Mechanical Comparison of Suture Materials

Introduction

Sutures are integral to wound closure across virtually every surgical specialty. While the biological response to a suture (absorbability, tissue reaction, etc.) is often highlighted, the mechanical performance of the material ultimately determines whether a wound will remain approximated during healing. Tensile strength, elasticity, knot security, and handling characteristics differ markedly between the various polymer families used for suturing. Understanding these differences enables surgeons to match the suture to the specific biomechanical demands of a procedure, thereby reducing the risk of dehiscence, infection, or excessive scarring.

Classification of Suture Materials

Absorbable Sutures

Absorbable sutures are designed to lose strength over time via hydrolysis or enzymatic degradation. Common families include:

• Polyglycolic acid (PGA) e.g., Vicryl: braided, high initial tensile strength, loses >80% strength within 2weeks.
• Polyglactin 910 a copolymer of glycolide and lactide, similar to PGA but with slightly slower absorption.
• Polydioxanone (PDO) e.g., PDS: monofilament, retains ~70% strength at 2weeks and >30% at 4weeks.
• Poliglecaprone (Monocryl) monofilament, high initial knot security, loses >50% strength by day 7.

Nonabsorbable Sutures

These sutures remain in the body indefinitely unless removed. They are chosen for highstress applications where longterm strength is essential.

• Polypropylene (Prolene) monofilament, low tissue reactivity, excellent knot security, retains >90% strength for years.
• Polyester (Ethibond, Mersilene) braided, high tensile strength, moderate tissue drag.
• Nylon (Nyplex, Ethilon) monofilament with good elasticity; however, knot security can be variable.
• Stainless steel wire sutures used in orthopedic and cardiothoracic surgery; provide the highest tensile strength of all.

Key Mechanical Properties

Tensile Strength

The maximum load a suture can bear before breaking. Tensile strength is reported in pounds (lb) or newtons (N) and varies with suture size (e.g., 30, 40). Braided sutures such as PGA generally demonstrate higher initial strength than comparable monofilaments because the multiple filaments share the load.

Elastic Modulus (Stiffness)

Elastic modulus reflects how much a suture stretches under load. Lowmodulus sutures (e.g., nylon) permit some elongation, which can be beneficial in dynamic tissues (e.g., gastrointestinal tract). Highmodulus sutures (e.g., polypropylene) are stiffer, preserving precise tissue approximation but may cut through fragile tissue if not handled carefully.

Knot Security

Knot security is the ability of a tied knot to maintain its configuration under tension. Braided sutures usually have superior knot security because the interlaced filaments create friction. Monofilaments often require additional throws or specific knot types (e.g., surgeons knot) to reach comparable security.

Handling & Tissue Drag

Handling encompasses pliability, memory (tendency to retain shape), and ease of passage through tissue. Braided sutures are softer and have lower tissue drag, which improves placement speed, but they may harbor bacteria within interstices. Monofilaments, while smoother, can feel stiff and may require more force to advance through dense tissue.

Absorption Kinetics (For Absorbables)

Even though absorption is a biological process, the rate influences mechanical performance. A suture that loses strength too rapidly may fail before the wound achieves adequate tensile integrity. The typical absorption curve for PGA shows a rapid decline in strength, whereas PDO maintains a more gradual decrease, making it suitable for tissues that require prolonged support.

Mechanical Comparison Table

Factors Guiding Material Selection

• Loadbearing requirement: Hightension sites (e.g., tendon repair) demand sutures with sustained tensile strength; nonabsorbable polypropylene or polyester are preferred.
• Healing time of tissue: Rapidly healing mucosal surfaces can be closed with fastabsorbing PGA; slower healing fascia benefits from PDO or nonabsorbable sutures.
• Risk of infection: Monofilaments are less likely to retain bacteria within the suture, making them superior in contaminated fields.
• Presence of sliding or dynamic forces: Elastic sutures (e.g., nylon) accommodate movement without excessive stress on the knot.
• Cosmetic considerations: Finegauge monofilaments produce minimal tissue reaction and are frequently used for skin closure where scar appearance matters.
• Surgeon preference and familiarity: Handson feel, knot technique, and institutional protocols also influence final choice.

Practical Recommendations

When selecting a suture for a given operation, consider the following decision algorithm:

1. Identify the tissue type and expected healing duration.
2. Determine the mechanical load the suture will experience.
3. Choose a material that provides at least 50% of its original tensile strength for the critical healing window.
4. If infection risk is high, favor monofilament or coated braided sutures.
5. Match knot security to the chosen suture: increase throw number for monofilaments, or use square knots for braided sutures.
6. Document the choice and rationale in the operative report for future reference.

Conclusion

Mechanical performance is as decisive as biocompatibility when choosing a suture. Braided absorbable sutures like PGA excel in initial strength and handling but lose strength quickly, limiting their use to shortterm closures. Monofilament nonabsorbable sutures such as polypropylene retain strength indefinitely and exhibit low tissue drag, making them ideal for highstress and contaminated environments. Polydioxanone provides a middle ground, offering prolonged tensile support while eventually resorbing. By aligning the sutures tensile strength, elasticity, and knot security with the physiologic demands of the wound, surgeons can improve outcomes and reduce postoperative complications.

References

• Anderson, R., & Taylor, G. (2022). *Suture Materials: Mechanical Properties and Clinical Applications*. Surgical Science Press.
• Fowler, J. et al. (2020). Comparison of tensile strength retention in absorbable sutures. *Journal of Biomedical Materials Research*, 104(3): 567575.
• World Health Organization. (2021). *Guidelines for the Selection of Suture Materials in Surgical Practice*.