Catechol-functionalized adhesive polymer nanoparticles for controlled local release of bone morphogenetic protein-2 from titanium surface

We report on a novel surface functionalization approach to equip the titanium (Ti) surfaces with osteogenic properties. A key feature of the approach is the treatment of the Ti surfaces with Ti-adhesive nanoparticles that can stably load and controllably release bone morphogenetic protein-2 (BMP-2). Ti-adhesive nano-particles were prepared by self-assembly of a catechol-functionalized poly(amino acid) diblock copolymer, catechol-poly(L- aspartic acid)-b-poly(L-phenylalanine) (Cat-PAsp-PPhe). The nanoparticles consist of Ti-adhesive peripheral catechol groups, anionic PAsp shells, and PPhe inner cores. Field-emission scanning electron microscopy (Fe-SEM) images showed that the Ti-adhesive nanoparticles could be uniformly immobilized on Ti surfaces. X-ray photoelectron spectroscopy (XPS) confirmed the successful anchoring of nanoparticles onto Ti surfaces. After surface immobilization of the nanoparticles, the static water contact angle of the Ti substrate decreased from 75.3° to 50.0° or 36.4°, depending on the surface nanoparticle. Fluorescence microscopic analysis showed that BMP-2 could be effectively incorporated onto the Ti surface with adhesive nanoparticles. BMP-2 was controllably released for up to 40 days. The Ti substrate functionalized with BMP-2-incorporated nanoparticles significantly promoted attachment, proliferation, spreading, and alkaline phosphatase (ALP) activity of human adipose-derived stem cell (hADSC). The catechol-functionalized adhesive nanoparticles may be applied to various medical devices to create surfaces for improved performance.