3D Printed Sensors for Biomedical Applications: A Review

Comparison of selective laser melting and stereolithography etching templates for guided endodontics

Background

With the increasing application of guided endodontics to treat complex root canal treatment, the entire process of root canal treatment has become more precise, reducing damage to tooth structure and improving success rates. However, due to the limitations of the operating space, the use of guided endodontic templates in posterior root canal treatment is less common. This study aims to compare the accuracy and reliability of selective laser melting (SLM) and traditional stereolithography etching (SLA) guided endodontic templates for posterior root canals, providing better treatment strategies for posterior root canal treatment.

Methods

The teeth were randomly assigned to either SLM or SLA group. Preoperative cone-beam computed tomography (CBCT) and a three-dimensional (3D) scanner were used to establish the 3D root canal system and the accurate occlusal models of the teeth. The virtual access to the canal access was designed using Mimics 19.0 and 3-Matic 11.0. The endodontic access was performed based on either SLM or SLA templates. The accuracy of endodontic preparation was measured in three-dimensions by calculating deviations from planned accesses. The template height and tooth substance loss rates in each group were measured.

Results

SLM-guided templates have a low average deviation at the entry point and apical portion of the bur of total posterior teeth (including premolars and molars) and individual molars (P < 0.05). Moreover, there was a significant difference in angular deviations and height of template in total posterior teeth and individual molars (P < 0.05). The mean substance loss rate of the SLA group was slightly greater than that of the SLM group, but the difference was not statistically (P > 0.05).

Conclusions

SLM-guided endodontics provides a more predictable and precise location of root canal orifice for the treatment of posterior teeth.

A Simple Method to Manufacture a Force Sensor Array Based on a Single-Material 3D-Printed Piezoresistive Foam and Metal Coating

Nowadays, 3D printing is becoming an increasingly common option for the manufacturing of sensors, primarily due to its capacity to produce intricate geometric shapes. However, a significant challenge persists in integrating multiple materials during printing, for various reasons. In this study, we propose a straightforward approach that combines 3D printing with metal coating to create an array of resistive force sensors from a single material. The core concept involves printing a sensing element using a conductive material and subsequently separating it into distinct parts using metal-coated lines connected to the electrical ground. This post-printing separation process involves manual intervention utilizing a stencil and metallic spray. The primary obstacle lies in establishing a sufficient contact surface between the sprayed metal and the structure, to ensure effective isolation among different zones. To address this challenge, we suggest employing a lattice structure to augment the contact surface area. Through experimental validation, we demonstrate the feasibility of fabricating two sensing elements from a single-material 3D-printed structure, with a maximum electrical isolation ratio between the sensors of above 30. These findings hold promise for the development of a new generation of low-tech 3D-printed force/displacement sensor arrays.

Recent Advances in Wearable Healthcare Devices: From Material to Application

In recent years, the proliferation of wearable healthcare devices has marked a revolutionary shift in the personal health monitoring and management paradigm. These devices, ranging from fitness trackers to advanced biosensors, have not only made healthcare more accessible, but have also transformed the way individuals engage with their health data. By continuously monitoring health signs, from physical-based to biochemical-based such as heart rate and blood glucose levels, wearable technology offers insights into human health, enabling a proactive rather than a reactive approach to healthcare. This shift towards personalized health monitoring empowers individuals with the knowledge and tools to make informed decisions about their lifestyle and medical care, potentially leading to the earlier detection of health issues and more tailored treatment plans. This review presents the fabrication methods of flexible wearable healthcare devices and their applications in medical care. The potential challenges and future prospectives are also discussed.

Recycled PETg embedded with graphene, multi-walled carbon nanotubes and carbon black for high-performance conductive additive manufacturing feedstock

The first report of conductive recycled polyethylene terephthalate glycol (rPETg) for additive manufacturing and electrochemical applications is reported herein. Graphene nanoplatelets (GNP), multi-walled carbon nanotubes (MWCNT) and carbon black (CB) were embedded within a recycled feedstock to produce a filament with lower resistance than commercially available conductive polylactic acid (PLA). In addition to electrical conductivity, the rPETg was able to hold >10 wt% more conductive filler without the use of a plasticiser, showed enhanced temperature stability, had a higher modulus, improved chemical resistance, lowered levels of solution ingress, and could be sterilised in ethanol. Using a mix of carbon materials CB/MWCNT/GNP (25/2.5/2.5 wt%) the electrochemical performance of the rPETg filament was significantly enhanced, providing a heterogenous electrochemical rate constant, k0, equating to 0.88 (±0.01) × 10-3 cm s-1 compared to 0.46 (±0.02) × 10-3 cm s-1 for commercial conductive PLA. This work presents a paradigm shift within the use of additive manufacturing and electrochemistry, allowing the production of electrodes with enhanced electrical, chemical and mechanical properties, whilst improving the sustainability of the production through the use of recycled feedstock.

Recent Advances in Scaffolds for Guided Bone Regeneration

The rehabilitation of alveolar bone defects of moderate to severe size is often challenging. Currently, the therapeutic approaches used include, among others, the guided bone regeneration technique combined with various bone grafts. Although these techniques are widely applied, several limitations and complications have been reported such as morbidity, suboptimal graft/membrane resorption rate, low structural integrity, and dimensional stability. Thus, the development of biomimetic scaffolds with tailor-made characteristics that can modulate cell and tissue interaction may be a promising tool. This article presents a critical consideration in scaffold's design and development while also providing information on various fabrication methods of these nanosystems. Their utilization as delivery systems will also be mentioned.

Bite Force Mapping Based on Distributed Fiber Sensing Network Approach

Bite force measurements are crucial in the realm of biomedical research, particularly in the areas of dentistry and orthodontic care. Various intraoral devices have been used to assess biting force, but each has limitations and drawbacks. Fiber optic sensors (FOSs) offer advantages such as electrical inertness, immunity to electromagnetic interference, and high sensitivity. Distributed fiber optic sensing allows an increase in the number of sensing points and can interrogate numerous reflections from scattering events within an optical fiber. We present four dental bites with heights of 6 mm, which enabled bilateral measurements. U-shaped sensors were prepared by embedding fibers into silicone by folding a single-mode fiber into four lines and multiplexing eight parallel nanoparticle-doped fibers. Dental bite models were created using two silicone materials (Sorta Clear 18 and Sorta Clear 40). The developed sensors were calibrated by applying weights up to 900 g, resulting in a linear response. Experiments were conducted to compare the efficacy of the dental bites. The collection of massive data was enabled by constructing a 2D map of the dental bites during multi-point sensing.

3D-Printed Alginate/Pectin-Based Patches Loaded with Olive Leaf Extracts for Wound Healing Applications: Development, Characterization and In Vitro Evaluation of Biological Properties

Traditional wound dressings may lack suitability for diverse wound types and individual patient requirements. In this context, this study aimed to innovate wound care by developing a 3D-printed patch using alginate and pectin and incorporating Olive Leaf Extract (OLE) as an active ingredient. Different polymer-to-plasticizer ratios were systematically examined to formulate a printable ink with optimal viscosity. The resultant film, enriched with OLE, exhibited a substantial polyphenolic content of 13.15 ± 0.41 mg CAE/g, showcasing significant antioxidant and anti-inflammatory properties. Notably, the film demonstrated potent scavenging abilities against DPPH, ABTS, and NO radicals, with IC50 values of 0.66 ± 0.07, 0.47 ± 0.04, and 2.02 ± 0.14 mg/mL, respectively. In vitro release and diffusion studies were carried out and the release profiles revealed an almost complete release of polyphenols from the patch within 48 h. Additionally, the fabricated film exhibited the capacity to enhance cell motility and accelerate wound healing, evidenced by increased collagen I expression in BJ fibroblast cells. Structural assessments affirmed the ability of the patch to absorb exudates and maintain the optimal moisture balance, while biocompatibility studies underscored its suitability for biomedical applications. These compelling findings endorse the potential application of the developed film in advanced wound care, with the prospect of tailoring patches to individual patient needs.

The 3D Printing of Nanocomposites for Wearable Biosensors: Recent Advances, Challenges, and Prospects

Notably, 3D-printed flexible and wearable biosensors have immense potential to interact with the human body noninvasively for the real-time and continuous health monitoring of physiological parameters. This paper comprehensively reviews the progress in 3D-printed wearable biosensors. The review also explores the incorporation of nanocomposites in 3D printing for biosensors. A detailed analysis of various 3D printing processes for fabricating wearable biosensors is reported. Besides this, recent advances in various 3D-printed wearable biosensors platforms such as sweat sensors, glucose sensors, electrocardiography sensors, electroencephalography sensors, tactile sensors, wearable oximeters, tattoo sensors, and respiratory sensors are discussed. Furthermore, the challenges and prospects associated with 3D-printed wearable biosensors are presented. This review is an invaluable resource for engineers, researchers, and healthcare clinicians, providing insights into the advancements and capabilities of 3D printing in the wearable biosensor domain.

Use of 3D Printing Techniques to Fabricate Implantable Microelectrodes for Electrochemical Detection of Biomarkers in the Early Diagnosis of Cardiovascular and Neurodegenerative Diseases

This Review provides a comprehensive overview of 3D printing techniques to fabricate implantable microelectrodes for the electrochemical detection of biomarkers in the early diagnosis of cardiovascular and neurodegenerative diseases. Early diagnosis of these diseases is crucial to improving patient outcomes and reducing healthcare systems' burden. Biomarkers serve as measurable indicators of these diseases, and implantable microelectrodes offer a promising tool for their electrochemical detection. Here, we discuss various 3D printing techniques, including stereolithography (SLA), digital light processing (DLP), fused deposition modeling (FDM), selective laser sintering (SLS), and two-photon polymerization (2PP), highlighting their advantages and limitations in microelectrode fabrication. We also explore the materials used in constructing implantable microelectrodes, emphasizing their biocompatibility and biodegradation properties. The principles of electrochemical detection and the types of sensors utilized are examined, with a focus on their applications in detecting biomarkers for cardiovascular and neurodegenerative diseases. Finally, we address the current challenges and future perspectives in the field of 3D-printed implantable microelectrodes, emphasizing their potential for improving early diagnosis and personalized treatment strategies.

Biomarkers as Biomedical Bioindicators: Approaches and Techniques for the Detection, Analysis, and Validation of Novel Biomarkers of Diseases

A biomarker is any measurable biological moiety that can be assessed and measured as a potential index of either normal or abnormal pathophysiology or pharmacological responses to some treatment regimen. Every tissue in the body has a distinct biomolecular make-up, which is known as its biomarkers, which possess particular features, viz., the levels or activities (the ability of a gene or protein to carry out a particular body function) of a gene, protein, or other biomolecules. A biomarker refers to some feature that can be objectively quantified by various biochemical samples and evaluates the exposure of an organism to normal or pathological procedures or their response to some drug interventions. An in-depth and comprehensive realization of the significance of these biomarkers becomes quite important for the efficient diagnosis of diseases and for providing the appropriate directions in case of multiple drug choices being presently available, which can benefit any patient. Presently, advancements in omics technologies have opened up new possibilities to obtain novel biomarkers of different types, employing genomic strategies, epigenetics, metabolomics, transcriptomics, lipid-based analysis, protein studies, etc. Particular biomarkers for specific diseases, their prognostic capabilities, and responses to therapeutic paradigms have been applied for screening of various normal healthy, as well as diseased, tissue or serum samples, and act as appreciable tools in pharmacology and therapeutics, etc. In this review, we have summarized various biomarker types, their classification, and monitoring and detection methods and strategies. Various analytical techniques and approaches of biomarkers have also been described along with various clinically applicable biomarker sensing techniques which have been developed in the recent past. A section has also been dedicated to the latest trends in the formulation and designing of nanotechnology-based biomarker sensing and detection developments in this field.

Implementation of 3D printing technologies to electrochemical and optical biosensors developed for biomedical and pharmaceutical analysis

Three-dimensional (3D) printing technology has been applied in many areas. In recent years, new generation biosensorshave been emerged with the progress on 3D printing technology (3DPT) . Especially in the development of optical and electrochemical biosensors, 3DPT provides many advantages such as low cost, easy to manufacturing, being disposable and allow point of care testing. In this review, recent trends in the development of 3DPT based electrochemical and optical biosensors with their applications in the field of biomedical and pharmaceutical are examined. In addition, the advantages, disadvantages and future opportunities of 3DPT are discussed.

Influence of instrument parameters on the electrochemical activity of 3D printed carbon thermoplastic electrodes

3D printing provides a reliable approach for the manufacture of carbon thermoplastic composite electrochemical sensors. Many studies have explored the impact of printing parameters on the electrochemical activity of carbon thermoplastic electrodes but limited is known about the influence of instrument parameters, which have been shown to alter the structure and mechanical strength of 3D printed thermoplastics. We explored the impact of extruder temperature, nozzle diameter and heated bed temperature on the electrochemical activity of carbon black/poly-lactic acid (CB/PLA) electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were conducted using standard redox probes. The electrode surface and cross-section of the electrode was visualised using scanning electron microscopy. We found that using extruder temperatures of 230 °C and 240 °C improved the electrochemical activity of CB/PLA electrodes, due to an increase in surface roughness and a reduction in the number of voids in-between print layers. Nozzle diameter, heated bed temperature of different 3D printers did not impact the electrochemical activity of CB/PLA electrodes. However high-end printers provide improved batch reproducibility of electrodes. These findings highlight the key instrument parameters that need to be considered when manufacturing carbon thermoplastic composite electrochemical sensors when using 3D printing.

A 3D-Printed Capacitive Smart Insole for Plantar Pressure Monitoring

Gait analysis refers to the systematic study of human locomotion and finds numerous applications in the fields of clinical monitoring, rehabilitation, sports science and robotics. Wearable sensors for real-time gait monitoring have emerged as an attractive alternative to the traditional clinical-based techniques, owing to their low cost and portability. In addition, 3D printing technology has recently drawn increased interest for the manufacturing of sensors, considering the advantages of diminished fabrication cost and time. In this study, we report the development of a 3D-printed capacitive smart insole for the measurement of plantar pressure. Initially, a novel 3D-printed capacitive pressure sensor was fabricated and its sensing performance was evaluated. The sensor exhibited a sensitivity of 1.19 MPa−1, a wide working pressure range (<872.4 kPa), excellent stability and durability (at least 2.280 cycles), great linearity (R2=0.993), fast response/recovery time (142−160 ms), low hysteresis (DH<10%) and the ability to support a broad spectrum of gait speeds (30−70 steps/min). Subsequently, 16 pressure sensors were integrated into a 3D-printed smart insole that was successfully applied for dynamic plantar pressure mapping and proven able to distinguish the various gait phases. We consider that the smart insole presented here is a simple, easy to manufacture and cost-effective solution with the potential for real-world applications.

Printed flexible mechanical sensors

Flexible mechanical sensors (e.g., strain, pressure, and force) fabricated primarily by printing technologies have emerged and evolved promptly in the past several years. 2D and 3D printing approaches enabled rapid prototyping of various flexible mechanical sensors that have demonstrated their unique applications in fields including robotics, human-machine interfaces, and biomedicine. Research efforts have primarily been focused on experimenting with different materials, device configurations, and sensing mechanisms to achieve better sensing performance. While great progress has been made, this field is still in its infancy where most research is exploratory; and even the performance standards and long-term objective/vision of these sensors are not clear. In this review, the state-of-the-art of three types of printed flexible mechanical sensors will be discussed and analyzed in terms of their fabrication methods, types of sensing materials and mechanisms, and challenges for future development.

A Comprehensive Review on Printed Electronics: A Technology Drift towards a Sustainable Future

Printable electronics is emerging as one of the fast-growing engineering fields with a higher degree of customization and reliability. Ironically, sustainable printing technology is essential because of the minimal waste to the environment. To move forward, we need to harness the fabrication technology with the potential to support traditional process. In this review, we have systematically discussed in detail the various manufacturing materials and processing technologies. The selection criteria for the assessment are conducted systematically on the manuscript published in the last 10 years (2012-2022) in peer-reviewed journals. We have discussed the various kinds of printable ink which are used for fabrication based on nanoparticles, nanosheets, nanowires, molecular formulation, and resin. The printing methods and technologies used for printing for each technology are also reviewed in detail. Despite the major development in printing technology some critical challenges needed to be addressed and critically assessed. One such challenge is the coffee ring effect, the possible methods to reduce the effect on modulating the ink environmental condition are also indicated. Finally, a summary of printable electronics for various applications across the diverse industrial manufacturing sector is presented.

Three-dimensional printing of smart constructs using stimuli-responsive biomaterials: A future direction of precision medicine

Three-dimensional (3D) printing, which is a valuable technique for the fabrication of tissue-engineered constructs and biomedical devices with complex architectures, has brought about considerable progress in regenerative medicine, drug delivery, and diagnosis of diseases. However, because of the static and inanimate properties of conventional 3D-printed structures, it is difficult to use them in therapies for active and precise medicine, such as improved tissue regeneration, targeted or controlled drug delivery, and advanced pathophysiological monitoring. The integration of stimuli-responsive biomaterials into 3D printing provides a potential strategy for designing and building smart constructs that exhibit programmed functions and controllable changes in properties in response to exogenous and autogenous stimuli. These features make 3D-printed smart constructs the next generation of tissue-engineered products. In this review, we introduce the prevalent 3D printing techniques (with an emphasis on the differences between 3D printing and bioprinting, and biomaterials and bioink), the working principle of each technique, and the advantages of using 3D printing for the fabrication of smart constructs. Stimuli-responsive biomaterials that are widely used for 3D printing of smart constructs are categorized, followed by a summary of their applications in tissue regeneration, drug delivery, and biosensors. Finally, the challenges and future perspectives of 3D-printed smart constructs are discussed.

Development of Phantoms for Multimodal Magnetic Resonance Imaging and Magnetic Particle Imaging

Phantoms are crucial for the development of imaging techniques based on magnetic nanoparticles (MNP). They serve as test objects to simulate application scenarios but are also used for quality assurance and interlaboratory comparisons. Magnetic particle imaging (MPI) is excellent for specifically detecting magnetic nanoparticles (MNP) without any background signals. To obtain information about the surrounding soft tissue, MPI is often used in combination with magnetic resonance imaging (MRI). For such application scenarios, this poses a challenge for phantom fabrication, as they need to accommodate MNP as well as provide MR visibility. Recently, layer-by-layer fabrication of parts using Additive Manufacturing (AM) has emerged as a powerful tool for creating complex and patient-specific phantoms, but these are characterized by poor MR visibility of the AM material. We present the systematic screening of AM materials as candidates for multimodal MRI/MPI imaging. Of all investigated materials, silicone (Dreve, Biotec) exhibited the best properties with sufficient MR-signal performance and the lowest absorption of MNP at the interface of AM materials. With the help of AM and the selection of appropriate materials, we have been able to produce suitable MRI/MPI phantoms.

Additive-Manufactured Platinum Thin-Film Strain Gauges for Structural Microstrain Testing at Elevated Temperatures

This paper investigates the feasibility and performance of the fabrication of platinum high-temperature thin-film strain sensors on nickel-based alloy substrates by additive manufacturing. The insulating layer was made of a dielectric paste by screen printing process. A 1.8-micron-thick platinum film was deposited directly on the insulating layer. The four-wire resistance measurement method was used to eliminate the contact resistance of the solder joints. Comprehensive morphological and electrical characterization of the platinum thin-film strain gauge was carried out, and good static and dynamic strain responses were obtained, which confirmed that the strain gauge was suitable for in situ strain monitoring of high-temperature complex components.

Three-Dimensional Printing and Its Potential to Develop Sensors for Cancer with Improved Performance

Cancer is the second leading cause of death globally and early diagnosis is the best strategy to reduce mortality risk. Biosensors to detect cancer biomarkers are based on various principles of detection, including electrochemical, optical, electrical, and mechanical measurements. Despite the advances in the identification of biomarkers and the conventional 2D manufacturing processes, detection methods for cancers still require improvements in terms of selectivity and sensitivity, especially for point-of-care diagnosis. Three-dimensional printing may offer the features to produce complex geometries in the design of high-precision, low-cost sensors. Three-dimensional printing, also known as additive manufacturing, allows for the production of sensitive, user-friendly, and semi-automated sensors, whose composition, geometry, and functionality can be controlled. This paper reviews the recent use of 3D printing in biosensors for cancer diagnosis, highlighting the main advantages and advances achieved with this technology. Additionally, the challenges in 3D printing technology for the mass production of high-performance biosensors for cancer diagnosis are addressed.

Advances in 3D Gel Printing for Enzyme Immobilization

Incorporating enzymes with three-dimensional (3D) printing is an exciting new field of convergence research that holds infinite potential for creating highly customizable components with diverse and efficient biocatalytic properties. Enzymes, nature’s nanoscale protein-based catalysts, perform crucial functions in biological systems and play increasingly important roles in modern chemical processing methods, cascade reactions, and sensor technologies. Immobilizing enzymes on solid carriers facilitates their recovery and reuse, improves stability and longevity, broadens applicability, and reduces overall processing and chemical conversion costs. Three-dimensional printing offers extraordinary flexibility for creating high-resolution complex structures that enable completely new reactor designs with versatile sub-micron functional features in macroscale objects. Immobilizing enzymes on or in 3D printed structures makes it possible to precisely control their spatial location for the optimal catalytic reaction. Combining the rapid advances in these two technologies is leading to completely new levels of control and precision in fabricating immobilized enzyme catalysts. The goal of this review is to promote further research by providing a critical discussion of 3D printed enzyme immobilization methods encompassing both post-printing immobilization and immobilization by physical entrapment during 3D printing. Especially, 3D printed gel matrix techniques offer mild single-step entrapment mechanisms that produce ideal environments for enzymes with high retention of catalytic function and unparalleled fabrication control. Examples from the literature, comparisons of the benefits and challenges of different combinations of the two technologies, novel approaches employed to enhance printed hydrogel physical properties, and an outlook on future directions are included to provide inspiration and insights for pursuing work in this promising field.

4D printing of soft orthoses for tremor suppression

Tremor is an involuntary and oscillatory movement disorder that makes daily activities difficult for affected patients. Hand tremor-suppression orthoses are noninvasive, wearable devices designed to mitigate tremors. Various studies have shown that these devices are effective, economical, and safe; however, they have drawbacks such as large weight, awkward shape, and rigid parts. This study investigates different types of tremor-suppression orthoses and discusses their efficiency, mechanism, benefits, and disadvantages. First, various orthoses (with passive, semi-active, and active mechanisms) are described in detail. Next, we look at how additive manufacturing (AM) has progressed recently in making sensors and actuators for application in tremor orthoses. Then, the materials used in AM are further analyzed. It is found that traditional manufacturing problems can be solved with the help of AM techniques, like making orthoses that are affordable, lighter, and more customizable. Another concept being discussed is using smart materials and AM methods, such as four-dimensional (4D) printing, to make orthoses that are more comfortable and efficient.

Graphic abstract

High-resolution deposition of conductive and insulating materials at micrometer scale on complex substrates

Additive manufacturing transforms the landscape of modern microelectronics. Recent years have witnessed significant progress in the fabrication of 2D planar structures and free-standing 3D architectures. In this work, we present a much-needed intermediary approach: we introduce the Ultra-Precise Deposition (UPD) technology, a versatile platform for material deposition at micrometer scale on complex substrates. The versality of this approach is related to three aspects: material to be deposited (conductive or insulating), shape of the printed structures (lines, dots, arbitrary shapes), as well as type and shape of the substrate (rigid, flexible, hydrophilic, hydrophobic, substrates with pre-existing features). The process is based on the direct, maskless deposition of high-viscosity materials using narrow printing nozzles with the internal diameter in the range from 0.5 to 10 µm. For conductive structures we developed highly concentrated non-Newtonian pastes based on silver, copper, or gold nanoparticles. In this case, the feature size of the printed structures is in the range from 1 to 10 µm and their electrical conductivity is up to 40% of the bulk value, which is the record conductivity for metallic structures printed with spatial resolution below 10 µm. This result is the effect of the synergy between the printing process itself, formulation of the paste, and the proper sintering of the printed structures. We demonstrate a pathway to print such fine structures on complex substrates. We argue that this versatile and stable process paves the way for a widespread use of additive manufacturing for microfabrication.

A comparison of trueness and precision of 12 3D printers used in dentistry

Introduction

Judging the dimensional accuracy of the resulting printed part requires comparison and conformity between the 3D printed model and its virtual counterpart. The resolution and accuracy of 3D model samples are determined by a wide array of factors depending on the technology used and related factors such as the print head/laser spot size/screen resolution, build orientation, materials, geometric features, and their topology.

Aims

The aim of this manuscript is to present a literature review on 12 3D printers, namely the Ackuretta Sol, Anycubic Photon and Photon S, Asiga Max UV, Elegoo Mars, Envisiontec Vida HD, Envisiontec One, Envisiontec D4K Pro, Formlabs Form 2 and Form 3, Nextdent 5100, and Planmeca Creo, studying the accuracy of these printers that are of a wide variety of budgets.

Design

The present study involves some of the recently released 3D printers that have not yet been studied for their accuracy. Since these new printers will replace current models that may have been included in the previous studies in the literature, it is important to study whether they are statistically more or less accurate and to discuss whether these results are clinically relevant. For the purposes of this study, the use of a standardised printable object was used to measure the accuracy of these recent 3D printers.

Materials and methods

In total, 12 3D printers produced test blocks. All test blocks were printed using the same settings with 100 micron Z layer thickness and the print time set to standard where applicable. To measure the resulting blocks a digital measurement was taken using a Dentsply Sirona Ineos X5 lab scanner to measure the XYZ dimensions of each block produced on each printer using CloudCompare to measure the deviation compared to the Master STL. Each measurement was taken from the central axis of that dimension.

Results

When grouped into homogenous subsets, the cheapest 3D printers in the group, namely the Anycubic printers and the Elegoo Mars, are statistically not dissimilar to the higher priced Asiga Max UV or even the mid-priced Formlabs printers in the X and Z dimensions. However, the Envisiontec One and D4K Pro, Ackuretta Sol and Asiga Max UV were statistically superior in terms of consistently accurate Y dimension. Although these printers use different technologies to print, no specific type of printer technology is more accurate than the others.

Discussion

The null hypothesis was proved to be true, in that no significant differences were found among the various technologies of 3D printing regarding trueness and precision. The evolution of 3D printers that leads to budget printers being as statistically accurate, for at least two of the dimensions of data recorded, as expensive printers is remarkable. Whilst clear differences in the mean error between the printers were found, the performance of these printers is considered exceptional. Albeit, the Envision One, Envision D4K, Ackuretta Sol and Asiga Max UV printers performed the best with overall trueness under 35 μm.

Conclusion

This study shows that the current range of 3D printers can produce clinically acceptable levels of accuracy. The present study also shows that there is no statistical difference in the results of budget printers and more expensive printers for the X and Z dimensions but this was not the case for the measurements in the Y dimension. This study confirms that all of the 3D printers can produce a reliable, reproducible model.

A Critical Review of Additive Manufacturing Techniques and Associated Biomaterials Used in Bone Tissue Engineering

With the ability to fabricate complex structures while meeting individual needs, additive manufacturing (AM) offers unprecedented opportunities for bone tissue engineering in the biomedical field. However, traditional metal implants have many adverse effects due to their poor integration with host tissues, and therefore new material implants with porous structures are gradually being developed that are suitable for clinical medical applications. From the perspectives of additive manufacturing technology and materials, this article discusses a suitable manufacturing process for ideal materials for biological bone tissue engineering. It begins with a review of the methods and applicable materials in existing additive manufacturing technologies and their applications in biomedicine, introducing the advantages and disadvantages of various AM technologies. The properties of materials including metals and polymers, commonly used AM technologies, recent developments, and their applications in bone tissue engineering are discussed in detail and summarized. In addition, the main challenges for different metallic and polymer materials, such as biodegradability, anisotropy, growth factors to promote the osteogenic capacity, and enhancement of mechanical properties are also introduced. Finally, the development prospects for AM technologies and biomaterials in bone tissue engineering are considered.

Low-cost and rapid prototyping of integrated electrochemical microfluidic platforms using consumer-grade off-the-shelf tools and materials

We present a low-cost, accessible, and rapid fabrication process for electrochemical microfluidic sensors. This work leverages the accessibility of consumer-grade electronic craft cutters as the primary tool for patterning of sensor electrodes and microfluidic circuits, while commodity materials such as gold leaf, silver ink pen, double-sided tape, plastic transparency films, and fabric adhesives are used as its base structural materials. The device consists of three layers, the silver reference electrode layer at the top, the PET fluidic circuits in the middle and the gold sensing electrodes at the bottom. Separation of the silver reference electrode from the gold sensing electrodes reduces the possibility of cross-contamination during surface modification. A novel approach in mesoscale patterning of gold leaf electrodes can produce generic designs with dimensions as small as 250 μm. Silver electrodes with dimensions as small as 385 μm were drawn using a plotter and a silver ink pen, and fluid microchannels as small as 300 μm were fabricated using a sandwich of iron-on adhesives and PET. Device layers are then fused together using an office laminator. The integrated microfluidic electrochemical platform has electrode kinetics/performance of ΔE_p = 91.3 mV, I_pa/I_pc = 0.905, characterized by cyclic voltammetry using a standard ferrocyanide redox probe, and this was compared against a commercial screen-printed gold electrode (ΔE_p = 68.9 mV, I_pa/I_pc = 0.984). To validate the performance of the integrated microfluidic electrochemical platform, a catalytic hydrogen peroxide sensor and enzyme-coupled glucose biosensors were developed as demonstrators. Hydrogen peroxide quantitation achieves a limit of detection of 0.713 mM and sensitivity of 78.37 μA mM^-1 cm^-2, while glucose has a limit of detection of 0.111 mM and sensitivity of 12.68 μA mM^-1 cm^-2. This rapid process allows an iterative design-build-test cycle in under 2 hours. The upfront cost to set up the system is less than USD 520, with each device costing less than USD 0.12, making this manufacturing process suitable for low-resource laboratories or classroom settings.

Materials for Implantable Surface Electrode Arrays: Current Status and Future Directions

Surface electrode arrays are mainly fabricated from rigid or elastic materials, and precisely manipulated ductile metal films, which offer limited stretchability. However, the living tissues to which they are applied are nonlinear viscoelastic materials, which can undergo significant mechanical deformation in dynamic biological environments. Further, the same arrays and compositions are often repurposed for vastly different tissues rather than optimizing the materials and mechanical properties of the implant for the target application. By first characterizing the desired biological environment, and then designing a technology for a particular organ, surface electrode arrays may be more conformable, and offer better interfaces to tissues while causing less damage. Here, the various materials used in each component of a surface electrode array are first reviewed, and then electrically active implants in three specific biological systems, the nervous system, the muscular system, and skin, are described. Finally, the fabrication of next-generation surface arrays that overcome current limitations is discussed.

Review on Microscale Sensors with 3D Engineered Structures: Fabrication and Applications

The intelligence of modern technologies relies on perceptual systems based on microscale sensors. However, because of the traditional top-down fabrication approaches performed on planar silicon wafers, a large proportion of existing microscale sensors have 2D structures, which severely restricts their sensing capabilities. To overcome these restrictions, over the past few decades, increasing efforts have been devoted to developing new fabrication methods for microscale sensors with 3D engineered structures, from bulk chemical etching and 3D printing to molding and stress-induced assembly. Herein, the authors systematically review these fabrication methods based on the applications of the resulting 3D sensors and discuss their advantages compared to their 2D counterparts. This is followed by a perspective on the remaining challenges and possible opportunities.

Material Design for Enhancing Properties of 3D Printed Polymer Composites for Target Applications

Polymer composites are becoming an important class of materials for a diversified range of industrial applications due to their unique characteristics and natural and synthetic reinforcements. Traditional methods of polymer composite fabrication require machining, manual labor, and increased costs. Therefore, 3D printing technologies have come to the forefront of scientific, industrial, and public attention for customized manufacturing of composite parts having a high degree of control over design, processing parameters, and time. However, poor interfacial adhesion between 3D printed layers can lead to material failure, and therefore, researchers are trying to improve material functionality and extend material lifetime with the addition of reinforcements and self-healing capability. This review provides insights on different materials used for 3D printing of polymer composites to enhance mechanical properties and improve service life of polymer materials. Moreover, 3D printing of flexible energy-storage devices (FESD), including batteries, supercapacitors, and soft robotics using soft materials (polymers), is discussed as well as the application of 3D printing as a platform for bioengineering and earth science applications by using a variety of polymer materials, all of which have great potential for improving future conditions for humanity and planet Earth.

The Automatic Design of Multimode Resonator Topology with Evolutionary Algorithms

Microwave electromagnetic devices have been used for many applications in tropospheric communication, navigation, radar systems, and measurement. The development of the signal preprocessing units including frequency-selective devices (bandpass filters) determines the reliability and usability of such systems. In wireless sensor network nodes, filters with microstrip resonators are widely used to improve the out-of-band suppression and frequency selectivity. Filters based on multimode microstrip resonators have an order that determines their frequency-selective properties, which is a multiple of the number of resonators. That enables us to reduce the size of systems without deteriorating their selective properties. Various microstrip multimode resonator topologies can be used for both filters and microwave sensors, however, the quality criteria for them may differ. The development of every resonator topology is time consuming. We propose a technique for the automatic generation of the resonator topology with required frequency characteristics based on the use of evolutionary algorithms. The topology is encoded into a set of real valued parameters, which are varied to achieve the desired features. The differential evolution algorithm and the genetic algorithm with simulated binary crossover and polynomial mutation are applied to solve the formulated problem using the dynamic penalties method. The experimental results show that our technique enables us to find microstrip resonator topologies with desired amplitude-frequency characteristics automatically, and manufactured devices demonstrate characteristics very close to the results of the algorithm. The proposed algorithmic approach may be used for automatically exploring the new perspective topologies of resonators used in microwave filters, radar antennas or sensors, in accordance with the defined criteria and constraints.

3D Printing Technologies in Biosensors Production: Recent Developments

Recent advances in 3D printing technologies and materials have enabled rapid development of innovative sensors for applications in different aspects of human life. Various 3D printing technologies have been adopted to fabricate biosensors or some of their components thanks to the advantages of these methodologies over the traditional ones, such as end-user customization and rapid prototyping. In this review, the works published in the last two years on 3D-printed biosensors are considered and grouped on the basis of the 3D printing technologies applied in different fields of application, highlighting the main analytical parameters. In the first part, 3D methods are discussed, after which the principal achievements and promising aspects obtained with the 3D-printed sensors are reported. An overview of the recent developments on this current topic is provided, as established by the considered works in this multidisciplinary field. Finally, future challenges on the improvement and innovation of the 3D printing technologies utilized for biosensors production are discussed.

Vibration Fatigue of FDM 3D Printed Structures: The Use of Frequency Domain Approach

Additive manufactured structures are replacing the corresponding ones realized with classical manufacturing technique. As for metallic structures, 3D printed components are generally subjected to dynamic loading conditions which can lead to fatigue failure. In this context, it is useful, and sometimes mandatory, to determine the fatigue life of such components through numerical simulation. The methods currently available in literature for the estimation of fatigue life were originally developed for metallic structures and, therefore, it is now necessary to verify their applicability also for components fabricated with different materials. To this end, in the current activity three of the most used spectral methods for the estimation of fatigue life were used to determine the fatigue life of a 3D printed Y-shaped specimen realized in polylactic acid subjected to random loads with the aim of determining their adaptability also for this kind of materials. To certify the accuracy of the numerical prediction, a set of experimental tests were conducted in order to obtain the real fatigue life of the component and to compare the experimental results with those numerically obtained. The obtained outcomes showed there is an excellent match between the numerical and the experimental data, thus certifying the possibility of using the investigated spectral methods to predict the fatigue life of additive manufactured components.

Scaffolds in Periodontal Regenerative Treatment

Successful periodontal regeneration requires the hierarchical reorganization of multiple tissues including periodontal ligament, cementum, alveolar bone, and gingiva. The limitation of conventional regenerative therapies has been attracting research interest in tissue engineering-based periodontal therapies where progenitor cells, scaffolds, and bioactive molecules are delivered. Scaffolds offer not only structural support but also provide geometrical clue to guide cell fate. Additionally, functionalization improves bioactive properties to the scaffold. Various scaffold designs have been proposed for periodontal regeneration. These include the fabrication of biomimetic periodontal extracellular matrix, multiphasic scaffolds with tissue-specific layers, and personalized 3D printed scaffolds. This review summarizes the basic concept as well as the recent advancement of scaffold designing and fabrication for periodontal regeneration and provides an insight of future clinical translation.

3D-Printed Liquid Cell Resonator with Piezoelectric Actuation for In-Line Density-Viscosity Measurements

The in-line monitoring of liquid properties, such as density and viscosity, is a key process in many industrial areas such as agro-food, automotive or biotechnology, requiring real-time automation, low-cost and miniaturization, while maintaining a level of accuracy and resolution comparable to benchtop instruments. In this paper, 3D-printed cuboid-shaped liquid cells featuring a rectangular vibrating plate in one of the sides, actuated by PZT piezoelectric layers, were designed, fabricated and tested. The device was resonantly excited in the 3rd-order roof tile-shaped vibration mode of the plate and validated as a density-viscosity sensor. Furthermore, conditioning circuits were designed to adapt the impedance of the resonator and to cancel parasitic effects. This allowed us to implement a phase-locked loop-based oscillator circuit whose oscillation frequency and voltage amplitude could be calibrated against density and viscosity of the liquid flowing through the cell. To demonstrate the performance, the sensor was calibrated with a set of artificial model solutions of grape must, representing stages of a wine fermentation process. Our results demonstrate the high potential of the low-cost sensor to detect the decrease in sugar and the increase in ethanol concentrations during a grape must fermentation, with a resolution of 10 µg/mL and 3 µPa·s as upper limits for the density and viscosity, respectively.

Reviews on Machine Learning Approaches for Process Optimization in Noncontact Direct Ink Writing

Recently, machine learning has gained considerable attention in noncontact direct ink writing because of its novel process modeling and optimization techniques. Unlike conventional fabrication approaches, noncontact direct ink writing is an emerging 3D printing technology for directly fabricating low-cost and customized device applications. Despite possessing many advantages, the achieved electrical performance of produced microelectronics is still limited by the printing quality of the noncontact ink writing process. Therefore, there has been increasing interest in the machine learning for process optimization in the noncontact direct ink writing. Compared with traditional approaches, despite machine learning-based strategies having great potential for efficient process optimization, they are still limited to optimize a specific aspect of the printing process in the noncontact direct ink writing. Therefore, a systematic process optimization approach that integrates the advantages of state-of-the-art machine learning techniques is in demand to fully optimize the overall printing quality. In this paper, we systematically discuss the printing principles, key influencing factors, and main limitations of the noncontact direct ink writing technologies based on inkjet printing (IJP) and aerosol jet printing (AJP). The requirements for process optimization of the noncontact direct ink writing are classified into four main aspects. Then, traditional methods and the state-of-the-art machine learning-based strategies adopted in IJP and AJP for process optimization are reviewed and compared with pros and cons. Finally, to further develop a systematic machine learning approach for the process optimization, we highlight the major limitations, challenges, and future directions of the current machine learning applications.

Additive Manufacturing as a Means of Gas Sensor Development for Battery Health Monitoring

Lithium-ion batteries (LIBs) still need continuous safety monitoring based on their intrinsic properties, as well as due to the increase in their sizes and device requirements. The main causes of fires and explosions in LIBs are heat leakage and the presence of highly inflammable components. Therefore, it is necessary to improve the safety of the batteries by preventing the generation of these gases and/or their early detection with sensors. The improvement of such safety sensors requires new approaches in their manufacturing. There is a growing role for research of nanostructured sensor’s durability in the field of ionizing radiation that also can induce structural changes in the LIB’s component materials, thus contributing to the elucidation of fundamental physicochemical processes; catalytic reactions or inhibitions of the chemical reactions on which the work of the sensors is based. A current method widely used in various fields, Direct Ink Writing (DIW), has been used to manufacture heterostructures of Al2O3/CuO and CuO:Fe2O3, followed by an additional ALD and thermal annealing step. The detection properties of these 3D-DIW printed heterostructures showed responses to 1,3-dioxolan (DOL), 1,2-dimethoxyethane (DME) vapors, as well as to typically used LIB electrolytes containing LiTFSI and LiNO3 salts in a mixture of DOL:DME, as well also to LiPF6 salts in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) at operating temperatures of 200 °C–350 °C with relatively high responses. The combination of the possibility to detect electrolyte vapors used in LIBs and size control by the 3D-DIW printing method makes these heterostructures extremely attractive in controlling the safety of batteries.

Recent developments in sensors for wearable device applications

Wearable devices are a new means of human-computer interaction with different functions, underlying principles, and forms. They have been widely used in the medical and health fields, in applications including physiological signal monitoring; sports; and environmental detection, while subtly affecting people's lives and work. Wearable sensors as functional components of wearable devices have become a research focus. In this review, we systematically summarize recent progress in the development of wearable sensors and related devices. Wearable sensors in medical health applications, according to the principle of measurement, are divided into physical and chemical quantity detection. These sensors can monitor and measure specific parameters, thereby enabling continuously improvements in the quality and feasibility of medical treatment. Through the detection of human movement, such as breathing, heartbeat, or bending, wearable sensors can evaluate body movement and monitor an individual's physical performance and health status. Wearable devices detecting aspects of the environment while maintaining high adaptability to the human body can be used to evaluate environmental quality and obtain more accurate environmental information. The ultimate goal of this review is to provide new insights and directions for the future development and broader application of wearable devices in various fields.Graphical abstract.

Tunable In Situ 3D-Printed PVDF-TrFE Piezoelectric Arrays

In the functional 3D-printing field, poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) has been shown to be a more promising choice of material over polyvinylidene fluoride (PVDF), due to its ability to be poled to a high level of piezoelectric performance without a large mechanical strain ratio. In this work, a novel presentation of in situ 3D printing and poling of PVDF-TrFE is shown with a d33 performance of up to 18 pC N−1, more than an order of magnitude larger than previously reported in situ poled polymer piezoelectrics. This finding paves the way forward for pressure sensors with much higher sensitivity and accuracy. In addition, the ability of in situ pole sensors to demonstrate different performance levels is shown in a fully 3D-printed five-element sensor array, accelerating and increasing the design space for complex sensing arrays. The in situ poled sample performance was compared to the performance of samples prepared through an ex situ corona poling process.

Fabrication of Microfluidic Devices for Emulsion Formation by Microstereolithography

Droplet microfluidics—the art and science of forming droplets—has been revolutionary for high-throughput screening, directed evolution, single-cell sequencing, and material design. However, traditional fabrication techniques for microfluidic devices suffer from several disadvantages, including multistep processing, expensive facilities, and limited three-dimensional (3D) design flexibility. High-resolution additive manufacturing—and in particular, projection micro-stereolithography (PµSL)—provides a promising path for overcoming these drawbacks. Similar to polydimethylsiloxane-based microfluidics 20 years ago, 3D printing methods, such as PµSL, have provided a path toward a new era of microfluidic device design. PµSL greatly simplifies the device fabrication process, especially the access to truly 3D geometries, is cost-effective, and it enables multimaterial processing. In this review, we discuss both the basics and recent innovations in PµSL; the material basis with emphasis on custom-made photopolymer formulations; multimaterial 3D printing; and, 3D-printed microfluidic devices for emulsion formation as our focus application. Our goal is to support researchers in setting up their own PµSL system to fabricate tailor-made microfluidics.

Temperature Measurement at Curved Surfaces Using 3D Printed Planar Resistance Temperature Detectors

In this article, novel 3D printed sensors for temperature measurement are presented. A planar structure of the resistive element is made, utilizing paths of a conductive filament embedded in an elastic base. Both electrically conductive and flexible filaments are used simultaneously during the 3D printing procedure, to form a ready–to–use measuring device. Due to the achieved flexibility, the detectors may be used on curved and irregular surfaces, with no concern for their possible damage. The geometry and properties of the proposed resistance detectors are discussed, along with a printing procedure. Numerical models of considered sensors are characterized, and the calculated current distributions as well as equivalent resistances of the different structures are compared. Then, a nonlinear influence of temperature on the resistance is experimentally determined for the exemplary planar sensors. Based on these results, using first–order and hybrid linear–exponential approximations, the analytical formulae are derived. Additionally, the device to measure an average temperature from several measuring surfaces is considered. Since geometry of the sensor can be designed utilizing presented approach and printed by applying fused deposition modeling, the functional device can be customized to individual needs.

Additive Manufacturing of Sensors for Military Monitoring Applications

The US Department of Defense (DoD) realizes the many uses of additive manufacturing (AM) as it has become a common fabrication technique for an extensive range of engineering components in several industrial sectors. 3D Printed (3DP) sensor technology offers high-performance features as a way to track individual warfighters on the battlefield, offering protection from threats such as weaponized toxins, bacteria or virus, with real-time monitoring of physiological events, advanced diagnostics, and connected feedback. Maximum protection of the warfighter gives a distinct advantage over adversaries by providing an enhanced awareness of situational threats on the battle field. There is a need to further explore aspects of AM such as higher printing resolution and efficiency, with faster print times and higher performance, sensitivity and optimized fabrication to ensure that soldiers are more safe and lethal to win our nation's wars and come home safely. A review and comparison of various 3DP techniques for sensor fabrication is presented.

Electrochemical Detection of Glucose Molecules Using Laser-Induced Graphene Sensors: A Review

This paper deals with recent progress in the use of laser-induced graphene sensors for the electrochemical detection of glucose molecules. The exponential increase in the exploitation of the laser induction technique to generate porous graphene from polymeric and other naturally occurring materials has provided a podium for researchers to fabricate flexible sensors with high dynamicity. These sensors have been employed largely for electrochemical applications due to their distinct advantages like high customization in their structural dimensions, enhanced characteristics and easy roll-to-roll production. These laser-induced graphene (LIG)-based sensors have been employed for a wide range of sensorial applications, including detection of ions at varying concentrations. Among the many pivotal electrochemical uses in the biomedical sector, the use of these prototypes to monitor the concentration of glucose molecules is constantly increasing due to the essentiality of the presence of these molecules at specific concentrations in the human body. This paper shows a categorical classification of the various uses of these sensors based on the type of materials involved in the fabrication of sensors. The first category constitutes examples where the electrodes have been functionalized with various forms of copper and other types of metallic nanomaterials. The second category includes other miscellaneous forms where the use of both pure and composite forms of LIG-based sensors has been shown. Finally, the paper concludes with some of the possible measures that can be taken to enhance the use of this technique to generate optimized sensing prototypes for a wider range of applications.

Mechanical Properties of FDM Printed PLA Parts before and after Thermal Treatment

Fused deposition modeling (FDM) is one of the most often-used technologies in additive manufacturing. Several materials are used with this technology, such as poly(lactic acid) (PLA), which is most commonly applied. The mechanical properties of 3D-printed parts depend on the process parameters. This is why, in this study, three-point bending tests were carried out to characterize the influence of build orientation, layer thickness, printing temperature and printing speed on the mechanical properties of PLA samples. Not only the process parameters may affect the mechanical properties, but heat after-treatment also has an influence on them. For this reason, additional samples were printed with optimal process parameters and characterized after pure heat treatment as well as after deformation at a temperature above the glass transition temperature, cooling with applied deformation, and subsequent recovery under heat treatment. These findings are planned to be used in a future study on finger orthoses that could either be printed according to shape or in a flat shape and afterwards heated and bent around the finger.

3D-Printed Microfluidics and Potential Biomedical Applications

3D printing is a smart additive manufacturing technique that allows the engineering of biomedical devices that are usually difficult to design using conventional methodologies such as machining or molding. Nowadays, 3D-printed microfluidics has gained enormous attention due to their various advantages including fast production, cost-effectiveness, and accurate designing of a range of products even geometrically complex devices. In this review, we focused on the recent significant findings in the field of 3D-printed microfluidic devices for biomedical applications. 3D printers are used as fabrication tools for a broad variety of systems for a range of applications like diagnostic microfluidic chips to detect different analytes, for example, glucose, lactate, and glutamate and the biomarkers related to different clinically relevant diseases, for example, malaria, prostate cancer, and breast cancer. 3D printers can print various materials (inorganic and polymers) with varying density, strength, and chemical properties that provide users with a broad variety of strategic options. In this article, we have discussed potential 3D printing techniques for the fabrication of microfluidic devices that are suitable for biomedical applications. Emerging diagnostic technologies using 3D printing as a method for integrating living cells or biomaterials into 3D printing are also reviewed.