## 4 Discussion
This conclusion can explain why the degradation of the scaffolds is delayed (during the first steps of the test) when they are plasma-treated or coated. As demonstrated by the WCA results (Figure 1), any of the strategies applied lead to a decrease of the hydrophobicity. Consequently, according to the conclusions of [PERSON] et al., this trend would hinder the adsorption of the enzymes on the PLA surface and delay the degradation process. The coating applied at pH 3 seems to limit this adsorption step especially, as this group of samples shows the lowest levels of degradation measured as mass loss (Table 2). The protein adsorption on solid surfaces is a complex process affected by different parameters [45], so the reason why the coating at this pH value limits the adsorption process needs to be further analyzed, although it is out of the scope of the present work. The trend evidenced by the mass loss results is also supported by the pH measurements of the degradation media (Figure 3), as the decrease of this parameter is explained by the presence of carboxylic acids released during the degradation process [46]. If the degradation is delayed (as it is especially for plasma-treated samples and pH 3 coated samples), the pH value of the media will be higher during the process, as confirmed in this experiment. The results obtained from the enzymatic degradation test open the possibility of controlling the degradation rate of the proposed constructs intended for bone regeneration, aiming to match this rate to the specific tissue growth rate. Finally, the results of the cell viability evaluation prove that the aloe vera coating offers an improvement on the ability of the bone cells to proliferate and remain viable on the scaffolds compared to the results from the structures that were plasma-treated but not coated. As plasma treatment is the most common method to modify the surface of PLA scaffolds [14; 47; 48], the results from this work confirm the potential of the coating strategy to increase the biological performance of PLA-based scaffolds for bone regeneration. In addition, the pH of the aloe vera extracts has been demonstrated to be a parameter that strongly affects the bioaffinity of the surface coating, as the best results were obtained for the aloe vera coating applied at pH 3. The adjustment of the pH may change the chemistry of the bioactive polysaccharides in the aloe vera extracts. According to different studies, the presence of the acetyl group in the acetaminophen structure (one of the most important components in the aloe vera extracts) seems to be a key parameter to explain its bioactivity [42]. [PERSON] et al. [49] have already proven that the deacetylation in alkaline conditions of acamannan decreases its bioactivity. Although in this work, the pH level is not aggressive enough to produce the deacetylation of the bioactive molecules, it is possible that the introduction of an alkali (NaOH used for pH adjustment of the extract solutions) changed the conformation of these active functional groups. This modification could hinder the effectiveness of the aloe vera attachment to the surface, leading to a lower bioactivity of the coating at pH 5 compared to the coating applied at pH 3.