Microrough implant surface topographies increase osteogenesis by reducing osteoclast formation and activity

Abstract

Titanium implant surfaces with rough microtopographies exhibit increased pullout strength in vivo suggesting increased bone-to-implant contact. This is supported by in vitro studies showing that as surface microroughness increases, osteoblast proliferation decreases whereas differentiation increases. Differentiation is further enhanced on microrough surfaces by factors stimulating osteogenesis including 1alpha,25(OH)2D3. Levels of PGE2 and TGF-beta1 are increased in cultures grown on rough microtopographies; this surface effect is enhanced synergistically by 1alpha,25(OH)2D3-treatment. PGE2 and TGF-beta1 regulate osteoclasts as well as osteoblasts, suggesting that surface microtopography may modulate release of other factors from osteoblasts that regulate osteoclasts. To test this hypothesis, we examined the effects of substrate microarchitecture on production of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL), which have been identified as a key regulatory system of bone remodeling. We also examined the production of 1alpha,25(OH)2D3, which regulates osteoblast differentiation and osteoclastogenesis. MG63 osteoblast-like cells were grown on either tissue culture plastic or titanium disks of different surface microtopographies: PT (Ra < 0.2 microm), SLA (Ra = 4 microm), and TPS (Ra = 5 microm). At confluence, cultures were treated for 24 h with 0, 10(-8) M or 10(-7) M 1alpha,25(OH)2D3. RANKL and OPG were determined at the transcriptional level by RT-PCR and real time PCR and soluble RANKL, OPG and 1alpha,25(OH)2D3 in the conditioned media were measured using immunoassay kits. Cell number was reduced on SLA and TPS surfaces and 1alpha,25(OH)2D3 caused further decreases. OPG mRNA levels increased on rougher surfaces and 1alpha,25(OH)2D3 treatment caused a further synergistic increase. While the cells expressed RANKL mRNA, levels were low and independent of surface microtopography. OPG protein was greater when cells were grown on SLA and TPS. 1alpha,25(OH)2D3 increased OPG by 50% on the smooth Ti surface but on SLA, 10(-8) M 1alpha,25(OH)2D3 caused a 100% increase and 10(-7) M 1alpha,25(OH)2D3 increased OPG by 200%. On TPS 10(-7) M 1alpha,25(OH)2D3 increased OPG 350%. Soluble RANKL was not detected in the conditioned media of any of the cultures. 1alpha,25(OH)2D3 was produced endogenously and levels were positively correlated with surface roughness. Thus, on surfaces with rough microtopographies, osteoblasts secrete factors that enhance osteoblast differentiation while decreasing osteoclast formation and activity.

Osteocytes as mechanosensors in the inhibition of bone resorption due to mechanical loading

“…Ikeda et al (14) found RANKL3 mRNA in ST2 and MC3T3-E1 cells. Nevertheless, many studies suggest bone cells either do not release or release very limited levels of soluble RANKL (9,22,33,45,60). In our study, we observed that MLO-Y4 cells released sRANKL into the media, and this was downregulated with mechanical stimulation.…”

Pulsed electromagnetic fields enhance BMP‐2 dependent osteoblastic differentiation of human mesenchymal stem cells

“…38 For example, osteoblasts exhibit greater response to BMP-2 when cultured on surfaces with micron-scale roughness. 39 In addition, they produce higher levels of growth factors and cytokines that regulate osteogenesis including PGE2, which is required for their differentiation, 40,41 and osteoprotegerin, 42 which can modulate osteoclastic bone resorption. 43 Similarly, osteoblastic differentiation of bone marrow stromal cells and fetal rat calvarial cells is also surface dependent, [44][45][46] but the role of surface properties on differentiation of isolated human MSCs was not previously examined.…”

Regulation of implant surface cell adhesion: characterization and quantification of S‐phase primary osteoblast adhesions on biomimetic nanoscale substrates

“…This has been demonstrated to occur on nanofabricated substrates, whereby ordered nanotopography can induce a state of ''superhydrophobicity'' on a material surface. 3 This, in turn, results in decreased protein adsorption, 6,33 as well as conformational changes in integrin specific ECM protein binding domains. 34 A third, and interesting possibility, is that of increased cellular motility at the substrate surface, whereby HOBs perceive the local topography as unfavorable for adhesion, leading to protein production and assembly via intercellular signaling cascades, resulting in contact guidance induced mobility.…”

“…Successful integration of an orthopedic prosthesis and bone must be associated with osseointegration and implant fixation, an ideal that can be approached via modification of the bone/ implant interface by either chemical or topographical means. [1][2][3] In vitro studies have shown that osteoblast response is influenced by substrate morphology, 4 and that extracellular matrix (ECM) synthesis and osteoblast differentiation are influenced by substrate microtopography, 5 factors that have consistently been shown to affect osteoblast infiltration and adhesion in vivo when applied to an orthopedic device. 6 Accordingly, nanogrooves, nanopits, and nanoislands have been shown to affect contact guidance in vitro and directly influence cell adhesion to a degree related to feature dimension, cell type, and cell density.…”