Improvement Of Early Osseointegration Of Strontium-substituted Biomimetic Implant Surfaces

In orthodontic treatment, anchorage control is essential for success. Orthodonticmini-implants for absolute anchorage are more widely used because of their ease ofinsertion and removal; wide range of insertion sites, low cost, lower patient morbidity anddiscomfort, and early/immediate loading. However, compared with implants, the failurerates of miniscrews is much higher.Studies are indicated that various surface characteristics, such as surface composition,roughness, topography, and energy, play a major role during the initial phases of boneintegration to the mini-implants. Bone tissues are composed of nanostructures includingnon-collageneous organic proteins, fbrillar collagen and hydroxyapatite crystals,microstructures including lamellae, osteons and Haversian systems, as well asmacrostructures such as cancellous and cortical bones. From the biomimetic viewpoint, ahierarchical structure composed of micro-and nanoscale components may provide a moresuitable surface topography for cell functions as it can better mimic the structure of thenatural extracellular matrix. Our previous study also evaluated the effects of the hierarchical hybrid micro/nanorough surface of the implant on osseointegration.However, one of the main concerns related to the existing hybrid micro/nanoscalestructures is the poor mechanical adhesion strengths; few studies about the effects ofhybrid micro/nanoscale structures with high mechanical adhesion strengths have beenreported.Magnetron sputtering methods are widely used in industrial products because thehigh quality films; high density, high adhesion, high hardness, etc., can be obtained at lowsubstrate temperature with good uniformity of the film thickness. Moreover, it waspossible to control the morphology of surface nanostructures via the adjustment of RFpower and growth temperatures. In addition, choosing a proper sputtering target couldmake it possible to bring new bioactive elements like Sr onto the surface.The aim of the present study was to form a hierarchical micro/nanotextured surfacecould improve mini-implant early osseointegration after implantation. TheStrontium-substituted biomimetic hierarchical micro/nano-textured surface topographieswas deposited by RF magnetron sputtering onto HF treated pure Ti disks andmini-implants using a SrTiO3target. The characterization of the surface topography,mechanical properties and biocompatibility of the surface topographies was discussed.Part1: Production of biomimetic hierarchical micro/nano-texturedsurface topographiesMethods: The characterization of the surface topographies were carried out usingscanning electron microscope(SEM), atomic force microscopy(AFM), Energy DispersiveX-ray Spectroscopy(EDS),Results: The SEM observation showed that the strontium-substituted coatingpresented a micro/nanorough structure. The EDS results showed that the content of Sr was1.2%.Conclusion: Strontium-substituted biomimetic hierarchical micro/nano-texturedsurface topographies could be produced. Part2: Bone Mesenchymal Stem Cells(BMSCs）characteristics onDifferent surfacesMethods: Cultured4th generation BMSCs were seeded onto the surface, SEMobservation of cell morphology and the adhesion of BMSCs on the surface of thematerialsResults: The cell morphology of the Strontium-substituted biomimetic hierarchicalmicro/nano-textured surface was significantly better than the two control groups.Adhesion and proliferation of BMSCs in the treatment group were significantly higherthan in the two control groups.Conclusion: The Strontium-substituted biomimetic hierarchical micro/nano-texturedsurface could promote the adhesion of BMSCs proliferation.Part3: Production of biomimetic hierarchical micro/nano-texturedsurface topographies onto mini-implantsMethods: Strontium-substituted biomimetic surface titanium implants weremanufactured by radio-frequency magnetron sputtering as the experimental group;machined-surface implants as the control group. The morphology and the component ofthe coatings were examined by scanning electron microscope (SEM) and energydispersive X-ray spectroscopy (EDS).Results: The SEM observation showed that the strontium-substituted coatingpresented a micro/nanorough structure. The EDS results showed that the content of Sr was1.2%.Conclusion: Strontium-substituted biomimetic hierarchical micro/nano-texturedsurface topographies could be produced onto mini-implants.Part4: Improvement of early osseointegration of Strontium-substitutedbiomimetic hierarchical micro/nano-textured surface topographiesMethods: All implants were implanted into the distal femurs of30SD rats randomlyusing dual fluorochrome sequential labeling.4weeks after the surgery, the morphology was evaluated by histological examination and light microscopy observation. Themaximal pull-out force of the specimens was measured by universal material testingmachine.Results: The experimental group exhibited stronger osteogenic activity at the earlystage of bone healing period in histological examination and light microscopy observation.There was significant difference between the two groups in the BIC and MAR value andthe Fmax.(P＜0.05)Conclusion: Modification with strontium-substituted biomimetic surface couldpromote mini-implants osseointegration in early stage of implantation.