• The tools of synthetic biology can be used to engineer living biosensors that report the presence of analytes. Although these engineered cellular biosensors have many potential applications for deployment outside of the lab, they are genetically modified organisms (GMOs) and are often considered dangerous. Mitigating the risk of releasing GMOs into the environment while enabling their use outside a laboratory is critical. Here, we describe the development of a biosensing system consisting of a synthetic biological circuit, which is engineered in Escherichia coli that are contained within a unique 3D-printed device housing. These GMOs detect the chemical quorum signal of Pseudomonas aeruginosa, an opportunistic pathogen. Using this device, the living biosensor makes contact with a specimen of interest without ever being exposed to the environment. Cells can be visually analyzed in the field within culture tubes, or returned to the lab for further analysis. Many biosensors lack the versatility required for deployment in the field, where many diseases can go undiagnosed due to a lack of resources and equipment. Our bioassay device utilizes 3D printing to create a portable, modular, and inexpensive device for the field deployment of living biosensors.

  • Additive manufacturing (AM) technologies, such as selective laser sintering (SLS) and fused deposition modeling (FDM), have become the powerful tools for direct manufacturing of complex parts. This breakthrough in manufacturing technology makes the fabrication of new geometrical features and multiple materials possible. Past researches on designs and design methods often focused on how to obtain desired functional performance of the structures or parts, specific manufacturing capabilities as well as manufacturing constraints of AM were neglected. However, the inherent constraints in AM processes should be taken into account in design process. In this paper, the enclosed voids, one type of manufacturing constraints of AM, are investigated. In mathematics, enclosed voids restriction expressed as the solid structure is simply-connected. We propose an equivalent description of simply-connected constraint for avoiding enclosed voids in structures, named as virtual temperature method (VTM). In this method, suppose that the voids in structure are filled with a virtual heating material with high heat conductivity and solid areas are filled with another virtual material with low heat conductivity. Once the enclosed voids exist in structure, the maximum temperature value of structure will be very high. Based upon this method, the simply-connected constraint is equivalent to maximum temperature constraint. And this method can be easily used to formulate the simply-connected constraint in topology optimization. The effectiveness of this description method is illustrated by several examples. Based upon topology optimization, an example of 3D cantilever beam is used to illustrate the trade-off between manufacturability and functionality. Moreover, the three optimized structures are fabricated by FDM technology to indicate further the necessity of considering the simply-connected constraint in design phase for AM.

  • Direct-write additive manufacturing refers to a rich and growing repertoire of well-established fabrication techniques that builds solid objects directly from computer-generated solid models without elaborate intermediate fabrication steps. At the macroscale, direct-write techniques such as stereolithography, selective laser sintering, fused deposition modeling ink-jet printing, and laminated object manufacturing have significantly reduced concept-to-product lead time, enabled complex geometries, and importantly, has led to the renaissance in fabrication known as the . The technological premises of all direct-write additive manufacturing are identical—converting computer generated three-dimensional models into layers of two-dimensional planes or slices, which are then reconstructed sequentially into three-dimensional solid objects in a layer-by-layer format. The key differences between the various additive manufacturing techniques are the means of creating the finished layers and the ancillary processes that accompany them. While still at its infancy, direct-write additive manufacturing techniques at the microscale have the potential to significantly lower the barrier-of-entry—in terms of cost, time and training—for the prototyping and fabrication of MEMS parts that have larger dimensions, high aspect ratios, and complex shapes. In recent years, significant advancements in materials chemistry, laser technology, heat and fluid modeling, and control systems have enabled additive manufacturing to achieve higher resolutions at the micrometer and nanometer length scales to be a viable technology for MEMS fabrication. Compared to traditional MEMS processes that rely heavily on expensive equipment and time-consuming steps, direct-write additive manufacturing techniques allow for rapid design-to-prototype realization by limiting or circumventing the need for cleanrooms, photolithography and extensive training. With current direct-write additive manufacturing technologies, it is possible to fabricate unsophisticated micrometer scale structures at adequate resolutions and precisions using materials that range from polymers, metals, ceramics, to composites. In both academia and industry, direct-write additive manufacturing offers extraordinary promises to revolutionize research and development in microfabrication and MEMS technologies. Importantly, direct-write additive manufacturing could appreciably augment current MEMS fabrication technologies, enable faster design-to-product cycle, empower new paradigms in MEMS designs, and critically, encourage wider participation in MEMS research at institutions or for individuals with limited or no access to cleanroom facilities. This article aims to provide a limited review of the current landscape of direct-write additive manufacturing techniques that are potentially applicable for MEMS microfabrication.

  • Additive manufacturing (AM) technology has been researched and developed for more than 20 years. Rather than removing materials, AM processes make three-dimensional parts directly from CAD models by adding materials layer by layer, offering the beneficial ability to build parts with geometric and material complexities that could not be produced by subtractive manufacturing processes. Through intensive research over the past two decades, significant progress has been made in the development and commercialization of new and innovative AM processes, as well as numerous practical applications in aerospace, automotive, biomedical, energy and other fields. This paper reviews the main processes, materials and applications of the current AM technology and presents future research needs for this technology.

  • Rapid prototyping (RP) or layered manufacturing (LM) technologies have been extensively used to manufacture prototypes composed mainly of plastics, polymers, paper, and wax due to the short product development time and low costs of these technologies. However, such technologies, with the exception of selective laser melting and sintering, are not used to fabricate metallic products because of the resulting poor life, short cycle, poor surface finish, and low structural integrity of the fabricated parts. The properties endowed by these parts do not match those of functional parts. Therefore, extensive research has been conducted to develop new additive manufacturing (AM) technologies by extending existing RP technologies. Several AM technologies have been developed for the fabrication of metallic objects. These technologies utilize materials, such as Ni-, Al-, and Ti-based alloys and stainless steel powders, to fabricate high-quality functional components. The present work reviews the type of materials used in laser-based AM processes for the manufacture of metallic products. The advantages and disadvantages of processes and different materials are summarized, and future research directions are discussed in the final section. This review can help experts select the ideal type of process or technology for the manufacturing of elements composed of a given alloy or material (Ni, Ti, Al, Pb, and stainless steel).
  • Electron beam selective melting (EBSM) is an additive manufacturing technique that directly fabricates three-dimensional parts in a layerwise fashion by using an electron beam to scan and melt metal powder. In recent years, EBSM has been successfully used in the additive manufacturing of a variety of materials. Previous research focused on the EBSM process of a single material. In this study, a novel EBSM process capable of building a gradient structure with dual metal materials was developed, and a powder-supplying method based on vibration was put forward. Two different powders can be supplied individually and then mixed. Two materials were used in this study: Ti6Al4V powder and Ti47Al2Cr2Nb powder. Ti6Al4V has excellent strength and plasticity at room temperature, while Ti47Al2Cr2Nb has excellent performance at high temperature, but is very brittle. A Ti6Al4V/Ti47Al2Cr2Nb gradient material was successfully fabricated by the developed system. The microstructures and chemical compositions were characterized by optical microscopy, scanning microscopy, and electron microprobe analysis. Results showed that the interface thickness was about 300 μm. The interface was free of cracks, and the chemical compositions exhibited a staircase-like change within the interface.

  • In order to build a ceramic component by inkjet printing, the object must be fabricated through the interaction and solidification of drops, typically in the range of 10−100 pL. In order to achieve this goal, stable ceramic inks must be developed. These inks should satisfy specific rheological conditions that can be illustrated within a parameter space defined by the Reynolds and Weber numbers. Printed drops initially deform on impact with a surface by dynamic dissipative processes, but then spread to an equilibrium shape defined by capillarity. We can identify the processes by which these drops interact to form linear features during printing, but there is a poorer level of understanding as to how 2D and 3D structures form. The stability of 2D sheets of ink appears to be possible over a more limited range of process conditions that is seen with the formation of lines. In most cases, the ink solidifies through evaporation and there is a need to control the drying process to eliminate the: "coffee ring" defect. Despite these uncertainties, there have been a large number of reports on the successful use of inkjet printing for the manufacture of small ceramic components from a number of different ceramics. This technique offers good prospects as a future manufacturing technique. This review identifies potential areas for future research to improve our understanding of this manufacturing method.

  • The most promising strategies in tissue engineering involve the integration of a triad of biomaterials, living cells, and biologically active molecules to engineer synthetic environments that closely mimic the healing milieu present in human tissues, and that stimulate tissue repair and regeneration. To be clinically effective, these environments must replicate, as closely as possible, the main characteristics of the native extracellular matrix (ECM) on a cellular and subcellular scale. Photo-fabrication techniques have already been used to generate 3D environments with precise architectures and heterogeneous composition, through a multi-layer procedure involving the selective photocrosslinking reaction of a light-sensitive prepolymer. Cells and therapeutic molecules can be included in the initial hydrogel precursor solution, and processed into 3D constructs. Recently, photo-fabrication has also been explored to dynamically modulate hydrogel features in real time, providing enhanced control of cell fate and delivery of bioactive compounds. This paper focuses on the use of 3D photo-fabrication techniques to produce advanced constructs for tissue regeneration and drug delivery applications. State-of-the-art photo-fabrication techniques are described, with emphasis on the operating principles and biofabrication strategies to create spatially controlled patterns of cells and bioactive factors. Considering its fast processing, spatiotemporal control, high resolution, and accuracy, photo-fabrication is assuming a critical role in the design of sophisticated 3D constructs. This technology is capable of providing appropriate environments for tissue regeneration, and regulating the spatiotemporal delivery of therapeutics.

  • Additive manufacturing and 3D printing technology have been developing rapidly in the last 30 years, and indicate great potential for future development. The promising future of this technology makes its impact on traditional industry unpredictable. 3D printing will propel the revolution of fabrication modes forward, and bring in a new era for customized fabrication by realizing the five "any"s: use of almost any material to fabricate any part, in any quantity and any location, for any industrial field. Innovations in material, design, and fabrication processes will be inspired by the merging of 3D-printing technology and processes with traditional manufacturing processes. Finally, 3D printing will become as valuable for manufacturing industries as equivalent and subtractive manufacturing processes.

  • A growing number of three-dimensional (3D)-printing processes have been applied to tissue engineering. This paper presents a state-of-the-art study of 3D-printing technologies for tissue-engineering applications, with particular focus on the development of a computer-aided scaffold design system; the direct 3D printing of functionally graded scaffolds; the modeling of selective laser sintering (SLS) and fused deposition modeling (FDM) processes; the indirect additive manufacturing of scaffolds, with both micro and macro features; the development of a bioreactor; and 3D/4D bioprinting. Technological limitations will be discussed so as to highlight the possibility of future improvements for new 3D-printing methodologies for tissue engineering.

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