MS Research
Coelho Lab
PI: Paulo G. Coelho, PhD, DDS
New York University
Department of Biomaterials and Biomimetics
Master’s thesis: Efficacy and viability analysis of BMP-2 coated titanium implants within a sheep iliac model
Increased Osseointegration Effect of BMP-2 on Titanium Implants
Dental implants and orthopedic prostheses rely on various factors for optimal function and survival, with a focus on achieving rapid osseointegration. Surface modifications, both topographical and chemical, play a crucial role in this process. Recently, the application of recombinant human bone morphogenetic protein 2 (rhBMP-2) to implant surfaces has garnered interest due to its osteoinductive potential. However, the optimal coating methodology remains unclear. This study aimed to determine whether immersing plasma-sprayed hydroxyapatite (PSCaP)-coated implants in rhBMP-2 before installation would enhance bone apposition. Using a sheep iliac model, titanium (Ti) and PSCaP-coated implants, both uncoated and coated with rhBMP-2, were assessed for osseointegration and new bone formation. After 3 and 6 weeks, bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) were evaluated. Results showed that rhBMP-2 on PSCaP surfaces significantly increased BIC and BAFO at 3 weeks, while direct adsorption onto titanium surfaces was less effective, though still better than uncoated titanium. These findings suggest that the combination of PSCaP surface and rhBMP-2 significantly enhances osseointegration, supporting the hypothesis that bioactive coatings improve implant success.
Publication reference: Yoo, D. et al., J Biomed Mat Res A, 2013, 102(6), 1921-1927.
Effects of Strain Rates on the Mechanical Properties and Fracture Patterns of Skeletal Muscle
Soft tissue injuries in the musculoskeletal system, such as those affecting ligaments, tendons, and muscles, require a thorough understanding of their mechanical behavior for effective treatment. While much research has focused on ligaments and tendons, muscle injuries, often resulting from overexertion, steroid use, or trauma, need further biomechanical study due to their complex structure. The present study aimed to characterize the mechanical response of beagle sartorius muscle fibers under strain rates of 0.1 mm/min, 1 mm/min, and 10 mm/min and analyze fracture patterns using scanning electron microscopy (SEM). Muscle tissue was excised, sectioned, and tested immediately following excision. The 10 mm/min group exhibited significantly lower strength (1.545 ± 0.50 MPa) compared to the 0.1 mm/min (2.560 ± 0.37 MPa) and 1 mm/min (2.702 ± 0.55 MPa) groups. At 0.1 mm/min and 1 mm/min, shear mode failure of the endomysium with significant fiber motion was the primary fracture mechanism. At 10 mm/min, fracture patterns changed significantly, showing little evidence of endomysial shear failure or significant fiber motion. These findings provide insights crucial for developing therapeutic approaches and medical devices.
Publication reference: Shapiro, M., Tovar, N., Yoo, D., et al., Mat Sci Eng C, 2014, 39(1), 100-104.
Physicochemical Characterization and In Vivo Response of Micro/Nanoporous Bioactive Ceramic Bone Graft Materials
Autogenous bone grafts, though the gold standard for large bone defect regeneration, have limitations such as harvesting complications, limited availability, and high resorption rates. Allogenous grafts also pose a risk of disease transmission, prompting the development of synthetic bone graft materials, or alloplasts, which are readily available, non-pathogenic, and customizable. Among these, calcium phosphate-based grafts like hydroxyapatite (HA) and tricalcium phosphate (TCP) have been studied for their varied degradation rates and osteoconductive properties. This study characterized the physicochemical properties and in vivo performance of calcium phosphate-based bioactive ceramics with different compositions and blends, focusing on materials with similar micro/nanoporosity and micrometer-scale surface texture. Evaluations included porosity, surface area, particle size distribution, phase quantification, and dissolution. Using a rabbit calvaria model, bone regenerative properties were assessed at 2, 4, and 8 weeks, followed by histologic observation and histomorphometric analysis. Results showed variations in particle size, porosity, and composition with different HA/TCP phase ratios. All materials were biocompatible and osteoconductive, with significant differences in bone formation over time. At 8 weeks, a ~55% TCP:45% HA blend showed the highest new bone regeneration and reduced soft tissue infiltration compared to other blends.
Publication reference: Tovar, N., Jimbo, R., Witek, L., Anchieta, R., Yoo, D. et al., Mat Sci Eng C, 2014, 43, 472-480.
Nanometer-scale features on micrometer-scale surface texturing
Micro- and nanoscale surface modifications have been the focus of multiple studies to accelerate bone apposition or osseointegration at implant surfaces. This study evaluated histological and nanomechanical properties, and gene expression for a microblasted surface with nanometer-scale texture within a micrometer-scale texture (MB) (Ossean™ Surface, Intra-Lock International, Boca Raton, FL) versus a dual-acid etched surface with micrometer-scale texture only (AA), in a rodent femur model over 1, 2, 4, and 8 weeks. Samples were analyzed post-sacrifice using histomorphometry, nanoindentation for biomechanical properties, and qRT-PCR for gene expression. Although histomorphometric and gene expression results were not significantly different between MB and AA at 4 and 8 weeks, significant differences were observed at 1 and 2 weeks. At 1 week, MB surfaces showed significantly higher expression of genes encoding collagen type I (COL-1) and osteopontin (OPN), indicating enhanced osteoprogenitor and osteoblast differentiation. At 2 weeks, MB surfaces had significantly up-regulated expression of COL-1, runt-related transcription factor 2 (RUNX-2), osterix, and osteocalcin (OCN), indicating progressive bone mineralization. Nanomechanical testing showed significantly higher hardness and elastic modulus for MB compared to AA at all time points. Overall, nanotopographical surfaces presented a higher host-to-implant response, with statistical differences in osteogenic gene expression shedding light on the role of surface texture in bone healing mechanisms.
Publication reference: Coelho, P.G., Takayama, T., Yoo, D. et al., Bone, 2014, 65, 25-32.
