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Sutures

1. n. (in anatomy) a type of immovable joint, found particularly in the skull, that is characterized by a minimal amount of connective tissue between the two bones. The cranial sutures include the coronal suture, between the frontal and parietal bones; the lambdoidal suture, between the parietal and occipital

bones; and the sagittal suture, between the two parietal bones.

2. n. (in surgery) the closure of a wound or incision with material such as silk or catgut, to facilitate the healing process. There is a wide variety of suturing techniques developed to meet the differing circumstances of injuries to and incisions in the body tissues.

3. n. the material - silk, catgut, nylon, any of various polymers, or wire - used to sew up a wound.

4. vb. to close a wound by suture.

Concise Medical Dictionary, Oxford University Press, © Market House Books Ltd 1998

History

Since the beginning of surgical history (5000-3000 BC), sutures have been used as the means of repairing damaged tissues, cut vessels, and surgical incisions.

Thou shouldst draw together for him his gash with stitching.

Edwin Smith Surgical Papyrus

As time has passed, a variety of suture materials have been used (to name only a few): flax, hair, linen strips, pig bristles, grasses, mandibles of pincher ants, cotton, silk, the gut of an animal, nylons, polyesters, metals. The earliest use of gut can be traced back to the ancient Greek physician Galen. The eighteenth century brought the use of buckskin and silver wire, and the nineteenth brought the ability to chemically alter the properties of gut. By the twentieth century, cotton and treated natural materials had come to be the most widely used materials for suturing. After the invention of nylon and polyester propagated the popularity of cotton and treated natural materials, polyethylene, polypropylene, polyglycolic acid, polyglactin 910, and a large number of textile materials entered into the menu of choices for sutures.

Sutures are probably the largest group of devices implanted in humans. Although they seem to be of small concern to the medical community, few devices have been made of so many different materials. By definition, a suture is a thread that either approximates and maintains tissues until the natural healing process has provided a sufficient level of wound strength or compresses blood vessels in order to stop bleeding.

Background

The United States Pharmacopoeia is one of the official compendium for the suture industry. It sets standards and guidelines for suture manufacture. Suture sizes are given by a number representing diameter ranging in descending order from 10 to 1 and then 1-0 to 12-0, 10 being the largest and 12-0 being the smallest at a diameter smaller than a human hair.

Prior to 1976, the Food and Drug Administration (FDA) regulated surgical sutures in the Center for Drugs.

When the Medical Device Amendments (the Amendments) to the Federal Food, Drug, and Cosmetic Act

(the Act) were passed in 1976, these products were classified as “transitional devices”, statutorily placed

in regulatory Class III, and reviewed under the premarket approval application (PMA) regulations.

In 1991, the Agency was petitioned for reclassification of the majority of sutures that were on the market

at the time from Class III to Class II. As a result of this petition, several sutures were reclassified from

Class III to Class II, and thus are no longer transitional devices.

The following is a list of procodes for sutures that are presently Class II and the dates that they were

reclassified:

GAM Absorbable Poly(glycolide/L-lactide) Surgical Suture September 14, 1989

GAL Absorbable Gut Suture September 19, 1988

GAT Nonabsorbable Poly(Ethylene Terephthalate) July 5, 1990

GAW Nonabsorbable Polypropylene Surgical Suture July 5, 1990

GAR Nonabsorbable Polyamide Surgical Suture February 15, 1990

GAP Natural Nonabsorbable Silk Surgical Suture September 11, 1990

GAQ Stainless Steel Surgical Suture July 30, 1986

NBY Nonabsorbable Expanded Polytetrafluoroethylene (ePTFE) Surgical Suture April 18, 2000

Types

FDA considers surgical sutures to fall into two broad categories; absorbable and nonabsorbable.

Absorbable sutures are, as the name implies, temporary due to their ability to be "absorbed" or decomposed by the natural reaction of the body to foreign substances. It is important to note that not all absorbable sutures have the same resistance level to absorption, but each can be formulated or treated in order to obtain a desired decomposition rate. Two major mechanisms of absorption result in the degradation of absorbable sutures. Sutures of biological origin such as surgical gut are gradually digested by tissue enzymes. Sutures manufactured from synthetic polymers are principally broken down by hydrolysis in tissue fluids and are preferred.

Nonabsorbable sutures are, in like manner, sutures that are not dissolved or decomposed by the body's natural action. Such sutures are generally not naturally occurring materials (with the exception of silk); some (silk and nylon) while being classified as nonabsorbable actually dissolve after a long period of time compared to that of the absorbable materials.

A further subdivision of suture materials is Monofilament and Multifilament. A monofilament suture is made of a single strand. It resists the harboring microorganisms and it ties smoothly, which can ease the judgment of the tightening of a knot but can also lead to knot slippage. A multifilament suture consists of several filaments twisted or braided together.

Sutures are manufactured with a wide variety of parameters. They can be monofilament or many filaments twisted together, spun together, or braided. They can also be dyed, undyed, coated, not coated. With the goal of understanding the effects of so many variations of suture type, the properties and material of which they are composed are and have been studied in depth. The use of sutures is one of the most common practices in the medical field and thus has direct effect on a great majority of the world's population.

The following list is a collection of many of the commercially available types of sutures; cellulose based (cotton), protein-cellulose (silk), processed collagen (catgut), nylon,polypropylene, Aramid, polyglycologic acid (Dexon*), polyesters (includes many of this list)

polytetraflourethylene, steel, copper, silver, aluminum, various alloys, Mersilene*, Ticron*

Ethilon*, Prolene*, Ethiflex*, Polyglactin 910*, polyglycolide-lactide polymer (Vicryl*)

polydioxanone (PDS*), polyglecaprone 25 (Monocryl*), polyglyconate (Maxon), Ethibond*

*denotes a registered trademark

Suture diameter and strength

The sizes and tensile strengths for all suture materials are standardized by U.S.P. Regulations. Size denotes the diameter of the material. Stated numerically, the more zeroes in the number, the smaller the size of the strand. 00000 is referred to as 5-0 for example which is smaller than a size 4-0. The smaller the diameter, the less tensile strength. Tensile strength of a suture is the measured pounds of tension that the

strand wil lwith stand before it breaks when knotted.

Suture Size:

1. General

1. Superficial facial lesions: 6-0 nylon

2. Other superficial skin lesions: Low skin tension areas: 5-0 nylon, Higher skin tension areas: 4-0 nylon

2. Annotation for suture size indications below

1. Skin: Superficial monofilament Nonabsorbable Suture

2. Deep: Dermal Absorbable Sutures

3. Size O: Largest suture

4. Size 2-O

5. Size 3-O

1. Skin: Foot

2. Deep: Chest, Abdomen, Back

6. Size 4-O

1. Skin: Scalp, Chest, Abdomen, Foot, Extremity

2. Deep: Scalp, Extremity, Foot

7. Size 5-O

1. Skin: Scalp, Brow, Oral, Chest, Abdomen, Hand, Penis

2. Deep: Brow, Nose, Lip, Face, Hand

8. Size 6-O

1. Skin: Ear, Lid, Brow, Nose, Lip, Face, Penis

9. Size 7-O: Smallest Suture

1. Skin: Eyelid, Lip, Face

Suture indications by location

Scalp, Torso(chest, back, abdomen), Extremities

Superficial Nonabsorbable Suture:4-O or 5-O

Deep Absorbable Suture: 3-O or 4-O

Face, Eyebrow, Nose, Lip

Superficial Nonabsorbable Suture: 6-O

Deep Absorbable Suture: 5-O

Ear, Eyelid

Superficial Nonabsorbable Suture: 6-O

Hand

Superficial Nonabsorbable Suture: 5-O

Deep Absorbable Suture: 5-O

Foot or sole

Superficial Nonabsorbable Suture:3-O or 4-O

Deep Absorbable Suture: 4-O

Penis

Superficial Nonabsorbable Suture:5-O or 6-O

Removal Date: When particular sutures (stitches) should be removed,

· Face 3-4 days

· Neck 5 days

· Scalp 6 days

· Chest or abdomen 7 days

· Arms and back of hands 7 days

· Legs and top of feet 10 days

· Back 10 days

· Palms and soles 14 days

Nonabsorbable Sutures

Absorbable Sutures

Silk Suture

Catgut Suture

Nylon Suture (Ethilon, Dermalon)

Treated Catgut Suture (Mild Chromic Gut)

Polypropylene suture (Prolene, Surgilene)

Polyglycolic Acid Suture (Dexon)

Braided Polyester Suture (Ethibond, Ethiflex, Dacron)

Polyglactic Acid Suture (Vicryl)

Polybutester (Novafil)

Polydioxanone (PDS)

Polyglyconate (Maxon)

Silk Suture

Category: Natural Nonabsorbable Suture (braided)

Indications: Rarely used now

- Eye and lip skin surgery

- Intraoral surgery

Advantages

Disadvantages

Best handling and tying of any Suture Material

Least tensile strength of any Suture Material

High tissue reactivity (similar to Catgut Suture)

Increases risk of infection due to high capillarity

Applications : General closure, G. I. Tract, Plastic, Skin, Opthalmic, Cardiovascular Surgeries. Widely used as ligature

Sterilization : By Gamma Radiation

Nylon Suture

Ethilon Dermalon

Category: Synthetic Nonabsorbable Suture (monofilament)

Advantages

Disadvantages

High tensile strength

High memory (requires 3 to 4 knot throws to hold)

Minimal tissue reactivity

Pliabilized ethilon in alcohol reduces memory

Excellent elasticity

Low cost

Absorption (Hydrolyzes in skin at very slow rate)

Year 1: 89% of tensile strength

Year 2: 72% of tensile strength

Year 11: 66% of tensile strength

Prolene

Polypropylene suture

Category: Synthetic Nonabsorbable Suture

Indications: Subcuticular skin closure

Advantages

Disadvantages

High tensile strength (similar to Ethilon)

Slippery (requires 4 knot throws to hold)

Minimal tissue reactivity (similar to Ethilon)

High plasticity (loose after wound edema resolves)

Slippery (allows for easy removal from tissues)

More expensive than Nylon Suture (Ethilon)

More difficult to use than Nylon Suture

Applications : General closure, Cardiovascular, Opthalmic, Orthopaedics, Plastic and Micro Surgeries

Sterilization : By Gamma Radiation

Braided Polyester Suture

Ethibond Mersilene Ethiflex Ethiflex

Category: Synthetic Nonabsorbable Suture

Advantages

Disadvantages

High tensile strength

High tissue drag (Ethibond and Mersilene)

Low tissue reactivity

Ethibond has less drag due to coating

Improved handling

Coating may crack after knot tied

Improved knot security

Higher cost than other Nonabsorbable Suture

Applications : General closure, Cardiovascular, Plastics, Orthopaedics, Opthalmic and Skin Surgery Sterilization : By Gamma Radiation

Polybutester

Novafil

Category: Synthetic Nonabsorbable Suture

Advantages

- High tensile strength

- Low tissue drag

Marked elasticity

- Elongates 50% of length at 25% of knot-breaking load

- Stretches with wound edema

- Snug after edema resolves

Mild Chromic Gut

Catgut

Category: Absorbable Suture

Indications: Use Vicryl or Dexon instead for Absorbable Suture

Catgut (rarely used now)

- Derived from sheep intestinal intima

- Poor tensile strength

- Poor knot security

- Quickly absorbed within 4-5 days

- High tissue reactivity (absorbed by proteolysis)

Chromic acid treated catgut (Mild Chromic Gut)

- Tensile strength longer than with cat gut

- Moderate tissue reactivity (absorbed by proteolysis)

- Poor knot security

Dexon

Polyglycolic Acid Suture

Category: First synthetic Absorbable Suture (1970)

See Also Dexon

Indications: Subcutaneous and intraoral closure

Category: Second synthetic Absorbable Suture (1974)

Polymer: Lactide, Glycolide

Coating (assists with handling and tying): Polyglactin 370, Calcium stearate

Absorption (Hydrolysis)

Tensile and knot strength roughly equivalent to Dexon

Day 28: 8% of tensile strength

Day 60 to 90: Suture completely absorbed, Much more rapid than Dexon

Preparations: Undyed braided Suture, Violet-dyed braided Suture, May be seen under skin in some cases

Maxon

Polyglyconate Suture

Category: Synthetic Absorbable Suture (monofilament)

Properties: Improved handling over Dexon and Vicryl, Excellent tensile strength (similar to PDS)

Absorption (Hydrolysis)

Day 14: 81% of tensile strength

Day 28: 59% of tensile strength

Day 42: 30% of tensile strength

Day 180 to 210: Complete absorption of Suture

Choosing the suture

The ideal suture would be totally biologically inert and cause no tissue reaction. It would be very strong but simply dissolve in body fluids and lose strength at the same rate that the tissue gains strength. It would be easy for the surgeon to handle and knot reliably. It would neither cause nor promote complications.

The natural absorbables tend to have unpredictable rates of absorption and tissue reaction. For the most part, these sutures have short half-lives, so they are not good for closing the fascia in an immunocompromised patient. The synthetic absorbables are broken down by hydrolyzation. They generally have a longer half-life, less tissue reaction, and a more consistent breakdown rate. The synthetic absorbables--polyglycolic acid (Dexon®) or polyglactin (VICRYL®) have decreased tissue reaction compared to the natural absorbables and knot security is fair.

Polyglactin 910 (VICRYL) keeps 75% of its tensile strength for about 2 weeks and 50% by 3 weeks. The coated sutures decrease the drag through tissue, so it is easier to use, but there are variable rates of absorption. Poliglecaprone 25 (MONOCRYL®) is a monofilament product that has easy passage through tissue, good handling, and is inert. It keeps tensile strength for only a week, but stays in the wound for almost 4 months. It is good for anastomoses, gynecologic work, and small vessel ligation and epithelial approximation. The delayed absorbable monofilament sutures such as polydioxanone (PDS®) and polyglyconate (Maxon®) that most of us are using for abdominal wound closure have pretty good tensile strength and low tissue reaction, but the knots are not as strong. Polydioxanone is also good for contaminated fields because it has a low affinity for bacteria. It is good for general use, tissue approximation, biliary work, anastomoses,

fascial closures, heart surgery, and orthopedics. Now we have PANACRYL®, which is a braided synthetic absorbable suture. It has good tensile strength, low tissue reaction, and good knot security. It maintains 60% of its tensile strength at 6 months. It is a good substitute for a nonabsorbable suture because it has complete absorption in 2½ years. It is good for fascial

closures ,closing tissues under tension.

In terms of suture diameter and elongation, there are significant variations even within the same suture size. For example, there is 15% variation between a #2 PANACRYL and a #2 ETHIBOND® polyester. Similarly, in elongation there is a 194% difference in elongation between a #2 PDS® II (polydioxanone) suture and #2 silk.

Surgeons consider the handling characteristics of suture to be one of the most important parameters in their selection of suture. Mechanical parameters of loops such as elasticity and stress relaxation as compared to the single thread of suture were not measured. In study (Ref 7), these two parameters were investigated in silk and nylon sutures for the knotted loop configuration and compared to the single thread. Silk and nylon sutures in 2/0 USP size were used. Single threads and knotted loops of four throws were tested.The loops were then

mounted on the the Zwick GmbH 1446 universal testing machine, using special clamps to hold the loop at both sides so that the knot was placed halfway between them. In the first experiment the elastic properties of the loop and single thread of silk and nylon sutures were determined using the American Society Testing Materials Standard Test method D1774. This method measures the elastic behavior of fibers, here suture fibers, by assessing their ability to recover strain energy, and to recover their original dimensions following a known extension. In the second experiment, the suture thread or knot was clamped between the jaws of the machine and the gauge length was set at 25 mm. It was loaded until a predetermined load Po was reached (taken as one third of the breaking load). Then the load was fixed and the decay was recorded over 1,5 and 45 five minutes. Results show that, comparing the knotted loops of both materials, the silk had higher elasticity than nylon at 2% and 5% extension levels. At 10% extension, the silk knot showed lower elasticity than the nylon knot. The stress relaxation curve is a time-dependent load curve. Once the extension required to develop the target tensile load was reached (11 N for silk thread, 14 N for nylon thread and 7 N for both knots) and the jaw separation was fixed, the measured load decreased in a characteristic manner. When a suture knot is very tightly tied across a vessel, blood flow is blocked and the vessel is strangulated. Over-tight approximation of skin and fascia is known to affect wound healing adversely. In this situation, the relaxation of stress within the suture loop may be advantageous in that the tension gradually falls. In other words, the decay of stress relieves excess tension that may cause necrosis of the tissue. Consequently, it enhances the healing process. Furthermore, the tension in the loop is proportional to the area which it encloses. The wider is the area, the lower is the bursting strength of the loop. In abdominal wound, the tensions imposed on the suture loop may well cause a considerable enlargement of the area it encloses, thus leading to its premature rupture. Stress decay manifested by the residual load fraction decreased with higher extension rate at 1 and 5 minutes. However, at 45 minutes, the residual load fraction was nearly constant at all rates used. It has been shown that it is a material characteristic. It is found that dependent on the configuration tested.

Some typical examples

- Polyglactin (coated vicryl) is braided. It is commonly used for bowel anastomosis, as a general tie for vessels and as a subcuticular suture for skin. It has 75% of its strength at 2 weeks and 50% at three weeks. It causes a minimal tissue reaction and is very close to being the ideal suture for almost all purposes. A more rapidly absorbing version (Vicryl Rapide) is now produced which loses all strength within 14 days.

- Polydioxanone (PDS) is monofilament. It absorbs slowly and there is minimal absorption until about 90 days. However, its in vivo tensile strength reduces more quickly to 70% at 2 weeks, 50% at four weeks and 25% at six weeks. It is widely used for abdominal wall muscle closure where is has replaced nylon/prolene as it does not cause chronic suture sinuses which occur with non-absorbable materials.

- Nylon (eg ethilon) is a synthetic monofilament material widely used for skin suture.

Polypropylene (prolene) is often preferred to nylon as it is thought to be slightly more inert. It is widely used for abdominal wall closure.

Design

Currently, sutures are designed to result in the most desirable effect for any given situation as determined by those administering the sutures. Taken into consideration in the manufacture and use of sutures are properties such as stress-strain relationship, tensile strength (and rate of retention), flexibility, intrinsic viscosity, wettability, surface morphology, degradation, thermal properties, contact angle of knots, and elasticity. In an attempt to achieve this "ideal" suture the textile industry has come up with many options. Properties such as stress-strain relationship and tensile strength have a direct effect on how much force at a given rate the closure will be able to withstand. For example, a cough would impose a fast rate of elongation whereas edema or hemorrage would impose a slow rate of elongation.

Surface morphology, the description and condition of the outer surface of the suture, has a direct effect on how the tissue in which the suture is located is affected when the suture is applied. For example, a braided suture can cause a type of sawing effect at the insertion points into the tissue. Flexibility in relation to tensile strength is also of high priority in suture manufacture. As in one comparative study of Vicryl and Dexon, both were braided because both become too stiff for handling if formed into monofilaments of sufficient diameter and strength to hold the tissue edges together. Rate of degradation is important due to the difference of required periods of time that a suture is needed to maintain its strength and placement within the tissue. In one comparison, degradation for four materials was compared with respect to total strength loss. It was found that Dexon was absorbed, or degraded, fastest, followed by Vicryl, PDS, and then Maxon (all textile materials). Suture application includes the knotting or tying off of the suture ends. Knotting causes a severe decrease of strength in the suture material, thus when there is a break in the suture, it occurs most frequently at the site of the knot. Design of the best suture for a given situation considers all of the above mentioned factors of suture use to produce the most efficient and best suited material.

Various models for simulating suture were studied, and a simple linear mass-spring model of the suture was determined to give good performance. A novel model for pulling a suture through a deformable surface is presented. By connecting two separate surfaces through the suture, the model can simulate a suturing task (Ref 8). The results are shown using software we developed that runs on a standard PC and models the action of a suturing device used in minimally invasive Laparoscopic surgery. Ref 8 paper presents an initial novel approach for simulating suture and the suturing task, where the suture and needle is being passed between two tissues in order to

connect them. The paper is organized as follows. Sections 2 and 3 describe the deformable models we used to represent the objects in our simulation (suture, and tissue), while section 4 describes the algorithm used to simulate the suturing. Section 5 outlines a demonstration we

developed using the techniques described, while Section 6 discusses possible directions for their future research. Using only a mass-spring surface model, one could not construct 3D deformable objects that could be compressed and stretched, since they would not return to their initial

shapes after deformation. One approach to solving this problem is to create an internal structure of springs to give the surface the support needed to maintain, and return to its initial shape after being deformed. For example, this method is used to model blood vessels in [7]. Although it

proves effective and stable for small models with small displacements, with more complicated objects or large deformations, the object can easily become unstable or permanently tangled.

Many different directions could be explored in future work on this simulator. Eventually they would like to be able to simulate suturing using a needle, a suture, and a pair of grippers. Performing suturing in this way will create several problems, such as how to grasp, move around, and release the needle using the gripper, and how to simulate the needle interacting with, and eventually penetrating, the deformable object. Another area of improvement is in collision detection. In the future it may be possible to have the tool be able to touch and deform the objects being sutured, prevent the suture from hanging down through the objects, and ideally have the suture and objects perform self-collision detection. Having the suture collide with itself could lead to the ability to tie knots in the thread, and/or perform more complicated types of suturing. Last but not least is force feedback. In the near future we intend to integrate a haptic force feedback device into our design of a system for training laparoscopic surgeons. This will not only provide the user with force feedback, but since the device has a handle identical to those used in laparoscopic surgery, it will also provide a more realistic interface to the simulation.

Application

Patient safety, as in every other area of the medical field, is one of the major determining factors of suture manufacture and use. As mentioned before, the composition and properties of a suture are the crucial elements in the decision of what type to use.

For example, an incision into the lung would need to be closed using a suture with a high elasticity level, slow degradation rate, and high tension strength level. If a suture is applied in a situation in which it is not suitable, the patient's safety is endangered. In short, a surgery is never successful if the wound, or insertion point, or incision is not sutured or closed in a proper manner as to promote healing in a timely and safe fashion.

Another factor to be taken into consideration is the effect of inserting the suture into the tissue. If the suture is of a rough morphology (e.g. braided), the tissue will swell more and is more susceptible to infection than if a smooth suture (e.g. monofilament) is used. A failure of a suture is simply its breaking or not meeting the requirements for which it was intended.

Absorbable suture materials have become increasingly popular despite the fact that they cause more immuno-logical and in¯ammatory reactions (Niessen et al.,1997). They obviate the need for clinic appointments for suture removal and also provide prolonged support to the wound edges (Guyuron and Vaughan, 1992). The study(Ref 9) was devised to ascertain whether there are speci®cadvantages or disadvantages associated with absorbable and non-absorbable suture materials. A prospective study was undertaken on 64 patients who underwent carpal tunnel decompression over a 6 month period. Patients under the age of 18 years or over 80 years old, pregnant women, patients on steroids and those who had had previous surgical or wound healing

problems were excluded from the study. After obtaining informed consent, the 64 patients were randomly allocated into groups A and B. Group A patients had their wound edges approximated with a single sub-cutaneous 4±0 absorbable polyglactin 910 (Vicryl 1 :Ethicon, Edinburgh, UK) suture placed in the middle of the wound. A continuous subcuticular 4 : 0 polyglactin

910 (Vicryl 1 ) suture was then used to close the wound, leaving a 5 mm opening at its proximal end for drainage. Group B patients had their wounds closed with non-absorbable interrupted 5 : 0 monoflament polypropy-lene (Prolene 1 Ethicon) sutures. At the 10 day assessment, there were no significant differences between the two treatment groups with regard to wound healing, dehiscence, swelling or inflammation. There were no cases of infection or haematoma in either group. At the 6 week assessment there were no statistically significant differences between the two groups in relation to residual pain (Table 2) and residual stiffness. Residual pain was more often reported in the polyglactin 910 group (Table 2), the opposite of the trend shown at the 10-day assessment (Table 1). Group A patients were off work for a mean of 5 weeks, compared with 4.5 weeks for Group B; this difference is not significant. As reported in earlier studies (Guyuran and Vaughan, 1992; Shetty et al., 1997), this study suggests that absorbable sutures such as polyglactin 910 (Vicryl 1 ) can be safely used after carpal tunnel decompression. The observed problem of suture extrusion could potentially be minimized by carefully burying the knots, or modification of the suturing technique.

Testing

As technology advances, testing techniques improve and become more specific for the application of sutures. The greatest percentage of testing that is done on sutures is done on those suture materials already existing in practice. This is due to the virtual newness of the application of testing techniques to the suture product although, a fairly small, yet increasingly important number of tests are done on possible new suture materials. In the testing of sutures, conclusions such as the fact that it is possible to predict long-term tensile properties of material under dynamic load from their dynamic loss factor and loss modulus are derived. Some of the research test areas for sutures: breaking strength, elongation-to-break, Young's modulus, knot security, viscoelastic propertiese, tissue reaction, cellular response, cellular enzyme activity, suture metabolism chronic toxicity, teratologics, mutagenicity, carcinogenicity, suture allergenicity, immunigenicity, cell cultures etc.

Physical tests for sutures are either standard methods used to demonstrate agreement or compliance with compendum requirements or research tests measuring fundamental properties simulating performance under use conditions. Some of the most common methods by which tests are conducted are also methods widely used in other areas of medicine or industry. A few examples of these methods or instruments are as follows: infrared spectrophotometers, nuclear magnetic resonance spectrophotometers, projection microscopes, tensile testers, light microscopy, and degradation studies in vivo.

Using these, for example, it is common that a researcher will put a great deal of effort into searching for a biodegradable osteosynthesis material with reference to the change in mechanical and physical properties and the histological reaction during degradation of that material in vitro and in vivo where applicable.

The study (Ref 10) has an investigation of morphological changes in hydrolytically degrade dpolydiox-anonesutures(PDSII) during in situ tensile deformation is reported.These changes werefollowed with the use of real-time small-angleX-ray scattering with simultaneous tensile deformation experiments. The results are correlated with separately performed wide-angle X-ray scattering, and optical microscopy experiments on the effects of tensile strain.

The microstructure of polydioxanone sutures, like most oriented semicrystalline polymers, is characterized by ex-tended fibrils, aligned in the fiber direction and connected by

interfibrillar amorphous chains. Each fibril is composed of lamellar stacks, consisting of layers of crystalline and inter-lamellar amorphous material, giving rise to ameridional long-period reflection in the SAXSpattern.The highbeam intensity of synchrotron radiation allows real-time X-ray measurements to be performed as a sample is deformed insitu.This allows changes in the long period to be correlated directly with the stress-strain curve, and micro mechanisms of

deformation to be deduced.This approach has been applied to the deformation in uniaxial tension of several polymeric materials including as polyethylene,1–3 polypropylene 4,5 and poly (ethylene-terephthalate). Simultaneous real-time SAXS / tensile deformation experi-ments, in combination with separately performed WAXS and optical microscopy, allow the balance between interfibrillar and interlamellar deformation of PDSII sutures to be mea-sured directly. Three stages of deformation may be identified. In Stage I, the load-strain curve is linear and the lamellar strain is equal to macro strain (εd= ε1 ), which indicates that the strain in the suture as a whole can be fully accounted for by the separation of lamellae by stretching interlamellar amorphous regions. In Stage II, the load-strain curve continiues to be linear, but the lamellar strain does not match the macro strain (εd< ε1) suggesting that both interlamellar separation and fibrillar shear take place. During Stage III, the load-strain curve flattens and the lamellar strain remains constant (εd= constant) implying that fibrillar shear accounts for all further macroscopic deformation.

Sutures are tested immediately after removal from their sterile packages without drying or conditioning, except when testing for compliance with BP (British Pharmacopoeia) or EP (European Pharmacopoeia) requirements which specify prior conditioning as described in the monographs for various suture types. Diameters of sutures are measured using a gauge of the dead-weight type with a presser-foot 12.7 +/- 0.02mm in diameter. The diameter of each strand is measured at three points corresponding roughly to one-fourth, one-half, and three-fourths of the strand length.

For knot pull breaking strength, the suture is tied with a surgeon's knot with one turn around a flexible rubber tubing of 6.5 mm inside diameter and 1.6 mm wall thickness. The suture is then attached to a suitable testing machine and tested at a rate such that the specimen breaks in less than twenty seconds.

In all strength tests, it is important to keep in mind that the breaking strength retention of absorbable and nonabsorbable sutures should be considered separately because the strength retention of the absorbable sutures will be quite different than that of the nonabsorbable suture.

Also, needle attachment tests are done in a similar manner to the knot pull breaking strength tests. Aside from the standard tests, research test contribute the majority of data concerning the characteristics of suture performance. Included in research test areas are breaking strength and elongation-to-break, Young's modulus, knot security, viscoelastic properties, tissue reaction and cellular response, cellular enzyme activity, suture metabolism, chronic toxicity, teratologics, mutagenicity and carcinogenicity, suture allergenicity and immunogenicity, and cell cultures.

One aspect that necessitates these types of tests is that the adhesion of cells to biomaterial surface will inevitably be a major factor in determining whether such material is accepted by the human body. The nature of cell-implant adhesions determines whether cells remain attached to a biomaterial implant (suture in this case). Poor adhesion can result in detachment of the tissue cells from the implant. Such detachment can then allow infection to take place at the tissue-implant interface.

Comparison

Recent developments in manufacturing techniques have led to the development of strong bioabsorbable materials such as self-reinforced poly l -lactide (SR-PLLA)sutures.The aim of the study (Ref 11) was to investigate the mechanical properties of SR-PLLA sutures in comparison with polyglyconate (Maxon R) and polydioxanone (PDS)sutures in vitro. Sutures made of SR-PLLA (0.3,0.5 and 0.7 mm +,Maxon R (0.3 and 0.5 mm +and PDS (0.3 and 0.5 mm +were studied by immersion in phosphate-buffered distilled water (pH 7.4)at 37 1 for 40 weeks.The breaking force of straight sutures and suture knots was measured.Tensile strength and percentage elongation were calculated.Means,standard deviations,differences between means, and con ?dence intervals for differences between means were evaluated. SR-PLLA,PDS and Maxon R sutures of 0.3 and 0.5 mm + of comparable initial tensile strength.Initial knot tensile strength values were lower than those of their counterpart straight sutures.Maxon R sutures had lost their tensile strength by 12 weeks;PDS sutures by 20 weeks.SR-PLLA sutures of 0.3 mm + had a strength of 161.6 MPa and those of 0.5 mm + had a strength of 134 MPa at 40 weeks.The highest percentage elongation of straight sutures (62.8%and 62%)was exhibited by PDS;the lowest by SR-PLLA (35.6%and 35%).In loop tests,PDS showed the highest percentage elongation (43.7%and 58.1%)and SR-PLLA had the lowest values (19.7%and 33%). SR-PLLA sutures had the most prolonged strength retention in vitro,but the lowest elongation (elasticity).Compared with straight sutures,knots had lower tensile strength and elongation values.SR-PLLA sutures can be applied to the closure of wounds that need prolonged support,such as bone. SR-PLLA,PDS and MaxonR sutures of 0.3 and 0.5 mm + comparable initial tensile strength values (Fig.2).Initial knot tensile strength values were lower than those obtained from their counterpart straight sutures.Breaks occurred just next to the knot.In the case of 0.3 mm +R sutures Table 1),the knots also sometimes slipped and gave way.Slippage also occurred twice with 0.5 mm + Maxon R. SR-PLLA sutures showed the most prolonged strength retention in vitro,but the lowest elongation (elasticity).Compared with straight sutures,knots had lower tensile strength and elongation values.SR-PLLA sutures can be applied to close wounds that need prolonged support,such as bone.

The use of absorbable sutures may avoid problems associated with long-term foreign body implantation, such as excessive ?brosis and stitch granuloma, that could interfere with the smooth gliding of tendon repairs.However,absorbable sutures are not commonly used for ?exor tendon repair. Several in vivo studies have evaluated the potential use of absorbable poly-glycolide-trimethylene carbonate mono ?lament (Max-on)(Mashadi and Amis,1992)and polydioxanone mono ?lament (PDS)(O ’Broin et al.,1995). Although both have adequate strength under conditions of immobilization, both cause an in ?ammatory response, adhesion formation and a bulbous thickening of the repair site. It is unclear whether tendons repaired with these absorbable sutures are able to withstand postoperative mobilization.Recent in vivo experimental (Wada et al., 2001a)and clinical (Gerard et al.,1998)studies demonstrated the efectiveness of absorbable polydiox- anone mono ?lament (PDS)for tendon repair in combination with active mobilization.Although in ?am-mation was found around the absorbable suture materials in one ofthese studies,it did not cause large adhesions or large tendon calluses (Wada et al.,2001a).Gerard et al.(1998)repaired 20 lacerated tendons in a clinical study using a four-strand double-modi?ed Tsuge technique and reported successful results. Polyglycolide-trimethylene carbonate mono ?lament (Maxon)sutures have not been evaluated in re-paired tendons rehabilitated with active mobilization. The study (Ref12) compared the mechanical properties ofpolygly-colide-trimethylene carbonate mono ?lament (Maxon) and polydioxanone mono ?lament (PDS2)sutures for ?exor tendon repair in combination with active mobilization. The gap and ultimate tensile strength values ofboth polyglycolide-trimethylene carbonate (Maxon)and polydioxanone (PDS2)specimens did not decrease

during the initial 7 days,but the polyglycolide-trimethy-lene carbonate (Maxon)repairs were signi .cantly

weaker at day 14.This was probably due to suture absorption rather than to tendon softening.

The core suture in this study was 5-0 gauge,whereas previous studies have used 4-0 gauge absorbable sutures. Smaller sutures were preferred because they reduce the severity ofany foreign body reactions,though their use also reduces the suture-holding capacity ofthe repaired tendons.

Fabrication

The making of sutures can be a fairly simple process or a quite intricate one. Processes for suture fabrication include extrusion, melt spinning, braiding, and many others. The synthesis of raw suture materials is accomplished by any number of processes within the textile industry. The optimal design and dimensions of an osteosynthesis (suture) should be developed on the basis of accurate information about material properties and functional demands.

Technological Advances

The use and need for a suture is clearly not a problem that needs a solution, but a solution that needs improvement. Currently there are many efforts to improve almost every aspect of the suture and its use. In this effort, the products of modern technology are necessary to achieve the high level of accuracy needed in suture manufacture and testing.

For example, in the testing of the surgical knot and its effects, it is important to be able to see exactly what happens to the suture material that causes it to lose sometimes half of its tensile strength. Advances in microscopy allow us to do that. Also, accuracy and consistency in the fabrication of the suture are absolute necessities. If a suture is not what it is designed to be, just as any other product, it is generally not acceptable for the use for which it was designed. It is again the technological advances that make it possible to fabricate a dependable product to the standards specified.

Also, new techniques for testing make it possible to gain a clearer understanding of the properties of the product. This is necessary so that the most efficient and best suited suture will be applied in every case where a suture is needed. If it were not for the technological advances that have occurred in society, modern suture production and use would not exist and sutures would not be dependable.

Alternative Applications

The purpose of the study (Ref14) was to evaluate the use of enbucrilate tissue adhesive compared with subcuticular polyglycolic acid sutures in episiotomy wound closure. In a prospective controlled trial, two groups were studied after undergoing an episiotomy skin wound repair using either enbucrilate tissue adhesive (n s32 ) or a subcuticular polyglycolic acid suture (n s 30 ).The variables measured included pain scores during selected activities in the first 5 postnatal days,the time taken to become pain free after childbirth and the time taken to resume pain free sexual intercourse.Suitable patients were invited by the midwives to participate in the trial.If they gave consent to the trial, the gynecologist was contacted.If available, he would performa repair using enbucrilate tissue adhesive.If he was not available,one of the midwives would perform a repair using subcuticular polyglycolic acid sutures.In this group,90%of the women were recruited and sutured by one midwife.

Patients treated with enbucrilate were found to have significantly less postnatal pain while walking,became pain free in a shorter period (mean s 25 days vs.18 days;P.... 0.01 )and were able to resume pain-free intercourse sooner (mean s 34 days vs.52 days;P.... 0.001 ).

Using enbucrilate tissue adhesive for skin closure resulted in less pain on micturition,walking, and defecation when compared with subcuticular Dexon but there was no significant difference when lying or sitting.The time taken for the wound and for sexual intercourse to become pain free was significantly less in the enbucrilate group. Episiotomy repairs performed using enbucrilate Maternal age range at delivery Group No.Age range (years )Mean (years )"S.D. resulted in a 28%improvement in the time taken to become pain free and a 35%reduction in the onset of pain-free intercourse when compared with sutures. Tissue adhesives incorporate the qualities of an ideal skin-closure material.The results demonstrate their advantage over the current standard suture-based methods of repair in the perineum.The use of adhesives merits further evaluation.

Latest Developments

A smart suture that ties itself into the perfect knot kicks off the first of many potential medical applications for new biodegradable plastics with "shape memory" developed at MIT and the University of Technology, Aachen, Germany. The materials are also biocompatible, or safe for use in a living animal.

The new plastics, reported in the April 25 online edition of Science, could first be shaped as a string, for example, then when heated could "change into a sheet (to prevent adhesion between two internal tissues after an operation), a screw (for, say, holding bones together), a stent or a suture," said Robert Langer, MIT’s Germeshausen Professor of Chemical and Biomedical Engineering. "I think there could be many different applications."

Photo shows how a fiber of the new biodegradable plastic with "memory" can be used to tie a smart suture. After forming a loose knot, the ends of the suture were fixed. The series shows from top to bottom how the knot tightened in 20 seconds when heated to 40 degrees C.

Langer co-authored the paper with Andreas Lendlein, a former MIT visiting scientist now managing director of mnemoScience GmbH, a company formed to commercialize the discovery. Lendlein is also a researcher at the University of Technology, Aachen, Germany, and just accepted a position as full professor at the University of Potsdam and as director of the GKSS research center in Teltow.

It is now possible to place small devices into the body by threading them through the tiny hollow tubes associated with minimally invasive surgery. "Such advances create new opportunities but also new challenges," write Lendlein and Langer. For example, "how does one implant a bulky device or knot a suture in a confined space?"

Some materials can be "taught" to have one shape at one temperature (or under one stress) and another shape at a second temperature. Much work, for example, has focused on "shape-memory" metallic alloys, which are used in applications such as stents for keeping blood vessels open. Shape-memory polymers have also been studied, but none have resulted in medical applications. "No shape-memory materials have been biodegradable," Langer said.

Picture shows an elongated fiber of the new biodegradable plastic with "memory" creating a permanent corkscrew form, such as those used in medical stents, when heated to a certain temperature. (Courtesy Langer Research Laboratory)

To create their new material, the two designed a biodegradable multiblockcopolymer, in which block-building segments are linked together in linear chains. Specifically, the polymer they created contains a hard segment and a "switching" segment, both with different thermal properties. One segment melts, or makes another kind of transition, at a higher temperature than the other.

By manipulating the temperature and stress applied to the overall material, Langer and Leindlin end up with a material that forms a temporary shape at one temperature, and a permanent shape at a higher temperature. They demonstrated this by creating the first "smart" degradable suture.

"We created a temporary shape in the form of an elongated fiber, which was then used to loosely tie a suture to close a wound on a rat," Langer said. After increasing the temperature, the suture material shrunk, creating a knot with just the right amount of tension on the surrounding tissue.

Lendlein and Langer note that it is difficult to create such a knot in the confined spaces associated with endoscopic surgery. "When the knot is fixed with a force that is too strong, necrosis of the surrounding tissue can occur. If the force is too weak, the formation of scar tissue which has poorer mechanical properties is observed, and may lead to the formation of hernias." Their shape-memory polymers appear to be one solution to the problem.

The researchers have also demonstrated another potential application of the new polymers: getting a long fiber of material to change into the corkscrew shape typical of a stent. Movies showing both the suture and corkscrew demonstrations are available.

REFERENCES

2. “Premarket Notification 510(K):Regulatory Requirements for Medical Devices,” (HHS Publication FDA 95-4158)home page at http://www.fda.gov/cdrh/ode/guidance

3. 1. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=search&db=PubMed&term=Howell [AU] AND 1997 [DP] AND Emerg Med Clin North Am [TA]Howell (1997) Emerg Med Clin North Am 15(2):417-25

4. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=search&db=PubMed&term=Moy [AU] AND 1991 [DP] AND Am Fam Physician [TA]Moy (1991) Am Fam Physician 44(6):2123-8

5. MIT News office

6. Phenninger (1994) Procedures, p. P3-6

7. Townsend (2001) Sabiston Textbook Surgery, p. 1552-3

8. BED-Vol. 50, 2001 Bioengineering Conference ASME 2001 "Elasticity And Stress Relaxation Of Suture Loops" Z. Babetty, S. Altinta, Department of Mechanical Engineering, University of Vermont, Burlington, VT Department of Mechanical Engineering, Bo aziçi university, Istanbul, Turkey.

9. "Toward Modeling of a Suturing Task" Matt LeDuc, Shahram Payandeh and John Dill Experimental Robotics and Graphics Laboratory School of Engineering Science Simon Fraser University Burnaby, BC V5A 1S6, Canada

10. "Absorbable Versus Non-Absorbable Suture In Carpal Tunnel Decompression" E. Erel, P. I. Pleasance, O. Ahmed And N. B. Hart From The Department Of Plastic And Reconstructive Surgery, Kingston General Hospital, Hull, UK Journal of Hand Surgery (British and European Volume, 2001) 26B: 2: 157±158

11. "The Hydrolytic Degradation of Polydioxanone (PDSII) Sutures. PartII: Micromechanisms of Deformation" Chui Ping Ooi, *Ruth E.Cameron Department of Materials Science and Metallurgy, University of Cambridge, New Museums Site, Pembroke Street, CambridgeCB23QZ Received 30 October 2000; revised 7 November 2001; accepted 20 November 2001 Published online 00 Month 2002 in Wiley InterScience(www.interscience.wiley.com).DOI:10.1002/jbm.10181

12. "Strength retention properties of self-reinforced poly l -lactide (SR-PLLA)sutures compared with polyglyconate (Maxon R) and polydioxanone (PDS)sutures.An in vitro study" Pirkka M .akel .aa,Timo Pohjonen b, Pertti T .orm .al .ab, Timo Waris c, Nureddin Ashammakhi a, *a Division of Surgery, Department of Plastic Surgery, Oulu University Hospital, P.O. Box 22, FIN-90220 Oulu, Finland b Institute of Biomaterials, University of Technology, P.O. Box 589, FIN-33101 Tampere, Finland c Division of Plastic Surgery, Department of Surgery, Tampere University Hospital and Tampere University, Tampere, Finland Received 3 July 2001;accepted 20 November 2001.

13. Comparison Of The Mechanical Properties Of Polyglycolide-Trimethylene Carbonate (Maxon) And Polydioxanone Sutures (Pds2) Used For Flexor Tendon Repair And Active Mobilization A.Wada,H.Kubota,M.Taketa,H.Miura And Y.Iwamoto From The Department Of Orthopaedic Surgery,Graduate School Of Medical Sciences,Kyushu University,Fukuoka, Japan Journal of Hand Surgery (British and European Volume,2002)27B:4:329 –332

14. Episiotomy closure comparing enbucrilate tissue adhesive with conventional sutures M.L.Bowen *,M.Selinger a , b Department of Obstetrics and Gynaecology, Northampton General Hospital, Northampton, UK Department of Obstetrics and Gynaecology, Royal Berkshire Hospital, Reading, UK b Received 25 January 2002;received in revised form13 May 2002;accepted 13 May 2002

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