Freeze–Thaw Durability of 3D Printed Concrete: A Comprehensive Review of Mechanisms, Materials, and Testing Strategies

In this work, crystallographic texture evolution in 3D printed trimodal polyethylene (PE) blends and high-density PE (HDPE) benchmark material were investigated to quantify the resulting material anisotropy, and the results were compared to materials made from conventional injection molded (IM) samples. Trimodal PE reactor blends consisting of HDPE, ultrahigh molecular weight PE (UHMWPE), and HDPE_wax have been used for 3D printing and injection molding. Changes in the preferred orientation and distribution of crystallites, i.e., texture evolution, were quantified utilizing the wide angle X-ray diffraction through pole figures and orientation distribution functions (ODFs) for 3D printed and IM samples. Since the change in weight-average molecular weight (Mw) of the blend was expected to significantly affect the resulting crystallinity and orientation, the overall Mw of the trimodal PE blend was varied while keeping the UHMWPE component weight fraction to 10% in the blend. The resulting texture was analyzed by varying the overall Mw of the trimodal blend and the process parameters in 3D printing and compared to the texture of conventional IM samples. The printing speed and orientation (defined with respect to the axis along the length of the samples) were used as the variable process parameters for 3D printing. The degree of anisotropy increases with an increase in the nonuniform distribution of intensities in pole figures and ODFs. All the highest intensity major texture components in IM and 3D printed samples (0° printing orientation) of reactor blends are observed to have crystals oriented in [001] or [001̅]. Overall, for the same throughput, 3D printed samples in the 0° orientation showed greater texture evolution and higher anisotropy compared to IM samples. Most notably, an increase in 3D printing speed increased the crystalline distribution closer to the 0° direction, increasing the anisotropy, while deviation from this printing orientation reduced crystalline distribution closer to the 0° direction, thus increasing isotropy. This demonstrates that tailoring material properties in specific directions can be achieved more effectively with 3D printing than with the injection molding process. Change in the overall Mw of the trimodal PE blend changed the preferential orientation distribution of the crystal planes to some degree. However, the degree of anisotropy remained the same in almost all cases, indicating that the effect of molecular weight distribution is not as significant as the printing speed and printing orientation in tailoring the resulting properties. The 3D printing process parameters (speed and orientation) were shown to have more influence on the texture than the material parameters associated with the blend.

Understanding the deterioration mechanism of concrete structures in cold climates that are susceptible to frost damage from repeated freezing and thawing cycles is imperative for ensuring their durability and serviceability. This study analyzed the impact of freeze–thaw (FT) exposure on concrete structural behavior by developing three machine-learning approaches—artificial neural networks (ANN), random forests (RF), and support vector machines (SVM)—to quantify the progressive loss in compressive strength after repeated FT cycles. The results demonstrate that all of the proposed models can predict the deteriorated compressive strength of concrete and align closely with the experimental results. The ANN model demonstrated the highest prediction accuracy with an R2 of 0.924, exhibiting a higher prediction accuracy than RF and SVM models. Sensitivity analysis using Shapley additive explanations (SHAP) revealed that concrete with an initially high strength, along with a lower water–cement ratio and air entrainment, exhibited the least reduction in compressive strength after freezing–thawing cycles, underlining the positive impact of these factors on the FT durability of concrete. The proposed modeling approach accurately predicts the residual compressive strength after FT exposure, enabling the selection of optimal concrete materials and structural designs for cold climates.

Application of three-dimensional (3D) printing is widely being applied from various fields of studies from mechanical manufacturing to civil constructions. Food is considered an essential factor for human survival. Modern day’s humans are considering food not only for survival but for other qualitative attributes and characteristic properties as well. With the development of 3D printing technologies, it is now possible to print with almost any kind of materials, including organics. This technological development had empowered the new generation food technologists/engineers to print almost all types of foods from chocolate to pizza, of desired characters, shape, size, color, texture, and other properties of interest. Foods with customized nutritional characteristics, lowered production price and processing time are various interesting applications of 3D printing for future foods. Decorated cakes and cookies and customized mobile-based 3D food printing applications, including the real-time printed picture of customers placing the food orders, make the future of food processing quite astonishing. 3D printing provides a wider platform for the food innovators to work more intensely on the new food product developments 52with much complex geometry that manually would be near to impossible. This chapter targets to provide information to the readers about various aspects of 3D printing in food processing, technological development for 3D food printing, and about different printable food component mixtures and recipes. Last part of the chapter discusses briefly the limitations and future scope of 3D food printing keeping in mind the future human needs and requirements.

The three-dimensional (3D) printing of hydrogel is an issue of interest in various applications to build optimized 3D structured devices beyond 2D-shaped conventional structures such as film or mesh. The materials design for the hydrogel, as well as the resulting rheological properties, largely affect its applicability in extrusion-based 3D printing. Here, we prepared a new poly(acrylic acid)-based self-healing hydrogel by controlling the hydrogel design factors based on a defined material design window in terms of rheological properties for application in extrusion-based 3D printing. The hydrogel is designed with a poly(acrylic acid) main chain with a 1.0 mol% covalent crosslinker and 2.0 mol% dynamic crosslinker, and is successfully prepared based on radical polymerization utilizing ammonium persulfate as a thermal initiator. With the prepared poly(acrylic acid)-based hydrogel, self-healing characteristics, rheological characteristics, and 3D printing applicability are deeply investigated. The hydrogel spontaneously heals mechanical damage within 30 min and exhibits appropriate rheological characteristics, including G′~1075 Pa and tan δ~0.12, for extrusion-based 3D printing. Upon application in 3D printing, various 3D structures of hydrogel were successfully fabricated without showing structural deformation during the 3D printing process. Furthermore, the 3D-printed hydrogel structures exhibited excellent dimensional accuracy of the printed shape compared to the designed 3D structure.

Spine surgery entails a wide spectrum of complicated pathologies. Over the years, numerous assistive tools have been introduced to the modern neurosurgeon's armamentarium including neuronavigation and visualization technologies. In this review, we aimed to summarize the available data on 3D printing applications in spine surgery as well as an assessment of the future implications of 3D printing. We performed a comprehensive review of the literature on 3D printing applications in spine surgery. Over the past decade, 3D printing and additive manufacturing applications, which allow for increased precision and customizability, have gained significant traction, particularly spine surgery. 3D printing applications in spine surgery were initially limited to preoperative visualization, as 3D printing had been primarily used to produce preoperative models of patient-specific deformities or spinal tumors. More recently, 3D printing has been used intraoperatively in the form of 3D customizable implants and personalized screw guides. Despite promising preliminary results, the applications of 3D printing are so recent that the available data regarding these new technologies in spine surgery remains scarce, especially data related to long-term outcomes.

ObjectivesTo evaluate the fabrication trueness of additively manufactured maxillary definitive casts with various tooth preparations fabricated with different 3-dimensional (3D) printers and print orientations. MethodsA maxillary typodont with tooth preparations for a posterior 3-unit fixed partial denture, lateral incisor crown, central incisor and canine veneers, first premolar and second molar inlays, and a first molar crown was digitized with an industrial scanner. This scan file was used to fabricate definitive casts with a digital light processing (DLP) or stereolithography (SLA) 3D printer in different orientations (0-degree, 30-degree, 45-degree, and 90-degree) (n = 7). All casts were digitized with the same scanner, and the deviations within each preparation site were evaluated. Generalized linear model analysis was used for statistical analysis (α = 0.05). ResultsThe interaction between the 3D printer and the print orientation affected measured deviations within all preparations (P ≤ 0.001) except for the lateral incisor crown and canine veneer (P ≥ 0.094), which were affected only by the main factors (P < 0.001). DLP-90 mostly led to the highest and DLP-0 mostly resulted in the lowest deviations within posterior tooth preparations (P ≤ 0.014). DLP-30 led to the lowest deviations within the first premolar inlay and DLP-45 led to the lowest deviations within the central incisor veneer preparation (P ≤ 0.045). ConclusionsPosterior preparations of tested casts had the highest trueness with DLP-0 or DLP-30, while central incisor veneer preparations had the highest trueness with DLP-45. DLP-90 led to the lowest trueness for most of the tooth preparations. Clinical Significance:Definitive casts with tooth preparations fabricated with the tested DLP 3D printer and the print orientation adjusted on tooth preparation may enable well-fitting restorations. However, 90-degree print orientation should be avoided with this 3D printer, as it led to the lowest fabrication trueness.

Recent advancements in science and technology have resulted in important changes in the medical field. Three-dimensional (3D) printing is a good example of such developments and has already achieved a considerable level of technical development in many industrial fields. Use of this innovative manufacturing technique is gradually expanding in the medical field. In clinics, application of 3D printing can be largely divided into diagnostic or treatment purposes. Meanwhile, research in the basic sciences is also advancing, allowing 3D printing of tissue or organs via cell bioprintings. This technology could potentially change the paradigm of the medical community1. Because of its usefulness, various applications of 3D printing should be considered in the area of oral and maxillofacial surgery. In fact, the field of oral and maxillofacial surgery has sought to apply a simple rudimentary form of 3D printing technique for a long time. Use of 3D-printed rapid prototyped models before oral cancer surgery or orthognathic surgery for treatment planning and simulation has been established to assure more precise and safe surgeries2. Moreover, surgical stents are fabricated using computed tomography (CT) images in the field of dental implantology3. It is necessary to move forward and adopt this technology in the fabrication of complex forms of molds in order to provide individualized medical services. For example, easier production of customized and reconstruction plates and morphologic reconstruction of bony defect areas are possible uses of 3D printing in fracture surgery or reconstructive surgery. The 3D printing technique can also be utilized in other areas of oral and maxillofacial surgery. For example, it would be very helpful to be able to design and fabricate a customized non-absorbable barrier of titanium mesh. In addition, 3D printing could be used in other fields of dentistry. For example, individual occlusion could be accurately determined and treated with a unique splint fabricated using 3D printing. It would be beneficial for patients if splints could be fabricated without the need for cast impressions. Orthodontic appliances also could be manufactured with 3D printing. Considering a wide variety of morphologies of the tooth surfaces, appliances with customized surfaces would be helpful4. Of course, there are still problems with 3D printing that need to be solved, such as the high cost; that this technology is not yet cost-effective. However, though it is difficult to justify the use of 3D printing on general surgery patients, the use of 3D printing might be much more appropriate for patients with special needs. For example, it is possible to greatly reduce the operation time if highly customized devices are prepared in advance, since it would exempt the time-consuming process of bending or modifying the appliance during the surgery. This would ultimately benefit the patient. Increased precision of the technique will also result in a wider range of applications for 3D printing. In addition, increased resolution in medical imaging such as CT will allow greater use of 3D printing5. Material science and engineering are also important areas in which 3D printing will be useful. Materials that are relatively easy to modify, such as polymers or plastics, are already at a high level of technological development, though materials such as metals, alloys, or other composites are still under development6. Many countries are increasing their national policies that support the developing 3D technology. In order to respond to the demands and remain competitive, oral and maxillofacial surgeons should have an interest in 3D printing and understand its various applications. Though it is important to have the source technology, its utilization in a variety of fields should not be overlooked. In target business models such as jewelry/accessory and interior, customized device/healthcare structure, early participation of the potential customer is also being encouraged. Moreover, since complex mold forms can be more readily manufactured using 3D printing, mass production is a future goal in applicable fields. In conclusion, the role of 3D printing in oral and maxillofacial surgery should be a focus of interest since the technique could offer endless developmental possibilities.

In cold climates, reinforced concrete structures (RCSs) are frequently and severely damaged by freeze–thaw (FT) and deicing-salt attack during winter periods. FT action can also cause additional water uptake known as frost suction. If a critical degree of water saturation is exceeded, severe deterioration of the microstructure of the concrete is likely, enhancing chloride ingress and increasing the probability of corrosion of its reinforcement. We present herein a test method to characterize the resistance of concrete to FT and chloride ingress. Chloride migration tests were performed on concretes with different degrees of FT deterioration, with and without deicing agents. The performance of RCSs is decisively affected under these combined actions. Quantitative description of the resulting FT damage is achieved using ultrasonic measurements and resonance frequency analysis. The test results confirm that the latter nondestructive test method provides more reliable evaluation of FT damage compared with usual ultrasonic pulse velocity measurements. Different concretes with supplementary cementitious materials and different degrees of FT deterioration with and without deicing agents were tested. While concrete made with air-entraining agents clearly showed the best FT resistance, concrete with ground-granulated blast-furnace slag showed superior resistance to both chloride migration and FT attack, both being positively affected by appropriate curing conditions.

Edge strength of definitive 3D-printed restorative resin materials.

Poly(ether ketone ketone) (PEKK) is a thermoplastic of the poly(aryl ether ketone) (PAEK) family, with excellent mechanical and thermal performances and high chemical resistance properties. This makes it an appealing material in high‐performance applications as a replacement for poly (ether ether ketone) (PEEK). PEKK was thus selected in this study as a base material for application in 3D printing. The effects of nozzle temperature, layer orientation and layer thickness on the final properties of 3D‐printed PEKK parts were investigated. Furthermore, we assessed the mechanical and morphological features of printed samples through tensile tests and scanning electron microscope, respectively. Thermal properties of samples were also evaluated through DSC and DMA analysis. Optimum printing parameters were found at 0.15 mm layer thickness, 380°C nozzle temperature, and [45/−45°] layer orientation. The printed PEKK samples were annealed at various temperatures to allow the relaxation of residual stress and enhance the degree of crystallinity. Samples annealed for 1 h at 240°C have shown an improved elastic modulus by ~14%, tensile strength by 17%, and glass transition temperature by 17.2°C from the increased by 24% degree of crystallinity.

Is This the Future of Medical Technology?

Three-dimensional (3D) printing, or additive manufacturing, technology has rapidly penetrated the medical device industry over the past several years, and innovative groups have harnessed it to create devices with unique composition, structure, and customizability. These distinctive capabilities afforded by 3D printing have introduced new regulatory challenges. The customizability of 3D-printed devices introduces new complexities when drafting a design control model for FDA consideration of market approval. The customizability and unique build processes of 3D-printed medical devices pose unique challenges in meeting regulatory standards related to the manufacturing quality assurance. Consistent material powder properties and optimal printing parameters such as build orientation and laser power must be addressed and communicated to the FDA to ensure a quality build. Postprinting considerations unique to 3D-printed devices, such as cleaning, finishing and sterilization are also discussed. In this manuscript we illustrate how such regulatory hurdles can be navigated by discussing our experience with our group's 3D-printed bioresorbable implantable device.

BackgroundThree-dimensional (3D) printing is increasingly used to fabricate dental restorations due to its enhanced precision, consistency and time and cost-saving advantages. The properties of 3D-printed resin materials can be influenced by the chosen printing orientation which can impact the mechanical characteristics of the final products. PurposeThe objective of this study was to evaluate the influence of printing orientation and artificial ageing on the Martens hardness (HM) and indentation modulus (EIT) of 3D-printed definitive and temporary dental restorative resins. MethodsDisk specimens (20 mm diameter × 2 mm height) were additively manufactured in three printing orientations (0°, 45°, 90°) using five 3D-printable resins: VarseoSmile Crownplus (VCP), Crowntec (CT), Nextdent C&B MFH (ND), Dima C&B temp (DT), and GC temp print (GC). The specimens were printed using a DLP 3D-printer (ASIGA MAX UV), while LavaTM Ultimate (LU) and Telio CAD (TC) served as milled control materials. Martens hardness (HM) and indentation modulus (EIT) were tested both before and after storage in distilled water and artificial saliva for 1, 30, and 90 days at 37 °C. Results90° printed specimens exhibited higher HM than the other orientations at certain time points, but no significant differences were observed in HM and EIT between orientations for all 3D-printed materials after 90 days of ageing in both aging media. LU milled control material exhibited the highest HM and EIT among the tested materials, while TC, the other milled control, showed similar values to the 3D printed resins. CT and VCP (definitive resins) and ND displayed higher Martens parameters compared to DT and GC (temporary resins). The hardness of the 3D-printed materials was significantly impacted by artificial ageing compared to the controls, with ND having the least hardness reduction percentage amongst all 3D-printed materials. The hardness reduction percentage in distilled water and artificial saliva was similar for all materials except for TC, where higher reduction was noted in artificial saliva. SignificanceThe used 3D printed resins cannot yet be considered viable alternatives to milled materials intended for definitive restorations but are preferable for use as temporary restorations.

To highlight the various applications of 3D printing in cardiovascular disease and discuss its limitations and future direction. Use of handheld 3D printed models of cardiovascular structures has emerged as a facile modality in procedural and surgical planning as well as education and communication. Three-dimensional (3D) printing is a novel imaging modality which involves creating patient-specific models of cardiovascular structures. As percutaneous and surgical therapies evolve, spatial recognition of complex cardiovascular anatomic relationships by cardiologists and cardiovascular surgeons is imperative. Handheld 3D printed models of cardiovascular structures provide a facile and intuitive road map for procedural and surgical planning, complementing conventional imaging modalities. Moreover, 3D printed models are efficacious educational and communication tools. This review highlights the various applications of 3D printing in cardiovascular diseases and discusses its limitations and future directions.

Lycium barbarum polysaccharides (LBPs), bioactive macromolecules derived from goji berries, have gained attention for their biocompatibility, water retention, and hydrogel-forming abilities. These properties make LBPs promising candidates for 3D printing applications in the food and pharmaceutical industries. This review comprehensively analyzes LBPs' chemical composition, structural characteristics, and biological functions. The study examines the rheological properties of LBPs, including flow behavior, shear-thinning, and gelation mechanisms, and explores network formation through physical and chemical gelation processes. The potential of LBPs in bio-ink formulations for 3D food printing and biomedical applications is discussed, focusing on cross-linking strategies to enhance printing performance. LBPs exhibit favorable rheological and gelation properties, supporting their use in 3D printing applications. However, challenges, such as thermal sensitivity, mechanical limitations, and scalability, remain significant hurdles. Strategies for optimization are proposed to enhance their application in food and biomedical 3D printing. Future research should focus on refining cross-linking methods, improving mechanical stability, and addressing challenges in large-scale production to fully leverage LBPs in advanced 3D printing technologies.