The role of stiffness-matching in avoiding stress shielding-induced bone loss and stress concentration-induced skeletal reconstruction device failure

Hierarchical design of silkworm silk for functional composites

Silk-reinforced composites (SRCs) manifest the unique properties of silkworm silk fibers, offering enhanced mechanical strength, biocompatibility, and biodegradability. These composites present an eco-friendly alternative to conventional synthetic materials, with applications expanding beyond biomedical engineering, flexible electronics, and environmental filtration. This review explores the diverse forms of silkworm silk fibers including fabrics, long fibers, and nanofibrils, for functional composites. It highlights advancements in composite design and processing techniques that allow precise engineering of mechanical and functional performance. Despite substantial progress, challenges remain in making optimally functionalized SRCs with multi-faceted performance and understanding the mechanics for reverse-design of SRCs. Future research should focus on the unique sustainable, biodegradable and biocompatible advantages and embrace advanced processing technology, as well as artificial intelligence-assisted material design to exploit the full potential of SRCs. This review on SRCs will offer a foundation for future advancements in multifunctional and high-performance silk-based composites.

Mandibular Implants: A Metamaterial-Based Approach to Reducing Stress Shielding

Biomechanical complications, such as stress shielding, bone resorption, and reconstruction failure, are prevalently associated with solid titanium mandible reconstruction plates. This study evaluates the potential of metamaterial designs with porous gyroid microarchitectures, to enhance biomechanical stimulation and mitigate these complications. A novel metamaterial reconstruction plate is compared with solid titanium plates, both patient-specifically designed and fabricated from Ti6Al4 V alloy. Stress shielding is assessed through photoelasticity experiments and validated with finite element analysis (FEA). Transparent mandible models are loaded incrementally (0-1000 N) to analyze stress distributions in the implants, screws, and mandible segments. The metamaterial plate reduces stress concentrations in the distant mandibular regions from the defect, while increasing stress around the screws near the defect, favoring local mechanical stimulation. FEA confirms improved load distribution (p = 0.003). However, the metamaterial plate exhibited a lower load-bearing capacity, failing at 775 N, while the solid plate withstood 1800 N without failure. Yet, the metamaterial design effectively reduced stress shielding, thereby enhancing biomechanical function near critical mandibular regions. Hence, despite their reduced load-bearing capacity, they can, potentially, preserve bone integrity and prevent implant failure that should be validated in future (pre-)clinical studies.

Structure and Property Evolution of Microinjection Molded PLA/PCL/Bioactive Glass Composite

In this study, the microinjection molding technology was adopted to prepare polylactic acid (PLA)/polycaprolactone (PCL)/bioactive glass (BG) composites with varying BG contents for biomedical applications. The various measurement techniques, including scanning electronic microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, the water contact angle (WCA) test, the mechanical test, and in vitro biological evaluations, were applied to characterize the above interesting biocomposites. The experimental results show that the extremely strong shear force field generated during the microinjection molding process could induce the in situ formation of micron PCL dispersed phase fibril structures and strongly promote the homogeneous dispersion of micron BG filler particles in the PLA/PCL polymer matrix, which therefore leads to a significant improvement in the specific mechanical property of the PLA/PCL/BG composite. For example, with BG fillers content increasing to 10 wt%, the Young's modulus of the above obtained PLA/PCL/BG composite could reach 2122.9 MPa, which is 1.47 times higher than that of the unfilled PLA/PCL blend material. In addition, it is also found that under the simulated body fluid (SBF) environment, the incorporated BG fillers in the PLA/PCL polymer matrix could be effectively transformed into hydroxyapatite (HA) components on the treated sample surface, thus being greatly advantageous to enhancing the material's in vitro bioactivity. Obviously, the microinjection molded PLA/PCL/BG biocomposites could exhibit excellent comprehensive performance, revealing that the microinjection molding processing method could hold great potential in industrialization applications of the resulting biodegradable biomedical materials.

Finite Element Analysis of a 3D-Printed Acetabular Prosthesis for an Acetabular Defect According to the Paprosky Classification

The treatment of Paprosky Type III acetabular defects is a significant challenge in orthopedic surgery, as standard components often do not fit properly. This study aims to evaluate the biomechanical efficacy of a custom 3D-printed PEEK acetabular prosthesis compared to a conventional titanium implant. A 3D model of the pelvis was created using a computed tomography scanner and a custom-made acetabular implant was designed. Finite element analysis (FEA) was performed using Ansys Workbench to evaluate the stress and strain distribution of two materials on the pelvic bone. The results showed that the titanium prosthesis model had less strain transmitted to the bone, while the PEEK model had better stress transmission and bone stimulation. The use of custom implants reduced the risk of stress shielding, potentially improving long-term bone health. Three-dimensional-printed acetabular prostheses therefore offer significant advantages over traditional implants, suggesting improved implant stability and reduced failure rates.

Composition design and performance analysis of binary and ternary Mg-Zn-Ti alloys for biomedical implants

Magnesium-based implants are highly valued in the biomedical field for biocompatibility and biodegradability, though their inherent low strength in body fluids is a limitation. This study addresses this by alloying magnesium with zinc and titanium to enhance its properties. Mechanical alloying was used to synthesize binary (Mg-Zn, Mg-Ti) and ternary (Mg-Zn-Ti) alloys, which were then compacted and sintered. The alloy powders, composed of 10 wt% Zn and 5 wt% Ti, were milled at 360 rpm for 10 h. Microstructural analysis revealed uniformly dispersed particles, with SEM confirming spherical and fine particles alongside laminates. XRD identified intermetallic compound formation. The ternary alloy demonstrated superior micro-hardness and Young's modulus similar to human bone, making it particularly promising for biomedical applications. Incorporating zinc and titanium into the magnesium matrix resulted in a ternary alloy that outperformed its binary counterparts.

The Mechanical Properties, Corrosion Resistance, and Biocompatibility of a Novel Ternary Ti-xNb-5Ta Alloy for Biomedical Applications

In recent years, advancements in dental implants have posed new challenges for the use of traditional orthopedic materials. This study prepared novel Ti-xNb-5Ta alloys via arc-melting and comprehensively evaluated the effects of Nb content on microstructure, mechanical properties, elastic modulus, electrochemical behavior, and in vitro performance. Interestingly, alloys with different Nb contents exhibited distinct properties. The results indicated that the 10 and 13 wt.% Nb alloys surpassed the TA4G surgical implant standard in strength while offering a lower elastic modulus and greater elongation. Electrochemical experiments showed that the corrosion resistance of the alloys improved with increasing Nb content. Furthermore, CCK-8 assay results, ALP semi-quantitative analysis, and RT-PCR demonstrated that Ti-xNb-5Ta alloys enhanced the early osteogenic differentiation of human bone marrow stromal cells (hBMSCs). This work not only reveals the potential of Ti-xNb-5Ta alloys as biomedical materials but also offers insights for developing novel biomaterials.

A Finite Element Study of Simulated Fusion in an L4-L5 Model: Influence of the Combination of Materials in the Screw-and-Rod Fixation System on Reproducing Natural Bone Behavior

The mechanical properties of materials for spinal fixation can significantly affect spinal surgical outcomes. Traditional materials such as titanium exhibit high stiffness, which can lead to stress shielding and adjacent segment degeneration. This study investigates the biomechanical performance of titanium and PEEK (polyetheretherketone) in spinal fixation using finite element analysis, through the evaluation of the Shielding Strength Factor (SSF). Methods: A three-dimensional finite element analysis (FEA) model of an L4/L5 functional spinal unit was developed to simulate the mechanical behavior of three fixation systems: titanium screws and rods (model A), titanium screws with PEEK rods (model B), and PEEK screws and rods (model C). The analysis evaluated stress distribution and load transfer under physiological conditions, in comparison with the intact spine (baseline model). Results: The analysis showed that titanium fixation systems resulted in higher stress shielding effects, with a significant difference in stress distribution compared to PEEK. The maximum stress recorded in the neutral position was 24.145 MPa for PEEK, indicating better biomechanical compatibility. Conclusions: The results suggest that PEEK may be an attractive alternative to titanium for spinal fixation, promoting more healthy load transfer and minimizing the risk of stress shielding complications.

Hydroxyapatite Chitosan Gradient Pore Scaffold Activates Oxidative Phosphorylation Pathway to Induce Bone Formation

BACKGROUND

In this study, we prepared a porous gradient scaffold with hydroxyapatite microtubules (HAMT) and chitosan (CHS) and investigated osteogenesis induced by these scaffolds.

METHODS

The arrangement of wax balls in the mold can control the size and distribution of the pores of the scaffold, and form an interconnected gradient pore structure. The scaffolds were systematically evaluated in vitro and in vivo for biocompatibility, biological activity, and regulatory mechanisms.

RESULTS

The porosity of the four scaffolds was more than 80%. The 50% and 70% HAMT-CHS scaffolds formed an excellent gradient pore structure, with interconnected pores. Furthermore, the 70% HAMT-CHS scaffold showed better anti-compressive deformation ability. In vitro experiments indicated that the scaffolds had good biocompatibility, promoted the expression of osteogenesis-related genes and proteins, and activated the oxidative phosphorylation pathway to promote bone regeneration. Eight weeks after implanting the HAMT-CHS scaffold in rat skull defects, new bone formation was observed in vivo by micro-computed tomographic (CT) staining. The obtained data were statistically analyzed, and the p-value < 0.05 was statistically significant.

CONCLUSION

HAMT-CHS scaffolds can accelerate osteogenesis in bone defects, potentially through the activation of the oxidative phosphorylation pathway. These results highlight the potential therapeutic application of HAMT-CHS scaffolds.

Exploring the frontiers of metal additive manufacturing in orthopaedic implant development

This paper provides a thorough analysis of recent advancements and emerging trends in the integration of metal additive manufacturing (AM) within orthopedic implant development. With an emphasis on the use of various metals and alloys, including titanium, cobalt-chromium, and nickel-titanium, the review looks at their characteristics and how they relate to the creation of various orthopedic implants, such as spinal implants, hip and knee replacements, and cranial-facial reconstructions. The study highlights how metal additive manufacturing (AM) can revolutionize the field by enabling customized implant designs that take patient anatomical variances into account. The review discusses the drawbacks of conventional manufacturing techniques and emphasizes the benefits of metal additive manufacturing (AM), such as increased design flexibility and decreased material waste. Important material selection factors, including mechanical qualities and biocompatibility, are covered in relation to metal additive manufacturing applications. The work ends with a summary of the issues facing metal AM today, such as surface finish and material certification, and suggestions for future developments, like the creation of advanced materials and the application of AI to design optimization.

Shape/properties collaborative intelligent manufacturing of artificial bone scaffold: structural design and additive manufacturing process

Artificial bone graft stands out for avoiding limited source of autograft as well as susceptibility to infection of allograft, which makes it a current research hotspot in the field of bone defect repair. However, traditional design and manufacturing method cannot fabricate bone scaffold that well mimics complicated bone-like shape with interconnected porous structure and multiple properties akin to human natural bone. Additive manufacturing, which can achieve implant's tailored external contour and controllable fabrication of internal microporous structure, is able to form almost any shape of designed bone scaffold via layer-by-layer process. As additive manufacturing is promising in building artificial bone scaffold, only combining excellent structural design with appropriate additive manufacturing process can produce bone scaffold with ideal biological and mechanical properties. In this article, we sum up and analyze state of art design and additive manufacturing methods for bone scaffold to realize shape/properties collaborative intelligent manufacturing. Scaffold design can be mainly classified into design based on unit cells and whole structure, while basic additive manufacturing and 3D bioprinting are the recommended suitable additive manufacturing methods for bone scaffold fabrication. The challenges and future perspectives in additive manufactured bone scaffold are also discussed.

A review of computational optimization of bone scaffold architecture: methods, challenges, and perspectives

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

Surface engineering of orthopedic implants for better clinical adoption

Musculoskeletal disorders are on the rise, and despite advances in alternative materials, treatment for orthopedic conditions still heavily relies on biometal-based implants and scaffolds due to their strength, durability, and biocompatibility in load-bearing applications. Bare metallic implants have been under scrutiny since their introduction, primarily due to their bioinert nature, which results in poor cell-material interaction. This challenge is further intensified by mechanical mismatches that accelerate failure, tribocorrosion-induced material degradation, and bacterial colonization, all contributing to long-term implant failure and posing a significant burden on patient populations. Recent efforts to improve orthopedic medical devices focus on surface engineering strategies that enhance the interaction between cells and materials, creating a biomimetic microenvironment and extending the service life of these implants. This review compiles various physical, chemical, and biological surface engineering approaches currently under research, providing insights into their potential and the challenges associated with their adoption from bench to bedside. Significant emphasis is placed on exploring the future of bioactive coatings, particularly the development of smart coatings like self-healing and drug-eluting coatings, the immunomodulatory effects of functional coatings and biomimetic surfaces to tackle secondary infections, representing the forefront of biomedical surface engineering. The article provides the reader with an overview of the engineering approaches to surface modification of metallic implants, covering both clinical and research perspectives and discussing limitations and future scope.

Medium-entropy Zr-Nb-Ti alloys with low magnetic susceptibility, high yield strength, and low elastic modulus through spinodal decomposition for bone-implant applications

Medium-entropy Zr-Nb-Ti (ZNT) alloys are being extensively investigated as load-bearing implant materials because of their exceptional biocompatibility and corrosion resistance, and low magnetic susceptibility. Nevertheless, enhancing their yield strength while simultaneously decreasing their elastic modulus presents a formidable obstacle, significantly constraining their broader utilization as metallic biomaterials. In this study, three medium-entropy ZNT alloys, i.e., Zr45Nb45Ti10, Zr42.5Nb42.5Ti15, and Zr40Nb40Ti20 (denoted ZNT10, ZNT15, and ZNT20, respectively), were designed based on the miscibility gap in the ZNT phase diagram and prepared by annealing of cold-rolled ingots. Their microstructures, mechanical properties, wear resistance, corrosion resistance, magnetic susceptibility, and biocompatibility were systematically studied. Spinodal decomposition occurred in the cold-rolled ZNT10 and ZNTi15 after annealing at 650 °C for 2 h and resulted in nanoscale Zr-rich β1 and (Nb, Ti)-rich β2 phases, which significantly improved their yield strength and reduced their elastic modulus. The wear resistance of the alloys decreased with an increase in Ti content. Dense ZrO2, Nb2O5, and TiO2 oxide layers were formed during the polarization process in Hanks' solution, which enhanced the corrosion resistance of the alloys. These ZNT alloys exhibited significantly lower magnetic susceptibility than medical Ti alloys. The ZNT alloys showed a cell viability of more than 94 % toward MG-63 cells after culturing for 3 d Overall, the spinodal ZNT15 showed the best combination of mechanical properties, wear resistance, corrosion resistance, low magnetic susceptibility, and sufficient biocompatibility among the three alloys. STATEMENT OF SIGNIFICANCE: This work reports on medium-entropy Zr-Nb-Ti (ZNT) alloys with heterostructure. Spinodal decomposition significantly improved their mechanical strength and reduced the elastic modulus of the alloys. The wear resistance of the ZNT alloys decreased with an increase in Ti content. Dense ZrO2, Nb2O5, and TiO2 oxide layers were formed during the polarization process in Hanks' solution, which enhanced the corrosion resistance of the alloys. The ZNT alloys exhibited significantly lower magnetic susceptibility than medical Ti alloys. The ZNT alloys showed a cell viability of >94 % toward MG-63 cells after culturing for 3 d The results demonstrate that spinodal ZNT alloys have enormous potential as bone-implant materials due to their outstanding overall mechanical properties, high corrosion resistance, wear resistance, low magnetic susceptibility, and sufficient biocompatibility.

The Principle of Limb Reconstruction-"One Walking, Two Lines, and Three Balances": A Retrospective Analysis of Post-Traumatic Lower Limb Deformity Correction

OBJECTIVE

The principles of limb reconstruction are crucial for treatment success, but there is no unified standard for complex limb deformities. The aim of this study was to analyze the characteristics of the cases of post-traumatic lower limb deformity and explore the new principle of limb reconstruction.

METHOD

A retrospective analysis was conducted of 148 patients with post-traumatic lower limb deformity who underwent surgery from May 1978 to December 2023; 85 were males (57.4%) and 63 were females (42.6%); 65 cases of left side (43.9%), 79 cases of right side(53.4%), and 4 cases were on both sides (2.7%), the average age was 24.64 years (5-69). There were 4 cases suffering hip deformities, 40 cases of femoral deformities, 18 cases from knee, 40 cases from tibiofibular, 93 cases of foot and ankle deformities, and some patients also had two or more types. All patients underwent surgical intervention in an average of 40.5 months (12-96) after injury. According to the evaluation of limb deformities, deformity correction and functional reconstruction with external fixation were implemented, following the principle of "one walking, two lines, and three balances." The clinical evaluation adopts the criteria of Qinsihe lower limb deformity correction and functional reconstruction.

RESULT

148 patients with post-traumatic lower limb deformities were followed up for 40.9 (12-356) months. The main surgical procedures implemented were tendon lengthening and soft tissue release (84 cases), osteotomy (93 cases), joint fusion (30 cases), and tendon transposition (16 cases); there were multiple surgical procedures in some patients. Among them, 124 cases used external fixators for stress control and 27 cases used internal fixation, while 3 cases used plaster or brace. There were 5 wire reactions postoperatively, which improved after dressing change and oral antibiotics. There were 2 pin infections, which improved by pin removing. No surgical related deep infections occurred, and no surgical related neurovascular damage occurred. At the last follow-up, all limb deformities were corrected, limb function improved, and the results of treatment was very satisfactory. According to Qinsihe evaluation criteria for lower limb deformities, 74 cases were excellent, 56 cases good, and 18 cases fair, with an excellent and good rate of 87.84%.

CONCLUSION

Stress control with external fixation is effective, safe, and controllable in correcting and reconstructing post-traumatic lower limb deformities. The principle of "one walking, two lines, and three balances" plays an important role in the entire process of stress control limb reconstruction.

Architecture of β-lactoglobulin coating modulates bioinspired alginate dialdehyde-gelatine/polydopamine scaffolds for subchondral bone regeneration

In this study, we developed polydopamine (PDA)-functionalized alginate dialdehyde-gelatine (ADA-GEL) scaffolds for subchondral bone regeneration. These polymeric scaffolds were then coated with β-Lactoglobulin (β-LG) at concentrations of 1 mg/ml and 2 mg/ml. Morphological analysis indicated a homogeneous coating of the β-LG layer on the surface of network-like scaffolds. The β-LG-coated scaffolds exhibited improved swelling capacity as a function of the β-LG concentration. Compared to ADA-GEL/PDA scaffolds, the β-LG-coated scaffolds demonstrated delayed degradation and enhanced biomineralization. Here, a lower concentration of β-LG showed long-lasting stability and superior biomimetic hydroxyapatite mineralization. According to the theoretical findings, the single-state, representing the low concentration of β-LG, exhibited a homogeneous distribution on the surface of the PDA, while the dimer-state (high concentration) displayed a high likelihood of uncontrolled interactions. β-LG-coated ADA-GEL/PDA scaffolds with a lower concentration of β-LG provided a biocompatible substrate that supported adhesion, proliferation, and alkaline phosphatase (ALP) secretion of sheep bone marrow mesenchymal stem cells, as well as increased expression of osteopontin (SPP1) and collagen type 1 (COL1A1) in human osteoblasts. These findings indicate the potential of protein-coated scaffolds for subchondral bone tissue regeneration. STATEMENT OF SIGNIFICANCE: This study addresses a crucial aspect of osteochondral defect repair, emphasizing the pivotal role of subchondral bone regeneration. The development of polydopamine-functionalized alginate dialdehyde-gelatine (ADA-GEL) scaffolds, coated with β-Lactoglobulin (β-LG), represents a novel approach to potentially enhance subchondral bone repair. β-LG, a milk protein rich in essential amino acids and bioactive peptides, is investigated for its potential to promote subchondral bone regeneration. This research explores computationally and experimentally the influence of protein concentration on the ordered or irregular deposition, unravelling the interplay between coating structure, scaffold properties, and in-vitro performance. This work contributes to advancing ordered protein coating strategies for subchondral bone regeneration, providing a biocompatible solution with potential implications for supporting subsequent cartilage repair.

Design, Manufacture, and Characterization of a Critical-Sized Gradient Porosity Dual-Material Tibial Defect Scaffold

This study proposed a composite tibia defect scaffold with radial gradient porosity, utilizing finite element analysis to assess stress in the tibial region with significant critical-sized defects. Simulations for scaffolds with different porosities were conducted, designing an optimal tibia defect scaffold with radial gradient porosity for repairing and replacing critical bone defects. Radial gradient porosity scaffolds resulted in a more uniform stress distribution, reducing titanium alloy stiffness and alleviating stress shielding effects. The scaffold was manufactured using selective laser melting (SLM) technology with stress relief annealing to simplify porous structure fabrication. The study used New Zealand white rabbits' tibia defect sites as simulation parameters, reconstructing the 3D model and implanting the composite scaffold. Finite element analysis in ANSYS-Workbench simulated forces under high-activity conditions, analyzing stress distribution and strain. In the simulation, the titanium alloy scaffold bore a maximum stress of 122.8626 MPa, while the centrally encapsulated HAp material delivered 27.92 MPa. The design demonstrated superior structural strength, thereby reducing stress concentration. The scaffold was manufactured using SLM, and the uniform design method was used to determine a collection of optimum annealing parameters. Nanoindentation and compression tests were used to determine the influence of annealing on the elastic modulus, hardness, and strain energy of the scaffold.