Mahmoud, D. | Search bioRxiv

bioRxiv2023

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

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 mineral ellipsoid packing at the interface of porous titanium implants. The characterization of mineral at the bone-implant interface offers insight into the osseointegration of titanium implants and the mechanical properties of the interfacial bone tissue. 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 2-3 m 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 an approximate 90{degrees} misorientation angle between neighbouring packets of mineral ellipsoid resolves with increasing distance from the titanium, possibly providing a strengthening mechanism to prevent crack propagation in the peri-implant bone. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=74 SRC="FIGDIR/small/524810v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@3c34a1org.highwire.dtl.DTLVardef@a3437borg.highwire.dtl.DTLVardef@a374e1org.highwire.dtl.DTLVardef@14e9572_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2023

Osseointegration of functionally-graded Ti6Al4V porous implants: Histology of the pore network

The additive manufacturing of titanium into porous geometries offers a means to generate low-stiffness endosseous implants with a greater surface area to improve osseointegration. In order to optimize pore size in the scaffolds, it is important to first understand the timeline of osseointegration in pre-clinical models. In this work, selective laser melting was used to produce gyroid-based scaffolds with a uniform pore size of 300 m or functionally-graded pore size from 600 m to 300 m before implantation in New Zealand white rabbit tibiae for 4 and 12 weeks. Initial in vitro assessment with Saos-2 cells showed favourable cell proliferation at pore sizes of 300 and 600 m. At four weeks, histological observations indicated some residual inflammation alongside neovessel infiltration into the scaffold interior and some early apposition of mineralized bone tissue. At twelve weeks, both scaffolds were filled with a mixture of adipocyte-rich marrow, micro-capillaries, and mineralized bone tissue. X-ray microcomputed tomography showed a higher bone volume fraction (BV/TV) and percentage of bone-implant contact (BIC) in the implants with 300 m pores than in the functionally-graded specimens, indicating that these smaller pore sizes may be favourable for osseointegration in leporine bone. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/521963v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@2e319aorg.highwire.dtl.DTLVardef@baa9deorg.highwire.dtl.DTLVardef@e66075org.highwire.dtl.DTLVardef@c6c8c4_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗