Metal Additive Manufacturing for Load-Bearing Implants

Surface modification of additive manufactured Ti6Al4V scaffolds with gelatin/alginate- IGF-1 carrier: An effective approach for healing bone defects

The study investigates the potential of porous scaffolds with Gel/Alg-IGF-1 coatings as a viable candidate for orthopaedic implants. The scaffolds are composed of additively manufactured Ti6Al4V lattices, which were treated in an alkali solution to obtain the anatase and rutile phases. The treated surface exhibited hydrophilicity of <11.5°. A biopolymer carrier containing Insulin-like growth factor 1 was coated on the samples using immersion treatment. This study showed that the surface-modified porous Ti6Al4V scaffolds increased cell viability and proliferation, indicating potential for bone regeneration. The results demonstrate that surface modifications can enhance the osteoconduction and osteoinduction of Ti6Al4V implants, leading to improved bone regeneration and faster recovery. The porous Ti6Al4V scaffolds modified with surface coating of Gel/Alg-IGF-1 exhibited a noteworthy increase in cell viability (from 80.7 to 104.1%viability) and proliferation. These results suggest that the surface modified scaffolds have potential for use in treating bone defects.

Additively Manufactured SiO2 and Cu-Added Ti Implants for Synergistic Enhancement of Bone Formation and Antibacterial Efficacy

Commercially pure titanium (CpTi), a bioinert metal, is used as an implant material at low load-bearing sites and as a porous coating on Ti6Al4V at high load-bearing sites. There is an unmet need for metallic biomaterials to improve osseointegration and inherent antimicrobial resistance. In this study, we have added 1 wt % SiO2 and 3 wt % Cu to the CpTi matrix and processed via metal additive manufacturing (AM). Si4+ ions promote angiogenesis and osteogenesis. CpTi-SiO2 composition exhibited 4.5 times higher bone formation at the bone-implant interface over CpTi in an in vivo study with a rat distal femur model. In vitro bacterial studies with Gram-positive Staphylococcus aureus bacterium revealed 85% antibacterial efficacy by CpTi-SiO2-3Cu than CpTi. CpTi-SiO2-3Cu did not show any inflammatory markers in vivo, indicating the absence of cytotoxicity, but displayed delayed osseointegration compared to CpTi-SiO2. CpTi-SiO2-3Cu displayed 3-fold higher mineralized bone formation than CpTi. Our results emphasize the synergistic effect of SiO2 and Cu addition in CpTi, promoting enhanced early stage osseointegration and inherent antibacterial efficacy, contributing toward implant longevity and stability in vivo.

Natural medicine delivery from 3D printed bone substitutes

Unmet medical needs in treating critical-size bone defects have led to the development of numerous innovative bone tissue engineering implants. Although additive manufacturing allows flexible patient-specific treatments by modifying topological properties with various materials, the development of ideal bone implants that aid new tissue regeneration and reduce post-implantation bone disorders has been limited. Natural biomolecules are gaining the attention of the health industry due to their excellent safety profiles, providing equivalent or superior performances when compared to more expensive growth factors and synthetic drugs. Supplementing additive manufacturing with natural biomolecules enables the design of novel multifunctional bone implants that provide controlled biochemical delivery for bone tissue engineering applications. Controlled release of naturally derived biomolecules from a three-dimensional (3D) printed implant may improve implant-host tissue integration, new bone formation, bone healing, and blood vessel growth. The present review introduces us to the current progress and limitations of 3D printed bone implants with drug delivery capabilities, followed by an in-depth discussion on cutting-edge technologies for incorporating natural medicinal compounds embedded within the 3D printed scaffolds or on implant surfaces, highlighting their applications in several pre- and post-implantation bone-related disorders.

Porous metal implants: processing, properties, and challenges

Porous and functionally graded materials have seen extensive applications in modern biomedical devices-allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although, easy to manufacture and lightweight, porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years. Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility-with the host bone-has been followed up with extensive methodical research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.

Understanding the influence of alloying elements on the print quality of powder bed fusion-based metal additive manufacturing: Ta and Cu addition to Ti alloy

Alloy design coupled with metal additive manufacturing (AM) opens many opportunities for materials innovation. Investigating the effect of printing parameters for alloy design is essential to achieve good part quality. Among different factors, laser absorptivity, heat diffusivity, and in situ intermetallic phase formations are critical. In this study, the first step employed was a reduction in Al and V contents in Ti6Al4V to design Ti3Al2V alloy, and further 10 wt.% tantalum (Ta) and 3 wt.% copper (Cu) were added to Ti3Al2V. A synergistic effect of Ta and Cu addition in Ti3Al2V negated their effect with higher porosities in Ti3Al2V-Ta-Cu. Ti3Al2V-Ta composition was more sensitive to the laser power, whereas Ti3Al2V-Ta-Cu to the overall energy density. Understanding the effect of energy density on these alloys' microstructural evolution and mechanical properties highlights the need for process-property optimization during alloy design using AM.

Improving Pure Titanium's Biological and Mechanical Characteristics through ECAP and Micro-Arc Oxidation Processes

Pure titanium is limited to be used in biomedical applications due to its lower mechanical strength compared to its alloy counterpart. To enhance its properties and improve medical implants feasibility, advancements in titanium processing technologies are necessary. One such technique is equal-channel angular pressing (ECAP) for its severe plastic deformation (SPD). This study aims to surface modify commercially pure titanium using micro-arc oxidation (MAO) or plasma electrolytic oxidation (PEO) technologies, and mineral solutions containing Ca and P. The composition, metallography, and shape of the changed surface were characterized using X-ray diffraction (XRD), digital optical microscopy (OM), and scanning electron microscope (SEM), respectively. A microhardness test is conducted to assess each sample's mechanical strength. The weight % of Ca and P in the coating was determined using energy dispersive spectroscopy (EDS), and the corrosion resistance was evaluated through potentiodynamic measurement. The behavior of human dental pulp cell and periodontal cell behavior was also studied through a biomedical experiment over a period of 1-, 3-, and 7-days using culture medium, and the cell death and viability can be inferred with the help of enzyme-linked immunosorbent assay (ELISA) since it can detect proteins or biomarkers secreted by cells undergoing apoptosis or necrosis. This study shows that the mechanical grain refinement method and surface modification might improve the mechanical and biomechanical properties of commercially pure (CP) titanium. According to the results of the corrosion loss measurements, 2PassMAO had the lowest corrosion rate, which is determined to be 0.495 mmpy. The electrode potentials for the 1-pass and 2-pass coated samples are 1.44 V and 1.47 V, respectively. This suggests that the coating is highly effective in reducing the corrosion rate of the metallic CP Ti sample. Changes in the grain size and the presence of a high number of grain boundaries have a significant impact on the corrosion resistance of CP Ti. For ECAPED and surface-modified titanium samples in a 3.6% NaCl electrolyte solution, electrochemical impedance spectroscopy (EIS) properties are similar to Nyquist and Bode plot fitting. In light of ISO 10993-5 guidelines for assessing in vitro cytotoxicity, this study contributes valuable insights into pulp and periodontal cell behavior, focusing specifically on material cytotoxicity, a critical factor determined by a 30% decrease in cell viability.