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67-455: This concept emerges due to the enormous design freedom provided by AM technologies. To take full advantages of unique capabilities from AM processes, DfAM methods or tools are needed. Typical DfAM methods or tools includes topology optimization , design for multiscale structures (lattice or cellular structures), multi-material design, mass customization , part consolidation, and other design methods which can make use of AM-enabled features. DfAM

134-476: A finite element method (FEM) to evaluate the design performance. The design is optimized using either gradient-based mathematical programming techniques such as the optimality criteria algorithm and the method of moving asymptotes or non gradient-based algorithms such as genetic algorithms . Topology optimization has a wide range of applications in aerospace, mechanical, bio-chemical and civil engineering. Currently, engineers mostly use topology optimization at

201-490: A central issue for mass customization. Several design methods have been proposed to help designers or users to obtain the customized product in an easy way. These methods or tools can also be considered as the DfAM methods. Due to the constraints of traditional manufacturing methods, some complex components are usually separated into several parts for the ease of manufacturing as well as assembly. This situation has been changed by

268-408: A function of implant characteristics. For example, implants using a screw-root form design achieve high initial mechanical stability through the action of their screws against bone. Following placement of the implant, healing typically takes several weeks or months before the implant is fully integrated into the bone. First evidence of integration occurs after a few weeks, while more robust connection

335-405: A helicopter engine with 16 parts instead of 900, with great potential impact on reducing the complexity of supply chains . It is this radical rethinking aspect that has led to themes such as that "DfAM requires 'enterprise-level disruption'." In other words, the disruptive innovation that AM can allow can logically extend throughout the enterprise and its supply chain, not just change the layout on

402-478: A known analytical solution. There are various implementation methodologies that have been used to solve topology optimization problems. Solving topology optimization problems in a discrete sense is done by discretizing the design domain into finite elements. The material densities inside these elements are then treated as the problem variables. In this case material density of one indicates the presence of material, while zero indicates an absence of material. Owing to

469-530: A machine shop floor. DfAM involves both broad themes (which apply to many AM processes) and optimizations specific to a particular AM process. For example, DFM analysis for stereolithography maximizes DfAM for that modality. Additive manufacturing is defined as a material joining process, whereby a product can be directly fabricated from its 3D model, usually layer upon layer. Comparing to traditional manufacturing technologies such as CNC machining or casting, AM processes have several unique capabilities. It enables

536-412: A part. However, the complex optimized shapes obtained from topology optimization are always difficult to handle for traditional manufacturing processes such as CNC machining. To solve this issue, additive manufacturing processes can be applied to fabricate topology optimization result. However, it should be noticed, some manufacturing constraints such as minimal feature size also need to be considered during

603-399: A problem is still infeasible owing to issues such as: Some techniques such as filtering based on image processing are currently being used to alleviate some of these issues. Although it seemed like this was purely a heuristic approach for a long time, theoretical connections to nonlocal elasticity have been made to support the physical sense of these methods. Fluid-structure-interaction

670-501: A role in modulating molecular and cellular behavior. While osseointegration has been observed using different materials, it is most often used to describe the reaction of bone tissues to titanium, or titanium coated with calcium phosphate derivatives. It was previously thought that titanium implants were retained in bone through the action of mechanical stabilization or interfacial bonding. Alternatively, calcium phosphate coated implants were thought to be stabilized via chemical bonding. It

737-474: A socket prosthesis. On December 7, 2015, two Operation Iraqi Freedom/Operation Enduring Freedom veterans, Bryant Jacobs and Ed Salau, became the first in America to get a percutaneous osseointegrated prosthesis . In the first stage, doctors at Salt Lake Veterans Affairs Hospital embedded a titanium stud in the femur of each patient. About six weeks later, they went back and attached the docking mechanism for

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804-463: A type of DfAM methods. Lattice structures is a type of cellular structures (i.e. open). These structures were previously difficult to manufacture, hence was not widely used. Thanks to the free-form manufacturing capability of additive manufacturing technology, it is now possible to design and manufacture complex forms. Lattice structures have high strength and low mass mechanical properties and multifunctionality. These structures can be found in parts in

871-480: Is resonance frequency analysis (RFA). A resonance frequency analyzer device prompts vibrations in a small metal rod temporarily attached to the implant. As the rod vibrates, the probe reads its resonance frequency and translates it into an implant stability quotient (ISQ), which ranges from 1–100, with 100 indicating the highest stability state. Values ranging between 57 and 82 are generally considered stable, though each case must be considered independently. One of

938-480: Is a mathematical method that optimizes material layout within a given design space, for a given set of loads , boundary conditions and constraints with the goal of maximizing the performance of the system. Topology optimization is different from shape optimization and sizing optimization in the sense that the design can attain any shape within the design space, instead of dealing with predefined configurations. The conventional topology optimization formulation uses

1005-544: Is a strongly coupled phenomenon and concerns the interaction between a stationary or moving fluid and an elastic structure. Many engineering applications and natural phenomena are subject to fluid-structure-interaction and to take such effects into consideration is therefore critical in the design of many engineering applications. Topology optimisation for fluid structure interaction problems has been studied in e.g. references and. Design solutions solved for different Reynolds numbers are shown below. The design solutions depend on

1072-405: Is in reality a cost factor, as we would not want to spend a lot of money on the material. To obtain the total material utilized, an integration of the selection field over the volume can be done. Finally the elasticity governing differential equations are plugged in so as to get the final problem statement. subject to: But, a straightforward implementation in the finite element framework of such

1139-402: Is inserted into the bone residuum of amputees and then connect through an opening in the skin to a robotic limb prosthesis. This lets amputees mobilize with more comfort and less energy consumption. Al Muderis also published the first series of combining osseointegration prosthesis with Joint replacement enabling below knee amputees with knee arthritis or short residual bone to walk without needing

1206-489: Is normally the case due to the absence of cementum progenitor cells in the area receiving the implant. However, when such cells are present, cement may form on or around the implant surface, and a functional collagen attachment may attach to it. Since 2005, a number of orthopedic device makers have introduced products with porous metal construction . Clinical studies on mammals have shown that porous metals, such as titanium foam, may allow formation of vascular systems within

1273-423: Is not always separate from broader DFM, as the making of many objects can involve both additive and subtractive steps. Nonetheless, the name "DfAM" has value because it focuses attention on the way that commercializing AM in production roles is not just a matter of figuring out how to switch existing parts from subtractive to additive. Rather, it is about redesigning entire objects (assemblies, subsystems) in view of

1340-416: Is not only mediated by mechanoreceptors but also by auditory receptors . This means that, rather than just feeling mechanical influences on the device, users also hear the movements of their prosthesis. This joint mechanical and auditory sensory perception is likely responsible for the improved environment perception of users of osseointegrated prostheses compared to traditional socket suspended devices. It

1407-581: Is now known that both calcium phosphate coated implants and titanium implants are stabilized chemically with bone, either through direct contact between calcium and titanium atoms, or by the bonding to a cement line-like layer at the implant/bone interface. While there are some differences (e.g. like the lack of chondrogenic progenitors), osseointegration occurs through the same mechanisms as bone fracture healing. For osseointegrated dental implants , metallic, ceramic, and polymeric materials have been used, in particular titanium . To be termed osseointegration

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1474-497: Is progressively effected over the next months or years. Implants that have a screw-root form design result in bone resorption followed by interfacial bone remodeling and growth around the implant. Implants using a plateau-root form design (or screw-root form implants with a wide enough gap between the pitch of the screws) undergo a different mode of peri-implant ossification. Unlike the aforementioned screw-root form implants, plateau-root form implants exhibit de novo bone formation on

1541-424: Is tapped against the implant carrier. The nature of the ringing that results is used as a qualitative measure of the implant's stability. An integrated implant will elicit a higher pitched "crystal" sound, whereas a non-integrated implant will elicit a dull, low-pitched sound. Another method is a reverse torque test, in which the implant carrier is unscrewed. If it fails to unscrew under the reverse torque pressure,

1608-529: Is the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant ("load-bearing" as defined by Albrektsson et al. in 1981). A more recent definition (by Schroeder et al.) defines osseointegration as "functional ankylosis (bone adherence)", where new bone is laid down directly on the implant surface and the implant exhibits mechanical stability (i.e., resistance to destabilization by mechanical agitation or shear forces ). Osseointegration has enhanced

1675-455: Is thus a key part of design for additive manufacturing . A topology optimization problem can be written in the general form of an optimization problem as: The problem statement includes the following: Evaluating u ( ρ ) {\displaystyle \mathbf {u(\rho )} } often includes solving a differential equation. This is most commonly done using the finite element method since these equations do not have

1742-417: The implant surface without interposed soft tissue layer. No scar tissue , cartilage or ligament fibers are present between the bone and implant surface. The direct contact of bone and implant surface can be verified microscopically . Osseointegration may also be defined as: Osseointegration was first observed—albeit not explicitly stated—by Bothe, Beaton, and Davenport in 1940. Bothe et al. were

1809-414: The (macro-)structure as well as the desirable microstructure depending on the expected performance of the specialized AM component under the known service load. In this context, multi-scale and multi-physics integrated computational materials engineering (ICME) for computational linkage of process-(micro)structure-properties-performance (PSPP) chain can be used to efficiently search an AM design subspace for

1876-432: The aerospace and biomedical industries. It has been observed that these lattice structures mimic atomic crystal lattice, where the nodes and struts represent atoms and atomic bonds, respectively, and termed as meta-crystals. They obey the metallurgical hardening principles (grain boundary strengthening, precipitate hardening etc.) when undergoing deformation. It has been further reported that the yield strength and ductility of

1943-749: The attainable topological complexity of the design being dependent on the number of elements, a large number is preferred. Large numbers of finite elements increases the attainable topological complexity, but come at a cost. Firstly, solving the FEM system becomes more expensive. Secondly, algorithms that can handle a large number (several thousands of elements is not uncommon) of discrete variables with multiple constraints are unavailable. Moreover, they are impractically sensitive to parameter variations. In literature problems with up to 30000 variables have been reported. The earlier stated complexities with solving topology optimization problems using binary variables has caused

2010-437: The bone-implant interface was needed to enable proper osseointegration. It was also noted that there is a critical threshold of micromotion above which a fibrous encapsulation process occurs, rather than osseointegration. Other complications may arise even in the absence of external impact. One issue is growth of cement . In normal cases, absence of cementum on the implant surface prevents attachment of collagen fibers. This

2077-511: The choice of process parameters for manufacture, in place of expensive empirical testing. Additively manufactured metallic structures with the same (macroscopic) shape and size but fabricated by different process parameters have strikingly different microstructures and hence mechanical properties. The abundant and highly flexible AM process parameters substantially influence the AM microstructures. Therefore, in principle, one could simultaneously 3D-print

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2144-411: The community to search for other options. One is the modelling of the densities with continuous variables. The material densities can now also attain values between zero and one. Gradient based algorithms that handle large amounts of continuous variables and multiple constraints are available. But the material properties have to be modelled in a continuous setting. This is done through interpolation. One of

2211-483: The concept level of a design process . Due to the free forms that naturally occur, the result is often difficult to manufacture. For that reason the result emerging from topology optimization is often fine-tuned for manufacturability. Adding constraints to the formulation in order to increase the manufacturability is an active field of research. In some cases results from topology optimization can be directly manufactured using additive manufacturing ; topology optimization

2278-404: The connection between the bone and the implant need not be 100%, and the essence of osseointegration derives more from the stability of the fixation than the degree of contact in histologic terms. In short it is a process where clinically asymptomatic rigid fixation of alloplastic materials is achieved, and maintained, in bone during functional loading. Implant healing time and initial stability are

2345-786: The conversion of thermal energy into electric energy and the Peltier effect concerns the conversion of electric energy into thermal energy. By spatially distributing two thermoelectric materials in a two dimensional design space with a topology optimisation methodology, it is possible to exceed performance of the constitutive thermoelectric materials for thermoelectric coolers and thermoelectric generators . The current proliferation of 3D printer technology has allowed designers and engineers to use topology optimization techniques when designing new products. Topology optimization combined with 3D printing can result in less weight, improved structural performance and shortened design-to-manufacturing cycle. As

2412-406: The derivatives of the objective function are non-zero when the density becomes zero. The higher the penalisation factor, the more SIMP penalises the algorithm in the use of non-binary densities. Unfortunately, the penalisation parameter also introduces non-convexities. There are several commercial topology optimization software on the market. Most of them use topology optimization as a hint how

2479-564: The design objective, depending on the thermo-chemo-mechanical service load, may include multiple functional aspects, such as specific energy absorption capacity, fatigue life/strength, high temperature strength, creep resistance, erosion/wear resistance and/or corrosion resistance. It is hypothesized that the optimal design approach is essential for unraveling the full potential of metal AM technologies and thus their widespread adoption for production of structurally critical load-bearing components. Topology optimization Topology optimization

2546-441: The design of a part with multiple materials or Functionally Graded Materials . These design methods also bring a challenge to traditional CAD system. Most of them can only deal with homogeneous materials now. Since additive manufacturing can directly fabricate parts from products’ digital model, it significantly reduces the cost and leading time of producing customized products. Thus, how to rapidly generate customized parts becomes

2613-523: The designs, while efficient, might not be realisable with more traditional manufacturing techniques. Internal contact can be included in topology optimization by applying the third medium contact method . The third medium contact (TMC) method is an implicit contact formulation that is continuous and differentiable. This makes TMC suitable for use with gradient-based approaches to topology optimization. Osseointegration Osseointegration (from Latin osseus " bony " and integrare "to make whole")

2680-569: The fabrication of parts with a complex shape as well as complex material distribution. These unique capabilities significantly enlarge the design freedom for designers. However, they also bring a big challenge. Traditional Design for manufacturing (DFM) rules or guidelines deeply rooted in designers’ mind and severely restrict designers to further improve product functional performance by taking advantages of these unique capabilities brought by AM processes. Moreover, traditional feature-based CAD tools are also difficult to deal with irregular geometry for

2747-418: The first researchers to implant titanium in an animal and remarked how it tended to fuse with bone. Bothe et al. reported that due to the elemental nature of the titanium, its strength, and its hardness, it had great potential to be used as future prosthesis material. Gottlieb Leventhal later described osseointegration in 1951. Leventhal placed titanium screws in rat femurs and said, "At the end of 6 weeks,

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2814-435: The fluid flow with indicate that the coupling between the fluid and the structure is resolved in the design problems. Thermoelectricity is a multi-physic problem which concerns the interaction and coupling between electric and thermal energy in semi conducting materials. Thermoelectric energy conversion can be described by two separately identified effects: The Seebeck effect and the Peltier effect. The Seebeck effect concerns

2881-441: The implant is stable. If the implant rotates under the pressure it is deemed a failure and removed. This method comes at the risk of fracturing bone that is mid-way in the process of osseointegration. It is also unreliable in determining the osseointegration potential of a bone region, as tests have yielded that a rotating implant can go on to be successfully integrated. A non-invasive and increasingly implemented diagnostic method

2948-407: The implant surface. The type of bone healing exhibited by plateau-root form implants is known as intramembranous-like healing. Though the osseointegrated interface becomes resistant to external shocks over time, it may be damaged by prolonged adverse stimuli and overload, which may cause implant failure. In studies done using "Mini dental implants," it was noted that the absence of micromotion at

3015-580: The improvement of functional performance. To solve these issues, design methods or tools are needed to help designers to take full advantages of design freedom provide by AM processes. These design methods or tools can be categorized as Design for Additive Manufacturing. Topology optimization is a type of structural optimization technique which can optimize material layout within a given design space. Compared to other typical structural optimization techniques, such as size optimization or shape optimization, topology optimization can update both shape and topology of

3082-548: The material to the scalar selection field. The value of the penalisation parameter p {\displaystyle p} is generally taken between [ 1 , 3 ] {\displaystyle [1,\,3]} . This has been shown to confirm the micro-structure of the materials. In the SIMP method a lower bound on the Young's modulus is added, E 0 {\displaystyle E_{0}} , to make sure

3149-483: The most implemented interpolation methodologies is the Solid Isotropic Material with Penalisation method (SIMP). This interpolation is essentially a power law E = E 0 + ρ p ( E 1 − E 0 ) {\displaystyle E\;=\;E_{0}\,+\,\rho ^{p}(E_{1}-E_{0})} . It interpolates the Young's modulus of

3216-435: The newfound availability of advanced AM. That is, it involves redesigning them because their entire earlier design—including even how, why, and at which places they were originally divided into discrete parts—was conceived within the constraints of a world where advanced AM did not yet exist. Thus instead of just modifying an existing part design to allow it to be made additively, full-fledged DfAM involves things like reimagining

3283-401: The optimal design should look like, and manual geometry re-construction is required. There are a few solutions which produce optimal designs ready for Additive Manufacturing. A stiff structure is one that has the least possible displacement when given certain set of boundary conditions. A global measure of the displacements is the strain energy (also called compliance ) of the structure under

3350-410: The optimum point with respect to the performance of the AM structure under the known service load. The comprehensive design space of metal AM is boundless and high dimensional, which includes all the possible combinations of alloy compositions, process parameters and structural geometries. However, always a constrained subset of the design space (design subspace) is under consideration. The performance, as

3417-504: The original implants still in place after 40 years of function. In the mid-1970s Brånemark entered into a commercial partnership with the Swedish defense company Bofors to manufacture dental implants and the instrumentation required for their placement. Eventually an offshoot of Bofors, Nobel Pharma, was created to concentrate on this product line. Nobel Pharma subsequently became Nobel Biocare. Brånemark spent almost 30 years fighting

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3484-442: The overall object such that it has fewer parts or a new set of parts with substantially different boundaries and connections. The object thus may no longer be an assembly at all, or it may be an assembly with many fewer parts. Many examples of such deep-rooted practical impact of DfAM have been emerging in the 2010s, as AM greatly broadens its commercialization. For example, in 2017, GE Aviation revealed that it had used DfAM to create

3551-550: The peculiarities of osseointegrated prostheses is that mechanical events at the prosthesis (e.g. touch) are transferred as vibrations through the bone. This "osseoperception" means that the prosthesis user regains a more accurate sense of how the prosthesis is interacting with the world. Users of bone-anchored lower limb prostheses report, for example, that they can tell which type of soil they are walking on due to osseoperception. Recent research on users of bone-anchored upper and lower limb prostheses showed that this osseoperception

3618-440: The porous area. For orthopedic uses, metals such as tantalum or titanium are often used, as these metals have high tensile strength and corrosion resistance with excellent biocompatibility . The process of osseointegration in metal foams is similar to that in bone grafts . The porous bone-like properties of the metal foam contribute to extensive bone infiltration, allowing osteoblast activity to take place. In addition,

3685-416: The porous structure allows for soft tissue adherence and vascularization within the implant. These materials are currently deployed in hip replacement , knee replacement and dental implant surgeries. There are a number of methods used to gauge the level of osseointegration and the subsequent stability of an implant. One widely used diagnostic procedure is percussion analysis, where a dental instrument

3752-440: The possibilities for human use. In dentistry the implementation of osseointegration started in the mid-1960s as a result of Brånemark's work. In 1965 Brånemark, who was at the time Professor of Anatomy at University of Gothenburg , placed dental implants into the first human patient—Gösta Larsson. This patient had a cleft palate defect and needed implants to support a palatal obturator . Gösta Larsson died in 2005, with

3819-485: The preferred properties. For example, in the aerospace field, lattice structures fabricated by AM process can be used for weight reduction. In the bio-medical field, bio-implant made of lattice or cellular structures can enhance osseointegration . Parts with multi-material or complex material distribution can be achieved by additive manufacturing processes. To help designers take advantage of this capability, several design and simulation methods have been proposed to support

3886-406: The prescribed boundary conditions. The lower the strain energy the higher the stiffness of the structure. So, the objective function of the problem is to minimize the strain energy. On a broad level, one can visualize that the more the material, the less the deflection as there will be more material to resist the loads. So, the optimization requires an opposing constraint, the volume constraint. This

3953-546: The prosthesis. In 2021 Professor Al Muderis published a thesis for the requirements for the Doctor of Medical Science discussing Osseointegration for Amputees: Past, Present and Future - Basic Science, Innovations in Surgical Technique, Implant Design and Rehabilitation Strategies. Osseointegration is a dynamic process in which characteristics of the implant (i.e. macrogeometry, surface properties, etc.) play

4020-523: The science of medical bone and joint replacement techniques as well as dental implants and improving prosthetics for amputees . Osseointegration is also defined as: "the formation of a direct interface between an implant and bone, without intervening soft tissue". An osseointegrated implant is a type of implant defined as "an endosteal implant containing pores into which osteoblasts and supporting connective tissue can migrate". Applied to oral implantology, this refers to bone grown right up to

4087-476: The scientific community for acceptance of osseointegration as a viable treatment. In Sweden he was often openly ridiculed at science conferences. His university stopped funding for his research, forcing him to open a private clinic to continue treating patients. Eventually an emerging breed of young academics started to notice the work being done in Sweden. Toronto's George Zarb, a Maltese-born Canadian prosthodontist,

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4154-480: The screws were slightly tighter than when originally put in; at 12 weeks, the screws were more difficult to remove; and at the end of 16 weeks, the screws were so tight that in one specimen the femur was fractured when an attempt was made to remove the screw. Microscopic examinations of the bone structure revealed no reaction to the implants, the trabeculation appeared to be perfectly normal." The reactions described by Leventhal and Bothe et al. would later be coined into

4221-553: The struts (meta-atomic bonds) can be increased drastically by taking advantage of the non-equilibrium solidification phenomenon in Additive Manufacturing, thus increasing the performance of the bulk structures. For AM processes that use heat to fuse powder or feedstock, process consistency and part quality are strongly influenced by the temperature history inside the part during manufacture, especially for metal AM. Thermal modelling can be used to inform part design and

4288-483: The term "osseointegration" by Per-Ingvar Brånemark of Sweden. In 1952, Brånemark did an experiment where he used a titanium implant chamber to study blood flow in rabbit bone. At the end of the experiment, when it became time to remove the titanium chambers from the bone, he discovered that the bone had integrated so completely with the implant that the chamber could not be removed. Brånemark called this "osseointegration", and, like Bothe et al. and Leventhal before him, saw

4355-432: The topology optimization process. Since the topology optimization can help designers to get an optimal complex geometry for additive manufacturing, this technique can be considered one of DfAM methods. Due to the unique capabilities of AM processes, parts with multiscale complexities can be realized. This provides a great design freedom for designers to use cellular structures or lattice structures on micro or meso-scales for

4422-505: The using of additive manufacturing technologies. Some case studies have been done to shows some parts in the original design can be consolidated into one complex part and fabricated by additive manufacturing processes. This redesigning process can be called as parts consolidation. The research shows parts consolidation will not only reduce part count, it can also improve the product functional performance. The design methods which can guide designers to do part consolidation can also be regarded as

4489-537: Was instrumental in bringing the concept of osseointegration to the wider world. The 1983 Toronto Conference is generally considered to be the turning point, when finally the worldwide scientific community accepted Brånemark's work. Osseointegration is now a highly predictable and common treatment modality. Since 2010, Professor Munjed Al Muderis in Sydney, Australia, used a high tensile strength titanium implant with plasma sprayed surface as an intramedullary prosthesis that

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