## 4 Discussion
However, Groups 3 and 4 experienced the greatest BV/TV in Sub-set 1, indicating that the novel scaffold both with and without BMC generated greater quality and quantity bone regeneration nearest to the joint surface; this is a promising result as this region experiences the greatest biomechanical forces and requires regenerated bone which can endure them. Despite the statistical insignificance of the DA measurements, other trends were observed. Scaffolds seeded with BMC experienced higher average DA values in 87.5% of the samples. Though low levels of uniformity (<0.5) were observed in these samples, this trend indicates that the addition of BMC to osteochondral scaffolds may aid in higher quality subchondral bone regeneration, again correlating with results seen in previous studies [38; 39]. Ti-PLA-collagen/PLGA scaffolds also generated a larger average DA in 87.5% of the samples, suggesting that the composition of the novel scaffolds examined in this study produce greater biomechanical stability and tissue uniformity than the control scaffolds. These results indicate that, with further examination, the novel scaffold and addition of BMC may lead to sufficient subchondral bone quality. Macroscopic evaluations of the samples corroborated the findings generated with the micro-CT images regarding tissue growth and unfilled voids in the subchondral compartments. Most of the control scaffolds (Group 1 and Group 2), and the collagenous layers in the Ti-PLA-collagen/PLGA scaffolds (Group 3 and Group 4) were degraded during the implantation period; in some instances, these were replaced with new tissue formation. Group 1 and Group 2 clearly exhibited areas of bone regeneration disproportionately throughout the sub-set regions. The collagen layer in Group 3 and Group 4 scaffolds was replaced with cartilage-like tissue, whilst the other regions experienced osseous growth. The Ti and PLA matrices in the tested scaffolds were still present and identifiable as expected because PLA does not begin to degrade until one and a half years after implantation, and Ti does not degrade once implanted. While the results of this study suggest that the tested scaffold composition and use of BMC did not generate significant differences in bone regeneration, there may be a few explanations for this occurrence. For example, the present study utilised large-bodied animals, while others studying scaffold treatments for osteochondral tissue defects often use small animals such as rabbits [2; 37]. Because larger bodies experience greater load transfers within joints and often larger defects to be healed, the test subjects used may have impacted the results. The use of HA-collagen scaffolds as control samples may have also decreased the observed differences between regeneration in the scaffold composition groups because natural polymers may also aid in osseous growth; this may also explain why studies leaving the defects untreated as a control do see significantly higher levels of growth within their treatments [37]. Finally, it is worth noting that the healing time prior to analysis was longer in the present study than in others [2; 36; 37]. This may account for the contrasting results observed between previous research and the present study because increased levels of subchondral bone occur earlier in the healing process due to the body's trauma response of depositing excess woven bone. Within the first 2-10 weeks following an injury, bone deposition increases in order to form a callus around the injury; the bone is then reconstructed at an increased rate for as long as a year before an adequate osseous structure is achieved [40]. Given this healing process, it is possible that studies have witnessed greater quantities of bone tissue due to shorter healing periods. It is also possible that the tissue observed in this study was still experiencing rapid remodelling in response to the injury.