Implant surfaces play important roles in regulating protein adsorption and determining subsequent cell responses, including cell attachment, proliferation, migration and differentiation. With rapid developments in micro- and nano-fabrication methods and additive manufacturing (3D printing) technologies, precisely controlled patterns such as partially ordered or ordered patterns can now be generated on bone implant surfaces, rather than restricted to randomly roughened surfaces. Over the last two decades, much effort has been dedicated to manipulating cell responses through surface topographical modifications. This review discusses the recent developments and understanding of surface topography in prompting or enhancing desired cell responses, particularly the roles of ordered and partially ordered surface topography under in vitro conditions. In addition, the challenges to translate research findings into implant applications are addressed.

Statistical data have consistently shown that implant loosening is a significant causative factor for revision surgeries. Both in vivo and in vitro studies have confirmed the positive influences of microgrooved titanium implant surfaces on improving orthopedic titanium implants compared with a smooth titanium surface. Complete cell–groove adhesion is a prerequisite for rapid and robust osseointegration. For the first time, this work has quantified the influence of the titanium groove width at the subcellular scale (5–20 μm) on osteoblast responses, using titanium-coated microgrooved silicon wafer specimens (surface roughness, R a = ∼1.5 nm), which can avoid the latent influence of variations in surface roughness from the use of normal titanium substrates. The cell–groove adhesion increased from 53.07% to 98.55% with an increasing groove width from 5 to 20 μm. In addition, both the cell spreading area and cell width were proportional to groove width. However, no statistically significant influence (p > 0.05) of groove width was identified on cell proliferation and differentiation. An exponential model was proposed to predict the groove geometries that can facilitate complete cell–groove adhesion. The underlying mechanisms were discussed. The experimental findings of this study provide a unique basis for the design of titanium implant surfaces.

Surface wettability plays a critical role in a variety of key areas including orthopaedic implants and chemical engineering. Anisotropy in wettability can arise from surface grooves, which are of particular relevance to orthopaedic implants because they can mimic collagen fibrils that are the basic components of the extracellular matrix. Titanium (Ti) and its alloys have been widely used for orthopaedic and dental implant applications. This study is concerned with the fabrication of Ti-coated microgrooves with different groove widths and the characterisation of the anisotropy in wettability through measuring water contact angles, compared with both the Wenzel and Cassie models. Experimental results revealed that there existed significant anisotropy in the wettability of Ti-coated microgrooves, and the degree of anisotropy (Δθ) increased with an increasing groove width from 5 μm to 20 μm. On average, the contact angle measured parallel to the groove direction (θ//) was about 50°–60° smaller than that measured perpendicular to the groove direction (θ⊥). In general, the Wenzel model predicted the contact angles along the surface groove direction reasonably, and so did the Cassie model for the contact angles perpendicular to the groove direction. Osteoblast spreading was affected by the anisotropy in wettability, which occurred preferably along, rather than perpendicular to, the groove direction. These findings are informative for the design of Ti implant surfaces when anisotropy in wettability matters.

The surface of an orthopaedic implant plays a crucial role in determining the adsorption of proteins and cell functions. A detailed comparative study has been made of the in vitro osteoblast responses to coarse-grained (grain size: 500 μm), ultrafine-grained (grain size: 100 nm), coarse-porous (pore size: 350 nm), and fine-porous (pore size: 155 nm) surfaces of Ti-20Mo alloy. The purpose was to provide essential experimental data for future design of orthopaedic titanium implants for rapid osseointegration. Systematic original experimental data was produced for each type of surfaces in terms of surface wettability, cell morphology, adhesion, growth, and differentiation. Microscopic evidence was collected to reveal the detailed interplay between each characteristic surface with proteins or cells. Various new observations were discussed and compared with literature data. It was concluded that the coarse-porous surfaces offered the optimum topographical environment for osteoblasts and that the combination of ultrafine grains and considerable grain boundary areas is not an effective way to enhance cell growth and osteogenic capacity. Moreover, pore features (size and depth) have a greater effect than smooth surfaces on cell growth and osteogenic capacity. It proves that cells can discern the difference in pore size in the range of 100-350 nm. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2020-2033, 2018.