Advanced Material Strategies for Next-Generation Additive Manufacturing

Injectable antioxidant hyaluronan/chitosan hydrogel as a platelet-rich plasma and stem cell carrier to promote endometrial regeneration and fertility restoration

Severe damage to the uterine endometrium can lead to thin endometrium and intrauterine adhesions (IUAs), resulting in infertility or complications during pregnancy. Therapies utilizing mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP) represent promising strategies for restoring thin endometrium. However, the low homing rate and functionality of transplanted cells, along with the rapid release of PRP growth factors, limit their therapeutic efficacy. In this study, we developed an in-situ formable and redox-responsive hydrogel composed of thiolated hyaluronan (tHA) and thiolated chitosan (tChi) (tHA-tChi) for encapsulating PRP and mouse adipose-derived stem cells (ADSCs). Our results demonstrate that the tHA-tChi hydrogel exhibits appropriate swelling, injectability, self-healing, and antioxidant properties, alongside a sustained release of PRP growth factors. In vitro experiments indicated that the PRP and ADSCs encapsulated within the hydrogel (ADSCs/tHA-tChi/PRP) stimulated angiogenesis in endothelial cells. In a mouse model of thin endometrium, the ADSCs/tHA-tChi/PRP significantly enhanced endometrial regeneration, as evidenced by increased endometrial thickness and reduced fibrosis. This improvement markedly enhanced endometrial receptivity and pregnancy rates in damaged endometria, correlating with increased angiogenesis and endometrial cell proliferation via activation of the VEGF/AKT/BAD pathway, as shown by Western blotting assays. Overall, the combination of antioxidant hydrogel, PRP, and ADSCs demonstrates promising potential for promoting endometrial regeneration and restoring fertility, offering new minimally invasive therapeutic options for endometrial diseases. STATEMENT OF SIGNIFICANCE: This research presents a potent approach to the treatment of thin endometrium, employing an injectable, biodegradable and antioxidant hydrogel comprising thiolated hyaluronic acid (tHA) and thiolated chitosan (tChi). The antioxidant capacity of the hydrogel improves the oxidative microenvironment of the injured uterus, while the hydrogel is designed to release adipose-derived stem cells (ADSCs) and growth factors from platelet-rich plasma (PRP) sustainably, promoting tissue regeneration by enhancing angiogenesis and endometrium cell proliferation. Demonstrated efficacy in a mouse model of thin endometrium indicates its great potential to significantly improve fertility restoration treatments. The administration of antioxidant hydrogel containing ADSCs and PRP represents a promising therapeutic strategy for patients with endometrial disease.

Fracture resistance, marginal and internal adaptation of innovative 3D-printed graded structure crown using a 3D jet printing technology

PURPOSE

This in vitro study aimed to create a graded structured dental crown using 3D printing technology and investigate the fracture resistance and the adaptation of this new design.

MATERIALS AND METHODS

A dental crown with a uniform thickness of 1.5 mm was designed, and the exported stereolithography file (STL) was used to manufacture 30 crowns in three groups (n = 10), solid (SC), bilayer (BL), and multilayer (ML) crowns using  3D jet printing technology. Marginal and internal gaps were measured using the silicone replica technique. Crowns were then luted to a resin die using a temporary luting agent and the fracture resistance was measured using a universal testing machine. One-way ANOVA and Tukey post hoc tests were used to compare the fracture resistance and the adaptation of crowns at a significance level of 0.05.

RESULTS

Mean marginal and internal gap of the ML group were 80 and 82 mm, respectively; which were significantly (p < 0.05) smaller than BL (203 and 183 mm) and SC (318 and 221 mm) groups. The SC group showed the highest mean load at fracture (2330 N) which was significantly (p < 0.05) higher than the BL (1716 N) and ML (1516 N) groups.

CONCLUSION

3D jet printing technology provides an opportunity to manufacture crowns in a graded structure with various mechanical properties. This study provided an example of graded structured crowns and presented their fracture resistance. SC group had the highest fracture resistance; however, ML had the best marginal and internal adaptation.

Effects of Using Laser Technology for Cutting Polymer Films

In connection with the need to obtain a properly made and cut material and the appearance of the surface layer, new manufacturing technologies were used for tests, namely the laser cutting technology. This article describes the laboratory stand built for the purpose of research, as well as the possibility of using laser cutting on several sample materials (polymer films), together with an indication of the results obtained. The idea was to elaborate on the cutting technology that will be proper for manufacturing the desired type of spacers for ion-exchange membranes separating while maintaining the required level of product quality and chemical purity. The latter criterion was the basic one, due to the scope of use of the manufactured elements. This article also describes the problem encountered during the construction of the stand or during the research. The last part of this article describes the further steps of the research that will be carried out in the future along with a discussion and summary of the research performed. It is important from the point of view of the development of production technology, but also because of the characteristics of materials for the production of surface layers and coatings resistant to mechanical or thermal wear used in industry. The introduction of innovative solutions is also aimed at studying the improvement of the economics of the production of materials that are significant, in particular, for small- and medium-sized enterprises.

Intelligent Optimization Method of Piezoelectric Ejection System Design Based on Finite Element Simulation and Neural Network

This study describes an intelligent method for modeling and optimization of piezoelectric ejection system design for additive manufacturing. It is a combination of neural network (NN) techniques and finite element simulation (FES) that allows designing each parameter of a piezoelectric ejection system faster and more reliably than conventional methods. Using experimental and literature data, a FE model of the droplet ejection process was developed and validated to predict two indexes of droplet ejection behavior (DEB): jetting velocity and droplet diameter. Two artificial neural network (ANN) models based on feed-forward back propagation were developed and optimized by genetic algorithm (GA). A database was established by FE calculations, and the models were trained to establish the relationship between the piezoelectric ejection system design input parameters and each DEB indicator. The results show that both NN models can independently predict the droplet jetting velocity and droplet diameter values from the training and testing data with high accuracy to determine the optimal piezoelectric ejection system design. Finally, the accuracy of the prediction results of the FES and ANN-GA models was verified experimentally. It was found that the errors between the predicted and experimental results were 4.48% and 3.18% for the jetting velocity and droplet diameter, respectively, verifying that the optimization method is reliable and robust for piezoelectric ejection system design optimization.

Multijet Gold Nanoparticle Inks for Additive Manufacturing of Printed and Wearable Electronics

Conductive and biofriendly gold nanomaterial inks are highly desirable for printed electronics, biosensors, wearable electronics, and electrochemical sensor applications. Here, we demonstrate the scalable synthesis of stable gold nanoparticle inks with low-temperature sintering using simple chemical processing steps. Multiprinter compatible aqueous gold nanomaterial inks were formulated, achieving resistivity as low as ∼10-6 Ω m for 400 nm thick films sintered at 250 °C. Printed lines with a resolution of <20 μm and minimal overspray were obtained using an aerosol jet printer. The resistivity of the printed patterns reached ∼9.59 ± 1.2 × 10-8 Ω m after sintering at 400 °C for 45 min. Our aqueous-formulated gold nanomaterial inks are also compatible with inkjet printing, extending the design space and manufacturability of printed and flexible electronics where metal work functions and chemically inert films are important for device applications.

The Art of Building Living Tissues: Exploring the Frontiers of Biofabrication with 3D Bioprinting

The scope of three-dimensional printing is expanding rapidly, with innovative approaches resulting in the evolution of state-of-the-art 3D bioprinting (3DbioP) techniques for solving issues in bioengineering and biopharmaceutical research. The methods and tools in 3DbioP emphasize the extrusion process, bioink formulation, and stability of the bioprinted scaffold. Thus, 3DbioP technology augments 3DP in the biological world by providing technical support to regenerative therapy, drug delivery, bioengineering of prosthetics, and drug kinetics research. Besides the above, drug delivery and dosage control have been achieved using 3D bioprinted microcarriers and capsules. Developing a stable, biocompatible, and versatile bioink is a primary requisite in biofabrication. The 3DbioP research is breaking the technical barriers at a breakneck speed. Numerous techniques and biomaterial advancements have helped to overcome current 3DbioP issues related to printability, stability, and bioink formulation. Therefore, this Review aims to provide an insight into the technical challenges of bioprinting, novel biomaterials for bioink formulation, and recently developed 3D bioprinting methods driving future applications in biofabrication research.

Application of 4D printing and bioprinting in cardiovascular tissue engineering

Cardiovascular diseases have remained the leading cause of death worldwide for the past 20 years. The current clinical therapeutic measures, including bypass surgery, stent implantation and pharmacotherapy, are not enough to repair the massive loss of cardiomyocytes after myocardial ischemia. Timely replenishment with functional myocardial tissue via biomedical engineering is the most direct and effective means to improve the prognosis and survival rate of patients. It is widely recognized that 4D printing technology introduces an additional dimension of time in comparison with traditional 3D printing. Additionally, in the context of 4D bioprinting, both the printed material and the resulting product are designed to be biocompatible, which will be the mainstream of bioprinting in the future. Thus, this review focuses on the application of 4D bioprinting in cardiovascular diseases, discusses the bottleneck of the development of 4D bioprinting, and finally looks forward to the future direction and prospect of this revolutionary technology.

Bioactive Injectable and Self-Healing Hydrogel Via Cell-Free Fat Extract for Endometrial Regeneration

The damaged endometrium and the formation of fibrosis are key barriers to pregnancy and further lead to infertility. However, how to promote endometrium repair is always a challenge. Here, a bioactive injectable and self-healing hydrogel is developed by physically combination of thiolated polyethylene (PEG), Cu²⁺ and cell-free fat extract (CEFFE, CF) for endometrial regeneration and fertility. By inheriting the advantages of various active proteins contained in CEFFE, it could induce the overall repair of endometrial microenvironment for intrauterine adhesion (IUA). In vitro, CF@Cu-PEG reduces endometrial cell apoptosis by more than 50%, and increases angiogenesis by 92.8%. In the IUA mouse, injection of CF@Cu-PEG significantly reduces the rate of uterine hydrometra and prevents the formation of endometrial fibrosis. Remarkably, CF@Cu-PEG contributes to the repair of endometrial microstructure, especially increases the number of endometrial pinopodes, significantly improves endometrial receptivity, and increases the pregnancy rate of IUA mice from 7.14% to 66.67%. In summary, through the physically combination of CEFFE and Cu-PEG, the construction of loaded bioactive injectable hydrogel not only inhibits the IUA, but also induces the self-repair of endometrial cells in situ and improves fertility, providing a new strategy for IUA repair in clinical application.

Intelligent geometry compensation for additive manufactured oral maxillary stent by genetic algorithm and backpropagation network

Recently, laser powder bed fusion (LPBF) has shown great potential in advanced manufacturing. However, the rapid melting and re-solidification of the molten pool in LPBF leads to the distortion of parts, especially thin-walled parts. The traditional geometric compensation method, which is used to overcome this problem, is simply based on mapping compensation, with the general effect of distortion reduction. In this study, we used a genetic algorithm (GA) and backpropagation (BP) network to optimize the geometric compensation of Ti6Al4V thin-walled parts fabricated by LPBF. The GA-BP network method can generate free-form thin-walled structures with enhanced geometric freedom for compensation. For the GA-BP network training, an arc thin-walled structure was designed and printed by LBPF and measured via optical scanning measurements. The final distortion of the compensated arc thin-walled part based on GA-BP was reduced by 87.9% compared with PSO-BP and mapping method. The effectiveness of this GA-BP compensation method is further evaluated in an application case using new data points, and the result shows that the final distortion of the oral maxillary stent was reduced by 71%. In summary, the GA-BP-based geometric compensation proposed in this study can better reduce the distortion of thin-walled parts with higher time and cost efficiencies.

Research Progress of Shape Memory Polymer and 4D Printing in Biomedical Application

As a kind of smart material, shape memory polymer (SMP) shows great application potential in the biomedical field. Compared with traditional metal-based medical devices, SMP-based devices have the following characteristics: 1) The adaptive ability allows the biomedical device to better match the surrounding tissue after being implanted into the body by minimally invasive implantation; 2) it has better biocompatibility and adjustable biodegradability; 3) mechanical properties can be regulated in a large range to better match with the surrounding tissue. 4D printing technology is a comprehensive technology based on smart materials and 3D printing, which has great application value in the biomedical field. 4D printing technology breaks through the technical bottleneck of personalized customization and provides a new opportunity for the further development of the biomedical field. This paper summarizes the application of SMP and 4D printing technology in the field of bone tissue scaffolds, tracheal scaffolds, and drug release, etc. Moreover, this paper analyzes the existing problems and prospects, hoping to provide a preliminary discussion and useful reference for the application of SMP in biomedical engineering.

Industry 4.0 as a Challenge for the Skills and Competencies of the Labor Force: A Bibliometric Review and a Survey

The latest technological development called Industry 4.0, like the previous industrial revolutions, has also brought a new challenge for people as a labor force because new technologies require new skills and competencies. By 2030 the existing generation in the labor market will have a skill gap threatening human replacement by machines. Based on bibliometric analysis and systematic literature review the main aims of this study are, on the one hand, to reveal the most related articles concerning skills, competencies, and Industry 4.0, and on the other hand, to identify the newset of skills and competencies which are essential for the future labor force. Determining the model of new skills and competencies in connection with Industry 4.0 technologies is the main novelty of the study. A survey carried out among the workers of mostly multinational organisations in Hungary has also been used to explore the level of awareness about those skills and Industry 4.0 related technologies, and this can be considered the significance of the empirical research.

Harnessing 4D Printing Bioscaffolds for Advanced Orthopedics

The development of programmable functional biomaterials makes 4D printing add a new dimension, time (t), based on 3D structures (x, y, z), therefore, 4D printed constructs could transform their morphology or function over time in response to environmental stimuli. Nowadays, highly efficient bone defect repair remains challenging in clinics. Combining programmable biomaterials, living cells, and bioactive factors, 4D bioprinting provides greater potential for constructing dynamic, personalized, and precise bone tissue engineering scaffolds by complex structure formation and functional maturation. Therefore, 4D bioprinting has been regarded as the next generation of bone repair technology. This review focuses on 4D printing and its advantages in orthopedics. The applications of different smart biomaterials and 4D printing strategies are briefly introduced. Furthermore, one summarizes the recent advancements of 4D printing in bone tissue engineering, uncovering the addressed and unaddressed medical requirements. In addition, current challenges and future perspectives are further discussed, which will offer more inspiration about the clinical transformation of this emerging 4D bioprinting technology in bone regeneration.

Two-Photon Absorption Cooperative Effects within Multi-Dipolar Ruthenium Complexes: The Decisive Influence of Charge Transfers

One- and two-photon characterizations of a series of hetero- and homoleptic [RuL_3-n(bpy)_n]²⁺ (n = 0, 1, 2) complexes carrying bipyridine π-extended ligands (L), have been carried out. These π-extended D−π−A−A−π−D-type ligands (L), where the electron donor units (D) are based on diphenylamine, carbazolyl, or fluorenyl units, have been designed to modulate the conjugation extension and the donating effect. Density functional theory calculations were performed in order to rationalize the observed spectra. Calculations show that the electronic structure of the π-extended ligands has a pronounced effect on the composition of HOMO and LUMO and on the metallic contribution to frontier MOs, resulting in strikingly different nonlinear properties. This work demonstrates that ILCT transitions are the keystone of one- and two-photon absorption bands in the studied systems and reveals how much MLCT and LLCT charge transfers play a decisive role on the two-photon properties of both hetero- and homoleptic ruthenium complexes through cooperative or suppressive effects.

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.

Additive Manufacturing of Micro-Electro-Mechanical Systems (MEMS)

Recently, additive manufacturing (AM) processes applied to the micrometer range are subjected to intense development motivated by the influence of the consolidated methods for the macroscale and by the attraction for digital design and freeform fabrication. The integration of AM with the other steps of conventional micro-electro-mechanical systems (MEMS) fabrication processes is still in progress and, furthermore, the development of dedicated design methods for this field is under development. The large variety of AM processes and materials is leading to an abundance of documentation about process attempts, setup details, and case studies. However, the fast and multi-technological development of AM methods for microstructures will require organized analysis of the specific and comparative advantages, constraints, and limitations of the processes. The goal of this paper is to provide an up-to-date overall view on the AM processes at the microscale and also to organize and disambiguate the related performances, capabilities, and resolutions.

Application of Bioactive Hydrogels for Functional Treatment of Intrauterine Adhesion

Intrauterine adhesion (IUA) is a common endometrial disease and one of the main causes of infertility in women of childbearing age. Current treatment strategies, such as hysteroscopic adhesion resection, hysteroscopic transcervical resection of adhesion (TCRA), the use of local hormone drugs, and anti-adhesion scaffold implantation, do not provide a satisfactory pregnancy outcome for moderate-severe IUA, which presents a great challenge in reproductive medicine. With the development of material engineering, various bioactive and functional hydrogels have been developed using natural and synthetic biomaterials. These hydrogels are not only used as barely physical barriers but are also designed as vectors of hormone drugs, growth factors, and stem cells. These characteristics give bioactive hydrogels potentially important roles in the prevention and treatment of IUA. However, there is still no systematic review or consensus on the current advances and future research direction in this field. Herein, we review recent advances in bioactive hydrogels as physical anti-adhesion barriers, in situ drug delivery systems, and 3D cell delivery and culture systems for seeded cells in IUA treatment. In addition, current limitations and future perspectives are presented for further research guidance, which may provide a comprehensive understanding of the application of bioactive hydrogels in intrauterine adhesion treatment.

Additively Manufactured Dental Crown with Color Gradient and Graded Structure: A Technique Report

To assess the feasibility of manufacturing a dental crown with internal color gradient and graded structure design using additive manufacturing technology, a mandibular first molar was prepared and a monolayer dental crown with 1.5 mm uniform thickness was designed in a dental software (STL_C1 ). The monolayer crown design was sliced into multiple layers of 0.1 mm thickness and a design for a multilayer crown was obtained (STL_C2 ). A multilayer crown was manufactured with gradient color and graded structure using a material jetting printer. Different materials with different colors and properties were used and mixed in different ratios during manufacturing to achieve the prospected design. The feasibility of manufacturing such a crown was reported. This report confirms that multilayer dental crowns with internal gradient color and graded structure are possible when using a multimaterial jetting printer.

3D Printing Technologies in Metallic Implants: A Thematic Review on the Techniques and Procedures

Additive manufacturing (AM) is among the most attractive methods to produce implants, the processes are very swift and it can be precisely controlled to meet patient's requirement since they can be produced in exact shape, dimension, and even texture of different living tissues. Until now, lots of methods have emerged and used in this field with diverse characteristics. This review aims to comprehensively discuss 3D printing (3DP) technologies to manufacture metallic implants, especially on techniques and procedures. Various technologies based on their main properties are categorized, the effecting parameters are introduced, and the history of AM technology is briefly analyzed. Subsequently, the utilization of these AM-manufactured components in medicine along with their effectual variables is discussed, and special attention is paid on to the production of porous scaffolds, taking pore size, density, etc., into consideration. Finally, 3DP of the popular metallic systems in medical applications such as titanium, Ti6Al4V, cobalt-chromium alloys, and shape memory alloys are studied. In general, AM manufactured implants need to comply with important requirements such as biocompatibility, suitable mechanical properties (strength and elastic modulus), surface conditions, custom-built designs, fast production, etc. This review aims to introduce the AM technologies in implant applications and find new ways to design more sophisticated methods and compatible implants that mimic the desired tissue functions.

Reliability-Based Evaluation of the Suitability of Polymers for Additive Manufacturing Intended for Extreme Operating Conditions

A reliability engineering program must be implemented from the conceptual phase of the physical asset to define the performance requirements of the components and equipment. Thus, in this work, the aim is to find the most optimal solution to manufacture polymer-based parts for the nuclear power industry using additive manufacturing routes. This case study application has been selected because polymers processed by additive manufacturing (AM) can be well suited for nuclear applications. The methodology includes-firstly-an analysis of the suitability of materials based on high-temperature resistance, thermal aging and irradiation tolerance, considering operation conditions. Secondly, an analysis of materials' processability considering their associated AM routes is performed based on thermal analysis and evaluation of physical properties of materials. A final assessment integrating the in-service suitability and AM processability is performed using a reliability approach, solving different emerging objective conflicts through defined constraints and selection criteria. According to the integrated in-service performance evaluation: Polypropylene-ethylene polyallomer (PPP), Epoxy (EP), Phenolics (Ph), Polyurethane (PU) and Acrylonitrile butadiene rubber (NBR) are the best options for mild operation conditions and EP, Ph and PU, considering high temperature along with radiation exposure. Considering AM techniques: EP and Ph can be manufactured using VAT photopolymerization-stereolithography (VP-SLA) with a good expected processability being these materials valid for high temperature environments. Consequently, this research work analyzes the viability, processability and in-service behavior of parts.

Norton I, Mills T. How to Formulate for Structure and Texture via Medium of Additive Manufacturing-A Review

Additive manufacturing, which is also known as 3D printing, is an emerging and growing technology. It is providing significant innovations and improvements in many areas such as engineering, production, medicine, and more. 3D food printing is an area of great promise to provide an indulgence or entertaining experience, personalized food product, or specific nutritional needs. This paper reviews the additive manufacturing methods and materials in detail as well as their advantages and disadvantages. After a full discussion of 3D food printing, the reports on edible printed materials are briefly presented and discussed. In the end, the current and future outlook of additive manufacturing in the food industry is shown.

Shape-driven arrest of coffee stain effect drives the fabrication of carbon-nanotube-graphene-oxide inks for printing embedded structures and temperature sensors

Carbon nanotube (CNT) based binder-free, syringe-printable inks, with graphene oxide (GO) being used as the dispersant, have been designed and developed. We discovered that the printability of the ink is directly attributed to the uniform deposition of the GO-CNT agglomerates, as opposed to the 'coffee-staining' despite these aggregates being micron-sized. The ellipsoidal nature of the micron-scale GO-CNT agglomerates/particles enables these particles to severely perturb the air-water interface, triggering a large long-range capillary interaction that causes the uniform deposition by overcoming the "coffee-stain"-forming forces from the evaporation-mediated flows. We evaluated the properties of this ink and identified a temperature-dependent resistance with a negative temperature coefficient of resistance (TCR) α ranging from ∼-10^-3 to -10^-2/°C depending on ink compositions. Finally, the printing is conducted on flat and curved surfaces, for developing polymer-ink embedded structures that might serve as precursors to syringe-printable CNT-based nanocomposites, and for fabricating sensor-like patterns that for certain ink compositions demonstrate α∼-10^-3/°C with a large averaged resistance drop (per unit temperature) of -3.5 Ω°C^-1.

A Review of Industry 4.0 Manufacturing Process Security Risks

The advent of three-dimensional (3D) printing has found a unique and prominent role in Industry 4.0 and is rapidly gaining popularity in the manufacturing industry. 3D printing offers many advantages over conventional manufacturing methods, making it an attractive alternative that is more cost-effective and efficient than conventional manufacturing methods. With the Internet of Things (IoT) at the heart of this new movement, control over manufacturing methods now enters the cyber domain, offering endless possibilities in manufacturing automation and optimization. However, as disruptive and innovative as this may seem, there is grave concern about the cyber-security risks involved. These security aspects are often overlooked, particularly by promising new start-ups and parties that are not too familiar with the risks involved in not having proper cyber-security measures in place. This paper explores some of the cyber-security risks involved in the bridge between industrial manufacturing and Industry 4.0, as well as the associated countermeasures already deployed or currently under development. These aspects are then contextualized in terms of Industry 4.0 in order to serve as a basis for and assist with future development in this field.

The Potential of Additive Manufacturing in the Smart Factory Industrial 4.0: A Review

Additive manufacturing (AM) or three-dimensional (3D) printing has introduced a novel production method in design, manufacturing, and distribution to end-users. This technology has provided great freedom in design for creating complex components, highly customizable products, and efficient waste minimization. The last industrial revolution, namely industry 4.0, employs the integration of smart manufacturing systems and developed information technologies. Accordingly, AM plays a principal role in industry 4.0 thanks to numerous benefits, such as time and material saving, rapid prototyping, high efficiency, and decentralized production methods. This review paper is to organize a comprehensive study on AM technology and present the latest achievements and industrial applications. Besides that, this paper investigates the sustainability dimensions of the AM process and the added values in economic, social, and environment sections. Finally, the paper concludes by pointing out the future trend of AM in technology, applications, and materials aspects that have the potential to come up with new ideas for the future of AM explorations.

Effects of Electropolishing on Mechanical Properties and Bio-Corrosion of Ti6Al4V Fabricated by Electron Beam Melting Additive Manufacturing

Electron beam melting (EBM) has become one of the most promising additive manufacturing (AM) technologies. However, EBM tends to result in products with rougher surfaces due to the melt pool which causes adjacent powder particles to be sintered to the surface without being melted. Hence, it is necessary to improve the surface quality by post processing. The current study evaluates the tensile response of Ti6Al4V EBMed samples subject to various electropolishing (EP) treatments. The surface roughness Ra readings can be improved from over 24 µm down to about 4.5 µm by proper EP, resulting in apparent tensile elongation improvement from 7.6% to 11.6%, or a tensile plasticity increment of 53%, without any loss of elastic modulus or tensile strength. Moreover, the in-vitro bio-corrosion test in simulating body fluid (SBF) of the as-EBMed and EP-processed samples is also conducted. The potentiodynamic polarization reveals that the bio-corrosion resistance is improved by the lower Ra through proper EP treatments. This is due to the formation of a denser and more completely passivated oxide layer with less defects after proper EP duration. But when the EBMed samples are over-electropolished, nano pitting would induce a degraded bio-corrosion performance.

Biomimetic cardiovascular platforms for in vitro disease modeling and therapeutic validation

Bioengineered tissues have become increasingly more sophisticated owing to recent advancements in the fields of biomaterials, microfabrication, microfluidics, genetic engineering, and stem cell and developmental biology. In the coming years, the ability to engineer artificial constructs that accurately mimic the compositional, architectural, and functional properties of human tissues, will profoundly impact the therapeutic and diagnostic aspects of the healthcare industry. In this regard, bioengineered cardiac tissues are of particular importance due to the extremely limited ability of the myocardium to self-regenerate, as well as the remarkably high mortality associated with cardiovascular diseases worldwide. As novel microphysiological systems make the transition from bench to bedside, their implementation in high throughput drug screening, personalized diagnostics, disease modeling, and targeted therapy validation will bring forth a paradigm shift in the clinical management of cardiovascular diseases. Here, we will review the current state of the art in experimental in vitro platforms for next generation diagnostics and therapy validation. We will describe recent advancements in the development of smart biomaterials, biofabrication techniques, and stem cell engineering, aimed at recapitulating cardiovascular function at the tissue- and organ levels. In addition, integrative and multidisciplinary approaches to engineer biomimetic cardiovascular constructs with unprecedented human and clinical relevance will be discussed. We will comment on the implementation of these platforms in high throughput drug screening, in vitro disease modeling and therapy validation. Lastly, future perspectives will be provided on how these biomimetic platforms will aid in the transition towards patient centered diagnostics, and the development of personalized targeted therapeutics.

Tailored Sample Mounting for Light-Sheet Fluorescence Microscopy of Clarified Specimens by Polydimethylsiloxane Casting

The combination of biological tissue clearing methods with light-sheet fluorescence microscopy (LSFM) allows acquiring images of specific biological structures of interest at whole organ scale and microscopic resolution. Differently to classical epifluorescence techniques, where the sample is cut into slices, LSFM preserves the whole organ architecture, which is of particular relevance for investigations of long-range neuronal circuits. This imaging modality comes with the need of new protocols for sample mounting. Gel matrix, hooks, tips, glues, and quartz cuvettes have been used to keep whole rodent organs in place during image acquisitions. The last one has the advantage of avoiding sample damage and optical aberrations when using a quartz refractive index (RI) matching solution. However, commercially available quartz cuvettes for such large samples are expensive. We propose the use of polydimethylsiloxane (PDMS) for creating tailor-made cuvettes for sample holding. For validation, we compared PDMS and quartz cuvettes by measuring light transmittance and performing whole mouse-brain imaging with LSFM. Moreover, imaging can be performed using an inexpensive RI matching solution, which further reduces the cost of the imaging process. Worth of note, the RI matching solution used in combination with PDMS leads to a moderate expansion of the sample with respect to its original size, which may represent an advantage when investigating small components, such as neuronal processes. Overall, we found the use of custom-made PDMS cuvettes advantageous in term of cost, image quality, or preservation of sample integrity with respect to other whole-mouse brain mounting strategies adopted for LSFM.

Electrohydrodynamic Printing of Microscale PEDOT:PSS-PEO Features with Tunable Conductive/Thermal Properties

Electrohydrodynamic (EHD) printing has been recently investigated as an effective technique to produce high-resolution conductive features. Most of the existing EHD printing studies for conductive features were based on metallic nanoparticle inks in a microdripping mode, which exhibited relatively low efficiency and commonly required high-temperature annealing process to achieve high conductivity. The EHD printing of high-resolution conductive features at a relatively low temperature and in a continuous cone-jetting mode is still challenging because the conductive inks might connect the charged nozzle, and the grounded conductive or semiconductive substrates to cause discharge and terminate the printing process. In this study, the EHD printing process of conductive polymers in a low-temperature cone-jetting mode was explored to fabricate conductive microstructures. The smallest width of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) lines was 27.25 ± 3.76 μm with a nozzle diameter of 100 μm. It was interesting to find that the electrohydrodynamically printed PEDOT:PSS-PEO features exhibited unique thermal properties when a dc voltage was applied. The conductive and thermal properties of the resultant features were highly dependent on the printing layer number. Microscale PEDOT:PSS features were further encapsulated into electrospun nanofibrous mesh to form a flexible sandwich structure. The EHD printing of PEDOT:PSS features with tunable conductive and thermal properties might be useful for the applications of flexible and wearable microdevices.

Special Issue: NextGen Materials for 3D Printing

Only a handful of materials are well-established in three-dimensional (3D) printing and well-accepted in industrial manufacturing applications. However, recent advances in 3D printable materials have shown potential for enabling numerous novel applications in the future. This special issue, consisting of 2 reviews and 10 research articles, intends to explore the possible materials that could define next-generation 3D printing.