Characterization of internal structure, polymer erosion and drug release mechanisms of biodegradable poly(ester anhydride)s by X-ray microtomography.

Surface-eroding biodegradable polymers can provide many advantages in drug delivery, such as controllable and zero-order drug release. Photocrosslinkable poly(ester anhydride)s are a recently developed family of surface-eroding polymers with readily modifiable oligomer chemistry allowing tailoring of polymer properties. For example, in vivo release rate of peptide from photocrosslinked poly(ester anhydride)s can be controlled by oligomer hydrophobicity. In this study, X-ray microtomography (micro-CT) was used to gain a deeper understanding on internal structure, polymer erosion and drug release mechanisms of photocrosslinked poly(ester anhydride)s. Micro-CT is non-destructive and able to provide quantitative and qualitative information on the 3D structure of the sample in micrometer resolution. Photocrosslinked poly(ester anhydride) samples with varying drug loading degrees (propranolol HCl 0%, 10% and 60% w/w) and hydrophobicity (with and without 12-carbon alkenyl chain) were prepared. The samples, both freshly prepared and exposed to buffer solution for varying durations were characterized by micro-CT. The results showed that drug release from photocrosslinked poly(ester anhydride)s was primarily controlled by the surface erosion. However, drug diffusion had also a significant role in drug release from less hydrophobic samples with very high (60% w/w) drug loading degrees. In conclusion, micro-CT is a valuable tool in the characterization of surface-eroding polymers.