The research objective of this Grant Opportunity for Academic Liaison with Industry (GOALI) Collaborative Research project is to investigate novel surgical fixation devices (screw, anchor, plate, pin, staple, etc.) that not only secure a graft in place, but incorporate bioactive materials such as growth factors, drugs, and cells, intended to promote bone tissue growth. The new devices can eliminate painful secondary operations, adverse effects of permanent implants, and the lack of bioactive features in existing surgical fixation devices. The research addresses challenges in biocompatible, biodegradable and bioactive materials for surgical fixation devices and investigates a new delivery method for bio-reagents through the surgical devices. The approach will be: 1. Identify suitable structural and bioactive materials for a strong fixation device body and efficient bone-tissue healing and growth. 2. Design a new bioactive interference screw, as a specific example and application with required mechanical integrity and bioactivity. 3. Explore a new technique, gradient cellular structure (GCS), to create interconnective porous structure to control screw mechanical strength and assist in bioactive materials delivery. 4. Through testing to find, control, optimize and integrate all required functionalities such as mechanical integrity, material degradation rate, and bioactive reagents delivery rate.
If successful, the benefits and broader impacts of this research will be: to replace current passive orthopedic surgery devices with active devices, i.e. the surgical devices not only serve fixation and support purposes but also have curing, healing and tissue-promoting biological functions; a long term research and educational relationship with Arthrex, Inc. will be built for the new technology development and transfer; three doctoral students and two senior design teams will be trained; three project-based learning modules will be created to strengthen the undergraduate mechanical and biomedical engineering curricula, engaging students with design projects in bioactive fixation devices and bio-reagents delivery. New findings from the research will be disseminated in professional journals and at conferences. The project will also be used in specially designed outreach workshops for local high school and community college students, including many underrepresented minority students to showcase high-tech mechanical and polymer engineering applications in biotechnology.
Around 300,000 surgical operations are performed every year to treat knee injuries in the United State; there are more than 90,000 anterior cruciate ligament (ACL) reconstructive surgeries worldwide annually. In orthopedic or spinal surgery, many fixation devices (such as plates, screws, pins, rods, anchors, staples, and others) are used in bone fractures fixation, autograft ankle stabilization, reconstruction surgery of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), replacement of the intervertebral discs, posterior spinal fixation, etc. However, currently used surgical fixation devices (made by either metals or polymers) have shortages in bioactive features. They may lead to a secondary operation and bring more pain to the patient, and may cause long term adverse effects. Furthermore, current surgical fixation devices do not promote bone healing and re-growth, subsequently leaving voids in the tissue once the implanted device is pulled out (metal device) or fully degraded (biopolymer device). The main objective of this GOALI, collaborative project led by Drexel University, Georgia Tech and Arthrex, Inc., was to develop novel materials and processes for new-generation surgical fixation devices that not only secure a graft in place but incorporate bioactive materials intended to promote bone tissue engineering. The main technical task conducted at Georgia Tech was to develop processing techniques for hierarchical porous materials with a gradient cellular structure (GCS) suitable for surgical fixation applications. With a GCS, variation of permeability throughout the device can be regulated. Further, variation of mechanical properties of the structure to match other materials at the interface is made possible. The primary research activities accomplished at Georgia Tech included 1) Developed a thermomechanical molding process for creating porous polymers with a gradient cellular structure; 2) Developed an micropatterning technique for porous devices with hierarchical structures; 3) Established a constitutive model for the dynamics and rheology of immiscible polymer blends; and 4) Investigated the relation of processing, structure and property in the new processes. These activities led to the development of a versatile manufacturing technology for porous polymer devices with precision external geometry and controllable internal morphology. In vitro and in vivo testing with the new porous materials showed promising results in applications for inducing and sustaining bone tissue repair. Fundamental understandings were also gained on the formation of co-continuous phase structures and the interplay among thermodynamics, kinetics and structural development. The new manufacturing technology developed in this research allows the fabrication of biopolymer devices with a gradient cellular structure in a cost-effective manner. Such materials and devices can find numerous medical applications wherever structural integrity and medium permeability are both required. The new technology is particularly useful in the design and manufacture of bioactive surgical tools for promoting healing and regeneration of osseous tissues. Furthermore, the framework of tuning the material structure by a controllable thermomechanical history would be equally useful in the development of other new manufacturing processes.
