Abstract
Titanium (Ti) and Ti alloys are used in orthopaedic/spine applications where biological implant fixation, or osseointegration, is required for long-term stability. These implants employ macro-scale features to provide mechanical stability until arthrodesis, features that are too large to influence healing at the cellular level. Micron-scale rough Ti alloy (Ti–6Al–4V) increases osteoblastic differentiation and osteogenic factor production in vitro and increases in vivo bone formation; however, effects of overall topography, including sub-micron scale and nanoscale features, on osteoblast lineage cells are less well appreciated. To address this, Ti6Al4V surfaces with macro/micro/nano-textures were generated using sand blasting and acid etching that had comparable average roughness values but differed in other roughness parameters (total roughness, profile roughness, maximum peak height, maximum valley depth, root-mean-squared roughness, kurtosis, skewness) (#5, #9, and #12). Human mesenchymal stem cells (HMSCs) and normal human osteoblasts (NHOst) were cultured for 7 days on the substrates and then analyzed for alkaline phosphatase activity and osteocalcin content, production of osteogenic local factors, and integrin subunit expression. All three surfaces supported osteoblastic differentiation of HMSCs and further maturation of NHOst cells, but the greatest response was seen on the #9 substrate, which had the lowest skewness and kurtosis. The #9 surface also induced highest expression of α2 and β1 integrin mRNA. HMSCs produced highest levels of ITGAV on #9, suggesting this integrin may play a role for early lineage cells. These results indicate that osteoblast lineage cells are sensitive to specific micro/nanostructures, even when overall macro roughness is comparable and suggest that skewness and kurtosis are important variables.
Highlights
Biomaterials such as titanium (Ti) and titanium alloys are used for many orthopaedic procedures due to their biocompatibility and mechanical properties.2,13,24 Macroscale roughened surfaces are incorporated into implant designs to stabilize the bone-implant interface and minimize micromotion during spinal fusion, known as arthrodesis
This study confirms our previous observations that osteoblasts exhibit a more differentiated phenotype when cultured on Ti6Al4V surfaces with a microtopography that includes submicron and nanoscale features,15,18 and expands upon our previous findings showing that nanoscale topography imposed on surfaces with rough micro- and submicro-scale topographies can enhance osteoblastic differentiation
Unlike normal human osteoblasts (NHOst) cells, Human mesenchymal stem cells (HMSCs) produced higher ITGAV mRNAs on #9 than on all other surfaces, but expression of mRNA for its partner b3 was not sensitive to the surface type. These results demonstrate clearly that surface properties in addition to chemistry and average roughness are important variables in determining how cells in the osteoblast lineage will respond to implants
Summary
Biomaterials such as titanium (Ti) and titanium alloys (titanium–aluminum–vanadium alloy [Ti6Al4V]) are used for many orthopaedic procedures due to their biocompatibility and mechanical properties. Macroscale roughened surfaces are incorporated into implant designs to stabilize the bone-implant interface and minimize micromotion during spinal fusion, known as arthrodesis. Macroscale roughened surfaces are incorporated into implant designs to stabilize the bone-implant interface and minimize micromotion during spinal fusion, known as arthrodesis These features are designed to create a mechanical interlock with the bone, but are too large in scale to affect the host response at a cellular level. These materials can be fabricated to have surfaces that are microtextured and a number of studies have shown that osteoblast lineage cells exhibit increased osteoblastic differentiation when they are cultured on Ti and Ti6Al4V substrates with microscale roughness in comparison to smooth surfaces.. We previously compared the responses of MG63 osteoblast-like cells to electromachined Ti substrates with well-defined macro and
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