Engineering a Bioactive Interference Screw for Accelerated Rehabilitation in ACL Reconstruction

The tearing of the anterior cruciate ligament (ACL) is a common occurrence in athletes. An increasing need for accelerated rehabilitation exists, given that the normal period of recovery from surgery is of 8-12 weeks. In spite of well-established physical rehabilitation programs, there is no net improvement to the overall recovery time required after surgery after patients go through physical therapy. In this thesis, a bioactive interference screw was designed to allow the sustained delivery of drug molecules (e.g. growth factors), capable of enhancing bone-to-ligament attachment, and capable of potentially reducing recovery time. This bioactive screw combined a drug delivery device with an existing interference screw modified for the application. The hydrogel was inserted in the central cavity of the cannulated screw, and the cannulated screw was provided with through orifices along its shaft, to allow the release of drugs from the internal cavity of the screw. Swelling and drug delivery studies were performed to characterize the hydrogel in its conditions of application; the release of growth factors was mimicked using a model drug: cytochrome c. A diffusion study was subsequently performed in COMSOL Multiphysics to determine the number of orifices needed on the screw, to ensure that the target drug is released at the desired rate, to promote accelerated bone growth. The results from this simulation were expressed as the ratio of the orifices to the volume of the screws cavity. The simulation results were then validated with in vitro release studies, confirming the trends observed in the models. The targeted release performance was observed for orifice-to-volume ratios varying between 0.02 and 0.05 orifices/mm3. Two models were developed for predicting drug release from such devices, linking the required number of orifices to the release rate desired. The impact of the presence of these perforations on the strength of the screw was studied in ABAQUS. A parametric analysis was developed to optimize the distribution of the orifices along the screw in FEA, to limit the reduction of the strength of the screw. A pull-out test was performed on injection molded screws to validate the ABAQUS results.Ph.D., Mechanical Engineering -- Drexel University, 201