## 4 Discussion  
This study analysed subchondral bone regeneration following osteochondral defects. Using HA-collagen and Ti-PLA-collagen/PLGA scaffolds with and without BMC, data for TbTh, BV/TV, and DA were collected and compared between scaffold groups and sub-set regions. Statistical analysis was used to assess if scaffold composition, the addition of BMC,  
Figure 9: Light microscopy images of resin embedded sections to examine the regenerated tissue and scaffold degradation extent. and sub-set region contributed to significant differences in subchondral bone regeneration. Finally, microscopic analysis of tissue formation and scaffold degradation was performed. Trabecular thickness measurements quantify bone growth. As outlined above, none of the TbTh measurements yielded significant results, suggesting that none of the study parameters affected subchondral tissue regeneration significantly. These results are inconsistent with previous researchers who have found that multi-layered scaffolds composed of titanium significantly enhance subchondral bone regeneration [2; 36; 37]. Given the limited scaffold testing in large-bodied animals and the uncertainty of how trabecular bone will mature both in quantity and quality in response to foreign objects, this is not entirely surprising. Other notable trends were also observed. For example, Sub-set 3 exhibited the largest average TbTh measurements in scaffold Groups 1, 2, and 3, suggesting that at six months post-implantation, the regions furthest from the joint surface experience thicker trabecular growth than those closer to the joint surface. This may be due to the increased biomechanical forces experienced in the subchondral bone closer to the joint surface. When comparing TbTh measurements between scaffold groups, the control and novel scaffolds without BMC exhibited the same average values, suggesting that neither scaffold group was better suited for generating thicker trabeculae. However, the control with BMC did have a higher average than the novel with BMC, indicating that the titanium scaffold utilised in this study did not significantly enhance trabecular thickness as hypothesised. The BV/TV provides bone volume as a percentage to relay the quantity of growth within the region of interest. Statistically significant results for this measurement were only observed when comparing the effects of the scaffold composition on osseous growth in the sub-set regions, indicating that the regions furthest from the surface experienced significant differences in subchondral bone regeneration between the control and novel scaffolds (irrespective of BMC addition). When visually assessing 3D models of the sub-set, it was initially thought that these results were generated due to the lack of defect repair often observed in that region when compared to Sub-set 1 and 2. While the fact that these measurements were largest in two of the four scaffold groups (Group 1 and Group 2) draws this assumption into question, it is important to cross reference these measurements with the DA to show osseous homogeneity and biomechanical durability of the newly deposited tissue. Sub-set 1 experienced the largest average DA measurements in all four scaffold groups, suggesting that there may not be a direct relationship between the quantity and durability of osseous growth because the anatomical regions with the largest BV/TV in Groups 1 and 2 did not experience sufficient bone quality. This observation is consistent with previous researchers who have reported an inverse correlation between regeneration quantity and quality following osteochondral tissue injuries [38; 39]. Additionally, this reinforces the commonly understood biological function, in which the bone closer to the articular surface of a joint experiences larger biomechanical stimuli which results in increased uniformity in the bone deposition.