Complex geometry and integrated macro-porosity: Clinical applications of electron beam melting to fabricate bespoke bone-anchored implants

Sustained slow-release TGF-β3 in a three-dimensional-printed titanium microporous scaffold composite system promotes ligament-to-bone healing

The treatment of tendon/ligament-to-bone injury is a long-standing research challenge in orthopedics and bone tissue engineering. Orderly healing of the fibrocartilage layer and mineralized bone layer is crucial for treating tendon-bone interface injuries. We designed a three-dimensional printed porous titanium scaffold composite system with thermosensitive collagen hydrogel loaded with transforming growth factor β3 (TGF-β3), formulated for the sustained slow release of TGF-β3 at a constant rate. In vitro, the composite system exhibited good biocompatibility and was beneficial for the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs), which showed high growth activity. Moreover, the composite system promoted the differentiation of BMSCs via osteogenesis and chondrogenesis. In vivo, the composite system provided active substances at the injured site, promoting the repair of the fibrocartilage layer and of the mineralized bone layer at the interface between the ligament and bone. Micro-CT results demonstrated that the complex promotes the osseointegration of titanium scaffolds in bone defects. Hard tissue sections showed that the new bone, ligament, and the titanium alloy scaffold system formed a closely integrated whole; the composite system provided suitable attachment points for ligament growth. Additionally, the biomechanical strength of the tendon interface improved to some extent. Our results indicate that the composite system has potential as a bioactive implant interface for repairing ligament and bone injuries.

Bio-functional niobium-based metallic biomaterials: Exploring their physicomechanical properties, biological significance, and implant applications

The significance of biomedical applications of bio-functional niobium (Nb)-based metallic biomaterials is underscored by their potential utilization in implant application. Nb-based metallic materials present reliable physicomechanical and biological properties, thus represent materials highly suitable for implant application. This review provides an overview on the advances of pure niobium and Nb-based metallic materials as implant materials over the past 20 years, and highlights the advantages of Nb-based metallic biomaterials for implant application in terms of their physicomechanical properties, corrosion resistance in biological media, magnetic resonance imaging (MRI) compatibility, cell compatibility, blood compatibility, osteogenesis, and bioactivity. An introduction is provided for the production and processing techniques for Nb-based metallic biomaterials, including traditional melting processes like vacuum arc remelting, additive manufacturing like selective laser melting (SLM), electron beam melting (EBM), spark plasma sintering (SPS), and severe plastic deformation like equal channel angular pressing (ECAP), multi-axial forging (MAF), high pressure torsion (HPT), as well as their physicomechanical properties and implant application. Also suggested are the critical issues, challenges, and prospects in the further development of Nb-based metallic biomaterials for implant applications. STATEMENT OF SIGNIFICANCE: Nb-based biomaterials have gained significant interest for bioimplantable scaffolds because of their appropriate mechanical characteristics and biocompatibility. No prior work has been published specifically reviewing bio-functional Nb-based biomaterials for exploring their physicomechanical properties, biological significance, and implant applications. This review provides an overview on the advances of niobium and Nb-based materials as implant materials over the past 20 years, and highlights the advantages of Nb-based biomaterials for implant application. An introduction is provided for the production and processing techniques for Nb-based biomaterials, as well as their physicomechanical properties and implant application. Also suggested are the critical issues, challenges, and prospects in the further development of Nb-based biomaterials for implant applications.

A Systematic Review of the Contribution of Additive Manufacturing toward Orthopedic Applications

Human bone holds an inherent capacity for repairing itself from trauma and damage, but concerning the severity of the defect, the choice of implant placement is a must. Additive manufacturing has become an elite option due to its various specifications such as patient-specific custom development of implants and its easy fabrication rather than the conventional methods used over the years. Additive manufacturing allows customization of the pore size, porosity, various mechanical properties, and complex structure design and formulation. Selective laser melting, powder bed fusion, electron beam melting, and fused deposition modeling are the various AM methods used extensively for implant fabrication. Metals, polymers, biocrystals, composites, and bio-HEA materials are used for implant fabrication for various applications. A wide variety of polymer implants are fabricated using additive manufacturing for nonload-bearing applications, and β-tricalcium phosphate, hydroxyapatite, bioactive glass, etc. are mainly used as ceramic materials in additive manufacturing due to the biological properties that could be imparted by the latter. For decades metals have played a major role in implant fabrication, and additive manufacturing of metals provides an easy approach to implant fabrication with augmented qualities. Various challenges and setbacks faced in the fabrication need postprocessing such as sintering, coating, surface polishing, etc. The emergence of bio-HEA materials, printing of shape memory implants, and five-dimensional printing are the trends of the era in additive manufacturing.

Graphene oxide-decorated microporous sulfonated polyetheretherketone for guiding osteoporotic bone regeneration

Recent studies have indicated that the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is an ideal therapeutic target for osteoporosis because it affects the differentiation of osteoblasts and osteoclasts. RNA sequencing utilizing multifunctional graphene oxide (GO) nanosheets revealed a correlation between GO nanomaterials and the NLRP3 inflammasome, as well as osteogenic genes in macrophages. This study aimed to construct a bone microenvironment-responsive multifunctional two-dimensional GO coating on the surface of microporous sulfonated polyetheretherketone (SPEEK) via polydopamine modification (SPEEK@PDA-GO). In vitro analysis showed that the SPEEK@PDA-GO implants weakened the STAT3-mediated NLRP3/caspase-1/IL-1β signaling pathway in macrophages and subsequently prevented the formation of an extracellular inflammatory microenvironment, which is crucial for osteoclastogenesis. SPEEK@PDA-GO displayed significantly higher expression of M2 macrophage markers and osteogenic genes, indicating that the multifunctional GO nanosheets could facilitate bone regeneration via their immunomodulatory properties. The ability of SPEEK@PDA-GO to stimulate new bone formation and block bone loss caused by estrogen loss due to ovariectomy was also analyzed. The findings of this study offer valuable information on the possible involvement of the NLRP3 inflammasome in the interaction between the immune system and bone health in patients with osteoporosis.

Mesoscale characterization of osseointegration around an additively manufactured genistein-coated implant

Given the hierarchical nature of bone and bone interfaces, osseointegration, namely the formation of a direct bone-implant contact, is best evaluated using a multiscale approach. However, a trade-off exists between field of view and spatial resolution, making it challenging to image large volumes with high resolution. In this study, we combine established electron microscopy techniques to probe bone-implant interfaces at the microscale and nanoscale with plasma focused ion beam-scanning electron microscopy (PFIB-SEM) tomography to evaluate osseointegration at the mesoscale. This characterization workflow is demonstrated for bone response to an additively manufactured Ti-6Al-4V implant which combines engineered porosity to facilitate bone ingrowth and surface functionalization via genistein, a phytoestrogen, to counteract bone loss in osteoporosis. SEM demonstrated new bone formation at the implant site, including in the internal implant pores. At the nanoscale, scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the gradual nature of the bone-implant interface. By leveraging mesoscale analysis with PFIB-SEM tomography that captures large volumes of bone-implant interface with nearly nanoscale resolution, the presence of mineral ellipsoids varying in size and orientation was revealed. In addition, a well-developed lacuno-canalicular network and mineralization fronts directed both towards the implant and away from it were highlighted.

Numerical evaluation of spinal reconstruction using a 3D printed vertebral body replacement implant: effects of material anisotropy

Background and objective

Artificial vertebral implants have been widely used for functional reconstruction of vertebral defects caused by tumors or trauma. However, the evaluation of their biomechanical properties often neglects the influence of material anisotropy derived from the host bone and implant's microstructures. Hence, this study aims to investigate the effect of material anisotropy on the safety and stability of vertebral reconstruction.

Material and methods

Two finite element models were developed to reflect the difference of material properties between linear elastic isotropy and nonlinear anisotropy. Their biomechanical evaluation was carried out under different load conditions including flexion, extension, lateral bending and axial rotation. These performances of two models with respect to safety and stability were analyzed and compared quantitatively based on the predicted von Mises stress, displacement and effective strain.

Results

The maximum von Mises stress of each component in both models was lower than the yield strength of respective material, while the predicted results of nonlinear anisotropic model were generally below to those of the linear elastic isotropic model. Furthermore, the maximum von Mises stress of natural vertebra and reconstructed system was decreased by 2-37 MPa and 20-61 MPa, respectively. The maximum reductions for the translation displacement of the artificial vertebral body implant and motion range of whole model were reached to 0.26 mm and 0.77°. The percentage of effective strain elements on the superior and inferior endplates adjacent to implant was diminished by up to 19.7% and 23.1%, respectively.

Conclusion

After comprehensive comparison, these results indicated that the finite element model with the assumption of linear elastic isotropy may underestimate the safety of the reconstruction system, while misdiagnose higher stability by overestimating the range of motion and bone growth capability.

Application of Reversible Four-Dimensional Printing of Shape Memory Alloys and Shape Memory Polymers in Structural Engineering: A State-of-the-Art Review

The rapid development and advancements in field of shape memory alloys (SMAA) has tremendously increased the progress in four-dimensional (4D) printing. The conventional 4D printing will require skilled manpower but utilization of reversibility aspect achieved using self adjusting external stimuli will eliminate the necessity of sophisticated devices and human intervention in 4D printing. The components created using reversible 4D printing can be reused after each recovery cycle that suits the current industry requirements. This review is divided into three sections: The first section starts with a detailed illustration of different mechanisms associated with SMAA and shape memory polymers SMPP along with an illustration of realistic 3D-printed SMAA and SMPP. The second section of this paper deals with the different methods of manufacture with the advantages and disadvantages of different types of SMAA. The third section deals with the mechanisms associated with SMPP, namely (1) Thermo-responsive mechanism, (2) Chemo-responsive mechanism, and (3) Photo-responsive mechanism along with a detailed insight into the aspect of repeatability and reversibility. The fourth section presents an exhaustive review of the application of SMAA and SMPP in civil engineering. The last section of this work throws light on the challenges faced in 4D reversible printing of SMAA and SMPP along with the potential solutions and presents directions for future research.

Accuracy of Three-dimensional Scan Technology and Its Possible Function in the Field of Hand Surgery

Background

Three-dimensional (3D) technology has become a standard manufacturing element in many industries and has gained significant interest in plastic surgery. The 3D scans are widely used for patient communication, virtual surgery planning, and intraoperative tool manufacturing, providing a more comprehensive view of procedures and their outcomes compared with 2D visualization.

Methods

We evaluated the performance of six commercially available 3D scanners by acquiring 3D models of a human hand and a 3D-printed replica of a human hand. We performed objective comparisons between the 3D models of the replica using color mapping techniques. Moreover, we compared the results of the human hand 3D scans.

Results

We achieved the highest precision with the Artec Space Spider 3D scanner (Artec 3D) when scanning the 3D-printed replica. The SD was ±0.05 mm, and the scan did not have major defects that needed manual correction. On the human hand scan, we achieved the best results using the Artec Eva (Artec 3D), the resulting scan was an accurate digital representation of the scanned human hand.

Conclusions

In our study, the Artec Space Spider 3D scanner demonstrated superior precision when scanning a 3D-printed replica, deviating only slightly from the original data, making it an optimal choice for nonmoving objects such as casts or medical instruments. For scanning human hands, the Artec Eva 3D scanner exhibited the highest performance, offering accuracy comparable to the Artec Space Spider, but with the added benefit of being able to scan larger objects.

High-cycle fatigue life prediction of L-PBF AlSi10Mg alloys: a domain knowledge-guided symbolic regression approach

The large scatter in high-cycle fatigue (HCF) life poses significant challenges to safe and reliable in-service assessment of additively manufactured metal components. Previous investigations have indicated that inherent manufacturing defects are a critical factor affecting the fatigue performance of the components, and the HCF life is significantly influenced by the geometric parameters of the critical defects inducing crack nucleation. Therefore, it is highly important to elucidate the correlation of the HCF life with the geometric parameters of critical defects. This study proposes a new fatigue life prediction model for laser additively manufactured AlSi10Mg alloys by including the combined effects of loading stress and defect geometries (size, location and morphology) in terms of domain knowledge-guided symbolic regression (SR). Domain knowledge is extracted from the semi-empirical Murakami, Z-parameter and X-parameter fatigue life models to establish the variable subtrees. The results show that compared with these semi-empirical models, the domain knowledge integration-based SR model has higher prediction accuracy and generalization ability. Moreover, compared with traditional 'black box' machine learning models, SR excels at balancing prediction accuracy and model interpretability, which provides useful insights into the relationship between fatigue life and defect geometries. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 2)'.

Synergistic effect of hierarchical topographic structure on 3D-printed Titanium scaffold for enhanced coupling of osteogenesis and angiogenesis

The significance of the osteogenesis-angiogenesis relationship in the healing process of bone defects has been increasingly emphasized in recent academic research. Surface topography plays a crucial role in guiding cellular behaviors. Metal-organic framework (MOF) is an innovative biomaterial with nanoscale structural and topological features, enabling the modulation of scaffold physicochemical properties. This study involved the loading of varying quantities of UiO-66 nanocrystals onto alkali-heat treated 3D-printed titanium scaffolds, resulting in the formation of hierarchical micro/nano topography named UiO-66/AHTs. The physicochemical properties of these scaffolds were subsequently characterized. Furthermore, the impact of these scaffolds on the osteogenic potential of BMSCs, the angiogenic potential of HUVECs, and their intercellular communication were investigated. The findings of this study indicated that 1/2UiO-66/AHT outperformed other groups in terms of osteogenic and angiogenic induction, as well as in promoting intercellular crosstalk by enhancing paracrine effects. These results suggest a promising biomimetic hierarchical topography design that facilitates the coupling of osteogenesis and angiogenesis.

In silico assessment of the bone regeneration potential of complex porous scaffolds

Mechanical environment plays a crucial role in regulating bone regeneration in bone defects. Assessing the mechanobiological behavior of patient-specific orthopedic scaffolds in-silico could help guide optimal scaffold designs, as well as intra- and post-operative strategies to enhance bone regeneration and improve implant longevity. Additively manufactured porous scaffolds, and specifically triply periodic minimal surfaces (TPMS), have shown promising structural properties to act as bone substitutes, yet their ability to induce mechanobiologially-driven bone regeneration has not been elucidated. The aim of this study is to i) explore the bone regeneration potential of TPMS scaffolds made of different stiffness biocompatible materials, to ii) analyze the influence of pre-seeding the scaffolds and increasing the post-operative resting period, and to iii) assess the influence of patient-specific parameters, such as age and mechanosensitivity, on outcomes. To perform this study, an in silico model of a goat tibia is used. The bone ingrowth within the scaffold pores was simulated with a mechano-driven model of bone regeneration. Results showed that the scaffold's architectural properties affect cellular diffusion and strain distribution, resulting in variations in the regenerated bone volume and distribution. The softer material improved the bone ingrowth. An initial resting period improved the bone ingrowth but not enough to reach the scaffold's core. However, this was achieved with the implantation of a pre-seeded scaffold. Physiological parameters like age and health of the patient also influence the bone regeneration outcome, though to a lesser extent than the scaffold design. This analysis demonstrates the importance of the scaffold's geometry and its material, and highlights the potential of using mechanobiological patient-specific models in the design process for bone substitutes.

3D printing metal implants in orthopedic surgery: Methods, applications and future prospects

Background

Currently, metal implants are widely used in orthopedic surgeries, including fracture fixation, spinal fusion, joint replacement, and bone tumor defect repair. However, conventional implants are difficult to be customized according to the recipient's skeletal anatomy and defect characteristics, leading to difficulties in meeting the individual needs of patients. Additive manufacturing (AM) or three-dimensional (3D) printing technology, an advanced digital fabrication technique capable of producing components with complex and precise structures, offers opportunities for personalization.

Methods

We systematically reviewed the literature on 3D printing orthopedic metal implants over the past 10 years. Relevant animal, cellular, and clinical studies were searched in PubMed and Web of Science. In this paper, we introduce the 3D printing method and the characteristics of biometals and summarize the properties of 3D printing metal implants and their clinical applications in orthopedic surgery. On this basis, we discuss potential possibilities for further generalization and improvement.

Results

3D printing technology has facilitated the use of metal implants in different orthopedic procedures. By combining medical images from techniques such as CT and MRI, 3D printing technology allows the precise fabrication of complex metal implants based on the anatomy of the injured tissue. Such patient-specific implants not only reduce excessive mechanical strength and eliminate stress-shielding effects, but also improve biocompatibility and functionality, increase cell and nutrient permeability, and promote angiogenesis and bone growth. In addition, 3D printing technology has the advantages of low cost, fast manufacturing cycles, and high reproducibility, which can shorten patients' surgery and hospitalization time. Many clinical trials have been conducted using customized implants. However, the use of modeling software, the operation of printing equipment, the high demand for metal implant materials, and the lack of guidance from relevant laws and regulations have limited its further application.

Conclusions

There are advantages of 3D printing metal implants in orthopedic applications such as personalization, promotion of osseointegration, short production cycle, and high material utilization. With the continuous learning of modeling software by surgeons, the improvement of 3D printing technology, the development of metal materials that better meet clinical needs, and the improvement of laws and regulations, 3D printing metal implants can be applied to more orthopedic surgeries.

The translational potential of this paper

Precision, intelligence, and personalization are the future direction of orthopedics. It is reasonable to believe that 3D printing technology will be more deeply integrated with artificial intelligence, 4D printing, and big data to play a greater role in orthopedic metal implants and eventually become an important part of the digital economy. We aim to summarize the latest developments in 3D printing metal implants for engineers and surgeons to design implants that more closely mimic the morphology and function of native bone.

Evaluating the Mechanical and Tribological Properties of 3D Printed Polylactic-Acid (PLA) Green-Composite for Artificial Implant: Hip Joint Case Study

Artificial implants are very essential for the disabled as they are utilized for bone and joint function in orthopedics. However, materials used in such implants suffer from restricted mechanical and tribological properties besides the difficulty of using such materials with complex structures. The current study works on developing a new polymer green composite that can be used for artificial implants and allow design flexibility through its usage with 3D printing technology. Therefore, a natural filler extracted from corn cob (CC) was prepared, mixed homogeneously with the Polylactic-acid (PLA), and passed through a complete process to produce a green composite filament suit 3D printer. The corn cob particles were incorporated with PLA with different weight fractions zero, 5%, 10%, 15%, and 20%. The physical, mechanical, and tribological properties of the PLA-CC composites were evaluated. 3D finite element models were constructed to evaluate the PLA-CC composites performance on a real condition implant, hip joints, and through the frictional process. Incorporating corn cob inside PLA revealed an enhancement in the hardness (10%), stiffness (6%), compression ultimate strength (12%), and wear resistance (150%) of the proposed PLA-CC composite. The finite element results of both models proved an enhancement in the load-carrying capacity of the composite. The finite element results came in line with the experimental results.

3D-Printing for Critical Sized Bone Defects: Current Concepts and Future Directions

The management and definitive treatment of segmental bone defects in the setting of acute trauma, fracture non-union, revision joint arthroplasty, and tumor surgery are challenging clinical problems with no consistently satisfactory solution. Orthopaedic surgeons are developing novel strategies to treat these problems, including three-dimensional (3D) printing combined with growth factors and/or cells. This article reviews the current strategies for management of segmental bone loss in orthopaedic surgery, including graft selection, bone graft substitutes, and operative techniques. Furthermore, we highlight 3D printing as a technology that may serve a major role in the management of segmental defects. The optimization of a 3D-printed scaffold design through printing technique, material selection, and scaffold geometry, as well as biologic additives to enhance bone regeneration and incorporation could change the treatment paradigm for these difficult bone repair problems.