No abstract

Objective Functionalizing surfaces with specific peptides may aid osteointegration of orthopedic implants by favoring attachment of osteoprogenitor cells and promoting osteoblastic differentiation. This study addressed the hypothesis that implant surfaces functionalized with peptides targeting multiple ligands will enhance osteoblast attachment and/or differentiation. To test this hypothesis, we used titanium (Ti) surfaces coated with poly-l-lysine-grafted polyethylene glycol (PLL-g-PEG) and functionalized with two peptides found in extracellular matrix proteins, arginine–glycine–aspartic acid (RGD) and lysine–arginine–serine–arginine (KRSR), which have been shown to increase osteoblast attachment. KSSR, which does not promote osteoblast attachment, was used as a control. Materials and methods Sandblasted acid-etched titanium surfaces were coated with PLL-g-PEG functionalized with varying combinations of RGD and KRSR, as well as KSSR. Effects of these surfaces on osteoblasts were assessed by measuring cell number, alkaline phosphatase-specific activity, and levels of osteocalcin, transforming growth factor beta-1 (TGF-β1), and PGE2. Results RGD increased cell number, but decreased markers for osteoblast differentiation. KRSR alone had no effect on cell number, but decreased levels of TGF-β1 and PGE2. KRSR and RGD/KRSR coatings inhibited osteoblast differentiation vs. PLL-g-PEG. KSSR decreased cell number and increased osteoblast differentiation, indicated by increased levels of osteocalcin and PGE2. Conclusions The RGD and KRSR functionalized surfaces supported attachment but did not enhance osteoblast differentiation, whereas KSSR increased differentiation. RGD decreased this effect, suggesting that multifunctional peptide surfaces can be designed that improve peri-implant healing by optimizing attachment and proliferation as well as differentiation of osteoblasts, but peptide combination, dose and presentation are critical variables.

Surface microroughness increases osteoblast differentiation and enhances responses of osteoblasts to 1,25-dihydroxyvitamin D 3 [1α,25(OH) 2 D 3 ]. β 1 integrin expression is increased in osteoblasts grown on Ti substrates with rough microarchitecture, and it is regulated by 1α,25(OH) 2 D 3 in a surface-dependent manner, suggesting that it has a role in mediating osteoblast response. Here, we silenced β 1 expression in MG63 human osteoblast-like cells using small interfering RNA (siRNA) and examined the responses of the β 1 -silenced osteoblasts to surface microtopography and 1α,25 (OH) 2 D 3 . MG63 cells were also treated with two different monoclonal antibodies to human β 1 to block ligand binding. β 1 -silenced MG63 cells grown on a tissue culture plastic had reduced alkaline phosphatase activity and levels of osteocalcin, transforming growth factor β1, prostaglandin E 2 , and osteoprotegerin in comparison with control cells. Moreover, β 1 -silencing inhibited the effects of surface roughness on these parameters and partially inhibited effects of 1α,25(OH) 2 D 3 . Anti β 1 antibody AIIB2 had no significant effect on cell number and osteocalcin, but decreased alkaline phosphatase; MAB2253Z decreased cell number and alkaline phosphatase and increased osteocalcin in a dose-dependent manner. Effects of 1α,25(OH) 2 D 3 on cell number and alkaline phosphatase were reduced and effects on osteocalcin were increased. These findings indicate that β 1 plays a major and complex role in osteoblastic differentiation modulated by either surface microarchitecture or 1α,25 (OH) 2 D 3 . The results also show that β 1 mediates, in part, the synergistic effects of surface roughness and 1α,25(OH) 2 D 3 .

We have developed a layered hydroxyapatite/diamondlike carbon/functionally gradient diamondlike carbon-silver/titanium carbide/titanium carbonitride/titanium nitride composite film using pulsed laser deposition. A diamondlike carbon interlayer between a hydroxyapatite coating and the Ti-6Al-4V alloy can serve several purposes, including preventing corrosion of Ti-6Al-4V alloy, overcoming poor adhesion between the hydroxyapatite coating and the titanium oxide surface, and reducing inflammation at the implant/tissue interface. Titanium nitride, titanium carbonitride (TiC x N y ), titanium carbide and functionally gradient diamondlike carbon-silver layers were used to improve the adhesion of diamondlike carbon films to Ti-6Al-4V alloy. We envision several potential medical applications for these multilayer materials, including use in orthopedic and dental devices.