Dr. Starr is Professor of Chemical Engineering and Director of the Rapid Prototyping Center in the J.B. Speed School of Engineering. He joined the University of Louisville in August 1998 and has served as Chair of the Chemical Engineering Department (2000-2004) and as Associate Dean for Research (2004-2015). Prior to joining UofL, Dr. Starr spent eighteen years at the Georgia Institute of Technology directing and managing research programs in the School of Materials Science and Engineering and in the Georgia Tech Research Institute. Dr. Starr earned a Ph.D. in Physical Chemistry from the University of Louisville and a B.S. in Chemistry from the University of Detroit.
- Ph.D. in Physical Chemistry, University of Louisville, 1976
- B.S. in Chemistry, University of Detroit, 1970
Purpose: This article describes the preliminary findings of the mechanical properties of functionally graded titanium with controlled distribution of porosity and a reduced Young's modulus on the basis of a computer-aided design (CAD) file, using the rapid-prototyping, direct metal laser sintering (DMLS) technique. Materials and Methods: Sixty specimens of Ti-6Al-4V were created using a DMLS machine (M270) following the standard for tensile testing of metals. One group was fabricated with only 170 W of laser energy to create fully dense specimens (control group). The remaining specimens all featured an outer fully dense "skin" layer and a partially sintered porous inner "core" region. The outer "skin" of each specimen was scanned at 170 W and set at a thickness of 0.35, 1.00, or 1.50 mm for different specimen groups. The inner "core" of each specimen was scanned at a lower laser power (43 or 85 W). Results: The partially sintered core was clearly visible in all specimens, with somewhat greater porosity with the lower laser power. However, the amount of porosity in the core region was not related to the laser power alone; thinner skin layers resulted in higher porosity for the same power values in the core structure. The lowest Young's modulus achieved, 35 GPa, is close to that of bone and was achieved with a laser power of 43 W and a skin thickness of 0.35 mm, producing a core that comprised 74% of the total volume. Conclusion: Additive manufacturing technology may provide an efficient alternative way to fabricate customized dental implants based on a CAD file with a functionally graded structure that may minimize stress shielding and improve the long-term performance of dental implants.