Web of Possibilities: The Healing Potential of Spider Silk
We all have seen the detailed construction of spider webs. Sometimes, when the morning dew is on them, they are beautiful. But, for most people, that is as far as our admiration goes. Spiders, in general, are not one of our favorite creatures. Although these 8-legged, fuzzy creatures can be very menacing in appearance, their ability to produce webs of incredible geometry and strength has been studied for centuries. The web silk itself has been used for everything from fabric to wound care. What was once considered ancient has now been resurrected and is the topic of solid research.
Human interest in the utility of spider silk is not new. There is documentation that the ancient Greeks used cobwebs to treat wounds.1 The silk served as a matrix for platelet and fibrin deposition to enhance hemostasis. The Greeks also observed that wounds treated by this method did not become infected as readily. Only in the last few decades have scientists discovered that some species of spiders secrete an antimicrobial protein coating on their silk fibers.
Despite its delicate appearance, spider silk is extremely strong, elastic, and resilient. Spider silk is 5 times as strong as steel, despite having a fraction of the density of steel, but by weight, and able to stretch and retract to a far greater degree than nylon.2 The strongest of spider silks requires 7 to 10 times more energy to fracture than an equivalent volume of synthetic Kevlar, which is designed to stop bullets,3 so it is no surprise that this super fiber is finding its way into unique and exciting biomedical applications.
Nerve damage has always been considered a catastrophic outcome in medicine. Whether traumatic or disease-related, loss or impairment of nerve function can result in major disability. Promising research is being conducted using sterilized frameworks of spider silk seeded with Schwann cells to regrow damaged nerves. One group conducted this procedure in vitro and showed that 48 hours after seeding Schwann cells into the culture media onto the silk matrix, there was complete coverage of the silk, with multiple wrapping layers of Schwann cells.4 The next step in the research was to devise a method that would direct the growing fibers to bridge gaps between proximal and terminal nerve stumps. This was accomplished using totally acellularized vein as a conduit to bridge the gap of the nerve ends.4 Another study showed successful in-vivo regeneration of a 20-mm sciatic nerve defect in rats.5 At the end of 6 months, the measurement of diminished degeneration of the gastrocnemius was significantly superior in the treated group over the control group.5
This same type of seeding has been shown to be successful using fibroblasts6 and chondrocytes.7 Researchers have successfully grown artificial skin by seeding spider silk matrices with fibroblasts. The skin cells grew into multilayered, well-ordered sheets of artificial skin that potentially could become the answer for human skin grafting. When examining the success of chondrocyte growth on spider silk matrices, these same researchers turned to braided spider silk, the suture used to repair structures such as flexor tendons in hand injuries.8 This suture has been shown to provide better long-term mechanical function without the risk for infection or foreign body reactions that occur with traditional suture material.8