In vitro Behavior of Silk Fibroin-Based Composite Resorbable Bone Fixation Devices

Abstract

There are between 12 and 15 million bone fractures in the United States annually, and many of them require the implantation of an internal fixation device, which helps anchor severely fractured bones to ensure they heal properly. The current standard for such a device relies on the use of met-als like stainless steel or titanium due to their superior mechanical properties and propensity to be bioinert. However, these materials are known to cause stress shielding and metal ion leaching, which often lead to the need for a second surgery to remove the implant. For these reasons, there has been considerable interest in creating a fixation device that would provide mechanical stability during healing, but then safely degrade over time, eventually leaving only the patient's own bone. While there are degradable fixation devices on the market, they are made of polymeric materials and have poor mechanical properties, limiting their use to none- and low-load-bearing applications, such as maxillofacial fracture fixation. The present study investigates the use of silk fibroin, hy-droxyapatite, and polylactic acid to make resorbable composites to be used as bone fixation devices for load-bearing applications. Using silk fibroin fibers, hydroxyapatite nanowhiskers, and a pol-ylactic acid matrix, three-phase composites were fabricated that has a flexural modulus and strength up to 21.1 GPa and 536 MPa, respectively. Additionally, in vitro analyses showed that the compo-sites degrade slowly via surface erosion and show good initial biocompatibility. These results show great promise for the use of these composites as load-bearing fracture fixation devices.

Keywords: orthopedic, fixation, silk fibroin, hydroxyapatite, composite, resorbable