Smart Materials in Manufacturing最新文献

New methods are emerging to combine the self-assembly of matter and additive manufacturing, so that new devices and constructs can simultaneously harness the unique molecular and nanostructural features afforded by self-assembly and the macroscale design freedom of additive manufacturing. The aim of this review is to analyse the body of literature and explore the crossover area where boundaries dissolve and self-assembly meets additive manufacturing (SAMAM). As a preliminary framework for this new area of research, the different experimental approaches to SAMAM can be grouped in three main categories, whereby SAMAM can be based on local interactions between molecules or nanoparticles, on 3D-printing induced forces, or on externally applied force fields. SAMAM offers numerous opportunities, such as the design of new printable materials, the ability to surpass conventional trade-offs in materials properties, the control of structural features across different length scales, process intensification and improved eco-sustainability. However, most research so far has been focused on polymer-based materials, and additional effort is needed to understand how SAMAM can be leveraged in metal- and ceramic-based additive manufacturing. On account of the weak inter-layer bonding often reported along the growth direction, it would also be interesting to explore whether SAMAM could effectively remediate undesidered anisotropic effects in additively manufactured parts.

The precision in the design and manufacturing of scaffolds with ideal properties such as biocompatibility, biodegradability, mechanical and surface characteristics is very crucial for applications in tissue engineering. Furthermore, these techniques should be able to translate manufactured scaffolds from bench to potential applications. Numerous fabrication technologies have been employed to design ideal three-dimensional scaffolds with controlled nano-to-micro-structures to achieve the final biological response. This review highlights the ideal parameters (biological, mechanical and biodegradability) of scaffolds for different biomedical and tissue engineering applications. It discusses in detail about the various designing methods developed and used for the fabrication of scaffolds, namely solvent casting/particle leaching, freeze drying, thermal induced phase separation (TIPS), gas foaming (GF), powder foaming, sol-gel, electrospinning, stereolithography (SLA), fused deposition modelling (FDM), selective laser sintering (SLS), binder jetting technique, inkjet printing, laser-assisted bioprinting, direct cell writing and metal based additive manufacturing with a focus on their benefits, limitations and applicability in tissue engineering.

Metallic biomaterials are widely used as short and long-term implantable devices by virtue of their outstanding mechanical properties, such as high load-bearing capacity and fatigue resistance. Due to their inherent bioinertness, potential corrosion, and some inferior surface properties, metallic biomaterials generally require coating and surface modification to improve their function and extend their lifespan in the body. High entropy alloys (HEAs) are a novel class of materials that are composed of at least five principal metallic elements with equiatomic or close-to-equiatomic compositions. Some of the unique properties of HEAs for surface modification and coating include excellent corrosion resistance, remarkable wear resistance, high strength/hardness, and strong diffusion resistance. The coating of HEAs on metallic substrates can be achieved through different techniques, including thermal spraying, laser deposition, and vapor deposition. HEAs have become a promising candidate for biomedical applications by combining tailor-made surface topography, excellent biocompatibility, appropriate surface chemistry, and element composition design. The present article is a thorough review of the research on the surface modification and coating of metallic biomaterials using HEAs.

Suture anchors are widely used for attaching soft tissue to bone due to their ease of insertion, fixation strength, and small size. The past few decades have seen great advances in the materials and designs of suture anchors. They were originally constructed of non-biodegradable metals and polymers, but in recent years there has been a considerable move toward biodegradable polymers. The biodegradable polymer anchors offer advantages such as gradual degradation over time, minimized risk of migration, less complex revision surgery, no need for a removal operation, and improved postsurgical imaging. However, these anchors have lower fixation strength than metal anchors and suffer from adverse local tissue reactions, inflammatory responses, and rapid degradation. Biodegradable metals appear to be ideal candidates for the future of suture anchors. They have high fixation strength and low elastic modulus close to that of bone, which promote osseointegration and allow the design of thinner and lower volume implants. The current article gives an overview of the application and manufacturing of biodegradable metallic suture anchors and summarizes their current concepts and properties in this area of continual development.

Elastomers known as rubber are ubiquitous in industrial applications, but they often contain chronic additives, such as zinc oxide, tetramethylthiuram monosulfide (denoted TMTM), and copper dimethyldithiocarbamate (CDD) that has a higher melting point than the common vulcanization temperature. These additives are released into the environment either through the wear and tear of tires and the landfilling of waste rubber. It is imperative to identify and adopt safe, cost-effective alternatives to replace zinc oxide and TMTM, both of which have moderate chronicity rating. Styrene-butadiene rubber (SBR) in this study is cured by using sulphur, zinc stearate, and dipentamethylenethiuram hexasulfide (TRA). The curing characteristics and the morphology and mechanical properties of the cured SBR are investigated. Zinc stearate and TRA exhibit a commendable rating of zero in terms of both chronicity and toxicity, making them promising candidates for substituting chronic additives. Adding 0.25 phr of zinc stearate into SBR can significantly enhance the crosslinking density while exhibiting anti-reversion performance, in comparison with a recipe that includes 5 phr of zinc oxide and 8 phr of TMTM. Transmission electron microscopy reveals that the zinc oxide (nano) particles are not soluble in SBR, and thus only the particle surface contributes to vulcanization. TRA is “dissolvable” in SBR, making it an ideal replacement for CDD which is insoluble due to its high melting point. Therefore, we strongly advise against the utilization of curing additives with melting points that exceed the vulcanization temperature. This work contributes to the green manufacture of elastomers.

With promising mechanical property and biodegradability, magnesium (Mg) alloys are considered as the potential candidates in biomedical application. Rapid degradation of Mg alloys compromises the mechanical performance and interfacial bioactivity, hindering clinical adoption. Deposition of a surface coating is an effective technique to improve the corrosion protection and bio-efficacy of Mg biomedical implants. Because of the natural degradability and corrosion, the surface is inevitably damaged in the complex physiological environment. Therefore, it is essential to form a self-healing coating that can repair damage to restore the stable mechanical structure and functions of biomedical Mg alloys. This paper reviews the recent advances in coating technology and the related properties including biodegradation behavior, self-repairing activity, biocompatibility, and other biological effects, and the healing mechanism is discussed. Self-healing coatings suitable for Mg alloys include conversion coatings, encapsulation coatings, and multilayered coatings, and their properties in vitro and in vivo are reviewed by focusing on drug-controlled and prolonged release, sterilization, cytocompatibility, osteogenesis, hemocompatibility, and angiogenesis. This review aims at providing guidance for the future research and development of practical healing coatings for biomedical Mg implants.

Equal channel angular extrusion (ECAE) has shown great potential for the consolidation of powdered materials. In the present article, the mechanical and corrosion properties of Mg–MgO and Mg–Al₂O₃ composites produced by the ECAE method were studied. Pure magnesium reinforced with 0, 10, 20, and 30 ​vol percentages of MgO and Al₂O₃ particles were hot consolidated at 600 ​MPa in an ECAE die without prior cold compaction or canning of the powders. Results indicated that the reinforcement content is directly proportional to the hardness, compressive strength, and corrosion resistance of the fabricated composites, while it has an inverse relationship with the relative density. The lowest relative density and the highest corrosion rate were obtained for the Mg+30%MgO composite samples, as opposed to the pure magnesium with the highest relative density and the lowest corrosion rate. Besides, composites reinforced with 30 and 20 ​vol percentages of alumina revealed the highest hardness and the highest compressive strength, which were 55% and 74% higher than that of the pure magnesium sample, respectively. Based on SEM and EDX analyses, it was shown that Mg–Al₂O₃ samples had finer grain sizes compared to Mg–MgO composites.

Titanium (Ti) alloys are often the materials of choice used in light-weighting strategies in manufacturing. However, their tribological performance needs to be improved. In this work, a laser surface engineering process using titania/alumina (TiO₂/Al₂O₃) composite powders was developed for Ti–6Al–4V alloy to enhance its wear resistance. This process resulted in the formation of a novel Al_xO_y/TiO_xN_y/α-Ti composite coating. The Al_xO_y particles were firmly embedded in the matrix, forming a semi-coherent interface with TiO_xN_y dendrites, which could strengthen the composite coating. The incorporation of fine Al₂O₃ particles also improved the laser absorptivity of the starting powders and decreased melt viscosities, leading to the considerable reduction in the porosity and crack density in the coatings. The wear resistance of the coatings made with the composite powders was superior to that made with the pure TiO₂ powder.

Surface charge of biomaterials is one of the most influential parameters on regulating the complex processes of cell responses in tissue engineering. This study explores the contributions of xTa (x ​= ​5; 10; 30 in wt%) interface with the Ti as matrix on the in-vitro cell growth when such composites were produced through cold spray additive manufacturing. Preliminary results reveal that formation of intimate contact between deposited Ti and Ta splats provides meaningful differences in work function, results in an estimated surface potential variation around 50 ​mV, that ultimately influence cell growth. Increasing mass fraction of Ta in the chosen cold sprayed Ti-xTa composites was beneficial to initial cell attachment and proliferation upon the surface. Electrochemical response of cold sprayed coatings indirectly proves that Ta may act as anode and Ti performs as cathode in the electrochemical cells with possible surface charge gradient that allow to design and adapt biomaterials surfaces to a specific application. Understanding the mechanism of cell growth upon the surface of cold sprayed Ti-xTa composites will contribute to design of biomaterial surface for promising osseointegrity in biomedical applications.

Graphene is an emerging class of multifunctional additives for plastic manufacturing. However, achieving the exfoliation and dispersion of graphene in polymers such as epoxy has been a significant challenge, typically requiring chemical modification or oxidation as well as organic solvents and/or surfactants, because exceptionally high-surface area graphene often stack themselves. Herein we report the preparation, exfoliation, surface modification, and dispersion of graphene nanomaterials in epoxy by a simple ball milling process. The prepared graphene nanomaterials exhibit a range of morphologies, i.e. nanoplatelets, nanoscrolls, and nanodots. These materials demonstrate high electrical conductivity, 1750 ​± ​41 ​S/cm, for a film of ∼6 μm in thickness. Furthermore, as the graphene nanomaterials' surface was functionalized with amine groups for affinity with epoxy, the nanomaterials were found to disperse readily in epoxy. At 0.25 ​vol% of graphene, the epoxy nanocomposite exhibited a 52% increment of fracture toughness and an 11% increment of Young's modulus. Notably, an electrical percolation threshold was observed at 0.52 ​vol% for the nanocomposites.