Efforts to improve bone response to biomaterials have focused on ligands that bind ␣5␤1 integrins. However, antibodies to ␣5␤1 reduce osteoblast proliferation but do not affect differentiation when cells are grown on titanium (Ti). ␤1-silencing blocks the differentiation stimulus of Ti microtopography, suggesting that other ␤1 partners are important. Stably ␣2-silenced MG63 human osteoblast-like cells were used to test whether ␣2␤1 specifically mediates osteoblast response to Ti surface micron-scale structure and energy. WT and ␣2-silenced MG63 cells were cultured on tissue culture polystyrene (TCPS) and Ti disks with different surface microtopographies: machined pretreatment (PT) surfaces [mean peak to valley roughness (R a) < 0.02 m], PT surfaces that were grit-blasted and acid-etched (SLA; R a ‫؍‬ 4 m), and SLA with high surface energy (modSLA). Alkaline phosphatase (ALP), ␣2 and ␤1 mRNA, but not ␣5, ␣v, ␤3, type-I collagen, or osteocalcin, increased on SLA and modSLA at 6 days. ␣2 increased at 8 days on TCPS and PT, but remained unchanged on SLA and modSLA. ␣2-protein was reduced 70% in ␣2-siRNA cells, whereas ␣5-mRNA and protein were unaffected. ␣2-knockdown blocked surface-dependent increases in ␤1 and osteocalcin and decreases in cell number and increases in ALP and local factors typical of MG63 cells grown on SLA and modSLA [e.g., prostaglandin E 2, osteoprotegerin, latent and active TGF-␤1, and stimulatory effects of 1␣,25(OH)2D3 on these parameters]. This finding indicates that ␣2␤1 signaling is required for osteoblastic differentiation caused by Ti microstructure and surface energy, suggesting that conclusions based on cell behavior on TCPS are not predictive of behavior on other substrates or the mechanisms involved.␣-2 integrin siRNA ͉ MG63 human osteoblasts ͉ titanium surface roughness T itanium (Ti) and Ti alloys are commonly used as biomaterials because their surface properties provide a biocompatible interface with peri-implant tissues. Strategies for modifying the nature of this interface frequently involve changes to the surface, thereby affecting protein adsorption, cell-substrate interactions, and tissue development (1). A common modification has been to create micron-scale and submicron scale roughness. Preclinical and clinical studies (2-12) show that these surfaces support greater bone-to-implant contact than smooth surfaces.How surface microstructure promotes an osteogenic response is an important question, because bone-forming osteoblasts preferentially colonize bone surfaces that have been preconditioned by bone-resorbing osteoclasts (13), resulting in complex micron-scale and submicron-scale morphologies (14). In vitro experiments using model surfaces indicate that migration, growth, and colony morphology of rat bone marrow cells (15) and osteoblasts (16-18) are sensitive to microstructure. These observations suggest that structural elements can modulate the spatial organization of cells and their ECM.The topography of osteoclast resorption pits in bone can be modeled by using Ti subs...

Increased micrometer-scale surface roughness increases osteoblast differentiation and local factor production in vitro, which may contribute to increased bone formation and osteointegration in vivo. There was a correlation between in vitro and in vivo observations, indicating that the use of screws with rough surfaces will result in better bone-implant contact and implant stability.

Background Biological barriers are commonly used to treat alveolar bone defects and guide tissue regeneration. Understanding the biological and mechanical properties of the available membranes is crucial for selecting the one that is optimal for enhancing clinical outcomes. Purpose To evaluate the mechanical behavior of three different collagen membranes to increasing tensile force in dry and wet conditions. Materials and Methods Three commercially collagen membranes were selected for analysis: Bio-Gide® (Geistlich Biomaterials, Baden-Baden, Germany), Remaix™ (RX; Matricel GmbH, Herzogenrath, Germany), and Ossix Plus® (Datum Dental Biotech, Lod, Israel). Increasing tensile forces were applied on 10 dry and wet membranes of standard size via a loading machine. Force and extension values were acquired up to maximum load before failure, and maximum stress, maximum extension, and amount of energy needed for membrane tearing were analyzed. Membranes' densities were also calculated. Results The Remaix membrane exhibited the highest values of maximum load tensile strength, maximum extension, and maximum energy required for membrane tearing, followed by Bio-Gide. Ossix Plus had the lowest scores in all these parameters. Dry membranes had the highest scores for all parameters except extension. Membrane density was directly and significantly correlated with all tested parameters. Conclusions The study was undertaken to provide clinicians with data upon which to base the selection of collagen membranes in order to achieve optimal clinical results. It emerged that the mechanical properties of dry and wet collagen membranes were significantly different from one another. Among the 3 tested membranes, Remaix exhibited higher performance results in all the mechanical tests. Collagen membrane density seems to have a significant influence upon mechanical resistance. These findings may also guide manufacturers in improving the quality of their product.

Osteoblasts are attachment-dependent cells that interact with their surface through integrin-mediated mechanisms. Their differentiation is regulated by 1,25-dihydroxyvitamin D3 [1alpha,25(OH)(2)D(3)] and is affected by substrate chemistry and microtopography, suggesting that 1alpha,25(OH)(2)D(3) may regulate integrin expression in a surface-specific manner. To test this hypothesis, osteoblast-like human MG63 cells were grown on tissue culture plastic and on grit-blasted and acid-etched titanium disks with a complex microtopography to induce osteoblast differentiation. Expression of alpha(2), alpha(5), alpha(v), beta(1), and beta(3) integrins were quantified by real-time polymerase chain reaction (PCR) as a function of time in culture and treatment with 1alpha,25(OH)(2)D(3). Results were correlated with expression of osteocalcin, a marker of a differentiated osteoblast. Osteocalcin mRNA increased with time and 1alpha,25(OH)(2)D(3) treatment and these changes were greater in cultures on the titanium disks. Integrin expression varied with time in culture and this was also surface dependent. At each time point, beta(1) and alpha(2) mRNAs were greater on titanium than on plastic, whereas alpha(5) expression was reduced and alpha(v),beta(3) expression was unaffected. 1alpha,25(OH)(2)D(3) increased beta(1) mRNA on both surfaces at all time points, but it increased alpha(2) expression only in 8-d cultures. 1alpha,25(OH)(2)D(3) caused reduced alpha(5) expression only in cultures grown on plastic for 8 d, and had no effect on either alpha(v) or beta(3) expression regardless of surface. These results show that integrin expression in human osteoblast-like cells is differentially modulated by 1alpha,25(OH)(2)D(3) in a time-dependent manner that is sensitive to the surface on which the cells are grown.

Rat costochondral growth plate chondrocytes exhibit sex-specific and cell maturation dependent responses to testosterone. Only male cells respond to testosterone, although testosterone receptors are present in both male and female cells, suggesting other mechanisms are involved. We examined the hypothesis that the sex-specific response of rat costochondral cartilage cells to testosterone requires further metabolism of the hormone to dihydrotestosterone (DHT). Resting zone (RC) and growth zone (GC, prehypertrophic and upper hypertrophic zones) chondrocytes from male and female Sabra strain rats exhibited sex-specific responses to testosterone and DHT: only male cells were responsive. Testosterone and DHT treatment for 24 h caused a comparable dose-dependent increase in [3H]-thymidine incorporation in quiescent preconfluent cultures of male GC cells, and a comparable increase in alkaline phosphatase specific activity in confluent cultures. RC cells responded in a differential manner to testosterone and DHT. Testosterone decreased DNA synthesis in male RC cells but DHT had no effect and alkaline phosphatase specific activity of male RC cells was unaffected by either hormone. Inhibition of steroid 5alpha-reductase activity with finasteride (1, 5, or 10 microg/ml), reduced the response of male GC cells to testosterone in a dose-dependent manner, indicating that metabolism to DHT was required. RT-PCR showed that both male and female cells expressed mRNAs for steroid 5alpha-reductase type 1 but lacked mRNAs for the type 2 form of the enzyme. Male cells also exhibited 5alpha-reductase activity but activity of this enzyme was undetectable in female cells. These observations show that sex-specific responses of rat growth zone chondrocytes to testosterone requires the further metabolism of the hormone to DHT and that the effect of DHT in the male growth plate is maturation-state dependent. Failure of female chondrocytes to respond to testosterone may reflect differences in testosterone metabolism, since these cells possess greater ability to aromatize the hormone to estradiol.