Fortifying the Bone-Implant Interface Part 2: An In Vivo Evaluation of 3D-Printed and TPS-Coated Triangular Implants

Schematic of device placement, device geometry, and test plan, highlighting how the implant was sectioned for postmortem evaluations, with the “A” section taken from the most closed section and the “B” section taken from the most open section of the additive manufactured (AM) device (A). The red dashed line indicates where the implant was bisected. Note: the solid titanium plasma spray-coated (TPS) implants were placed and processed in the same respective locations. Representative anteroposterior radiographic images at necropsy of TPS (B) and AM (C) implants. Representative lateral radiographic image at necropsy of both implant types (D).

Schematic of quantitative histomorphometric regions of interest for A and B sections of AM and TPS implants (Figure 2A). Note: A and B sections for TPS implants have the same cross-section. Top row: Green outline indicates the surface length available for bone in contact (BIC) measurements. Pores within the porous coatings were included in the available surface length. Middle row: Orange area indicates the available area for bone to grow into the porous surface and within the open fenestration between the substrate of the B section of the AM implant and the boundary line drawn between the peaks of the porous coating. The area also includes any open pores within the porous coating available for bone to grow in. Bottom row: Blue area indicates the available area for bone to grow into the central region of the AM implants. This metric was not measured for the TPS implants. AM = additive manufactured, TPS = titanium plasma spray.

Biomechanical push-out testing results for ultimate shear strength (A). Dashed line and gray shaded region indicate the average ultimate shear strength and standard deviation, respectively, of bovine cancellous bone.³³ Representative gross images of post-push-out samples at 12 weeks show different failure modes (B). TPS implants failed primarily at the bone-implant interface, with some large “spot-welding” patches remaining, while a ~2-3mm ring of bone remained securely attached to all AM groups even after being subjected to ≥ 2500N. Tissue can also be observed growing into the open fenestrations and through the central core of all AM groups. Gross examination at 6 weeks revealed similar findings. Data are represented as mean ± standard deviation, * = p < 0.01 within time-point factor, scale bar = 5 mm. TPS = titanium plasma spray, AM = additive manufactured, AM+HA = additive manufactured with hydroxyapatite, AM+Auto = additive manufactured with autograft.

Microcomputed tomographic images of implants at necropsy, corresponding to the “A” histological cross-sections. Peri-implant bone is evident around all implants. Scattering artifact can be observed at implant corners. TPS = titanium plasma spray, AM = additive manufactured, AM+HA = additive manufactured with hydroxyapatite, AM+Auto = additive manufactured with autograft.

Representative A and B histological cross-sections from all treatment groups shown at original magnification (1x). Qualitative assessment showed that bone ongrowth/ingrowth to all treatment groups was substantial by 6 weeks and changed with time as the bone matured. Some soft tissue was also seen in contact with the implants, which was mainly composed of a collagen-rich transitional tissue. Bone could also be seen within the central region through the open fenestrations in all AM implant groups. Note that bone forms continuously around the periphery of the implants, and within the open core of the AM implant groups, indicating the dark regions observed under μCT to be artifact. TPS = titanium plasma spray, AM = additive manufactured, AM+HA = additive manufactured with hydroxyapatite, AM+Auto = additive manufactured with autograft.

Quantitative histomorphometric results of the outer surface of A sections for available surface length (A) and available area within the surface (B). Results for both metrics were significantly greater in the AM surfaces (averaged across all three AM implant groups) compared to the TPS implants (‡ = p < 0.0001). Bone area (BA) within the porous surface and central region is shown in (C). For AM implant groups, the “hashed” regions of (C) signify the contribution of BA within the central region, whereas the “unhashed” regions signify the contribution of BA within the porous surface. Bars having the same letter are significantly different (p < 0.05). Roman letters refer to 6 week results, while Greek letters refer to 12 week results. Data are represented as mean ± standard deviation. TPS = titanium plasma spray, AM = additive manufactured, AM+HA = additive manufactured with hydroxyapatite, AM+Auto = additive manufactured with autograft.