High Productivity Milling of Calcium Polyphosphate

The main objective of this thesis is to further reduce the machining cycle time for producing Calcium Polyphosphate (CPP) implant constructs. To achieve this, the impregnation of the CPP lattice with various polymers is investigated, with the aim of improving the toughness of the material. By applying Taguchi’s orthogonal array method it was determined that CPP infiltrated with an ionic bonding polymer produces the best material for generating high quality machined surfaces and features. While there is some loss in surface porosity, in comparison to cutting uninfiltrated CPP, the porosity loss was deemed acceptable for the clinical purpose of the implant, and in many cases, would be trimmed off during a consecutive finish machining operation. The 2 fluted 4 mm diameter flat end mill at a cutting speed of 30 m/min and ¾ immersion up-milling, 0.1 mm chip load and 3 mm depth of cut were determined to be highly suitable for achieving both high productivity as well as excellent surface integrity. These conditions produced a material removal rate of 4,302 mm3/min, which was 14 times higher than the material removal rate achieved in machining pure CPP in earlier studies. The constructed machining model was highly successful in predicting the cutting forces, and therefore can be used in process planning and optimization in the production of tissue engineered implant constructs out of CPP. The Finite Element analyses predicted that the implant would not chip or break during the roughing operation, as validated experimentally. This allowed the roughing cycle time to be reduced from 159 min to 19 min, effectively achieving a productivity improvement of 8 times over the earlier work done in this area

Rapid Fabrication Techniques for Anatomically-Shaped Calcium Polyphosphate Substrates for Implants to Repair Osteochondral Focal Defects

The purpose of the present study is to develop techniques for manufacturing anatomically-shaped substrates of implants made from calcium polyphosphate (CPP) ceramic. These substrates have tissue-engineered cartilage growing on their top surfaces and can be used as implants for osteochondral focal defect repair. While many research groups have been fabricating such substrates using standard material shapes, e.g., rectangles and circular discs, it is considered beneficial to develop methods that can be integrated in the substrate fabrication process to produce an implant that is specific to a patient’s own anatomy (as obtained from computer tomography data) to avoid uneven and/or elevated stress distribution that can affect the survival of cartilage. The custom-made, porous CPP substrates were fabricated with three-dimensional printing (3DP) and computer numerically controlled (CNC) machining for the first time to the best of the author’s knowledge. The 3DP technique was employed in two routines: indirect- and direct-3DP. In the former, 3DP was used to fabricate molds for pre-shaping of the CPP substrates from two different powder size ranges (<75 μm and 106-150 μm). In the latter, CPP substrates were produced directly from the retrofitted 3DP apparatus in a layer-by-layer fashion from 45-75 μm CPP powder with a polymeric binder. The prototyped samples were then sintered to obtain the required porosity and mechanical properties. These substrates were characterized in terms of their dimensional shrinkage and density. Also, SEM images were used to assess the particle distribution and neck and bond formations. The substrates produced using the indirect-3DP method yielded densities (<75 μm: 66.28 ± 11.62% and 106-150 μm: 65.87 ± 6.12%), which were comparable to the substrates used currently and with some success in animal studies. Geometric adjustment factors were devised to compensate for the slight expansion inherent in the 3DP mold fabricating process. These equations were used to bring the plaster molds into true dimension. The direct-3DP method has proven to be the ultimate choice due to its ability to produce complex anatomically-shaped substrates without the use of a chemical solvent. In addition, it allows for precise control of both pore size and internal architectures of the substrates. Thus, the direct-3DP was considered to be superior than the indirect-3DP as a fabrication method. In the alternative CNC machining approach to fabrication, the ability to machine the CPP ceramic was feasible and by careful selection of the machining conditions, anatomically-shaped CPP substrates were produced. To develop strategies for optimizing the machining process, a mechanistic model was developed based on curve fitting the average cutting forces to determine the cutting coefficients for CPP. These cutting coefficients were functions of workpiece material, axial depth of cut, chip width, and cutter geometry. To explore the utility of this modelling approach, cutting forces were predicted for a helical ball-end mill and compared with experimental results. The cutting force simulation exhibits good agreement in predicting the fundamental force magnitude and general shape of the actual forces. However, there were some discrepancies between the predicted and measured forces. These differences were attributed to internal microstructure defects, density gradients, and the use of a shear plane model in force prediction that was not entirely appropriate for brittle materials such as CPP. The present study successfully developed 3DP and CNC fabrication methods for manufacturing anatomically-shaped CPP substrates. Future studies were recommended to explore further optimization of these fabrication methods and to demonstrate the utility of accurate substrates shapes to the clinical application of focal defect repair implants

Solid Freeform Fabrication of Porous Calcium Polyphosphate Structures for Use in Orthopaedics

The focus of this dissertation is on the development of a solid freeform fabrication (SFF) process for the design and manufacture of porous biodegradable orthopaedic implants from calcium polyphosphate (CPP). Porous CPP structures are used as bone substitutes for regenerating bone defects and/or as substrates in formation of so-called “biphasic” implants for repair of damaged osteochondral tissues. The CPP implants can be utilized in the treatment of many musculoskeletal diseases, osteochondral defects, and bone tumours while replacement of the defect site is required. In this study, the fabrication of CPP structures was developed through a powder-based SFF technique known as adhesive bonding 3D-printing. SFF is an advanced alternative to the “conventional” fabrication method consisting of gravity sintering of CPP pre-forms followed by machining to final form, as SFF enables rapid manufacturing of complex-shaped bio-structures with controlled internal architecture. To address the physical and structural properties of the porous SFF-made components, they were characterized using scanning electron microscopy, micro-CT scanning and mercury intrusion porosimetry. Specific surface area and permeability of the porous structures were also determined. Additionally, the chemical properties (crystallinity) of the specimens were identified by X-ray diffraction. The mechanical properties of the crystalline CPP material were also measured by micro- and nano-indentation. Moreover, the porous structures were tested by uniaxial and diametral mechanical compression to determine the compressive and tensile strengths, respectively. Furthermore, the effect of the stacked-layer orientation on the mechanical properties of the SFF-made constructs was investigated through the production of samples with horizontal or vertical stacked-layers. The properties of the SFF-made samples were compared with those of the conventionally-made CPP constructs. The SFF-made implants showed drastically higher compressive mechanical strength compared to the conventionally-formed samples with identical porosity. It was also shown that the orientation of the stacked-layer has substantial influence on the mechanical strengths. Moreover, this thesis examined the ability of in vitro forming of cartilaginous tissue on the SFF-made substrates where the chondrocytes cellular response to the CPP implants was evaluated histologically and biochemically. In addition, an initial in vivo assessment of the CPP structures as bone substitutes was conducted using a rabbit medial femoral site model. Significant amount of new-bone was formed within the CPP porous constructs during the 6-week implantation period demonstrating appropriate biological response of SFF-made CPP structures for bone substitute applications. Another accomplishment of this thesis was the development of a mathematical model which predicts the compact density of powder layers spread by a counter-rotating roller in the SFF technique. The results may be used in the control of the apparent density of the final implant. The potential of the developed SFF method as an efficient and reproducible technique for the production of porous CPP structures for use in orthopaedics and musculoskeletal tissue regenerative applications was concluded

Design of Materials for Bone Tissue Scaffolds

The book proposes extensive and varied design strategies for bone tissue engineering. The design process of materials for bone tissue scaffolds presently represents an issue of crucial importance and is being studied by many researchers throughout the world. A number of studies have been conducted, aimed at identifying the optimal material, geometry, and surface that the scaffold must possess to stimulate the formation of the largest amounts of bone in the shortest time possible

New Trends in 3D Printing

A quarter century period of the 3D printing technology development affords ground for speaking about new realities or the formation of a new technological system of digital manufacture and partnership. The up-to-date 3D printing is at the top of its own overrated expectations. So the development of scalable, high-speed methods of the material 3D printing aimed to increase the productivity and operating volume of the 3D printing machines requires new original decisions. It is necessary to study the 3D printing applicability for manufacturing of the materials with multilevel hierarchical functionality on nano-, micro- and meso-scales that can find applications for medical, aerospace and/or automotive industries. Some of the above-mentioned problems and new trends are considered in this book

Engineered Wood Products for Construction

Wood is a gift from nature. It is a sustainable and renewable bio-composite material that possesses a natural ability to mitigate carbon dioxide. However, due to deforestation and climate change, it has become necessary to develop alternative building and construction materials. Engineered wood products (EWPs) such as parallel strand lumber, laminated veneer lumber, and cross-laminated timber are promising substitutions for conventional lumber products. This book presents a comprehensive overview of EWPs, including information on their classification, design, synthesis, properties, and more. It is divided into two sections: “General Overviews and Applications of EWPs” and “Recent Research and Development of EWPs”. The book is a valuable reference for manufacturers, engineers, architects, builders, researchers, and students in the field of construction

Experimental Protocols for Polymeric Binder Selection in the Binder Jetting of Metallic Particles in Three-Dimensional Printing

RÉSUMÉ: L’impression par jets de liant est une technique avancée de fabrication à base de poudres où un lit de poudre, puis un liant polymérique sont déposées de manière alternée jusqu’à ce qu’une pièce à trois dimensions soit formée. La pièce résultante est appelée un corps vert. Elle est composée de particules de poudre tenues ensemble par le liant. Pour obtenir une pièce purement métallique, la pièce doit être traitée thermiquement pour pyrolyser le polymère et fritter les particules de poudre. C’est l’une des techniques d’impression 3D de métaux les plus prometteuses. Cependant, la sélection des liants est souvent abordée par essai-erreur, ce qui mène à des corps verts avec une faible résistance, cause des pertes grandes de production et décroit la capacité du processus d’impression de produire des détails délicats.----------ABSTRACT: Binder-jet printing is an advanced manufacturing technique where the alternating deposition of a metal powder bed, then printing of a polymeric binder are repeated until a three-dimensional part is formed. The resulting piece is called green body. It is composed of powder particles held together by the binder. To obtain a pure metallic part, the piece must be treated thermally to pyrolyze the polymer and to sinter the powder particles. It is one of the most promising metal 3D printing techniques. However, the selection of binders is often approached by trial and error, which leads to poor green bodies strength, causes high production loses and decreases the printing process capacity to produce delicate features

Modeling and simulation in tribology across scales: An overview

This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and micro-scales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions