El Modelo Académico del ITCR: del papel a las aulas

After we have demonstrated that the incorporations of different polymers change the structures of CSH by the analysis of XANES, especially that of the CSH/PVA

composites, it would be necessary to investigate whether or not these interactions may influence the drug loading capacities (DLCs) and drug release kinetics. Hence, IBU loading capacities results into different CSH/polymer composites are shown in Figure 7- 11. Compared with the CSH nanosheets alone, all the DLCs of IBU decrease to some extent after the formation of CSH/polymer composites. This is due to the interactions between different polymers and CSH nanosheets: parts of the active sites (Ca-OH and Si- OH groups) interact with different polymers molecules, leading to the reduction of the number of active sites for the IBU molecules’ attachment. It should be noted that the IBU DLCs of CSH/mPEG-PLGA decrease significantly compared with that of CSH

the other is the steric and entropic effects, which is one of the key factors that prevents the IBU molecules’ attachment on the surface of CSH composites.

Figure 7-11 Drug loading capacities (DLCs) of different CSH/polymer composites (the DLC of CSH nanosheets for comparison).

Figure 7-12 shows the IBU drug release profiles of the IBU-CSH/polymer composites drug delivery systems in the PBS medium. In Chapter 6, it is shown that the CSH drug carriers alone do not provide good ability of controlled drug release: there was a burst drug release effect at the early stage; about 97-98 % of loaded IBU were released in the first several hours [36], and so are the situations of CSH/PDDA and CSH/mPEG-PLGA in this study. However, compared with the other two composites, the CSH/PVA-IBU system shows a relative controlled drug release kinetics, which is largely due to the intercalation of PVA into the CSH structures, and the combined effects of PVA and IBU on the structure changes of Ca ions which slowed down the IBU release from the

Figure 7-12 Drug release profiles of different CSH/polymer composites.

7.4 Conclusions

In this chapter, we have shown the structural changes of CSH nanosheets upon the formation of different polymers composites and the incorporations of IBU molecules by XANES spectra analysis as summarized below.

 PVA molecules can intercalate into to the interlayers of CSH structures and as a result modify the local structure of interlayer Ca ions and silicate tetrahedra on the surface; while mPEG-PLGA and PDDA can only adsorb on the surface of CSH nanosheets leading to the distortion the silicate tetrahedra chains on the surface because of steric effects.

 The IBU loading on these composites further changes the local structure of Ca and silicate simultaneously by the interactions between the carboxylic acid groups of IBU and the Ca-OH and Si-OH groups of CSH, which has been extensively studied in previous chapters already.

 However, the CSH/polymer composites do not enhance the drug loading capacities of IBU because the active sites for drug molecules’ attachment have been reduced by the interaction CSH with polymers.

 Compared with the other two composite systems, the CSH/PVA composite has a relatively better controlled drug release profile (delayed release). In our opinions, this may be due to the PVA intercalation into CSH structures and has a combined effect with IBU on the structure of interlayer Ca ions after drug loading.

Finally, we have demonstrated that XANES is a sensitive tool to track these effects from different elemental point of view, and opens up future possibilities for the study of drug delivery and drug release of bioceramics and their composites.

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Chapter 8

8

Summary, Conclusions, and Future Work