Understanding instability and rupture of poly(alkyl-2-cyanoacrylate) capsules

Introduction: Poly(alkyl-2-cyanoacrylates) (PACAs) are degradable biomaterials that are clinically applied as surgical glue and studied as a matrix for particulate drug carriers such as nanoparticles or micro/nanocapsules. The stability of capsule walls is essential to avoid leakage of encapsulated compounds. Methods: PACA capsules and (co)polymer films were prepared and characterization of their morphologies and thermal properties was performed. Results: Thin-walled capsules that allow for a large internal volume to carry the payload were instable due to the high brittleness of PACA. Strategies to reduce the glass transition temperature (T(g)) from values as high as similar to 120 degrees C included plasticization by solvents and copolymerization approaches. By using the latter, the T(g) of commonly used n-butylcyanoacrylate could be reduced up to 30 K, following predictions of mixed-system glass transition temperatures obtained, for example, by the Fox equation. Conclusions: Thin-walled PACA capsules may allow for large payloads in the field of drug delivery and beyond, but require modifications of the PACA to improve capsule stability by more elastic capsule walls.