Investigation of strontium transport and strontium quantification in cortical rat bone by time-of-flight secondary ion mass spectrometry

Abstract

Next-generation bone implants will be functionalized with drugs for stimulating bone growth. Modelling of drug release by such functionalized biomaterials and drug dispersion into bone can be used as predicting tool for biomaterials testing in future. Therefore, the determination of experimental parameters to describe and simulate drug release in bone is essential. Here, we focus on Sr 2+ transport and quantification in cortical rat bone. Sr 2+ dose-dependently stimulates bone-building osteoblasts and inhibits bone-resorbing osteoclasts. It should be preferentially applied in the case of bone fracture in the context of osteoporotic bone status. Transport properties of cortical rat bone were investigated by dipping experiments of bone sections in aqueous Sr 2+ solution followed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling. Data evaluation was carried out by fitting a suitable mathematical diffusion equation to the experimental data. An average diffusion coefficient of D = (1.68 ± 0.57) · 10 −13 cm 2 s −1 for healthy cortical bone was obtained. This value differed only slightly from the value of D = (4.30 ± 1.43) · 10 −13 cm 2 s −1 for osteoporotic cortical bone. Transmission electron microscopy investigations revealed a comparable nano- and ultrastructure for both types of bone status. Additionally, Sr 2+ -enriched mineralized collagen standards were prepared for ToF-SIMS quantification of Sr 2+ content. The obtained calibration curve was used for Sr 2+ quantification in cortical and trabecular bone in real bone sections. The results allow important insights regarding the Sr 2+ transport properties in healthy and osteoporotic bone and can ultimately be used to perform a simulation of drug release and mobility in bone.

Gelatin-Modified Calcium/Strontium Hydrogen Phosphates Stimulate Bone Regeneration in Osteoblast/Osteoclast Co-Culture and in Osteoporotic Rat Femur Defects—In Vitro to In Vivo Translation

“…Even though PPGC + S 5:5 has a less rapid decrease in mass in vivo owing to its bioactivity, the Sr 2+ ions are released during the in vivo experiment and incorporated into existing or newly formed bone tissue, as shown by ToF-SIMS. These findings of strontium incorporation in bone tissue after release from bone cements are in line with previous ToF-SIMS studies of strontium containing bone cements [32,33]. The lower initial amount of strontium in PPGC + S 5:5 caused a lower anti-osteoclastic effect than PPGC + S 3:7 but still a good stimulation of new bone formation.…”

The Influence of Strontium on Bone Tissue Metabolism and Its Application in Osteoporosis Treatment

“…Sr 2+ dissipation is more advanced and therefore faster in osteoporotic bone, which could be due to different bone nanostructure. Using ToF-SIMS, it is proven that strontium is localized in newly formed bone regions and within the pre-existing osteoporotic bone [ 74 , 75 , 76 ].…”

Spatially resolved indiffusion behavior of Cu2+ and Ni2+ in polypropylene

“…A mathematical fit (Equation 3) was carried out with the obtained ion signal intensities from ToF-SIMS depth profiles, due to the proportionality between species concentration and secondary ion intensity in ToF-SIMS. [31] c x ð…”

“…In this fit, c bg is the background concentration of metal ions (Cu 2+ or Ni 2+ ); c 0 is the concentration of the infinite source; x is the depth; x 0 is the starting point of the diffusion profile; D is the diffusion coefficient and t the diffusion time. [31] The diffusion profiles for each metal ion species were plotted after summing up the mass spectrometric data of each analysis layer from ToF-SIMS depth profiles. Thus, diffusion profiles show ion intensity versus depth (Figures 4 and 5).…”

“…Due to possible contamination of the sample surface and dotation effects, which can lead to an unsteady matrix with non-reliable secondary ion data, the first measured data points of diffusion profiles were not considered for the fitting process. [31] To validate the experimental approach for the investigation of metal ion diffusion into PP by ToF-SIMS, a time-dependent experimental series was conducted to confirm whether the obtained diffusion coefficient keeps constant. For this time series, copper diffusion into water-saturated PP was chosen.…”