Facile Method to Create Poly(d,l-lactide) Composite Membranes with Sequential Chitin Whisker Layers for Tunable Strength and Cell Adhesion

To date, designing a perfect poly(d,l-lactide) (PDLLA) bone repair material still remains a major challenge. Inspired by the superior cell affinity, osteogenic activity, and mechanical properties of polysaccharide chitin whiskers, here, positively charged chitin whiskers (HCHW) and negatively charged maleated chitin whiskers (mCHW) are prepared for strengthening and biofunctionalizing the PDLLA membrane via a layer-by-layer (LBL) electrostatic self-assembly method. At a pH value of 4.3, the process of LBL electrostatic self-assembly between the HCHW and mCHW on the membranes is successfully performed, which can be directly proved by the cross-sectional morphology, light transmittance, surface composition, and topography of the membranes. Especially, polydopamine, as an intermediate layer, can greatly enhance the stability and adhesion of the first chitin whisker layer on the PDLLA substrate. Compared with the PDLLA membrane, the mechanical properties of self-assembly membranes are highly enhanced and controllable by adjusting the number of self-assembly whisker layers. Furthermore, in vitro biological evaluations indicate that the HCHW-assembled surface has a higher cell affinity than that of the mCHW-assembled one, which may be attributed to different protein adsorption. Meanwhile, interesting directional cell migration behavior is observed on the HCHW-assembled surface, which can be explained by the guiding effect of surface ordered topology and collective cell migration. These findings provide a new strategy for designing bioactive PDLLA composites with superior and tunable mechanical properties for bone regeneration materials.