Synthesis of biodegradable poly(ε-caprolactone)-organosiloxane hybrid with carboxylate groups

Biodegradable poly(ε-caprolactone)-organosiloxane hybrid with carboxylate groups was newly synthesized by a sol-gel method with the capacity to conjugate cell adhesion ligands for the potential applications as a bone tissue engineering scaffold material. An intermediate hybrid contained positively charged amine groups was synthesized by end-capping α,ω-hydroxyl poly(ε-caprolactone) with (3-isocyanatopropyl)triethoxysilane and a subsequent sol-gel reaction with (3-aminopropyl)triethoxysilane. This resulted in a new hybrid composed of biodegradable organic poly(ε-caprolactone) segments connected by inorganic siloxane linkages containing positively charged amine groups. The successive succinlylation of amine groups created amide bonds and converted the cationic sites of succinic anhydride into negatively charged carboxylate groups. New formations of amine and carboxylate groups could be directly and indirectly confirmed using Fourier transformed infrared spectrometry, zeta potentials, and atomic force microscopy. Biodegradability of hybrid with carboxylate groups was also examined by weight loss in phosphate buffered saline, and it was about 14 wt % after 8 weeks. Conjugating capacity of a cell adhesion ligand was examined by comparing the relative fluorescent intensities of covalently and noncovalently immobilized synthetic GGGGRGDASSK-FITC oligopeptides onto the carboxylated groups of the hybrid using confocal laser scanning microscopy; the relative fluorescent intensity of covalently conjugated RGD peptide was about three times higher than that of noncovalently coated RGD peptide. The hybrid covalently conjugated by GGGGRGDASSK oligopeptides improved proliferation and differentiation activities of preosteoblastic MC3T3-E1 cells. The results suggest that this hybrid possesses an encouraging potential to be used as a bone tissue engineering scaffold material due to its biodegradability and high capacity for conjugating cell adhesion ligands.