## 3 Results
### Biocompatibility  
#### 3.2.1 Live/Dead Assay  
Figure 5 shows an increase in cell number for the MG-63 cells over the study period. On day 3, there are areas on the scaffold surface where only isolated cells can be seen, while on day 7 the surface is already confluently covered. In addition, by day 7, cells begin to colonize the pores by bridging the corners of the pores. By day 10, some of the pores are fully colonized and bridged. The number of dead cells also increases over the course of the experiment. However, the number of dead cells is significantly lower compared to the live cells. Table 3 shows the cell numbers per mm\({}^{2}\) for the three different cell lines, sorted according to total cells, dead cells and percentage of dead cells (%). A continuous increase in cell number/mm\({}^{2}\) can be seen during the course of the experiment. In addition, the proportion of dead cells is very low compared to the total number of cells. While the total number of cells increases fivefold from day 3 to day 10, the number of dead cells only increases by a factor of two. The proportion of dead cells was still about 17% on day 3 of the experiment, about 7% on day 7 and only about 6% on day 10.  
Figure 4: Fluorescence Images of (**a**): uncoated PCL scaffolds; (**b**): collagen-I coated PCL scaffolds; immunoassay with Alexa Fluor 488 (excitation at 495 nm (blue), emission 519 nm (green); Images taken with Olympus BX 53 Fluorescence Microscope, 10x magnification; (**c**): ESEM image of collagen-I coated scaffold Magnification 6400x (HFW 46.6 μm); (**d**):enlargement of a specific area of the ESEM image (red square in Figure 4c) of the collagen-I coating 12800x (HFW 23.3 μm), ESEM images taken with FEI Quanta 250 FEG with Large Field Detector, 10 kV acceleration voltage; 130 Pa.  
Figure 5: _Cont_.  
The MLO-Y4 cells, like the MG-63 cells, showed an increase in live cells over the experimental days (Figure 5). However, a striking feature of the MLO-Y4 cells is that the live cells were difficult to identify under the microscope. Some cells were only slightly green in color and were barely distinguishable from the background. Therefore, it was difficult to quantify the percentage of live cells versus dead cells. DAPI staining was essential in this case. In contrast, the dead cells were easy to recognize. Their proportion also increased over the experimental days. Particularly from day 7 to day 10, there was a strong increase in dead cells. Table 3 illustrates the cell number progression on the scaffold surface over the experimental period of 10 days. It can be observed that the number of all cells per mm\({}^{2}\) increases sharply from day 3 to day 7, before it starts to decrease from day 7 to day 10. The number of dead cells increases continuously throughout the experimental days. This increase is particularly strong from day 3 to day 7. In percentage terms, the percentage of dead cells on day 3 is about 10%. It also increases continuously with 16% on day 7 and 23% on day 10.  
Figure 5: Comparison of total, living and dead cells of three different cell types (MG-63, MLO-4 and MSC) on the surface of the collagen coated PCL scaffolds at 3 different time points, images taken with Olympus BX-53 flourescense microscope.  
The number of living MSC increases rapidly from day 3 to day 7, so that already on day 7 the pores of the scaffolds are populated over a large area. On day 10, it can be seen how the cells span the pores. The number of dead cells also increases with the days, but their proportion is significantly lower (see Figure 5). The number of all cells increases from day 3 to day 7 and then starts to decrease. Compared to this, the number of dead cells is significantly lower, but increases steadily over the test days. After three days, their percentage is about 7%, after 7 days 8% and after 10 days 10% (see Table 3)