Functionally Graded Orthopedic Implants via the Slurry Mixing and Dispensing Process

0930365

Shaw

The materials used for internal fracture fixations and joint replacements are all currently made of metals. However, metallic implants suffer from two shortcomings, one being the poor or non-existent interfacial bonding between the metallic surface and surrounding bone, and the other the higher rigidity of metallic implants than that of natural bone. As a result, the life expectancy of metallic implants is not commensurate with the life expectancy of the recipient, and revision surgery has to be performed every 12-15 years. Surgical revision, however, can be twice as expensive as the primary operation and may lead to significant complications, including infection, deformity, pain, and loss of mobility. This research project is proposed to address these issues.

Intellectual Merit: A new family of functionally graded, porous Ti-6Al-4V/apatite implant materials with a hierarchy of engineered microstructures will be investigated and developed through innovative integration of engineering and life science. This new family of orthopedic implants is the first of its kind because they have a Ti-rich core and a hydroxyapatite (HA)-rich surface with a controlled level of micro- and macro-porosity. Together, these carefully designed composition gradients and engineered microstructures will impart to orthopedic implants the excellent corrosion resistance, adequate strength, enhanced mechanical compatibility, and good bioactivity for promoting bone tissue regeneration and fixation of implants. These revolutionary functionally graded orthopedic implants will offer an unparalleled solution to all of the issues faced by the present metallic implants with or without coatings. A novel solid freeform fabrication (SFF) method, termed as the slurry mixing and dispensing (SMD) process for making functionally graded materials (FGMs), has been developed to fabricate such a new family of orthopedic implants. The green orthopedic implants produced from the SMD process will be converted to solid implants using a novel sintering method developed recently in our laboratory. This novel sintering method uses HA nano-rods as the starting powder, and leads to dense HA bodies at sintering temperatures as low as 8500C, which is the lowest temperature ever reported in the literature. We have chosen hip implants as the vehicle to study and demonstrate this new family of orthopedic biomaterials because hip fracture is by far the most devastating type of broken bone and it accounts for about 300,000 hospitalizations every year in U.S. To achieve the research goals, five technical tasks have been identified, and a research team with all of the requisite expertise has been formed. We firmly believe that the synergism of this research team will allow us to successfully conduct this multidisciplinary project and push the frontier of the field of orthopedic biomaterials.

Broader Impacts: If successful, this project will have favorable social and economical impacts on society because many patients will benefit from this novel technology. The quality of patient life could be improved greatly. Moreover, a reduction in the need for revision surgery could translate into reduced health care costs. Additionally, the SMD process developed in this study can be applied in the future to fabricate other orthopedic implants (e.g., spinal fixation devices, maxillofacial implants, bone graft materials to fill tumor defects, etc.) and many other FGMs for a wide range of applications such as gradient-index lenses, graded armor materials, bipolar plates for fuel cells, and advanced nanocomposites for aerospace, automobile and tool industries. The broad impacts of this program will also be evident in our strong commitment to education, human resource development and outreach, which will have direct impacts on undergraduate students, graduate students, and middle/high school students. We will work with the Connecticut Pre- Engineering Program (CPEP) to increase the number of underrepresented minorities in engineering, science, and technology. We will host CPEP students during summer to provide the students with hands-on labs related to SMD fabrication and orthopedic implants. Mini-projects will be developed so that CPEP students can conduct these mini-projects in one week with the help from graduate students and PIs. Through this new initiative, we will nurture underrepresented minorities towards positive thinking, increase their interest in science and technology, and motivate them to pursue higher education and become future leaders of the society.