Polycrystalline Diamond Coating on Orthopaedic Implants: Realization, and Role of Surface Topology and Chemistry in Adsorption of Proteins and Cell Proliferation

Polycrystalline diamond has the potential to improve the osseointegration of orthopaedic implants compared to conventional osteo-implant materials such as titanium. However, despite the excellent biocompatibility and superior mechanical properties, the major challenge of using diamond for implants such as those used for hip arthroplasty is the limitations of microwave plasma chemical vapor deposition (CVD) techniques to synthesize diamond on complex-shaped objects. Here, for the first time we demonstrate diamond growth on titanium acetabular shells using surface wave plasma CVD method. Polycrystalline diamond coatings were synthesized at low temperatures (~400 °C) on three types of acetabular shells with different surface structure and porosity. We achieved diamond growth on highly porous surfaces designed to mimic the structure of the trabecular bone and improve osseointegration. Biocompatibility was investigated on nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) coatings terminated either with hydrogen or oxygen. To understand the role of diamond surface topology and chemistry in attachment and proliferation of mammalian cells we investigated adsorption of extracellular matrix (ECM) proteins, and monitored metabolic activity of fibroblasts, osteoblasts, and bone marrow-derived mesenchymal stem cells (MSCs). The interaction of bovine serum albumin (BSA) and Type I collagen with diamond surface was investigated by confocal fluorescence lifetime imaging microscopy (FLIM). We found that proliferation of MSCs was better on hydrogen terminated UNCD than on oxygen terminated counterpart. These findings corelate to the behaviour of collagen on diamond substrates observed by FLIM. Hydrogen terminated UNCD provides better adhesion and proliferation for MSCs, compared to titanium, while growth of fibroblasts is poorest on hydrogen terminated NCD and osteoblasts behave similarly on all tested surfaces. These results open new opportunities for application of diamond coatings on orthopaedic implants.

An Alternative Formulation for Modeling Self-Excited Vibrations of Drillstring with PDC Bits

This work describes an alternative formulation of a system of nonlinear state-dependent delay differential equations (SDDDEs) that governs the coupled axial and torsional vibrations of a 2 DOF drillstring model considering a Polycrystalline Diamond Compact (PDC) bit with realistic cutter layout. Such considerations result in up to 100 state-dependent delays due to the regenerative effect of the drilling process, which renders the computational efficiency of conventional solution strategies unacceptable. The regeneration of the rock surface, associated with the bit motion history, can be described using the bit trajectory function, the evolution of which is governed by a partial differential equation (PDE). Thus the original system of SDDDEs can be replaced by a nonlinear coupled system of a PDE and ordinary differential equations (ODEs). Via the application of the Galerkin method, this system of PDE-ODEs is transformed into a system of coupled ODEs, which can be readily solved. The algorithm is further extended to a linear stability analysis for the bit dynamics. The resulting stability boundaries are verified with time-domain simulations. The reported algorithm could, in principle, be applied to a more realistic drillstring model, which may lead to an in-depth understanding of the mitigation of self-excited vibrations through PDC bit designs.

Numerical Study on Fragmentation Characteristics of Granite Under a Single Polycrystalline Diamond Compact Cutter in Rotary-Percussive Drilling

Fragmentation characteristics of granite in rotary-percussive drilling are studied using the distinct element method. We developed a model to investigate the interaction between the rock and a Polycrystalline Diamond Compact cutter. The micro contact parameters in the model are calibrated by conducting a series of simulated mechanical tests of the rock. Sensitivity analyses are then conducted according the drilling performances which are quantified as the penetration displacement, the fragmentation volume and the specific energy, as well as the lateral force and the particle size distribution. Results show that the model can well represent the typical fracture system under indentation of the cutter, the torque fluctuation phenomenon in drilling and the formation of lateral chips, which verify the reliability of the model. The cutter with a back rake angle of 55°and impact frequency of 30Hz has the best penetration performance in evaluated parameters. Increasing the frequency has a great effect on the rock breaking speed under the coupling effect of impact and cutting in the low frequency range. Considering crushing efficiency, 50 Hz is the recommended impact frequency. This paper provides a useful tool to represent the fragmentation performance of rotary-percussive drilling and sensitivity analyses shed light on the potential ways to improve the performance.

RESEARCH OF A LATERAL REAMER BIT FOR DIGGING PLANTING HOLE IN ROCKY ABANDONED MINE AREA

In the abandoned mine area with Karst landform in China, soils are few and thin but rocks are common, traditional planting hole diggers are unequal to work in rocks for vegetation restoration. A reamer bit with variable lateral drilling radius was designed based on the PDC (polycrystalline diamond compact) bit technology and metamorphic mechanism. Two lateral camber blades with PDC teeth were installed inside the bit body, a screw mechanism was employed as the actuation and a spatial double triangle mechanism was taken for the transmission. The curve of the camber blade was specially defined thus the reaming load was decentralized to 85.7% teeth on the blade. The kinematics of the lateral reamer bit was analysed, the mapping models from the actuation to the reaming radius and speed were established. Concrete samples were reamed indoors from 240mm to 407mm in diameter, the reaming cutting load and time length were measured and analysed. The lateral reamer bit was approved with the experiment results, this study provided equipment support for digging the planting hole in rocky abandoned mine areas and also expanded the PDC bit application.

Optimization of Machining Parameters for Milling Zirconia Ceramics by Polycrystalline Diamond Tool

Zirconia ceramics are widely used in many fields because of their excellent physical and mechanical properties. However, there are some challenges to machine zirconia ceramics with high processing efficiency. In order to optimize parameters for milling zirconia ceramics by polycrystalline diamond tool, finite element method was used to simulate machining process based on Johnson-Cook constitutive model. The effects of spindle speed, feed rate, radial and axial cutting depth on cutting force, tool flank wear and material removal rate were investigated. The results of the simulation experiment were analyzed and optimized by the response surface method. The optimal parameter combination was obtained when the spindle speed, feed rate, radial and axial cutting depth were 8000 r/min, 90.65 mm/min, 0.10 mm and 1.37 mm, respectively. Under these conditions, the cutting force was 234.81 N, the tool flank wear was 33.40 μm when the milling length was 60 mm and the material removal rate was 44.65 mm3/min.

Special Device for Diamond Grinding of the Backup Surfaces and Perimeter of Articles from Nonmetallic Ceramic Materials

In developed countries, material scientists are working intensively to create high-strength (metallic) technical ceramics. If such a material is created, it will be possible to manufacture such parts of power units (transmissions) of cars as shafts, turbines, etc. In the future, the latest composite ceramic materials with unique properties will gradually replace metals in the production of machine parts. Special device for diamond grinding of articles from composite, non-metallic, brittle materials (technical ceramics on the base of SiC, Al2O3; polycrystalline diamond, composite – Si + SiC + diamond etc.) is a universal flat grinding machine that enables to grind with high productivity both supporting main surfaces and lateral side surfaces – perimeter of an article of prismatic shape. It is also possible to grind substrates of other configurations – round, oval, etc. Grinding depending on sizes of articles can be done of both single and group of articles. The grinding takes place by the means of spring feeding of the article by pneumatic system that enables to prevent breakage of articles from brittle non-metallic materials in process of machining and obtain maximum high quality of the machined surface.

Diamond Grinding Technology of Flexural Strength Test Pieces of Super hard, Brittle, Composite-ceramic Materials and Technological Equipment

At the present stage of the revolutionary development of technologies, scientists from the leading countries of the world are working intensively to create qualitatively new materials whose physical-mechanical, electrical, thermal or other properties far exceed the basic constructions, armament or other metals used. Such materials are surface, brittle, composite ceramic materials (based on oxide and carbide ceramics, state-of-the-art surface compositions, polycrystalline diamond + Si  SiC and etc.). A progressive process for diamond grinding test samples from composite ceramic materials to determine the bending strength is discussed. The proposed technological process is based on an original and effective method for polishing the flat surfaces of articles made of difficult-to-process and composite materials - low-temperature precision grinding (LPG). Based on the results of many years and multilateral studies in the field of diamond processing of various non-metallic, composite and ceramic materials, optimum conditions for diamond polishing of mentioned materials have been determined and recommended. Technological equipment and equipment for processing composite and ceramic materials are also disclosed.