Selective Laser Melting and Electron Beam Melting of Ti6Al4V for Orthopedic Applications: A Comparative Study on the Applied Building Direction

Recent Advances and Prospects in β-type Titanium Alloys for Dental Implants Applications

Titanium and its alloys, especially Ti-6Al-4V, are widely studied in implantology for their favorable characteristics. However, challenges remain, such as the high modulus of elasticity and concerns about cytotoxicity. To resolve these issues, research focuses on β-type titanium alloys that incorporate elements such as Mo, Nb, Sn, and Ta to improve corrosion resistance and obtain a lower modulus of elasticity compatible with bone. This review comprehensively examines current β titanium alloys, evaluating their mechanical properties, in particular the modulus of elasticity, and corrosion resistance. To this end, a systematic literature search was carried out, where 81 articles were found to evaluate these outcomes. In addition, this review also covers the formation of the alloy, processing methods such as arc melting, and its physical, mechanical, electrochemical, tribological, and biological characteristics. Because β-Ti alloys have a modulus of elasticity closer to that of human bone compared to other metal alloys, they help reduce stress shielding. This is important because the alloy allows for a more even distribution of forces by having a modulus of elasticity more similar to that of bone. In addition, these alloys show good corrosion resistance due to the formation of a noble titanium oxide layer, facilitated by the incorporation of β stabilizers. These alloys also show significant improvements in mechanical strength and hardness. Finally, they also have lower cytotoxicity and bacterial adhesion, depending on the β stabilizer used. However, there are persistent challenges that require detailed research in critical areas, such as optimizing the composition of the alloy to achieve optimal properties in different clinical applications. In addition, it is crucial to study the long-term effects of implants on the human body and to advance the development of cutting-edge manufacturing techniques to guarantee the quality and biocompatibility of implants.

Characterisation of 3D-printed acetabular hip implants

Three-dimensional printing is a rapidly growing manufacturing method for orthopaedic implants and it is currently thriving in several other engineering industries. It enables the variation of implant design and the construction of complex structures which can be exploited in orthopaedics and other medical sectors. In this review, we develop the vocabulary to characterise 3D printing in orthopaedics from terms defined by industries employing 3D printing, and by fully examining a 3D-printed off-the-shelf acetabular cup (Fig. 1). This is a commonly used 3D-printed implant in orthopaedics, and it exhibits a range of prominent features brought about by 3D printing. The key features and defects of the porous and dense regions of the implant are clarified and discussed in depth to determine reliable definitions and a common understanding of characteristics of 3D printing between engineers and medical experts in orthopaedics. Despite the extensive list of terminology derived here, it is clear significant gaps exist in the knowledge of this field. Therefore, it is necessary for continued investigations of unused implants, but perhaps more significantly, examining those in vivo and retrieved to understand their long-term impact on patients and the effects of certain features (e.g. surface-adhered particles). Analyses of this kind will establish an understanding of 3D printing in orthopaedics and additionally it will help to update the regulatory approach to this new technology.

Titanium: A systematic review of the relationship between crystallographic profile and cell adhesion

Dental implant surface properties such as roughness, wettability, and porosity ensure cell interaction and tissue integration. The clinical performance of dental implants depends on the crystallographic texture and protein and cell bonds to the substrates, where grain size, orientation, and inclination are parameters responsible for favoring osteoblast adhesion and limiting bacterial adhesion. The lack of consensus on the best crystallographic plan for cell adhesion prompted this systematic review, which aims to answer the following question: "What is the influence of the crystallographic plane on titanium surfaces on cell adhesion?" by evaluating the literature on the crystallographic characteristics of titanium and how these dictate topographical parameters and influence the cell adhesion of devices made from this material. It followed the Preferred Reporting Standards for Systematic Reviews and Meta-Analyses (PRISMA 2020) registered with the Open Science Framework (OSF) (osf.io/xq6kv). The search strategy was based on the PICOS method. It chose in vitro articles that analyzed crystallographic structure correlated with cell adhesion and investigated the microstructure and its effects on cell culture, different crystal orientation distributions, and the influence of crystallinity. The search strategies were applied to the different electronic databases: PubMed, Scopus, Science Direct, Embase, and Google Scholar, and the articles found were attached to the Rayyan digital platform and assessed blindly. The Joanna Bringgs Institute (JBI) tool assessed the risk of bias. A total of 248 articles were found. After removing duplicates, 192 were analyzed by title and abstract. Of these, 18 were selected for detailed reading in their entirety, 9 of which met the eligibility criteria. The included studies presented a low risk of bias. The role of the crystallographic orientation of the exposed faces in a multicrystalline material is little discussed in the scientific literature and its impact is recognized as dictating the topographical characteristics of the material that facilitate cell adhesion.

Surface characteristics of additively manufactured CoCr and Ti6Al4V dental alloys: The effects of carbon and gold thin film coatings, and alkali-heat treatment

This study investigates the impact of surface modifications on additively manufactured CoCr and Ti6Al4V dental alloys, focusing on surface properties. Thin film carbon (C) and gold (Au) coatings, as well as alkali-heat treatment, were applied to the high- and low-polished specimens. Scanning electron microscopy (SEM) showed that thin film coatings retained the underlying surface topography, while the alkali-heat treatment induced distinct morphological changes. Energy-dispersive x-ray spectroscopy (EDS) analysis revealed that C-coating enriched surfaces with C, and Au-coating introduced detectable amounts of Au. Nevertheless, signs of coating delamination were observed in the high-polished specimens. Alkali-heat treatment led to the formation of a sodium titanate layer on Ti6Al4V surfaces, confirmed by sodium presence and Fourier transform infrared spectroscopy (FTIR) results showing carbonate bands. Surface roughness measurements with atomic force microscopy (AFM) showed that C-coating increased surface roughness in both high- and low-polished alloys. Au-coating slightly increased roughness, except for low-polished Au-coated Ti6Al4V, where a decrease in roughness was observed compared to low-polished bare Ti6Al4V, likely due to surface defects present in the latter resulting from the additive manufacturing process. Alkali-heat treatment led to a pronounced increase in roughness for both alloys, particularly for Ti6Al4V. Both thin film coatings decreased the water contact angles in all specimens in varying magnitudes, indicating an increase in wettability. However, the alkali-heat treatment caused a substantial decrease in contact angles, resulting in a highly hydrophilic state for Ti6Al4V. These findings underscore the substantial impact of surface modifications on additively manufactured dental alloys, potentially influencing their clinical performance. RESEARCH HIGHLIGHTS: Thin film coatings and chemical/heat treatment modify the surface properties of additively manufactured dental alloys. The surfaces of the alloys get rougher and more hydrophilic after alkali-heat treatment. Thin gold coatings exhibit potential adhesion challenges.

Influence of building direction on physical and mechanical properties of titanium implants: A systematic review

The objective of the systematic review is to find an answer to a question: "What is the influence of the building direction of titanium implants produced by additive manufacturing on their physical and mechanical properties?" This review followed the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA 2020) and was registered in the Open Science Framework (OSF) (osf.io/rdc84). Searches were performed in PubMed, Scopus, Science Direct, Embase, and Google Scholar databases on February 17th, 2024. Articles were chosen in 2 steps by 2 blinded reviewers based on previously selected inclusion criteria: In vitro studies that evaluated the influence of the impression direction of titanium implants produced by additive manufacturing on their physical and mechanical properties were selected. Articles were excluded that (1) did not use additive technology to obtain the implants, 2) used surfaces other than titanium, 3) did not evaluate the direction of impression, 4) Studies with only in vivo analyses, clinical studies, systematic reviews, book chapters, short communications, conference abstracts, case reports, and personal opinions.). In the initial search, 581 results were found. Of this total, 108 were excluded for duplication and, after applying the eligibility criteria, 16 articles were included in the present review. The risk of bias was analyzed using the RoBDEMAT. The risk of bias was analyzed using the RoBDEMAT. In addition, the coefficient of interagreement of the reviewers (Cohen's Kappa) and the certainty of evidence by GRADE were analyzed. In general, different impression angles showed variations in the physical and mechanical characteristics of the groups evaluated, including roughness, tensile strength, hardness, and modulus of elasticity. While some impression orientations resulted in greater strength or hardness, others showed greater elasticity or lower surface roughness. These findings suggest that print orientation plays a significant role in determining material properties. It can be concluded that printing directions influence the physical and mechanical properties of titanium implants and the studies included showed that the 0°, 45°, and 90° directions are the most evaluated as they present lower probabilities of structural anisotropies and provide better results in their roughness, hardness, tensile and compressive strength.

3D printed arrowroot starch-gellan scaffolds for wound healing applications

Skin, the largest organ in the body, blocks the entry of environmental pollutants into the system. Any injury to this organ allows infections and other harmful substances into the body. 3D bioprinting, a state-of-the-art technique, is suitable for fabricating cell culture scaffolds to heal chronic wounds rapidly. This study uses starch extracted from Maranta arundinacea (Arrowroot plant) (AS) and gellan gum (GG) to develop a bioink for 3D printing a scaffold capable of hosting animal cells. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction analysis (XRD) prove that the isolated AS is analogous to commercial starch. The cell culture scaffolds developed are superior to the existing monolayer culture. Infrared microscopy shows the AS-GG interaction and elucidates the mechanism of hydrogel formation. The physicochemical properties of the 3D-printed scaffold are analyzed to check the cell adhesion and growth; SEM images have confirmed that the AS-GG printed scaffold can support cell growth and proliferation, and the MTT assay shows good cell viability. Cell behavioral and migration studies reveal that cells are healthy. Since the scaffold is biocompatible, it can be 3D printed to any shape and structure and will biodegrade in the requisite time.

Advanced Ti-Nb-Ta Alloys for Bone Implants with Improved Functionality

The additive manufacturing of titanium-niobium-tantalum alloys with nominal chemical compositions Ti-xNb-6Ta (x = 20, 27, 35) by means of laser beam powder bed fusion is reported, and their potential as implant materials is elaborated by mechanical and biological characterization. The properties of dense specimens manufactured in different build orientations and of open porous Ti-20Nb-6Ta specimens are evaluated. Compression tests indicate that strength and elasticity are influenced by the chemical composition and build orientation. The minimum elasticity is always observed in the 90° orientation. It is lowest for Ti-20Nb-6Ta (43.2 ± 2.7 GPa) and can be further reduced to 8.1 ± 1.0 GPa for open porous specimens (p < 0.001). Furthermore, human osteoblasts are cultivated for 7 and 14 days on as-printed specimens and their biological response is compared to that of Ti-6Al-4V. Build orientation and cultivation time significantly affect the gene expression profile of osteogenic differentiation markers. Incomplete cell spreading is observed in specimens manufactured in 0° build orientation, whereas widely stretched cells are observed in 90° build orientation, i.e., parallel to the build direction. Compared to Ti-6Al-4V, Ti-Nb-Ta specimens promote improved osteogenesis and reduce the induction of inflammation. Accordingly, Ti-xNb-6Ta alloys have favorable mechanical and biological properties with great potential for application in orthopedic implants.

The Upper Limb Orthosis in the Rehabilitation of Stroke Patients: The Role of 3D Printing

Stroke represents the third cause of long-term disability in the world. About 80% of stroke patients have an impairment of bio-motor functions and over half fail to regain arm functionality, resulting in motor movement control disorder with serious loss in terms of social independence. Therefore, rehabilitation plays a key role in the reduction of patient disabilities, and 3D printing (3DP) has showed interesting improvements in related fields, thanks to the possibility to produce customized, eco-sustainable and cost-effective orthoses. This study investigated the clinical use of 3DP orthosis in rehabilitation compared to the traditional ones, focusing on the correlation between 3DP technology, therapy and outcomes. We screened 138 articles from PubMed, Scopus and Web of Science, selecting the 10 articles fulfilling the inclusion criteria, which were subsequently examined for the systematic review. The results showed that 3DP provides substantial advantages in terms of upper limb orthosis designed on the patient's needs. Moreover, seven research activities used biodegradable/recyclable materials, underlining the great potential of validated 3DP solutions in a clinical rehabilitation setting. The aim of this study was to highlight how 3DP could overcome the limitations of standard medical devices in order to support clinicians, bioengineers and innovation managers during the implementation of Healthcare 4.0.

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.

3D printed biomedical devices and their applications: A review on state-of-the-art technologies, existing challenges, and future perspectives

3D printing, also known as Additive manufacturing (AM), has emerged as a transformative technology with applications across various industries, including the medical sector. This review paper provides an overview of the current status of AM technology, its challenges, and its application in the medical industry. The paper covers the different types of AM technologies, such as fused deposition modeling, stereolithography, selective laser sintering, digital light processing, binder jetting, and electron beam melting, and their suitability for medical applications. The most commonly used biomedical materials in AM, such as plastic, metal, ceramic, composite, and bio-inks, are also viewed. The challenges of AM technology, such as material selection, accuracy, precision, regulatory compliance, cost and quality control, and standardization, are also discussed. The review also highlights the various applications of AM in the medical sector, including the production of patient-specific surgical guides, prosthetics, orthotics, and implants. Finally, the review highlights the Internet of Medical Things (IoMT) and artificial intelligence (AI) for regulatory frameworks and safety standards for 3D-printed biomedical devices. The review concludes that AM technology can transform the healthcare industry by enabling patients to access more personalized and reasonably priced treatment alternatives. Despite the challenges, integrating AI and IoMT with 3D printing technology is expected to play a vital role in the future of biomedical device applications, leading to further advancements and improvements in patient care. More research is needed to address the challenges and optimize its use for medical applications to utilize AM's potential in the medical industry fully.

Surface Modification Techniques to Produce Micro/Nano-scale Topographies on Ti-Based Implant Surfaces for Improved Osseointegration

Titanium and titanium alloys are used as artificial bone substitutes due to the good mechanical properties and biocompatibility, and are widely applied in the treatment of bone defects in clinic. However, Pure titanium has stress shielding effect on bone, and the effect of titanium-based materials on promoting bone healing is not significant. To solve this problem, several studies have proposed that the surface of titanium-based implants can be modified to generate micro or nano structures and improve mechanical properties, which will have positive effects on bone healing. This article reviews the application and characteristics of several titanium processing methods, and explores the effects of different technologies on the surface characteristics, mechanical properties, cell behavior and osseointegration. The future research prospects in this field and the characteristics of ideal titanium-based implants are proposed.

Main Applications and Recent Research Progresses of Additive Manufacturing in Dentistry

In recent ten years, with the fast development of digital and engineering manufacturing technology, additive manufacturing has already been more and more widely used in the field of dentistry, from the first personalized surgical guides to the latest personalized restoration crowns and root implants. In particular, the bioprinting of teeth and tissue is of great potential to realize organ regeneration and finally improve the life quality. In this review paper, we firstly presented the workflow of additive manufacturing technology. Then, we summarized the main applications and recent research progresses of additive manufacturing in dentistry. Lastly, we sketched out some challenges and future directions of additive manufacturing technology in dentistry.

Functionalization of screw implants with superelastic structured Nitinol anchoring elements

Background

Demographic change is leading to an increase in the number of osteoporotic patients, so a rethink is required in implantology in order to be able to guarantee adequate anchoring stability in the bone. The functional modification of conventional standard screw implants using superelastic, structured Ti6Al4V anchoring elements promises great potential for increasing anchoring stability.

Methods

For this purpose, conventional screw implants were mechanically machined and extended so that structured-superelastic-positionable-Ti6Al4V anchoring elements could be used. The novel implants were investigated with three tests. The setup of the anchoring elements was investigated in CT studies in an artificial bone. In a subsequent simplified handling test, the handling of the functional samples was evaluated under surgical conditions. The anchorage stability compared to standard screw implants was investigated in a final pullout test according to ASTM F543—the international for the standard specification and test methods for metallic medical bone screws.

Results

The functionalization of conventional screw implants with structured superelastic Ti6Al4V anchoring elements is technically realizable. It was demonstrated that the anchoring elements can be set up in the artificial bone without any problems. The anchorage mechanism is easy to handle under operating conditions. The first simplified handling test showed that at the current point of the investigations, the anchoring elements have no negative influence on the surgical procedure (especially under the focus of screw implantation). Compared to conventional standard screws, more mechanical work is required to remove the functional patterns completely from the bone.

Conclusion

In summary, it was shown that conventional standard screw implants can be functionalized with Ti6Al4V-structured NiTi anchoring elements and the new type of screws are suitable for orthopedic and neurosurgical use. A first biomechanical test showed that the anchoring stability could be increased by the anchoring elements.

Porous Titanium by Additive Manufacturing: A Focus on Surfaces for Bone Integration

Additive manufacturing (AM) is gaining increasing interest for realization of customized porous titanium constructs for biomedical applications and, in particular, for bone substitution. As first, the present review gives a short introduction on the techniques used for additive manufacturing of Ti/Ti-Alloys (Direct Energy Deposition—DED, Selective Laser Melting—SLM and Electron Beam Melting—EBM) and on the main bulk properties of additively manufactured titanium porous structures. Then, it discusses the main advancements in surface modifications of additively manufactured titanium constructs for bone contact applications. Even if specific surface modifications of constructs from AM are currently not widely explored, it is a critical open issue for application in biomedical implants. Some thermal, chemical, electrochemical, and hydrothermal treatments as well as different coatings are here described. The main aim of these treatments is the development of surface micro/nano textures, specific ion release, and addition of bioactivity to induce bone bonding and antibacterial activity. Physicochemical characterizations, in vitro bioactivity tests, protein absorption, in vitro (cellular/bacterial) and in vivo tests reported in the literature for bare and surface modified AM Ti-based constructs are here reviewed. Future perspectives for development of innovative additively manufactured titanium implants are also discussed.

Cubic Lattice Structures of Ti6Al4V under Compressive Loading: Towards Assessing the Performance for Hard Tissue Implants Alternative

Porous Lattice Structure (PLS) scaffolds have shown potential applications in the biomedical domain. These implants’ structural designs can attain compatibility mechanobiologically, thereby avoiding challenges related to the stress shielding effect. Different unit cell structures have been explored with limited work on the fabrication and characterization of titanium-based PLS with cubic unit cell structures. Hence, in the present paper, Ti6Al4V (Ti64) cubic PLS scaffolds were analysed by finite element (FE) analysis and fabricated using selective laser melting (SLM) technique. PLS of the rectangular shape of width 10 mm and height 15 mm (ISO: 13314) with an average pore size of 600–1000 μm and structure porosity percentage of 40–70 were obtained. It has been found that the maximum ultimate compressive strength was found to be 119 MPa of PLS with a pore size of 600 μm and an overall relative density (RD) of 57%. Additionally, the structure’s failure begins from the micro-porosity formed during the fabrication process due to the improper melting along a plane inclined at 45 degree.

Toward Bactericidal Enhancement of Additively Manufactured Titanium Implants

Implant-associated infections (IAIs) are among the most intractable and costly complications in implant surgery. They can lead to surgery failure, a high economic burden, and a decrease in patient quality of life. This manuscript is devoted to introducing current antimicrobial strategies for additively manufactured (AM) titanium (Ti) implants and fostering a better understanding in order to pave the way for potential modern high-throughput technologies. Most bactericidal strategies rely on implant structure design and surface modification. By means of rational structural design, the performance of AM Ti implants can be improved by maintaining a favorable balance between the mechanical, osteogenic, and antibacterial properties. This subject becomes even more important when working with complex geometries; therefore, it is necessary to select appropriate surface modification techniques, including both topological and chemical modification. Antibacterial active metal and antibiotic coatings are among the most commonly used chemical modifications in AM Ti implants. These surface modifications can successfully inhibit bacterial adhesion and biofilm formation, and bacterial apoptosis, leading to improved antibacterial properties. As a result of certain issues such as drug resistance and cytotoxicity, the development of novel and alternative antimicrobial strategies is urgently required. In this regard, the present review paper provides insights into the enhancement of bactericidal properties in AM Ti implants.

Interlayer Adhesion Analysis of 3D-Printed Continuous Carbon Fibre-Reinforced Composites

Carbon fibre-reinforced materials are becoming more and more popular in various fields of industries because of their lightweight and perfect mechanical properties. Additive manufacturing technologies can be used for the production of complex parts from various materials including composites. Fused deposition modelling (FDM) is an excellent technology for the production of composite structures reinforced with short or continuous carbon fibre. In this study, modified FDM technology was used for the production of composites reinforced with continuous carbon fibre. The main aim of this study is to evaluate the shear strength of 3D-printed composite structures. The influence of printing layer height and line width on shear strength was analysed. Results showed that layer height has a significant influence on shear strength, while the influence of printing line width on shear strength is slightly smaller. Reduction of layer height from 0.4 mm to 0.3 mm allows increasing shear strength by about 40 percent. Moreover, the influence of the shear area and overlap length on shear force showed linear dependency, in which the shear area is increasing the shear force increasing proportionally. Finally, the results obtained can be used for the design and development of new 3D-printed composite structures.

Performance Analysis of Electrochemical Micro Machining of Titanium (Ti-6Al-4V) Alloy under Different Electrolytes Concentrations

Titanium alloy is widely used in modern automobile industries due to its higher strength with corrosion resistance. Such higher strength materials can be effectively machined using unconventional machining processes, especially the electro-chemical micro machining (ECMM) process. It is important to enhance the machining process by investigating the effects of electrolytes and process parameters in ECMM. The presented work describes the influence of three different combinations of Sodium Chloride-based electrolytes on machining Titanium (Ti-6Al-4V) alloy. Based on the ECMM process parameters such as applied voltage, electrolytic concentration, frequency and duty cycle on response, characteristics are determined by the Taguchi design of experiments. The highest material removal rate (MRR) was achieved by the Sodium Chloride and Sodium Nitrate electrolyte. The combination of Sodium Chloride and Citric Acid achieve highest Overcut and Circularity. The optimal overcut was observed from the Sodium Chloride and Glycerol electrolyte due to the presence of glycerol. The better conicity was obtained from Sodium Chloride and Citric Acid in comparison with other electrolytes. A Sodium Chloride and Glycerol combination could generate better machined surface owing to the chelating effect of Glycerol.