Posted October 17, 2014
Warren Haggard, Ph.D., University of Memphis, Memphis, Tennessee
Today, complex extremity injuries are a common occurrence in the battlefield and often result in devitalization and extensive tissue loss. These injuries are typically treated using autograft, allograft, and xenograft tissues, which can elicit adverse immune responses that delay tissue healing and hinder return to duty. Engineered soft tissue replacements have been explored as a method for bypassing the immunological response; however, to date, engineered tissues have been shown to be limited in their initial loading strength, which can increase rehabilitation time for the patient.
Transition tissue repair strategies for improving tendon-to-bone repair are difficult, partially due to the material properties in the tendon-bone interface transitioning from elastic tendon to hard bone. These material properties are necessary for the stretching function of tendons and the load-bearing function of bone. Dr. Warren Haggard, at the University of Memphis, recipient of a Fiscal Year 2009 Peer Reviewed Orthopaedic Research Program Hypothesis Development Award, explored whether mechanical stimulation of a co-cultured biomaterial scaffold can improve healing of a tendon-to-bone interface for soft tissue repair. Dr. Haggard and his research team tested a number of potential scaffold materials to determine the best configuration for promoting cell adhesion and proliferation. Results suggested that scaffolds made from a polylactic acid (PLA) fabric are the best candidates because these scaffolds are degradable and have higher tensile strength than the other materials tested. Dr. Haggard's team also co-cultured the PLA scaffolds with fibroblasts and osteoblasts on separate ends of the fabric to create discrete tendon regions and bone regions of the scaffold. Thus, they were able to show that separate, tissue-specific regions could be cultured on a single scaffold.
After successfully characterizing the co-culture conditions for the scaffold, Dr. Haggard's team went on to determine the effect of stimulation parameters. His group developed a custom bioreactor consisting of a sterile chamber connected to an actuator arm that was able to mechanically stretch the fibroblast region of the scaffold while keeping the osteoblast region fixed. Using this protocol, they found that mechanical stimulation leads to an increase in collagen deposition. Dr. Haggard is currently working to fine-tune the bioreactor settings to identify the optimal parameters for tendon-to-bone tissue engineering. He has identified an industry partner to further develop this technology and is moving forward to test the scaffolds in an in vivo animal preclinical model, which could provide crucial insight into alleviating the complications of tendon-to-bone healing.