Abstract
Surface modification of titanium implants is used to enhance osseointegration. The study objective was to evaluate five modified titanium surfaces in terms of cytocompatibility and pro-osteogenic/pro-angiogenic properties for human mesenchymal stromal cells: amorphous microporous silica (AMS), bone morphogenetic protein-2 immobilized on AMS (AMS + BMP), bio-active glass (BAG) and two titanium coatings with different porosity (T1; T2). Four surfaces served as controls: uncoated Ti (Ti), Ti functionalized with BMP-2 (Ti + BMP), Ti surface with a thickened titanium oxide layer (TiO2) and a tissue culture polystyrene surface (TCPS). The proliferation of eGFP-fLuc (enhanced green fluorescence protein-firefly luciferase) transfected cells was tracked non-invasively by fluorescence microscopy and bio-luminescence imaging. The implant surface-mediated effects on cell differentiation potential was tracked by determination of osteogenic and angiogenic parameters [alkaline phosphatase (ALP); osteocalcin (OC); osteoprotegerin (OPG); vascular endothelial growth factor-A (VEGF-A)]. Unrestrained cell proliferation was observed on (un)functionalized Ti and AMS surfaces, whereas BAG and porous titanium coatings T1 and T2 did not support cell proliferation. An important pro-osteogenic and pro-angiogenic potential of the AMS + BMP surface was observed. In contrast, coating the Ti surface with BMP did not affect the osteogenic differentiation of the progenitor cells. A significantly slower BMP-2 release from AMS compared to Ti supports these findings. In the unfunctionalized state, Ti was found to be superior to AMS in terms of OPG and VEGF-A production. AMS is suggested to be a promising implant coating material for bioactive agents delivery.
Highlights
Continuous progress in understanding the concept of osseointegration has lead clinicians to achieve high success rates in implant therapy [1,2,3]
Four surfaces served as controls: uncoated titanium surface (Ti) surface (Ti), Ti surface with adsorbed bone morphogenetic protein 2 (BMP-2) (Ti + BMP), Ti surface with a thickened titanium oxide layer (TiO2) and tissue culture polystyrene surface (TCPS)
T1 and T2, on the other hand, had a significantly higher contact angle (CA) compared to the control Ti surface
Summary
Continuous progress in understanding the concept of osseointegration has lead clinicians to achieve high success rates in implant therapy [1,2,3]. In order to achieve successful implant osseointegration in those situations, increasing interest has emerged to find new ways to improve the quality and kinetics of osseointegration, by means of biomechanical interventions and implant macro- and micro-design optimization, amongst others [7,8,9]. Implant surface modifications stimulating the recruitment of premature osteogenic cells may lead to an enhanced peri-implant bone formation and implant osseointegration [10]. It is, difficult to predict cell behavior, even on a surface of well-known properties [11]. It is desirable to apply implant surface modification techniques that evoke cell stimulation towards bone regeneration
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