The primary function of a surgical suture is to hold wound edges together, or approximate tissue, until the body’s natural healing process restores sufficient strength to the repair site. For a surgical closure to be successful, the thread must possess mechanical properties that resist the physical forces attempting to pull the wound apart. This capacity to withstand tension without breaking is known as tensile strength, and it represents the most important mechanical feature dictating the material’s suitability for a given procedure. Suture strength is a complex outcome determined by its chemical composition, physical architecture, and overall diameter.
Material Composition
The fundamental source of a suture’s breaking strength lies in the chemical structure of the material used to manufacture the thread. Synthetic polymers offer a higher initial breaking strength compared to natural fibers derived from biological sources. For instance, a synthetic braided polyglycolide (PGA) material can exhibit a tensile strength of over 1000 Megapascals (MPa), substantially higher than natural absorbable materials like chromic catgut. This superior mechanical performance is due to the controlled polymerization process, which allows for the creation of uniform, high-density molecular chains.
Common synthetic materials like polypropylene and nylon are engineered to have highly stable molecular bonds, resulting in exceptional tensile load limits. Polypropylene is often noted for having maximum tensile strength among non-absorbable options, with nylon following closely. In contrast, natural sutures like catgut are primarily made of purified collagen and are degraded by the body’s enzymatic processes, leading to less predictable strength characteristics. Synthetic absorbable sutures, such as those made from polyglycolic acid, predictably lose their strength through hydrolysis, where water molecules break the polymer chains.
Physical Structure
The way individual strands are assembled greatly affects the overall strength and mechanical behavior of the suture. Sutures are manufactured in two main physical architectures: monofilament (a single, solid strand) and multifilament (multiple fine filaments braided or twisted together). Multifilament sutures generally achieve a higher overall tensile strength than a monofilament of the same diameter because the load is distributed across numerous interwoven fibers. This construction method also results in better knot security, meaning the knot is less likely to slip or fail under tension.
The strength benefits of the multifilament structure come with trade-offs in surgical application. The braided surface creates a rougher texture, leading to greater friction and increased tissue drag as the suture is pulled through the wound. Conversely, monofilament sutures are smoother, gliding through tissue with minimal resistance, which reduces the potential for tissue trauma during placement. Although a monofilament’s knot may be less secure due to its slick surface, the architecture minimizes the risk of bacterial colonization because it lacks the small, capillary spaces found between the fibers of a braided material.
Suture Diameter
The most direct physical feature influencing suture strength is the thickness, or diameter, of the thread itself. The tensile strength of any given material is directly proportional to its cross-sectional area, meaning that a thicker suture is inherently stronger than a thinner one. Surgeons rely on the globally recognized United States Pharmacopeia (USP) gauge system to classify and select the appropriate suture diameter.
This sizing system is centered on the number “0.” Sizes numerically greater than 0, such as USP size 1 or 2, are progressively thicker and stronger. Conversely, sizes that incorporate a zero followed by a number (e.g., 2-0, 4-0, or 6-0) are progressively thinner and weaker as the number of zeros increases. For example, a 6-0 suture is significantly finer and weaker than a 2-0 suture. This system ensures the smallest necessary diameter is used to minimize tissue trauma while providing adequate mechanical support.
Strength Retention Profile
For absorbable sutures, strength retention measures how long the thread maintains its mechanical integrity within the body. This feature is important because the suture must retain sufficient tensile strength throughout the critical period when the wound is weakest and most likely to dehisce. Strength retention is defined as the percentage of the initial breaking strength that remains after a specified number of days post-implantation.
Materials vary widely in their retention profiles, which determines where they can be safely used. Polydioxanone (PDS), a slow-absorbing material, retains approximately 70% of its initial strength after two weeks and 50% after four weeks, making it suitable for slow-healing tissues like fascia.
In contrast, materials like poliglecaprone 25 (Monocryl) are designed for rapid loss, retaining 50% to 60% of their strength for only about seven days before the strength is completely gone by three weeks. Non-absorbable sutures, such as silk or polypropylene, are characterized by indefinite or very long-term strength retention. They remain intact for over 60 days to provide permanent or extended support where the tissue will never fully recover its original strength.