3D Printing-Based Integrated Water Quality Sensing System

3D Printing Technology: Role in Safeguarding Food Security

The rising threats to food security include several factors, such as population growth, low agricultural investment, and poor distribution systems. Consequently, food insecurity results from a confluence of issues, including diseases, processing limitations, and distribution deficiencies. Food insecurity usually occurs in vulnerable areas where certain technologies and traditional food safety testing are not a viable solution for foodborne disease detection. In this regard, 3D printing technologies and 3D printed sensors open the platform to produce portable, accurate, and low-cost sensors that address the gaps and challenges in food security. In this paper, we discuss the perspective role of 3D printed sensors in food security in terms of food safety and food quality monitoring to provide reliable access to nutritious, affordable food. In each section, we highlight the advantages of 3D printing technology in terms of cost-effectiveness, accuracy, accessibility, and reproducibility compared to traditional manufacturing methodologies. Recent developments in robotic technologies for mechanization, such as food handling with soft grippers, are also discussed. Lastly, we delve into the applications of advanced 3D printing technologies in agricultural monitoring, particularly the future of plant wearables, environmental sensing, and overall plant health monitoring.

A 3D-printed analytical device seamlessly integrating sample treatment for electrochemical detection of IAA in Marchantia polymorpha

Because of the pivotal point of Marchantia polymorpha (M. polymorpha) in plant evolution, its auxin (mainly indole-3-acetic acid, IAA) levels could provide useful evidence for the study of the evolution of IAA. However, M. polymorpha could not be easily pretreated for electrochemical detection because they are at the entry level of land plants. Herein, we designed a three-dimensional (3D)-printed analytical device for seamless integration of sample treatment and electrochemical detection. Specifically, the electrochemical cell could be used as a mortar in which a tiny plant sample could be ground with a 3D-printed pestle, followed by mixing with the buffer solution under vibration for electrochemical detection of IAA with a disposable working electrode at the bottom of the cell. Using our strategy, the limits of quantification could reach 0.05 μmol L^-1 after optimization of parameters. We were able to demonstrate that IAA in different tissues of wild-type and mutant M. polymorpha could be successfully differentiated after they were treated with the 3D-printed analytical device. The obtained results were comparable to the samples blended with zirconium beads while the differences of IAA levels in different tissues of M. polymorpha agreed well with previous reports. This study suggested the potential of sample treatment integrated with electrochemical detection for analysis of IAA using the 3D printing techniques and their possible applications in the research of plants and other fields.

Application of 3D Printing Technology in Sensor Development for Water Quality Monitoring

The development of sensors for water quality monitoring is crucial to protect water quality, aquatic biota and human health. Traditional sensor manufacturing methods have significant drawbacks, such as low fabrication freedom, limited material choice and expensive manufacturing cost. As a possible alternative method, 3D printing technologies are increasingly popular in sensor development due to their high versatility, fast fabrication/modification, powerful processing of different materials and ease of incorporation with other sensor systems. Surprisingly, a systematic review examining the application of 3D printing technology in water monitoring sensors has not yet been conducted. Here, we summarized the development history, market share and advantages/disadvantages of typical 3D printing techniques. Specifically focused on the 3D-printed sensor for water quality monitoring, we then reviewed the applications of 3D printing in the development of sensors' supporting platform, cell, sensing electrode as well as all-3D-printed sensors. The fabrication materials and processing, and the sensor's performances regarding detected parameters, response time and detection limit/sensitivity, were also compared and analyzed. Finally, the current drawbacks of 3D-printed water sensors and potential directions for future study were discussed. This review will substantially promote the understanding of 3D printing technology used in water sensor development and benefit the protection of water resources.

3D Printed Platform for Impedimetric Sensing of Liquids and Microfluidic Channels

Fused deposition modeling 3D printing (FDM-3DP) employing electrically conductive filaments has recently been recognized as an exceptionally attractive tool for the manufacture of sensing devices. However, capabilities of 3DP electrodes to measure electric properties of materials have not yet been explored. To bridge this gap, we employ bimaterial FDM-3DP combining electrically conductive and insulating filaments to build an integrated platform for sensing conductivity and permittivity of liquids by impedance measurements. The functionality of the device is demonstrated by measuring conductivity of aqueous potassium chloride solution and bottled water samples and permittivity of water, ethanol, and their mixtures. We further implement an original idea of applying impedance measurements to investigate dimensions of 3DP channels as base structures of microfluidic devices, complemented by their optical microscopic analysis. We demonstrate that FDM-3DP allows the manufacture of microchannels of width down to 80 μm.

A miniaturized 3D printed pressure regulator (µPR) for microfluidic cell culture applications

Well-defined fluid flows are the hallmark feature of microfluidic culture systems and enable precise control over biophysical and biochemical cues at the cellular scale. Microfluidic flow control is generally achieved using displacement-based (e.g., syringe or peristaltic pumps) or pressure-controlled techniques that provide numerous perfusion options, including constant, ramped, and pulsed flows. However, it can be challenging to integrate these large form-factor devices and accompanying peripherals into incubators or other confined environments. In addition, microfluidic culture studies are primarily carried out under constant perfusion conditions and more complex flow capabilities are often unused. Thus, there is a need for a simplified flow control platform that provides standard perfusion capabilities and can be easily integrated into incubated environments. To this end, we introduce a tunable, 3D printed micro pressure regulator (µPR) and show that it can provide robust flow control capabilities when combined with a battery-powered miniature air pump to support microfluidic applications. We detail the design and fabrication of the µPR and: (i) demonstrate a tunable outlet pressure range relevant for microfluidic applications (1-10 kPa), (ii) highlight dynamic control capabilities in a microfluidic network, (iii) and maintain human umbilical vein endothelial cells (HUVECs) in a multi-compartment culture device under continuous perfusion conditions. We anticipate that our 3D printed fabrication approach and open-access designs will enable customized µPRs that can support a broad range of microfluidic applications.

Biocompliant Composite Au/pHEMA Plasmonic Scaffolds for 3D Cell Culture and Noninvasive Sensing of Cellular Metabolites

The field of 3D printing is an area of active research, with a substantial focus given to the design and construction of customized tools for applications in technology. There exists a particular need in these developing areas of opportunity for new multi-functional soft materials that are biologically compatible for the growth and directed culturing of cells. Herein, a composite material consisting of gold nanoparticles with useful plasmonic properties embedded within a highly hydrophilic poly-2-hydroxyethylmethacrylate matrix is described and characterized. This composite material serves dual functions as both host framework scaffold for cell lines such as pre-osteoblasts as well as a plasmonic biosensor for in situ measurements of living cells. The plasmonic properties of this system are characterized as a function of the material properties and related to compositional features of the material through a proposed light-directed mechanism. This chemistry provides a tunable, 3D printable plasmonic composite material of encapsulated gold nanoparticles in a biologically-compliant, acrylate-based hydrogel matrix. Surface-enhanced Raman scattering studies of 3D-microcultures supported by the scaffolds are carried out and the strong influence of perm-selective molecular diffusion in its analytical responses is established. Most notably, specific, largely hydrophilic, cellular metabolites are detected within the supported live cultures.

Integrated 3D printed heaters for microfluidic applications: Ammonium analysis within environmental water

A multi-material 3D printed microfluidic reactor with integrated heating is presented, which was applied within a manifold for the colorimetric determination of ammonium in natural waters. Graphene doped polymer was used to provide localised heating when connected to a power source, achieving temperatures of up to 120 °C at 12 V, 0.7 A. An electrically insulating layer of acrylonitrile butadiene styrene (ABS) polymer or a new microdiamond-ABS polymer composite was used as a heater coating. The microdiamond polymer composite provided higher thermal conductivity and uniform heating of the serpentine microreactor which resulted in greater temperature control and accuracy in comparison to pure ABS polymer. The developed heater was then applied and demonstrated using a modified Berthelot reaction for ammonium analysis, in which the microreactor was configured at a predetermined optimised temperature. A 5-fold increase in reaction speed was observed compared to previously reported reaction rates. A simple flow injection analysis set up, comprising the microfluidic heater along with an LED-photodiode based optical detector, was assembled for ammonium analysis. Two river water samples and two blind ammonium standards were analysed and estimated concentrations were compared to concentrations determined using benchtop IC. The highest relative error observed following the analysis of the environmental samples was 11% and for the blind standards was 5%.

Dynamic Measurements Using FDM 3D-Printed Embedded Strain Sensors

3D-printing technology is opening up new possibilities for the co-printing of sensory elements. While quasi-static research has shown promise, the dynamic performance has yet to be researched. This study researched smart 3D structures with embedded and printed sensory elements. The embedded strain sensor was based on the conductive PLA (Polylactic Acid) material. The research was focused on dynamic measurements of the strain and considered the theoretical background of the piezoresistivity of conductive PLA materials, the temperature effects, the nonlinearities, the dynamic range, the electromagnetic sensitivity and the frequency range. A quasi-static calibration used in the dynamic measurements was proposed. It was shown that the temperature effects were negligible, the sensory element was linear as long as the structure had a linear response, the dynamic range started at ∼ 30 μ ϵ and broadband performance was in the range of few kHz (depending on the size of the printed sensor). The promising results support future applications of smart 3D-printed systems with embedded sensory elements being used for dynamic measurements in areas where currently piezo-crystal-based sensors are used.

Increasing the functionalities of 3D printed microchemical devices by single material, multimaterial, and print-pause-print 3D printing

3D printing has emerged as a valuable approach for the fabrication of fluidic devices and may replace soft-lithography as the method of choice for rapid prototyping. The potential of this disruptive technology is much greater than this - it allows for functional integration in a single, highly automated manufacturing step in a cost and time effective manner. Integration of functionality with a 3D printer can be done through spatial configuration of a single material, inserting pre-made components mid-print in a print-pause-print approach, and/or through the precise spatial deposition of different materials with a multimaterial printer. This review provides an overview on the ways in which 3D printing has been exploited to create and use fluidic devices with different functionality, which provides a basis for critical reflection on the current deficiencies and future opportunities for integration by 3D printing.

3D-Printed Graphene/Polylactic Acid Electrodes Promise High Sensitivity in Electroanalysis

Additive manufacturing provides a unique tool for prototyping structures toward electrochemical sensing, due to its ability to produce highly versatile, tailored-shaped devices in a low-cost and fast way with minimized waste. Here we present 3D-printed graphene electrodes for electrochemical sensing. Ring- and disc-shaped electrodes were 3D-printed with a Fused Deposition Modeling printer and characterized using cyclic voltammetry and scanning electron microscopy. Different redox probes K₃Fe(CN)₆:K₄Fe(CN)₆, FeCl₃, ascorbic acid, Ru(NH₃)₆Cl₃, and ferrocene monocarboxylic acid) were used to assess the electrochemical performance of these devices. Finally, the electrochemical detection of picric acid and ascorbic acid was carried out as proof-of-concept analytes for sensing applications. Such customizable platforms represent promising alternatives to conventional electrodes for a wide range of sensing applications.

In Situ 3D Monitoring of Geometric Signatures in the Powder-Bed-Fusion Additive Manufacturing Process via Vision Sensing Methods

Lack of monitoring of the in situ process signatures is one of the challenges that has been restricting the improvement of Powder-Bed-Fusion Additive Manufacturing (PBF AM). Among various process signatures, the monitoring of the geometric signatures is of high importance. This paper presents the use of vision sensing methods as a non-destructive in situ 3D measurement technique to monitor two main categories of geometric signatures: 3D surface topography and 3D contour data of the fusion area. To increase the efficiency and accuracy, an enhanced phase measuring profilometry (EPMP) is proposed to monitor the 3D surface topography of the powder bed and the fusion area reliably and rapidly. A slice model assisted contour detection method is developed to extract the contours of fusion area. The performance of the techniques is demonstrated with some selected measurements. Experimental results indicate that the proposed method can reveal irregularities caused by various defects and inspect the contour accuracy and surface quality. It holds the potential to be a powerful in situ 3D monitoring tool for manufacturing process optimization, close-loop control, and data visualization.