## 3 Results
### In Vitro Cell Viability and Cytotoxicity  
The data in Figure 6a compare the viability of untreated cells with those treated with drug-loaded microparticles after 6, 24, 48, and 72 h post treatment. At all durations, cell viability was lower for breast cancer MDA-MB-231 cells treated with drug-loaded PLGA-CS-PEG microparticles encapsulating drugs vs. the untreated cells. In addition, the cells treated with paclitaxel-loaded microparticles were less viable than their prodigiosin-loaded counterparts. Among the treated cells, increasing the concentration of prodigiosin and paclitaxel in PLGA-CS-PEG microparticles resulted in decreased cell viability, as manifested in the lower normalized percentage Alamar blue reduction values. There was an initial decline in the viability of the treated cells after 6 h of exposure followed by a gradual rise in cell viability until 72 h. In the case of the paclitaxel-loaded PLGA-PEG-CS microparticles at 8 mg/mL, the viability continued to decrease after 6 h. There was an initial decline in the viability of the treated cells after 6 h of exposure followed by a gradual rise in cell viability until 72 h, except for the paclitaxel-loaded PLGA-PEG-CS microparticles at 8 mg/mL concentration, which continued to decline further. The initial decline in cell viability was probably due to the initial burst release of the drugs from the microparticles that shocked the cells, which were still in their lag growth phase and in their most fragile state.  
Figure 5: A graph of Gibbs free energy vs. temperature for PLGA-CS-PEG microspheres at different temperatures.  
Figure 6: (**a**) Percentage Alamar blue reduction for untreated MDA-MB-231 cells and MDA-MB-231 cells treated with nonloaded microspheres, PGS, PGS-loaded microspheres, PTX, and PTX-loaded microspheres at 6, 24, 48, and 72 h post treatment. Error bars represent the standard deviation for \(n=3\); * \(p<0.05\) (significantly different from untreated cells). (**b**) A graph of percentage cell growth inhibition vs. time for MDA-MB-231 cells treated with nonloaded microspheres, PGS, PGS-loaded microspheres, PTX, and PTX-loaded microspheres at 6, 24, 48 and 72 h post treatment. Error bars represent the standard deviation for \(n=3\); * \(p<0.05\); # \(p<0.05\) (significantly lower than the others).  
The data in Figure 6b show the effect of adding PLGA-CS-PEG microspheres encapsulating drugs to the cells inhibit MDA-MB-231 breast cancer cell growth after 6, 24, 48 and 72 h exposure when compared to the untreated MDA-MB-231 breast cancer cells. Percentage cell growth inhibition was used as a measure of the drug-induced cytotoxicity level. A higher percent inhibition value implies an elevated cytotoxicity level due to drug treatment. Again, the data show that at all durations, paclitaxel-loaded microparticles exhibited higher percent inhibition values than prodigiosin-loaded microparticles, meaning that cells exposed to the former were more cytotoxic than the latter. In addition, increasing the concentration of drugs in the microparticles resulted in higher cytotoxicity levels as manifested in the higher percent growth inhibition values. In effect, loading the microparticles with 8 mg/mL of paclitaxel was more effective in impeding the growth of MDA-MB-231 breast cancer cells, while prodigiosin at a concentration of 5 mg/mL was least effective.