Additive Manufacturing Implants Research Articles

Corrosion and Wear Behavior of Additively Manufactured Metallic Parts in Biomedical Applications

Today, parts made by additive manufacturing (AM) methods have found many applications in the medical industry, the main reasons for which are the ability to custom design and manufacture complex structures, their short production cycle, their ease of utilization, and on-site fabrication, leading to the fabrication of next-generation intricate patient-specific biomedical implants. These parts should fulfill numerous requirements, such as having acceptable mechanical strength, biocompatibility, satisfactory surface characteristics, and excellent corrosion and wear performance. It was known that AM techniques may lead to some uncertainties influencing part properties and causing significant evaluation conflicts in corrosion outcomes. Meanwhile, the corrosion and wear behavior of additively manufactured materials are not comprehensively discussed. In this regard, the present work is a review of the state-of-the-art knowledge dedicated to reviewing the actual scientific knowledge about the corrosion and wear response of additively manufactured biomedical components, elucidating the relevant mechanism and influential factors to enhance the performance of AM-manufactured implants specifically for the physiological human body fluids. Furthermore, there is a focus on the use of reinforced composites, surface engineering, and a preparation stage that can considerably affect the tribocorrosion behavior of AM-produced parts. The improvement of tribocorrosion performance can have a key role in the production of advanced AM implants and the present study can pave the way toward facile production of high-throughput AM biomedical parts that have very high resistance to corrosion and wear.

Ankle and Foot Arthroplasty and Prosthesis: A Review on the Current and Upcoming State of Designs and Manufacturing.

The foot and ankle serve vital roles in weight bearing, balance, and flexibility but are susceptible to many diverse ailments, making treatment difficult. More commonly, Total Ankle Arthroplasty (TAA) and Total Talus Replacement (TTR) are used for patients with ankle degeneration and avascular necrosis of the talus, respectively. Ankle prosthesis and orthosis are also indicated for use with lower limb extremity amputations or locomotor disability, leading to the development of powered exoskeletons. However, patient outcomes remain suboptimal, commonly due to the misfitting of implants to the patient-specific anatomy. Additive manufacturing (AM) is being used to create customized, patient-specific implants and porous implant cages that provide structural support while allowing for increased bony ingrowth and to develop customized, lightweight exoskeletons with multifunctional actuators. AM implants and devices have shown success in preserving stability and mobility of the joint and achieving fast recovery, as well as significant improvements in gait rehabilitation, gait assistance, and strength for patients. This review of the literature highlights various devices and technologies currently used for foot and ankle prosthesis and orthosis with deep insight into improvements from historical technologies, manufacturing methods, and future developments in the biomedical space.

Additively Manufactured Patient Specific Cranioplasty Implants with Antibacterial Properties

Cranioplasty is the surgical procedure to repair the bone defects in the cranium. Poly(methylmethacrylate) (PMMA) is the most common used biomaterial as it showed better long-term outcomes. Cranioplasty is usually performed through in-situ forming approach. However, the heat and shrinkage and the release of unreacted monomers represent the main drawbacks. Studies also shown a rate of graft infection higher than 10% in surgical PMMA cranioplasty. To overcome these, prefabricating the implants using additive manufacturing (AM) has been proposed. The AM implants could be tailored according to the defect and reduce surgical time, blood loss and the risk of infection. However, the insufficient disinfection of the AM implants may increase the risk of infection. Therefore, the implants can be loaded with antimicrobial agents prior to the cranioplasty. This study synthesised a chemically modified PMMA that can be loaded with antimicrobial agent for AM. The PMMA was sulfonated under different sulfonation temperature, duration, and ratio of PMMA to sulfuric acid. The ionic exchange capacity and degree of sulfonation of the sulfonated PMMA (SPMMA) was determined. In the future, SPMMA with the optimal IEC and DS will be loaded with antimicrobial agent and will be evaluated using the zone of inhibition assay.

Osseointegration of Titanium and Steel Additive Manufactured Implant in Rabbit Tibia under External Fixation: Comparative Study

Relevance. The main goals of successful prosthesis remain ensuring the osseointegration and infectious safety of implants.The purpose of the study — the comparative analysis of osseointegration of titanium and steel additive manufactured implants in the rabbit tibia under additional fixation by Ilizarov apparatus.Materials and Methods. The study was performed on 20 chinchilla male rabbits. The animals of the first group (n = 8 ) were implanted a stainless steel product EOS PH1 (EOS, Germany), the animals of the second group (n = 12) — a titanium alloy Ti6Al4V product. The implant was additionally fixed by Ilizarov apparatus. The implants were processed with additive technology by selective laser fusion at the EOSINT M 280 installation (EOS, Germany). The survival and safety of the implants were assessed using clinical, histological, laboratory and statistical methods.Results. The implant fall due to chronic inflammation was found in 2 animals of group 1 and none in group 2. The formation of weakly mineralized bone tissue on the surface of the implant was noted in 3 weeks in all cases. The bone became more mineralized by the 12th week of the experiment. However, in group 2, the calcium content and Ca / P ratio of the newly formed bone tissue at the 3rd and 12th week after implantation were significantly higher than in the animals of group 1. This indicated the greater maturity of the bone tissue in animals of group 2 at all stages of the experiment. In group 1, the compact plate osteoporosis and calcium-phosphorus balance disturbance were greater.Conclusion. The results of the study indicate that the survival rate (osseointegration) and safety of the product made of the titanium alloy were higher compared with the stainless steel product.

Immunomodulation of surface biofunctionalized 3D printed porous titanium implants

Additive manufacturing (AM) techniques have provided many opportunities for the rational design of porous metallic biomaterials with complex and precisely controlled topologies that give rise to unprecedented combinations of mechanical, physical, and biological properties. These favorable properties can be enhanced by surface biofunctionalization to enable full tissue regeneration and minimize the risk of implant-associated infections (IAIs). There is, however, an increasing need to investigate the immune responses triggered by surface biofunctionalized AM porous metals. Here, we studied the immunomodulatory effects of AM porous titanium (Ti-6Al-4V) printed using selective laser melting, and of two additional groups consisting of AM implants surface biofunctionalized using plasma electrolytic oxidation (PEO) with/without silver nanoparticles. The responses of human primary macrophages and human mesenchymal stromal cells (hMSCs) were studied in terms of cell viability, cell morphology and biomarkers of macrophage polarization. Non-treated AM porous titanium triggered a strong pro-inflammatory response in macrophages, albeit combined with signs of anti-inflammatory effects. The PEO treatment of AM porous titanium implants showed a higher potential to induce polarization towards a pro-repair macrophage phenotype. We detected no cytotoxicity against hMSCs in any of the groups. However, the incorporation of silver nanoparticles resulted in strong cytotoxicity against attached macrophages. The results of this study indicate the potential immunomodulatory effects of the AM porous titanium enhanced with PEO treatment, and point towards caution and further research when using silver nanoparticles for preventing IAIs.

Additive manufacturing of fracture fixation implants: Design, material characterization, biomechanical modeling and experimentation

Recent advancements in additive manufacturing (AM) have motivated researchers to consider this fabrication technique as a solution for challenges in patient-specific orthopaedic needs. Although there is an increasing trend in the applications of AM in medical fields, there is a critical need to understand the biomechanical performance of AM implants. In particular, design opportunities, anisotropic material properties and resulting stability of AM implant constructs for large bone defects such as osteosarcoma, comminuted fractures and infections are unexplored. This study aims to evaluate metal AM for complex fracture fixation using both computational and experimental methods. In addition, this research highlights the role of AM in the entire workflow to fabricate metal AM fixation plates for treatment of comminuted proximal humerus fractures. A new AM-centric patient-specific implant design for reducing common postoperative complications such as varus collapse and screw cutout is investigated. Biocompatible 316L stainless steel specimens processed in laser-powder bed fusion (L-PBF) is subjected to tensile testing and post-hoc microhardness to obtain orthotropic material properties of the AM implants. Subsequently, risk of screw cut-out is evaluated using finite element modelling (FEM) of AM implant-bone constructs. Parallel experiments included synthetic bones that are evaluated using a 3D motion capture system. The biomechanical tests are analyzed to quantify the medial fracture gap displacement among study groups subject to different loading conditions. The outcomes of this study suggest that the proposed AM-centric fixation plate design reduces average varus collapse (i.e. medial fracture gap displacement) by 47.2 % and risk of screw cut-out by 14.6 % when compared to the conventional plate design. Findings from this study can be extended to other patient anatomy, loading conditions, and AM processes.

Adoption and Diffusion of Disruptive Technologies: The Case of Additive Manufacturing in Medical Technology Industry in Australia

This paper provides the preliminary findings of a newly granted two-year project investigating the adoption of disruptive technologies, by focusing on the case of additive manufacturing (AM) in the medical technology (MedTech) industry, particularly implant applications. This is done by (I) stakeholder mapping of the industry in Australia. This included members of industry, researchers, academics, regulatory experts and MedTech consultants. (II) Identifying the top four major opportunity areas in which innovation can foster the adoption of AM implants, them being developments in Materials Science, Technology, Business Models, and Regulation & Quality Management. (III) Identifying and discussing the barriers in realizing such opportunity areas in practice, and finally (IV) recommending solutions based on the discussion and understanding of the proposed barriers that are hindering the widespread adoption and diffusion of 3-D printed medical implants. The impact of the project will be to unlock the potential of AM applications in the medical technology, which will benefit potential new entrants to the industry, incumbent firms, health care system, and patients in Australia.

A COMPUTATIONAL STUDY OF DIFFERENT ADDITIVE MANUFACTURING-BASED TOTAL ANKLE REPLACEMENT DEVICES USING THREE-DIMENSIONAL HUMAN LOWER EXTREMITY MODELS WITH VARIOUS ANKLE POSTURES

Total ankle replacement (TAR) surgery is one of the useful methods to treat ankle arthritis. Selective laser melting that is an additive manufacturing (AM) technique has made it possible to fabricate orthopedic implants. However, there are rare studies to analyze AM implants using finite element method. Thus, the purpose of this study was to investigate the effect of the various porous designs with three types of tibial shapes for five ankle postures using three-dimensional (3D) human lower extremity models. The variable-axis-mobile-bearing (VAMB) TAR models were developed in one solid TAR design and three porous TAR designs on the tibial and talar components. Additionally, three shape designs (curved, flat, and tilted) of the tibial component were also evaluated. Each TAR design was assembled on the human lower extremity model with standing, inversion, eversion, plantar flexion, and dorsiflexion ankle postures. The results showed that there was a minor effect among the solid and porous TAR designs on the implant stability, the bone stress, and the implant stress. However, those performances in the plantar flexion were significantly reduced compared to that in the other ankle postures. Although the porous TAR designs have a higher risk of implant failure and bone breakage, it may have better bone-implant bonding ability. This study could help engineers and surgeons to understand the design rationale and biomechanics of AM-based TAR devices.

Design and 3D-printing of titanium bone implants: brief review of approach and clinical cases.

Additive manufacturing (AM) is an alternative metal fabrication technology. The outstanding advantage of AM (3D-printing, direct manufacturing), is the ability to form shapes that cannot be formed with any other traditional technology. 3D-printing began as a new method of prototyping in plastics. Nowadays, AM in metals allows to realize not only net-shape geometry, but also high fatigue strength and corrosion resistant parts. This success of AM in metals enables new applications of the technology in important fields, such as production of medical implants. The 3D-printing of medical implants is an extremely rapidly developing application. The success of this development lies in the fact that patient-specific implants can promote patient recovery, as often it is the only alternative to amputation. The production of AM implants provides a relatively fast and effective solution for complex surgical cases. However, there are still numerous challenging open issues in medical 3D-printing. The goal of the current research review is to explain the whole technological and design chain of bio-medical bone implant production from the computed tomography that is performed by the surgeon, to conversion to a computer aided drawing file, to production of implants, including the necessary post-processing procedures and certification. The current work presents examples that were produced by joint work of Polygon Medical Engineering, Russia and by TechMed, the AM Center of Israel Institute of Metals. Polygon provided 3D-planning and 3D-modelling specifically for the implants production. TechMed were in charge of the optimization of models and they manufactured the implants by Electron-Beam Melting (EBM®), using an Arcam EBM® A2X machine.

Additive manufactured metallic implants for orthopaedic applications

Metallic implants are commonly used in various orthopaedic surgeries, like fracture fixation, spinal instrumentation, joint replacement and bone tumour surgery. Patients may need to adapt to the fixed dimensions of the standard implants. It may result in suboptimal fit to the host bones and possible adverse clinical results. The standard traditional implants may not address the reconstructive challenges such as severe bone deformity or bone loss after implant loosening and bone tumour resection. With the advent of digital technologies in medical imaging, computer programming in three-dimensional (3D) modelling and computer-assisted tools in precise placement of implants, patient-specific implants (PSI) have gained more attention in complex orthopaedic reconstruction. Additive manufacturing technology, in contrast to the conventional subtractive manufacturing, is a flexible process that can fabricate anatomically conforming implants that match the patients’ anatomy and surgical requirements. Complex internal structures with porous scaffold can also be built to enhance osseointegration for better implant longevity. Although basic studies have suggested that additive manufactured (AM) metal structures are good engineered biomaterials for bone replacement, not much peer-reviewed literature is available on the clinical results of the new types of implants. The article gives an overview of the metallic materials commonly used for fabricating orthopaedic implants, describes the metal-based additive manufacturing technology and the processing chain in metallic implants; discusses the features of AM implants; reports the current status in orthopaedic surgical applications and comments on the challenges of AM implants in orthopaedic practice.

Fortifying the Bone-Implant Interface Part 2: An In Vivo Evaluation of 3D-Printed and TPS-Coated Triangular Implants.

Minimally invasive surgical fusion of the sacroiliac (SI) joint using machined solid triangular titanium plasma spray (TPS) coated implants has demonstrated positive clinical outcomes in SI joint pain patients. Additive manufactured (AM), i.e. 3D-printed, fenestrated triangular titanium implants with porous surfaces and bioactive agents, such as nanocrystalline hydroxyapatite (HA) or autograft, may further optimize bony fixation and subsequent biomechanical stability. A bilateral ovine distal femoral defect model was used to evaluate the cancellous bone-implant interfaces of TPS-coated and AM implants. Four implant groups (n=6/group/time-point) were included: 1)TPS-coated, 2)AM, 3)AM+HA, and 4)AM+Autograft. The bone-implant interfaces of 6- and 12-week specimens were investigated via radiographic, biomechanical, and histomorphometric methods. Imaging showed peri-implant bone formation around all implants. Push-out testing demonstrated forces greater than 2500 N, with no significant differences among groups. While TPS implants failed primarily at the bone-implant interface, AM groups failed within bone ~2-3mm away from implant surfaces. All implants exhibited bone ongrowth, with no significant differences among groups. AM implants had significantly more bone ingrowth into their porous surfaces than TPS-coated implants (p<0.0001). Of the three AM groups, AM+Auto implants had the greatest bone ingrowth into the porous surface and through their core (p<0.002). Both TPS and AM implants exhibited substantial bone ongrowth and ingrowth, with additional bone through growth into the AM implants' core. Overall, AM implants experienced significantly more bone infiltration compared to TPS implants. While HA-coating did not further enhance results, the addition of autograft fostered greater osteointegration for AM implants. Additive manufactured implants with a porous surface provide a highly interconnected porous surface that has comparatively greater surface area for bony integration. Results suggest this may prove advantageous toward promoting enhanced biomechanical stability compared to TPS-coated implants for SI joint fusion procedures.

Histological and biomechanical analysis of porous additive manufactured implants made by direct metal laser sintering: A pilot study in sheep

It was the aim of this study to analyze osseointegrative properties of porous additive manufactured titanium implants made by direct metal laser sintering in a sheep model after an implantation period of 2 and 8 weeks. Three different types of implants were placed in the pelvis of six sheep. In each sheep were placed three standard machined (M), three sandblasted and etched (SE), and three porous additive manufactured (AM) implants. Of these three implants (one per type) were examined histologically and six implants were tested biomechanically. Additionally a semiquantitative histomorphometrical and qualitative fluorescent microscopic analysis were performed. After 2 and 8 weeks bone-to-implant-contact (BIC) values of the AM surface (2w: 20.49% ± 5.18%; 8w: 43.91% ± 9.69%) revealed no statistical significant differences in comparison to the M (2w: 20.33% ± 11.50%; 8w: 25.33% ± 4.61%) and SE (2w: 43.67 ± 12.22%; 8w: 53.33 ± 8.96%) surfaces. AM surface showed the highest increase of the BIC between the two observation time points. Considering the same implantation period histomorphometry and fluorescent labelling disclosed no significant differences in the bone surrounding the three implants groups. In contrast Removal-torque-test showed a significant improve in fixation strength (P ≤ 0.001) for the AM (1891.82 ± 308, 44 Nmm) surface after eight weeks in comparison to the M (198.93±88,04 Nmm) and SE (730.08 ± 151,89 Nmm) surfaces. All three surfaces (M, SE, and AM) showed sound osseointegration. AM implants may offer a possible treatment option in clinics for patients with compromised bone situations.