## 3 Results and Discussion
### Drug Release Profile  
From the drug release data illustrated in Figure 8, it can be observed that the release of Met (a) is slightly higher than that of Ceph (b). This can be attributed to the relatively smaller molecular size of Met (C\({}_{6}\)H\({}_{9}\)N\({}_{3}\)O\({}_{3}\)) than Ceph (C\({}_{16}\)H\({}_{17}\)N\({}_{3}\)O\({}_{4}\)S), which enables Met to penetrate through the small pore of MOF-5 easily leading to a higher loading and release rate [49]. Figure 7: TGA plots of PCL, PCL-met@MOF-5 and PCL-ceph@MOF-5 compared, (a) and plots of PLGA, PLGA-met@MOF-5 and PLGA-ceph@MOF-5 (b). It is also evident from the data that across all six days of the study, PLGA-met@MOF-5 produced the release of lower concentrations than in met@MOF-5 alone, which comparatively releases drugs faster and in higher concentrations. This is assigned to the fact that the PLGA-met@MOF-5 composite will have to undergo the degradation of the PLGA polymer before the incorporated MOF-5 will also begin to break down for the release of the Met drug molecules [50]. In addition, as confirmed by the XRD patterns shown in Figure 1 above, the amorphous structure of met@MOF-5 results in the drug molecules being loosely held and not captured deep into the crystal lattice of the MOF-5, hence the release of the drugs in higher concentrations [31, 51]. Similar observations can be noted for PLGA-ceph@MOF-5, as it also provides releases of lower concentrations than releases from ceph@MOF-5 for the same reasons stated above. It can therefore be deduced that the drug-release rate from the loaded polymer composites as compared to the release rate from the loaded MOF-5 is slower, more gradual and more sustained over the six-day period of the study. It was also observed that the release from loaded PLGA-MOF composites was in relatively higher concentrations compared to PCL-MOF composites. For example, PLGA-met@MOF-5 drug release had a concentration of 0.025 mg mL\({}^{-1}\) compared to 0.02 mg mL\({}^{-1}\) for PCL- met@MOF-5, an observation similar to that of PLGA-ceph@MOF-5 compared with PCL-ceph@MOF-5. This observation is assigned to the fact that PCL belongs to the class of slow-degrading polymers [52] that take longer to degrade and enhance the release of the drug molecules loaded into the polymer matrix, resulting in the subsequent release of drugs in lower concentrations, especially under physiological conditions, which isotonic to the PBS release medium used in this study [53]. PLGA is an amorphous polymer, while PCL is a semi-crystalline polymer [51], and the morphologies are shown in Figure 3. The amorphous nature of PLGA is possibly responsible for the loosely held loaded MOF particles leading to quicker drug release than in PCL [54]. The hydrophobicity of PLGA may also contribute positively to the release in higher concentrations [54]. Earlier studies demonstrated the use of PCL-loaded composites for a rather long term prolonged drug delivery [54], while other studies reported the use of PLGA-loaded composites for a comparatively shorter term of release [26]. This work agrees with these previously reported studies, as the data suggest the slower release rate of drugs from the PCL-loaded composites compared to PLGA, and the concentrations from the release are significant enough to inhibit the growth of the various bacterial strains that were studied, as shown in the next Section 3.6. From the release studies, it can be inferred that the concentrations exceed the limit needed for the effective inhibition of clinically relevant, infection-causing pathogens. For example, the minimum inhibitory concentration (MIC) of cephalexin required to treat methicillin-sensitive _Staphylococcus aureus_ (MSSA) infections is 2 \(\mu\)g mL\({}^{-1}\)[55]. For Met,  
Figure 8: Release studies of drug-loaded MOFs and composites over 6 days for (**a**) met@MOF-5, PLGA@met@MOF-5 and PCL@met@MOF-5. (**b**) ceph@MOF-5, PLGA@ceph@MOF-5 and PCL@ceph@MOF-5.