A suture is a specialized medical thread used to hold body tissues together after an injury or surgical incision. This thread provides temporary support, allowing the body’s natural healing processes to close the wound securely. Silk holds a unique position as one of the oldest and most traditional choices for wound closure. Its continued use in modern medicine speaks to its advantageous physical characteristics, even as newer synthetic alternatives emerge.
Material Source and Manufacturing
Surgical silk begins as a natural protein fiber spun by the domesticated silkworm, Bombyx mori. The raw silk filament consists primarily of two proteins: fibroin, which forms the structural core, and sericin, a gummy coating that binds the fibers together. Since sericin can trigger an excessive inflammatory reaction in human tissue, the raw silk must undergo a rigorous process called degumming. This purification step removes the sericin, leaving behind only the pure, non-reactive fibroin protein.
The purified fibers are then processed into a multifilament strand, typically through braiding or twisting several fine filaments together. This braided structure provides the surgical thread with strength and flexibility. To enhance its passage through tissue and reduce its capillarity—the tendency to draw fluid along its surface—the braided silk is often coated with substances like silicone or wax. The finished product is usually dyed black to maximize visibility against tissue during a surgical procedure.
Key Handling Properties and Classification
Silk’s enduring popularity stems from its superior handling properties, often considered the benchmark for all suture materials. The natural pliability of the braided fiber allows it to be manipulated and tied with ease, offering excellent tactile control. This flexibility is compounded by its exceptional knot-holding capacity, meaning a knot tied with silk requires fewer throws to remain secure compared to many other materials.
The United States Pharmacopeia (USP) classifies silk as a non-absorbable suture, meaning it is not designed to be broken down quickly by the body’s enzymatic processes. However, this classification is nuanced because silk is a natural protein. Over time, the body’s immune system slowly encapsulates the foreign material, leading to a gradual loss of tensile strength, often beginning after about one year. While it may take up to two years for the fibers to fully degrade, silk is not considered a permanent implant and is distinct from true synthetic non-absorbables.
Common Surgical Applications
The combination of superior handling and knot security makes silk the preferred material for specific surgical applications. It is widely used for vessel ligation—tying off blood vessels to control bleeding—where the ability to quickly and reliably secure a knot is paramount. The high friction of the braided surface ensures the ligature will not slip from the vessel.
Silk is also commonly utilized for skin closure, especially in areas like the oral mucosa, where its soft, smooth characteristics make it comfortable for the patient. Because of its excellent visibility and ease of manipulation, it is frequently used to secure surgical drains or tubes to the skin. In delicate procedures, such as ophthalmology or neurosurgery, the fine control afforded by the pliable thread helps surgeons achieve precise tissue approximation without causing excessive trauma.
Limitations and Synthetic Replacements
Despite its advantages, silk suture has drawbacks that have limited its use for deep, internal closures in favor of modern synthetics. Its multifilament, braided structure creates microscopic spaces between the fibers where bacteria can harbor and multiply. This characteristic, known as the wicking effect, increases the risk of surgical site infection, making it unsuitable for use in contaminated wounds.
As a natural protein, silk elicits a higher inflammatory tissue reaction compared to most synthetic polymers, which are designed to be inert. This reaction can lead to more noticeable scar formation and is why silk is generally avoided for long-term internal use. Synthetic non-absorbable sutures, such as Nylon (Polyamide) and Polypropylene, have largely replaced silk for internal work because they are monofilament threads. The single-strand structure of these synthetics resists bacterial wicking and provokes minimal tissue response, offering a safer profile for support.