According to the current requirements for surgical suture materials, the
following properties are postulated:
- High thread tear and knot break strength
- Triggering minimal tissue reactions/tissue damage
- No capillarity and thus no swelling in the tissue
- Infection inhibition
- Minimal extensibility or reversible, calculable extensibility (rubber band effect)
- Good handling (flexibility, suppleness, knotability)
- Optimal knot security
- Resorbability
Synthetic non-resorbable suture materials:
- Polyvinyl alcohol (Synthofil®): Polyvinyl alcohol was introduced to the market in 1931 in collaboration between B.Braun-Melsungen and Wacker-Chemie as the first synthetic suture material.
- Polyamides (Nylon®, Perlon®, Supramid®): The fibers made from polyamide have high strength, suppleness, and elasticity and also have the advantage that they are hydrophobic and do not swell in water (Braun, B. 1954). However, they have the property of disintegrating over months or years, with the fragments remaining in the organism.
- Polyolefins (Polyethylene, Polypropylene = Synthofil®, Mersilene®)
Synthetic resorbable suture materials:
- Polyglycolic acid: It shows high tensile strength as well as uniform thread thickness, so that the surgeon can use a smaller thread thickness compared to catgut with the same suture strength (Walsch G. 1976). In contrast to catgut, which is enzymatically degraded, the degradation of PGA occurs through hydrolysis; it gradually breaks down in the tissue to glycolic acid and has a functional time of about 25 days (short-term resorbable). The tissue reaction around the thread is significantly less than with catgut (Artandi C. 1980). In 1979, the improved Dexon-S® was introduced to the market (B.Braun-Dexon).
- Polyglactin 910: In 1974, Polyglactin 910, known as Vicryl® (violet, braided), was developed; it is created through copolymerization of glycolic acid and lactic acid (Ethicon). Similar to PGA threads, Polyglactin 910 threads have a functional time of about 30 days and are classified as short-term resorbable. Vicryl ®rapid is undyed. It is resorbed faster with high initial tensile strength.
- Polydioxanone (PDS®) and Polyglyconate (Maxon®): In 1981, the first production of a monofilament resorbable suture material was achieved with polydioxanone (PDS®). In 1983, Lünstedt and Thiede published results on tensile strength tests on the new suture material and demonstrated the medium-term resorbability of the thread with a functional time of 60 to 80 days. Polyglyconate produced in 1984 behaves similarly (a mixture of polyglycolic acid and trimethylene carbonate). It is monofilament and has a functional time of 40-60 days (Knoop et al. 1987) (Lünstedt B. Thiede A. 1983).
- Polyglecaprone: In 1992, Polyglecaprone was added as Monocryl®. It is monofilament and resorbable; violet or undyed (for skin suture) available commercially. Despite its ultra-short-term functional time, it has high initial tensile strength and a favorable tensile strength profile.
Multifilament
A braided thread is obtained by braiding (bobbin lace) thin yarns. In this technique of combining individual threads into a stronger thread, the fibers lie more or less transverse to the thread's longitudinal axis (Nockemann P. F. 1992). The braided polyamide thread is soft compared to the monofilament form, but also very elastic. This high elasticity requires a certain adjustment in suture technique and requires three- to four-fold knotting if ligatures are to hold firmly. (Braun B. 1954)
Monofilament
Monofilament threads consist of a single thread, have a smooth surface and, compared to multifilament threads of the same raw material, higher stiffness, meaning they are characterized by lower flexibility compared to multifilament threads. In thicker threads, this stiffness, which all monofilament threads possess, worsens handling. In particular, they are harder to knot. However, the smooth, closed surface as well as the completely closed interior prevent capillarity in monofilament threads. At the same time, they have the best gliding ability through the tissue (Nockemann P. F. 1992). All three forms of thread construction can be traced in the history of nylon: Initially, nylon came to the market as a monofilament synthetic thread, showing the specific properties of such. The thread ends in the knot acted like spikes due to the homogeneity. Thus, due to the identified disadvantages of a monofilament thread, there was a call for a twisted nylon thread. The cutting into the tissue should be kept as low as possible. By melting and extruding the polyamides, bristles and threads of any thickness could be produced. Thus, monofilament polyamide threads, especially in fine diameters for skin, tendon, vascular, nerve sutures, specifically for use in micro- and neurosurgery as well as (29) ophthalmology, came to the market and enabled further development and improvement of surgical disciplines.
Pseudomonofilament
Between the two groups of monofilament and multifilament threads are the pseudomonofilament threads. Here, the thread interior, the so-called thread core, consists of a multifilament material, which gives the thread its suppleness in handling, especially when knotting. The smooth surface, which gives the suture material its external property, forms a sheath-like coating. This can consist of the same raw material as the thread core. In the other case, the twisted or braided fiber bundles are subsequently thinly coated with a second gliding mass. Generally, this better gliding outer skin is only 1-2% of the thread diameter. Usually, the coating is sprayed on after the thread is completed. This results in merely a very thin or punctually applied gliding layer on the thread braid (Nockemann P. F. 1980).
Initially, the polyamides come to the market as monofilament and find use in sub-areas of surgery with the special properties of a monofilament thread. The next development stage of polyamide (specially developed for surgical purposes) already leads to the production of pseudomonofilament threads. B.Braun reports in 1954 on modern plastics and their application in surgery and discusses the modified polyamide thread: “A special form between the monofilament and the braided thread is Supramid from Badische Anilin- und Soda-Fabrik, Ludwigshafen. This is a twisted Perlon thread that is enveloped with a sheath of the same material. Due to its smooth surface, it requires multiple knotting” (Braun B. 1954).
While the thread construction was originally braided multifilament, PGA threads today are pseudomonofilament, only very small thicknesses are still monofilament (Thiede A. Hamelmann H. 1982). Today, these threads are additionally coated, namely Dexon with polyol, Vicryl with Polyglactin 370 and calcium stearate.
Surface Properties
Monofilament threads have a smooth surface, whereby only few tissue cells are crushed during tissue suturing. Furthermore, as homogeneous threads, they do not act as a drain, so no bacterial migration from the skin into the wound can occur.
Coating
With suture material, the effort was evident early on to have threads that do not swell by absorbing wound secretion and thus traumatize the suture channels; hence the recurring instruction to use strongly and firmly twisted, well-waxed threads.
In the 1960s and 1970s, coatings for non-resorbable threads were developed, and from the mid-1970s, fully synthetic coated, resorbable threads like DexonBicolor® and Vicryl® were introduced to the market. The coating also consists of resorbable material.
Smailys et al. (1979) coated various medical materials, including suture materials, with antibiotics or heparin using electrophoresis and ultrasound. However, this attempt has not matured to clinical use, although this approach is also being investigated in the form of coating with chemotherapeutics (e.g., to avoid anastomotic recurrences).
Suture materials of the 20th and 21st centuries like PGA threads, coated with polyol, and polyglactin threads, surrounded by Polyglactin 370 and calcium stearate, are intended to no longer traumatize in the puncture channel (Thiede A. Hamelmann H. 1982).
Armoring
With the spring eye needle, the thread jumps into the eye by slight pull. The development and conception of the atraumatic suture, i.e., a stepless, firm connection between needle and thread, was an important further development of needle and thread material. The thread is mounted in the needle end, using single bores and channel shaft bores. The thread appears as a direct needle extension. The tissue trauma is accordingly low, as only a small step formation remains at the armoring zone. The latest development is the so-called tear-off thread, where the needle detaches from the thread by slight pull on the needle holder. The armoring zone is set so weakly that the suturing process itself is not impaired, but a force of about 3-10 N (i.e., 30-100g) is sufficient to induce the detachment process. With this atraumatic needle-thread combination, threading the thread and time-consuming cutting are eliminated once. Originally conceived for vascular surgery, this needle-thread combination has meanwhile conquered a firm place in almost all areas of surgical activity (Thiede A.Hamelmann H. 1982). Needle-thread connections were initially only supplied in individual packaging. The plastic or aluminum foil brought a significant improvement: The already externally sterile threads are opened directly for use. The second outer tear foil protects the sterility of the outside of the inner foil with the thread, so that the surgeon now has a perfectly sterile thread available.
Basics and Techniques of Surgical Suturing
The different layers of a wound must be brought together either with individual or continuous sutures. Subcutaneous fatty tissue should only be sutured if a Scarpa's fascia is present. In randomized studies, the negative effect of subcutaneous sutures could be shown after saphenous vein excision. An additional suture of the fatty tissue leads here to tissue ischemia as well as necrosis and thus to an increased infection risk (P.M Vogt.M.A Altintas. C Radkte. M. Meyer-Marcotty Basics and Techniques of Surgical Suturing Surgeon 2009 80: 437-447).
To achieve relief of tension at the wound edges and at the same time sufficient tensile strength, dermal sutures are important. Currently, resorbable suture material is preferred, which is sunk under the dermis through deep dermal punctures with inverted stitch direction, so that the knot lies subdermally. This measure maximally reduces the tension on the final skin suture. The sunk knot reduces the rate of thread extrusions.
Modern synthetically produced non-resorbable suture materials (nylon, polypropylene) as well as resorbable monofilaments (polyglecaprone) are minimally tissue-reactive and are thus preferred for wound closure, especially when cosmetic aspects are in the foreground. An important property of modern suture materials is to trigger as little inflammatory reaction as possible during resorption. Already at the level of non-resorbable materials, sutures generate fewer inflammations than staples.
The holding strength of a suture is determined by the tensile strength of the material. In wounds under low tension, subcutaneous or intracutaneous continuous sutures yield cosmetically very good results. In contrast to single sutures, however, they do not allow differentiated adjustment of suture tension, which may be necessary in some complex wounds. Therefore, subcutaneous continuous sutures require correctly placed dermal punctures.
Greve and colleagues showed that very good cosmetic results were achieved in more than 1500 sutures of up to 30 cm length with a resorbable polydioxanone thread. In particular, the proximity of the suture material to the epidermis plays a role here. If the threads are placed too superficially and the mass of the material is increased by thick knots, increased inflammatory reactions result. Therefore, with all resorbable single sutures, attention must be paid to a clearly subdermal stitch orientation with eversion of the wound edges in order to then not place a continuous intracutaneous suture too superficially.
Wound closure with tissue adhesive has been favored repeatedly in recent years. Clinical application is so far limited to small superficial wounds and is preferably used in children. In a newer prospective randomized study, a remarkable difference in wound healing was observed. In 26% of cases, wound dehiscences occurred in the adhesive group, whereas no dehiscences occurred in the suture group. Therefore, the authors recommend that in children, wounds should better be closed surgically with a resorbable intracutaneous suture.
In a study by Stockley and Elson, the use of skin staples showed a higher incidence of inflammatory reaction and corresponding complaints upon removal, as well as less favorable scar healing compared to sutures. The only advantage of staples was the speed of wound closure. Regarding the properties of resorbable and non-resorbable sutures, no differences were found in terms of scar quality. However, a trend for better healing was observed with the use of thinner, inner subcutaneous sutures. Among the various resorbable materials, the tissue of monofilament threads proved to be less reactive than that of braided threads.