Porous Implants Research Articles

In vitro evaluation of cytotoxicity and genotoxicity of porous nickel titanium dental implants produced by metal injection molding technique.

Porous NiTi (pNiTi) is a promising biomaterial for functional long-term implantation that has been produced using various manufacturing techniques and tested for biocompatibility. pNiTi produced using a more recent technology of Metal Injection Molding (MIM) has shown better physical and mechanical properties than those produced by earlier manufacturing methods, but its biocompatibility has yet to be determined. Hence, extracts from pNiTi dental implants produced by MIM were tested for cytotoxicity and genotoxicity in this work. Its toxicity was evaluated at the cellular and in vitro levels using elution and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays. Short-term testing revealed that pNiTi extract was cytocompatible with L-929 fibroblast and V79-4 lung cells, with no cell lysis or reactivity observed, respectively (USP grade 0). Following exposure to varied extract concentrations, good cell viability was observed where the lowest concentration showed the highest optical density (OD) and cell viability (2.968 ± 0.117 and 94%, respectively), and the highest concentration had the least OD and cell viability (2.251 ± 0.054 and 71%, respectively). pNiTi extracts demonstrated genocompatibility in two independent assays: mutagenic potential using a bacterial reverse mutation test and a clastogenic effect on chromosomes using the micronucleus test. Similar to the negative control reactions, there was no significant increase in revertant colonies following exposure to 100% pNiTi extract with and without metabolic activation (p = .00). No DNA clastogenic activity was caused by pNiTi at varied extract concentrations as compared to the negative control when tested with and without metabolic activation (p = .00). As a result, both cytotoxic and genotoxic investigations have confirmed that pNiTi dental implants utilizing the MIM process are cytocompatible and genocompatible in the short term, according to the International Standard, ISO 10993 - Parts 3, 5, and 33.

Mechanical properties, in vitro biodegradable behavior, biocompatibility and osteogenic ability of additively manufactured Zn-0.8Li-0.1Mg alloy scaffolds

Alloying and structural design provide flexibility to modulate performance of biodegradable porous implants manufactured by laser powder bed fusion (L-PBF). Herein, bulk Zn-0.8Li-0.1Mg was first fabricated to indicate the influence of the ternary alloy system on strengthening effect. Porous scaffolds with different porosities, including 60 % (P60), 70 % (P70) and 80 % (P80), were designed and fabricated to study the influence of porosity on mechanical properties, in vitro degradation behavior, biocompatibility and osteogenic ability. Pure Zn (Zn-P70) scaffolds with a porosity of 70 % were utilized for the comparison. The results showed Zn-0.8Li-0.1Mg bulks had an ultimate tensile strength of 460.78 ± 5.79 MPa, which was more than 3 times that of pure Zn ones and was the highest value ever reported for Zn alloys fabricated by L-PBF. The compressive strength (CS) and elastic modulus (E) of scaffolds decreased with increasing porosities. The CS of P70 scaffolds was 24.59 MPa, more than 2 times that of Zn-P70. The weight loss of scaffolds during in vitro immersion increased with increasing porosities. Compared with Zn-P70, a lower weight loss, better biocompatibility and improved osteogenic ability were observed for P70 scaffolds. P70 scaffolds also exhibited the best biocompatibility and osteogenic ability among all the used porosities. Influence mechanism of alloying elements and structural porosities on mechanical behaviors, in vitro biodegradation behavior, biocompatibility and osteogenic ability of scaffolds were discussed using finite element analysis and the characterization of degradation products. The results indicated that the proper design of alloying and porosity made Zn-0.8Li-0.1Mg scaffolds promising for biodegradable applications.

Characterizing Mineral Ellipsoids in New Bone Formation at the Interface of Ti6Al4V Porous Implants

AbstractThe hierarchy of newly formed bone contains elements of disorder within an ordered multiscale structure, spanning from the macroscale to below the nanoscale. With mineralized structures presenting in the shape of ellipsoids in mature and mineralizing tissue, this work characterizes the heterogeneity in the mineral ellipsoid packing at the interface of porous titanium implants. Using scanning transmission electron microscopy and plasma‐focused ion beam–scanning electron microscopy, mineral ellipsoids are characterized at the implant interface in both 2D and 3D. Heterogeneous in their size and shape within the newly formed bone tissue, ellipsoids are observed with alternating orientations corresponding to unique lamellar packets within 23 µm of the titanium implant interface—although this motif is not universal, and a mineral‐dense zone can also appear at the implant interface. Short‐order ellipsoid orientation shifts are also present in the 3D probe of the implant interface, where a ≈90° misorientation angle between neighboring packets of mineral ellipsoids (and an intervening organic layer) resolves with increasing distance from the titanium. Combined with local patches of woven‐to‐lamellar transition, the early heterogeneity and transformation of peri‐implant bone structure is a quintessential step in the development of a functional connection between implant and bone.

Letter to the Editor Regarding the Article "Results of a Highly Porous Metal-Backed Cementless Patella Implant: A Minimum 5-Year Follow-Up".

Letter to the Editor Regarding the Article "Results of a Highly Porous Metal-Backed Cementless Patella Implant: A Minimum 5-Year Follow-Up".

Compressive properties and deformation mechanism of selective laser melting of Ti6Al4V porous femoral implants based on topological optimization

Although the design and mechanical properties of the porous structure have been widely explored, the porous structure and the unit cell with excellent mechanical properties matching the demands of femur should be further investigated. In this research, a porous structure based on face-centered cubic unit cell was constructed to match the femur's natural state and vertical direction at an angle of 7° via structural topology optimization. Three types of Ti6Al4V porous structures with different pore sizes were produced by selective laser melting (SLM). The influence of porosity on the compressive properties and deformation mechanisms was analyzed by experiments and simulations. In the compression process of three porous structures with different porosities, there are four obvious stages: the early elastic stage, the abrupt drop stage following stress increase, the Area III, and the ultimate densification stage. However, the four stages of porous structure vary in porosity. When the porosity is 81.5 %, the stress fluctuates in the region where the abrupt drop stage following stress increase. With increasing porosity, Young's modulus and yield strength decrease. Only the porous structure with a pore diameter of 0.7 mm and porosity of 67.5 % has a Young's modulus and yield strength meeting the requirements of bones, and is the best bone replacement. Bending is the unit cell's main deformation mechanism based on Maxwell equation analysis. Both the Johnson-Cook constitutive model and the experimental data demonstrate the shear deformation of porous structures. In comparison to the compressive performance of unit cells designed using traditional methods, the topology optimization's unit cells exhibit higher relative Young's modulus.

A Brief Review of Current Trends in the Additive Manufacturing of Orthopedic Implants with Thermal Plasma-Sprayed Coatings to Improve the Implant Surface Biocompatibility

The demand for orthopedic implants is increasing, driven by a rising number of young patients seeking an active lifestyle post-surgery. This has led to changes in manufacturing requirements. Joint arthroplasty operations are on the rise globally, and recovery times are being reduced by customized endoprostheses that promote better integration. Implants are primarily made from metals and ceramics such as titanium, hydroxyapatite, zirconium, and tantalum. Manufacturing processes, including additive manufacturing and thermal plasma spraying, continue to evolve. These advancements enable the production of tailored porous implants with uniform surface coatings. Coatings made of biocompatible materials are crucial to prevent degradation and enhance biocompatibility, and their composition, porosity, and roughness are actively explored through biocompatibility testing. This review article focuses on the additive manufacturing of orthopedic implants and thermal plasma spraying of biocompatible coatings, discussing their challenges and benefits based on the authors’ experience with selective laser melting and microplasma spraying of metal-ceramic coatings.

The Concept of Scaffold-Guided Bone Regeneration for the Treatment of Long Bone Defects: Current Clinical Application and Future Perspective.

The treatment of bone defects remains a challenging clinical problem with high reintervention rates, morbidity, and resulting significant healthcare costs. Surgical techniques are constantly evolving, but outcomes can be influenced by several parameters, including the patient's age, comorbidities, systemic disorders, the anatomical location of the defect, and the surgeon's preference and experience. The most used therapeutic modalities for the regeneration of long bone defects include distraction osteogenesis (bone transport), free vascularized fibular grafts, the Masquelet technique, allograft, and (arthroplasty with) mega-prostheses. Over the past 25 years, three-dimensional (3D) printing, a breakthrough layer-by-layer manufacturing technology that produces final parts directly from 3D model data, has taken off and transformed the treatment of bone defects by enabling personalized therapies with highly porous 3D-printed implants tailored to the patient. Therefore, to reduce the morbidities and complications associated with current treatment regimens, efforts have been made in translational research toward 3D-printed scaffolds to facilitate bone regeneration. Three-dimensional printed scaffolds should not only provide osteoconductive surfaces for cell attachment and subsequent bone formation but also provide physical support and containment of bone graft material during the regeneration process, enhancing bone ingrowth, while simultaneously, orthopaedic implants supply mechanical strength with rigid, stable external and/or internal fixation. In this perspective review, we focus on elaborating on the history of bone defect treatment methods and assessing current treatment approaches as well as recent developments, including existing evidence on the advantages and disadvantages of 3D-printed scaffolds for bone defect regeneration. Furthermore, it is evident that the regulatory framework and organization and financing of evidence-based clinical trials remains very complex, and new challenges for non-biodegradable and biodegradable 3D-printed scaffolds for bone regeneration are emerging that have not yet been sufficiently addressed, such as guideline development for specific surgical indications, clinically feasible design concepts for needed multicentre international preclinical and clinical trials, the current medico-legal status, and reimbursement. These challenges underscore the need for intensive exchange and open and honest debate among leaders in the field. This goal can be addressed in a well-planned and focused stakeholder workshop on the topic of patient-specific 3D-printed scaffolds for long bone defect regeneration, as proposed in this perspective review.

Biomechanical Investigation of Patient-Specific Porous Dental Implants: A Finite Element Study

The design of the implant and osseointegration play an important role in the long-term stability of implants. This study aims to investigate the impact of porous implants on full and partial osseointegration in varying bone qualities. Finite element models of porous implants were modeled and assembled with normal and weak bones considering full and partial osseointegration. These assemblies were simulated under an occlusal load of 200 N when the outer surfaces of bones were fixed in all directions. The results showed that in the case of full osseointegration, the stresses in surrounding bones were increased with decreasing implant stiffness, while decreased in partial osseointegration. Moreover, the maximum octahedral shear strain in the weak bone exceeded 3000 µε in all the cases but decreased (from 7256 to 3632 µε) with decreasing implant stiffness. According to the mechanostat hypothesis, using porous implants in normal bone may enhance bone density in full osseointegration, while susceptivity of bone damage may reduce in weak bones using porous implants. Thus, careful selection of implant material and design based on the patient’s specific bone quality is crucial for successful outcomes.

Bionic Porous Design and Mechanical Response of Short Implants

Due to the material itself and the traditional geometric design, short implants have the problems of high stiffness, less osseointegrated area, and lower long-term reliability in clinical application. In this research, short implants with various porous structures were constructed and their biomechanical responses were evaluated, including biomechanical properties, compression capability, and stress distribution of surrounding bone tissue. Thus, three types of short implants were built: the diamond-like porous short implant (5.0 × 5.0 mm), the hexahedral porous short implant (5.0 × 5.0 mm), and the solid short implant (5.0 × 5.0 mm). Three implant-supported prosthetic models were built based on the above three implants, and their static mechanical properties were assessed. Besides, the average stiffness of regular cylindrical samples was calculated by compression test simulation. The result confirmed that hexahedral porous short implants showed minimum peak stress compared with the diamond-like porous and solid short implants. Similarly, the value of stress peaks in the bone-implant interface for the hexahedral porous short implant appeared lower than the other two short implants. Compression simulation indicated the average stiffness of cylinders after diamond-like and hexahedral porous design was 92.2% and 56.3% lower than the solid cylinder. Compared with the other two designs, the hexahedral porous short implant obtained better stress distribution, even avoiding bone overstress.

Design and Additive Manufacturing of Acetabular Implant with Continuously Graded Porosity.

Porous structured metallic implants are preferable as bone graft substitutes due to their faster tissue integration mediated by bone in-growth and vascularization. The porous scaffolds/implants should also mimic the graded structure of natural bone to ensure a match of mechanical properties. This article presents a method for designing a graded porous structured acetabular implant and identifies suitable parameters for manufacturing the model through additive manufacturing. The design method is based on slice-wise modification to ensure continuity of gradation. Modification of the slices was achieved through the binary image processing route. A geodesic dome-type design was adopted for developing the acetabular cup model from the graded porous structure. The model had a solid shell with the target porosity and pore size gradually changing from 65% and 950 µm, respectively, in the inner side to 75% and 650 µm, respectively, towards the periphery. The required dimensions of the unit structures and the combinations of pore structure and strut diameter necessary to obtain the target porosity and pore size were determined analytically. Suitable process parameters were identified to manufacture the model by Direct Metal Laser Sintering (DMLS) using Ti6Al4V powder after carrying out a detailed experimental study to minimize the variation of surface roughness and warping over different build angles of the strut structures. Dual-contour scanning was implemented to simplify the scan strategy. The minimum diameter of struts that could be manufactured using the selected scanning strategy and scanning parameters was found to be 375 µm. Finally, the model was built and from the micro-CT data, the porosities and pore sizes were found to be closely conforming to the designed values. The stiffness of the structures, as found from compression testing, was also found to match with that of human trabecular bone well. Further, the structure exhibited compliant bending-dominated behaviour under compressive loading.

Surface modification improving the biological activity and osteogenic ability of 3D printing porous dental implants

Objective: To explore the mechanical properties, biological activity, and osteogenic ability of 3D printed TC4 titanium (Ti) alloy dental implants treated with surface modification.Methods: Dental implants with 30% porosity were manufactured using selective laser melting (SLM) technology (group 3D), while traditional numerically-controlled machine tools (CNC) were used to manufacture implants without porosity (group SL). The implants were then surface modified through sandblasting and acid etching (groups 3DA1 and SLA1), and then alkali etching (groups 3DA2 and SLA2). The physicochemical properties of the implants were measured using a Vickers hardness instrument, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and profilograph before and after surface modification. Next, the biocompatibility, bioactivity, and osteogenic ability of the implants were evaluated using apatite deposition experiments, alkaline phosphatase (ALP) activity, and semiquantitative analysis of extracellular matrix mineralization.Results: There were significant differences in morphology, geometric accuracy, mechanical properties, surface roughness, and hydrophilicity between groups 3D and SL. Furthermore, surface modification improved the physicochemical properties of the porous implants. Implants with sandblasting, acid etching, and alkali etching demonstrated better biocompatibility, bioactivity, and osteogenic ability than implants without surface modification in both groups 3D and SL. Additionally, the implants of groups 3D have higher bioactivity than that of groups SL.Conclusion: Surface modification and the macroporous structure of implants can improve their bioactivity and osteogenic ability, enhancing the application of Ti alloy dental implants.

Mechanical Properties and in Vivo Assessment of Electron Beam Melted Porous Structures for Orthopedic Applications

Electron beam melting (EBM) is an additive manufacturing technique with the ability to produce porous implants with desired properties for orthopedic applications. This paper systematically investigated the mechanical properties and in vivo performance of two commonly used stochastic porous structures (the Voronoi structure and the randomized structure) fabricated by the EBM process. The pore geometries of two porous structures were characterized through micro-computed tomography (μCT). In addition, clinically relevant mechanical performances were evaluated for both structures, including tensile testing, shear testing and abrasion resistance testing. In vivo assessment of the two porous structures was further conducted in a dog model for three different follow-up periods. It was found that the Voronoi structures showed a higher mechanical strength compared to the randomized structures, even though both structures exhibited similar pore geometries. Further analysis revealed that the non-uniform stress distribution caused by the sample size and boundary effects led to a decrease in strength in the randomized structures. The in vivo assessments revealed the Voronoi structure exhibited a higher bone ingrowth ratio compared to the randomized structure due to its radially oriented pore geometry and homogenous pore size distribution. This study suggested that the EBM Ti-6Al-4V Voronoi porous structure has favorable mechanical performance and good osseointegration properties for orthopedic implants.

Results of a differential approach to surgical treatment of proximal humerus fractures in patients with osteoporosis

Objective. To conduct a comparative retrospective analysis of the anatomical and functional results of surgical treatment of proximal humerus fractures AO/OTA 11-B, 11-C using different methods in patients over 50 years old with osteoporosis to justify a differential approach. Methods. The study included 102 patients aged 50 years and older with osteoporosis and proximal humerus fractures AO/OTA 11-B, 11-C. The patients were divided into three groups: I — 50 (16 men, 34 women) whom were performed open reduction and internal fixation (ORIF) with the PHILOS plate; II — 44 (8 men, 36 women) — ORIF with the PHILOS plate and using 3D polylactide (PLA) porous implants were applied; III — 8 (2 men, 6 women) whom were performed primary reversed total shoulder arthroplasty (RTSA) with developed total reversible endoprosthesis. The results of treatment were evaluated according to the Constant-Murley Shoulder Score system after 3, 6, 12 months. The results. Positive results in the first group were obtained in 72.0 % of patients (the average Constant-Murley Shoulder Score after 12 months was 78.4 points); in the second — in 81.8 % (88.0 points); in the third — 75.0 % (82.0 points). A differentiated approach to the choice of surgical treatment of patients aged 50 years and older with fractures AO/OTA 11-B, 11-C is proposed. The clinical trial of the reverse total modular shoulder endoprosthesis developed by us using porous 3D titanium parts, manufactured by additive technologies, showed positive short-term results. The design features of the device increase the reliability and durability of proposed endoprosthesis. Conclusions. RTSA in the case of unstable proximal humerus fracture or in the case of metal structure migration after primary ORIF in patients with low bone mineral density is the effective surgical intervention that allows to achieve satisfactory functional results in up to 3 years.

Embedded 3D printing of porous silicon orbital implants and its surface modification

To prepare customized porous silicone orbital implants using embedded 3D printing and assess the effect of surface modification on the properties of the implants. The transparency, fluidity and rheological properties of the supporting media were tested to determine the optimal printing parameters of silicone. The morphological changes of silicone after modification were analyzed by scanning electron microscopy, and the hydrophilicity and hydrophobicity of silicone surface were evaluated by measuring the water contact angle. The compression modulus of porous silicone was measured using compression test. Porcine aortic endothelial cells (PAOECs) were co-cultured with porous silicone scaffolds for 1, 3 and 5 days to test the biocompatibility of silicone. The local inflammatory response to subcutaneous porous silicone implants was evaluated in rats. The optimal printing parameters of silicone orbital implants were determined as the following: supporting medium 4% (mass ratio), printing pressure 1.0 bar and printing speed 6 mm/s. Scanning electron microscopy showed that the silicone surface was successfully modified with polydopamine and collagen, which significantly improved hydrophilicity of the silicone surface (P < 0.05) without causing significant changes in the compression modulus (P > 0.05). The modified porous silicone scaffold had no obvious cytotoxicity and obviously promoted adhesion and proliferation of PAOECs (P < 0.05). In rats bearing the subcutaneous implants, no obvious inflammation was observed in the local tissue. Poprous silicone orbital implants with uniform pores can be prepared using embedded 3D printing technology, and surface modification obviously improves hydrophilicity and biocompatibility of the silicone implants for potential clinical application.

Design and manufacturing of patient-specific Ti6Al4V implants with inhomogeneous porosity

Stress shielding remains a challenge in orthopaedic implants, including total hip arthroplasty. Recent development in printable porous implants offers improved patient-specific solutions by providing adequate stability and reducing stress shielding possibilities. This work presents an approach for designing patient-specific implants with inhomogeneous porosity. A novel group of orthotropic auxetic structures is introduced, and their mechanical properties are computed. These auxetic structure units were distributed at different locations on the implant along with optimized pore distribution to achieve optimum performance. A computer tomography (CT) based finite element (FE) model was used to evaluate the performance of the proposed implant. The optimized implant and the auxetic structures were manufactured using laser powder bed-based laser metal additive manufacturing. Validation was done by comparing FE results with experimentally measured directional stiffness and Poisson's ratio of the auxetic structures and strain on the optimized implant. The correlation coefficient for the strain values was within a range of 0.9633–0.9844. Stress shielding was mainly observed in Gruen zones 1, 2, 6, and 7. The average stress shielding on the solid implant model was 56%, reduced to 18% when the optimized implant was used. This significant reduction in stress shielding can decrease the risk of implant loosening and create an osseointegration-friendly mechanical environment on the surrounding bone. The proposed approach can be effectively applied to the design of other orthopaedic implants to minimize stress shielding.

Numerical analysis of the mechanical response of novel swelling bone implants in polyurethane foams

In this study, a numerical framework was developed in order to analyze the swelling properties, mechanical response and fixation strength of swelling bone anchors. Using this framework, fully porous and solid implants, along with a novel hybrid design (consisting of a solid core and a porous sleeve), were modeled and studied. Free swelling experiments were conducted to investigate their swelling characteristics. The finite element model of swelling was validated using the conducted free swelling. Compared with the experimental data, results obtained from the finite element analysis proved the reliability of this frame-work. Afterwards, the swelling bone anchors were studied embedded in artificial bones with different densities with two different interface properties: considering frictional interface between the bone anchors and artificial bones (simulating the stages prior to osteointegration, when the bone and implant are not fully bonded and the surface of the implant can slide along the interface), and perfectly bonded (simulating the stages subsequent to osteointegration, when the bone and implant are fully bonded). It was observed that the swelling considerably decreases while the average radial stress on the lateral surface of the swelling bone anchor surges in the denser artificial bones. Ultimately, the pull-out experiments and simulations of the swelling bone anchors from the artificial bones were conducted to look into the fixation strength of the swelling bone anchors. It was found that the hybrid swelling bone anchor exhibits mechanical and swelling properties close to those of solid bone anchors, while also bone in-growth is expected to happen, which is an integral factor to these bone anchors.

Repair of Congenital Enlarged Parietal Foramina With Porous Polyethylene Implants.

Enlarged biparietal foramina is an autosomal dominant disorder that is caused by a failure of completion of ossification within the parietal bones. Enlarged parietal foramina measuring more than a few millimeters are uncommon. Even though spontaneous regression has been described, closure is rarely complete, and depending on the size of the resulting defect, an unprotected brain is a concern. There are few reports on the surgical management of persistent enlarged biparietal foramina. This is the first report describing our experience with a custom porous polyethylene implant.

Plasma Polishing as a New Polishing Option to Reduce the Surface Roughness of Porous Titanium Alloy for 3D Printing.

Porous titanium alloy implants with simulated trabecular bone fabricated by 3D printing technology have broad prospects. However, due to the fact that some powder adheres to the surface of the workpiece during the manufacturing process, the surface roughness in direct printing pieces is relatively high. At the same time, since the internal pores of the porous structure cannot be polished by conventional mechanical polishing, an alternative method needs to be found. As a surface technology, plasma polishing technology is especially suitable for parts with complex shapes that are difficult to polish mechanically. It can effectively remove particles and fine splash residues attached to the surface of 3D printed porous titanium alloy workpieces. Therefore, it can reduce surface roughness. Firstly, titanium alloy powder is used to print the porous structure of the simulated trabecular bone with a metal 3D printer. After printing, heat treatment, removal of the supporting structure, and ultrasonic cleaning is carried out. Then, plasma polishing is performed, consisting of adding a polishing electrolyte with the pH set to 5.7, preheating the machine to 101.6 °C, fixing the workpiece on the polishing fixture, and setting the voltage (313 V), current (59 A), and polishing time (3 min). After polishing, the surface of the porous titanium alloy workpiece is analyzed by a confocal microscope, and the surface roughness is measured. Scanning electron microscopy is used to characterize the surface condition of porous titanium. The results show that the surface roughness of the whole porous titanium alloy workpiece changed from Ra (average roughness) = 126.9 µm to Ra = 56.28 µm, and the surface roughness of the trabecular structure changed from Ra = 42.61 µm to Ra = 26.25 µm. Meanwhile, semi-molten powders and ablative oxide layers are removed, and surface quality is improved.

Biomechanical Effects of the Porous Structure of Gyroid and Voronoi Hip Implants: A Finite Element Analysis Using an Experimentally Validated Model.

Total hip arthroplasty (THA) is most likely one of the most successful surgical procedures in medicine. It is estimated that three in four patients live beyond the first post-operative year, so appropriate surgery is needed to alleviate an otherwise long-standing suboptimal functional level. However, research has shown that during a complete THA procedure, a solid hip implant inserted in the femur can damage the main arterial supply of the cortex and damage the medullary space, leading to cortical bone resorption. Therefore, this study aimed to design a porous hip implant with a focus on providing more space for better osteointegration, improving the medullary revascularisation and blood circulation of patients. Based on a review of the literature, a lightweight implant design was developed by applying topology optimisation and changing the materials of the implant. Gyroid and Voronoi lattice structures and a solid hip implant (as a control) were designed. In total, three designs of hip implants were constructed by using SolidWorks and nTopology software version 2.31. Point loads were applied at the x, y and z-axis to imitate the stance phase condition. The forces represented were x = 320 N, y = -170 N, and z = -2850 N. The materials that were used in this study were titanium alloys. All of the designs were then simulated by using Marc Mentat software version 2020 (MSC Software Corporation, Munich, Germany) via a finite element method. Analysis of the study on topology optimisation demonstrated that the Voronoi lattice structure yielded the lowest von Mises stress and displacement values, at 313.96 MPa and 1.50 mm, respectively, with titanium alloys as the materials. The results also indicate that porous hip implants have the potential to be implemented for hip implant replacement, whereby the mechanical integrity is still preserved. This result will not only help orthopaedic surgeons to justify the design choices, but could also provide new insights for future studies in biomechanics.

A comprehensive study of the impact on the microstructure and corrosion behavior of magnesium alloy-based porous bone implants

Magnesium orthopedic implants have been categorized to be one of the potential metallic biomaterial candidates due to their better biocompatibility nature, excellent biodegradability feature and its comparable mechanical properties with natural human bone. But, magnesium scaffolds experience unstable biocorrosion under physiological solutions, thus hindering their utility in implant applications. Moreover, conventional and typical metallic implants are non-porous in nature and also often result in stress shielding. To this end, this research has examined the outcome of adding metallic alloying elements (Ca, Zn and Fe) into the Mg metal matrix, while varying porosity was produced by incorporating carbamide. The corrosion behavior of the produced samples post-immersion in Hank’s solution was observed. This investigation established that the corrosion rates of the alloyed samples could be controlled by tuning the sample compositions. The corroded samples were also observed under optical microscopy, which revealed the protective layer, which could have retarded the corrosion of the immersed samples. X-ray micro-computed tomography results confirm the gradient porosity with interconnected pores in the produced samples, a vital feature for an implant. Therefore, this investigation confirms that the behavior of biocorrosion could be tailored by fabricating customized Mg-alloy-based bone implants.