Chitosan scaffolds incorporating lysozyme into CaP coatings produced by a biomimetic route : a novel concept for tissue engineering combining a self-regulated degradation system with in situ pore formation

Abstract

This study describes an innovative self-regulated degrading material with gradual in situ pore formation ability for bone tissue engineering applications. This approach is based on the incorporation of the lysozyme enzyme into calcium phosphate (CaP) coatings, prepared on the surface of chitosan scaffolds by means of a biomimetic coating technique with the aim of controlling their degradation rate and subsequent formation of pores. However, because lysozyme has antibacterial properties, these coatings may act as a carrier for its sustained release, preventing infection upon implantation. In order to prove the concept of in situ pore formation, the coated scaffolds (with and without lysozyme) were incubated in two different solutions at different pH to simulate normal physiological conditions (pH 7.4) and inflammatory response (pH 5). The weight loss and morphology of the scaffolds was monitored over time. At pH 7.4, the scaffolds remained more stable than at pH 5. The scaffolds incubated at pH 5 showed a rapid decrease in their initial weight, and scanning electron microscopy imaging revealed the formation of a highly porous structure. Furthermore, evaluation of the activity of the incorporated lysozyme revealed that the enzyme was able to hydrolyse the peptidoglycan of the bacteria cell walls (as detected by the decrease in optical density with time), indicating that the enzyme remained active after being incorporated into the CaP coating.This work was supported by the European NoE EXPERTISSUES (NMP3-CT-2004-500283), the European STREP HIPPOCRATES (NMP3-CT-2003-505758), the Portuguese Foundation for Science and Technology (FCT) through POCTI and/or FEDER programmes