Organic montmorillonite produced an interlayer locking effect in a polymer scaffold to enhance interfacial bonding

Abstract

The interfacial bonding between an inorganic clay and an organic polymer is weak although clay is usually used as a reinforcement phase in polymers. In this study, montmorillonite (MMT) was organically modified with (3-aminopropyl)triethoxysilane (KH550) and incorporated into poly(ε-caprolactone) (PCL) to enhance the interfacial bonding in bone scaffolds. In detail, KH550 intercalated into the interlayer of MMT through cation exchange, and then one end of KH550 with NH₃⁺ was adsorbed onto the negatively charged surface of MMT while the other end with a long alkylammonium carbon chain extended outward in the opposite direction, stretching the interlayer spacing of MMT for the easy intercalation of PCL molecular chains. More importantly, the interfacial bonding between PCL and MMT was enhanced since Si–OH from KH550 hydrolysis formed siloxane linkages with –OH of MMT firstly, and then formed hydrogen bonding with CO of PCL. Consequently, the movement of PCL molecular chains was restricted in MMT galleries due to the interlayer locking effect. The results showed that the interlayer spacing of MMT after modifying was extended from 1.23 to 1.77 nm and homogeneous dispersion of MMT in the PCL matrix was obtained. Besides, the tensile strength of the PCL + 10% modified MMT scaffold increased to 3.46 times compared with the PCL scaffold. In addition, the scaffold fabricated via selective laser sintering possessed good biodegradability and cytocompatibility, which may be attributed to the fact that the presence of hydroxyl groups increased adsorbed water and the release of Ca and Si ions contributed to cell growth, respectively.