Topological design and additive manufacturing of porous metals for bone scaffolds and orthopaedic implants: A review

A novel porous titanium with engineered surface for bone defect repair in load-bearing position

Porous titanium exhibits low elastic modulus and porous structure is thought to be a promising implant in bone defect repair. However, the bioinert and low mechanical strength of porous titanium have limited its clinical application, especially in load-bearing bone defect repair. Our previous study has reported an infiltration casting and acid corrosion (IC-AC) method to fabricate a novel porous titanium (pTi) with 40% porosity and 0.4 mm pore diameter, which exerts mechanical property matching with cortical bone and interconnected channels. In this study, we introduced a nanoporous coating and incorporated an osteogenic element strontium (Sr) on the surface of porous titanium (named as Sr-micro arch oxidation [MAO]) to improve the osteogenic ability of the pTi by MAO. Better biocompatibility of Sr-MAO was verified by cell adhesion experiment and cell counting kit-8 (CCK-8) test. The in vitro osteogenic-related tests such as immunofluorescence staining, alkaline phosphatase staining and real-time polymerase chain reaction (RT-PCR) demonstrated better osteogenic ability of Sr-MAO. Femoral bone defect repair model was employed to evaluate the osseointegration of samples in vivo. Results of micro-CT scanning, sequential fluorochrome labeling and Van Gieson staining suggested that Sr-MAO showed better in vivo osteogenic ability than other groups. Taking results of both in vitro and in vivo experiment together, this study indicated the Sr-MAO porous titanium could be a promising implant load-bearing bone defect.

The effects of different grading approaches in additively manufactured dental implants on peri-implant bone stress: A finite element analysis

Additive manufacturing enables local grading of the stiffness of dental implants through targeted adjustment of the manufacturing parameters to meet patient specific requirements. The extent to which such a manufacturing approach affects the interaction between the implant body and the surrounding bone, and what grading is optimal, is currently insufficiently investigated. This study investigates the effect of different Young's modulus grading approaches on stresses in the peri-implant bone via finite element analysis. The implant geometry was kept constant and in the case of the implant a node-dependent elastic modulus was assigned. In this way, a vertical, a radial and three torus based grading approaches were created and examined. A load was then applied directly to the occlusal surface of the implant crown. It was found that a local grading utilizing a torus shape was most favourable in terms of an effective stress peak reduction. The best torus shape tested achieved a 22 % reduction of maximum principal stress and 6 % reduction of minimum principal stress compared to the uniform material. In clinical settings, this may provide benefits in situations of overload. Based on the results, a graded stiffness in dental implants appears to be of interest for developing advanced, patient-specific implant solutions.

Gradient gyroid Ti6Al4V scaffolds with TiO2 surface modification: Promising approach for large bone defect repair

Large bone defects, particularly those exceeding the critical size, present a clinical challenge due to the limited regenerative capacity of bone tissue. Traditional treatments like autografts and allografts are constrained by donor availability, immune rejection, and mechanical performance. This study aimed to develop an effective solution by designing gradient gyroid scaffolds with titania (TiO2) surface modification for the repair of large segmental bone defects. The scaffolds were engineered to balance mechanical strength with the necessary internal space to promote new bone formation and nutrient exchange. A gradient design of the scaffold was optimized through Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) simulations to enhance fluid flow and cell adhesion. In vivo studies in rabbits demonstrated that the G@TiO2 scaffold, featuring a gradient structure and TiO2 surface modification, exhibited superior healing capabilities compared to the homogeneous structure and TiO2 surface modification (H@TiO2) and gradient structure (G) scaffolds. At 12 weeks post-operation, in a bone defect representing nearly 30 % of the total length of the radius, the implantation of the G@TiO2 scaffold achieved a 27 % bone volume to tissue volume (BV/TV) ratio, demonstrating excellent osseointegration. The TiO2 surface modification provided photothermal antibacterial effects, enhancing the scaffold's biocompatibility and potential for infection prevention. These findings suggest that the gradient gyroid scaffold with TiO2 surface modification is a promising candidate for treating large segmental bone defects, offering a combination of mechanical strength, bioactivity, and infection resistance.

3D printing of polysaccharide-based hydrogel scaffolds for tissue engineering applications: A review

In tissue engineering, 3D printing represents a versatile technology employing inks to construct three-dimensional living structures, mimicking natural biological systems. This technology efficiently translates digital blueprints into highly reproducible 3D objects. Recent advances have expanded 3D printing applications, allowing for the fabrication of diverse anatomical components, including engineered functional tissues and organs. The development of printable inks, which incorporate macromolecules, enzymes, cells, and growth factors, is advancing with the aim of restoring damaged tissues and organs. Polysaccharides, recognized for their intrinsic resemblance to components of the extracellular matrix have garnered significant attention in the field of tissue engineering. This review explores diverse 3D printing techniques, outlining distinctive features that should characterize scaffolds used as ideal matrices in tissue engineering. A detailed investigation into the properties and roles of polysaccharides in tissue engineering is highlighted. The review also culminates in a profound exploration of 3D polysaccharide-based hydrogel applications, focusing on recent breakthroughs in regenerating different tissues such as skin, bone, cartilage, heart, nerve, vasculature, and skeletal muscle. It further addresses challenges and prospective directions in 3D printing hydrogels based on polysaccharides, paving the way for innovative research to fabricate functional tissues, enhancing patient care, and improving quality of life.

Self-Assembly Reinforced Alginate Fibers for Enhanced Strength, Toughness, and Bone Regeneration

Material reinforcement commonly exists in a contradiction between strength and toughness enhancement. Herein, a reinforced strategy through self-assembly is proposed for alginate fibers. Sodium alginate (SA) microstructures with regulated secondary structures are assembled in acidic and ethanol as reinforcing units for alginate fibers. Acidity increases the flexibility of the helix and contributes to enhanced extendibility. Ethanol is responsible for formation of a stiff β-sheet, which enhances the modulus and strength. The structurally engineered SA assembly exhibits robust mechanical compatibility, and thus reinforced alginate fibers possess an improved tensile strength of 2.1 times, a prolonged elongation of 1.5 times, and an enhanced toughness of 3.0 times compared with SA fibers without reinforcement. The reinforcement through self-assembly provides an understanding of strengthening and toughening mechanism based on secondary structures. Due to a similar modulus with bones, reinforced alginate fibers exhibit good efficacy in accelerating bone regeneration in vivo.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Multiscale topology optimization of pelvic bone for combined walking and running gait cycles

We propose a multiscale topology optimization procedure of pelvic bone using weighted compliance minimization. In macroscale optimization, a level set-based method is used, which gives a binary structure. In microscale optimization, cubic lattice-based homogenization is done while keeping the global geometry fixed. For the macroscale, a volume constraint equal to the volume of the pelvic bone is imposed, whereas, for the microscale, a mass constraint equal to the mass of the pelvic bone is imposed. The optimal geometries are compared with pelvic bone using different metrics and show good similarity with the same. Designed geometries are additively manufactured and experimentally tested for stiffness.

Computational analysis of prosthesis production via topology optimization

This work investigates the use of Topology Optimization (TO) to support the design of femur prosthesis to obtain more efficient solutions from the point of view of material distribution and internal forces. Computational tests were performed by the Interior-Point OPTimizer (IPOPT) method, seeking to explore the elastic mechanical characteristics of three real scenarios of daily loads on the femur. Numerical examples are presented to verify the novelty of the proposed method. The results obtained indicate that it is possible to reduce the volume of material up to 30% of the customize human femoral prosthesis, respecting all the boundary conditions.

Construction of multileveled and oriented micro/nano channels in Mg doped hydroxyapitite bioceramics and their effect on mimicking mechanical property of cortical bone and biological performance of cancellous bone

Drawing on the structure and components of natural bone, this study developed Mg-doped hydroxyapatite (Mg-HA) bioceramics, characterized by multileveled and oriented micro/nano channels. These channels play a critical role in ensuring both mechanical and biological properties, making bioceramics suitable for various bone defects, particularly those bearing loads. Bioceramics feature uniformly distributed nanogrooves along the microchannels. The compressive strength or fracture toughness of the Mg-HA bioceramics with micro/nano channels formed by single carbon nanotube/carbon fiber (CNT/CF) (Mg-HA(05-CNT/CF)) are comparable to those of cortical bone, attributed to a combination of strengthened compact walls and microchannels, along with a toughening mechanism involving crack pinning and deflection at nanogroove intersections. The introduction of uniform nanogrooves also enhanced the porosity by 35.4 %, while maintaining high permeability owing to the capillary action in the oriented channels. This leads to superior degradation properties, protein adsorption, and in vivo osteogenesis compared with bioceramics with only microchannels. Mg-HA(05-CNT/CF) exhibited not only high strength and toughness comparable to cortical bone, but also permeability similar to cancellous bone, enhanced cell activity, and excellent osteogenic properties. This study presents a novel approach to address the global challenge of applying HA-based bioceramics to load-bearing bone defects, potentially revolutionizing their application in tissue engineering.

Fabrication of a cell culture scaffold that mimics the composition and structure of bone marrow extracellular matrix

Cell culture models that mimic tissue environments are useful for cell and extracellular matrix (ECM) function analysis. Decellularized tissues with tissue-specific ECM are expected to be applied as cell culture scaffolds, however, it is often difficult for seeded cells to permeate their structures. In this study, we evaluated the adhesion and proliferation of mouse fibroblasts seeded onto decellularized bone marrow scaffolds that we fabricated from adult and fetal porcine. Decellularized fetal bone marrow displays more cell attachment and faster cell proliferation than decellularized adult bone marrow. Our findings suggest that decellularized fetal bone marrow is useful as a cell culture scaffold with bone marrow ECM and structure.

Leveraging the Recent Advancements in GelMA Scaffolds for Bone Tissue Engineering: An Assessment of Challenges and Opportunities

The field of bone tissue engineering has seen significant advancements in recent years. Each year, over two million bone transplants are performed globally, and conventional treatments, such as bone grafts and metallic implants, have their limitations. Tissue engineering offers a new level of treatment, allowing for the creation of living tissue within a biomaterial framework. Recent advances in biomaterials have provided innovative approaches to rebuilding bone tissue function after damage. Among them, gelatin methacryloyl (GelMA) hydrogel is emerging as a promising biomaterial for supporting cell proliferation and tissue regeneration, and GelMA has exhibited exceptional physicochemical and biological properties, making it a viable option for clinical translation. Various methods and classes of additives have been used in the application of GelMA for bone regeneration, with the incorporation of nanofillers or other polymers enhancing its resilience and functional performance. Despite promising results, the fabrication of complex structures that mimic the bone architecture and the provision of balanced physical properties for both cell and vasculature growth and proper stiffness for load bearing remain as challenges. In terms of utilizing osteogenic additives, the priority should be on versatile components that promote angiogenesis and osteogenesis while reinforcing the structure for bone tissue engineering applications. This review focuses on recent efforts and advantages of GelMA-based composite biomaterials for bone tissue engineering, covering the literature from the last five years.

The Dual Angiogenesis Effects via Nrf2/HO-1 Signaling Pathway of Melatonin Nanocomposite Scaffold on Promoting Diabetic Bone Defect Repair

Purpose

Given the escalating prevalence of diabetes, the demand for specific bone graft materials is increasing, owing to the greater tendency towards bone defects and more difficult defect repair resulting from diabetic bone disease (DBD). Melatonin (MT), which is known for its potent antioxidant properties, has been shown to stimulate both osteogenesis and angiogenesis.

Methods

MT was formulated into MT@PLGA nanoparticles (NPs), mixed with sodium alginate (SA) hydrogel, and contained within a 3D printing polycaprolactone/β-Tricalcium phosphate (PCL/β-TCP) scaffold. The osteogenic capacity of the MT nanocomposite scaffold under diabetic conditions was demonstrated via in vitro and in vivo studies and the underlying mechanisms were investigated.

Results

Physicochemical characterization experiments confirmed the successful fabrication of the MT nanocomposite scaffold, which can achieve long-lasting sustained release of MT. The in vitro and in vivo studies demonstrated that the MT nanocomposite scaffold exhibited enhanced osteogenic capacity, which was elucidated by the dual angiogenesis effects activated through the NF-E2-related factor 2/Heme oxygenase 1 (Nrf2/HO-1) signaling pathway, including the enhancement of antioxidant enzyme activity to reduce the oxidative stress damage of vascular endothelial cells (VECs) and directly stimulating vascular endothelial growth factor (VEGF) production, which reversed the angiogenesis-osteogenesis uncoupling and promoted osteogenesis under diabetic conditions.

Conclusion

This study demonstrated the research prospective and clinical implications of the MT nanocomposite scaffold as a novel bone graft for treating bone defect and enhancing bone fusion in diabetic individuals.

DLP Fabrication of Multiple Hierarchical Biomimetic GelMA/SilMA/HAp Scaffolds for Enhancing Bone Regeneration

Severe bone defects resulting from trauma and diseases remain a persistent clinical challenge. In this study, a hierarchical biomimetic microporous hydrogel composite scaffold was constructed by mimicking the hierarchical structure of bone. Initially, gelatin methacrylamide (GelMA) and methacrylic anhydride silk fibroin (SilMA) were synthesized, and GelMA/SilMA inks with suitable rheological and mechanical properties were prepared. Biomimetic micropores were then generated by using an aqueous two-phase emulsification method. Subsequently, biomimetic microporous GelMA/SilMA was mixed with hydroxyapatite (HAp) to prepare biomimetic microporous GelMA/SilMA/HAp ink. Hierarchical biomimetic microporous GelMA/SilMA/HAp (M-GSH) scaffolds were then fabricated through digital light processing (DLP) 3D printing. Finally, in vitro experiments were conducted to investigate cell adhesion, proliferation, and inward migration as well as osteogenic differentiation and vascular regeneration effects. In vivo experiments indicated that the biomimetic microporous scaffold significantly promoted tissue integration and bone regeneration after 12 weeks of implantation, achieving 42.39% bone volume fraction regeneration. In summary, this hierarchical biomimetic microporous scaffold provides a promising strategy for the repair and treatment of bone defects.

Method of computational design for additive manufacturing of hip endoprosthesis based on basic-cell concept

Endoprosthetic hip replacement is the conventional way to treat osteoarthritis or a fracture of a dysfunctional joint. Different manufacturing methods are employed to create reliable patient-specific devices with long-term performance and biocompatibility. Recently, additive manufacturing has become a promising technique for the fabrication of medical devices, because it allows to produce complex samples with various structures of pores. Moreover, the limitations of traditional fabrication methods can be avoided. It is known that a well-designed porous structure provides a better proliferation of cells, leading to improved bone remodeling. Additionally, porosity can be used to adjust the mechanical properties of designed structures. This makes the design and choice of the structure's basic cell a crucial task. This study focuses on a novel computational method, based on the basic-cell concept to design a hip endoprosthesis with an unregularly complex structure. A cube with spheroid pores was utilized as a basic cell, with each cell having its own porosity and mechanical properties. A novelty of the suggested method is in its combination of the topology optimization method and the structural design algorithm. Bending and compression cases were analyzed for a cylinder structure and two hip implants. The ability of basic-cell geometry to influence the structure's stress-strain state was shown. The relative change in the volume of the original structure and the designed cylinder structure was 6.8%. Computational assessments of a stress-strain state using the proposed method and direct modeling were carried out. The volumes of the two types of implants decreased by 9% and 11%, respectively. The maximum von Mises stress was 600 MPa in the initial design. After the algorithm application, it increased to 630 MPa for the first type of implant, while it is not changing in the second type of implant. At the same time, the load-bearing capacity of the hip endoprostheses was retained. The internal structure of the optimized implants was significantly different from the traditional designs, but better structural integrity is likely to be achieved with less material. Additionally, this method leads to time reduction both for the initial design and its variations. Moreover, it enables to produce medical implants with specific functional structures with an additive manufacturing method avoiding the constraints of traditional technologies.

Build parameter influence on strut thickness and mechanical performance in additively manufactured titanium lattice structures

Additively manufactured lattices have been adopted in applications ranging from medical implants to aerospace components. For solid AM components, the effect of build parameters has been well studied but comparably little attention has been paid to the influence of build parameters on lattice performance. For this project, the main aim was to evaluate static compressive mechanical performance of regular and stochastic lattices as a function of build parameters. The second aim was to compare strut dimensions of the metal lattice structures as build parameters were changed. Both regular and stochastic lattices were fabricated with a designed strut diameter of either 200 μm or 300 μm on a laser powder bed fusion machine. A range of laser power (140-180 W), scan speed (1700-2100 mm/s), and laser offset (0-45 μm) were used in fabricating each lattice. Compression tests were performed following the ISO 13314 (2011) standard to measure modulus, yield strength, and ultimate compressive strength values. Laser power adjustments produced the most significant effect on lattice performance. A change of 50 W resulted in roughly a 2X increase in maximum load and modulus for both regular and stochastic lattice structures. Regular lattice structures had a higher mechanical response during the mechanical evaluation. Internal strut diameters varied between build parameters as well, with laser offset adjustments producing the most noticeable change in strut geometry between lattice samples. These findings suggest that build parameter optimization, in lieu of using OEM parameters developed for solid structures, is necessary to ensure the optimum mechanical performance of AM lattice structures.

Single-Atom Cu Nanozyme-Loaded Bone Scaffolds for Ferroptosis-Synergized Mild Photothermal Therapy in Osteosarcoma Treatment

The rapid multiplication of residual tumor cells and poor reconstruction quality of new bone are considered the major challenges in the postoperative treatment of osteosarcoma. It is a promising candidate for composite bone scaffold which combines photothermal therapy (PTT) and bone regeneration induction for the local treatment of osteosarcoma. However, it is inevitable to damage the normal tissues around the tumor due to the hyperthermia of PTT, while mild heat therapy shows a limited effect on antitumor treatment as the damage can be easily repaired by stress-induced heat shock proteins (HSP). This study reports a new type of single-atom Cu nanozyme-loaded bone scaffolds, which exhibit exceptional photothermal conversion properties as well as peroxidase and glutathione oxidase mimicking activities in vitro experiments. This leads to lipid peroxidation (LPO) and reactive oxygen species (ROS) upregulation, ultimately causing ferroptosis. The accumulation of LPO and ROS also contributes to HSP70 inactivation, maximizing PTT efficiency against tumors at an appropriate therapeutic temperature and minimizing the damage to surrounding normal tissues. Further, the bone scaffold promotes bone regeneration via a continuous release of bioactive ions (Ca2+ , P5+ , Si4+ , and Cu2+ ). The results of in vivo experiments reveal that scaffolds inhibit tumor growth and promote bone repair.

Silk-Fabric Reinforced Silk for Artificial Bones

Bone implants for different body parts require varying mechanical properties, dimensions, and biodegradability rates. Currently, it is still challenging to produce artificial bones with perfect compatibility with human bones. In this study, a silk-fabric reinforced silk material (SFS) composed of pure silk with exceptional biocompatibility, osteogenesis, and biodegradability is reported, and demonstrates its outstanding performance as a bone implant material. The SFS is fabricated using a simple hot-pressing technique, with degummed silk fabric as the reinforcement and silk fibroin as the matrix. The SFS as a self-reinforced composite, has exceptional mechanical properties due to the almost perfect interface between the matrix and reinforcement. More importantly, its mechanical properties, biodegradability rates, and density can be tailored by adjusting the reinforcement structure and the ratio of the reinforcement to the matrix to align with the requirements for bone implantation in different parts of the human body. Besides, the SFS can improve osteoblastic proliferation and increase osteogenic activity, which is not the case with clinically used titanium alloy artificial bone. Therefore, the SFS holds significant potential to replace conventional metal or ceramic implants in the field of medical fracture repair.

Multifunctional coatings of nickel-titanium implant toward promote osseointegration after operation of bone tumor and clinical application: a review

Metal implants, especially Ni-Ti shape memory alloy (Ni-Ti SMA) implants, have increasingly become the first choice for fracture and massive bone defects after orthopedic bone tumor surgery. In this paper, the internal composition and shape memory properties of Ni-Ti shape memory alloy were studied. In addition, the effects of porous Ni-Ti SMA on osseointegration, and the effects of surface hydrophobicity and hydrophilicity on the osseointegration of Ni-Ti implants were also investigated. In addition, the effect of surface coating modification technology of Ni-Ti shape memory alloy on bone bonding was also studied. Several kinds of Ni-Ti alloy implants commonly used in orthopedic clinic and their advantages and disadvantages were introduced. The surface changes of Ni-Ti alloy implants promote bone fusion, enhance the adhesion of red blood cells and platelets, promote local tissue regeneration and fracture healing. In the field of orthopaedics, the use of Ni-Ti shape memory alloy implants significantly promoted clinical development. Due to the introduction of the coating, the osseointegration and biocompatibility of the implant surface have been enhanced, and the success rate of the implant has been greatly improved.

Influence of Process Energy on the Formation of Imperfections in Body-Centered Cubic Cells with Struts in the Vertical Orientation Produced by Laser Powder Bed Fusion from the Magnesium Alloy WE43

The low specific density and good strength-to-weight ratio make magnesium alloys a promising material for lightweight applications. The combination of the properties of magnesium alloys and Additive Manufacturing by the Laser Powder Bed Fusion (LPBF) process enables the production of complex geometries such as lattice or bionic structures. Magnesium structures are intended to drastically reduce the weight of components and enable a reduction in fuel consumption, particularly in the aerospace and automotive industries. However, the LPBF processing of magnesium structures is a challenge. In order to produce high-quality structures, the process parameters must be developed in such a way that imperfections such as porosity, high surface roughness and dimensional inaccuracy are suppressed. In this study, the contour scanning strategy is used to produce vertical and inclined struts with diameters ranging from 0.5 to 3 mm. The combination of process parameters such as laser power, laser speed and overlap depend on the inclination and diameter of the strut. The process parameters with an area energy of 1.15-1.46 J/mm2 for struts with a diameter of 0.5 mm and an area energy of 1.62-3.69 J/mm2 for diameters of 1, 2 and 3 mm achieve a relative material density of 99.2 to 99.6%, measured on the metallographic sections. The results are verified by CT analyses of BCCZ cells, which achieve a relative material density of over 99.3%. The influence of the process parameters on the quality of struts is described and discussed.

3D printed osteochondral scaffolds: design strategies, present applications and future perspectives

Articular osteochondral (OC) defects are a global clinical problem characterized by loss of full-thickness articular cartilage with underlying calcified cartilage through to the subchondral bone. While current surgical treatments can relieve pain, none of them can completely repair all components of the OC unit and restore its original function. With the rapid development of three-dimensional (3D) printing technology, admirable progress has been made in bone and cartilage reconstruction, providing new strategies for restoring joint function. 3D printing has the advantages of fast speed, high precision, and personalized customization to meet the requirements of irregular geometry, differentiated composition, and multi-layered boundary layer structures of joint OC scaffolds. This review captures the original published researches on the application of 3D printing technology to the repair of entire OC units and provides a comprehensive summary of the recent advances in 3D printed OC scaffolds. We first introduce the gradient structure and biological properties of articular OC tissue. The considerations for the development of 3D printed OC scaffolds are emphatically summarized, including material types, fabrication techniques, structural design and seed cells. Especially from the perspective of material composition and structural design, the classification, characteristics and latest research progress of discrete gradient scaffolds (biphasic, triphasic and multiphasic scaffolds) and continuous gradient scaffolds (gradient material and/or structure, and gradient interface) are summarized. Finally, we also describe the important progress and application prospect of 3D printing technology in OC interface regeneration. 3D printing technology for OC reconstruction should simulate the gradient structure of subchondral bone and cartilage. Therefore, we must not only strengthen the basic research on OC structure, but also continue to explore the role of 3D printing technology in OC tissue engineering. This will enable better structural and functional bionics of OC scaffolds, ultimately improving the repair of OC defects.

High temperature oxidation treated 3D printed anatomical WE43 alloy scaffolds for repairing periarticular bone defects: In vitro and in vivo studies

Reconstruction of subarticular bone defects is an intractable challenge in orthopedics. The simultaneous repair of cancellous defects, fractures, and cartilage damage is an ideal surgical outcome. 3D printed porous anatomical WE43 (magnesium with 4 wt% yttrium and 3 wt% rare earths) scaffolds have many advantages for repairing such bone defects, including good biocompatibility, appropriate mechanical strength, customizable shape and structure, and biodegradability. In a previous investigation, we successfully enhanced the corrosion resistance of WE43 samples via high temperature oxidation (HTO). In the present study, we explored the feasibility and effectiveness of HTO-treated 3D printed porous anatomical WE43 scaffolds for repairing the cancellous bone defects accompanied by split fractures via in vitro and in vivo experiments. After HTO treatment, a dense oxidation layer mainly composed of Y2O3 and Nd2O3 formed on the surface of scaffolds. In addition, the majority of the grains were equiaxed, with an average grain size of 7.4 μm. Cell and rabbit experiments confirmed the non-cytotoxicity and biocompatibility of the HTO-treated WE43 scaffolds. After the implantation of scaffolds inside bone defects, their porous structures could be maintained for more than 12 weeks without penetration and for more than 6 weeks with penetration. During the postoperative follow-up period for up to 48 weeks, radiographic examinations and histological analysis revealed that abundant bone gradually regenerated along with scaffold degradation, and stable osseointegration formed between new bone and scaffold residues. MRI images further demonstrated no evidence of any obvious damage to the cartilage, ligaments, or menisci, confirming the absence of traumatic osteoarthritis. Moreover, finite element analysis and biomechanical tests further verified that the scaffolds was conducive to a uniform mechanical distribution. In conclusion, applying the HTO-treated 3D printed porous anatomical WE43 scaffolds exhibited favorable repairing effects for subarticular cancellous bone defects, possessing great potential for clinical application.

The effect of porous compliance bushings in a dental implant on the distribution of occlusal loads

Porous dental implants are clinically used, but the mechanism of load distribution for stepped implant shaft surrounded by compliance bushings is still not known, especially for different bone conditions. The aim of the study was to assess the impact of the design of a dental implant with compliance bushings (CBs) on the occlusal load distribution during primary and secondary stability using finite element simulation (FEA), with a distinction between low and high quality cervical support under primary stability. The FEA of the oblique occlusal load transfer (250 N; 45°) was carried out for implants under variable bone conditions. The stepped shaft in the intermediate part of the dental implant was surrounded by CBs with an increasing modulus of elasticity of 2, 10 and 50 GPa. With a smaller Young's modulus of the bushings the increase of stress in the trabecular bone indicated that more bone tissue can be protected against disuse. The beneficial effect for the trabecular bone derived from the reduction of the stiffness of the bushings in relation to the loss of the implant's load bearing ability can be assessed using the FEM method.

Achieving the ideal balance between biological and mechanical requirements in composite bone scaffolds through a voxel-based approach

Achieving successful bone regeneration necessitates the design of scaffolds that meet diverse biological and mechanical requirements, often leading to conflicts in the design parameters. A key conflict arises between scaffold porosity and stiffness. Increasing porosity facilitates cell infiltration and nutrient exchange, promoting bone regeneration. However, higher porosity compromises scaffold stiffness, which is crucial for providing structural support in the defective region. Furthermore, appropriate scaffold stiffness is crucial for preventing stress shielding. Conventional geometry-based design methods utilizing single-phase materials have limited flexibility in resolving such conflicts. To address this challenge, we propose a voxel-based method for designing composite scaffolds composed of hydroxyapatite (HA) and polylactic acid (PLA). Our strategy involves first satisfying primary biological requirements by selecting appropriate porosity, pore shape, and size. Subsequently, scaffold stiffness requirements are met by selecting suitable phase materials and tuning their contents. The study demonstrates that the voxel-based approach effectively balances both biological and mechanical requirements in scaffold design. This method addresses the limitations of traditional designs by achieving an optimal balance between porosity and stiffness, which is crucial for scaffold performance in biomedical applications. Moreover, the scaffolds designed using this method can be manufactured using voxel-based 3D printing technology, which is emerging in the field. Future advancements in voxel-based 3D printing technology will further enhance the feasibility and practicality of this approach for bone tissue engineering applications.

Customized design and biomechanical property analysis of 3D-printed tantalum intervertebral cages

BACKGROUND

Intervertebral cages used in clinical applications were often general products with standard specifications, which were challenging to match with the cervical vertebra and prone to cause stress shielding and subsidence.

OBJECTIVE

To design and fabricate customized tantalum (Ta) intervertebral fusion cages that meets the biomechanical requirements of the cervical segment.

METHODS

The lattice intervertebral cages were customized designed and fabricated by the selective laser melting. The joint and muscle forces of the cervical segment under different movements were analyzed using reverse dynamics method. The stress characteristics of cage, plate, screws and vertebral endplate were analyzed by finite element analysis. The fluid flow behaviors and permeability of three lattice structures were simulated by computational fluid dynamics. Compression tests were executed to investigate the biomechanical properties of the cages.

RESULTS

Compared with the solid cages, the lattice-filled structures significantly reduced the stress of cages and anterior fixation system. In comparison to the octahedroid and quaddiametral lattice-filled cages, the bitriangle lattice-filled cage had a lower stress shielding rate, higher permeability, and superior subsidence resistance ability.

CONCLUSION

The inverse dynamics simulation combined with finite element analysis is an effective method to investigate the biomechanical properties of the cervical vertebra during movements.

Metallic Materials for Bone Repair

Repair of large bone defects caused by trauma or disease poses significant clinical challenges. Extensive research has focused on metallic materials for bone repair because of their favorable mechanical properties, biocompatibility, and manufacturing processes. Traditional metallic materials, such as stainless steel and titanium alloys, are widely used in clinics. Biodegradable metallic materials, such as iron, magnesium, and zinc alloys, are promising candidates for bone repair because of their ability to degrade over time. Emerging metallic materials, such as porous tantalum and bismuth alloys, have gained attention as bone implants owing to their bone affinity and multifunctionality. However, these metallic materials encounter many practical difficulties that require urgent improvement. This article systematically reviews and analyzes the metallic materials used for bone repair, providing a comprehensive overview of their morphology, mechanical properties, biocompatibility, and in vivo implantation. Furthermore, the strategies and efforts made to address the short-comings of metallic materials are summarized. Finally, the perspectives for the development of metallic materials to guide future research and advancements in clinical practice are identified.

Influence of structural parameters of 3D-printed triply periodic minimal surface gyroid porous scaffolds on compression performance, cell response, and bone regeneration

In this study, multi-scale triply periodic minimal surface (TPMS) porous scaffolds with uniform and radial gradient distribution on pore size were printed based on the selective laser melting technology, and the influences of porosity, pore size and radial pore size distribution on compression mechanical properties, cell behavior, and bone regeneration behavior were analyzed. The results showed that the compression performance of the uniform porous scaffolds with high porosity was similar to that of cancellous bone of pig tibia, and the gradient porous scaffolds have higher elastic modulus and compressive toughness. After 4 days of cell culture, cells were distributed on the surface of scaffolds mostly, and the number of adherent cells was higher on the small pore size porous scaffolds; After 7 days, the area and density of cell proliferation on the scaffolds were improved; After 14 days, the cells on the small pore size scaffolds tended to migrate to adjacent pores. Animal implantation experiments showed that collagen fiber osteoid was intermittent on scaffolds with high porosity and large pore size, which was not conducive to bone formation. The appropriate pore size and porosity of bone regeneration were 792 um and 83%, respectively, and the regenerative ability of gradient pore size was better than that of uniform pore size. Our study explains the rules of TPMS gyroid structure parameters on compression performance, cell response and bone regeneration, and provides a reference value for the design of bone repair scaffolds for clinical orthopedics.

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

It is well documented that overly stiff skeletal replacement and fixation devices may fail and require revision surgery. Recent attempts to better support healing and sustain healed bone have looked at stiffness-matching of these devices to the desired role of limiting the stress on fractured or engrafted bone to compressive loads and, after the reconstructed bone has healed, to ensure that reconstructive medical devices (implants) interrupt the normal loading pattern as little as possible. The mechanical performance of these devices can be optimized by adjusting their location, integration/fastening, material(s), geometry (external and internal), and surface properties. This review highlights recent research that focuses on the optimal design of skeletal reconstruction devices to perform during and after healing as the mechanical regime changes. Previous studies have considered auxetic materials, homogeneous or gradient (i.e., adaptive) porosity, surface modification to enhance device/bone integration, and choosing the device's attachment location to ensure good osseointegration and resilient load transduction. By combining some or all of these factors, device designers work hard to avoid problems brought about by unsustainable stress shielding or stress concentrations as a means of creating sustainable stress-strain relationships that best repair and sustain a surgically reconstructed skeletal site. STATEMENT OF SIGNIFICANCE: Although standard-of-care skeletal reconstruction devices will usually allow normal healing and improved comfort for the patient during normal activities, there may be significant disadvantages during long-term use. Stress shielding and stress concentration are amongst the most common causes of failure of a metallic device. This review highlights recent developments in devices for skeletal reconstruction that match the stiffness, while not interrupting the normal loading pattern of a healthy bone, and help to combat stress shielding and stress concentration. This review summarises various approaches to achieve stiffness-matching: application of materials with modulus close to that of the bone; adaptation of geometry with pre-defined mechanical properties; and/or surface modification that ensures good integration and proper load transfer to the bone.

Clinical, Radiographic, and Patient-Reported Outcomes of First Metatarsophalangeal Interposition Arthrodesis Using Porous Titanium Wedges

BACKGROUND

First metatarsophalangeal (MTP) arthrodesis is a common surgical procedure for addressing hallux MTP pathology. In the setting of revision procedures with significant bone loss, porous titanium wedges may provide an alternative to structural bone autograft or allograft.

OBJECTIVE

The purpose of this study is to report the clinical and radiographic outcomes achieved in first MTP interposition arthrodesis using porous titanium wedges.

METHODS

A retrospective analysis of 9 patients with a mean age 65.4 years (45-82 years) who underwent first MTP interposition arthrodesis with the use of porous titanium wedges from February 2014 to September 2017 was performed. Outcomes were assessed using both plain-film radiographs and computed tomography (CT) scans, as well as patient-reported outcome measures, including Foot and Ankle Ability Measure (FAAM) (Sports and Activities of Daily Living), pain Visual Analogue Scale (VAS), and 36-Item Short Form Survey (SF-36). Average follow-up time was 34.2 months (14-72 months).

RESULTS

At final follow-up, the average FAAM score was 91.1 ± 14.7 (75.1 ± 5.3 FAAM Activities of Daily Living; 17.9 ± 9.9 FAAM Sports). Average pain VAS score was 1.9 ± 1.7. Postoperative computed tomography (CT) imaging was obtained for 5 patients, all of which demonstrated good bony apposition or osseous integration of the wedge. Four patients underwent subsequent surgical procedures, including 3 isolated dorsal fixation revisions, and 1 complete MTP arthrodesis revision.

CONCLUSION

To our knowledge, this study represents the first reported clinical and radiographic outcomes in patients undergoing first MTP interposition arthrodesis with use of porous titanium wedges. While we found this technique to be a viable alternative to bone grafting for this difficult problem, further research should focus on comparative data with other commonly performed operative techniques.

LEVEL OF EVIDENCE

Level IV: Case series.

Bone Regeneration Induced by Patient-Adapted Mg Alloy-Based Scaffolds for Bone Defects: Present and Future Perspectives

Treatment of bone defects resulting after tumor surgeries, accidents, or non-unions is an actual problem linked to morbidity and the necessity of a second surgery and often requires a critical healthcare cost. Although the surgical technique has changed in a modern way, the treatment outcome is still influenced by patient age, localization of the bone defect, associated comorbidities, the surgeon approach, and systemic disorders. Three-dimensional magnesium-based scaffolds are considered an important step because they can have precise bone defect geometry, high porosity grade, anatomical pore shape, and mechanical properties close to the human bone. In addition, magnesium has been proven in in vitro and in vivo studies to influence bone regeneration and new blood vessel formation positively. In this review paper, we describe the magnesium alloy's effect on bone regenerative processes, starting with a short description of magnesium's role in the bone healing process, host immune response modulation, and finishing with the primary biological mechanism of magnesium ions in angiogenesis and osteogenesis by presenting a detailed analysis based on a literature review. A strategy that must be followed when a patient-adapted scaffold dedicated to bone tissue engineering is proposed and the main fabrication technologies are combined, in some cases with artificial intelligence for Mg alloy scaffolds, are presented with examples. We emphasized the microstructure, mechanical properties, corrosion behavior, and biocompatibility of each study and made a basis for the researchers who want to start to apply the regenerative potential of magnesium-based scaffolds in clinical practice. Challenges, future directions, and special potential clinical applications such as osteosarcoma and persistent infection treatment are present at the end of our review paper.

Effects of Zr Addition on the Microstructural Evolution, Mechanical Properties, and Corrosion Behavior of Novel Biomedical Ti-Zr-Mo-Mn Alloys

β-Type Ti alloys have been widely investigated as implant materials owing to their excellent mechanical properties, corrosion resistance, and biocompatibility. In the present work, the effects of Zr on the microstructure, mechanical properties, and corrosion behaviors of Ti-Zr-Mo-Mn alloys were systematically studied. With the increase of Zr content, the phase composition gradually changed from intragranular-α + β of (TZ)5:1MM alloy to grain-boundary-α + β of (TZ)2:1MM alloy and finally transferred to a single β phase structure of (TZ)1:1MM alloy. The (TZ)1:1MM alloy exhibited a good mechanical combination with a yield strength of 750.8 MPa, an elastic modulus of 61.3 GPa, and a tensile ductility of 14.6%. Moreover, the addition of Zr can effectively stabilize the passivation film and reduce the sensitivity of microgalvanic corrosion in simulated body fluid, leading to enhanced corrosion resistance in the TZMM alloys. X-ray photoelectron spectroscopy analysis together with the ion-sputtering technique revealed that the passivation films formed on TZMM alloys possessed a bilayered structure (outer Ti+Zr mixed-oxide layer and inner Zr-oxide-rich layer), in which the inner Zr oxide layer plays an important role in the corrosion resistance of the TZMM alloys. In vitro biocompatibility evaluations demonstrated that the TZMM alloys can support cell adhesion and proliferation with high biocompatibility comparable to that of CP-Ti, while in vivo biocompatibility evaluations validated the bone osteointegration ability of TZMM alloys after long-term implantation. The above results indicate that novel TZMM alloys are promising candidates for implant material.

Design of 3D-printed prostheses for reconstruction of periacetabular bone tumors using topology optimization

Background: Prostheses for the reconstruction of periacetabular bone tumors are prone to instigate stress shielding. The purpose of this study is to design 3D-printed prostheses with topology optimization (TO) for the reconstruction of periacetabular bone tumors and to add porous structures to reduce stress shielding and facilitate integration between prostheses and host bone. Methods: Utilizing patient CT data, we constructed a finite element analysis (FEA) model. Subsequent phases encompassed carrying out TO on the designated area, utilizing the solid isotropic material penalization model (SIMP), and this optimized removal area was replaced with a porous structure. Further analyses included preoperative FEA simulations to comparatively evaluate parameters, including maximum stress, stress distribution, strain energy density (SED), and the relative micromotion of prostheses before and after TO. Furthermore, FEA based on patients' postoperative CT data was conducted again to assess the potential risk of stress shielding subsequent to implantation. Ultimately, preliminary follow-up findings from two patients were documented. Results: In both prostheses, the SED before and after TO increased by 143.61% (from 0.10322 to 0.25145 mJ/mm3) and 35.050% (from 0.30964 to 0.41817 mJ/mm3) respectively, showing significant differences (p < 0.001). The peak stress in the Type II prosthesis decreased by 10.494% (from 77.227 to 69.123 MPa), while there was no significant change in peak stress for the Type I prosthesis. There were no significant changes in stress distribution or the proportion of regions with micromotion less than 28 μm before and after TO for either prosthesis. Postoperative FEA verified results showed that the stress in the pelvis and prostheses remained at relatively low levels. The results of follow-up showed that the patients had successful osseointegration and their MSTS scores at the 12th month after surgery were both 100%. Conclusion: These two types of 3D-printed porous prostheses using TO for periacetabular bone tumor reconstruction offer advantages over traditional prostheses by reducing stress shielding and promoting osseointegration, while maintaining the original stiffness of the prosthesis. Furthermore, in vivo experiments show that these prostheses meet the requirements for daily activities of patients. This study provides a valuable reference for the design of future periacetabular bone tumor reconstruction prostheses.

Fused Filament Fabrication for Metallic Materials: A Brief Review

Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) technology mostly used to produce thermoplastic parts. However, producing metallic or ceramic parts by FFF is also a sintered-based AM process. FFF for metallic parts can be divided into five steps: (1) raw material selection and feedstock mixture (including palletization), (2) filament production (extrusion), (3) production of AM components using the filament extrusion process, (4) debinding, and (5) sintering. These steps are interrelated, where the parameters interact with the others and have a key role in the integrity and quality of the final metallic parts. FFF can produce high-accuracy and complex metallic parts, potentially revolutionizing the manufacturing industry and taking AM components to a new level. In the FFF technology for metallic materials, material compatibility, production quality, and cost-effectiveness are the challenges to overcome to make it more competitive compared to other AM technologies, like the laser processes. This review provides a comprehensive overview of the recent developments in FFF for metallic materials, including the metals and binders used, the challenges faced, potential applications, and the impact of FFF on the manufacturing (prototyping and end parts), design freedom, customization, sustainability, supply chain, among others.

Fatigue behaviour of load-bearing polymeric bone scaffolds: A review

Bone scaffolds play a crucial role in bone tissue engineering by providing mechanical support for the growth of new tissue while enduring static and fatigue loads. Although polymers possess favourable characteristics such as adjustable degradation rate, tissue-compatible stiffness, ease of fabrication, and low toxicity, their relatively low mechanical strength has limited their use in load-bearing applications. While numerous studies have focused on assessing the static strength of polymeric scaffolds, little research has been conducted on their fatigue properties. The current review presents a comprehensive study on the fatigue behaviour of polymeric bone scaffolds. The fatigue failure in polymeric scaffolds is discussed and the impact of material properties, topological features, loading conditions, and environmental factors are also examined. The present review also provides insight into the fatigue damage evolution within polymeric scaffolds, drawing comparisons to the behaviour observed in natural bone. Additionally, the effect of polymer microstructure, incorporating reinforcing materials, the introduction of topological features, and hydrodynamic/corrosive impact of body fluids in the fatigue life of scaffolds are discussed. Understanding these parameters is crucial for enhancing the fatigue resistance of polymeric scaffolds and holds promise for expanding their application in clinical settings as structural biomaterials. STATEMENT OF SIGNIFICANCE: Polymers have promising advantages for bone tissue engineering, including adjustable degradation rates, compatibility with native bone stiffness, ease of fabrication, and low toxicity. However, their limited mechanical strength has hindered their use in load-bearing scaffolds for clinical applications. While prior studies have addressed static behaviour of polymeric scaffolds, a comprehensive review of their fatigue performance is lacking. This review explores this gap, addressing fatigue characteristics, failure mechanisms, and the influence of parameters like material properties, topological features, loading conditions, and environmental factors. It also examines microstructure, reinforcement materials, pore architectures, body fluids, and tissue ingrowth effects on fatigue behaviour. A significant emphasis is placed on understanding fatigue damage progression in polymeric scaffolds, comparing it to natural bone behaviour.

Osseointegration of functionally graded Ti6Al4V porous implants: Histology of the pore network

The additive manufacturing of titanium into porous geometries offers a means to generate low-stiffness endosseous implants with a greater surface area available for osseointegration. In this work, selective laser melting was used to produce gyroid-based scaffolds with a uniform pore size of 300 μm or functionally graded pore size from 600 μm to 300 μm. Initial in vitro assessment with Saos-2 cells showed favourable cell proliferation at pore sizes of 300 and 600 μm. Following implantation into rabbit tibiae, early histological observations at four weeks indicated some residual inflammation alongside neovessel infiltration into the scaffold interior and some early apposition of mineralized bone tissue. At twelve weeks, both scaffolds were filled with a mixture of adipocyte-rich marrow, micro-capillaries, and mineralized bone tissue. X-ray microcomputed tomography showed a higher bone volume fraction (BV/TV) and percentage of bone-implant contact (BIC) in the implants with 300 μm pores than in the functionally graded specimens. In functionally graded specimens, localized BV/TV measurement was observed to be higher in the innermost region containing smaller pores (estimated at 300-400 μm) than in larger pores at the implant exterior. The unit cell topology of the porous implant was also observed to guide the direction of bone ingrowth by conducting along the implant struts. These results suggest that in vivo experimentation is necessary alongside parametric optimization of functionally graded porous implants to predict short-term and long-term bone apposition.

Highly anisotropic and elastic cellulosic scaffold guiding cell orientation and osteogenic differentiation via topological and mechanical cues

Inspired by the similarity of anisotropic channels in wood to the canals of bone, the elastic wood-derived (EW) scaffolds with anisotropic channels were prepared via simple delignification treatment of natural wood (NW). We hypothesize that the degree of delignification will lead to differences in mechanical properties of scaffolds, which in turn directly affect the behaviors and fate of stem cells. The delignification process did not destroy the anisotropic channel structure of the scaffolds, but endowed the scaffolds with good elasticity and rapid stress relaxation. Interestingly, the micron-scale anisotropic channels of the scaffolds can highly promote the polarization of cells along the direction of channels. We also found that the alkaline phosphatase of EW scaffold can reach to about 13.1 U/gprot, which was about double that of NW scaffold. Moreover, the longer the delignification time, the better the osteogenic activity of the EW scaffolds. We further hypothesize that the osteogenic activity of scaffolds is related to the stress relaxation properties. The immunofluorescence staining showed that when the stress relaxation time of scaffold was shortened to about 10 s, the nuclear ratio of YAP of scaffold increased to 0.22, which well supports our hypothesis.

Forged to heal: The role of metallic cellular solids in bone tissue engineering

Metallic cellular solids, made of biocompatible alloys like titanium, stainless steel, or cobalt-chromium, have gained attention for their mechanical strength, reliability, and biocompatibility. These three-dimensional structures provide support and aid tissue regeneration in orthopedic implants, cardiovascular stents, and other tissue engineering cellular solids. The design and material chemistry of metallic cellular solids play crucial roles in their performance: factors such as porosity, pore size, and surface roughness influence nutrient transport, cell attachment, and mechanical stability, while their microstructure imparts strength, durability and flexibility. Various techniques, including additive manufacturing and conventional fabrication methods, are utilized for producing metallic biomedical cellular solids, each offering distinct advantages and drawbacks that must be considered for optimal design and manufacturing. The combination of mechanical properties and biocompatibility makes metallic cellular solids superior to their ceramic and polymeric counterparts in most load bearing applications, in particular under cyclic fatigue conditions, and more in general in application that require long term reliability. Although challenges remain, such as reducing the production times and the associated costs or increasing the array of available materials, metallic cellular solids showed excellent long-term reliability, with high survival rates even in long term follow-ups.

Biomedical Applications of Electro-Initiated Polymerisation on Ti6Al4 V Titanium Alloy using Silk Fibroin Coatings for Antibiotic Delivery and Improved Cell Metabolism

Silk fibroin interactions with metallic surfaces can provide utility for medical materials and devices. Toward this goal, titanium alloy (Ti6Al4 V) was covalently grafted with polyacrylamide via electrochemically reducing 4-nitrobenzene diazonium salt in the presence of acrylamide. Analysis of the modified surfaces with FT-IR spectra, SEM and AFM were consistent with surface grafting. Functionalised titanium samples with a silk fibroin membrane, with and without impregnated therapeutics, were used to assess cytocompatibility and drug delivery. Initial cytocompatibility experiments using fibroblasts showed that the functionalised samples, both with and without silk fibroin coatings, supported significant increases between 72-136 % in cell metabolism, compared to the controls after 7 days. A 7-days release profiling showed consistent bacterial inhibition through gentamicin release with average inhibition zones of 239 mm2 . Over a 5-week period, silk fibroin coated samples, both with and without growth factors, supported better human mesenchymal stem cell metabolism with increases reaching 1031 % and 388 %, respectively, compared to samples without the silk fibroin coating with.

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.

Construction of functional surfaces for dental implants to enhance osseointegration

Dental implants have been extensively used in patients with defects or loss of dentition. However, the loss or failure of dental implants is still a critical problem in clinic. Therefore, many methods have been designed to enhance the osseointegration between the implants and native bone. Herein, the challenge and healing process of dental implant operation will be briefly introduced. Then, various surface modification methods and emerging biomaterials used to tune the properties of dental implants will be summarized comprehensively.

Development of Bioactive Scaffolds for Orthopedic Applications by Designing Additively Manufactured Titanium Porous Structures: A Critical Review

We overview recent findings achieved in the field of model-driven development of additively manufactured porous materials for the development of a new generation of bioactive implants for orthopedic applications. Porous structures produced from biocompatible titanium alloys using selective laser melting can present a promising material to design scaffolds with regulated mechanical properties and with the capacity to be loaded with pharmaceutical products. Adjusting pore geometry, one could control elastic modulus and strength/fatigue properties of the engineered structures to be compatible with bone tissues, thus preventing the stress shield effect when replacing a diseased bone fragment. Adsorption of medicals by internal spaces would make it possible to emit the antibiotic and anti-tumor agents into surrounding tissues. The developed internal porosity and surface roughness can provide the desired vascularization and osteointegration. We critically analyze the recent advances in the field featuring model design approaches, virtual testing of the designed structures, capabilities of additive printing of porous structures, biomedical issues of the engineered scaffolds, and so on. Special attention is paid to highlighting the actual problems in the field and the ways of their solutions.

Preliminary exploration of the biomechanical properties of three novel cervical porous fusion cages using a finite element study

BACKGROUND

Porous cages are considered a promising alternative to high-density cages because their interconnectivity favours bony ingrowth and appropriate stiffness tuning reduces stress shielding and the risk of cage subsidence.

METHODS

This study proposes three approaches that combine macroscopic topology optimization and micropore design to establish three new types of porous cages by integrating lattices (gyroid, Schwarz, body-centred cubic) with the optimized cage frame. Using these three porous cages along with traditional high-density cages, four ACDF surgical models were developed to compare the mechanical properties of facet articular cartilage, discs, cortical bone, and cages under specific loads.

RESULTS

The facet joints in the porous cage groups had lower contact forces than those in the high-density cage group. The intervertebral discs in all models experienced maximum stress at the C5/6 segment. The stress distribution on the cortical bone surface was more uniform in the porous cage groups, leading to increased average stress values. The gyroid, Schwarz, and BCC cage groups showed higher average stress on the C5 cortical bone. The average stress on the surface of porous cages was higher than that on the surface of high-density cages, with the greatest difference observed under the lateral bending condition. The BCC cage demonstrated favourable mechanical stability.

CONCLUSION

The new porous cervical cages satifies requirements of low rigidity and serve as a favourable biological scaffold for bone ingrowth. This study provides valuable insights for the development of next-generation orthopaedic medical devices.

A novel artificial vertebral implant with Gyroid porous structures for reducing the subsidence and mechanical failure rate after vertebral body replacement

BACKGROUND

Prosthesis subsidence and mechanical failure were considered significant threats after vertebral body replacement during the long-term follow-up. Therefore, improving and optimizing the structure of vertebral substitutes for exceptional performance has become a pivotal challenge in spinal reconstruction.

METHODS

The study aimed to develop a novel artificial vertebral implant (AVI) with triply periodic minimal surface Gyroid porous structures to enhance the safety and stability of prostheses. The biomechanical performance of AVIs under different loading conditions was analyzed using the finite element method. These implants were fabricated using selective laser melting technology and evaluated through static compression and subsidence experiments.

RESULTS

The results demonstrated that the peak stress in the Gyroid porous AVI was consistently lower than that in the traditional porous AVI under all loading conditions, with a maximum reduction of 73.4%. Additionally, it effectively reduced peak stress at the bone-implant interface of the vertebrae. Static compression experiments demonstrated that the Gyroid porous AVI was about 1.63 times to traditional porous AVI in terms of the maximum compression load, indicating that Gyroid porous AVI could meet the safety requirement. Furthermore, static subsidence experiments revealed that the subsidence tendency of Gyroid porous AVI in polyurethane foam (simulated cancellous bone) was approximately 15.7% lower than that of traditional porous AVI.

CONCLUSIONS

The Gyroid porous AVI exhibited higher compressive strength and lower subsidence tendency than the strut-based traditional porous AVI, indicating it may be a promising substitute for spinal reconstruction.

Continued Stabilization of a Cementless 3D-Printed Total Knee Arthroplasty: Five-Year Results of a Randomized Controlled Trial Using Radiostereometric Analysis

BACKGROUND

Three-dimensional (3D) printing of highly porous orthopaedic implants aims to promote better osseointegration, thus preventing aseptic loosening. However, short-term radiostereometric analysis (RSA) after total knee arthroplasty (TKA) has shown higher initial migration of cementless 3D-printed tibial components compared with their cemented counterparts. Therefore, critical evaluation of longer-term tibial component migration is needed. We investigated migration of a cementless 3D-printed and a cemented tibial component with otherwise similar TKA design during 5 years of follow-up, particularly the progression in migration beyond 2 years postoperatively.

METHODS

Seventy-two patients were randomized to a cementless 3D-printed Triathlon Tritanium (Stryker) cruciate-retaining (CR) TKA or a cemented Triathlon CR (Stryker) TKA implant. Implant migration was evaluated with RSA at baseline and postoperatively at 3 months and at 1, 2, and 5 years. The maximum total point motion (MTPM) of the tibial component was compared between the groups at 5 years, and progression in migration was assessed between 2 and 5 years. Individual implants were classified as continuously migrating if the MTPM was ≥0.1 mm/year beyond 2 years postoperatively. Clinical scores were evaluated, and a linear mixed-effects model was used to analyze repeated measurements.

RESULTS

At 5 years, the mean MTPM was 0.66 mm (95% confidence interval [CI], 0.56 to 0.78 mm) for the cementless group and 0.53 mm (95% CI, 0.43 to 0.64 mm) for the cemented group (p = 0.09). Between 2 and 5 years, there was no progression in mean MTPM for the cementless group (0.02 mm; 95% CI, -0.06 to 0.10 mm) versus 0.07 mm (95% CI, 0.00 to 0.14) for the cemented group. One implant was continuously migrating in the cementless group, and 4 were continuously migrating in the cemented group. The clinical scores were comparable between the groups across the entire time of follow-up.

CONCLUSIONS

No significant difference in mean migration was found at 5 years between the cementless and cemented TKA implants. Progression of tibial component migration was present beyond 2 years for the cemented implant, whereas the cementless implant remained stable after initial early migration.

LEVEL OF EVIDENCE

Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

Microstructural and mechanical behaviours of Y-TZP prepared via slip-casting and fused deposition modelling (FDM)

This paper reports the microstructural characteristics and mechanical properties of yttria-stabilized zirconia prepared via fused deposition modelling and slip casting. X-Ray Diffraction peaks indicated that yttria-stabilized zirconia crystallized in tetragonal structure for both slip casted(SC) and fused deposition modelled(FDM) samples. Further, scanning electron microscopy of slip casted sample showcased closely packed structure with fine grains and an average grain size of ∼65 nm whilst fused deposition modelled samples showcased non-homogeneous pores with ∼20 nm grain size. Average relative density of slip casted samples was ∼99.4 % while that of fused deposition modelled sample exhibited ∼96.2 %. The Vickers Hardness of slip casted (∼15.26 ± 0.4 GPa) was ∼10 % higher than the fused deposition modelled samples (∼13.79 ± 0.3 GPa). Likewise, indentation fracture toughness of slip casted (5.78 ± 0.5 MPa m1/2) was 14 % higher than fused deposition modelled samples which could have been due to the change in grain size as well as porosity of the ceramics. Compressive strength of the fused deposition modelled samples was 32 % less than slip casted samples (∼510 ± 10 MPa) due to its non-homogenous pores which led to weakening van der Waals force of attraction.

Optimize the pore size-pore distribution-pore geometry-porosity of 3D-printed porous tantalum to obtain optimal critical bone defect repair capability

The treatment and reconstruction of large or critical size bone defects is a challenging clinical problem. Additive manufacturing breaks the technical difficulties of preparing complex conformation and anatomically matched personalized porous tantalum implants, but the ideal pore structure for 3D-printed porous tantalum in critical bone defect repair applications remains unclear. Guiding appropriate bone tissue regeneration by regulating proper pore size-pore distribution-pore geometry-porosity is a challenge for its fabrication and application. We fabricated porous tantalum (PTa) scaffolds with six different combinations of pore structures using powder bed laser melting (L-PBF) technology. In vitro biological experiments were conducted to systematically investigate the effects of pore structure characteristics on osteoblast behaviors, showing that the bionic trabecular structure with both large and small poress facilitated cell permeation, proliferation and differentiation compared to the cubic structure with uniform pore sizes. The osteogenesis of PTa with different porosity of trabecular structures was further investigated by a rabbit condyle critical bone defect model. Synthetically, T70% up-regulated the expression of osteogenesis-related genes (ALP, COLI, OCN, RUNX-2) and showed the highest bone ingrowth area and bone contact rate in vivo after 16 weeks, with the best potential for critical bone defect repair. Our results suggested that the bionic trabecular structure with a pore size distribution of 200-1200 μm, an average pore size of 700 μm, and a porosity of 70 % is the best choice for repairing critical bone defects, which is expected to guide the clinical application of clinical 3D-printed PTa scaffolds.

Understanding of trabecular-cortical transition zone: Numerical and experimental assessment of multi-morphology scaffolds

Applications of additive manufacturing (AM) in tissue engineering develop rapidly. AM offers layer-by-layer creation of complex objects, developed to restore functionality of, or replace, damaged tissues. Porous 3D-printed functional gradient structures are of particular interest: their special architecture makes it possible to simulate the heterogeneity of the replaced tissue and, by continuously changing the mechanical properties, to avoid the concentration of stresses that can be caused by abrupt geometric changes. Such structures also allow combinations of different types of unit cells and a smooth transition between them, making design of personalised scaffolds with optimal parameters for the replacement of damaged host tissue at the interface between tissues possible. This paper presents the results of development of scaffold structures with gradients of porosity and multi-morphology using unit cells based on triply periodic minimal surfaces (TPMS). The mechanical behaviour of additively manufactured scaffold prototypes made of polylactide acid (PLA) was studied under compressive loading. Strain fields on their surface were captured using the Vic-3d Micro-DIC digital image correlation system and compared with those obtained with detailed numerical simulations, employing elastic-plastic properties of PLA, obtained in experiments. The effect of gradient parameters and unit-cell morphology on the stress distribution in scaffolds was analysed. A smooth gradient transition between cells with different morphologies was found to reduce the probability of structural failure under intense compressive loading. A good agreement between numerical results and experimental data was achieved, which justifies application of the developed approach to design of personalised bone scaffolds.

Machine learning-enabled constrained multi-objective design of architected materials

Architected materials that consist of multiple subelements arranged in particular orders can demonstrate a much broader range of properties than their constituent materials. However, the rational design of these materials generally relies on experts' prior knowledge and requires painstaking effort. Here, we present a data-efficient method for the high-dimensional multi-property optimization of 3D-printed architected materials utilizing a machine learning (ML) cycle consisting of the finite element method (FEM) and 3D neural networks. Specifically, we apply our method to orthopedic implant design. Compared to uniform designs, our experience-free method designs microscale heterogeneous architectures with a biocompatible elastic modulus and higher strength. Furthermore, inspired by the knowledge learned from the neural networks, we develop machine-human synergy, adapting the ML-designed architecture to fix a macroscale, irregularly shaped animal bone defect. Such adaptation exhibits 20% higher experimental load-bearing capacity than the uniform design. Thus, our method provides a data-efficient paradigm for the fast and intelligent design of architected materials with tailored mechanical, physical, and chemical properties.

A Hybrid Data-Driven Metaheuristic Framework to Optimize Strain of Lattice Structures Proceeded by Additive Manufacturing

This research is centered on optimizing the mechanical properties of additively manufactured (AM) lattice structures via strain optimization by controlling different design and process parameters such as stress, unit cell size, total height, width, and relative density. In this regard, numerous topologies, including sea urchin (open cell) structure, honeycomb, and Kelvin structures simple, round, and crossbar (2 × 2), were considered that were fabricated using different materials such as plastics (PLA, PA12), metal (316L stainless steel), and polymer (thiol-ene) via numerous AM technologies, including stereolithography (SLA), multijet fusion (MJF), fused deposition modeling (FDM), direct metal laser sintering (DMLS), and selective laser melting (SLM). The developed deep-learning-driven genetic metaheuristic algorithm was able to achieve a particular strain value for a considered topology of the lattice structure by controlling the considered input parameters. For instance, in order to achieve a strain value of 2.8 × 10-6 mm/mm for the sea urchin structure, the developed model suggests the optimal stress (11.9 MPa), unit cell size (11.4 mm), total height (42.5 mm), breadth (8.7 mm), width (17.29 mm), and relative density (6.67%). Similarly, these parameters were controlled to optimize the strain for other investigated lattice structures. This framework can be helpful in designing various AM lattice structures of desired mechanical qualities.

Customized Additive Manufacturing in Bone Scaffolds-The Gateway to Precise Bone Defect Treatment

In the advancing landscape of technology and novel material development, additive manufacturing (AM) is steadily making strides within the biomedical sector. Moving away from traditional, one-size-fits-all implant solutions, the advent of AM technology allows for patient-specific scaffolds that could improve integration and enhance wound healing. These scaffolds, meticulously designed with a myriad of geometries, mechanical properties, and biological responses, are made possible through the vast selection of materials and fabrication methods at our disposal. Recognizing the importance of precision in the treatment of bone defects, which display variability from macroscopic to microscopic scales in each case, a tailored treatment strategy is required. A patient-specific AM bone scaffold perfectly addresses this necessity. This review elucidates the pivotal role that customized AM bone scaffolds play in bone defect treatment, while offering comprehensive guidelines for their customization. This includes aspects such as bone defect imaging, material selection, topography design, and fabrication methodology. Additionally, we propose a cooperative model involving the patient, clinician, and engineer, thereby underscoring the interdisciplinary approach necessary for the effective design and clinical application of these customized AM bone scaffolds. This collaboration promises to usher in a new era of bioactive medical materials, responsive to individualized needs and capable of pushing boundaries in personalized medicine beyond those set by traditional medical materials.

Development of Biocompatible 3D-Printed Artificial Blood Vessels through Multidimensional Approaches

Within the human body, the intricate network of blood vessels plays a pivotal role in transporting nutrients and oxygen and maintaining homeostasis. Bioprinting is an innovative technology with the potential to revolutionize this field by constructing complex multicellular structures. This technique offers the advantage of depositing individual cells, growth factors, and biochemical signals, thereby facilitating the growth of functional blood vessels. Despite the challenges in fabricating vascularized constructs, bioprinting has emerged as an advance in organ engineering. The continuous evolution of bioprinting technology and biomaterial knowledge provides an avenue to overcome the hurdles associated with vascularized tissue fabrication. This article provides an overview of the biofabrication process used to create vascular and vascularized constructs. It delves into the various techniques used in vascular engineering, including extrusion-, droplet-, and laser-based bioprinting methods. Integrating these techniques offers the prospect of crafting artificial blood vessels with remarkable precision and functionality. Therefore, the potential impact of bioprinting in vascular engineering is significant. With technological advances, it holds promise in revolutionizing organ transplantation, tissue engineering, and regenerative medicine. By mimicking the natural complexity of blood vessels, bioprinting brings us one step closer to engineering organs with functional vasculature, ushering in a new era of medical advancement.