Insights from a comparative analysis of Rangifer tarandus tibia and antler

Abstract

Rangifer tarandus, commonly known as reindeer, inhabits circumpolar areas and is widely distributed in the Finnish Lapland. Because of its unique ability to regenerate antlers annually, this species offers an exceptional model for studying bone regeneration. The aim of this thesis was to characterize the material properties of temporary reindeer antler in comparison to permanent tibia across a cohort of reindeer individuals (n=9) to understand differences in bone growth dynamics and how they appear in material properties. X-Ray diffraction (XRD), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and micro-computed tomography (Micro-CT) were employed to evaluate crystallinity, composition, and microarchitecture between these two biologically and functionally distinct tissues. XRD and Micro-CT results showed that tibia samples had significantly greater crystallite size (ANOVA p = 0.006), higher bone mineral density (p = <0.001), and lower open and total porosity (ANOVA p = < 0.001) compared to antler. Porosity and trabecular-specific parameters showed variance across antler sample location (base, tip) and regions (central, intermediate, peripheral), the central part of the tip possessing the highest porosity, while the intermediate region of the antler base exhibited the greatest proportion of mineralized tissue (BV/TV) and trabecular thickness. ATR-FTIR results further demonstrated differences in chemical composition between the tissues. Mineral to matrix ratio was significantly higher (ANOVA p = <0.001) in tibia and lowest in antler tip, whereas amide parameters exhibited the opposite pattern. Both the carbonate-to mineral ratio (ANOVA p = <0.029) and the carbonate content of bioapatite to phosphate (ANOVA p = <0.001) showed the highest carbonate content in antler tips. In contrast, carbonate accumulation exhibited a different pattern, with tibia having the highest presence of carbonate, and tip the lowest (ANOVA p = <0.001). These results highlight how differences in maturation time are reflected in the structures and compositional properties of bone.