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

Mechanical and biological characteristics of 3D-printed auxetic structure in bone tissue engineering

The auxetic structures are highly effective in bone implants due to their unique deformation characteristics. However, ideal tissue engineering scaffolds must possess suitable mechanical properties and biocompatibility. The biological effects of auxetic structures require further study. In this study, three types of 3D re-entrant honeycomb structures with varying angles of 75°, 90°, and 105° were designed. These structures were fabricated by stereolithography 3D printing technology. Finite element simulations and compression tests were conducted to evaluate their mechanical properties. Scaffolds were inoculated with preosteoblast MC3T3-E1 cells, and cyclic loading was applied to investigate the influence of structural and mechanical stimulation on cell arrangement and proliferation. The results demonstrated that the 75° scaffold exhibited auxetic characteristics in all compression directions and possessed anti-fracture properties. The 75° scaffold also promoted cell proliferation by structural design. Cyclic compression facilitated the nuclear translocation of YAP, further enhancing cell growth. The combination of anti-fracture properties and the promotion of cell proliferation makes auxetic structures highly promising for extensive applications.

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.

Biomechanics and Mechanobiology of Additively Manufactured Porous Load-Bearing Bone Implants

Given that they can replicate both the biomechanical and mechanobiological functions of natural bone, metal additively manufactured porous load-bearing bone implants present a significant advancement in orthopedic applications. Additive manufacturing (AM) of metals enables precise control over pore geometry, resulting in implants that provide effective mechanical support and minimize stress shielding. In addition to its mechanical benefits, the porous architecture of the implants facilitates essential mechanobiological processes, including the transmission of mechanical signals that regulate cellular processes such as adhesion, proliferation, and differentiation. Before clinical use, the implants should first be engineered to achieve a comparable elastic modulus to native bone, mitigating implant-induced bone resorption while promoting tissue regeneration. It is also noteworthy that the microstructural features of these implants support angiogenesis-a critical process for oxygen and nutrient delivery during bone healing. Despite their potential benefits, challenges remain in balancing mechanical stability for load-bearing applications with biofunctionality for effective integration and controlled degradation. This review comprehensively discusses the biomechanical and mechanobiological factors influencing the design and performance of additively manufactured porous bone implants, highlighting their potential to enhance clinical outcomes in bone repair and regeneration.

Functional morphology of trabecular system in human proximal femur: a perspective from P45 sectional plastination and 3D reconstruction finite element analysis

BACKGROUND

The trabecular architecture of proximal femur plays a crucial role in hip stability and load distribution and is often ignored in hip fracture fixation due to limited anatomical knowledge. This study analyses trabecular morphology and stress distribution, aiming to provide an anatomical foundation for optimising implant designs.

MATERIALS AND METHODS

Twenty-one formalin-fixed human pelvises (twelve male, nine female) were prepared using P45 sectional plastination. They were sliced into 3 mm sections in the coronal, sagittal, and horizontal planes and then photographed. A 3D femur model was created from computed tomographic scans and analysed for finite element analysis (FEA) using Mimics, 3-matics, and Abaqus software to simulate static and dynamic loads, visualising stress paths for compressive and tensile regions and identifying fracture-vulnerable zones.

RESULTS

Two main trabecular systems were identified: the medial and lateral systems. The medial system includes a primary vertical trabecular group extending from the femoral shaft's medial calcar to the head and two primary horizontal groups arching from the lateral shaft, greater trochanter, and femoral neck's anterolateral and posterolateral walls toward the medial side, intersecting with the primary vertical group in the head. Secondary vertical group intersects with secondary horizontal group at the neck-trochanteric junction to form the lateral system. FEA showed peak compressive stress along the vertical groups, calcar, and medial cortex, and tensile stress along the horizontal groups, greater trochanter, and lateral cortex, creating balanced support that stabilises the femoral neck and shaft.

CONCLUSION

The strength of proximal femur depends on dense cortical bone, calcar femorale, lateral and medial trabecular systems, and greater trochanter. While anterolateral and posterolateral areas of femoral neck and intertrochanteric regions are potential weak zones. Trabecular pattern follows stress paths, optimising load distribution. These insights aid in designing robotic and bionic implants that mimic natural stress patterns, reducing complications.

Auxetic Biomedical Metamaterials for Orthopedic Surgery Applications: A Comprehensive Review

Poisson's ratio in auxetic materials shifts from typically positive to negative, causing lateral expansion during axial tension. This scale-independent characteristic, originating from tailored architectures, exhibits specific physical properties, including energy adsorption, shear resistance, and fracture resistance. These metamaterials demonstrate exotic mechanical properties with potential applications in several engineering fields, but biomedical applications seem to be one of the most relevant, with an increasing number of articles published in recent years, which present opportunities ranging from cellular repair to organ reconstruction with outstanding mechanical performance, mechanical conduction, and biological activity compared with traditional biomedical metamaterials. Therefore, focusing on understanding the potential of these structures and promoting theoretical and experimental investigations into the benefits of their unique mechanical properties is necessary for achieving high-performance biomedical applications. Considering the demand for advanced biomaterial implants in surgical technology and the profound advancement of additive manufacturing technology that are particularly relevant to fabricating complex and customizable auxetic mechanical metamaterials, this review focuses on the fundamental geometric configuration and unique physical properties of negative Poisson's ratio materials, then categorizes and summarizes auxetic material applications across some surgical departments, revealing efficacy in joint surgery, spinal surgery, trauma surgery, and sports medicine contexts. Additionally, it emphasizes the substantial potential of auxetic materials as innovative biomedical solutions in orthopedics and demonstrates the significant potential for comprehensive surgical application in the future.

Orthopedic meta-implants

Meta-biomaterials, engineered materials with distinctive combinations of mechanical, physical, and biological properties stemming from their micro-architecture, have emerged as a promising domain within biomedical engineering. Correspondingly, meta-implants, which serve as the device counterparts of meta-biomaterials, offer exceptional functionalities, holding great potential for addressing complex skeletal diseases. This paper presents a comprehensive overview of the various types of meta-implants, including hybrid, shape-morphing, metallic clay, and deployable meta-implants, highlighting their unprecedented properties and recent achievement in the field. This paper also delves into the potential future developments of meta-implants, addressing the exploration of multi-functionalities in meta-biomaterials and their applications in diverse biomedical fields.

Advancement in total hip implant: a comprehensive review of mechanics and performance parameters across diverse novelties

The UK's National Joint Registry (NJR) and the American Joint Replacement Registry (AJRR) of 2022 revealed that total hip replacement (THR) is the most common orthopaedic joint procedure. The NJR also noted that 10-20% of hip implants require revision within 1 to 10 years. Most of these revisions are a result of aseptic loosening, dislocation, implant wear, implant fracture, and joint incompatibility, which are all caused by implant geometry disparity. The primary purpose of this review article is to analyze and evaluate the mechanics and performance factors of advancement in hip implants with novel geometries. The existing hip implants can be categorized based on two parts: the hip stem and the joint of the implant. Insufficient stress distribution from implants to the femur can cause stress shielding, bone loss, excessive micromotion, and ultimately, implant aseptic loosening due to inflammation. Researchers are designing hip implants with a porous lattice and functionally graded material (FGM) stems, femur resurfacing, short-stem, and collared stems, all aimed at achieving uniform stress distribution and promoting adequate bone remodeling. Designing hip implants with a porous lattice FGM structure requires maintaining stiffness, strength, isotropy, and bone development potential. Mechanical stability is still an issue with hip implants, femur resurfacing, collared stems, and short stems. Hip implants are being developed with a variety of joint geometries to decrease wear, improve an angular range of motion, and strengthen mechanical stability at the joint interface. Dual mobility and reverse femoral head-liner hip implants reduce the hip joint's dislocation limits. In addition, researchers reveal that femoral headliner joints with unidirectional motion have a lower wear rate than traditional ball-and-socket joints. Based on research findings and gaps, a hypothesis is formulated by the authors proposing a hip implant with a collared stem and porous lattice FGM structure to address stress shielding and micromotion issues. A hypothesis is also formulated by the authors suggesting that the utilization of a spiral or gear-shaped thread with a matched contact point at the tapered joint of a hip implant could be a viable option for reducing wear and enhancing stability. The literature analysis underscores substantial research opportunities in developing a hip implant joint that addresses both dislocation and increased wear rates. Finally, this review explores potential solutions to existing obstacles in developing a better hip implant system.

Musculoskeletal Biomaterials: Stimulated and Synergized with Low Intensity Pulsed Ultrasound

Clinical biophysical stimulating strategies, which have significant effects on improving the function of organs or treating diseases by causing the salutary response of body, have shown many advantages, such as non-invasiveness, few side effects, and controllable treatment process. As a critical technique for stimulation, the low intensity pulsed ultrasound (LIPUS) has been explored in regulating osteogenesis, which has presented great promise in bone repair by delivering a combined effect with biomaterials. This review summarizes the musculoskeletal biomaterials that can be synergized with LIPUS for enhanced biomedical application, including bone regeneration, spinal fusion, osteonecrosis/osteolysis, cartilage repair, and nerve regeneration. Different types of biomaterials are categorized for summary and evaluation. In each subtype, the verified biological mechanisms are listed in a table or graphs to prove how LIPUS was effective in improving musculoskeletal tissue regeneration. Meanwhile, the acoustic excitation parameters of LIPUS that were promising to be effective for further musculoskeletal tissue engineering are discussed, as well as their limitations and some perspectives for future research. Overall, coupled with biomimetic scaffolds and platforms, LIPUS may be a powerful therapeutic approach to accelerate musculoskeletal tissue repair and even in other regenerative medicine applications.

Advances in Dental Implants, Tissue Engineering and Prosthetic Materials

Scientific research has achieved numerous milestones in the field of materials applied to medicine for biomedical prosthetics [...].