Design, Optimization, and Evaluation of Additively Manufactured Vintiles Cellular Structure for Acetabular Cup Implant

Nazir A., Abate K.M., Kumar A., Jeng J.

Cellular structures are made up of an interconnected network of plates, struts, or small unit cells and acquire many unique benefits such as, high strength-to-weight ratio, excellent energy absorption, and minimizing material requirements. When compared with the complicated conventional processes, additive manufacturing (AM) technology is capable of fabricating geometries in almost all types of shapes, even with the small cellular structures inside, by adding material layer-by-layer directly from the digital data file. All major industries have been exploiting the benefits of cellular structures due to their prevalence over a wide range of research fields. To date, there are a few state-of-the-art reviews compiled focusing on a specific area of lattice structures, but many aspects still need to be reviewed. Therefore, this paper aims to provide a comprehensive review of the various lattice morphologies, design, and the AM of the cellular structures. Furthermore, the superior properties of the additively fabricated structure, as well as the applications and challenges, are presented. The conducted review has identified the significant limitations and gaps in the existing literature and has highlighted the areas that need further research in the design, optimization, characteristics, and applications, and the AM of the cellular structures. This review would provide a more precise understanding and the state-of-the-art of AM with the cellular structures for engineers and researchers in both academia and industrial applications.

Delikanli Y.E., Kayacan M.C.

This study aims to design, analyze and manufacture lightweight hip implants which have sufficient fatigue performance to enable use in total hip arthroplasty (THA).The lattice structure was applied on an implant geometry, which is frequently used in THA, to provide a reduction in mass and increase flexibility. The implant surfaces were roughened using semispherical pores to improve the osseointegration. The specimens were manufactured by means of direct metal laser sintering (DMLS) and fatigue tests were performed according to ISO 7206-4:2010. Moreover, fatigue analyses of the designed implants were numerically carried out using the finite element method.The applied lattice structure on implant geometry leads to 15-17% reduction in the masses of implants compared to a solid one. It has also been determined that the lightweight implants show more flexible behavior with increasing pore diameter used on the implant surfaces while keeping the lattice structure geometry constant. The fatigue test and finite element analysis (FEA) results are in reasonable agreement. In addition, additively manufactured solid implants have exhibited similar fatigue performance with one produced by conventional methods.This paper presents design, analysis, manufacturing and fatigue test processes of lightweight hip implants. The lattice structure and the semispherical pores were applied on a reference implant geometry and they were manufactured by DMLS. The fatigue tests and FEA were performed to evaluate newly designed implant performance. All the implants successfully completed the fatigue tests without any damage.

Li J., Li W., Li Z., Wang Y., Li R., Tu J., Jin G.

A type of canine fully porous Ti6Al4V acetabular cup was fabricated by a well-controlled powder sintering technique. The traditional hydroxyapatite-coated (HA-coated) cups were also prepared as the control. The characteristics, mechanical and biological properties of the two types of cups were evaluated by scanning electron microscopy, mechanical tests, finite element analysis and canine total hip arthroplasty (THA). Results showed that the porous cup had high porosity and large pore size with good mechanical properties without obvious stress shielding, and it had sufficient safety for implantation according to the finite element analysis. Both groups showed good biocompatibility and osteogenic ability after the THA surgeries, but the porous group had more bone ingrowth and higher bone-implant contact rate according to the micro-CT and histopathologic results. Therefore, the canine fully porous Ti6Al4V acetabular cup fabricated by the sintering technique could provide sufficient space and adequate mechanical support without obvious stress shielding effect for bone ingrowth. Compared with the traditional HA-coated cup, the porous cup may be more effective in achieving in vivo stability, which could contribute to reducing the risk of aseptic loosening.

Affatato S., Merola M., Ruggiero A.

A hip joint replacement is considered one of the most successful orthopedic surgical procedures although it involves challenges that must be overcome. The patient group undergoing total hip arthroplasty now includes younger and more active patients who require a broad range of motion and a longer service lifetime of the implant. The current replacement joint results are not fully satisfactory for these patients’ demands. As particle release is one of the main issues, pre-clinical experimental wear testing of total hip replacement components is an invaluable tool for evaluating new implant designs and materials. The aim of the study was to investigate the cup tensional state by varying the clearance between head and cup. For doing this we use a novel hard-on-soft finite element model with kinematic and dynamic conditions calculated from a musculoskeletal multibody model during the gait. Four different usual radial clearances were considered, ranging from 0 to 0.5 mm. The results showed that radial clearance plays a key role in acetabular cup stress-strain during the gait, showing from the 0 value to the highest, 0.5, a difference of 44% and 35% in terms of maximum pressure and deformation, respectively. Moreover, the presented model could be usefully exploited for complete elastohydrodynamic synovial lubrication modelling of the joint, with the aim of moving towards an increasingly realistic total hip arthroplasty in silico wear assessment accounting for differences in radial clearances.

Wang Y., Zhang L., Daynes S., Zhang H., Feih S., Wang M.Y.

Additive manufacturing (AM) enables fabrication of multiscale cellular structures as a whole part, whose features can span several dimensional scales. Both the configurations and layout pattern of the cellular lattices have great impact on the overall performance of the lattice structure. In this paper, we propose a novel design method to optimize cellular lattice structures to be fabricated by AM. The method enables an optimized load-bearing solution through optimization of geometries of global structures and downscale mesostructures, as well as global distributions of spatially-varying graded mesostructures. A shape metamorphosis technology is incorporated to construct the graded mesostructures with essential interconnections. Experimental testing is undertaken to verify the superior stiffness properties of the optimized graded lattice structure compared to the baseline design with uniform mesostructures.

Wang G., Huang W., Song Q., Liang J.

This study aims to analyze the contact areas and pressure distributions between the femoral head and mortar during normal walking using a three-dimensional finite element model (3D-FEM).Computed tomography (CT) scanning technology and a computer image processing system were used to establish the 3D-FEM. The acetabular mortar model was used to simulate the pressures during 32 consecutive normal walking phases and the contact areas at different phases were calculated.The distribution of the pressure peak values during the 32 consecutive normal walking phases was bimodal, which reached the peak (4.2 Mpa) at the initial phase where the contact area was significantly higher than that at the stepping phase. The sites that always kept contact were concentrated on the acetabular top and leaned inwards, while the anterior and posterior acetabular horns had no pressure concentration. The pressure distributions of acetabular cartilage at different phases were significantly different, the zone of increased pressure at the support phase distributed at the acetabular top area, while that at the stepping phase distributed in the inside of acetabular cartilage.The zones of increased contact pressure and the distributions of acetabular contact areas had important significance towards clinical researches, and could indicate the inductive factors of acetabular osteoarthritis.

Simoneau C., Terriault P., Jetté B., Dumas M., Brailovski V.

This paper focuses on the development of a porous metallic biomimetic femoral stem designed to reduce stress shielding and to provide firm implant fixation through bone ingrowth. The design of this stem starts with the creation of the diagram allowing the establishment of a relationship between the bone ingrowth requirements and the metal additive manufacturing technology limitations. This diagram is then used to determine the optimum porosity (33%) that should compose the porous part of the stem. Afterward, selective laser melting is used to manufacture the porous stem altogether with its fully dense replica. Finite element analysis and numerical homogenization methods are then employed to predict the mechanical behavior of the stem. Both stems are finally tested following the ISO 7206-4 (2010) requirements under static loading conditions. The digital image correlation technique is employed to obtain the displacement and strain fields during the tests, and to validate the finite element model. While the finite element model of the dense stem has been successfully validated, that of the porous stem has shown ~ 40% higher stiffness than that measured experimentally. It has been proven that this discrepancy is due to the difference between the experimentally-measured (42%) and the numerically-targeted (33%) porosities.

Limmahakhun S., Oloyede A., Sitthiseripratip K., Xiao Y., Yan C.

The use of cobalt chromium (CoCr) in orthopaedic joint replacement shields the peri-implant bone stress, contributing to a premature loosening of the implants. In order to reduce the need for revision surgeries, light weight implants with tailored functionalities need to be developed. In this study, the compressive mechanical properties of laser-melted CoCr cellular structures with a pillar octahedral architecture [0° ± 45°] were investigated. Four types of graded cellular structures, based on grading orientations along radial and longitudinal planes, were manufactured using selective laser melting techniques. The cellular structures in this study have the mechanical properties (E = 2.3–3.1 GPa, σ = 113–523 MPa) compatible with bone structures. Grading a porosity of the CoCr cellular structures provides a greater stress transfer to the proximal peri-implant area. The axially graded cellular structures demonstrated significant reduction of the peri-implant stress shielding. Incorporation of CoCr graded cellular structures into a structure like femoral stems is expected to have the potential to reduce the revision surgeries.

Xiao L., Song W., Wang C., Tang H., Liu N., Wang J.

The initial yield behavior of Ti–6Al–4V rhombic dodecahedron lattice structures under biaxial loading at different temperatures is investigated. A modified yield criterion based on the hypothesis that the yield of materials is determined by total strain energy density, is proposed to derive the biaxial yield surface of isotropic cellular materials at different temperatures. The core advantage of this model is that the multi-axial yield behavior can be predicted by uniaxial tests instead of taking multi-axial tests. Temperature is taken into consideration by adding the thermal stress term into the model, which influences the hydrostatic pressure in the yield criterion. Then the effect on the yield surface caused by the temperature is discussed. Afterwards, the yield surfaces of Ti–6Al–4V lattice at elevated temperatures are predicted by the modified model. In order to verify the analytical framework, numerical approach is used by coupling the thermal and mechanical analysis to simulate the biaxial loading process at different temperatures. The numerical results match well with the prediction of the modified model.

Mengucci P., Barucca G., Gatto A., Bassoli E., Denti L., Fiori F., Girardin E., Bastianoni P., Rutkowski B., Czyrska-Filemonowicz A.

Direct Metal Laser Sintering (DMLS) technology based on a layer by layer production process was used to produce a Co-Cr-Mo-W alloy specifically developed for biomedical applications. The alloy mechanical response and microstructure were investigated in the as-sintered state and after post-production thermal treatments. Roughness and hardness measurements, and tensile and flexural tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate the microstructure in different conditions. Results showed an intricate network of ε-Co (hcp) lamellae in the γ-Co (fcc) matrix responsible of the high UTS and hardness values in the as-sintered state. Thermal treatments increase volume fraction of the ε-Co (hcp) martensite but slightly modify the average size of the lamellar structure. Nevertheless, thermal treatments are capable of producing a sensible increase in UTS and hardness and a strong reduction in ductility. These latter effects were mainly attributed to the massive precipitation of an hcp Co3(Mo,W)2Si phase and the contemporary formation of Si-rich inclusions.

Wang X., Xu S., Zhou S., Xu W., Leary M., Choong P., Qian M., Brandt M., Xie Y.M.

One of the critical issues in orthopaedic regenerative medicine is the design of bone scaffolds and implants that replicate the biomechanical properties of the host bones. Porous metals have found themselves to be suitable candidates for repairing or replacing the damaged bones since their stiffness and porosity can be adjusted on demands. Another advantage of porous metals lies in their open space for the in-growth of bone tissue, hence accelerating the osseointegration process. The fabrication of porous metals has been extensively explored over decades, however only limited controls over the internal architecture can be achieved by the conventional processes. Recent advances in additive manufacturing have provided unprecedented opportunities for producing complex structures to meet the increasing demands for implants with customized mechanical performance. At the same time, topology optimization techniques have been developed to enable the internal architecture of porous metals to be designed to achieve specified mechanical properties at will. Thus implants designed via the topology optimization approach and produced by additive manufacturing are of great interest. This paper reviews the state-of-the-art of topological design and manufacturing processes of various types of porous metals, in particular for titanium alloys, biodegradable metals and shape memory alloys. This review also identifies the limitations of current techniques and addresses the directions for future investigations.

Yan C., Hao L., Hussein A., Young P.

Triply periodic minimal surface (TPMS) structures have already been shown to be a versatile source of biomorphic scaffold designs. Therefore, in this work, Ti-6Al-4V Gyroid and Diamond TPMS lattices having an interconnected high porosity of 80-95% and pore sizes in the range of 560-1600 μm and 480-1450 μm respectively were manufactured by selective laser melting (SLM) for bone implants. The manufacturability, microstructure and mechanical properties of the Ti-6Al-4V TPMS lattices were evaluated. Comparison between 3D micro-CT reconstructed models and original CAD models of the Ti-6Al-4V TPMS lattices shows excellent reproduction of the designs. The as-built Ti-6Al-4V struts exhibit the microstructure of columnar grains filled with very fine and orthogonally oriented α' martensitic laths with the width of 100-300 nm and have the microhardness of 4.01 ± 0.34 GPa. After heat treatment at 680°C for 4h, the α' martensite was converted to a mixture of α and β, in which the α phase being the dominant fraction is present as fine laths with the width of 500-800 nm and separated by a small amount of narrow, interphase regions of dark β phase. Also, the microhardness is decreased to 3.71 ± 0.35 GPa due to the coarsening of the microstructure. The 80-95% porosity TPMS lattices exhibit a comparable porosity with trabecular bone, and the modulus is in the range of 0.12-1.25 GPa and thus can be adjusted to the modulus of trabecular bone. At the same range of porosity of 5-10%, the moduli of cortical bone and of the Ti-6Al-4V TPMS lattices are in a similar range. Therefore, the modulus and porosity of Ti-6Al-4V TPMS lattices can be tailored to the levels of human bones and thus reduce or avoid "stress shielding" and increase longevity of implants. Due to the biomorphic designs, and high interconnected porosity and stiffness comparable to human bones, SLM-made Ti-6Al-4V TPMS lattices can be a promising material for load bearing bone implants.

Kadkhodapour J., Montazerian H., Darabi A.C., Anaraki A.P., Ahmadi S.M., Zadpoor A.A., Schmauder S.

Since the advent of additive manufacturing techniques, regular porous biomaterials have emerged as promising candidates for tissue engineering scaffolds owing to their controllable pore architecture and feasibility in producing scaffolds from a variety of biomaterials. The architecture of scaffolds could be designed to achieve similar mechanical properties as in the host bone tissue, thereby avoiding issues such as stress shielding in bone replacement procedure. In this paper, the deformation and failure mechanisms of porous titanium (Ti6Al4V) biomaterials manufactured by selective laser melting from two different types of repeating unit cells, namely cubic and diamond lattice structures, with four different porosities are studied. The mechanical behavior of the above-mentioned porous biomaterials was studied using finite element models. The computational results were compared with the experimental findings from a previous study of ours. The Johnson-Cook plasticity and damage model was implemented in the finite element models to simulate the failure of the additively manufactured scaffolds under compression. The computationally predicted stress-strain curves were compared with the experimental ones. The computational models incorporating the Johnson-Cook damage model could predict the plateau stress and maximum stress at the first peak with less than 18% error. Moreover, the computationally predicted deformation modes were in good agreement with the results of scaling law analysis. A layer-by-layer failure mechanism was found for the stretch-dominated structures, i.e. structures made from the cubic unit cell, while the failure of the bending-dominated structures, i.e. structures made from the diamond unit cells, was accompanied by the shearing bands of 45°.

Amin Yavari S., Ahmadi S.M., Wauthle R., Pouran B., Schrooten J., Weinans H., Zadpoor A.A.

Meta-materials are structures when their small-scale properties are considered, but behave as materials when their homogenized macroscopic properties are studied. There is an intimate relationship between the design of the small-scale structure and the homogenized properties of such materials. In this article, we studied that relationship for meta-biomaterials that are aimed for biomedical applications, otherwise known as meta-biomaterials. Selective laser melted porous titanium (Ti6Al4V ELI) structures were manufactured based on three different types of repeating unit cells, namely cube, diamond, and truncated cuboctahedron, and with different porosities. The morphological features, static mechanical properties, and fatigue behavior of the porous biomaterials were studied with a focus on their fatigue behavior. It was observed that, in addition to static mechanical properties, the fatigue properties of the porous biomaterials are highly dependent on the type of unit cell as well as on porosity. None of the porous structures based on the cube unit cell failed after 10(6) loading cycles even when the applied stress reached 80% of their yield strengths. For both other unit cells, higher porosities resulted in shorter fatigue lives for the same level of applied stress. When normalized with respect to their yield stresses, the S-N data points of structures with different porosities very well (R(2)>0.8) conformed to one single power law specific to the type of the unit cell. For the same level of normalized applied stress, the truncated cuboctahedron unit cell resulted in a longer fatigue life as compared to the diamond unit cell. In a similar comparison, the fatigue lives of the porous structures based on both truncated cuboctahedron and diamond unit cells were longer than that of the porous structures based on the rhombic dodecahedron unit cell (determined in a previous study). The data presented in this study could serve as a basis for design of porous biomaterials as well as for corroboration of relevant analytical and computational models.

Jung J.W., Park J.H., Hong J.M., Kang H., Cho D.

This study is a part of ongoing research conducted to develop an ideal implant for augmentation rhinoplasty using a combination of cartilage tissue engineering and 3D printing (3DP) techniques. A promising nasal implant-shaped (NIS) scaffold for rhinoplasty should have flexibility similar enough to native cartilage tissue to maintain its mechanical stability after implantation into a nose. In scaffold fabrication using 3DP, the pore pattern or architecture has a significant effect on the mechanical properties of a scaffold. In this study, we proposed octahedron pore architecture inspired by a zigzag spring, which stores more mechanical energy than a simple rod. Therefore, we assumed that the scaffold having octahedron pore architecture is more flexible than one that has the cube or lattice pore architecture that is widely used in tissue engineering based on 3DP. To verify this assumption, scaffolds having octahedron, cube, or lattice pore architecture with the same porosity and same unit cell size were fabricated using projection-based micro-stereolithography and sacrificial molding, and their mechanical behaviors were analyzed using compression and three-point bending tests. Compared to the other pore types, the octahedron pore architecture had superior flexibility, which is beneficial for clinical application of NIS scaffolds.

Abdullah N.N., Ammarullah M.I., Salaha Z.F., Baharuddin M.H., Kadir M.R., Ramlee M.H.

Wang Y., Chen J., Li C., Ma C., Chen L., Wu Y., Gao D., Wang H.

H. Foroughi A., Valeri C., Razavi M.J.

Abstract The design and optimization of bone scaffolds are critical for the success of bone tissue engineering (BTE) applications. This review paper provides a comprehensive analysis of computational optimization methods for bone scaffold architecture, focusing on the balance between mechanical stability, biological compatibility, and manufacturability. Finite Element Method (FEM), Computational Fluid Dynamics (CFD), and various optimization algorithms have been discussed for their roles in simulating and refining scaffold designs. The integration of multiobjective optimization and topology optimization has been highlighted for developing scaffolds that meet the multifaceted requirements of BTE. Challenges such as the need for consideration of manufacturing constraints, and the incorporation of degradation and bone regeneration models into the optimization process have been identified. The review underscores the potential of advanced computational tools and additive manufacturing techniques in evolving the field of BTE, aiming to improve patient outcomes in bone tissue regeneration. The reliability of current optimization methods is examined, with suggestions for incorporating non-deterministic approaches and in vivo validations to enhance the practical application of optimized scaffolds. The review concludes with a call for further research into artificial intelligence-based methodologies to drive the next generation of scaffold design and optimization.

Gunay M., Meral T.

In biomedical applications, various additive manufacturing (AM) techniques such as fused deposition modeling (FDM), inkjet, stereolithography (STL), direct powder extrusion (DPE), and selective laser sintering (SLS), as well as other digitally controlled 3D printing (3DP) techniques, are used. Advances in AM methods have led to the development of tissues, microdevices, artificial organs, personalized prostheses and orthoses, dental and various bone implants, biopharmaceutical applications and drug delivery system (DDS), and patient-specific surgical models, etc. that require multiscale structures, materials and functions. It enables the three-dimensional (3D) design and manufacturing of biomedical products with complex geometries. Additionally, it enables the modeling and 3DP using the biomimetic approach for applications that require lightweight and durable structures as well as biocompatibility. The purpose of this study is to review macro-to-nano multiscale AM technologies, design and modeling status, materials, and applications used for biomedical applications. Additionally, recommendations are given on what needs to be done to overcome the current limitations and challenges of micro/-nano printing in current AM technologies.

Dias J.M., da Silva F.S., Gasik M., Miranda M.G., Bartolomeu F.J.

AbstractThe prospect of improved quality of life and the increasingly younger age of patients benefiting from Total Hip Arthroplasty will soon lead to the landmark of 10 million interventions per year worldwide. More than 10% of these procedures lead to significant bone resorption, increasing the need for revision surgeries. Current research focuses on the development of hip implant designs to achieve a stiffness profile closer to the natural bone. Additive Manufacturing has emerged as a viable solution by offering promising results in the fabrication of implant architectures based on metallic cellular structures that have demonstrated their capacity to replicate bone behavior mechanically and biologically. Aiming to offer an up-to-date overview of titanium cellular structures in hip implants, for both acetabular and femoral components, produced by Additive Manufacturing, including its design intricacies and performance, this comprehensive review meticulously examines the historical development of hip implants, encompassing commercial solutions and innovative attempts. A broad view of the practical applications and transformative potential of hip implants incorporating cellular structures is presented, aiming to outline opportunities for innovation.

Gowtham S., Dharanidharan M., Manoj S., Balakumar B.S., Bharathram B.

Nazir A., Gohar A., Lin S., Jeng J.

Wang Y., Hsu C.

This study utilizes the Taguchi method and sub-model analysis technique to create a novel optimization lattice for the hypo-loading region. The lattice is designed to mimic the mechanical properties of bone and promote the growth of immature bone under appropriate loading to enhance the osseointegration capacity of implants. The Maxillary lattice implant (ML implant) was developed to address the case of Maxillary antral carcinoma. The implant's structural parameters, including Angle of rotation (A), Concave angle (B), Pillar diameter (C), and Fillet radius (D), were analyzed to design and optimize the Hypo-Loading lattice (HL lattice) with various structures. Through the analysis, the optimal structural parameters for the HL lattice were determined, resulting in the creation of the Optimal HL lattice with exceptional Elastic Admissible Strain (EAS), a comparable elastic modulus to bone, and outstanding mechanical robustness. This feature of the Optimal HL lattice improves the bionic performance.

Rehman M., Wang Y., Ishfaq K., Mushtaq R.T., Kumar M.S., Yang H.

The fabrication of cellular structures with biocompatible materials for implants has increased in recent years because of human aging and traffic road accidents. Laser powder bed fusion or Selective laser melting (SLM) can fabricate various load-bearing implants with mass customization in design and manufacturing. This work involves a manufacturability study in selective laser melting of biomedical Ti alloy implant plug for Osteoarthritis patients. The investigation involved the control variables like laser power (175,185,195) watt, scanning speed (1100,1250,1400) mm/s, and hatch spacing (0.065,0.0725,0.08) mm alongwith output responses such as Compressive yield strength, Elastic modulus, porosity, and surface roughness. The experiments were performed using Box Behnken design in Response surface modelling for collaborative optimization. The results were explicitly explained with an in-depth process physics supported with Characterization involving Scanning electron microscopy, Electro-dispersive spectroscopy, X-ray diffraction, micro-computed tomography, optical profilometry analyses, and process schematics. The optimal setting with laser power (195 W), scanning speed (1100 mm/s), and hatch spacing (0.068 mm) yielded high compressive yield strength (22.41 MPa), near trabecular bone Elastic modulus (0.891GPa), controlled porosity formation (29.32 %), and optimal surface roughness (3.647 μm). Topography resulted in a prominent lack of fusion pores because of low energy density levels, whereas the optimal settings produced around 15 % improvement from design of experiments data.

Distefano F., Pasta S., Epasto G.

The progress in additive manufacturing has remarkably increased the application of lattice materials in the biomedical field for the fabrication of scaffolds used as bone substitutes. Ti6Al4V alloy is widely adopted for bone implant application as it combines both biological and mechanical properties. Recent breakthroughs in biomaterials and tissue engineering have allowed the regeneration of massive bone defects, which require external intervention to be bridged. However, the repair of such critical bone defects remains a challenge. The present review collected the most significant findings in the literature of the last ten years on Ti6Al4V porous scaffolds to provide a comprehensive summary of the mechanical and morphological requirements for the osteointegration process. Particular attention was given on the effects of pore size, surface roughness and the elastic modulus on bone scaffold performances. The application of the Gibson–Ashby model allowed for a comparison of the mechanical performance of the lattice materials with that of human bone. This allows for an evaluation of the suitability of different lattice materials for biomedical applications.

Safavi S., Yu Y., Robinson D.L., Gray H.A., Ackland D.C., Lee P.V.

Abstract Background Total joint replacements are an established treatment for patients suffering from reduced mobility and pain due to severe joint damage. Aseptic loosening due to stress shielding is currently one of the main reasons for revision surgery. As this phenomenon is related to a mismatch in mechanical properties between implant and bone, stiffness reduction of implants has been of major interest in new implant designs. Facilitated by modern additive manufacturing technologies, the introduction of porosity into implant materials has been shown to enable significant stiffness reduction; however, whether these devices mitigate stress-shielding associated complications or device failure remains poorly understood. Methods In this systematic review, a broad literature search was conducted in six databases (Scopus, Web of Science, Medline, Embase, Compendex, and Inspec) aiming to identify current design approaches to target stress shielding through controlled porous structures. The search keywords included ‘lattice,’ ‘implant,’ ‘additive manufacturing,’ and ‘stress shielding.’ Results After the screening of 2530 articles, a total of 46 studies were included in this review. Studies focusing on hip, knee, and shoulder replacements were found. Three porous design strategies were identified, specifically uniform, graded, and optimized designs. The latter included personalized design approaches targeting stress shielding based on patient-specific data. All studies reported a reduction of stress shielding achieved by the presented design. Conclusion Not all studies used quantitative measures to describe the improvements, and the main stress shielding measures chosen varied between studies. However, due to the nature of the optimization approaches, optimized designs were found to be the most promising. Besides the stiffness reduction, other factors such as mechanical strength can be considered in the design on a patient-specific level. While it was found that controlled porous designs are overall promising to reduce stress shielding, further research and clinical evidence are needed to determine the most superior design approach for total joint replacement implants.

ZHANG Q., LI B., WEI G., LIU G., LIU J.

Structure unit type is the most important factor for the mechanical properties and permeability of biomedical porous scaffolds. Therefore, in this work, four kinds of commonly used structure units including three periodic minimal surface (Primitive (P) and Gyroid (G) structures), body-centered cubic (BCC) and diamond (D) structures were chosen to design the structure units and porous scaffolds with the same porosity, and the mechanical and permeability of the structure units and scaffolds were systematically analyzed by using the finite element method. The results show that the elastic modulus of scaffolds decreases with the increase of porosity, and the order of elastic modulus is: P [Formula: see text] D [Formula: see text] G [Formula: see text] BCC structure. P structure unit and porous scaffolds exhibit the best deformation resistance, but the structures have the most severe stress concentration at the joints. BCC structure unit and porous scaffolds have the worst deformation resistance, and the stress concentration at the joints is also obvious. Fluid simulation shows that the porous scaffolds exhibit good permeability and can meet the requirements for the use of biomedical porous scaffolds. The results of this paper provide a theoretical basis for the design and manufacture of porous scaffolds, and have a certain reference value.

Torres Pérez A.I., Fernández Fairén M., Torres Pérez Á.A., Gil Mur J.

The application of porous materials is increasingly being used in orthopaedic surgery due to its good results. Bone growth within the pores results in excellent mechanical fixation with the bone, as well as good bone regeneration. The pores, in addition to being colonised by bone, produce a decrease in the modulus of elasticity that favours the transfer of loads to the bone. This research shows the results of an experimental study where we have created critical osteoperiosteal defects of 10 mm on rabbit’s radius diaphysis. In one group of 10 rabbits (experimental group) we have implanted a bioactive porous titanium cylinder, and in another group we have allowed spontaneous regeneration (control group). Mechanical tests were performed to assess the material. Image diagnostic techniques (X-ray, scanner and 3D scan: there are no references on the literature with the use of CT-scan in bone defects) and histological and histomorphometric studies post-op and after 3, 6 and 12 months after the surgery were performed. All the control cases went through a pseudoarthrosis. In 9 of the 10 cases of the experimental group complete regeneration was observed, with a normal cortical-marrow structure established at 6 months, similar to normal bone. Titanium trabecular reached a bone percentage of bone inside the implant of 49.3% on its surface 3 months post-op, 75.6% at 6 months and 81.3% at 12 months. This porous titanium biomaterial has appropriate characteristics to allow bone ingrowth, and it can be proposed as a bone graft substitute to regenerate bone defects, as a scaffold, or as a coating to achieve implant osteointegration.

Alqahtani A.S., AlFadda A.M., Eldesouky M., Alnuwaiser M.K., Al-Saleh S., Alresayes S., Alshahrani A., Vohra F., Abduljabbar T.

The purpose of the present study was to evaluate the influence of fabrication techniques on the surface micro-roughness (Ra) and marginal misfit of cobalt chromium (CoCr) copings. A mandibular first molar was prepared for a metal ceramic crown. Forty metal copings were prepared and divided into groups (n = 10). Group 1, Casting-Lost wax technique (Cast-LWT), Group 2, CAD-CAM, Group 3, Selective laser melting (SLM), and Group 4, Digital light processing-Cast (DLP-Cast). Ra was measured using laser profilometry and marginal misfit was analyzed with Micro-CT. Analysis of variance (ANOVA), Tukey multiple comparison, and correlation coefficient tests were applied (p < 0.05). SLM technique showed the highest Ra (2.251 ± 0.310 μm) and the Cast-LWT group presented the lowest Ra (1.055 ± 0.184 μm). CAD-CAM copings showed statistically lower Ra compared with SLM samples (p = 0.028), but comparable Ra to DLP-Cast (p > 0.05). CoCr copings fabricated from the DLP-Cast technique demonstrated the highest marginal misfit (147.746 ± 30.306 μm) and the lowest misfit was established by SLM copings (27.193 ± 8.519 μm). The SLM technique displayed lower marginal misfit than DLP-Cast and CAD-CAM (p = 0.001), but comparable misfit to Cast-LWT copings. Ra influenced the marginal misfit in CAD-CAM, SLM, and DLP-Cast technique-fabricated copings. (p < 0.01). Marginal misfit and Ra of CoCr copings are contingent on the different fabrication techniques.

Abulkhanov S., Bairikov I., Goryainov D., Slesarev O., Bairikov A.

The article suggests the technique of constructing a transplant to compensate the loss of lower jaw bone tissue. We chose the cellular structure of the transplant, which allows restoring vital functions to the patient in the shortest possible time. The implant design consists of the following steps: 1. On the basis of X-rays of the affected jaw, we constructed a 3D geometric model of the lost bone fragment. 2. On the basis of X-rays of the affected jaw, statistical data, clinical experience, and available information about the patient's jaw state before its destruction, we built a geometric full 3D model of the jaw before losing the bone fragment. 3. We obtained a 3D geometric model of the lost bone fragment of the lower jaw by subtracting a 3D model of the jaw without the bone fragment from the 3D model of the jaw before losing the bone fragment. A cellular structure was assigned to the 3D model of the lost bone fragment. 4. Using the ANSYS software environment we determined the deformations of the damaged jaw under the impact of the implant with a pre-selected form, size and periodicity of cells. We applied the force of 180 N to the implant, which corresponds to the nominal teeth force. We also considered the variant when the force applied by the teeth on the jaw reached 4000 N. For the chosen implant fixation means on the affected jaw and for the chosen parameters of the implant cell structure we determined that the deformations of the affected jaw are minimal for the nominal teeth forces applied to the jaw. This leads to the reduction of the patient's rehabilitation time. Bone tissue germination inside the implant cells can cause the increase of its volume (mass) two times. The developed technique can be used to create implants that compensate the loss of bone tissue of other human skeleton bones.