Development of a density-based topology optimization of homogenized lattice structures for individualized hip endoprostheses and validation using micro-FE

Tailored 3D Lattice Microstructures for Enhanced Functionality in Blood-Gas Exchange

Current membrane oxygenators for extracorporeal life support (ECLS) are facing their limits regarding gas exchange efficiency and long-term stability. One aspect adding to these limitations is inhomogeneous blood flow distribution inside the oxygenator's membrane structure. Triply periodic minimal surface (TPMS) lattice structures are proposed to provide increased mass transfer efficiency and local adaptability introducing heterogeneous properties. However, the adaptation of these structures for blood flow, as in ECLS, is challenging as a hemocompatible flow distribution must be established. In this study, this study proposes a novel method for the smooth, multi-scale modification of TPMS lattice structures creating a tailored flow distribution suited for blood-gas exchange. It implements this method into an automatic structure optimization within an oxygenator. After manufacturing prototypes, it experimentally evaluate the 3D flow distribution using time-resolved, contrast enhanced computed tomography comparing the optimized structure to reference geometries. The TPMS structure modification provides a significant change in flow distribution, improving homogeneity by up to 12%. The approach to creating tailored 3D TPMS lattice structures can be directly transferred to various other applications in the field of heat and mass transfer to enhance functionality, e.g., for heat exchangers or membrane contactors.

A Neural Network-Accelerated Approach for Orthopedic Implant Design and Evaluation Through Strain Shielding Analysis

The design of orthopedic implants is a complex challenge, requiring the careful balance of mechanical performance and biological integration to ensure long-term success. This study focuses on the development of a porous femoral stem implant aimed at reducing stiffness and mitigating stress shielding effects. To accelerate the design process, neural networks were trained to predict the optimal density distribution of the implant, enabling rapid optimization. Two initial design spaces were evaluated, revealing the necessity of incorporating the femur's anatomical features into the design process. The trained models achieved a median error near 0 for both conventional and extended design spaces, producing optimized designs in a fraction of the computational time typically required. Finite element analysis (FEA) was employed to assess the mechanical performance of the neural network-generated implants. The results demonstrated that the neural network predictions effectively reduced stress shielding compared to a solid model in 50% of the test cases. While the graded porosity implant design did not show significant differences in stress shielding prevention compared to a uniform porosity design, it was found to be significantly stronger, highlighting its potential for enhanced durability. This work underscores the efficacy of neural network-accelerated design in improving implant development efficiency and performance.

Comparison of Stress between Three Different Functionally Graded Hip Stem Implants Made of Different Titanium Alloys and Composite Materials

This study aims to evaluate the mechanical behavior, by ways of the FEM, of three femoral stems made of a Ti-6Al-4V titanium alloy with transverse holes in the proximal zone and a stem made of a β-type titanium alloy with a stiffness varying from 65 GPa in the proximal zone to 110 GPa in the distal zone and the CFRP composite material. The purpose of the study was to evaluate the effect of stress shielding on an intact femoral bone. A three-dimensional model of the intact femur was created, and the three prostheses were inserted with perfect stem bone fit. Applying constraint conditions such as fixation in all directions of the distal part of the femur and the application of a static load simulating standing still during a gait cycle allowed the stresses of both the implants and the bone to be compared. Evaluating the stress shielding for the three proposed materials was possible by identifying the seven Gruen zones. We can see from the results obtained that the metal alloys produced observable stress shielding in all the Gruen zones. There was a difference for the β-type alloy which, as a result of its stiffness variation from the proximal to the distal zone, did not show any level of stress shielding in Gruen zones 1 and 2. The CFRP composite, in contrast, showed no stress shielding in all of the Gruen zones and is an excellent material for the fabrication of total hip replacements. Further in vitro and in vivo validation studies are needed to make the modeling more accurate and understand the biological effects of the use of the three materials.

Advanced porous hip implants: A comprehensive review

The field of orthopaedic implants has experienced significant advancements in recent years, transforming the approach to orthopaedic treatments. Amongst these advancements, porous structures have emerged as a promising solution to address the limitations of traditional solid implants. This comprehensive review paper offers a thorough overview of the importance of advanced porous hip implants, focusing on three key areas bone morphology and biomechanical parameters, complications associated with solid implants, and the benefits of porous structures and porous implants. Understanding the intricate interplay between bone morphology and biomechanical parameters is crucial when designing orthopaedic implants. Mimicking the native bone structure ensures optimal osseointegration, load distribution, and long-term success. Porous implants closely resemble natural bone structures, facilitating improved integration and biomechanical compatibility. Complications with solid implants are a significant concern in orthopaedic procedures. Stress shielding, cortical hypertrophy, and micromotion can lead to implant failure or revision surgeries. By contrast, porous structures promise to mitigate these issues by promoting bone ingrowth, reducing stress concentrations, and providing stability at the bone-implant interface. The benefits of porous structures and porous implants go beyond addressing solid implant complications. These structures enhance bone in-growth potential, strengthening integration and long-term stability. The interconnected porosity promotes nutrient diffusion and new blood vessel formation, supporting healing and minimizing infection risk. Furthermore, porous implants exhibit improved mechanical properties, such as lower elastic modulus and higher energy absorption, that better match those of bone. This feature helps alleviate stress shielding and enhances the overall performance and longevity of the implant. In conclusion, advanced porous implants have tremendous potential in orthopaedics. By closely mimicking native bone structure and reducing complications associated with solid implants, they can revolutionize orthopaedic treatments. Further research and development are warranted to fully exploit the potential of these innovative solutions and improve patient outcomes.

Current Perspectives of Protein in Bone Tissue Engineering: Bone Structure, Ideal Scaffolds, Fabrication Techniques, Applications, Scopes, and Future Advances

In view of their exceptional approach, excellent inherent biocompatibility and biodegradability properties, and interaction with the local extracellular matrix, protein-based polymers have received attention in bone tissue engineering, which is a multidisciplinary field that repairs and regenerates fractured bones. Bone is a multihierarchical complex structure, and it performs several essential biofunctions, including maintaining mineral balance and structural support and protecting soft organs. Protein-based polymers have gained interest in developing ideal scaffolds as emerging biomaterials for bone fractured healing and regeneration, and it is challenging to design ideal bone substitutes as perfect biomaterials. Several protein-based polymers, including collagen, keratin, gelatin, serum albumin, etc., are potential materials due to their inherent cytocompatibility, controlled biodegradability, high biofunctionalization, and tunable mechanical characteristics. While numerous studies have indicated the encouraging possibilities of proteins in BTE, there are still major challenges concerning their biodegradability, stability in physiological conditions, and continuous release of growth factors and bioactive molecules. Robust scaffolds derived from proteins can be used to replace broken or diseased bone with a biocompatible substitute; proteins, being biopolymers, provide excellent scaffolds for bone tissue engineering. Herein, recent developments in protein polymers for cutting-edge bone tissue engineering are addressed in this review within 3-5 years, with a focus on the significant challenges and future perspectives. The first section discusses the structural fundamentals of bone anatomy and ideal scaffolds, and the second section describes the fabrication techniques of scaffolds. The third section highlights the importance of proteins and their applications in BTE. Hence, the recent development of protein polymers for state-of-the-art bone tissue engineering has been discussed, highlighting the significant challenges and future perspectives.