Plastic Surgery Research Council

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Evaluation of Porous Fluoridated Apatites as Bone Scaffolds
Sujee Jeyapalina, PhD, Brian T. Bennett, MSc, Barbu Gociman, MD, PhD, James Peter Beck, MD, Steven Naleway, PhD, Jayant P. Agarwal, MD.
University of Utah, SALT LAKE CITY, UT, USA.

PURPOSE: More than half a million patients are treated for bone defect repairs in the US, with a yearly cost greater than $2.5 billion. The best current approach for bone defect repair remains the use of bone autografts. There are unfortunately significant limitations with the use of bone autografts. These are related mainly to the limited availability and the donor site morbidity. Multiple attempts to create a perfect bone autograft alternative were made in the past to circumvent these limitations, but none of them have been fully successful. In order to create the ideal bone autograft substitute, we fabricated fully interconnecting porous fluorapatite (FA) and fluorohydroxyapatite (FHA) scaffolds by adopting "freeze-cast" and "foam-cast" processes. The substitution of hydroxyl group with fluoride in HA structure (i.e., to make FHA and FA) is known to increase the dissolution resistance, which is often a concern when utilizing pure HA. Moreover, HA, FA and FHA all known to have poor mechanical strengths. Interestingly, we have used heat treatment to improve the mechanical strength, which now allows us the shape the scaffolds to fit any type of bony defect. Although HA scaffoldings are used clinically, the use of FA and FHA scaffoldings are largely neglected. Thus, we hypothesized that FA and FHA heat-treated scaffolding would have better osteogenic properties than HA. METHODS: This hypothesis was tested both in vivo and in vitro studies. All apatites (i.e., HA, FHA, and FA) were synthesized in house and compressed into 10 mm diameter pellets and heat-treated. Cell-culture studies were performed using primary osteoblast cell-line (ATCC CRL-11372) and total RNAs were then extracted. mRNA expression levels of Alkaline Phosphatase (ALP), Secreted Phosphoprotein-1 (SPP1) and Osteopontin (OPN) were quantified using RT-PCR. Based on these data, a selected temperature range was used for fabrication of porous scaffold, the porosity and the surface properties of which were quantified using SEM (Figure 1). These selected samples were then subjected to a four-week biocompatibility study in a rat back model. These scaffolds are now planned to be tested in a bone defect rat model.
RESULTS: Examination of the strength of the various apatite revealed no distinct variances. All apatites sintered at the lower temperatures had a reduced number of adherent cells suggesting a temperature-dependent effect on cell adhesion, proliferation, and differentiation rates. Interestingly, FA sintered at 1250C had a significantly increased rate of cell adhesion (p<0.05), and had the most cells of any experimental group. Analysis of mRNA expression data showed FHA samples sintered at 1150C and FA samples sintered at 1050 and 1150C had the statistically significant increase (p<0.05) in the bone markers SPP1 and OCN expressions, indicating their osteogenic properties. In vivo biocompatibility study revealed that, within the samples that were sintered at 1150C, FHA formed a thinner capsule, indicating its enhanced biocompatibility.
CONCLUSIONS: It was concluded that FHA/FA surfaces could be used successfully as bone scaffoldings.


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