Abstract
Strontium (Sr) can promote the process of bone formation. To improve bioactivity, porous allograft bone scaffolds (ABS) were doped with Sr and the mechanical strength and bioactivity of the scaffolds were evaluated. Sr-doped ABS were prepared using the ion exchange method. The density and distribution of Sr in bone scaffolds were investigated by inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). Controlled release of strontium ions was measured and mechanical strength was evaluated by a compressive strength test. The bioactivity of Sr-doped ABS was investigated by a simulated body fluid (SBF) assay, cytotoxicity testing, and an in vivo implantation experiment. The Sr molar concentration [Sr/(Sr+Ca)] in ABS surpassed 5% and Sr was distributed nearly evenly. XPS analyses suggest that Sr combined with oxygen and carbonate radicals. Released Sr ions were detected in the immersion solution at higher concentration than calcium ions until day 30. The compressive strength of the Sr-doped ABS did not change significantly. The bioactivity of Sr-doped material, as measured by the in vitro SBF immersion method, was superior to that of the Sr-free freeze-dried bone and the Sr-doped material did not show cytotoxicity compared with Sr-free culture medium. The rate of bone mineral deposition for Sr-doped ABS was faster than that of the control at 4 weeks (3.28±0.23 µm/day vs. 2.60±0.20 µm/day; p<0.05). Sr can be evenly doped into porous ABS at relevant concentrations to create highly active bone substitutes.
Highlights
The long recovery time for bone defect healing highlights the need for a superior osteogenic scaffold [1,2]
Sr has been incorporated into hydroxyapatite (HA), tricalcium phosphate (TCP), and calcium phosphate cement (CPC) to improve their bioactivities and physicochemical properties [4,5,6,7]
When the concentration of the SrCl2 solution was above 30 mM, incorporated Sr density surpassed 5%
Summary
The long recovery time for bone defect healing highlights the need for a superior osteogenic scaffold [1,2]. Improving the osteogenic potential of implantable scaffolds will effectively shorten recovery time and provide a robust solution to critical sized bone defects, while reducing the occurrence of nonunion [3]. Incorporation of Sr into allograft bone is an attractive method for developing a superior osteogenic scaffold. The application of Sr to allograft bone is comparatively safe and practical when compared with other cytokines [8]. The method for Sr incorporation is very specific for bone scaffold. Sr cannot be mixed into the raw materials or added to the structure from the beginning. Allograft bone cannot withstand any extreme conditions during preparation
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