Polyester for Tissue. ePTFE for Blood.

Why a woven polyester and ePTFE composite outperforms either material alone in sutured, blood-contacting implants.

One wall, two opposite jobs

Many implants are sewn into place with tissue on one face and flowing blood on the other. Vascular patches, graft cuffs, sewn sleeves and fabric covers all share this geometry, and the two faces ask for opposite behavior.

The tissue side should be incorporated by the host, so the device is anchored and sealed. The blood side should give platelets as little as possible to hold on to while healing proceeds. The wall between them must also hold a suture without tearing, and close around the needle holes that every suture line creates.

No single implant material does all of this well. Woven polyester (PET, Dacron) is strong, holds sutures and is readily incorporated by tissue, but in head-to-head studies it collects more platelets than ePTFE. Expanded PTFE offers a quieter blood-contacting surface, but thin ePTFE is weak in suture retention and does not recover around a needle puncture. A hybrid composite membrane stops asking one material to do both jobs, and places each where the published evidence says it performs best.

Anatomy of the hybrid membrane

The hybrid membrane is a three-layer laminate, bonded into a single sheet so the layers behave as one wall rather than a loose stack.

Layer	Faces	Job	Property that does the job
Woven polyester	Tissue	Host incorporation; carries suture load	Textile surface with interyarn spaces for tissue; continuous yarns that carry tension
Elastic polymer binder	Internal	Joins the two materials; closes needle holes	Elastic recovery after puncture; bonds fabric to ePTFE without stitches between layers
ePTFE	Blood	Low-thrombogenicity flow surface	Hydrophobic node-and-fibril microstructure with low surface energy

Each layer supplies a property the others lack. The four sections below take each functional claim in turn and set out the published evidence behind it.

1. Polyester for tissue: incorporation on the outer face

Textile polyester is incorporated by host tissue more readily than standard microporous ePTFE. Its fibrous surface and interyarn spaces give cells and collagen a structure to grow into and anchor against.

• Animal comparison. In a canine study of eight prosthesis designs (40 implants), Mathisen and colleagues reported that "healing was much more advanced in the knitted and woven prostheses than in the Gore-Tex" [1].

• Human explants. In 298 ePTFE arterial grafts excised from patients, "cellular and collagen infiltration of the microporous expanded polytetrafluoroethylene structure was generally poor," and occurred mainly in the outer region of the wall [2]. These were grafts removed from patients, often for complications, so the sample is not random.

• Soft-tissue repair. In the hernia literature, standard ePTFE is described as a material that "does not incorporate into human tissue and becomes encapsulated" [3].

Three qualifications shape how the hybrid uses this. Incorporation depends on textile construction, porosity, implant site and time, not on the polymer alone. Porosity can even reverse the ranking: in baboons, an experimental high-porosity ePTFE (60 µm internodal distance, not a clinical product) was fully lined with endothelium at 12 weeks, while only one of five knitted Dacron grafts was [4].

A vigorous tissue response is also an asset outside a device and a liability in the lumen. In a sheep stent-graft model, a polyester-covered device developed a neointimal area of 14.98 mm² against 9.88 and 6.52 mm² for two ePTFE-covered devices, although the stent frames also differed [5]. Polyester therefore belongs on the tissue face, and only there.

2. ePTFE for blood: a quieter surface on the inner face

On the blood side the goal reverses: give platelets as little as possible to react with. Classic head-to-head studies, in animals and in small patient groups, found less platelet deposition on the tested ePTFE grafts than on the tested polyester grafts.

Study	Model	Polyester (Dacron)	ePTFE
Schneider et al., 1989 [6]	Baboon arterial shunt, 1 hour	49.0 × 10⁹ platelets per graft	3.7 × 10⁹ platelets per graft
Eldrup-Jorgensen et al., 1985 [7]	Baboon ex vivo shunt	Most thrombogenic surface tested	Least platelet-reactive material tested
Goldman et al., 1982 [8]	Human femoropopliteal bypass, indium-111 platelets	Thrombogenicity index 0.24	Thrombogenicity index 0.13 (P < 0.05)
Wakefield et al., 1989 [9]	Human aortic grafts, randomized (6 vs 6), at 3 months	87% more uptake than native artery	47% more uptake than native artery

The baboon study adds a systemic signal. Dacron lowered circulating platelet counts and raised β-thromboglobulin, while ePTFE did neither [6].

The strongest clinical signal comes from a randomized carotid endarterectomy trial of 200 procedures. Collagen-impregnated Dacron patches had more perioperative strokes than PTFE (7% vs 0%, P = .02), five carotid thromboses against none (P = .07), and more early restenosis of 50% or greater (12% vs 2%, P = .013) [18]. The Dacron was collagen-sealed, so material was not the only difference, but the direction matches the platelet data.

The evidence supports a relative claim, not an absolute one. ePTFE was less thrombogenic than polyester in these studies, not non-thrombogenic, and platelet uptake is a surrogate rather than a clinical endpoint. In the randomized human study the difference was not yet present at one week and had faded by six months [9], and a Cochrane review found no clear difference in above-knee bypass primary patency between the two materials, with low-quality evidence favoring Dacron for secondary patency [10].

The practical value of ePTFE on the blood face is a quieter surface during the early period after implantation, before healing has progressed. Pairing it with polyester means the device no longer has to trade that early advantage for tissue anchorage.

3. Suture retention: woven yarns carry the load

Thin ePTFE is often the weak point at the suture line. Its node-and-fibril structure is oriented, and a loaded suture can cut along it rather than tear through it.

In bench tests on ePTFE graft, Mine and colleagues observed "a sharp cut in the longitudinal direction" through the nodes, and noted that "a break starts much earlier than the peak suture retention strength" [11]. The peak value on a test report can therefore overstate the load at which damage begins.

Thickness is the usual remedy. A thick ePTFE hernia patch recorded the highest suture retention among the barrier meshes in one comparison [12], and in polymer graft walls generally, suture retention rises with wall thickness (0.375 N at 0.20 mm to 1.383 N at 0.32 mm in one electrospun series) [13]. Each added micron, however, costs profile and flexibility.

A textile layer offers a different route. A suture passing through a woven fabric bears on continuous yarns that share the load across the weave, instead of on a film it can cut. Reinforcement studies show the effect: a polyester braid raised the suture retention of a hydrogel graft from 6.8 to 8.4 N, with the authors identifying the fiber strut as the dominant contributor [14], and in knitted-mesh grafts the suture retention was attributed to the textile layer [15].

In the hybrid membrane, the woven polyester is that load path, which is why the composite holds a suture better than ePTFE alone. As with any laminate, that advantage has to be shown on the finished, sterilized construction: suture retention under ISO 7198 [16] in both principal directions, at the design's wall thickness, recording the onset of tearing as well as the peak load.

4. Needle holes close on the thread

Every suture line is also a row of holes, and ePTFE does not recover after a needle passes. As Sergeant and colleagues put it, "due to the absence of elasticity of the ePTFE graft, the needle-hole defect remains the same size of the needle after it is passed through" [17]. In their pulsatile model at 120/80 mmHg, average leak rates through ePTFE ranged from 0.63 to 1.94 mL/min per needle hole, depending on the needle and suture combination [17].

Clinically, the effect shows up as time to hemostasis. In the same carotid trial, plain PTFE patches took a mean 14.4 minutes to stop bleeding against 3.4 minutes for collagen-impregnated Dacron (P < .001) [18]. That comparison changes the sealant as well as the substrate, and the faster-sealing Dacron patch was the one with more strokes and thromboses.

An elastic layer addresses the cause. When the needle is withdrawn, an elastomer recovers and closes on the suture instead of leaving a needle-sized channel.

• Elastic interlayer in ePTFE patches. A commercial ePTFE patch built with "a middle layer of a proprietary thermoplastic fluoropolymer with elastic properties" was designed on this principle [20]. In a randomized trial by the same group it reached hemostasis in a mean 5.1 minutes [19], against 14.4 minutes for plain PTFE in the earlier trial [18].

• Elastomeric access grafts. In hemodialysis access, where the punctures come from cannulation needles rather than sutures, a polyurethaneurea graft sealed in a mean 3.5 minutes against 7.4 minutes for ePTFE [21].

Three cautions keep the claim accurate. The 14.4 to 5.1 minute comparison spans two trials and is not randomized, and the elastic-layer patch was still slower than sealed Dacron (5.1 vs 3.7 minutes) [19]. Both studies compared complete commercial products that differ in more than elasticity, so they support the design principle without isolating the elastic layer or validating every elastic binder. Needle-to-suture ratio also drives needle-hole bleeding independently of the wall material [17].

The hybrid membrane places its elastic binder directly against the ePTFE, so the layer that recovers sits where the blood barrier is punctured. Needle-hole leak rate under pulsatile pressure is the bench test that demonstrates it for a given design.

Where the hybrid fits, and why the joint matters

The hybrid suits implants that are sewn in place and see tissue on one face and blood on the other:

• Vascular patches and patch-type closures

• Graft cuffs and sewn sleeves

• Fabric covers that are sutured to a frame rather than laminated to it

The concept is simple. The joint is the hard part. ePTFE's low surface energy, the same property that makes it a quiet blood surface, makes it difficult to bond. Stacking the two materials and stitching them together leaves a delamination path between them and punches needle holes through the barrier the ePTFE was there to provide.

Medibrane bonds the woven polyester, the elastic binder and the ePTFE into a single membrane, so the composite behaves as one wall under load. It can be supplied as flat sheet or formed to shape in one piece, rather than cut into panels and sewn back together.

Each benefit above is established for the individual materials. For the composite, it has to be demonstrated on the finished, sterilized membrane: tissue-side pores left open after bonding, a clean blood-side face including cut edges and needle sites, interlayer peel strength under cyclic load, suture retention and pressurized needle-hole leakage.

If you are specifying a covering that has to heal into tissue, stay quiet to blood and hold a stitch, book a 20 minute consultation with a Medibrane covering engineer: RSVP your consultation.

Elad Einav, CEO & Co-Founder, Medibrane · San Jose, CA

References

1. Mathisen SR, Wu HD, Sauvage LR, Usui Y, Walker MW. An experimental study of eight current arterial prostheses. J Vasc Surg. 1986;4(1):33-41. doi:10.1016/0741-5214(86)90320-4

2. Guidoin R, Chakfé N, Maurel S, et al. Expanded polytetrafluoroethylene arterial prostheses in humans: histopathological study of 298 surgically excised grafts. Biomaterials. 1993;14(9):678-693. doi:10.1016/0142-9612(93)90067-C

3. Bilsel Y, Abci I. The search for ideal hernia repair; mesh materials and types. Int J Surg. 2012;10(6):317-321. doi:10.1016/j.ijsu.2012.05.002

4. Zacharias RK, Kirkman TR, Clowes AW. Mechanisms of healing in synthetic grafts. J Vasc Surg. 1987;6(5):429-436. doi:10.1016/0741-5214(87)90300-4

5. Cejna M, Virmani R, Jones R, et al. Biocompatibility and performance of the Wallstent and the Wallgraft, Jostent, and Hemobahn stent-grafts in a sheep model. J Vasc Interv Radiol. 2002;13(8):823-830. doi:10.1016/S1051-0443(07)61992-7

6. Schneider PA, Kotzé HF, Heyns AD, Hanson SR. Thromboembolic potential of synthetic vascular grafts in baboons. J Vasc Surg. 1989;10(1):75-82. doi:10.1016/0741-5214(89)90288-7

7. Eldrup-Jorgensen J, Mackey WC, Connolly RJ, et al. Evaluation of arterial prostheses in a baboon ex vivo shunt: the effect of graft material and flow on platelet deposition. Am J Surg. 1985;150(2):185-190. doi:10.1016/0002-9610(85)90116-3

8. Goldman M, Norcott HC, Hawker RJ, Hail C, Drolc Z, McCollum CN. Femoropopliteal bypass grafts: an isotope technique allowing in vivo comparison of thrombogenicity. Br J Surg. 1982;69(7):380-382. doi:10.1002/bjs.1800690708

9. Wakefield TW, Shulkin BL, Fellows EP, Petry NA, Spaulding SA, Stanley JC. Platelet reactivity in human aortic grafts: a prospective, randomized midterm study of platelet adherence and release products in Dacron and polytetrafluoroethylene conduits. J Vasc Surg. 1989;9(2):234-243. doi:10.1016/0741-5214(89)90042-6

10. Ambler GK, Twine CP. Graft type for femoro-popliteal bypass surgery. Cochrane Database Syst Rev. 2018;(2):CD001487. doi:10.1002/14651858.CD001487.pub3

11. Mine Y, Mitsui H, Oshima Y, Noishiki Y, Nakai M, Sano S. Suture retention strength of expanded polytetrafluoroethylene (ePTFE) graft. Acta Med Okayama. 2010;64(2):121-128. https://www.lib.okayama-u.ac.jp/www/acta/pdf/64_2_121.pdf

12. Deeken CR, Abdo MS, Frisella MM, Matthews BD. Physicomechanical evaluation of absorbable and nonabsorbable barrier composite meshes for laparoscopic ventral hernia repair. Surg Endosc. 2011;25(5):1541-1552. doi:10.1007/s00464-010-1432-0

13. Meng X, Wang X, Jiang Y, Zhang B, Li K, Li Q. Suture retention strength of P(LLA-CL) tissue-engineered vascular grafts. RSC Adv. 2019;9:21258-21264. doi:10.1039/C9RA04529E

14. Guan G, Yu C, Xing M, et al. Hydrogel small-diameter vascular graft reinforced with a braided fiber strut with improved mechanical properties. Polymers. 2019;11(5):810. doi:10.3390/polym11050810

15. Fernández-Colino A, Wolf F, Rütten S, et al. Small caliber compliant vascular grafts based on elastin-like recombinamers for in situ tissue engineering. Front Bioeng Biotechnol. 2019;7:340. doi:10.3389/fbioe.2019.00340

16. ISO 7198:2016. Cardiovascular implants and extracorporeal systems: vascular prostheses, tubular vascular grafts and vascular patches. Geneva: International Organization for Standardization; 2016. https://www.iso.org/standard/50661.html

17. Sergeant P, Kocharian R, Patel B, Pfefferkorn M, Matonick J. Needle-to-suture ratio, as well as suture material, impacts needle-hole bleeding in vascular anastomoses. Interact Cardiovasc Thorac Surg. 2016;22(6):813-816. doi:10.1093/icvts/ivw042

18. AbuRahma AF, Hannay RS, Khan JH, Robinson PA, Hudson JK, Davis EA. Prospective randomized study of carotid endarterectomy with polytetrafluoroethylene versus collagen-impregnated Dacron (Hemashield) patching: perioperative (30-day) results. J Vasc Surg. 2002;35(1):125-130. doi:10.1067/mva.2002.119034

19. AbuRahma AF, Stone PA, Flaherty SK, AbuRahma Z. Prospective randomized trial of ACUSEAL (Gore-Tex) versus Hemashield-Finesse patching during carotid endarterectomy: early results. J Vasc Surg. 2007;45(5):881-884. doi:10.1016/j.jvs.2007.01.038

20. AbuRahma AF, Stone PA, Elmore M, Flaherty SK, Armistead L, AbuRahma Z. Prospective randomized trial of ACUSEAL (Gore-Tex) vs Finesse (Hemashield) patching during carotid endarterectomy: long-term outcome. J Vasc Surg. 2008;48(1):99-103. doi:10.1016/j.jvs.2008.01.057

21. Glickman MH, Stokes GK, Ross JR, et al. Multicenter evaluation of a polyurethaneurea vascular access graft as compared with the expanded polytetrafluoroethylene vascular access graft in hemodialysis applications. J Vasc Surg. 2001;34(3):465-473. doi:10.1067/mva.2001.117330