Search Results for nanofibers

This article discusses electrospinning as a method for obtaining nanofibers, some of the challenges and limitations of the technique, advancements in the field, and how it may be used in key functional applications. The key drawbacks of traditional electrospinning processes include relatively slow speed of nanofiber production, low product yield, and relatively high cost. The article also addresses novel high-throughput techniques and methods designed for the scalable synthesis of nanofibers and nanofibrous mats that are of reasonable cost.

This article provides a summary of the concepts discussed in the articles under the Section “Constituent Materials” in ASM Handbook, Volume 21: Composites. The Section describes the major matrix resins and reinforcing fibers used in composite materials, as well as some of the intermediate material forms available for composite fabrication.

Additive manufacturing (AM) has been growing as a significant research interest in academic and industry research communities. This article presents flexible and biocompatible energy-harvesting devices using AM technology. First, it discusses material selection for achieving piezoelectricity and triboelectricity. Then, the article highlights the structures of energy harvesters and describes their working mechanisms. Next, it covers the additively manufactured implantable piezoelectric and triboelectric energy harvesters. Further, the article describes the 3D-printed wearable energy harvesters as well as their applications. An overview of additively manufactured self-powered sensors is highlighted. Finally, the article discusses the issues for 3D-printed energy harvesters and their roadmap.

Thermogravimetric analysis (TGA) is a thermal analysis technique that measures the amount and rate of change in the weight of a material as a function of temperature or time in a controlled atmosphere. This article provides a detailed account of the concepts of TGA, covering the various criteria to be considered for specimen preparation and calibration of TGAs. The use of thermogravimetric analysis data in the assessment of failure analysis of plastics and the combined usage of TGA with other techniques to understand the changes in the sample are also covered. The article provides examples of applications and provides information on the interpretation of TGA.

This article describes the determination of wear loss by measuring either mass change or dimensional change of lubricants and materials. It discusses the principles, advantages and disadvantages of mass loss measures and dimensional measures of wear. The article details wear measurement at the nanoscale, such as atomic force microscopy (AFM) measurement and scanning electron microscopy measurement. It reviews the techniques of wear measurement at the atomic level, namely, transmission electron microscopy (TEM) measurement and AFM combined with TEM measurement.

Polymer materials are key building blocks of the modern world, commonly used in packaging, automobiles, building materials, electronics, telecommunications, and many other industries. These commercial applications of polymeric materials would not be possible without the use of additives. This article is divided into five sections: mechanical property modifiers, physical property modifiers, biological function modifiers, processing aids, and colorants. It describes three classes of additives that are used to inhibit biological activity, six classes of mechanical property modifiers, three classes of physical property modifiers, and two classes of both colorants and processing aids.

Polymers and polymer composites have become attractive for tribological applications due to their specific material properties. This article begins by discussing the fundamentals of polymer friction and wear. It summarizes the main polymer materials used in tribological applications. The article explains the effects of load, sliding velocity, and temperature on the friction coefficient. It describes three types of wear modes, namely, abrasive, adhesion, and fatigue. The article discusses the frictional behavior of polymer composites and polymer coatings. It concludes by providing information on tribotesting of polymers and polymer composites.

This article begins with a description of extrusion-based bioprinting for tissue scaffold fabrication. It also examines various extrusion-based bioprinting processes and related tissue scaffolding strategies, presents the selection criteria of various bioinks with various polymers and their printed scaffolds for applications in tissue engineering and regenerative medicines, and provides future research recommendations to address the shortcomings and issues found in current extrusion-based bioprinting processes.

The field of bioprinting is a subset of additive manufacturing (AM) that is rapidly expanding to meet the needs of regenerative medicine and tissue engineering. Bioprinting encompasses a broad spectrum of issues, from cell expansion and novel bioink development to cell/stem cell printing, from organoid-based tissue organization to bioprinting of human-scale tissue structures, and from building cell/tissue/organ-on-a-chip to biomanufacturing of multicellular engineered living systems. This article focuses on two challenges regarding bioprinting: bioinks and crosslinking. It describes the methods for characterizing the performance of bioink formulations and the effectiveness of crosslinking strategies. The topics covered include modalities of bioprinting, characteristics of bioink, rheological properties of bioink sols, rheological measurements, mathematical models of bioink rheology, postfabrication polymer network mechanics, mechanical properties of crosslinked bioinks, and printability of bioinks. Finally, specific strategies used for crosslinking bioinks, as well as some emerging strategies to further improve bioinks and their crosslinking, are summarized.

The biocompatibility of a material relates to its immunological response, toxicity profile, and ability to integrate with surrounding tissue without undesirable local or systemic effects on a patient. This article underscores the transformation of the medical device design ecosystem engaged as an integral part of the device ecosystem. It discusses the applications of biomaterials, including orthopedic, cardiovascular, ophthalmic, and dental applications. The article describes four major categories of biomaterials such as metals, polymers, glass and ceramics, and composites. A discussion on natural materials, nanomaterials, and stem cells is also provided. The article concludes with examples of biomaterials applications, such as endovascular devices, knee implants, and neurostimulation.

According to International Organization for Standardization (ISO)/ASTM International 52900, additive manufacturing (AM) can be classified into material extrusion, material jetting, vat photo polymerization, binder jetting, sheet lamination, powder-bed fusion (PBF), and directed-energy deposition. This article discusses the processes involved in polymer powder 3D printing using laser fusion/ sintering and fusing agents and energy, as well as the thermally fused PBF. It provides information on polymer powder parameters and modeling, the powder-handling system, powder characterization, the flowability of powder feedstock, and polymer part characteristics. The article describes the types of polymers in PBF, the processes involved in powder recycling, and the prospects of PBF in AM. In addition, the biomedical application of polyether ether ketone (PEEK) is also covered.

This article focuses on laboratory atomic force microscopes (AFMs) used in ambient air and liquid environments. It begins with a discussion on the origin of AFM and development trends occurring in AFM. This is followed by a section on the general principles of AFM and a comprehensive list of AFM scanning modes. There is a brief description of how each mode works and what types of applications can be made with each mode. Some of the processes involved in preparation of samples (bulk materials and those placed on a substrate) scanned in an AFM are then presented. The article provides information on the factors applicable to the accuracy and precision of AFM measurements. It ends by discussing the applications for AFMs in the fields of science, technology, and engineering.

Aluminum alloys are widely used in engineered components because of their excellent strength-to-weight ratio. Their use in applications requiring wear resistance is more limited. One of the main limitations of aluminum alloys is the poor tribological behavior mainly due to their relatively low hardness, which favors large plastic deformation under sliding conditions. This article discusses the classes and mechanisms of wear in aluminum-silicon alloys, aluminum-tin bearing alloys, and aluminum-matrix composites; describes the effect of material-related parameters on wear behavior of these alloys; and reviews their applications in a variety of tribological applications in the automotive industry ranging from aluminum-tin alloys for plain bearings to alloys with hard anodizing for machine elements. Methods to improve wear resistance and alloy hardness are also discussed.

This article begins by describing the designations of cast and wrought aluminum alloys. It explains the effects of main alloying elements in aluminum alloys: boron, chromium, copper, iron, lithium, magnesium, manganese, nickel, phosphorus, silicon, sodium, strontium, titanium, and zinc. The article describes the microstructure of cast and wrought aluminum alloys and the various strengthening mechanisms, including solid solution, grain refinement, strain or work hardening, precipitation (or age) hardening, and dispersoid strengthening. The article explicates the tribological behavior of aluminum alloys, aluminum-base composites, and metal-matrix composites. It presents the effect of material-related parameters and external factors on wear behavior and transitions of aluminum-silicon alloys. The article also presents the most important factors affecting the dry sliding wear behavior of particle-reinforced aluminum-base composites against a steel counterface.

This article discusses three types of powder-feeder systems that are commonly used throughout the thermal spray (TS) industry: gravity-based devices, rotating wheel devices, and fluidized-bed systems. It provides information on the various mechanical methods for producing powders, namely, crushing, milling, attriting, and machining. The article describes two prime methods of agglomeration. One method uses a binder by way of agglutination, while the other relies on a sintering operation. The article discusses the technology and principles of the processes that relate to thermal spraying, and offers an understanding for choosing particular feedstock materials that are classified based on the thermal spray process, material morphology, chemical nature of the material, and applications. Sieving, the most common method of separating powders into their size fractions, is also reviewed. The article also provides information on the topical areas and precautions to be undertaken to protect the operator from safety hazards.