Biomimetic ECM Based On RGD-grafted And Bmp-loaded Polyelectrolyte Multilayer Films On Titanium Surfaces

Titanium and its alloy are widely used biomedical metals. However, they are lack of bioactivity. Immobilizing biomolecules, such as polysaccharides, cell adhesive peptides and growth factors, on Ti surfaces is an effective method to enhance bioactivity of Ti surfaces, In this study, layer by layer (LbL) self-assembling was used to build RGD grafted and BMP-2loaded polyelectrolyte multilayers (PEM) on titanium surface, which has biomimetic structures and functions of extracellular matrix (ECM).. This study includes the following three parts:In the first part, oxidized sodium alginate/chitosan (OALg/Chi) crosslinked multilayers with good degradation stability were prepared on Ti surfaces by LbL self-assembling. First, the substrates was treated with dopamine to obtain amino-rich surfaces. Then, sodium alginate was oxidized into multi-aldehyde sodium alginate (O-Alg) by sodium periodate, and negatively charged O-Alg and positively charged chitosan (Chi) was deposited on the pretreated Ti surfaces through LbL self-assembling to form OALg/Chi multilayers. O-Alg and Chi layers were bound through electrostatic attraction and covalent crosslink between the aldehyde group of O-Alg and amino group of Chi. The degradability of crosslinked OAlg/Chi PEM was examined in lysozyme solution, and the results shows that crosslinked OAlg/Chi PEM has better stability than Alg/Chi. Bone marrow stem cells(BMSCs) were cultured on the PEM to evaluate the biological performance of the PEM, and the results demonstrated that the PEM favors cell growth.In the second part,, RGD grafted OAlg/Chi PEM was prepared. First, RGD was grafted onto OAlg through covalent bond between the amino group of RGD sequence (including GRGDS and RGD) and the aldehyde group of OAlg. Then, RGD-grafted OAlg and Chi was self-assembled to prepare PEM by the same method in the first part. BMSCs was cultured on the RGD-grafted OA1g/Chi PEM, and the results show that the RGD grafting significantly promotes cell adhesion and proliferation. GRGDS-grafted PEM shows the better cell adhesive performance than RGD-grafted PEM.Finally, RGD grafted and BMP embeded OA1g/Chi crosslinked PEM were prepared as biomimetic ECM. Firstly, BMP-2was encapsulated in BSA/Chi nanoparticles (NPs). Then, NPs, GRGDS-OAlg and Chi were self-assembled on Ti surfaces. Covalent bond between the amino of NP and aldehyde of OAlg realize the immobilizing of BMP while protecting its activity. Release of growth factors was systematically controlled by the location of Nps in LbL films, hydrolysis of PEM and degradation of Nps. The release of the model protein ALP shows that protein was sustained released from the self-assembled particles/films structures. The results of BMSC culture confirmed that the GRGDS grafted and BMP-2loaded self-assembly PEM not only promote cell adhesion but also induce BMSCs osteogenetic differentiation.