Key Engineering Materials Vol. 1038

Abstract: Coral reefs face significant damage from factors such as climate change, pollution, and careless tourism. Although vertebrates and corals differ in substance, their skeletal formation mechanisms are very similar. Titanium (Ti) and its alloys are widely utilised as biomedical materials for orthopaedic and dental implants due to their excellent mechanical properties, biocompatibility, and corrosion resistance. Various surface modifications have been developed to enhance cell adhesion and bone formation. This study aimed to investigate polyp adhesion and skeletal formation on Ti nonwoven materials after chemical surface modifications. Polyps were isolated by increasing the salinity of artificial seawater (viesalt, MARINETECH) in which coral fragments were immersed. Ti nonwoven fabric was anodised. The polyp adhered to the substrate on Day1 and expanded along the fibres over a period of about Day15. The moderate roughness and the oxide film formed on the surface improved the wettability of the substrate.

Abstract: Anatase-type TiO₂ films synthesised on quartz glass demonstrated cell adhesion control when illuminated from the backside with a 150 W Xe lamp emitting white light. The UV component was fully absorbed by the TiO₂ film, preventing cell exposure to it. By selectively applying localised light, non-contact control of cell adhesion areas was achieved. If non-toxic films responsive to conventional LED panels could be used, this would enable precise and easy control of cell adhesion areas. The purpose of this study was to synthesise inorganic semiconductor films with a narrower bandgap than TiO₂, responding to visible light from LED, and to investigate their photo-responsive properties. α-Fe₂O₃ films were deposited on borosilicate glass or ITO-coated quartz glass using RF sputtering with the corresponding metallic targets under an Ar or Ar/O₂ mixed atmosphere. XRD analysis showed sharp diffraction peaks, confirming the successful synthesis of the films. The absorption edges of the oxides shifted to longer wavelengths compared to that of TiO₂, corresponding to their bandgap differences. When a tablet device (HUAWEI MediaPad M3 Lite 10wp) displaying a white image was used as a light source, the oxide films showed a noticeable photocurrent. In the photocurrent profile during the on/off cycle of the light, a phenomenon of current flowing in the reverse direction when the light was turned off was observed. Moreover, this current reversal was more pronounced when the grains were fine. This suggests that the grain boundaries acted like a capacitor and induced polarisation behaviour.

Abstract: Advanced biocompatible piezoelectric composites have gained significant attention for the development of flexible medical devices and especially related to materials structures that mimic the natural tissue structures. Natural piezoelectricity within the human tissues is reviewed, together with nature-based piezoelectric materials, their advantages and potential for designing the structures for biomedical applications. Electrospun Polyvinylidene fluoride (PVDF) nanofiber matrix, reinforced with silver nanoparticles (AgNPs) is discussed, including specific applications in bone grafts, biosensors and energy harvesting. Processing parameters of the electrospinning fabrication technology have a strong influence on the composite piezoelectricity. Computational models of piezoelectric composites have become a major support in material design for the real case applications. Existing approaches to the numerical modeling of piezoelectric composites have been shortly reviewed toward a recent trend of AI supported modeling for providing effective composite properties, prediction and optimization of material properties and behavior, such as the output voltage and power. Polymer-based biomedical piezoelectric composites have shown excellent results in laboratory research from aspects of their flexibility and possibility to tailor their electro-mechanical properties. However, output piezoelectric signals are still much lower than in the case of traditional ceramic-based materials, including challenges related to the stability of the electric signal, signal noise, piezoelectric impedance and durability of composites with nature-based reinforcements. Future directions in custom composite design, including currently available computational models to enable more rapid development of biomedical piezoelectrics are elaborated at the end.

Abstract: Shape setting is a particular thermo-mechanical process used to imprint the desired shape in Nitinol (NiTi) shape memory alloy semi-finished products. It is a critical step as it must simultaneously ensure precise shape definition and specific transformation temperatures (TTs), on which the achievement of functional properties is based. Once a shape setting treatment has been optimized, it becomes highly relevant in industrial production to assess whether the same parameters can be applied to components with different geometries, therefore involving different mold designs. This study investigates the influence of mold geometry on the TTs of NiTi tubes, shape set to obtain different kinds of annuloplasty rings. Starting from the same tube batch and applying identical heat treatment parameters, two mold designs were used to impart different shapes and the phase transformation behavior was investigated. The results show that mold geometry does not significantly affect the TTs, indicating that the same shape setting parameters can be applied across different component geometries.

Abstract: The advancement of 3-dimensional printing technology over the past ten years has raised interest in and accessibility to these devices. Due to its consistent growth and demand, 3D printing is becoming a consumer-friendly, reasonably priced craft. Due to technological advancements, it is becoming increasingly integrated into broader fields of science and research, as well as the manufacturing sector. The need for customized solutions is constantly growing across several industries. The 3D extrusion of hydrogels is advancing in the field of biomaterials with a broad spectrum of biomedical applications. Hydrogel extrusion prints heads often use stepper motors or pneumatic pressure systems to push the substrate onto a surface. These techniques are well-suited for materials with high viscosity. While these systems are usually bound to the syringe volume, a refillable reservoir enables them to print above the syringe's limitations. We developed a low-cost standalone heating system for flexible tubes to control the temperature, hence avoiding jellification and clogging of the tubing system leading to the nozzle of the print head. The system connects to an in-house made peristaltic pump, which forces the e.g. gelatin through the nozzle with low pulsation, enabling us to extrude multiple layers of precise tempered gelatin. The heating system is based on easily available materials and electronic components and does not require expensive tools.

Abstract: This paper investigates tribocorrosion properties of binder jet additive-manufactured Co-Cr-Mo (F75) parts. Various parameters, including sintering atmosphere and post heat treatment processing, were examined to understand their effect on open circuit potential, friction, wear coefficient, and hardness. Results demonstrated that samples sintered in N₂-5%H₂ atmosphere have more noble potential up to-0.13V and lower wear coefficient down to 4.85e-6 mm³/N.m in comparison with samples sintered in vacuum. Solutionizing and aging (SHT-A) significantly increases hardness up to 626HV and lowers wear coefficient which means that the sample is more resistant to wear compared to as-sintered (AS) samples. However, heat-treated samples present slightly lower initial potential which means that these samples are more chemically active. This is because of the phase transformation of the matrix from FCC Co (γ phase) in AS condition to HCP Co (ε phase) + Co-Cr intermetallic (σ phase) in SHT-A condition, and different precipitate (carbides and nitrides) formation between these samples.

Abstract: This study explores the additive manufacturing of porous Ti-6Al-4V reticular structures using Powder Bed Fusion Laser Beam, with a focus on their morphological and mechanical properties for biomedical implant applications. Three triply periodic minimal surface (TPMS) designs—diamond, primitive, and split-P—were fabricated with both constant and radial density gradients, and subjected to electropolishing and chemical etching to enhance surface quality. The results showed that split-P structures exhibited the highest yield strength (274.93–288.95 MPa) and a moderate Young’s modulus (7.16–7.76 GPa), making them strong candidates for load-bearing implants due to their mechanical behavior closely resembling that of trabecular bone. Diamond structures had the highest stiffness (6.95–8.65 GPa) but showed brittle behavior, while primitive structures presented the lowest modulus and strength, offering ductility suitable for flexible applications. The findings underscore the potential of optimized TPMS lattices to improve mechanical compatibility and reduce stress shielding in next-generation orthopedic implants.

Abstract: This study aims to address these challenges by evaluating the displacement and interfacial damage of acetabular components with auxetic inner structures under cyclic loading conditions. Aseptic loosening of the acetabular cup is one of the primary causes of implant failure in hip replacements. However, assessing the damage behavior of implants in vivo remains a significant challenge, particularly when evaluating implant displacement and interfacial damage. A cantilever device for displacement measurements was designed and calibrated using a laser displacement sensor. The cantilever device successfully measured the displacement of the acetabular cup by monotonic and cyclic loading up to-2.3kN. Both AE sensors and cantilever devices could measure the increasing displacement in both the rotational and embedding directions. Finally, the loosening mechanism of the acetabular cup with an auxetic texture was discussed.

Abstract: Titanium and its alloys are considered the gold standard for bone contact implants due to their suitable mechanical properties and biological performances. However, their long-term performance remains impaired, mainly due to insufficient integration with surrounding tissues and infections. To overcome these problems, several strategies, particularly coatings, are explored. However, certain drawbacks remain such as lack of adhesion or low mechanical resistance. Among these coatings, diamond-like carbon (DLC) has emerged as a promising material due to its superior mechanical and tribological properties, chemical inertness and stability. In addition, the microstructure of DLC allows the incorporation of other species such as antibacterial agents (Ag, ZnO, etc.), leading to multifunctional protective coating. However, due to the high intrinsic stresses of DLC compared to the native oxide layer, the adhesion of DLC to metallic surfaces remains rather low. Therefore, in order to overcome adhesion issues, this work investigates the impact of different pretreatments, namely etching, carburization or both, on the adhesion of DLC deposited by plasma-assisted chemical vapor deposition, on titanium substrates. The results showed that carburizing 10 min was the most promising pretreatment for improving the DLC adhesion on Ti surfaces. Furthermore, the DLC coating appeared stable even after 7 days of aging in pseudo-physiological conditions, making the process promising for improving Ti implants.