Surface roughness affects bone formation around orthopaedic implants in vivo and osteoblast functions in vitro. Osteoblast-like MG63 cells cultured on rough surfaces exhibited decreased cell number, increased differentiation and increased local factor production when compared to cells grow on smooth surfaces. In these experiments, roughness was characterized as average peak to valley height (Ra) which is not equal throughout the surface. Other features of roughness, including peak and valley area distributions and curvature of the valleys, will affect cell functions. In this study, novel titanium surfaces were prepared by photolithography to produce well designed microstructure and nanostructure. Smooth disks were made by producing craters of 10 micrometer, 30 micrometer and 100 micrometer diameters on titanium disks with constant curvatures. Craters were placed sparsely (10/1, 30/1, 100/1) or compactly (10/6, 30/6, 100/6). Smooth disks were also acid etched to make an overall roughness of Ra 0.7 micrometer or anodized to produce volcano-like nanostructure of Ra 0.4 micrometer. The results revealed the distinguishing contributions of microcrater size, crater spacing and nanostructures to surface effect on cell number, differentiation (alkaline phosphatase; osteocalcin) and local factor levels (TGF-beta1; PGE2). Cell attachment depends on crater spacing; cell growth and aggregation depend on crater dimension and cell morphology depends on the presence of nanostructural features. Cell differentiation and local factor production are modulated by acid etched roughness in concert with microstructure, and active TGF-beta1 level depends on nanoscale roughness.

Electrochemical machining (ECM) and especially electrochemical micromachining (μECM) became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications such as microfluidics systems and stressfree drilled holes in the automotive and aerospace sectors. Electrochemical machining is considered as a non-conventional machining process based on the phenomenon of electrolysis. This process requires maintaining a small gap - the interelectrode gap (IEG) - between the anode (workpiece) and the cathode (tool-electrode) in order to achieve acceptable machining results (i.e. accuracy, high aspect ratio with appropriate material removal rate and efficiency). This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has 3 axes of motion (X, Y and Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2nmresolution encoders for ultra-precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. A pulse power supply unit (PSU) and a special control algorithm have been implemented. The pulse power supply provides not only ultra-short pulses (50ns), but also plus and minus biases as well as a polarity switching functionality. It fulfils the requirements of tool preparation with reversed ECM on the machine. Moreover, the PSU is equipped with an ultrafast over current protection which prevents the tool-electrode from being damaged in case of short-circuits. Two different process control algorithms were made: one is fuzzy logic based and the other is adapting the feed rate according to the position and time at which short-circuits were detected. The developed machine is capable of drilling micro holes in hard-to-machine materials but also machine micro-styli and micro-needles for the metrology (micro CMM) and medical sectors. This work also presents drilling trials performed with the machine with an orbiting tool. Machining experiments were also carried out using electrolytes made of a combination of HCl and NaNO₃ aqueous solutions. The developed machine was used to fabricate micro tools out of 170μm WC-Co alloy shafts via micro electrochemical turning and drill deep holes via μECM in disks made of 18NiCr6 alloy. Results suggest that this process can be used for industrial applications for hard-to-machine materials. The author also suggests that the developed machine can be used to manufacture micro-probes and micro-tools for metrology and micro-manufacturing purposes.

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