An Introduction to SUTURES and AEOS ePTFE Monofilament

Sutures are filaments, fibers or thread-like materials used to hold a wound or tissue together. In surgical language, sutures are used for apposition – that is, the positioning (of tissue) side by side to allow healing. Sutures offer tensile support for wounds until the healing tissue has recovered adequate strength to exist without the sutures. As ligatures, sutures are also used to tie off vessels to arrest bleeding. Today, these tools are taken for granted as they have become universal, and it is difficult to think about performing any kind of surgery without them.

In fact, sutures have been in use since before recorded memory and long before the earliest days of civilization. Eyed needles for sutures date back to nearly 30,000 B.C.E. in Europe. By 20,000 B.C.E., bone needles were in use and continued to be state-of-the-art until the 14th century.

East Africans are said to have used tendons as ligatures to tie off blood vessels as well as acacia thorns with strips of vegetation as sutures. By 2000 B.C.E., sutures were being made from plant fibers such as hemp, cotton, flax, bark fiber and even hair. By 1600 B.C.E., catgut (braided or twisted animal intestines), and later silk, had become main suture materials.

Apart from the suture materials themselves, early physicians were aware of how these ancient devices performed. The Greek Surgeon Galen (ca. 150 A.D.), for instance, recommended that sutures be made of a material that would not “rot,” possibly giving birth to the concept of a permanently implantable type of suture. Later and juxtaposed to this idea, the 11th century Persian physician Avicenna perceived that sutures made of certain natural fibers were inclined to break down rapidly when used on infected wounds.

To overcome this issue, Avicenna used pig bristles, thus inventing the first monofilament suture. Avicenna’s realization that sutures could decompose hinted at the possibility for a deliberate dissolvable suture.

In spite of their long-standing presence in medicine, by the turn of the 18th century sutures were still not commonly preferred. Many renowned physicians still chose to stick to methods such as cauterization for hemostasis and wound closure. Moreover, some adhesive bandages were known to dissolve when contacted with the drainage from wounds. American born and Scottish trained physician Philip Syng Physick quickly realized that ligatures which acted in this way could be of major value and a lot less painful alternative to cauterization. Physick’s experimental – and absorbable – buckskin ligature was truly successful.

Taking this idea forward, Joseph Lister (1827-1912), founder of aseptic technique, pioneered sterile sutures treated with his specialized carbolic acid solution. Lister’s carbolized absorbable catgut ligature was soon in use almost everywhere.

Today’s Sutures

Today’s sutures are varied and made in numerous forms and from a wide scope of materials. Absorbable and non-absorbable sutures are widely used. Most people would have had them both during the course of their lives. Absorbable sutures have reached new levels of specialization and sophistication and can be tailored to remain in the body for pre-determined lengths of time.

Non-absorbable sutures resist the body’s efforts to dissolve them and have been enhanced to support tissue growth. Non-absorbable sutures may be taken off or they can be left in the body as a permanent implant. Absorbable and non-absorbable sutures have their specific applications while providing a considerably extended surgical portfolio.

As earlier physicians learned, suture materials factor considerably in a suture’s application. Nowadays, sutures are made from both natural and artificial materials. Silk, catgut and linen are but a few of the natural materials used, while artificial materials include poly(p-dioxanone), polyglycolic acid and nylons. Polyesters, nylons, steel and silk represent some of the popular non-absorbable suture types, while catgut and glycolides are some of the common absorbable suture types. Suture location, such as the outside of the body or internal, and the ease and requirement of suture removal impact the decision on whether to apply absorbable or non-absorbable sutures.

Equally significant in governing how the suture will be applied is suture form: monofilament or multifilament. Monofilament sutures comprise of a single thread or fiber. Multifilament sutures comprise of numerous strands or fibers that may be braided or twisted together to create a larger filament. Monofilament sutures have low surface drag and pass through tissue more easily than braided or twisted multifilament sutures; these sutures normally carry lower risk of infection. Multifilament sutures, on the other hand, are easier to knot and have greater knot strength.

Besides suture form, the mechanical properties of the suture figure highly into its performance and application. Tensile strength, elasticity and knot strength are all important attributes that result from suture material, form and size. Knot strength, for instance, can be as low as 50% of the tensile strength of the straight unknotted suture. As another example, stiffness (occasionally referred to as memory) affects the ease of handling and tying the suture. Sutures possessing high memory are stiff and resistant to mechanical deformation; this could mean that they unravel easily or are tough to manipulate during stitching. Together, suture mechanical properties help guide the surgeon’s choice of suture materials for particular surgeries.

Finally, how the body reacts towards the sutures must be taken into consideration. As a foreign entity in the body, sutures can cause an immune response. Furthermore, damaged tissue resulting from the suture implantation will produce concomitant inflammation. Immune reaction and inflammation can occur with both absorbable and non-absorbable sutures. Usually noticeable as redness and swelling (and pain) at the suture site, inflammation can be considerable resulting in fever, anaphylaxis, loss of function of the affected area, reduced blood pressure and further tissue damage.

In certain cases, the body rejects absorbable sutures instead of absorbing it. The degree to which sutures produce immune and inflammatory responses plays an important role in determining the extent to which the wound site is repaired to its earlier state.

Biocompatible Plastics and Sutures

Based upon the numerous considerations for implantable sutures, it was a natural changeover towards artificial sutures whose properties could be custom-made to enhance outcomes. Usually made of polymer plastics, materials such as polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), polycarbonate (PC), polyvinyl chloride (PVC) and polyether ether ketone (PEEK) have paved the way for many new applications for plastics in the medical device sector. Biocompatible plastics in their unadulterated form have integral properties mainly suited to medical use. With marginal to no chemical reactivity within the body, for instance, many of these durable plastics are perfect as removable or permanent implants and exhibit little to no lethal side effects.

PTFE, for instance, has a wide-ranging and successful history of use in medical applications. This very unreactive fluoropolymer has been used for implantable device parts such as vascular stent coverings and anastomosis for over two decades. A revised variant of PTFE known as expanded PTFE (ePTFE) has also found approval in the medical device sector. Developed by expanding PTFE following extrusion under regulated conditions, ePTFE is a material with exclusive microporous and mechanical properties. ePTFE has been used in such varied applications ranging from membranes to gasket material to sealer for flange joints. In biomedical applications, ePTFE was used as an artery tube as far back as 1979. Currently, ePTFE medical applications include surgical meshes, ligament and tendon repair, and vascular stent grafts.

ePTFE Sutures

ePTFE sutures signify a sustained evolution of this extremely successful biocompatible material. Extruded as a monofilament, these non-absorbable sutures have been applied for about 30 years. ePTFE monofilament has increased in popularity in the medical device sector because it has several benefits over other non-absorbable sutures. ePTFE has a very low coefficient of friction allowing sutures composed from this material to pull through tissue easily. The compressible nature of the expanded polymer material likewise results in a knot that does not slip or loosen. Compared to absorbable and braided sutures, ePTFE monofilament does not absorb bacteria, saliva or blood, thus supporting healing. Finally, and perhaps most significantly, ePTFE sutures overall do not cause irritation.

Of specific note in relation to ePTFE sutures is needle size. Earlier generations of sutures such as polypropylene normally only allowed needles to be swaged (pressed or crimped) onto them that were of somewhat larger diameter than the suture fiber or filament. The result was a suture that created a hole in the tissue bigger than the suture fiber resulting in increased bleeding. ePTFE monofilament, however, is highly compressible. Therefore, when swaged onto needles, the diameter of the unswaged portion of the filament stays almost equal to that of the swage itself. The result is a suture with a filament or fiber that more fully fills the hole in the tissue caused by the needle, thus decreasing bleeding. Another advantage of ePTFE sutures is that they move through tissue more easily causing a lot less trauma to tissue when switching from needle to filament.

Zeus Aeos® ePTFE Suture Monofilament

For a number of years, many types of ePTFE sutures have been available. However, and with sporadic exemptions, these sutures were only available in the market as branded and complete products with needles swaged onto the suture fibers. Considering this status of the market, Zeus Industrial Products Inc. (headquartered in Orangeburg, SC), has developed a unique line of ePTFE suture monofilament: Zeus’ Aeos® ePTFE monofilament non-absorbable suture as shown in Figure 1. This suture is proposed for permanent implantation within the body. These sutures are unbranded and can be purchased in bulk (without needles) by users who want to make their own suture lines. Offering this suture material unbranded solves a significant market preference and allows secondary vendors such as packaging and swaging companies to raise their brand awareness.

Zeus Aeos® ePTFE monofilament non-absorbable suture

Figure 1. Zeus Aeos® ePTFE monofilament non-absorbable suture. Left Aeos® ePTFE monofilament swaged onto a needle. Right Enlargement of Aeos® ePTFE monofilament.

As ePTFE material, Zeus Aeos® sutures possess all of the advantageous traits of PTFE: These sutures have highest biocompatibility, superior durability and are chemically inert within the body. The very low coefficient of friction of PTFE allows these sutures to pull through tissue with marginal drag. These sutures can also be swaged onto needles up to a 1:1 needle-to-suture (N:S) ratio as illustrated in Figure 2.

These latter two elements specifically lower tissue trauma at the surgical site resulting in less bleeding and negligible associated inflammation. As a microporous material, Aeos® sutures are extremely amenable to new tissue growth into the sutures with long-term implantation resulting in very high levels of tissue encapsulation. Aeos® ePTFE sutures can also be sterilized by autoclaving and ethylene oxide (ETO), and PTFE is USP Class VI compliant as a medical polymer plastic.

Comparison of needle-to-suture

Figure 2. Comparison of needle-to-suture (N:S) size ratios. Top Aeos® ePTFE suture monofilament swaged onto needle with N:S of 1:1. Bottom Braided polyester suture multifilament swaged onto needle with N:S > 1:1. Aeos® ePTFE suture monofilament can be swaged onto needles up to a 1:1 N:S ratio allowing the monofilament to more completely fill the hole in the tissue created by the needle resulting in less bleeding.

In a surgical setting, Zeus Aeos® ePTFE sutures are easily incorporated into any scenario where ePTFE sutures are applicable. These sutures are easy to handle, and have excellent drape and soft feel in the Surgeon’s hand. The memory or stiffness of Aeos® sutures offers them reliable knot strength, and their high surface smoothness allows Surgeons to position knots precisely (Figure 3).

The white color of Aeos® sutures results in superior visibility in an application site. Once in the body, Aeos® ePTFE sutures preserve high tensile strength making them suitable for stressful anatomical environments. Aeos® sutures are also radiologically lucent and thus do not hamper with processes such as angiography, MRI or X-ray.

Aeos® ePTFE knotted suture monofilament

Figure 3. Aeos® ePTFE knotted suture monofilament.

Aeos® ePTFE Suture Applications

Zeus Aeos® ePTFE suture monofilament is especially suitable for applications as a permanently implantable medical device component. For anastomosis, as an example, Aeos® ePTFE sutures can be used to combine vessels to circumvent damage, clots and other disturbances in circulation. Aeos® sutures can be used for hernia repair to shut the abdominal wall directly or to suture mesh in place. For stent deployment, the very high lubricity of Aeos® sutures allows surgeons to effortlessly pull these sutures through the delivery system freeing the stent for final placement.

For stent grafts or covered stents, Aeos® sutures can be used to suture the graft material to the wire stent frame. Lastly, and perhaps most significantly, ePTFE sutures have gained wide approval for replacement of chordae tendineae or mitral valve repair in the heart. These sutures can efficiently treat mitral valve regurgitation, and sutures of this type have exhibited safe and repeatable long-term benefits. Indeed, the biocompatibility and versatility of Aeos® ePTFE monofilament have placed sutures created from this material in a much greater demand.

Conclusion/Summary

Sutures were invented thousands of years ago to treat wounds. Trial and error educated the earliest humans that suture materials acted in different ways and that certain materials dissolved while others did not. With the development of civilization and the advancement and distribution of human knowledge, early physicians comprehended that they might be able to direct the behavior of some sutures types based upon the material and type of wound.

While substantial improvements to sutures were slow in the beginning, the 19th century saw the creation of sterile dissolvable and nondissolvable sutures. The invention of plastics and their application towards sutures was a great step in suture evolution. Currently, there are numerous suture types including natural, synthetic, absorbable and non-absorbable materials.

Possibly one of the most ground-breaking uses of artificial materials in suture applications is PTFE and its variant, expanded PTFE (ePTFE). Because of its novel microporous properties, ePTFE has substantial advantages over a number of other polymers used in medical devices and has specific benefit for use as a suture. The Zeus Aeos® ePTFE suture is the latest innovation in biocompatible sutures. With nearly years of well-established durability and safety behind Zeus’ ePTFE solutions, the Aeos® sutures offer a broad range of applications.

Anastomosis, stent replacement, hernis repair and heart chordae tendineae repair are just a few of the many applications that can be realized using Aeos® ePTFE sutures. This specialized suture monofilament offers all the trademarks for safe surgical interventions while being easily obtainable for non-exclusive or even unbranded use.

This information has been sourced, reviewed and adapted from materials provided by Zeus Industrial Products, Inc.

For more information on this source, please visit Zeus Industrial Products, Inc.

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