Characterizing Mineral Ellipsoids in New Bone Formation at the Interface of Ti6Al4V Porous Implants

Abstract The hierarchy of newly formed bone contains elements of disorder within an ordered multiscale structure, spanning from the macroscale to below the nanoscale. With mineralized structures presenting in the shape of ellipsoids in mature and mineralizing tissue, this work characterizes the heterogeneity in the mineral ellipsoid packing at the interface of porous titanium implants. Using scanning transmission electron microscopy and plasma‐focused ion beam–scanning electron microscopy, mineral ellipsoids are characterized at the implant interface in both 2D and 3D. Heterogeneous in their size and shape within the newly formed bone tissue, ellipsoids are observed with alternating orientations corresponding to unique lamellar packets within 23 µm of the titanium implant interface—although this motif is not universal, and a mineral‐dense zone can also appear at the implant interface. Short‐order ellipsoid orientation shifts are also present in the 3D probe of the implant interface, where a ≈90° misorientation angle between neighboring packets of mineral ellipsoids (and an intervening organic layer) resolves with increasing distance from the titanium. Combined with local patches of woven‐to‐lamellar transition, the early heterogeneity and transformation of peri‐implant bone structure is a quintessential step in the development of a functional connection between implant and bone.