Fully porous 3D printed titanium femoral stem to reduce stress-shielding following total hip arthroplasty

Enhanced antimicrobial properties and bioactivity of 3D-printed titanium scaffolds by multilayer bioceramic coating for large bone defects

The restoration of large bone defects caused by trauma, tumor resection, or infection is a major clinical problem in orthopedics and dentistry because postoperative infections, corrosion, and limited osteointegration of metal implants can lead to loosening of the implant. The aim of this study was to improve the surface properties of a 3D-printed (electron beam melting) Ti6Al4V-based macroporous scaffold by multilayer coating with bioactive silicate glasses (BAGs) and hydroxyapatite doped with a silver (AgHAP) or AgHAP additionally sonochemically modified with ZnO (ZnO-AgHAP). The coated scaffolds AgHAP_BAGs_Ti and ZnO-AgHAP_BAGs_Ti enhanced cytocompatibility in L929 and MRC5 cell lines and expressed bioactivity in simulated body fluid. A lower release of vanadium ions in coated samples compared to bare Ti scaffold indicates decreased dissolution of Ti alloy in coated samples. The coated samples reduced growth ofEscherichia coliandStaphylococcus aureusfor 4-6 orders of magnitude. Therefore, the 3D-printed Ti-based scaffolds coated with BAGs and (ZnO-)AgHAP have great potential for application as a multifunctional implant with antibacterial properties for the restoration of defects in load-bearing bones.

Static compression and fatigue behavior of heat-treated selective laser melted titanium alloy (Ti6Al4V) gyroid cylinders

Porous additively-manufactured structures could have a niche in orthopaedic implants, due to their potential to reduce stiffness (stress-shielding), improve bony ingrowth, and potential to house reservoirs of drug-eluting non-structural biomaterials. Computer aided design and finite element (FE) modelling plays an important role in the design of porous structured biomedical implants; however it is important to validate both their static and fatigue behaviours using experimental testing. This study compared the mechanical behaviors of titanium cylindrical gyroid structures of varying porosities using physical testing of additively manufactured prototypes and FE models. There was agreement in the measured and predicted relationships between porosity and apparent modulus of elasticity. As porosity increased (and wall thickness decreased), the structures failed at a lower number of cycles when loaded at the same percentage of their yield strengths. Calibration of the fatigue strength coefficient from a previously published value of 1586.5 MPa-1225 MPa greatly improved the fatigue life prediction accuracy for all the gyroid structures. Nevertheless, differences of up to 54% in the predicted versus experimental fatigue lives remained, which could be attributed to difficulties with how the precise time and location of failure is defined in the simulations, and/or minor differences in nominal and actual porosities. Although further calibration and validation should be explored, this study demonstrates that static and fatigue FE-modelling techniques could be used to aid in the design of porous prosthetics.

Biomechanical analysis of functionally graded porous interbody cage for lumbar spinal fusion

Functionally graded porous (FGP) interbody cage might offer a trade-off between porosity-based reduction of stiffness and mechanical properties. Using finite element models of intact and implanted lumbar functional spinal unit (FSU), the study investigated the quantitative deviations in load transfer and adaptive changes in bone density distributions around FGP interbody cages. The cage had three graded porosities: FGP-A, -B, and -C corresponded to a maximum porosity levels of 48%, 65% and 78%, respectively. Efficacy of the FGP cages were evaluated by comparing the numerically predicted results of solid-Ti and uniformly porous 78% porosity (P78) cage. Variations in stiffness and interface condition affected the strain distribution and bone remodelling around the cages. Peak strains of 0.5-1% were observed in less number of peri-prosthetic bone elements for the FGP cages as compared to the solid-Ti cage. Strains and bone apposition were considerably higher for the bonded implant-bone interface condition than the debonded case. For the FGP-C with bonded interface condition, bone apposition of 11-20% was predicted in the L4 and L5 regions of interest (ROIs); whereas the debonded model exhibited 6-10% increase in bone density. The deviations in bone density change between FGP-C and P78 model were 3-8% for L4 and L5 ROIs. FGP resulted in a reduced average micromotion (∼70-106 μm) as compared to solid-Ti (116 μm), for all physiologic movements. Compared to solid-Ti and uniformly porous cages, the FGP cage seems to be a viable alternative considering the conflicting nature of strength and porosity.

Stress-dependent design and optimization methodology of gradient porous implant and application in femoral stem

Gradient porous structure made by additive manufacturing (AM) technology is potential to improve the long-term stability of orthopaedic implants through bone ingrowth while maintaining mechanical safety. In this study, a parametrical optimization methodology for the customized gradient porous implants was developed based on a stress-dependent design algorithm. Clinical requirements and manufacturing capabilities of AM were considered in the design procedure. A femoral stem with a minimum bone loss proportion of 2.4% by optimizing the control parameters. This study provided a feasible and flexible design approach for the customized implant with gradient porous structure or material components.

Structural optimization of orthopedic hip implant using parametric and non-parametric optimization techniques

This research investigates the reduction in weight of hip implant by the application of parametric and non-parametric optimization techniques. Orthopaedic hip implants can be made from metals, ceramics, composites, or metallic alloys and are generally solid structures. The stiffness of orthopaedic hip implant is a pertaining problem when implanted in the human body as Hip implant are stiffer than bone material and causes stress shielding. This results in bone weakening which causes osteoporosis. Reduction in mass of femur stem results in stiffness reduction of femur stem. Non-Parametric topology optimization results in 34.9% mass reduction and parametric optimization based on Central Composite Design technique in Design of Experiments (DoE) uses hole diameters as parameters and performs structural optimization that results in 22% mass reduction.

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.

Nano-Mechanical Behavior of Ti6Al4V Alloy Manufactured Using Laser Powder Bed Fusion

The microstructure of Ti6Al4V alloy, manufactured using laser powder bed fusion (L-PBF), is affected by process parameters and heat treatment. However, their influence on the nano-mechanical behavior of this widely applicable alloy is still unknown and scarcely reported. This study aims to investigate the influence of the frequently used annealing heat treatment on mechanical properties, strain-rate sensitivity, and creep behavior of L-PBF Ti6Al4V alloy. Furthermore, the influence of different utilized L-PBF laser power-scanning speed combinations on mechanical properties of annealed specimens has been studied as well. It has been found that the effect of high laser power remains present in the microstructure even after annealing, resulting in increase in nano-hardness. Moreover, the linear relation between the Young's modulus and the nano-hardness after annealing has been established. Thorough creep analysis revealed dislocation motion as a dominant deformation mechanism, both for as-built and annealed conditions of the specimens. Although annealing heat treatment is beneficial and widely recommended, it reduces the creep resistance of Ti6Al4V alloy manufactured using L-PBF. The results presented within this research article contribute to the L-PBF process parameter selection, as well as to understanding the creep behavior of these novel and widely applicable materials.

Design of titanium uncemented femoral stems for hip prosthesis suitable for the Colombian young adult population

The increase of revision surgeries in hip replacement procedure in Colombian young adult population can be addressed by a new design of femoral stem that reduces stress shielding. A new femoral stem was designed using topology optimization as a design aid to reduce the mass in the femoral stem and its overall stiffness, combined with the theoretical, computational, and experimental assessment of the new design that complies with a static and fatigue safety factor greater than one. The new femoral stem design can be used as a design tool to reduce the number of revision surgeries caused by stress shielding.

On the need of a scale-dependent material characterization to describe the mechanical behavior of 3D printed Ti6Al4V custom prostheses using finite element models

Additive manufacturing is widely used in the orthopaedic industry for the high freedom and flexibility in the design and production of personalized custom implants made of Ti6Al4V. Within this context, finite element modeling of 3D printed prostheses is a robust tool both to guide the design phase and to support clinical evaluations, possibly virtually describing the in-vivo behavior of the implant. Given realistic scenarios, a suitable description of the overall implant's mechanical behavior is unavoidable. Considering typical custom prostheses' designs (i.e. acetabular and hemipelvis implants), complex designs involving solid and/or trabeculated parts, and material distribution at different scales hinder a high-fidelity modeling of the prostheses. Moreover, uncertainties in the production and in the material characterization of small parts approaching the accuracy limit of the additive manufacturing technology still exist. While recent works suggest that the mechanical properties of thin 3D-printed parts may be peculiarly affected by specific processing parameters (i.e. powder grain size, printing orientation, samples' thickness) as compared to conventional Ti6Al4V alloy, the current numerical models make gross simplifications in describing the complex material behavior of each part at different scales. The present study focuses on two patient-specific acetabular and hemipelvis prostheses, with the aim of experimentally characterizing and numerically describing the dependency of the mechanical behavior of 3D printed parts on their peculiar scale, therefore, overcoming one major limitation of current numerical models. Coupling experimental activities with finite element analyses, the authors initially characterized 3D printed Ti6Al4V dog-bone samples at different scales, representative of the main material components of the investigated prostheses. Afterwards, the authors implemented the characterized material behaviors into finite element models to compare the implications of adopting scale-dependent vs. conventional scaleindependent approaches in predicting the experimental mechanical behavior of the prostheses in terms of their overall stiffness and the local strain distribution. The material characterization results highlighted the need for a scale-dependent reduction of the elastic modulus for thin samples compared to the conventional Ti6Al4V, which is fundamental to properly describe the overall stiffness and local strain distribution on the prostheses. The presented works demonstrate how an appropriate material characterization and a scale-dependent material description is needed to develop reliable FE models of 3D printed implants characterized by a complex material distribution at different scales.

Development of biodegradable customized tibial scaffold with advanced architected materials utilizing additive manufacturing

In the last decade, the development of customized biodegradable scaffolds and implants has attracted increased scientific interest due to the fact that additive manufacturing technologies allow for the rapid production of implants with high geometric complexity constructed via commercial biodegradable polymers. In this study, innovative designs of tibial scaffold in form of bone-brick configuration were developed to fill the bone gap utilizing advanced architected materials and bio-inspired diffusion canals. The architected materials and canals provide high porosity, as well as a high surface area to volume ratio in the scaffold facilitating that way in the tissue regeneration process and in withstanding the applied external loads. The cellular structures applied in this work were the Schwarz Diamond (SD) and a hybrid SD&FCC hybrid cellular material, which is a completely new architected material that derived from the combination of SD and Face Centered Cubic (FCC) structures. These designs were additively manufactured utilizing two biodegradable materials namely Polylactic acid (PLA) and Polycaprolactone (PCL), using the Fused Filament Fabrication (FFF) technique, in order to avoid the surgery, for the scaffold's removal after the bone regeneration. Furthermore, the additively manufactured scaffolds were examined in terms of compatibility and assembly with the bone's physical model, as well as, in terms of mechanical behavior under realistic static loads. In addition, non-linear finite element models (FEMs) were developed based on the experimental data to accurately simulate the mechanical response of the examined scaffolds. The Finite Element Analysis (FEA) results were compared with the experimental response and afterwards the stress concentration regions were observed and identified. Τhe proposed design of scaffold with SD&FCC lattice structure made of PLA material with a relative density of 20% revealed the best overall performance, showing that it is the most suitable candidate for further investigation (in-vivo test, clinical trials, etc.) and commercialization.

A Machine-Learning-Based Approach for Predicting Mechanical Performance of Semi-Porous Hip Stems

Novel designs of porous and semi-porous hip stems attempt to alleviate complications such as aseptic loosening, stress shielding, and eventual implant failure. Various designs of hip stems are modeled to simulate biomechanical performance using finite element analysis; however, these models are computationally expensive. Therefore, the machine learning approach is incorporated with simulated data to predict the new biomechanical performance of new designs of hip stems. Six types of algorithms based on machine learning were employed to validate the simulated results of finite element analysis. Afterwards, new designs of semi-porous stems with outer dense layers of 2.5 and 3 mm and porosities of 10-80% were used to predict the stiffness of the stems, stresses in outer dense layers, stresses in porous sections, and factor of safety under physiological loads using machine learning algorithms. It was determined that decision tree regression is the top-performing machine learning algorithm as per the used simulation data in terms of the validation mean absolute percentage error which equals 19.62%. It was also found that ridge regression produces the most consistent test set trend as compared with the original simulated finite element analysis results despite relying on a relatively small data set. These predicted results employing trained algorithms provided the understanding that changing the design parameters of semi-porous stems affects the biomechanical performance without carrying out finite element analysis.

The combined effect of zinc and calcium on the biodegradation of ultrahigh-purity magnesium implants

Magnesium (Mg)-based implants are promising candidates for orthopedic interventions, because of their biocompatibility, good mechanical features, and ability to degrade completely in the body, eliminating the need for an additional removal surgery. In the present study, we synthesized and investigated two Mg-based materials, ultrahigh-purity ZX00 (Mg-Zn-Ca; <0.5 wt% Zn and <0.5 wt% Ca, in wt%; Fe-content <1 ppm) and ultrahigh-purity Mg (XHP-Mg, >99.999 wt% Mg; Fe-content <1 ppm), in vitro and in vivo in juvenile healthy rats to clarify the effect of the alloying elements Zn and Ca on mechanical properties, microstructure, cytocompatibility and degradation rate. Potential differences in bone formation and bone in-growth were also assessed and compared with state-of-the-art non-degradable titanium (Ti)-implanted, sham-operated, and control (non-intervention) groups, using micro-computed tomography, histology and scanning electron microscopy. At 6 and 24 weeks after implantation, serum alkaline phosphatase (ALP), calcium (Ca), and Mg level were measured and bone marrow stromal cells (BMSCs) were isolated for real-time PCR analysis. Results show that ZX00 implants have smaller grain size and superior mechanical properties than XHP-Mg, and that both reveal good biocompatibility in cytocompatibilty tests. ZX00 homogenously degraded with an increased gas accumulation 12 and 24 weeks after implantation, whereas XHP-Mg exhibited higher gas accumulation already at 2 weeks. Serum ALP, Ca, and Mg levels were comparable among all groups and both Mg-based implants led to similar relative expression levels of Alp, Runx2, and Bmp-2 genes at weeks 6 and 24. Histologically, Mg-based implants are superior for new bone tissue formation and bone in-growth compared to Ti implants. Furthermore, by tracking the sequence of multicolor fluorochrome labels, we observed higher mineral apposition rate at week 2 in both Mg-based implants compared to the control groups. Our findings suggest that (i) ZX00 and XHP-Mg support bone formation and remodeling, (ii) both Mg-based implants are superior to Ti implants in terms of new bone tissue formation and osseointegration, and (iii) ZX00 is more favorable due to its lower degradation rate and moderate gas accumulation.

Patient-specific femoral implant design using metamaterials for improving load transfer at proximal-lateral region of the femur

Loading configuration of hip joint creates resultant bending effect on femoral implants. So, the lateral side of femoral implant which is under tension retracts from peri‑implant bone due to positive Poisson's ratio. This retraction of implant leads to load shielding and gap opening in proximal-lateral region, thereby allowing entry of wear particle to implant-bone interface. Retraction of femoral implant can be avoided by introducing auxetic metamaterial to the retracting side. This allows the implant to push peri‑implant bone under tensile condition by virtue of their auxetic (negative Poisson's ratio) nature. To develop such implants, a patient-specific conventional solid implant was first designed based on computed-tomography scan of a patient's femur. Two types of metamaterials (2D: type-1) and (3D: type-2) were employed to design femoral meta-implants. Type-1 and type-2 meta-implants were fabricated using metallic 3D printing method and mechanical compression testing was conducted. Three finite element (FE) models of the femur implanted with solid implant, type-1 meta-implant and type-2 meta-implant were developed and analysed under compression loading. Significant correlation (R² = 0.9821 and R² = 0.9977) was found between the experimental and FE predicted strains of the two meta-implants. In proximal-lateral region of the femur, an increase of 7.1% and 44.1% von-Mises strain was observed when implanted with type-1 and type-2 meta-implant over the solid implant. In this region, bone remodelling analysis revealed 2.5% bone resorption in case of solid implant. While bone apposition of 0.5% and 7.7% was observed in case of type-1 and type-2 meta-implants, respectively. The results of this study indicates that concept of introduction of metamaterial to the lateral side of femoral implant can prove to provide higher osseointegration-friendly environment in the proximal-lateral region of femur.

Study of the efficacy of 3D-printed prosthetic reconstruction after pelvic tumour resection

The purpose of this study is to explore the effect of using 3D printed pelvic prosthesis to reconstruct bone defect after pelvic tumor resection. From June 2018 to October 2021, a total of 10 patients with pelvic tumors underwent pelvic tumor resection and 3D printed customized hemipelvic prosthesis reconstruction in our hospital. Enneking pelvic surgery subdivision method was used to determine the degree of tumor invasion and the site of prosthesis reconstruction. 2 cases in Zone I, 2 cases in Zone II, 3 cases in Zone I + II, 2 cases in Zone II + III and 1 case in Zone I + II + III. Patients had preoperative VAS scores of 6.5 ± 1.3, postoperative VAS scores of 2.2 ± 0.9, preoperative MSTS-93 scores of 9.4 ± 5.3 and postoperative 19.4 ± 5.9(p < 0.05), all patients had improvement in pain after surgery; Postoperative complications included joint dislocation in 2 cases, myasthenia caused by Guillain-Barre syndrome in 1 case, delayed wound healing in 3 cases and wound infection in 2 cases. Postoperative wound-related complications and dislocations were associated with the extent of the tumor. Patients with tumor invasion of the iliopsoas and gluteus medius muscles had higher complication rates and worse postoperative MSTS scores (p < 0.05). The patients were followed up for 8 ∼ 28 months. During the follow-up period, 1 case recurred, 4 cases metastasized and 1 case died. All pelvic CTs reviewed 3-6 months after surgery showed good alignment between the 3D printed prosthesis and the bone contact, and tomography showed the growth of trabecular structures into the bone. Overall pain scores decreased and functional scores improved in patients after 3D printed prosthesis replacement for pelvic tumor resection. Long-term bone ingrowth could be seen on the prosthesis-bone contact surface with good stability.

Does preclinical analysis based on static loading underestimate post-surgery stem micromotion in THA as opposed to dynamic gait loading?

The success of cementless hip stems depends on the primary stability of the implant quantified by the amount of micromotion at the bone-stem interface. Most finite element (FE)-based preclinical studies on post-surgery stem stability rely on static analysis. Hence, the effect of dynamic gait loading on bone-stem relative micromotion remains virtually unexplored. Furthermore, there is a paucity of research on the primary stability of grooved stems as opposed to plain stem design. The primary aim of this FE study was to understand whether transient dynamic gait had any incremental effect on the net micromotion results and to further draw insights into the effects of grooved texture vis-à-vis a plain model on micromotion and proximal load transfer in host bone. Two musculoskeletal loading regimes corresponding to normal walking (NW) and stair climbing (SC) were considered. Although marginally improved load transfer was predicted proximally for the grooved construct under static loading, the micromotion values (max: NW ~ 7 μm; SC ~ 10 μm) were found to be considerably less in comparison to plain stem (max: NW ~ 50 μm; SC ~ 20 μm). For both physiological load cases, a significant surge in micromotion values was predicted in dynamic analyses as opposed to static analyses for the grooved stem (~ 390% greater). For the plain model, the increase in these values from static to dynamic loading is relatively moderate yet clinically significant (~ 230% greater). This suggests that the qualitative similarities notwithstanding, there were significant dissimilarities in the quantitative trends of micromotion for different cases under both analyses.

A novel hybrid design and modelling of a customised graded Ti-6Al-4V porous hip implant to reduce stress-shielding: An experimental and numerical analysis

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of hip prostheses and exacerbates revision surgery rates. In order to minimise post-hip replacement stress variations, this investigation proposes a low-stiffness, porous Ti6Al4V hip prosthesis, developed through selective laser melting (SLM). The stress shielding effect and potential bone resorption properties of the porous hip implant were investigated through both in vitro quasi-physiological experimental assays, together with finite element analysis. A solid hip implant was incorporated in this investigation for contrast, as a control group. The stiffness and fatigue properties of both the solid and the porous hip implants were measured through compression tests. The safety factor of the porous hip stem under both static and dynamic loading patterns was obtained through simulation. The porous hip implant was inserted into Sawbone/PMMA cement and was loaded to 2,300 N (compression). The proposed porous hip implant demonstrated a more natural stress distribution, with reduced stress shielding (by 70%) and loss in bone mass (by 60%), when compared to a fully solid hip implant. Solid and porous hip stems had a stiffness of 2.76 kN/mm and 2.15 kN/mm respectively. Considering all daily activities, the porous hip stem had a factor of safety greater than 2. At the 2,300 N load, maximum von Mises stresses on the hip stem were observed as 112 MPa on the medial neck and 290 MPa on the distal restriction point, whereby such values remained below the endurance limit of 3D printed Ti6Al4V (375 MPa). Overall, through the strut thickness optimisation process for a Ti6Al4V porous hip stem, stress shielding and bone resorption can be reduced, therefore proposing a potential replacement for the generic solid implant.

Mechanical Properties of AISI 316L Lattice Structures via Laser Powder Bed Fusion as a Function of Unit Cell Features

The growth of additive manufacturing processes has enabled the production of complex and smart structures. These fabrication techniques have led research efforts to focus on the application of cellular materials, which are known for their thermal and mechanical benefits. Herein, we studied the mechanical behavior of stainless-steel (AISI 316L) lattice structures both experimentally and computationally. The lattice architectures were body-centered cubic, hexagonal vertex centroid, and tetrahedron in two cell sizes and at two different rotation angles. A preliminary computational study assessed the deformation behavior of porous cylindrical samples under compression. After the simulation results, selected samples were manufactured via laser powder bed fusion. The results showed the effects of the pore architecture, unit cell size, and orientation on the reduction in the mechanical properties. The relative densities between 23% and 69% showed a decrease in the bulk material stiffness up to 93%. Furthermore, the different rotation angles resulted in a similar porosity level but different stiffnesses. The simulation analysis and experimental results indicate that the variation in the strut position with respect to the force affected the deformation mechanism. The tetrahedron unit cell showed the smallest variation in the elastic modulus and off-axis displacements due to the cell orientation. This study collected computational and experimental data for tuning the mechanical properties of lattice structures by changing the geometry, size, and orientation of the unit cell.

Evaluation of Biodegradable Alloy Fe30Mn0.6N in Rabbit Femur and Cartilage through Detecting Osteogenesis and Autophagy

Biodegradable iron alloy implants have become one of the most ideal possible candidates because of their biocompatibility and comprehensive mechanical properties. Iron alloy's impact on chondrocytes is still unknown, though. This investigation looked at the biocompatibility and degradation of the Fe30Mn0.6N alloy as well as how it affected bone formation and chondrocyte autophagy. In vivo implantation of Fe30Mn0.6N and Ti6Al4V rods into rabbit femoral cartilage and femoral shaft was carried out to evaluate the degradation of the alloy and the cartilage and bone response at different intervals. After 8 weeks of implantation, the cross-sectional area of the Fe30Mn0.6N alloys lowered by 50.79 ± 9.59%. More Ca and P element deposition was found on the surface Fe30Mn0.6N rods by using energy dispersive spectroscopy (EDS) and scanning electron microscopy (P < 0.05). After 2, 4, and 8 weeks of implantation, no evident inflammatory infiltration was seen in peri-implant cartilage and bone tissue of Fe30Mn0.6N and Ti6Al4V alloys. Also, implantation of Fe30Mn0.6N alloy promoted autophagy in cartilage by detecting expression of LC3-II compared with Ti6Al4V after implantation (P < 0.05). Fe30Mn0.6N alloy also stimulated early osteogenesis at the peri-implant interface compared with Ti6Al4V after implantation (P < 0.05). In the in vitro test, we found that low concentrations of Fe30Mn0.6N extracts had no influence on cell viability. 15% and 30% extracts of Fe30Mn0.6N could upregulate autophagy compared to the control group by detecting beclin-1, LC3, Atg3, and P62 on the basis of WB and IHC (P < 0.05). Also, the PI3K-AKT-mTOR signaling pathway mediated in the upregulation of autophagy of chondrocytes resulting in exposure to extract of Fe30Mn0.6N alloy. It is concluded that Fe30Mn0.6N showed degradability and biocompatibility in vivo and upregulated autophagy activity in chondrocytes.

Additively manufactured controlled porous orthopedic joint replacement designs to reduce bone stress shielding: a systematic review

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.

Evaluation of Compressive and Permeability Behaviors of Trabecular-Like Porous Structure with Mixed Porosity Based on Mechanical Topology

The mechanical properties and permeability properties of artificial bone implants have high-level requirements. A method for the design of trabecular-like porous structure (TLPS) with mixed porosity is proposed based on the study of the mechanical and permeability characteristics of natural bone. With this technique, the morphology and density of internal porous structures can be adjusted, depending on the implantation requirements, to meet the mechanical and permeability requirements of natural bone. The design parameters mainly include the seed points, topology optimization coefficient, load value, irregularity, and scaling factor. Characteristic parameters primarily include porosity and pore size distribution. Statistical methods are used to analyze the relationship between design parameters and characteristic parameters for precise TLPS design and thereby provide a theoretical basis and guidance. TLPS scaffolds were prepared by selective laser melting technology. First, TLPS under different design parameters were analyzed using the finite element method and permeability simulation. The results were then verified by quasistatic compression and cell experiments. The scaling factor and topology optimization coefficient were found to largely affect the mechanical and permeability properties of the TLPS. The corresponding compressive strength reached 270-580 MPa; the elastic modulus ranged between 6.43 and 9.716 GPa, and permeability was 0.6 × 10^-9-21 × 10^-9; these results were better than the mechanical properties and permeability of natural bone. Thus, TLPS can effectively improve the success rate of bone implantation, which provides an effective theory and application basis for bone implantation.

The application of additive manufacturing technology in pelvic surgery: A bibliometrics analysis

With the development of material science, additive manufacturing technology has been employed for pelvic surgery, addressing the challenges, such as the complex structure of the pelvis, difficulty in exposing the operative area, and poor visibility, of the traditional pelvic surgery. However, only limited studies have been done to review the research hotspots and trends of the additive manufacturing technology applied for pelvic surgery. In this study, we comprehensively analyzed the literatures related to additive manufacturing technology in pelvic surgery by a bibliometrics analysis and found that additive manufacturing technology is widely used in several aspects of preoperative diagnosis, preoperative planning, intraoperative navigation, and personalized implants for pelvic surgery. Firstly, we searched and screened 856 publications from the Web of Science Core Collection (WoSCC) with TS = (3D printing OR 3D printed OR three-dimensional printing OR additive manufacturing OR rapid prototyping) AND TS = (pelvis OR sacrum OR ilium OR pubis OR ischium OR ischia OR acetabulum OR hip) as the search strategy. Then, 565 of these were eliminated by evaluating the titles and abstracts, leaving 291 pieces of research literature whose relevant information was visually displayed using VOSviewer. Furthermore, 10 publications with high citations were selected by reading all publications extensively for carefully evaluating their Titles, Purposes, Results, Limitations, Journal of affiliation, and Citations. Our results of bibliometric analysis demonstrated that additive manufacturing technology is increasingly applied in pelvic surgery, providing readers with a valuable reference for fully comprehending the research hotspots and trends in the application of additive manufacturing technology in pelvic surgery.

On the Evolution of Additive Manufacturing (3D/4D Printing) Technologies: Materials, Applications, and Challenges

The scientific community is and has constantly been working to innovate and improve the available technologies in our use. In that effort, three-dimensional (3D) printing was developed that can construct 3D objects from a digital file. Three-dimensional printing, also known as additive manufacturing (AM), has seen tremendous growth over the last three decades, and in the last five years, its application has widened significantly. Three-dimensional printing technology has the potential to fill the gaps left by the limitations of the current manufacturing technologies, and it has further become exciting with the addition of a time dimension giving rise to the concept of four-dimensional (4D) printing, which essentially means that the structures created by 4D printing undergo a transformation over time under the influence of internal or external stimuli. The created objects are able to adapt to changing environmental variables such as moisture, temperature, light, pH value, etc. Since their introduction, 3D and 4D printing technologies have extensively been used in the healthcare, aerospace, construction, and fashion industries. Although 3D printing has a highly promising future, there are still a number of challenges that must be solved before the technology can advance. In this paper, we reviewed the recent advances in 3D and 4D printing technologies, the available and potential materials for use, and their current and potential future applications. The current and potential role of 3D printing in the imperative fight against COVID-19 is also discussed. Moreover, the major challenges and developments in overcoming those challenges are addressed. This document provides a cutting-edge review of the materials, applications, and challenges in 3D and 4D printing technologies.

Stress Shielding and Bone Resorption of Press-Fit Polyether-Ether-Ketone (PEEK) Hip Prosthesis: A Sawbone Model Study

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of the hip prostheses and increases the rates of revision surgery. This study proposes a low stiffness polyether-ether-ketone (PEEK) hip prostheses, produced by fused deposition modelling to minimize the stress difference after the hip replacement. The stress shielding effect and the potential bone resorption of the PEEK implant was investigated through both experimental tests and FE simulation. A generic Ti6Al4V implant was incorporated in this study to allow fair comparison as control group. Attributed to the low stiffness, the proposed PEEK implant showed a more natural stress distribution, less stress shielding (by 104%), and loss in bone mass (by 72%) compared with the Ti6Al4V implant. The stiffness of the Ti6Al4V and the PEEK implant were measured through compression tests to be 2.76 kN/mm and 0.276 kN/mm. The factor of safety for the PEEK implant in both static and dynamic loading scenarios were obtained through simulation. Most of the regions in the PEEK implant were tested to be safe (FoS larger than 1) in terms of representing daily activities (2300 N), while the medial neck and distal restriction point of the implant attracts large von Mises stress 82 MPa and 76 MPa, respectively, and, thus, may possibly fail during intensive activities by yield and fatigue. Overall, considering the reduction in stress shielding and bone resorption in cortical bone, PEEK could be a promising material for the patient-specific femoral implants.

Recent Developments in Additive-Manufactured Intermetallic Compounds for Bio-Implant Applications

Purpose

This paper reviews the recent developments of two newly developed intermetallic compounds (IMCs) of metallic glasses (MGs) and high-entropy alloys (HEAs) as potential implantable biomaterials.

Methods

The paper commences by summarizing the fundamental properties of recently developed MGs and high-entropy alloys (HEAs). A systematic review is presented of the recent literature about the use of AM technology in fabricating MG and HEA components for biological implant applications.

Results

The high strength, low Young’s modulus, and excellent corrosion resistance make these IMCs good candidates as bio-implantable materials. Recent studies have shown that additive manufacturing (AM) techniques provide an advantageous route for the preparation of glassy metallic components due to their intrinsically rapid cooling rates and ability to fabricate parts with virtually no size or complexity constraints. A practical example is conducted by AM producing a porous gradient Ti-based MG spinal cage. The produced MG powders and the in vivo test results on an 18 M-old Lanyu pig confirm the feasibility of the AM technique for producing implantable IMC-based prosthesis.

Conclusion

The non-crystalline structure of MGs alloy and the random crystalline composition of HEAs provide unique material properties that will substantially impact the development of future implantable prostheses.

Analytical review on the biocompatibility of surface-treated Ti-alloys for joint replacement applications

INTRODUCTION

With the advancement of joint replacements such as total hip replacement (THR), Titanium (Ti) and its alloys are widely used as implant materials. The bearing surface of Ti improves the longevity of implants. In this perception, researchers design a Ti-alloy that increases the wear and corrosion resistance to enhance osteogenesis and mechanical stability.

AREAS COVERED

: This paper is dedicated to finding the major causes of the failure of THR. Further, this paper provides an overview of the application of metallic alloys and their influencing factors that influence biocompatibility. The most contributing part of this paper focuses on the post-treatment impact on Ti-alloys biocompatibility.

EXPERT OPINION

This paper revealed and discussed that Ti alloys' biocompatibility for orthopedic applications mainly depends on antibacterial activities that decide tissue-implant compatibility. Therefore, performing surface treatment enhances the biocompatibility of Ti alloys. It was also observed that more water contact angle (WCA) induces bacterial growth and enhances cell adhesion. In contrast, the treated surface increases the antibacterial activities at lower WCA. Surface heat treatment with sintering or micro-arc oxidation achieves suitable antibacterial or antimicrobial activities.

Minimum 2-Year Outcomes of a Novel 3D-printed Fully Porous Titanium Acetabular Shell in Revision Total Hip Arthroplasty

Background

Fully porous acetabular shells are an appealing choice for patients with extensive acetabular defects undergoing revision total hip arthroplasty (rTHA). This study reports on the early outcomes of a novel 3-D printed fully porous titanium acetabular shell in revision acetabular reconstruction.

Methods

A multicenter retrospective study of patients who received a fully porous titanium acetabular shell for rTHA with a minimum of 2 years of follow-up was conducted. The primary outcome was rate of acetabular revision.

Results

The final study cohort comprised 68 patients with a mean age of 67.6 years (standard deviation 10.4) and body mass index of 29.5 kg/m² (standard deviation 5.9). Ninety-four percent had a preoperative Paprosky defect grade of 2A or higher. The average follow-up duration was 3.0 years (range 2.0-5.1). Revision-free survivorship at 2 years was 81% for all causes, 88% for acetabular revisions, and 90% for acetabular revision for aseptic acetabular shell failure. Eight shells were explanted within 2 years (12%): 3 for failure of osseointegration/aseptic loosening (4%) after 15, 17, and 20 months; 3 for infection (4%) after 1, 3, and 6 months; and 2 for instability (3%). At the latest postoperative follow-up, all unrevised shells showed radiographic signs of osseointegration, and none had migrated.

Conclusions

This novel 3-D printed fully porous titanium shell in rTHA demonstrated good survivorship and osseointegration when used in complex acetabular reconstruction at a minimum of 2 years.

Level of evidence

IV, case series.

Investigation of the Performance of Ti6Al4V Lattice Structures Designed for Biomedical Implants Using the Finite Element Method

The development of medical implants is an ongoing process pursued by many studies in the biomedical field. The focus is on enhancing the structure of the implants to improve their biomechanical properties, thus reducing the imperfections for the patient and increasing the lifespan of the prosthesis. The purpose of this study was to investigate the effects of different lattice structures under laboratory conditions and in a numerical manner to choose the best unit cell design, able to generate a structure as close to that of human bone as possible. Four types of unit cell were designed using the ANSYS software and investigated through comparison between the results of laboratory compression tests and those of the finite element simulation. Three samples of each unit cell type were 3D printed, using direct metal laser sintering technology, and tested according to the ISO standards. Ti6Al4V was selected as the material for the samples. Stress-strain characteristics were determined, and the effective Young's modulus was calculated. Detailed comparative analysis was conducted between the laboratory and the numerical results. The average Young's modulus values were 11 GPa, 9 GPa, and 8 GPa for the Octahedral lattice type, both the 3D lattice infill type and the double-pyramid lattice and face diagonals type, and the double-pyramid lattice with cross type, respectively. The deviation between the lab results and the simulated ones was up to 10%. Our results show how each type of unit cell structure is suitable for each specific type of human bone.

Hybrid Ti6Al4V/Silk Fibroin Composite for Load-Bearing Implants: A Hierarchical Multifunctional Cellular Scaffold

Despite the tremendous technological advances that metal additive manufacturing (AM) has made in the last decades, there are still some major concerns guaranteeing its massive industrial application in the biomedical field. Indeed, some main limitations arise in dealing with their biological properties, specifically in terms of osseointegration. Morphological accuracy of sub-unital elements along with the printing resolution are major constraints in the design workspace of a lattice, hindering the possibility of manufacturing structures optimized for proper osteointegration. To overcome these issues, the authors developed a new hybrid multifunctional composite scaffold consisting of an AM Ti6Al4V lattice structure and a silk fibroin/gelatin foam. The composite was realized by combining laser powder bed fusion (L-PBF) of simple cubic lattice structures with foaming techniques. A combined process of foaming and electrodeposition has been also evaluated. The multifunctional scaffolds were characterized to evaluate their pore size, morphology, and distribution as well as their adhesion and behavior at the metal-polymer interface. Pull-out tests in dry and hydrated conditions were employed for the mechanical characterization. Additionally, a cytotoxicity assessment was performed to preliminarily evaluate their potential application in the biomedical field as load-bearing next-generation medical devices.

Additively manufactured metallic biomaterials

Metal additive manufacturing (AM) has led to an evolution in the design and fabrication of hard tissue substitutes, enabling personalized implants to address each patient's specific needs. In addition, internal pore architectures integrated within additively manufactured scaffolds, have provided an opportunity to further develop and engineer functional implants for better tissue integration, and long-term durability. In this review, the latest advances in different aspects of the design and manufacturing of additively manufactured metallic biomaterials are highlighted. After introducing metal AM processes, biocompatible metals adapted for integration with AM machines are presented. Then, we elaborate on the tools and approaches undertaken for the design of porous scaffold with engineered internal architecture including, topology optimization techniques, as well as unit cell patterns based on lattice networks, and triply periodic minimal surface. Here, the new possibilities brought by the functionally gradient porous structures to meet the conflicting scaffold design requirements are thoroughly discussed. Subsequently, the design constraints and physical characteristics of the additively manufactured constructs are reviewed in terms of input parameters such as design features and AM processing parameters. We assess the proposed applications of additively manufactured implants for regeneration of different tissue types and the efforts made towards their clinical translation. Finally, we conclude the review with the emerging directions and perspectives for further development of AM in the medical industry.

Musculoskeletal modeling-based definition of load cases and worst-case fracture orientation for the design of clavicle fixation plates

Mechanical performance of clavicle fracture fixation plates is often evaluated using finite element (FE) analysis. Typically, these studies use simplified loading conditions and assume a transversal fracture orientation. However, the loading conditions and fracture orientation influence how the fracture site and thus fixation plate is loaded. In this study, a musculoskeletal model that included the clavicle muscles and scapulohumeral rhythm was defined based on previously published models. The standard OpenSim workflow (inverse kinematics, inverse dynamics, static optimization, and joint reaction analysis) was used to calculate muscle and joint contact forces based on 3D marker data collected in three subjects during seven activities of daily living (ADL). These loading conditions were then applied to a 3D clavicle model with three different fracture orientations and the mean resulting moments on both fragments were calculated to assess fracture stability. Magnitude of glenohumeral contact forces showed good agreement with instrumented shoulder prosthesis data, whereas simulated muscle activations were comparable to experimental EMG data. An oblique fracture orienting from superomedial to inferolateral was the least self-stabilizing. The loading to which the clavicle is exposed during ADL tasks is more complex than the simplified loading conditions typically used as boundary conditions in FE analyses of clavicle fracture fixation plates. Additionally, transversal fractures did not represent the least self-stabilizing fracture orientation, and thus calculated stresses in the plate could be underestimated. Therefore, more complex loading conditions and evaluation of a midshaft fracture running from superomedial to inferolateral is more relevant in FE analyses of midshaft clavicle fracture fixation plates.

Synergetic osteogenesis of extracellular vesicles and loading RGD colonized on 3D-printed titanium implants

Titanium (Ti) and its alloys have been universally used as surgical implants, and the clinical need for modifying titanium surfaces to accelerate early stage osseointegration and prevent implant loosening is in huge demand. 3D printing technology is an accurate and controllable method to create titanium implants with complex nanostructures, which provide enough space to react and fit in the microenvironment of cells. Recently, extracellular vesicles (EVs) have attracted attention in promoting osteogenesis. The vesicles derived from bone marrow mesenchymal stem cells (BMSC-EVs) have been proved to pack osteogenic-relative RNAs thereby regulating the osteogenic differentiation and mineralization of the target BMSCs. Arg-Gly-Asp (RGD)-derived peptides are typical peptides used to improve cell attachment and proliferation in bone tissue engineering. A novel strategy is proposed to load RGD-derived peptides on EVs with a fusion peptide (EVsRGD) and colonize EVsRGD on the titanium surface via a specific bonding peptide. In this study, we verify that the presence of EVsRGD enables the realization of the synergetic effect of EVs and RGD, enhancing the osteogenic differentiation and mineralization of BMSCs in vitro, resulting in satisfactory osseointegration around implants in vivo.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Biomechanical Comparison Between Porous Ti6Al4V Block and Tumor Prosthesis UHMWPE Block for the Treatment of Distal Femur Bone Defects

Purpose: The management of bone defects is a crucial content of total knee revision. This study compared the biomechanical performance of porous Ti6Al4V block and tumor prosthesis UHMWPE block in treating distal femoral bone defects.

Methods: The finite element models of AORI type 3 distal femoral bone defect treated with porous Ti6Al4V block and UHMWPE block were established. Sensitivity analysis was performed to obtain the appropriate mesh size. The biomechanical performance of treatment methods in bone defects were evaluated according to the peak stress, the Von Mises stress distribution, and the average stresses of regions of interest under the condition of standing on one foot and flexion of the knee. Statistical analysis was conducted by independent samples t-test in SPSS (p < 0.05).

Results: In the standing on one-foot state, the peak stress of the porous Ti6Al4V block was 12.42 MPa and that of the UHMWPE block was 19.97 MPa, which is close to its yield stress (21 MPa). Meanwhile, the stress distribution of the UHMWPE block was uneven. In the flexion state, the peak stress of the porous Ti6Al4V block was 16.28 MPa, while that of the UHMWPE block was 14.82 MPa. Compared with the porous Ti6Al4V block group, the average stress of the region of interest in UHMWPE block group was higher in the standing on one foot state and lower in the flexion state (p < 0.05).

Conclusion: More uniform stress distribution was identified in the porous Ti6Al4V block application which could reserve more bone. On the contrary, uneven stress distribution and a larger high-stress concentration area were found in the UHMWPE block. Hence, the porous Ti6Al4V block is recommended for the treatment of AORI type 3 distal femoral bone defect.

Biomechanical in silico evaluation of a 3D novel total hip implant with cemented fixation using finite elements

This paper presents the biomechanical evaluation of a proposed replacement implant for a total hip arthroplasty considering both the effect of the material and using a numerical tool. The use of titanium, alumina, polycarbonate urethane (PCU), and nitride titanium allows the manufacture of a cemented hip prosthesis with better resistance to corrosion, greater biocompatibility, greater mechanical resistance for physiological conditions, and does not present plastic deformation. This article provides an analysis of biomaterials and adequate geometries for a total hip prosthesis, with the aim of finding the optimal model, thus avoiding complications such as loosening or fatigue that current models present. Ultimately, the proposed design of the prosthesis was modeled using finite elements, simulating the static loads to which the prosthesis is subjected and evaluating the chosen biomaterials. Clinical Relevance - Osteoarthritis is a degenerative disease that affects 20% of the population above 60 years of age, particularly the hip joint, which is why, in most cases, a total arthroplasty of the expressed joint is required. In this procedure, the hip is replaced with an implant, which failure is usually related with either geometrical conditions or selected materials. An exponential increase of 136% in the incidence of total hip arthroplasty is expected by 2030.

Efficient Entropic Security with Joint Compression and Encryption Approach Based on Compressed Sensing with Multiple Chaotic Systems

This paper puts forward a new algorithm that utilizes compressed sensing and two chaotic systems to complete image compression and encryption concurrently. First, the hash function was utilized to obtain the initial parameters of two chaotic maps, which were the 2D-SLIM and 2D-SCLMS maps, respectively. Second, a sparse coefficient matrix was transformed from the plain image through discrete wavelet transform. In addition, one of the chaotic sequences created by 2D-SCLMS system performed pixel transformation on the sparse coefficient matrix. The other chaotic sequences created by 2D-SLIM were utilized to generate a measurement matrix and perform compressed sensing operations. Subsequently, the matrix rotation was combined with row scrambling and column scrambling, respectively. Finally, the bit-cycle operation and the matrix double XOR were implemented to acquire the ciphertext image. Simulation experiment analysis showed that the compressed encryption scheme has advantages in compression performance, key space, and sensitivity, and is resistant to statistical attacks, violent attacks, and noise attacks.

Additive Manufacturing: An Opportunity for the Fabrication of Near-Net-Shape NiTi Implants

Nickel–titanium (NiTi) is a shape-memory alloy, a type of material whose name is derived from its ability to recover its original shape upon heating to a certain temperature. NiTi falls under the umbrella of metallic materials, offering high superelasticity, acceptable corrosion resistance, a relatively low elastic modulus, and desirable biocompatibility. There are several challenges regarding the processing and machinability of NiTi, originating from its high ductility and reactivity. Additive manufacturing (AM), commonly known as 3D printing, is a promising candidate for solving problems in the fabrication of near-net-shape NiTi biomaterials with controlled porosity. Powder-bed fusion and directed energy deposition are AM approaches employed to produce synthetic NiTi implants. A short summary of the principles and the pros and cons of these approaches is provided. The influence of the operating parameters, which can change the microstructural features, including the porosity content and orientation of the crystals, on the mechanical properties is addressed. Surface-modification techniques are recommended for suppressing the Ni ion leaching from the surface of AM-fabricated NiTi, which is a technical challenge faced by the long-term in vivo application of NiTi.

Scientometric Analysis of the Top 50 Most-Cited Joint Arthroplasty Papers: Traditional vs Altmetric Measures

BACKGROUND

Alternative scientometric measures have introduced a novel view of the scientific literature. This study aimed to identify the top 50 most-cited recent articles in the field of knee and hip arthroplasty, characterize their traditional and alternative scientometric measures, and determine the relationship between traditional and alternative scientometric measures.

MATERIAL AND METHODS

The 50 most-cited articles with the term "arthroplasty" in the title that were published between 2015 and 2019 were retrieved from the Scopus database. Alternative scientometric parameters such as Altmetric Attention Score (AAS) from Altmetrics bookmarklet (Altmetrics.com) were retrieved. Scientometric variables such as journal impact factor, first author H-index, and keywords were also extracted.

RESULTS

The 50 most-cited papers accrued 7955 total citations, with a mean of 159.10 ± 56.4 citations per article. The overall mean AAS across the papers was 63.4 ± 164.8. The mean first author's H-index was 23.8 ± 18.9. Papers published in 2017 and 2018 had a significantly higher mean AAS than those published in 2015 and 2016 (35.1 vs 22.5, P = .009). Citation count was weakly correlated with the AAS (correlation coefficient = 0.379, P = .009). Also, AAS had significant correlations with the journal's impact factor (P < .001).

CONCLUSION

We found that the AAS was highest in more recently published papers, while citation count had the opposite trend. The AAS was significantly correlated with the journal's impact factor and citation count, but the correlation is weak. This suggests that the alternative scientometric measures are complementary to, and not substitutes for, complement traditional measures such as citation count and impact factor.

Analysis of different geometrical features to achieve close-to-bone stiffness material properties in medical device: A feasibility numerical study

BACKGROUND AND OBJECTIVE

In orthopedic medical devices, elasto-plastic behavior differences between bone and metallic materials could lead to mechanical issues at the bone-implant interface, as stress shielding. Those issue are mainly related to knee and hip arthroplasty, and they could be responsible for implant failure. To reduce mismatching-related adverse events between bone and prosthesis mechanical properties, modifying the implant's internal geometry varying the bulk stiffness and density could be the right approach. Therefore, this feasibility study aims to assess which in-body gap geometry improves, by reducing, the bulk stiffness.

METHODS

Using five finite element models, a uniaxial compression test in five cubes with a 20 mm thickness was simulated and analyzed. The displacements, strain and Young Modulus were calculated in four cubes, each containing internal prismatic gaps with different transversal sections (squared, hexagonal, octagonal, and circular). Those were compared with a fifth full-volume cube used as control.

RESULTS

The most significant difference have been achieved in displacement values, in cubes containing internal gaps with hexagonal and circular transversal sections (82 µm and 82.5 µm, respectively), when compared to the full-volume cube (69.3 µm).

CONCLUSIONS

This study suggests that hexagonal and circular shape of the gaps allows obtaining the lower rigidity in a size range of 4 mm, offering a starting approach to achieve a "close-to-bone" material, with a potential use in prosthetic devices with limited thickness.

Load Sharing in the Femur Using Strut Allografts: A Biomechanical Study

Background

Femoral strut allografts are used in revision hip arthroplasty for management of bone loss associated with implant failure or periprosthetic fractures. They have also been used to treat unremitting thigh pain in well-fixed cementless femoral stems, to address the differential in structural stiffness between the stem and femoral shaft. Our study used an in vitro biomechanical model to measure the effect of placement of allografts on femoral strains, to determine their load-sharing capacity.

Material and methods

Three rosette strain gauges were applied to the femoral surface of each of 6 cadaveric femurs, at the stem tip level on anterior, medial, and lateral cortices. After stem implantation, cortical strut allografts were applied to the lateral femoral shaft and secured with 4 Dall-Miles cables. A fourth gauge was placed on the midpoint of the allograft. Strains were recorded in the intact femur, then the implanted femur with and without the allograft under simulated physiologic loading in a load frame.

Results

Reduction in distal femoral principal strains, between 12% and 59%, was seen in all cortices following placement of the allograft. Under axial loading, 30% of the strain in the lateral cortex was borne by the allograft. Greater reductions in strain, by as much as 59%, occurred under axial load and torque.

Conclusion

The results of this biomechanical model indicate that by placement of an allograft, cortical strains can be reduced to levels approaching those in an intact femur, supporting this technique for treatment of unremitting thigh pain in well-fixed prostheses.

Nanostructured Titanium Implant Surface Facilitating Osseointegration from Protein Adsorption to Osteogenesis: The Example of TiO2 NTAs

Titanium implants have been widely applied in dentistry and orthopedics due to their biocompatibility and resistance to mechanical fatigue. TiO₂ nanotube arrays (TiO₂ NTAs) on titanium implant surfaces have exhibited excellent biocompatibility, bioactivity, and adjustability, which can significantly promote osseointegration and participate in its entire path. In this review, to give a comprehensive understanding of the osseointegration process, four stages have been divided according to pivotal biological processes, including protein adsorption, inflammatory cell adhesion/inflammatory response, additional relevant cell adhesion and angiogenesis/osteogenesis. The impact of TiO₂ NTAs on osseointegration is clarified in detail from the four stages. The nanotubular layer can manipulate the quantity, the species and the conformation of adsorbed protein. For inflammatory cells adhesion and inflammatory response, TiO₂ NTAs improve macrophage adhesion on the surface and induce M2-polarization. TiO₂ NTAs also facilitate the repairment-related cells adhesion and filopodia formation for additional relevant cells adhesion. In the angiogenesis and osteogenesis stage, TiO₂ NTAs show the ability to induce osteogenic differentiation and the potential for blood vessel formation. In the end, we propose the multi-dimensional regulation of TiO₂ NTAs on titanium implants to achieve highly efficient manipulation of osseointegration, which may provide views on the rational design and development of titanium implants.

Sensitivity of the stress field of the proximal femur predicted by CT-based FE analysis to modeling uncertainties

Proximal femur anatomy and bone mineral density vary widely among individuals, precluding the use of one predefined finite element (FE) model to determine the stress field for all proximal femurs. This variability poses a challenge in current prosthetic hip design approach. Given the numerous options for generating computed tomography (CT)-based FE models, selecting the best methods for defining the mechanical behavior of the proximal femur is difficult. In this study, a combination of computational and experimental approaches was used to explore the susceptibility of the predicted stress field of the proximal femur to different combinations of density-elasticity relationships, element type, element size, and calibration error. Our results suggest that FE models with first-order voxelized elements generated by the Keyak and Falkinstein density-elasticity relationship or quadratic tetrahedral elements generated by the Morgan density-elasticity relationship lead to accurate estimations of the mechanical behavior of human femurs. Other combinations of element size, element type, and mathematical relationships produce less accurate results, especially in the cortical bone of the femoral neck and calcar region. The voxelized model was more susceptible to variation of element size and density-elasticity relationships than FE models with quadratic tetrahedral elements. Regardless of element type, the stress fields predicted by the Keyak and Falkinstein and the Morgan relationships were the most robust to calibration error when deriving material density from CT-generated Hounsfield data. These results provide insight into the implementation of a robust platform for designing patient-specific implants capable of maintaining or modifying the stress in bones.

Stiffness optimization and reliable design of a hip implant by using the potential of additive manufacturing processes

BACKGROUND

Due to the steadily increasing life expectancy of the population, the need for medical aids to maintain the previous quality of life is growing. The basis for independent mobility is a functional locomotor system. The hip joint can be so badly damaged by everyday wear or accelerated by illness that reconstruction by means of endoprostheses is necessary.

RESULTS

In order to ensure a high quality of life for the patient after this procedure as well as a long service life of the prosthesis, a high-quality design is required, so that many different aspects have to be taken into account when developing prostheses. Long-term medical studies show that the service life and operational safety of a hip prosthesis by best possible adaptation of the stiffness to that of the bone can be increased. The use of additive manufacturing processes enables to specifically change the stiffness of implant structures.

CONCLUSIONS

Reduced implant stiffness leads to an increase in stress in the surrounding bone and thus to a reduction in bone resorption. Numerical methods are used to demonstrate this fact in the hip implant developed. The safety of use is nevertheless ensured by evaluating and taking into account the stresses that occur for critical load cases. These results are a promising basis to enable longer service life of prostheses in the future.

Craniofacial Reconstruction with Personalized Lightweight Scaffold Fabricated Using Electron-Beam Additive Manufacturing

Implants are the most popular option for restoring the facial anatomy in the event of a mishap. The commercially available craniofacial implants are of standard shapes, which need to be tailored and shaped to accurately fit the patient’s anatomy. The manual shaping of the implant to match the bone contours is conducted during surgical operation, and is a cumbersome and inaccurate process. Recent breakthroughs in computer-aided design, analysis, and additive manufacturing (AM) have allowed the precise and rapid manufacture of bespoke scaffolds for difficult anatomical restoration. The goal of this research is to investigate the use of scaffolds for craniofacial reconstruction and their fabrication using electron-beam additive manufacturing (EBAM). Personalized cheekbone scaffolds are additively fabricated using Ti6Al4V and subjected to compression testing. Finally, the scaffold design with the highest compressive strength is subjected to biomechanical analysis. The biomechanical analysis results indicate that the maximum Von Mises stress (40 MPa) and equivalent strain (0.4 µm) are significantly low in magnitude, thus providing a desirable implant that is both flexible and stable. The custom-designed cheekbone scaffold manufactured with AM technology not only aids in bone-implant ingrowth but also helps in reducing implant weight and ensuring implant stability and long-term effectiveness.

When the Total Hip Replacement Fails: A Review on the Stress-Shielding Effect

Total hip arthroplasty is one of the most common and successful orthopedic surgeries. Sometimes, periprosthetic osteolysis occurs associated with the stress-shielding effect: it results in the reduction of bone density, where the femur is not correctly loaded, and in the formation of denser bone, where stresses are confined. This paper illustrates the stress shielding effect as a cause of the failing replacement of the hip joint. An extensive literature survey has been accomplished to describe the phenomenon and identify solutions. The latter refer to the design criteria and the choice of innovative materials/treatments for prosthetic device production. Experimental studies and numerical simulations have been reviewed. The paper includes an introduction to explain the scope; a section illustrating the causes of the stress shielding effect; a section focusing on recent attempts to redefine prosthetic device design criteria, current strategies to improve the osteointegration process, and a number of innovative biomaterials; functionally graded materials are presented in a dedicated section: they allow customizing prosthesis features with respect to the host bone. Conclusions recommend an integrated approach for the production of new prosthetic devices: the “engineering community” has to support the “medical community” to assure an effective translation of research results into clinical practice.

Structural analysis of hollow versus solid-stemmed shoulder implants of proximal humeri with different bone qualities

Stress shielding of the proximal humerus following total shoulder arthroplasty (TSA) can promote unfavorable bone remodeling, especially for osteoporotic patients. The objective of this finite element (FE) study was to determine if a hollow, rather than solid, titanium stem can mitigate this effect for healthy, osteopenic, and osteoporotic bone. Using a population-based model of the humerus, representative average healthy, osteopenic, and osteoporotic humerus FE models were created. For each model, changes in bone and implant stresses following TSA were evaluated for different loading scenarios and compared between solid versus hollow-stemmed implants. For cortical bone, using an implant decreased von Mises stress with respect to intact values up to 34.4%, with a more pronounced effect at more proximal slices. In the most proximal slice, based on changes in strain energy density, hollow-stemmed implants outperformed solid-stemmed ones through reducing cortical bone volume with resorption potential by 11.7% ± 2.1% (p = .01). For cortical bone in this slice, the percentage of bone with resorption potential for the osteoporotic bone was greater than the healthy bone by 8.0% ± 1.4% using the hollow-stemmed implant (p = .04). These results suggest a small improvement in bone-implant mechanics using hollow-stemmed humeral implants and indicate osteoporosis could exacerbate stress shielding to some extent. The hollow stems maintained adequate strength and using even thinner walls may further reduce stress shielding. After further developing these models, future studies could yield optimized implant designs tuned for varying bone qualities.

Design optimization of functionally graded lattice infill total hip arthroplasty stem for stress shielding reduction

Reducing stress shielding of stem-inserted femurs in total hip arthroplasty caused by the high stiffness of the stem is an emerging medical engineering issue. In this study, a numerical design optimization methodology lattice infill stem was developed to realize a stem, balancing the low stiffness and strength requirements. Two pairs of models and loading conditions were introduced for the stress shielding and strength criteria. The objective function was set as the weighted sum of the criteria. Its effective density distribution was optimized by handling the representative size of the lattice as a design variable, assuming that the so-called body-centered cubic lattice was the base shape of the lattice. In the optimization, the approximated model of the lattice was handled as a solid material with the effective physical properties of the lattice derived by the homogenization method. After optimization, the detailed lattice stem geometry was modeled based on the obtained optimal lattice distribution, and the actual performance was numerically evaluated. The developed stem increased the stress applied to the remaining femur by 32.4% compared with the conventional stem.

Genetic-Based Optimization of 3D Burch–Schneider Cage With Functionally Graded Lattice Material

A Burch–Schneider (BS) cage is a reinforcement device used in total hip arthroplasty (THA) revision surgeries to bridge areas of acetabular loss. There have been a variety of BS cages in the market, which are made of solid metal. However, significant differences in structural configuration and mechanical behavior between bone and metal implants cause bone resorption and interface loosening, and hence lead to failure of the implant in the long term. To address this issue, an optimal design framework for a cellular BS cage was investigated in this study by genetic algorithm and topology optimization, inspired by porous human bone with variable holes. In this optimization, a BS cage is constructed with functionally graded lattice material which gradually evolves to achieve better mechanical behavior by natural selection and natural genetics. Clinical constraints that allow adequate bone ingrowth and manufacturing constraint that ensures the realization of the optimized implant are considered simultaneously. A homogenization method is introduced to calculate effective mechanical properties of octet-truss lattice material in a given range of relative density. At last, comparison of the optimum lattice BS cage with a fully solid cage and a lattice cage with identical element density indicates the validity of the optimization design strategy proposed in this article.