE fibers resembling a cotton mass with uniform thickness and length. At the final stage, fibers with uneven lengths or thicknesses were removed under visual observation to achieve uniformity, which simplified the intraoperative manufacturing process (Figure 1C and D).

Formability equivalence study

To compare formability, five volunteers with no experience in prosthesis manufacturing measured the time taken to create five slings on five different occasions using both conventional PTFE felt and prototype materials.

1. PTFE felt was pulled apart into a cotton-like form, targeting a mass of 0.01 g ± 10%. The time required for molding was measured.

2. Five sling-shaped forms were created from cotton-like test substances, and the time required for the molding process was subsequently determined. To avoid producing results favorable to the novel material, the order of testing was arranged so that the new material was processed first, followed by the conventional one.

3. The prototype was already in a cotton-like form and had a molding time of zero seconds.

4. An example ball (indicated lower left in Figure 1D, 0.01 g) made using the prototype was disassembled and reformed into fibers to demonstrate its uniformity (Figure 1D).

Tensile strength test

Tensile and adhesive strength tests were performed using a modified method described by Hayashi et al.³⁰⁾ Each specimen (weighing 0.010 ± 0.001 g) was measured using an electronic balance (MC210P; Sartorius Japan, Kitashinagawa, Japan) and twisted into a sling-like shape. The slings used for these tests were prepared by the first author with the intention of actual surgical use. Each sling was placed in a tensile testing machine (AIKOH Engineering Co., Higashiosaka, Japan). The tensile strength was measured at the point of sling breakage (gauge length, 10 mm; tensile speed, 20 mm/min, Figure 1E).

Adhesive strength test

To assess adhesive strength, one side of the sling was secured using clamps, whereas the other side was attached to an aluminum plate using fibrin glue (Beriplast P Combi-Set Tissue Adhesion; CSL Behring, King of Prussia, PA, USA) with an adhesive area of 15 × 10 mm (150 mm²). Reflecting the intended clinical application, these slings were also designed to mimic conditions of actual surgical use. The test was performed under the same conditions as the tensile test (gauge length, 10 mm; tensile speed, 20 mm/min; Figure 1F), and the maximum strength at which all the slings detached from or fractured on the aluminum plate was recorded as the adhesive strength.

Clinical study

Patient selection

This study is a retrospective case series of MVD surgeries performed by a single senior neurosurgeon (MH). Following the regulatory approval of a new prosthesis (CIRRAX; total weight, 0.30 g) by the PMDA and Ministry of Health, Labour and Welfare of Japan,³¹⁾ the device was clinically applied to all MVD surgeries. Among them, 40 consecutive cases with more than 9 months of follow-up period were included. One case of TN treated via the anterior petrosal approach was excluded because of a different approach, leaving 39 cases for analysis (26 cases of HFS and 13 cases of TN).

To evaluate the clinical non-inferiority of the new prosthesis, outcomes were compared with those of 70 consecutive cases previously treated with conventional PTFE felt (Teflon felt^Ⓡ, FCR Bard, Inc., Bard Implants Division, Billerica, MA, and Crown Jun PTFE Felt^Ⓡ, Kono Seisakusho Co., Ichikawa, Japan) before the introduction of the new prosthesis (August 9, 2017, to January 6, 2021). Parameters assessed included preoperative symptom duration, operative time, postoperative symptom improvement, and non-neurological complications.

Statistical analysis

To demonstrate non-inferiority, statistical analysis was performed using t-tests for continuous variables. Values are presented as mean ± standard deviation. Statistical significance was set at p < 0.05.

Results

In the traditional PTFE felt group, the felts were plucked using Kocher forceps into a mass of thin lints/filaments (Figure 1A), twisted into slings (sling-forming time), or rolled into a ball for use as an MVD prosthesis (ball-forming time) (Figure 1B). The time required for each was denoted as cottonoid-, sling-, and ball-forming times. Therefore, in the PTFE felt group, cottonoids were produced manually, and the fiber length varied, resulting in uneven sling lengths with minor injuries. However, during the manufacturing process of the newly made cotton-like prototype (Figure 1C), fibers with uneven lengths or thicknesses were removed to achieve uniformity in the last procedure, resulting in thin filaments with a uniform length of 70 mm (Figure 1D).

Non-inferiority trials

The time required to make five slings and five cotton-like balls from each cottonoid material (0.069 ± 0.002 vs. 0.069 ± 0.001 g for slings, and 0.040 ± 0.001 vs. 0.041 ± 0.002 g for balls) was measured in five volunteers. As the prototype product (prototype group) was already in a cotton-like shape (Figure 1C), there was no need for cottonoid-forming time from PTFE felt to the clumping of plucked fibers. Therefore, the time required to prepare the cottonoid material was considered zero in the prototype group. The sling-forming time of the prototype group (sling-forming time only, 60.5 ± 4.81 s) was much shorter than that of the conventional group (sling-forming time added to cottonoid-forming time, 155.0 ± 6.59 s, p < 0.001, Figure 2A). The ball-forming time of the prototype was shorter than that of the PTFE felt group (84.0 ± 8.51 vs. 141.1 ± 7.02 s, p < 0.001, Figure 2B). The time to make five slings (from clump of already plucked fibers to slings) in the prototype was significantly shorter than that in the felt group (60.5 ± 4.81 vs. 68.8 ± 5.00 s, p < 0.01, Figure 3A). The ball formation time (from clump of plucked fiber to ball) was, on the contrary, shorter in the felt group (84.0 ± 8.51 vs. 60.6 ± 5.51 s, p < 0.01, Figure 3B).

Figure 2.

A and B show the total time (in seconds) required to form five slings (A) and balls (B) in the commercially available polytetrafluoroethylene (PTFE) felt group (n = 5) and the prototype group (n = 5) including cottonizing time. These figures represent the total time taken to convert the original shape (cotton-shaped prototype, PTFE felt) into the final shape (sling and ball), which includes the sum of the time required to create a cotton-like form and the time needed to shape it into a sling or ball. In the prototype group, the time required to form both slings (A, p < 0.001) and balls (B, p < 0.001) was significantly shorter compared to the conventional PTFE felt group.

Figure 3.

A and B show the time (in seconds) required to form five slings (A) and balls (B) in the prototype group (n = 5) and the group using pre-processed cotton-like polytetrafluoroethylene (PTFE) felt (n = 5), excluding the time required for cotton-like processing. The left panels represent the formation time from materials already in a cotton-like state, while the right panels represent the formation time from PTFE felt after subtracting the cotton-processing time. The prototype material’s tendency to accumulate static electricity and naturally form filamentous bundles likely facilitated faster sling formation (p < 0.01). Conversely, the prolonged time required for ball formation in the prototype group (p < 0.01) may be attributable to the absence of short fragments necessary for efficient formation of small, compact balls.

Uniformity

An example ball (0.01 g) made of the prototype was disassembled and reformed into fibers to demonstrate its uniformity. The ball comprised 90 fibers, almost all of which were uniform (Figure 1D).

Tensile strength test

The tensile strength was measured (gauge length = 10 mm, tensile speed = 20 mm/min) at the point of sling breakage. The measurements for each group, conducted five times, showed tensile strengths of 6.2 ± 2.12 N for the group made from the prototype and 1.56 ± 0.647 N for the group made from PTFE felt (Figure 4), showing that the prototype group had 3.88 times stronger tensile strength than conventionally made slings from the felt group (p = 0.012).

Figure 4.

Comparison of tensile strengths (N) of the five samples.

The tensile strength is significantly higher in the prototype group (p = 0.012).

Adhesion test

The measurements for each group, conducted five times, showed adhesive strengths of 0.137 ± 0.05 N for the group made from the prototype and 0.108 ± 0.05 N for the group made from PTFE felt (Figure 5). The adhesion study showed equivalent adhesive strength (p = 0.40). As the glued surface area was approximately 10 mm × 15 mm, the adhesive strengths for each group, when converted, were 0.0931 ± 0.034 gf/mm² and 0.0734 ± 0.034 gf/mm², respectively.

Figure 5.

Adhesive strength test (N).

There are no significant differences between the two groups in the adhesive test for the five samples (p = 0.40).

Clinical results

The details of 39 MVD surgery cases using the new prosthesis and the preceding 70 consecutive cases without it are shown in Table 1. There were no significant differences between the two groups in terms of age, sex, or underlying disease. Additionally, no significant differences were observed in preoperative symptom duration (p = 0.13), operative time (p = 0.57), or degree of postoperative symptom improvement (p = 0.41). There were no adverse events related to the materials.

Table 1.

Comparison of 39 MVD Surgery Cases with New Prosthesis vs. 70 Consecutive Cases without New Prosthesis

	n	Age	Male/female	TN/HFS	Duration of symptoms (year)	Operation time (min)	Functional evaluation (T0/1/2/3)	Non-neurological perioperative complications
prototype Gr	39*	57.9 ± 12.5	19/20	13/26	6.37 ± 5.10	273 ± 56.7	33/5/1/0	CSF rhinorrhea 1#
PTFE felt Gr	70	57.1 ± 13.7	24/46	20/50	4.83 ± 3.95	266 ± 45.6	61/4/3/2	CSF rhinorrhea 1#, cerebellar hematoma 1$
p-value	-	p = 0.84	p = 0.16	p = 0.60	p = 0.13	p = 0.57	p = 0.41	-

CSF: cerebrospinal fluid; HFS: hemifacial spasm; MVD: microvascular decompression; PTFE: polytetrafluoroethylene; TN: trigeminal neuralgia

*Among the 40 consecutive cases, only one was performed via the anterior petrosal approach and was excluded from the current comparison. All remaining MVD procedures were conducted using the retrosigmoid approach.

^#Improved with spinal drainage.

^$No deficit with conservative treatment.

Discussion

Validity of the procedure and types of materials used

MVD is achieved by moving the responsible blood vessels away from the root entry/exit zone (REZ). Various prosthetic materials can be used in this procedure, including inserting small pieces of material, shaping them into balls, using slings to move vessels away from the REZ without contact,²⁹⁾ or elevating vessels by placing materials on both sides.^17,32) Over the history of MVD, a wide variety of absorbable and non-absorbable prosthetic materials have been employed. Gardner first reported the use of gelatin sponge in 1959,¹⁾ and Jannetta subsequently described the use of Ivalon^Ⓡ sponge, autologous muscle grafts, and Teflon (PTFE) felt in 1977.³⁾ Since then, numerous other prostheses have been adopted, depending on the pathology of the offending vessel, including aneurysm clips (Laws et al.,¹¹⁾ 1986), silastic rubber slings (Rawlinson and Coakham,⁹⁾ 1988), Dacron (polyethylene terephthalate),^12,17) titanium plates (Banczerowski et al.,¹⁰⁾ 2014), PVA foam (Shimizu et al.,¹⁵⁾ 2015), and collagen sponge coated with glue (TachoSil^Ⓡ, Otani et al.,¹⁶⁾ 2018). Expanded PTFE belts have also been used.^13,14) Our previous nationwide survey in Japan revealed that non-absorbable prostheses were used in 96.5% of MVD procedures, with PTFE felt being the most common (80.5%), followed by polyurethane foam (11.9%). Although few direct comparisons among materials have been published, some institutions in the United States reported that the efficacy and complication profile of Ivalon^Ⓡ (PVA foam) in TN was equivalent to that of PTFE.^25,26) More recently, autologous muscle grafts have again been shown to provide satisfactory decompression in both TN⁷⁾ and HFS.³³⁾ Nevertheless, the long-term stability of prosthetic materials remains a critical concern. Kondo et al.,³⁴⁾ 2018 reported structural degradation of polyurethane sponge, while Klun,³⁵⁾ 1992 demonstrated that autologous muscle may be absorbed over time, both leading to recurrent REZ compression. These findings highlight that the choice of prosthesis should take into account not only intraoperative handling and short-term decompression efficacy but also the potential for degeneration or resorption that could compromise long-term durability.

Medical-grade plastics and adverse effects: Teflon adhesion and granuloma

Implanted plastics must exhibit high biocompatibility, durability, and minimal foreign body reactions to ensure their effectiveness and safety.^36-38) The following materials are widely used in medical applications because of their properties. PTFE is known for its exceptional chemical and heat resistance and biocompatibility. It is commonly used in artificial blood vessels and shunts.³⁹⁾ Polyethylene is durable, has low friction, and is biocompatible, making it ideal for use in artificial joints.^40,41) PVA is highly water-soluble, with moderate mechanical strength and good biocompatibility. It is frequently used in drug delivery systems, medical films, and wound dressings.⁴²⁾ Polypropylene is strong, heat-resistant, and chemically stable and is often used in sutures and gastrointestinal implants.³⁸⁾ Polycarbonate is a transparent and impact-resistant material used in artificial eyes and bone reinforcement.⁴³⁾ Silicone is flexible, highly biocompatible, and associated with minimal allergic reactions, making it suitable for pacemaker leads, breast implants, and catheters.^44,45) Polylactic acid a biodegradable material commonly used in sutures and drug delivery systems.⁴⁶⁾ Polyurethane is flexible, durable, and elastic and is widely used in stents, catheters, and artificial blood vessels.⁴⁷⁾ Polymethyl methacrylate (PMMA, acrylic) is transparent, strong, and chemically resistant and is used in intraocular lenses and dental implants.⁴⁸⁾ Nylon (polyamide) is frequently used in sutures, catheters, and artificial ligaments.⁴⁹⁾

Despite these advantages, the use of PTFE in medical applications, particularly in MVD surgery, has been linked to granuloma formation, with reported incidence rates ranging from 1.5%¹⁹⁾ to 5%.⁵⁰⁾ Granulomas can occasionally cause mass effects⁵¹⁾ and are of significant concern because of potential complications, including cranial nerve dysfunction, infection, tissue rejection, and adhesion. PTFE^52,53) and Ivalon^Ⓡ27) show recurrence of symptoms because of the adhesion of interposed materials. To mitigate these risks, prostheses with high fixation strengths and smaller quantities are preferred. Minimizing the amount of material used can enhance surgical outcomes by improving visibility and ease of handling and reduce complications such as cranial nerve damage. In this context, the development of a PTFE prosthesis that reduces foreign body reactions while maintaining its effectiveness in small quantities is highly desirable. Recognizing the widespread use of PTFE in Japan and its ease of shaping, this study focused on designing a user-friendly and uniform PTFE fiber material. These findings suggest that this material has the potential to retain its strength while significantly reducing granuloma formation, even when used in small quantities.

Quality and strength

In MVD surgery, thin fibers or filament bundles have traditionally been empirically pulled from PTFE felt, manually twisted into slings, and rolled into balls or pads for use as prostheses to decompress the REZ. This process is both time-consuming and labor-intensive. Moreover, because fiber lengths are inconsistent and potential damage caused by the pulling process remains unknown, producing uniform prostheses has been difficult. To date, no data have been available on the actual diameter, length, or strength of the slings used in MVD. Furthermore, since the materials previously employed were not approved by the PMDA, surgeons bore responsibility not only for surgical outcomes but also for material selection, creating substantial psychological stress. The new cotton-like PTFE material evaluated in this study consists of clumps of fine PTFE fibers of uniform length and thickness, enabling the rapid and reproducible fabrication of balls and slings. As its strength was demonstrated for the first time, this material has recently been approved by the PMDA in Japan. In the present study, sling formation was achieved more quickly, whereas ball formation required additional time. This may have been due to the prototype's tendency to accumulate static electricity and adhere to itself. In addition, the individual fibrils, each approximately 7 cm in length, may have hindered the formation of small balls with diameters of only a few millimeters. These hypotheses require further investigation. Because the slings consisted of twisted fiber bundles, their diameters were not uniform along their lengths. This study is the first to report tensile and adhesive strengths, expressed in Newtons (force) rather than Pascals (force per unit area). The prototype exhibited a tensile strength of 6.2 ± 2.12 N, whereas the conventional sling (prepared from loosened felt) showed a tensile strength of 1.6 ± 0.65 N. The prototype thus demonstrated a significantly higher tensile strength (p = 0.012).

Adhesive strength test

In the measurement of the adhesive strength for each group (five measurements per group), the prototype group showed 0.137 N and the PTFE felt group showed 0.108 N, with no significant difference between the two groups (p = 0.40). When the area of the glued surface was measured to be 10 mm × 15 mm, the adhesive strength was converted to 0.093 and 0.073 gf/mm², respectively.

In our previous study, where we compared the adhesive strength of two types of glue using pig skin with an adhesive area of 5 × 20 mm², the adhesive strengths were measured as 1.99 and 1.39 gf/mm², respectively.³⁰⁾ In comparison, the adhesive strength obtained in this study was approximately 1/20th of these values. This difference is likely because of the variation in the direction of the applied stress and the difference in the material of the adhesive surface (pig skin vs. aluminum). Additionally, the process by which the sling detached from the glue surface before breaking indicated that the affinity between the sling and glue was sufficient.

Significance of pharmaceutical approval

To manufacture and sell pharmaceuticals and medical devices, companies must obtain approval from regulatory agencies in each country, such as the PMDA in Japan, the Food and Drug Administration in the United States, and the European Medicines Agency in Europe. These agencies ensure the quality, safety, and efficacy of products. In Japan, the PMDA governs these approvals,³¹⁾ and manufacturing and selling without approval is illegal. Regarding medical service reimbursement, the Central Social Insurance Medical Council in Japan and the Centers for Medicare and Medicaid Services in the US determine insurance coverage. Surgeons can use materials not covered by insurance; however, they must explain the benefits and risks to patients and obtain their consent. Furthermore, these materials must meet the current medical standards. “Mixed billing,” which combines public insurance with out-of-pocket payments, is restricted in countries such as Japan, complicating the approval of non-covered materials. In Japan, there are issues regarding the use of non-absorbable prostheses in MVD surgery. This study aimed to clarify the length, thickness, uniformity, and strength of the material, approval for manufacturing, and insurance coverage of new surgical materials for MVD procedures. This is the only material currently approved for intradural use during MVD surgery in Japan, making this a groundbreaking study. Teflon has been used previously, and its safety is considered high; however, long-term follow-up of the use of this new shape is required to confirm its safety.

Limitation

The limitations of this study include the fact that, although we measured the tensile and adhesive strength of both existing and newly developed PTFE fibers for the first time and demonstrated the superiority of the latter, no data are available on the strength and adhesion of other prostheses, making direct comparisons impossible. In the future, it will be necessary to accumulate strength data for various prostheses. Additionally, the strength of a prosthesis varies depending on its application (e.g., interposition or transposition in the case of PTFE fibers), its shape (e.g., balls, slings, or tiny pieces), and the type and amount of glue used. We have previously reported that the type of glue can affect prosthesis strength.³⁰⁾ While increasing the adhesion area is expected to enhance strength, using a greater amount of material may also increase the risk of foreign body reactions and granulation formation. Therefore, selecting the optimal prosthesis and determining the appropriate strength, amount, and method of use for each individual case is a complex task. In the future, improving preoperative predictions will be necessary by considering factors such as the shape of the vessel to be repositioned, blood pressure, the degree of arteriosclerosis, and the distance and direction of movement. Furthermore, developing intraoperative measurement techniques will be essential.

In conclusion, an ideal prosthesis for MVD surgery should have: (1) uniform length and thickness with high reproducibility, (2) sufficient tensile strength and durability, (3) excellent biocompatibility, (4) flexibility for easy molding and vessel conformity during surgery, and (5) approval from regulatory authorities such as the PMDA. The prosthesis presented in this study meets these criteria and may contribute to improved surgical outcomes and patient recovery. Future efforts should focus on obtaining international regulatory approval.

Disclaimer

Author YH is one of the Editorial Board members of the Journal. This author was not involved in the peer-review or decision-making process for this paper.

Author Contributions

Mitsuhiro Hasegawa: Conceptualization, Methodology, Writing - original draft, Writing - review and editing, Data curation, Formal analysis, Visualization, Project administration, Validation, Yuya Nishiyama: Formal analysis, Validation, Writing - review and editing, Takuro Hayashi, Methodology, Writing - review and editing, Yuichi Hirose, Project administration, Supervision, Writing - review and editing.

Conflicts of Interest Disclosure

All authors have no conflict of interest.

Ethics Approval

Ethics committee approval from both institutes was obtained: HM24-565 in Fujita Health University and ERC20250403 in Tokyo D Tower Hospital.

Informed Consent

Informed consent was obtained from all patients treated with conventional PTFE felt and with the new prosthesis before and after PMDA approval, or obtained in the form of the opt-out option as available on the hospital's website because of the retrospective design of the study.