In vitro behavior of silk fibroin-based composite resorbable bone fixation devices

Bryant Heimbach, University of Connecticut
Le Yu, University of Connecticut
Mei Wei, University of Connecticut


© 2020 Acta Materialia Inc. 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 metals 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, hydroxyapatite, 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 polylactic 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 composites 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. Statement of Significance: Silk fibroin fibers and hydroxyapatite nanowhiskers were used to fabricate a three-phase composite material for the purpose of load-bearing bone fracture fixation devices. Currently, the bone fixation market is dominated by metals, which cause stress shielding and metal ion leaching, often requiring a second surgery to remove the implant. There are bioresorbable options, made from polymers like poly(lactic-co-glycolic acid), which safely degrade in vivo, leaving only the patient's natural bone and eliminating the need for a second surgery. This study seeks to bridge the gap, creating a device that supports load-bearing fractures while remaining fully resorbable in vivo. The material in this study exhibits the highest bending modulus and strength of any bioresorbable composite found in literature.