## 4 Discussion
The strain amplitude applied in this case was between 10 and 11%, which could prevent the fluid from escaping, thus resulting in the fluid within the pores of the scaffold bearing the applied compressive strain than the solid matrix. The changes in the dynamic modulus scaffold with degradation are the least in comparison to the other properties (ramp, equilibrium moduli), which could be due to the limited permeability of the fluid from the scaffold at the applied strain rates (1%), which resulted in high levels of interstitial fluid pressurisation from the large pore sizes. Having comparable mechanical properties of the scaffold retained for over 56 days of degradation can have favourable outcomes in vivo as it is within the clinical timeline for cartilage to regenerate [6; 7]. The degradation of the scaffolds must not cause any excessive inflammatory response that may affect the regenerating tissue [47]. Studies in the past have found other grades of PLGA (PLGA 50:50, PLGA 75:25) to affect cell viability in vivo within 28 days of incubation due to the significant release of acidic oligomers [3; 48]. Hence, a study was conducted to assess the effect of the degrading PLLGA 85:15 scaffolds on HBMSCs. HBMSCs were prominent in all samples, demonstrating successful attachment and biocompatibility of the degrading structure. Visually comparing day 1 images to day 28, an increase in cells is noted, suggesting good attachment, cell proliferation, and a low rate of cell death-all indices of biocompatibility. The cells also aligned along the cell structs, which is a common behaviour for these cells to show spatial alignment [48; 49]. The increase in acidic byproducts with degrading PLGA has been known to be a leading cause of cell death [48], but a decrease in pH until 6.8 does not affect cell viability and morphology in vivo [27; 48]. In the scaffolds fabricated in this study, the pH after 28 days of degradation had dropped to 7.33 \(\pm\) 0.02 (Figure 12), which is indicative of the low release of acidic oligomers from the fabricated scaffolds. The initial molecular weight of the polymer is also known to have a significant effect on cell viability. [PERSON] et al. [3] found that the Mw of PLGA 50:50 scaffolds decreased by 56% in 28 days, which decreased the cell viability to 74% in vitro. The Mw of the scaffold fabricated in this study decreased by 13.3% in 56 days, further demonstrating the stable degradation of the scaffolds. This relative stability in Mw and pH, in conjunction with high levels of porosity and well-connected pores, likely contributes to the positive cell response seen in these initial biocompatibility studies. Furthermore, [PERSON] et al. [49] evaluated the cytotoxic response of pre-degraded PLLGA 85:15 discs to macrophages, displaying a low cytotoxic effect of the material and lack of inflammatory reaction. It will be necessary to fully understand the cell response to these materials in terms of safety and functionality in more extensive in vitro studies, but the initial results are promising. Furthermore, the study has not incorporated a quantitative measurement of the proliferating HBMSCs on the scaffold which has been semi-quantitatively measured from the live/dead images. This is a limitation in this study. To understand the long-term degradation behaviour of scaffolds for cartilage tissue engineering, an elevated temperature methodology has been adopted that can decrease the period of evaluation while ensuring the results remain relevant. Fundamentally, the degrading mechanism should closely resemble the in vivo system. On accelerating this degradation, the rate of degradation was more rapid due to higher energy available within the molecules of the polymer [9; 22]. The accelerated degradation demonstrated the scaffolds maintained their volumetric structure for 28 days with a white-like appearance and visible swelling in the strands by the end of the time point. The timeline of the swelling and the whitish appearance could depend on the material and architecture of the scaffold. [PERSON] et al.