Wound closure is a complex process that relies on a variety of tools and materials to achieve the best outcome for the patient. Using a single suture to close all fascia is undesirable and should be avoided. This article aims to introduce the reader to the properties and uses of various synthetic polymer materials and their applications as surgical sutures.

I. Introduction

Raw materials extracted from bone needles, kangaroo tendons, and cow stomach lining. Although this list may sound a bit scary, as if it were the ingredients of some witch's potion, these items help illuminate the history of surgery and surgical suture. From the first eyed needle about 50,000 years ago to the use of kangaroo tendons and cow stomach lining as wound closure materials, surgery has adopted a wide variety of materials to promote wound closure and healing. Currently, the field relies extensively on synthetic materials to replace these seemingly old natural materials. Wound closure requires a large number of materials with different compositions and geometries, depending on the location and nature of the surgery. Relying on only one type of suture material will lead to reduced quality of care and increased complications. Therefore, a wide range of wound management solutions are currently available. This article aims to highlight and distinguish the suture materials currently available to doctors and look forward to the future of suture materials. It strives to provide an updated status of existing biomaterials.

Sutures are strands or fibers used to suture parts of the human body. Given the broad definition of sutures, there are naturally many different types of sutures. Although many sutures are made of natural materials, this review will focus primarily on synthetic materials. The ubiquity of surgical procedures ensures a huge size for the surgical suture market. In 2021, the market size for surgical sutures exceeded $4.4 billion. During this period, it is expected to grow at a rate of 5% per year, driven by the increase in the number of surgeries and the introduction of new suture materials.

For the purpose of discussing the different synthetic sutures, sutures will be categorized into absorbable and non-absorbable sutures. We will discuss the composition, geometry, and purpose of each suture family to provide a useful reference for those seeking to compare the properties of different suture materials. This will include features such as size, color, and any special features used to differentiate between sutures. In addition to the distinction between absorbable and non-absorbable sutures, there is also a distinction between braided sutures and monofilament sutures. This will be included in the discussion of each suture material.

01.Absorbable vs. non-absorbable sutures:

The choice of absorbable or non-absorbable sutures depends primarily on the time required for the wound to heal properly, whether the sutures need to be removed, and the location of the tissue approximation.

Absorbable sutures are designed to degrade over time after implantation in the human body without removal. These suture materials are designed to be easily hydrolyzed and eroded by enzymes in the body and exhibit a certain tensile strength curve at a specific time after implantation. Absorbable sutures are made using materials that are easily metabolized by the body and do not produce harmful byproducts. Generally speaking, absorbable sutures are used for approximation of fascia in the body, and their tensile strength requirements range from a few days to a few months. The most commonly used absorbable suture is synthetic polyester, but natural products such as catgut can also be used.

Non-absorbable sutures are made using materials that do not degrade after implantation in the human body. Instead, the sutures are wrapped by the tissue and remain in place as the wound heals. Therefore, the sutures must be made of materials that do not cause adverse reactions. Polypropylene, nylon, and silk are commonly used materials for making non-absorbable sutures. Non-absorbable sutures can be used for surface approximation or internal wound suturing where prolonged healing time is required. This type of suture is commonly used in cardiovascular and neurosurgery, external wound closure, intracavitary wound closure, and prosthetic connection.

02.Monofilament vs. multifilament sutures:

Sutures can be divided into monofilament sutures and multifilament (or braided) sutures. Monofilament sutures consist of a single strand of material, are usually uncoated and non-absorbable. Because monofilament sutures have a smaller surface area, they cause less inflammatory response than braided sutures. Although monofilament sutures are easier to move through tissues than braided sutures, their handling characteristics are inferior. Monofilament sutures usually require more knots to ensure secure fixation.

Multifilament sutures are braided from many monofilaments. Braided sutures are usually coated and absorbable. The increase in surface area does increase the chance of infection and also the difficulty of passing through tissues. Therefore, braided sutures are usually coated with a layer of material to provide a more uniform surface. Braided sutures are stronger than monofilament sutures of the same size, which improves the safety of knotting.

03. Coated vs. Uncoated Sutures:

Adding coating materials to sutures is an important part of ensuring stable performance and improved operation. Typically, coating materials are added to braided sutures to improve the passage of the suture through the tissue and reduce the surface area for infection. Coatings can also be used to introduce antimicrobial agents (such as triclosan and chlorhexidine gluconate, etc.) into the suture to provide an inhibition zone. Commonly used coatings include calcium stearate, wax, polytetrafluoroethylene, silicone, and a variety of copolymers.

04. Suture size:

Suture size refers to the diameter of a monofilament suture or braided suture and can be divided into metric sizes or USP (United States Pharmacopeia) sizes. In the USP size system, absorbable sutures range in size from the smallest 10-0 to the largest 4. In the metric size system, absorbable sutures range in size from 0.2 (same as USP 10-0) to 6 (same as USP 4). Non-absorbable sutures also meet these size standards, but the range is larger. In the USP sizing system, nonabsorbable sutures range in size from 12-0 (metric size 0.01) to 10 (metric size 12). As stated in USP <861>, the diameters of at least 10 strands of suture must be measured when determining these sizes.

2. Monomers

As with any polymer, the monomers used must be considered when producing the final product. Currently, five monomers have been approved by the FDA for use in the synthesis of absorbable sutures. The approved monomers are glycolide, lactide, p-dioxanone, trimethylene carbonate, and ε-caprolactone.

01.  Lactide:

Lactide ((3S,6S)-3,6-dimethyl-1,4-dioxane-2,5-dione) is formed by the dimerization of lactic acid. Since direct reaction of lactic acid produces a low molecular weight polymer, polymerization from the dimer is required. This low molecular weight product can be used to produce lactide by heating and vacuum. Due to the presence of chiral centers, lactide exists in both d and l conformations, resulting in a variety of polymerization possibilities. Homopolymer PLLA uses the naturally occurring l isomer, while PDLLA uses a mixture of d and l isomers. Homopolymer PDLA has a higher crystallinity than PLA, but currently has no applications in surgical sutures. The synthesis of polylactic acid is most commonly achieved by ring-opening polymerization of lactide in the presence of stannous octoate catalyst. While stannous octoate is the most common catalyst, other metal catalysts such as zinc powder and aluminum isopropoxide have been shown to be effective for PLA polymerization.

02.  Glycolide:

Glycolide (1,4-dioxane-2,5-dione) is formed by the dimerization of glycolic acid and has become one of the most common monomers in the field of synthetic absorbable sutures. Glycolic acid is the simplest alpha-hydroxy acid and its direct polymerization is not suitable for the preparation of high molecular weight polymers. The condensation of the monomers is a reversible reaction and is easily depolymerized by hydrolysis. Therefore, cyclic dimers made by heating low molecular weight polyglycolic acid under reduced pressure are used instead of glycolic acid. Glycolide is heated in the presence of a catalyst to initiate the ring-opening polymerization. Typical catalysts include stannous octoate (tin(II) ethylhexanoate), zinc nitrate, antimony trioxide, or antimony trihalides. Stannous octoate is the most commonly used catalyst because it is FDA-approved for use with resins intended for food contact. For most polymers used in suture production, the glycolide content is controlled. With a few exceptions, glycolide constitutes the majority of the suture backbone. Glycolide and lactide are often referred to as the hard or rigid portion of the polymer backbone due to the reduced freedom of movement compared to monomers such as p-dioxanone or ε-caprolactone.

03. P-Dioxanone:

P-Dioxanone, sometimes called PDO, is the common name for 1,4-dioxane-2-one. The traditional method for preparing PDO is the reaction of ethylene glycol monosodium salt with chloroacetic acid under an inert atmosphere. The conversion of the starting material to sodium hydroxyethoxyacetate is achieved, followed by the formation of free hydroxy acid in the presence of HCl. The crude product is obtained by precipitation in ethanol followed by filtration. Multiple recrystallizations and distillations are then performed to obtain the purified product. This synthetic route has been used for the manufacture of PDO monomer for many years until a more efficient route was proposed. Another more widely used synthetic route relies on the dehydrogenation of diethylene glycol at high temperature in the presence of copper chromite catalyst. The reaction product is dried over molecular sieves and filtered under vacuum. Benzyl bromide and pyridine are added, and the reaction mixture is distilled under reduced pressure and then added to excess ethyl acetate. The solution is cooled to -20°C and seed crystals are added, and the mixture is then further cooled to -34°C. Additional filtration and recrystallization are performed to obtain the final purified product.

04. Trimethylene carbonate:

Trimethylene carbonate (1,3-dioxan-2-one), sometimes referred to as TMC, is an FDA-approved monomer used in the manufacture of Caprosyn, Monosyn, Biosyn, Maxon, and Maxon CV suture products. TMC undergoes spontaneous polymerization above 100°C and can be synthesized from 1,3-propylene glycol and ethyl chloroformate or oxetane and carbon dioxide in the presence of VO(acac) catalyst. Although TMC is capable of ring-opening polymerization to form poly (trimethylene carbonate) PTMC, the polymer has low mechanical strength and is not suitable as a suture material. Therefore, TMC is coupled with glycolide and other approved monomers to form multi-block copolymers.

05. ε-Caprolactone:

ε-Caprolactone, often referred to as caprolactone, is a seven-membered cyclic lactone of caproic acid. This monomer is commercially synthesized from cyclohexanone by Baeyer-Villiger oxidation, a common technique for converting cyclic ketones to lactones. Much like TMC, caprolactone is capable of ring-opening polymerization to produce polycaprolactone PCL. However, much like PTMC, PCL homopolymers do not possess favorable properties for use as suture materials. In the case of PCL, the disadvantage is that it has a degradation time of several years. To increase the degradation rate, caprolactone is added to other monomers to produce multi-block polymers suitable for use as sutures.

III．Homopolymers

01. Polyglycolide:

The first synthetic absorbable suture, polyglycolide (PGA), was first marketed in 1970 by Davis and Geck under the name Dexon. Although Dexon is still on the market, it is now a product of Covidien. Dexon is available in monofilament and braided, coated and uncoated, and undyed or dyed (green). In addition to the polyoxyethylene oxypropylene copolymer-coated suture Dexon Plus and the polycaproate-coated suture Dexon II, an uncoated version, Dexon S30, is also available. PGA sutures are available in sizes 8-0 to 2 as braided sutures and sizes 10-0 to 8-0 as monofilament sutures. For sizes 6-0 or larger, PGA retains approximately 65% of its tensile strength two weeks after implantation and approximately 35% three weeks after implantation. For sizes 7-0 or smaller, PGA retains approximately 55% of its tensile strength two weeks after implantation and approximately 20% after three weeks {Covidien, #109}. Other PGA sutures are available on the market under the trade names Petcryl (Dolphin Sutures), Visorb (CP Medical), Truglyde (Sutures India), Safil (B. Braun AG), PGA Resorba (Resorba). Ethicon recently received 510(k) clearance for its PGA suture under the trade name Pliasure.

PGA offers an alternative to catgut because of its known degradation characteristics. Since its introduction, polyglycolide sutures have found significant use in short-term wound closure. Although PGA has a high initial tensile strength, it loses approximately 50% of its strength after two weeks and 100% of its strength after four weeks. The material completely degrades within four to six months after implantation. Like most synthetic absorbable sutures, PGA is synthesized by ring-opening polymerization of glycolide in the presence of an organometallic catalyst. Common catalysts include stannous chloride and trialkylaluminum. This polymerization process can produce products with molecular weights ranging from 20 to 140 kDa. Products in this range are suitable for extrusion into suture materials. Dexon is the best known polyglycolide suture, manufactured by melt spinning PGA chips followed by stretching, annealing, and processing in a vacuum oven. Due to the highly crystalline nature of PGA, this suture is typically produced as a braided multifilament suture, or very small monofilament sutures. Sterilization of PGA is accomplished by the use of ethylene oxide gas, as exposure to gamma radiation has been shown to reduce the tensile strength of the final product.

02. Polylactide:

Although PLA has a similar structural backbone to PGA, the properties of the polymers are significantly different. There are currently no sutures on the market that use PDLA or PLDLA. The only FDA-approved 100% PLLA suture is Orthodek, manufactured by Teleflex. Due to its longer absorption time (5.6 years), Orthodek is indicated for soft tissue ligatures that require extended approximation times, such as ligament or tendon repairs. Orthodek is approved for use in undyed, braided, and coated sutures in size 2 (metric size 5). Little information is available about this product, and as of December 26, 2014, the trademark status for Orthodek is listed as "Not Applied for Continued Use within Grace Period, Irrevocable."

03. Polydioxanone:

The synthesis of polydioxanone (commonly referred to as PDS, PPDO, or PDO) is achieved by ring opening of the highly pure monomer 1,4-dioxane-2-one. The introduction of PDS sutures by Ethicon provided the first large-size (2-0 and larger) monofilament absorbable sutures. PDS offers an alternative to Vicryl and Dexon for fascia suturing because it maintains tensile strength for six weeks, compared to Vicryl's three to four weeks. As a monofilament suture, PDS offers reduced drag and less tissue inflammation compared to braided sutures. In 1982, advancements in the production of PDS were made with the introduction of PDSII. While chemically identical, the suture is annealed above its melting temperature, softening the exterior of the suture and increasing the flexibility of the final product.

PDS is available as a monofilament suture in USP sizes 7-0 through 2. For sizes 3-0 and larger, PDS retains approximately 80% of its tensile strength two weeks after implantation and approximately 60% at six weeks after implantation. For sizes 4-0 and smaller, PDS retains approximately 60% of its tensile strength two weeks after implantation and 35% at six weeks after implantation {Ethicon, 2017 #119}. It can be purchased undyed or stained with D&C Violet #2. Polydioxanone is sold under the trade names PDS II (Ethicon), PDS Plus (Ethicon), MonoPlus (Aesculap), Monodek (Teleflex), Surusynth (Suru International), DemeDIOX (DemeTech), and Duracryl (Dolphin). Sterilization of polydioxanone is accomplished with ethylene oxide gas.

04. Poly(4-hydroxybutyrate):

Poly(4-hydroxybutyrate) or P4HB is a unique polymer used in the manufacture of surgical sutures because it is not made by ring-opening polymerization of any traditional monomer. Instead, P4HB is produced by microorganisms through in situ polymerization of hydroxybutyryl-CoA. P4HB sutures are FDA-approved for use and are marketed under the names TephaFLEX (Tepha, Inc.) and MonoMax (Aesculap). P4HB sutures are available in sizes 5-0 to 2 and retain approximately 50% of their initial tensile strength after 30 weeks. Degradation is complete within 12 to 18 months after implantation {Tepha, #160}. Sterilization of P4HB is accomplished by the use of ethylene oxide gas, as exposure to gamma radiation has been shown to reduce the molecular weight of the final product.

IV. Polymers of Two Monomers

In many cases, the properties of homopolymer sutures do not meet the surgeon's needs and the tensile strength of the tissue is not adequate. Therefore, several polymers with multiple components in the polymer backbone are used. This section will focus on diblock polymers, which are also the most used class of polymers, for making sutures.

01. Poly(glycolide-lactide):

Poly(glycolide-lactide), also known as PLGA or polylactic acid, is a class of copolymers used in the medical device industry. By varying the mole percentage of each monomer, the physical properties of the final polymer can be adjusted. The most common molar ratio in this class of copolymers is 90% glycolide to 10% lactide, also known as polylactic acid 910. Polyglactin 910 was first introduced in 1974 under the name Vicryl (Ethicon) to provide an alternative to the rapid degradation of PGA sutures. While most Polyglactin 910 sutures are braided, several smaller monofilament sizes (10-0 and 9-0) are also available. Monofilament Polyglactin 910 retains approximately 75% of its tensile strength at two weeks post-implantation and 25% at four weeks post-implantation. Braided Polyglactin 910 is available in USP sizes 8-0 through 3 and can be undyed or dyed with D&C Violet #2. Braided Polyglactin 910 retains approximately 75% of its tensile strength two weeks after implantation and approximately 40% at three weeks after implantation. Monofilament and braided Polyglactin 910 are fully resorbed within 56 to 70 days after implantation. In the Vicryl product line, multifilament sutures are coated with a mixture of equal parts Polyglactin 370 and calcium stearate to reduce resistance to penetration through tissue. Polyglactin 370 is another copolymer composed of 65% lactide and 35% glycolide. Petcryl 910 and Trusynth also use the same coating copolymer. Polyglactin 910 is marketed as Vicryl (Ethicon), Petcryl 910 (Dolphin), DemeCRYL (DemeTech), and Trusynth (Sutures India). Sterilization of PG910 is achieved by using ethylene oxide gas.

Vicryl Rapide (Ethicon) is a version of Vicryl that has been gamma-irradiated to increase absorption while still providing the same initial tensile strength. Vicryl Rapide loses all tensile strength after 14 days, while untreated Vicryl retains some tensile strength after 4 weeks. Similar products are marketed as DemeQUICK57 (DemeTech), Petcryl 910 Fast (Dolphin), and Trusynth Fast (Sutures India). Sterilization is achieved by using ethylene oxide gas.

Vicryl Plus60 (Ethicon) is another suture available, and unlike Vicryl and Vicryl Rapide, Irgacare MP (a purified form of triclosan) is also coated on the suture surface to provide an antibiotic barrier during the wound healing process. A similar product is marketed as Trusynth Plus (Sutures India). Dolphin Sutures offers another antimicrobial polylactic acid 910 suture called Petcryl CS. The Petcryl CS coating replaces the antimicrobial triclosan with antimicrobial chlorhexidine. Polysorb (Covidien) should also be mentioned at this time, as it is a polylactic acid composed of 93% glycolide and 7% lactide. Like other Polyglactin 910 sutures, Polysorb is a multifilament suture that is available undyed or dyed with D&C Violet #2. However, unlike other polylactic acid sutures, the coating is composed of poly(ε-caprolactone-co-glycolide) and calcium stearoyl lactylate. Sterilization is performed using ethylene oxide gas.

In addition to Polyglactin 910 and Polyglactin 370, there is another member of the Polyglactin suture portfolio, Panacryl. By essentially reversing the monomer ratios of polylactic acid 910, Panacryl, which is composed of 95% lactide and 5% glycolide, is able to maintain 60% of its strength after 6 months. Panacryl is an undyed, braided suture coated with a copolymer of 90% ε-caprolactone and 10% glycolide. It was first approved by the FDA in 1996, offering the longest lasting absorbable suture on the market. However, the product was recalled and removed from the market in 2006 due to a number of complications. It was found that many patients had adverse reactions to the suture material and their bodies rejected it as a foreign body.

02. Poly(dioxanone-co-glycolide):

Poly(dioxanone-co-glycolide) (PDG) is a copolymer that is not currently marketed as a suture material. In 2015, Ethicon patented the invention of a PDG copolymer composed of 92% dioxanone and 8% glycolide.

03. Poly(dioxanone-trimethylene carbonate):

Poly(dioxanone-trimethylene carbonate) is a copolymer that is not currently marketed as a suture material. Some work has been done to evaluate its suitability as a drug delivery system, but there are currently no patents for the use of this material in sutures.

04. Poly(glycolide-trimethylene carbonate):

Poly(glycolide-trimethylene carbonate), also known as PGTMC or polyglycolate, is a copolymer used exclusively by Covidien in Maxon sutures. The molar ratio of this copolymer is 64% glycolide to 36% TMC. Maxon is an uncoated monofilament suture that is available undyed or dyed with D&C Green #6 and maintains 50% of its tensile strength at 4 weeks after implantation. The Maxon suture is available in USP sizes 7-0 to 1. In addition to Maxon, a version of this suture, the Maxon CV, is also approved for use in pediatric cardiovascular surgery. Like Maxon, this suture is an uncoated monofilament suture. However, the Maxon CV is only available in USP sizes 7-0 to 4-0 and is dyed with D&C Green #6. Sterilization of the Maxon is achieved by the use of ethylene oxide gas.

05. Poly(glycolide-co-ε-caprolactone):

Poly(glycolide-co-ε-caprolactone), also known as PGCL or polycaprolactone 25, is a block copolymer composed of 75% glycolide and 25% ε-caprolactone. Poliglecaprone 25 is a monofilament suture that is available undyed or dyed with D&C Violet #2. PGCL is available in USP sizes 6-0 to 1. The key difference between PGCL and other monofilament sutures, such as PDS, is its flexibility, which is superior to other monofilament sutures such as PDS. This is achieved by synthesizing a prepolymer of caprolactone and glycolide to produce a soft polymer chain. This prepolymer does not have the same monomer composition as the final product. Therefore, more glycolide is then added to the prepolymer to incorporate hard segments into the polymer chain. This improves the physical properties of the final product, achieving high tensile strength while also improving flexibility. The undyed suture has a high initial tensile strength that decreases to 50-60% of the initial strength after one week and 20-30% of the initial strength after two weeks. The dyed suture degrades slightly more slowly, retaining 60-70% of its initial strength after one week and 30-40% after two weeks. The suture is completely hydrolyzed and absorbed between 91 and 119 days after implantation. Poliglecaprone 25 is marketed as Monocryl (Ethicon), Petcryl Mono (Dolphin), DemeCAPRONE (DemeTech), Monoglyde (Sutures India). Monocryl Plus (Ethicon) is another available poliglecaprone 25 suture that is coated with Irgacare MP to provide an antibiotic barrier during wound healing. Sterilization of poliglecaprone 25 is achieved by using ethylene oxide gas.

06. Poly(lactide-ε-caprolactone):

Poly(lactide-ε-caprolactone), also known as P(LA/CL), was first reported as a potential suture material in 1998. Using commonly used suture monomers, a copolymer consisting of 75% lactide and 25% ε-caprolactone can be synthesized by ring-opening polymerization. Currently, the only commercially available P(LA/CL) suture is Surgisorb M (Sutures - UK), which is available undyed or dyed with D&C Violet #2. It is a monofilament suture in sizes 8-0 to 2 that is coated with a mixture of calcium stearate and P(LA/CL). Studies have shown that P(LA/CL) sutures retain 75% of their initial tensile strength after 4 weeks and lose all tensile strength after 25 weeks. No FDA 510(k) approval could be found for this suture, but this polymer has been approved as part of a nerve capping device and as an absorbable sheet for wound support.

V．Polymer of three monomers

01. Poly(glycolide-co-trimethylene carbonate-co-ε-caprolactone):

Poly(glycolide-trimethylene carbonate-ε-caprolactone), commonly known as Monosyn, is a suture produced by Aesculap. Monosyn is a triblock copolymer consisting of 72% glycolide, 14% trimethylene carbonate, and 14% ε-caprolactone. As a triblock polymer, Monosyn has an ABA structure. In this naming scheme, the A block is polyglycolide, the rigid component of the polymer. The B block, which imparts flexibility, is a poly(glycolide-co-trimethylene carbonate-co-ε-caprolactone) block copolymer. To synthesize the final polymer, the soft segments are first polymerized in the melt at temperatures above 150°C to produce a dihydroxy-terminated terpolymer. The terpolymer is then melted along the glycolide at between 200 and 250°C. This is done in the presence of an appropriate catalyst or bifunctional initiator. Through this reaction, the synthesis of the final ABA triblock copolymer is achieved. The polymer is then melt-spun into a water bath and then stretched and annealed. Monosyn is an uncoated monofilament suture available undyed or dyed with D&C Violet #2. It retains 50% of its tensile strength two weeks after implantation. Hydrolysis is complete within 60-90 days after implantation. The USP size of Monosyn is 7-0 to 2. Sterilization of Monosyn is achieved by using ethylene oxide gas.

02. Poly(glycolide-co-trimethylene carbonate-co-p-dioxanone):

Poly(glycolide-trimethylene carbonate-p-dioxanone), also known as Glycomer 631 and commonly known as Biosyn, is a suture produced by Covidien. Biosyn is a triblock copolymer composed of 60% glycolide, 14% p-dioxanone, and 26% trimethylene carbonate. Like Monosyn, Biosyn is an ABA copolymer. However, unlike Monosyn, the center block is not a terpolymer, but rather a copolymer of 35% p-dioxanone and 65% trimethylene carbonate. This copolymer is end-capped with a copolymer containing at least 50% glycolide and less than 50% p-dioxanone. The ratio of the end-capped copolymers is adjusted to achieve a final ratio of Glycomer 631. Biosyn is an uncoated monofilament suture that is available undyed or dyed with D&C Violet #2. Hydrolysis is complete within 90-110 days after implantation. Biosyn degrades comparable to Vicryl, maintaining tensile strength for three weeks and retaining approximately 8% after four weeks. Details on the degradation of Biosyn are not available at this time. The USP size of Biosyn is 6-0 to 1. Sterilization of Biosyn is accomplished by the use of ethylene oxide gas.

03. Poly(ε-caprolactone-co-trimethylene carbonate-co-p-dioxanone):

Poly(ε-caprolactone-co-trimethylene carbonate-co-p-dioxanone) is a material that is not currently marketed as a commercially available suture, but has shown promise as a potential suture material. A series of poly(trimethylene carbonate-co-ε-caprolactone)-block poly(p-dioxanone) copolymers were synthesized via a two-step polymerization process. The synthetic polymers were evaluated for their potential as suture materials. The polymer composed of 90% p-dioxanone, 5% trimethylene carbonate, and 5% ε-caprolactone showed excellent potential as a suture material. The suture began to degrade between 120 and 150 days after implantation and was completely absorbed between 210 and 240 days after implantation. This potential material was evaluated in vivo as an uncoated monofilament suture. The performance of this material showed that it is comparable to other monofilament sutures such as PDSII and Maxon.

VI. Copolymer of four monomers

01. Poly(glycolide-co-L-lactide-co-trimethylene carbonate-co-ε-caprolactone):

Poly(glycolide-co-L-lactide-co-trimethylene carbonate-co-ε-caprolactone), also known as polyglyconone 6211, commonly known as Caprosyn, is unique in the field of synthetic sutures. It is the only suture currently on the market that contains four different monomers. Caprosyn, manufactured by Covidien, is a suture used for short-term suturing of tissues. Due to its rapid degradation, Caprosyn offers an alternative to traditional gut sutures that can induce an inflammatory response in tissues. It retains 60% of its initial tensile strength 5 days after implantation and 20-30% of its initial tensile strength 10 days after implantation. Hydrolysis is essentially complete within 56 days after implantation. Caprosyn is an uncoated monofilament suture that can be undyed or stained with D&C Violet #2. Caprosyn is available in USP sizes 6-0 to 1. Sterilization of Caprosyn is achieved by using ethylene oxide gas.

VII. non-absorbable sutures

01. Polyamides:

There are two types of polyamides that have been used as non-absorbable surgical sutures: nylon 6 and nylon 6,6. Nylon 6, or polycaprolactam, is manufactured by ring-opening polymerization of ε-caprolactam. Nylon 6,6 is a copolymer formed by the polycondensation of hexamethylenediamine and adipic acid. Nylon sutures are available in both monofilament and braided configurations, depending on their intended application.

Braided sutures are made from nylon 6,6 and can be either undyed or dyed black with log dye for enhanced visibility. Braided nylon 6,6 sutures are available in sizes 6/0 to 1 and are marketed under the names of wax-coated Nurolon (Ethicon) and silicone-coated Surgilon (Covidien). Sterilization of monofilament nylon sutures can be achieved by gamma sterilization using Cobalt-6091 or ethylene oxide gas.

Monofilament nylon sutures are made from nylon 6 and nylon 6,6 and are available undyed, dyed black with log dye, dyed green with D&C Green #5, or dyed blue with D&C Blue #2. Monofilament nylon sutures are available in sizes 11/0 to 2 and are marketed as Ethilon (Ethicon), Monosof (Covidien), Dermalon (Covidien), and Nylon (Teleflex). Sterilization of monofilament nylon sutures can be achieved by gamma sterilization using Cobalt-60 or ethylene oxide gas.

02.Polyester:

Polyethylene terephthalate, commonly known as PET or polyester, is a material used as nonabsorbable sutures. Polyester sutures are available as monofilament sutures, or braided sutures with or without PTFE coating. It can be undyed, dyed green with D&C Green #6, or braided with green and undyed sutures. Braided sutures are available in the largest sizes, USP sizes 6/0 through 5. Monofilament sutures are available in USP sizes 11/0 through 8/0. Polyester sutures are marketed under the names Mersilene (Ethicon), Procare (Dolphin Sutures), Cottony II (Deknatel - uncoated), Polydek (Deknatel - light PTFE coated), and Tevdek (Deknatel - heavy PTFE coated). Sterilization of polyester sutures can be accomplished by gamma sterilization using Cobalt-60 or ethylene oxide gas.

The use of high molecular weight PET is also noteworthy for its suitability in cardiovascular applications. Several polyester sutures are made specifically for this purpose and differ slightly from typical PET sutures. Sutures made from high molecular weight PET are available in a variety of coatings and can be either undyed or dyed green with D&C Green #6. These sutures are available in USP sizes 5 through 7/0. Ethibond Excel (Ethicon) is coated with polybutyrate. Surgidac (Covidien) is available uncoated or with a polybutylene adipate coating. Ti-Cron (Covidien) is coated with silicone. Sterilization of high molecular weight PET sutures can be achieved by gamma sterilization using Cobalt-60 or ethylene oxide gas.

Polybutylene terephthalate (PBT) is a monofilament suture offered by B. Braun Company under the name Miralene. Limited information is available about this suture and it is not currently listed in the Aesculap suture portfolio overview.

Polybutylene terephthalate (PBE) is also used in Novafil (Covidien) and Vascufil (Covidien) sutures. These sutures are composed of a copolymer of 84% butylene terephthalate and 16% polytetramethylene ether glycol. Covidien claims that this makes the suture "creep-resistant" and able to return to its original shape after edema subsides. Because the suture is more elastic than traditional non-absorbable sutures, it is able to stretch and retract as the wound site swells, reducing tissue damage caused by pulling on the suture. The material is also more abrasion-resistant than polypropylene and may reduce premature breakage. Both sutures are monofilament sutures, but Vascufil is coated with Polytribolate, an absorbable polymer composed of 51% ε-caprolactone, 9% glycolide, and 40% Poloxamer 188. Poloxamer 188 is a copolymer of polyoxyethylene and polyoxypropylene. Novafil is available in USP sizes 2 to 7/0 and is available in clear or dyed blue with copper phthalocyanine. Vascufil is available in sizes 2/0 to 7/0 and is dyed blue with copper phthalocyanine. Sterilization of polybutylene sutures is accomplished by gamma irradiation using Cobalt-60.

03. Polyvinylidene fluoride:

Polyvinylidene fluoride (PVDF) is a nonabsorbable suture with handling characteristics similar to polyester and polypropylene sutures, but is less prone to clot formation than polyester sutures and less prone to failure than polypropylene sutures. In most applications, PVDF performs comparable to polypropylene sutures, but with better handling and longer durability. PVDF is an uncoated monofilament suture available in black or blue dyed with copper phthalocyanine. This suture is available in USP sizes 10/0 to 2 and is marketed under the names Resopren (Resorba), Centidene (Centenial), PVDF (Eye4Vision), PVDF (Daps Tech), and PVDF (Acufirm). Teflene is a name for PVDF sutures that was a trademark of Peters Laboratories but has since been abandoned. Sterilization of PVDF sutures is achieved with ethylene oxide gas, although it can also be gamma sterilized using Cobalt60.

Poly(hexafluoropropylene-vinylidene fluoride) is a copolymer of hexafluoropropylene and vinylidene fluoride and is sold under the trade name Pronova (Ethicon). The composition of the monomers depends on the size of the suture, with the vinylidene fluoride content ranging from 20% to 50%. Ethicon claims that by incorporating additional monomers into the structure, the handling characteristics of PVDF are improved by reducing compliance without making the material "stretchy." Pronova is an uncoated monofilament suture available undyed or dyed blue with copper phthalocyanine. The suture is available in USP sizes 8/0 to 2/0. Sterilization of PVDF sutures is achieved with the use of ethylene oxide gas.

04. Poly(tetrafluoroethylene) :

Polytetrafluoroethylene (PTFE), commonly known as Teflon, is a material that can be used as both a suture and a suture coating. PTFE is an uncoated monofilament suture available in white and black and is often used with a black needle for increased visibility. This suture has a USP size of 6/0 to 2/0 and is marketed under the names Cytoplast (Osteogenics), PTFE (Omnia), PTFE (Coreflon), Cyto Surg (Salvin), and Gore-Tex (Gore Medical). Gore-Tex sutures do not conform to USP sizes and are sold in cardiovascular (CV) sizes of CV8 to CV0. However, these sizes are based on measurements of the suture before it is expanded. This is because approximately 50% of the volume of the suture is air. Gore-Tex is very porous and its diameter after expansion is much larger than other similar sutures. This allows the suture diameter to be comparable to the needle diameter, reducing the gap left when the needle penetrates the tissue. This reduces the amount of bleeding at the opening. In addition, the high porosity greatly reduces the stiffness of the suture, making it 100 times less stiff than a polypropylene suture of the same size. Sterilization of polytetrafluoroethylene sutures is achieved with ethylene oxide gas.

05. Polyolefins:

Isotactic polypropylene, often abbreviated as PP, is widely used as a non-absorbable monofilament suture. For more than 40 years, polypropylene sutures have been used in cardiovascular surgery and for suturing tissue with superficial injuries. Due to its long history of use, it is often used as a suture that requires a non-absorbable material. Most non-absorbable sutures are intended as an alternative to polypropylene sutures, as this is the established system for non-absorbable monofilament sutures. Isotactic polypropylene is polymerized by propylene using a Ziegler-Natta catalyst. It can be undyed or dyed blue with copper phthalocyanine. Polypropylene sutures are available in sizes ranging from USP 10/0 to 2 and are marketed under the names Prolene (Ethicon), Duracare (Dolphin Sutures), Surgipro II (Covidien), Deklene II (Deknatel), Surulene (Suru), and Premilene (B. Braun). In recent years, there have been reports of the use of syndiotactic polypropylene in sutures. Sterilization of polypropylene sutures is achieved with ethylene oxide gas.

06. Ultra-high molecular weight polyethylene:

Ultra-high molecular weight polyethylene (UHMWPE) is a polyethylene with a molecular weight between 2 and 6 megadaltons. Due to its extremely high molecular weight, UHMWPE sutures are stronger than other sutures of the same size, allowing for smaller suture sizes to be used when a certain tensile strength is required. UHMWPE is an uncoated braided suture available in USP sizes 5/0 to 5 and is marketed under the names Force Fiber (Teleflex), FiberWire (Arthrex), TigerWire (Arthrex), Orthocord (Depuy), PowerFiber (CP Medical), and CP-Fiber (CP Medical). Most UHMWPE sutures are co-braided with another polymer to impart color and good handling properties. PowerFiber is available in white or white with a green polyethylene tracer. CP-Fiber is available in white or with a blue or black polyethylene tracer. Force Fiber is available in white and blue and contains no braided polymer. Green Force Fiber is a co-braid between UHMWPE and polyester. The Green/White version as well as the White/Green version are realized in the same way. The White/Blue version is braided with UHMWPE and blue polypropylene. The White/Black version is braided with UHMWPE and black nylon 6,6. Orthocord is a composite braid of 62% polydioxanone (Ethicon) and 38% UHMWPE. PDS can be dyed with D&C Violet #2 or D&C Blue #6 to give the suture a blue or purple color. PDS is also coated with a copolymer composed of 90% ε-caprolactone and 10% glycolide. Sterilization of UHWMPE sutures is accomplished by the use of ethylene oxide gas.

 VIII. Future Development Direction

01. Barbed Sutures:

Several advances have been made in the area of barbed or knotless sutures. The addition of structure to the surface of the suture, which is located opposite the direction the suture passes through the tissue, allows for uniform force to be applied throughout the length of the suture. This also eliminates the need to tie knots in the suture along the length of the wound closure. This incorporation of structure is achieved through the use of a cutting die. The large suture is passed through the cutting die and excess suture material is cut away to achieve the final configuration. This allows surgeons to perform complex surgeries, most commonly laparoscopically, in less time and with less blood loss. Knotless sutures are made from a variety of polymers, including polydioxanone, poliglecaprone 25, polypropylene, and nylon. These products are available in sizes USP 5-0 to 1 and are marketed under names such as Stratafix (Ethicon), Quill (Surgical Specialties Corporation), and V-Loc (Covidien).

02. Polypropylene Oxide Sutures:

A recent patent application reports the use of polypropylene oxide (PPO) in the design of block copolymers. This suture is currently in development and is called Voyager. This marks the first synthetic absorbable suture that is different from the five monomers approved for use by the FDA. The main advantage of the device is the long-lasting knot pull force, which even exceeds that of PDS sutures. After about five weeks, the tensile strength of PDS sutures decreases dramatically. Although the initial tensile strength of PPO sutures is lower, the designers claim that the strength over the past five-week period is higher than that of PDS. This is critical for the approximation of tissues that are slow to fully heal. For example, during laparotomy, the abdominal wall is opened. It takes about two months for the abdominal wall to heal in healthy patients, but many patients may take longer to heal. The Voyager device will allow for an expanded approximation of the abdominal wall and ensure complete wound closure. This has the benefit of reducing incisional hernias, which are quite common during laparotomy (~20%). It is estimated that the incidence of incisional hernias could be reduced by 50%.

03. Diacetyl chitosan coated sutures:

It has recently been proposed that diacetyl chitosan (DAC) coated silk sutures could be an alternative to current suture technology due to the abundance of chitosan in nature and the lack of biological response to the material. DAC silk sutures showed similar degradation rates to current products and comparable mechanical properties. Evaluations of antimicrobial activity and tensile strength showed good results compared to commercial alternatives. Furthermore, the authors reported that the natural antimicrobial properties of chitosan could be used as a suture coating and that the suture appeared to accelerate the healing process compared to control sutures. In addition, chitosan-based dressings have been approved and are currently available on the market.

04. Antibiotic-releasing sutures:

Techniques for the introduction of antibiotics into the body of sutures have not yet been introduced to the market. Typical antibiotic loading of suture materials is achieved at the coating stage, where the suture is passed through a slurry containing the compound of interest. However, it has recently been proposed to produce sutures using poly(L-lactide), PEG, and levofloxacin wet electrospinning onto silk. The coated wire with a diameter of 45 μm has the potential to be applied to fine-sized or braided sutures. The handling characteristics of the silk sutures are comparable to those of unmodified silk sutures, but with antibiotic activity against Staphylococcus aureus and Escherichia coli. Silk sutures containing antibiotics are a product that is not currently available in the suture market. Since silk is the preferred suture material in most parts of the world, the addition of antibiotic activity to silk has a significant impact on the silk suture market.

05. Amino Acid Nanogel Composite Sutures:

Introducing triclosan-containing biodegradable nanogels to silk sutures. By preparing triclosan-loaded l-lysine macromolecular gels and enzymatically digesting the macromolecular gels using trypsin, the silk sutures are degummed in ethanol and then immersed in the nanogel to attach them to the outside. With the introduction of triclosan, this standard antibiotic has been approved as a suture coating material, which provides a possible alternative to traditional silk sutures.