Enhancing the Functionality of Trabecular Allografts Through Polymeric Coating for Factor Loading

Allografts are commonly used as an alternative to autografts for bone defect repair, but in some instances suffer from reduced host incorporation that can lead to complications 5 and 10 years post-implantation. We have previously demonstrated that using a thin polymeric coating along the outer surfaces of cortical bone can improve the biofunctionality of devitalized bone allografts by permitting the upload and delivery of growth factors from the thin coating. Here, we expand on our previous work to develop a methodology to coat porous trabecular allografts with a similar polymer coating with careful attention to maintaining an open pore network within the allograft and establishing the effect of varying the polymer solution viscosity on coating extent and thickness. Results indicate that varying the polymer solution viscosity by changing the polymer to solvent ratio used to coat the samples allows for variations in coating thickness and extent of surface area coverage, each perhaps allowing for greater control over growth factor loading and release concentration and kinetics. Further, we develop a dynamic coating method that produces a continuous and consistent coating throughout the pore structure vs. the previously used static method that resulted in a discontinuous coating throughout the pore network. The work demonstrated here provides important techniques for varying the payload of polymer-coated, factor-loaded trabecular allografts which would provide another tool to the orthopedic surgeon when healing large-scale defects with trabecular allograft. Large scale bone defects are traditionally treated with either autografts or allografts. Allografts suffer from poor incorporation in part due to the processing undertaken to render them safe to transplant from one individual to another. We sought to add back some of the biological functionality that is removed in this processing by loading growth factors into a very thin polymeric coating that we apply to the surface of the allograft. Our results indicate a thin, continuous polymeric coating throughout the trabecular allograft, with the amount of this coating varying as we vary the concentration of this polymer solution prior to coating. Future studies will evaluate the ability of this varied concentration of polymer coating to permit the delivery of varying amounts of growth factors, imparting a greater degree of control over the amount of growth factor delivered from the coated allografts.