Introduction

1. Development of Bone Coated Ti Implants for Enhanced Implant IntegrationJon Swaim, Lester Smith1, Karen Haberstroh1 and Thomas Webster1Department of Biomedical EngineeringUniversity of Alabama at Birmingham, Birmingham, AL1Weldon School of Biomedical Engineering and School of Materials EngineeringPurdue University, West Lafayette, IN Introduction Each year in the United States, more than 300,000 people require hip and knee replacements to restore function to damaged tissue.1 The lifetime of these implants, however, is typically only 10 to 15 years. The performance of an implant is greatly dependent upon the cellular and molecular events that occur at the tissue-implant interface. Implants being used today often fail due to an insufficient bond between the implant and juxtaposed bone or ligament.2 For this reason, much of current implantology research aims to enhance implant integration by developing a tissue-implant interface that is not only biocompatible, but osteoconductive as well. PICTURE OF THE TISSUE-IMPLANT INTERFACE GOES HERE Figure 1: Metallic biomaterials containing calcium phosphate, particularly hydroxyapatite (HA; Ca10(PO4)6(OH)2), the natural ceramic in the bone matrix secreted by osteoblasts, have shown to be good biological performers.3,4 However, the efficacy of using a metal coated with an HA-containing polymer scaffold to enhance bone growth at the tissue-implant interface has remained to be elucidated. PICTURE OF THE TI/PLGA/HA COMPOSITE GOES HERE Figure 2: The principle objective of this study is to construct the composite shown in Figure 2, seed osteoblast-like cells on to the composite, and investigate the degree of intramembranous bone growth. The PLGA/HA scaffolds will be created using both conventional HA and nanophase HA, and the osteoblast adhesion to the scaffolds will be compared with a control PLGA scaffold. Materials and Methods Conventional HA synthesis. Conventional HA was synthesized using a precipitation process. Twenty milliliters of concentrated NH4OH was added to 300 ml of dH2O. Thirty milliliters of 0.6 M (NH4)2HPO4 solution was then added to dH2O, and 36 ml of 1M Ca(NO3)2 solution was dripped into the mixture at a rate of 3.6 ml/min. The solution was stirred for 24 hr at room temperature, and the HA precipitation occurred as indicated by the reaction below: 10Ca(NO3)2 + 6(NH4)2HPO4 + 8NH4OH → Ca10(PO4)6(OH)2 + 6H2O + 20NH4NO3 (1) The precipitates were centrifuged and rinsed twice with dH2O, and then dried in oven (TEMPERATURE ????) for 24 hr. Nanophase HA synthesis. Nanophase HA was synthesized using a precipitation and heat treatment process. Twenty milliliters of concentrated NH4OH was added to 300 ml of dH2O. Thirty milliliters of 0.6 M (NH4)2HPO4 solution was then added to dH2O, and 36 ml of 1M Ca(NO3)2 solution was dripped into the mixture at a rate of 3.6 ml/min. The solution was stirred for 10 min at room temperature, and the HA precipitation occurred as indicated by reaction 1. The precipitates were centrifuged, rinsed with dH2O, and then placed in (MODEL # ???) hydrothermal tanks (manufacturer??) at 200 °C for 20 hr. After the tanks were cooled, the solution was centrifuged and rinsed with dH2O three times, and then dried in an oven (TEMP ???) for 24 hr. PLGA/HA Scaffold Composites. PLGA (50:50 wt% PLA:PGA; Polysciences Inc.) pellets (0.5 g) were dissolved in 6 ml of chloroform for 40 min at 45 °C. HA (1.125 g) was added to the polymer solution and stirred continuously for 2 hr. (It should be noted that scaffolds containing both conventional and nanophase HA were made.) Salt (4.375 g; NaCl, 150-250 µm diameter) was then added and mixed for 5 min. The polymer solution was poured into a Teflon-coated Petri dish, dried for 24 hr in air and then 48 hr in a vacuum oven (15 inHg). The scaffold was then soaked in dH2O for 3 days, changing the water every 3 hours to leach the salt and leave 150-250 µm pores. PICTURE OF THE PLGA/HA PROCESSING GOES HERE Figure 3: Future Work The effects of HA on the adhesion of osteoblast-like cells to the scaffold will be investigated using a cytotoxicity assay. Cells (0.5x106/well) will be seeded on to the scaffolds and cultured in a 12-well plate under standard cell culture conditions (a sterile, humidified, 37 °C, 5% CO2/95% air environment) in DMEM supplemented with 10 % Fetal Bovine Serum (FBS) and 1 % Penicillin/Streptomycin (P/S) for 4 hr. PICTURE OF THE 12-WELL PLATE w/ PLGA, PLGA/cHA, PLGA/nHA Figure 5: After the incubation time, the scaffolds will be washed twice with Phosphate Buffered Saline (PBS) solution, and then placed into a new 12-well plate. The cells will be frozen and thawed three times to lyse the cells, and the absorbance of the lysates at 490 nm will be measured using a spectrophotometer. Commercially pure grade II Titanium will be machined into 1 cm x 1 cm x 0.64 cm substrates with a well density of 16 wells/cm2. The dimensions of the wells will be a 0.5 mm diameter and a depth of 0.32 cm. The PLGA/HA scaffold will be produced as previously described, but allowed to cure for 24 hr on top of the Titanium substrate to ensure that there is porous scaffold in the wells. Osteoblast-like cells will be seeded on the top of the substrates and allowed to proliferate and difference for ____some amount of time____. They will be analyzed using ______ ___at some point in time____. • References • Puleo D.A., Nanci A. Understanding and controlling the bone-implant interface. Biomaterials 20 (1999) 23-24. • Webster, TJ. Nanophase ceramics: The future orthopedic and dental implant material. Advances in Chemical Engineering 27 (1991). • Habibovica et al. Biological performance of uncoated and octacalcium phosphate-coated Ti6Al4V. Biomaterials 26 (2005) 23–36 • Hayashi K, Mashima T, and Uenoyama K. The effect of hydroxyapatite coating on bony ingrowth into grooved titanium implants. Biomaterials 20 (1999) 111–119 Preliminary Results SEM PICTURES OF SCAFFOLDS Figure 4: Acknowledgements The authors would like to thank the National Science Foundation (GrantNumber: 0353901-EEC) for Research Experiences for Undergraduatesfunding. Furthermore, we would like to thank Jennifer McCann, Brian Ward, and Michiko Sato for their help with this study.