Polydopamine-Lysophosphatidate-Functionalised Titanium: A Novel Hybrid Surface Finish for Bone Regenerative Applications

Aseptic loosening of total joint replacements (TJRs) continues to be the main cause of implant failures. The socioeconomic impact of surgical revisions is hugely significant; in the United Kingdom alone, it is estimated that £135m is spent annually on revision arthroplasties. Enhancing the longevity of titanium implants will help reduce the incidence and overall cost of failed devices. In realising the development of a superior titanium (Ti) technology, we took inspiration from the growing interest in reactive polydopamine thin films for biomaterial surface functionalisations. Adopting a “one-pot” approach, we exposed medical-grade titanium to a mildly alkaline solution of dopamine hydrochloride (DHC) supplemented with (3S)1-fluoro-3-hydroxy-4-(oleoyloxy)butyl-1-phosphonate (FHBP), a phosphatase-resistant analogue of lysophosphatidic acid (LPA). Importantly, LPA and selected LPA analogues like FHBP synergistically cooperate with calcitriol to promote human osteoblast formation and maturation. Herein, we provide evidence that simply immersing Ti in aqueous solutions of DHC-FHBP afforded a surface that was superior to FHBP-Ti at enhancing osteoblast maturation. The facile step we have taken to modify Ti and the biological performance of the final surface finish are appealing properties that may attract the attention of implant manufacturers in the future.

Analysis of finishing forces and surface finish during magnetorheological abrasive flow finishing of asymmetric workpieces

Magnetorheological abrasive flow finishing (MRAFF) is an advanced hybrid process for producing ultrafine finished surfaces. Such surfaces reduce frictional forces and thereby minimize wear and tear to increase functional lifetime of the components. In the present research work, a model has been developed for simulating the results of MRAFF process. First, magnetic field is simulated and then a detailed study on the rheology of the magnetorheological polishing (MRP) fluid is conducted to develop a viscosity model for the flow of non-Newtonian shear thinning fluid. To calculate the forces acting in the process of material removal, the flow of MRP fluid around an asymmetric workpiece (knee joint) in a spatially varying magnetic field is simulated. Finishing forces exerted by the abrasive particles on the workpiece surface are analysed to develop a model for predicting surface roughness. A methodology has been proposed to evolve a variable correction factor to determine active abrasive particles at different locations on the workpiece surface for accurate simulation of surface finish operation. It is found that the magnetic field greatly influences the process performance by governing the viscosity of the MRP fluid and the distribution of the abrasive particles in the medium. During finishing of an asymmetric workpiece, the surface finish obtained at different locations on the workpiece surface is different. The developed model is capable to predict final surface finish within the acceptable accuracy when compared with the experimental results.

Study of Ultra-precision Finishing Techniques for Brittle Materials

Wide application of hard and brittle advanced ceramics, glasses and semiconductors in Mechanical, Optical and Electronic industry has led to the development of new ultra-precision finishing processes. With an increase in the applications of these materials, the need of finishing these materials has also become a great challenge. Dimensional and finish accuracies are the parameters that needs to be focused and improved with minimum time and cost. Another crucial parameter is the subsurface damages that are quiet common with these materials during finishing process. New processes have been developed to overcome the drawbacks of the existing processes for Nano finishing. These processes can be classified as Conventional, Precision and Ultra-precision finishing based on the degree of dimensional accuracy and final surface finish. Both loose and bonded abrasives have been used for these processes. This paper deals with the study of some of the significant advances in ultra-precision finishing processes of hard and brittle materials.

MEMS Fabrication on LTCC Substrates for RF Applications: Challenges and Perspectives

Microelectromechanical Systems (MEMS) are often used in transceiver modules, especially for telecommunication and radar applications. In this paper, we present recent progress in the development on a MEMS-on-LTCC process. We focus on the Low Temperature Co-fired Ceramic (LTCC) substrate issues and we present a successful solution for overcoming the substrate challenges through surface pre-treatment using a chemical mechanical surface polishing (CMP) process which allows us to reach the required smoothness for the fabrication of MEMS devices. We discuss various process parameters such as slurry type, rotating pad and rotation speed, and show their impact on the final surface finish. With an optimized process, the maximum roughness was decreased from more than 10μm to less than 0.5 μm over a 640 × 640 μm2 LTCC sample. Also, we present the various MEMS process steps starting with the deposition and patterning of various layers to a prototype switch highlighting the validated steps and the challenges encountered. A brief discussion of the perspectives for the integration of MEMS and LTCC technologies is also presented.

Stepwise Comparison of Expert and Nonexpert Preparations of a Polished Metallographic Surface

The carburizing process requires metallurgical inspection by means of polished metallurgical mounts. Metallographic preparation for a metallurgical mount is an important process. The purpose of this study is to clarify the differences in ground and polished surface finishes of metallurgical mounts for carburized parts at each step of the process as executed by an expert and a nonexpert on a semi-automated grinding and polishing machine. To clarify the differences between expert and nonexpert preparations, microscopic images of the surface finish obtained at each step of grinding and polishing were compared. The surface profile of each of the final finishes was also examined with measuring device. Each inspector has either 20 (expert) or 0.5 years (nonexpert) of experience in metallographic preparation. The ground and polished finish produced by the expert was well balanced over the entire surface. In contrast, the surface finish produced by the nonexpert was dispersed. The number of scratches and edge rounding depth apparent in the final surface finish of the expert were less than those of the nonexpert.

Design of Optimum Planetary Electro Discharge Machining Strategies

The use of Electrical Discharge Machining (EDM) for the manufacturing of moulds and dies is generally accomplished by using different cutting regimens, from roughing to finishing, until the specified surface finish and dimensional tolerances are met. Multistage planetary EDM can be used to simplify the production process. Benefits such as the reduction of machining time, the need for less electrodes, electrode wear minimization and the improvement of the final surface finish of the component can be obtained. Design of multistage planetary EDM strategies requires a sound knowledge of the optimum radius for each orbit that assures surface roughness and dimensional accuracy together with a minimum machining time. Therefore, it is necessary to know the “exact” value of the gap at each stage. In this paper the influence of different process variables on the design of multistage planetary EDM strategies is analyzed.

Generating Spiral Paths for Sculptured Surfaces Machining

To machine sculptured surfaces, ball end mills are mainly used to reach the final surface finish requirements. During machining, the cusp height is one of the major factors defining the final surface finish smoothness. A cutter path that maintains a high cutting efficiency as well as a constant cusp height is desired. Spiral curves, with the property of not requiring extra linkage segments between two adjacent arms can be used to generate a smooth cutter path. In this paper, a geometric algorithm for generating spiral cutter paths for ball end milling in machining sculptured surfaces is presented.

Finding Cutter Engagement for Ball End Milling of Tessellated Free-Form Surfaces

In fabricating free-form surfaces, ball end mills are mainly used to reach the final surface finish requirements. In the milling processes, cutter engagement value measures what portion of the cutter is involved in machining at a given instant of time. This paper presents geometric algorithms for estimating cutter engagement values for ball end milling processes of tessellated free-form surfaces. The cutter engagement value calculated here can be used later on in generating efficient cutter paths, as well as performing adaptive feed rate controls.

Ground surface finishes in carbonized resorcinol/formaldehyde foam

Low-density resorcinol/formaldehyde foams developed by Pekala are stabilized by carbonizing (CRF). These delicate foams require machining for critical applications in the Inertial Confinement Fusion program at LLNL. The machining was preformed by first diamond-point turning and then grinding to final dimension. The first several grinding passes removed about 10 (μm per pass, several more passes were made at about 5 (μm per pass, and as the part approached final dimensions, the grinding depth was decreased to about 2 μ.m, and several passes were made at each setting. The final surface finish could be controlled to some extent by adjusting a scraper nozzle that removed grinding debris from the grinding wheel to leave a slight amount of debris on the wheel. During preliminary studies, inconsistencies were observed in the visual appearances of machined surfaces. Some specimens had moderately reflective surfaces, but others had a dull, flat appearance. Therefore, ground CRF surface microstructures were examined to determine the cause of the differences in reflectivity. Secondary-electron images of the specimens were obtained with a Hitachi S-800 FESEM at 25 kV; the specimens were uncoated. Specimens chosen for this study had dull, partially reflective, and reflective surfaces.