Fig 1.
Selection of an appropriate stand-off distance during the HA coatings deposition process: Single splats spreading behavior upon plasma spraying at different stand-off distances 300 mm, 400 mm and 500 mm.
Pictures obtained using scanning electron microscope (back-scattered electrons).
Fig 2.
a) Cranium with the modeled medium-size defect. The magnified inset shows the Ti6Al4V implant detail including the HA coating deposited onto its rim, and the fixation mini-plate and micro-screws. (b) Two different thicknesses of HA coating (320 μm–orange and 160 μm–yellow). (c) Three different sizes of the cranial implant, small, medium, and large. The circular red areas (~ 310 mm2) correspond to the location of the applied external force caused by the head weight (50 N).
Fig 3.
(a) The cylindrical thread-less and screws with micro-thread used in the coarse and sub-model computations, respectively. (b) Illustration of the sub-areas division of the peripheral HA coatings (pink-grey) used to simulate the implant (green) osseointegration in Approach II. (c) FE mesh of coarse model.
Table 1.
Mechanical properties of the used materials.
Fig 4.
Microstructure of the HA coatings produced on Ti6Al4V substrate (sample T320 shown).
Given the thermal spray production method, the coating contained some pores, voids and cracks. The magnified inset shows network of inter-splat voids forming by improper droplet spreading and contact, as well as vertical segmentation cracks in the coating, a consequence of internal stresses alleviation upon cooling to room temperature.
Fig 5.
Reduction in the total implant displacements for different implant sizes with increasing frictional coefficient at BIC surface area computed according to Approach I.
The increase in frictional coefficient simulated osseointegration in Approach I.
Fig 6.
The maximum values of von Mises stresses in implant (blue colors), fixation mini-plates (red colors) and screws with micro-thread (green colors).
The values of as-fixed state were labeled with ,,a-f” and the values of partly osseointegrated state (FC = 0.75) with, ,,o”.
Fig 7.
Reduction in the total implant displacements for different implant sizes with increasing osseointegration levels simulated in Approach II.
The “% of osseointegration” was modeled by the percentage of the BIC surface area that was bonded.
Fig 8.
The maximum values of von Mises stresses in implant (blue colors), fixation mini-plates (red colors) and screws with micro-thread (green colors).
The values of as-fixed state were labeled with ,,a-f” and the values of 30% osseointegration levels (30% of bonded contact at BIC) with ,,o”.
Fig 9.
Typical results of von Mises stress distribution in (a) implant (implant holes) and fixation components (b—screws and c–mini-plates) for S320 variant. As-fixed states were labeled with ,,a-f”, the values of partly osseointegrated states were labeled with ,,FC = 0.75” (Approach I) and ,,~30% Oss” (Approach II).
Table 2.
A comparison of results obtained for a small-sized cranial Ti6Al4V implant without and with HA coating.