3D Printing Research Articles

Polymerization kinetics of 3D-printed orthodontic aligners under different UV post-curing conditions

BackgroundThe purpose of the study was to measure the degree of conversion (DC) of direct-printed aligners (DPA) that were post-cured under ambient and nitrogen atmosphere at specific time intervals and investigate the kinetics of polymerization reaction of this material.MethodsA total of 48 aligners were produced in 4 printing series by a 3D printer with TC-85DAC resin (Graphy Inc). From each series of printing, 12 aligners were included. The aligners were divided into two groups according to their post-curing conditions. One group was post-cured under ambient air with the presence of oxygen and the other under a nitrogen atmosphere, both using the same UV post-curing unit recommended by the company. The aligners were post-cured at six different time intervals: 1, 2, 3, 5, 10, and 20 min. Each time interval included 8 aligners, with 2 aligners from each series. The DC of the cured aligners was measured by means of attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) through acquisition of the respective spectra for each UV-curing condition. Statistical analysis was performed to compare the results and differences within each atmosphere post-curing protocol, as well as between the different selected atmosphere conditions. Statistical significance level was set at p-value ≤ 0.05.ResultsPairwise analysis between post-curing protocols showed statistically significant differences only at the first minute of polymerization. Post-curing with nitrogen did not yield statistically significant results across different time intervals. Post-curing in ambient air showed some significant differences on the 1st and 2nd minute of the post-curing process.ConclusionsAlmost complete double bond conversion was observed. Significant differences were observed only during the first minute of polymerization under the nitrogen atmosphere.

FDM 3D Printing and Properties of WF/PBAT/PLA Composites

Fused deposition molding (FDM) is a commonly used 3D printing method, and polylactic acid (PLA) has become one of the most important raw materials for this technology due to its excellent warping resistance. However, its mechanical properties are insufficient. Polybutylene adipate terephthalate (PBAT) is characterized by high toughness and low rigidity, which can complement the performance of PLA. The biodegradable polymers produced by blending the two have thus been used to replace petroleum-based plastics in recent years, but the high cost of the blends has limited their wide applications. Introducing plant fibers into the blends can not only maintain biodegradability and improve the overall performance of the plastics but also reduce their costs greatly. In this study, the PBAT/PLA blends with a mass ratio of 70/30 were selected and mixed with wood flour (WF) to prepare ternary composites using a FDM 3D printing technique. The effects of WF dosage on the mechanical properties, thermal properties, surface wettability, and melt flowability of the composites were investigated. The results showed that the proper amount of WF could improve the tensile and flexural moduli of the composites, as well as the crystallinity and hydrophobicity of the printed specimens increased with the content of WF, while the melt flow rate decreased gradually. Compared to PBAT/PLA blends, WF/PBAT/PLA composites are less costly, and the composite containing 20 wt.% WF has the best comprehensive performance, showing great potential as raw material for FDM 3D printing.

A review on layerless 3D printing: challenges and applications

Purpose This paper aims to provide a full introduction, new classification, comparison and investigation of the challenges as well as applications of layerless 3D printing, which is one of the industry 4.0 pioneers. Design/methodology/approach Given the significance and novelty of uniform 3D printing, more than 250 publications were collected and reviewed in an unbiased and clear manner. Findings As a result, the majority of uniform parts printed in polymer form are known up to this point. In a novel division for better researchers’ comprehension, uniform printing systems were classified into three categories: oxygen inhibition (OI), liquid lubrication (LL) and photon penetration (PP), and each was thoroughly investigated. Furthermore, these three approaches were evaluated in terms of printing speed, precision and accuracy, manufacturing scale and cost. Originality/value The parameters of each approach were compared independently, and then a practical comparison was conducted among these three approaches. Finally, a variety of technologies, opportunities, challenges and advantages of each significant method, as well as a future outlook for layerless rapid prototyping, are presented.

Architected Design and Fabrication of Soft Mechanical Metamaterials

This study proposes a systematic design approach to 3D print soft mechanical metamaterials by tuning material flow behavior and using optimal toolpaths and print parameters. Planar printing tool paths, utilized in layer‐by‐layer printing such as fused deposition modeling (FDM) and prevalently used in most slicing algorithms, severely limit the realization of complex topologies required in metamaterials. Utilizing parametric design principles, the proposed approach employs discrete and continuous 3D freeform tool paths for supported and unsupported direct ink writing (DIW) of elastomeric structures. The resulting textured, soft topologies significantly enhance the performance of various mechanisms in soft robotics and impact energy‐absorbing wearable devices. Various bioinspired structures such as cilia, webs, leaf‐like structures, and lattices are explored using extrusion‐based silicone 3D printing, achieving features with high aspect ratios (L/D ≤ 12) without support. These complex structures are challenging to 3D print using conventional planar toolpaths. To demonstrate the enhanced functionalities enabled by these new topologies, cilia arrays added to suction cups increased the pull‐off forces by 18%. Additionally, 3D‐printed elastomeric lattice slabs used as energy‐absorbing structures reduced the maximum impact peak forces by 85%. Further functionalities, including magnetic, thermochromic, and signal transmission properties, are also showcased using functional soft mechanical metamaterials.

Emerging Technological Advancement for Chronic Wound Treatment and Their Role in Accelerating Wound Healing.

Chronic wounds are a major healthcare burden and may severely affect the social, mental, and economic status of the patients. Any impairment in wound healing stages due to underlying factors leads to a prolonged healing time and subsequently to chronic wounds. Traditional approaches for the treatment of chronic wounds include dressing free local therapy, dressing therapy, and tissue engineering based scaffold therapies. However, traditional therapies need improvisation and have been advanced through breakthrough technologies. The present review spans traditional therapies and further gives an extensive account of advancements in the treatment of chronic wounds. Cutting edge technologies, such as 3D printing, which includes inkjet printing, fused deposition modeling, digital light processing, extrusion-based printing, microneedle array-based therapies, gene therapy, which includes microRNAs (miRNAs) therapy, and smart wound dressings for real time monitoring of wound conditions through assessment of pH, temperature, oxygen, moisture, metabolites, and their use for planning of better treatment strategies have been discussed in detail. The review further gives the future direction of treatments that will aid in lowering the healthcare burden caused due to chronic wounds.

Wear and Dynamic Mechanical Analysis (DMA) of Samples Produced via Fused Deposition Modelling (FDM) 3D Printing Method

In recent years, plastic and metal 3D printing has experienced massive development in the professional and hobby spheres, especially for rapid prototyping, reverse engineering, maintenance and quick repairs. However, this technology is limited by a number of factors, with the most common being the cost and availability of the technology but also the lack of information on material properties. This study focuses on investigating the material properties of PLA, PETG, HIPS, PA, ABS and ASA in order to elucidate their behavior in terms of wear and thermal resistance. The research builds on previous studies focusing on the mechanical properties of these materials and includes wear testing and DMA analysis. Weight loss, frictional forces, and frictional work including relative frictional work are recorded as part of this testing. The storage modulus and loss modulus including tan(δ) were then measured using DMA.

Developing endoscopic cell sheet delivery device using a beating human heart simulator and a pig model for minimally invasive cardiac regenerative therapy

Abstract Introduction Recently, clinical trials have commenced for cardiac regenerative therapy utilizing stem cells in patients with heart failure. Among the various transplantation approaches, there is a growing demand for less invasive methods to transplant sheet/patch-shaped cell products onto the heart surface, rather than resorting to conventional open surgery. This is particularly important considering the need for immunosuppressants due to allogeneic cell transplantation. Objective This study aims to develop a device for endoscopic transplantation of cell sheets onto the beating heart surface. Methods Prototype devices, initially developed in our prior study using a static heart model (Regenerative Therapy, 2020), were refined to better suit the cell sheet transplantation procedure onto a beating heart. We constructed a three-dimensional (3D) model of a beating heart located inside a thoracic cavity model, based on human computed tomography data and a 3D printer dedicated to simulating endoscopic surgical procedures. Human mesenchymal stromal cell (MSC)-derived cell sheets were prepared using temperature-responsive culture dishes and transferred onto a beating heart model pulsating at 80 beats per minute. We assessed the technical feasibility (N=8). Furthermore, skeletal muscle tissue was harvested from the thigh of the Clawn miniature pigs, and skeletal myoblasts were cultured from enzymatically digested tissue to create a cell sheet for autologous transplantation (8.0×10⁶ cells/sheet). Subsequently, the cell sheets labeled with Hoechst 33342 were endoscopically transplanted onto the pig heart surface (N=2). The pigs were sacrificed one week later, and the engraftment of the cell sheet was histologically evaluated. Results Successful deployment of MSC sheets onto the beating heart model was achieved in all procedures with one trial (100% success rate). The procedure duration from device insertion to the completion of cell sheet transplantation averaged 142±19 seconds. In experiments on autologous transplantation of myoblast cell sheets, two cases were successfully accomplished, with the transplanted cell sheet positive for Hoechst 33342 observed on the heart surface. Conclusion We have developed an endoscopic cell sheet delivery device using a pulsating heart model and a pig model, which holds promise for minimally invasive cardiac regenerative therapy in the future. Further investigations into the safety of the procedure are warranted for the clinical application of this system.

Clinically Relevant and Precisely Printable Live Adipose Tissue-Based Bio-Ink for Volumetric Soft Tissue Reconstruction.

Autologous fat is widely used in soft tissue reconstruction; however, significant volume reduction owing to necrosis and degradation of the transplanted adipose tissue (AT) remains a major challenge. To address this issue, a novel live AT micro-fragment-based bio-ink (ATmf bio-ink) compatible with precision 3D printing, is developed. Live AT micro-fragments of ≈280µm in size are prepared using a custom tissue micronizer and they are incorporated into a fibrinogen/gelatin mixture to create the ATmf bio-ink. AT micro-fragments exhibit high viability and preserve the heterogeneous cell population and extracellular matrix of the native AT. The developed bio-ink enables precise micropatterning and provides an excellent adipo-inductive microenvironment. AT grafts produced by co-printing the bio-ink with polycaprolactone demonstrate a 500% improvement in volume retention and a 300% increase in blood vessel infiltration in vivo compared with conventional microfat grafts. In vivo engraftment of AT grafts is further enhanced by using a stem cell-laden ATmf bio-ink. Last, it is successfully demonstrated that the bio-ink is enabled for the creation of clinically relevant and patient-specific AT grafts for patients undergoing partial mastectomy. This novel ATmf bio-ink for volumetric soft tissue reconstruction offers a pioneering solution for addressing the limitations of existing clinical techniques.

Voxel Interface Control in Multimaterial Extrusion 3D Printing.

Interfaces are crucial in natural and engineered systems, dictating essential biological, ecological, and technological properties that augment performance, functionality, and user experience. Yet, achieving precise interfacial control poses significant challenges in both conventional and additive manufacturing, where scalability constraints impede the controlled deposition of quasi-2D layers within 3D objects. This paper introduces Voxel-Interface 3D Printing (VI3DP), which enables comprehensive control over extruded voxel interfaces irrespective of the printhead diameter that conventionally dictates feature size. Various optical, mechanical, and electrical functionalizations, attaining interface thicknesses up to three orders of magnitude smaller than the voxel size are reported. Notable applications include encoding data in soft matter through fluorescent interfaces, creating tight fits and movable mechanisms through non-adhesive interfaces, fabricating bio-inspired composites with tailored failure modes, and developing a single filament capacitive touch sensor. VI3DP opens new avenues for enhanced functionality and efficiency across multiple fields, including biomedical technology, electronics, optics, andnanotechnology.

Suitability of UR5 Robot for Robotic 3D Printing

The present paper describes the measurement of the drift of unidirectional pose accuracy, repeatability, and static compliance of a collaborative robot employing a measurement methodology that relies on the description of a virtual ISO cube placed in the robot’s workspace. The measurements aimed to investigate and assess the suitability of the UR5 six-axis collaborative robot for its application in robotic 3D printing. An experimental laboratory measurement workstation was constructed to perform the measurements, and control measurements were performed. The measurements involved describing the TCP point of the robot tool at five measurement points located in a virtual ISO cube during a minimum of 30 repeated measurement cycles. A camera and six linear incremental sensors with assessment units were used for the measurements. The measurements were performed in compliance with the regulations of STN ISO 9283 standard for this type of measurement. As a result of the measurements, the technical specifications of the drift and static compliance of the controlled robotic arm were verified, and the results were compared with the values specified by the manufacturer. Following the measurements and assessment of the results, it was possible to assess the suitability of the used UR5 robotic arm for its application in robotic 3D printing and to propose possible recommendations for the calibration of the robot and the process settings of the printing system for the production of objects using FDM technology.

Programmable and flexible wood-based origami electronics

Natural polymer substrates are gaining attention as substitutes for plastic substrates in electronics, aiming to combine high performance, intricate shape deformation, and environmental sustainability. Herein, natural wood veneer is converted into a transparent wood film (TWF) substrate. The combination of 3D printing and origami technique is established to create programmable wood-based origami electronics, which exhibit superior flexibility with high tensile strength (393 MPa) due to the highly aligned cellulose fibers and the formation of numerous intermolecular hydrogen bonds between them. Moreover, the flexible TWF electronics exhibit editable multiplexed configurations and maintain stable conductivity. This is attributed to the strong adhesion between the cellulose-based ink and TWF substrate by non-covalent bonds. Benefiting from its anisotropic structure, the programmability of TWF electronics is achieved through sequentially folding into predesigned shapes. This design not only promotes environmental sustainability but also introduces its customizable shapes with potential applications in sensors, microfluidics, and wearable electronics.

Synergistic regulation of sintering temperature in calcium silicide-infused porcelain ceramic 3D printing for dephosphorization and deoxygenation

Synergistic regulation of sintering temperature in calcium silicide-infused porcelain ceramic 3D printing for dephosphorization and deoxygenation

Development and characterization of whole-grain buckwheat biscuit formula based on extruded 3D printing technology

Development and characterization of whole-grain buckwheat biscuit formula based on extruded 3D printing technology

Development of modular extrusion bioprinter prototype

Introduction: The aim of this work was to develop a prototype of a modular extrusion bioprinter capable of performing 2D and 3D printing with hydrogels based on sodium alginate and gelatin. Materials and methods: The bioprinter uses Cartesian coordinate system, the print head is movable in Y and Z axes, the printing platform is in X axis and equipped with cooling system. Constructs were printed with 3 types of gels: based on gelatin with the addition various concentrations of xanthan gum; based on combination of gelatin and sodium alginate; based on gelatin and xanthan gum with the addition of carbon nanotubes. Results: The constructs from various gels corresponded to the structure determined by their digital models. Conclusions: The developed system allows performing 2D and 3D printing with gels based on gelatin, sodium alginate, including those containing carbon nanotubes and/or xanthan gum for a wide range of experimental tasks.

Precision 4D Printing of Multifunctional Olive Oil‐Based Acrylate Photo‐resin for Biomedical Applications

AbstractSince the advent of 3D printing technology, a significant effort has been made to develop new 3D printable materials. Despite the recent progress in the field of 3D printing, the limited availability of photoactive resins has motivated continuous research endeavors to develop novel photoresins with multifunctional capabilities. Herein a biobased photoresin derived is reported from modified olive oil, designed for high‐resolution solvent‐free 4D printing with multifunctional capabilities. The physicochemical properties of the printed polymers are fine‐tuned using acrylic acid as a diluent cum comonomer. The mechanical properties of the printed polymers are similar to various soft tissues, such as ligaments, articular cartilage, and soft collagenous bone, showcasing its potential for soft tissue engineering applications. While the excellent temperature‐responsive shape memory 4D attributes coupled with exceptional antimicrobial properties toward gram‐negative and gram‐positive bacteria highlight the multifunctional nature of the printed polymers. Moreover, the printed polymers exhibited outstanding hemocompatibility and good cytocompatibility toward mouse fibroblast cells, suggesting their potential soft tissue engineering applications. In sum, the newly developed biobased resin can be employed to minimize the environmental impact of additive manufacturing while being competitive with existing fossil‐based photoresins, thereby meeting the growing demand for advanced photoresins with superior high‐resolution printing and smart properties for biomedical applications.

Mechanical, thermal, and microstructure analysis of 3D printed polyolefin elastomer-acrylonitrile butadiene styrene blends for tunable mechanical properties

Fused Deposition Modeling (FDM) has emerged as a cost-effective and user-friendly technique that has garnered significant attention in recent years. However, challenges persist when printing soft materials using FDM technology. This study proposes a solution by blending a soft polyolefin elastomer (POE) with a stiffer material, acrylonitrile butadiene styrene (ABS). A comprehensive experimental investigation utilizing a direct pellet printing method was conducted to 3D print POE-ABS blends in various ratios (10%, 30%, and 50% ABS content). The study encompassed material preparation, 3D printing, SEM (Scanning Electron Microscopy) analysis, Dynamic Mechanical Thermal Analysis (DMTA), uniaxial tensile testing, and compression testing to assess the mechanical properties and energy absorption capabilities of the 3D printed blends. The results of the DMTA showed that the blends with a higher amount of ABS have a larger area under the Tan δ curve, indicating their ability to absorb more energy. The SEM images revealed that as the proportion of ABS increases, the gaps between layers and beads become smaller. The mechanical properties of the pure printed POE, such as its elongation at break and tensile strength, were 2138% and 2.83 MPa, respectively. However, as the ABS content increased, the samples exhibited more rigid behavior, with a final transition to 50/50 ratio resulting in 9.4 MPa tensile strength and 160% elongation at break. The energy absorption test demonstrated that the sample with 30% ABS content has the highest energy absorption capability among all the tested samples. This research underscores the potential of blending soft and stiff materials to tailor properties for additive manufacturing applications, emphasizing the significance of material composition in achieving desired mechanical performance, printability, and functionality in printed objects.

A 3D-Printed, High-Fidelity Pelvis Training Model: Cookbook Instructions and First Experience

Background: Since laparoscopic surgery became the gold standard for colorectal procedures, specific skills are required to achieve good outcomes. The best way to acquire basic and advanced skills and reach the learning curve plateau is by using dedicated simulators: box-trainers, video-trainers and virtual reality simulators. Laparoscopic skills training outside the operating room is cost-beneficial, faster and safer, and does not harm the patient. When compared to box-trainers, virtual reality simulators and cadaver models have no additional benefits. Several laparoscopic trainers available on the market as well as homemade box and video-trainers, most of them using plastic boxes and standard webcams, were described in the literature. The majority of them involve training on a flat surface without any anatomical environment. In addition to their demonstrated benefits, box-trainers which add anatomic details can improve the training quality and skills development of surgeons. Methods: We created a 3D-printed anatomic pelvi-trainer which offers a real-size narrow pelvic space environment for training. The model was created starting with a CT-scan performed on a female pelvis from the Anatomy Museum (Cluj-Napoca University of Medicine and Pharmacy, Romania), using Invesalius 3 software (Centro de Tecnologia da informação Renato Archer CTI, InVesalius open-source software, Campinas, Brazil) for segmentation, Fusion 360 with Netfabb software (Autodesk software company, Fusion 360 with Netfabb, San Francisco, CA, USA) for 3D modeling and a FDM technology 3D printer (Stratasys 3D printing company, Fortus 380mc 3D printer, Minneapolis, MN, USA). In addition, a metal mold for casting silicone valves was made for camera and endoscopic instruments ports. The trainer was tested and compared using a laparoscopic camera, a standard full HD webcam and “V-Box” (INTECH—Innovative Training Technologies, Milano, Italia), a dedicated hard paper box. The pelvi-trainer was tested by 33 surgeons with different qualifications and expertise. Results: We made a complete box-trainer with a versatile 3D-printed pelvi-trainer inside, designed for a wide range of basic and advanced laparoscopic skills training in the narrow pelvic space. We assessed the feedback of 33 surgeons regarding their experience using the anatomic 3D-printed pelvi-trainer for laparoscopic surgery training in the narrow pelvic space. Each surgeon tested the pelvi-trainer in three different setups: using a laparoscopic camera, using a webcam connected to a laptop and a “V-BOX” hard paper box. In the experiments that were performed, each participant completed a questionnaire regarding his/her experience using the pelvi-trainer. The results were positive, validating the device as a valid tool for training. Conclusions: We validated the anatomic pelvi-trainer designed by our team as a valuable alternative for basic and advanced laparoscopic surgery training outside the operating room for pelvic organs procedures, proving that it supports a much faster learning curve for colorectal procedures without harming the patients.

Mechanical and Dimensional Stability of Gelatin-Based Hydrogels Through 3D Printing-Facilitated Confined Space Assembly.

Hydrogels have emerged as promising biomaterials for tissue regeneration; yet, their inherent swelling can cause deformation and reduced mechanical properties, posing challenges for practical applications in biomedical engineering. Traditional methods to reduce hydrogel swelling often involve complex synthesis procedures with limited flexibility. Inspired by nature's efficient designs, we present here the approach to improve hydrogel performance using 3D printing-assisted microstructure engineering. By utilizing polymerization-induced phase separation of hydrogel from copolymerization of gelatin methacrylate and hydroxyethyl methacrylate (poly(GelMA-co-HEMA)) in the confined space during vat photopolymerization (VPP) 3D printing, we replicate the cuttlebone-like microstructure of hydrogels with enhanced mechanical properties and swelling resistance. We demonstrate here a 4-fold increase in elastic modulus compared to bulk polymerization of poly(GelMA-co-HEMA), together with improved mechanical and dimensional stability. This method offers promising opportunities for practical biomedical and tissue engineering applications, overcoming previous limitations in the design and performance.

Three-dimensional-printed guide plate for direct percutaneous pedicle screw implantation in minimally invasive transforaminal lumbar interbody fusion surgery: a retrospective study of 162 patients

BackgroundThis study aimed to investigate the impact of three-dimensional (3D)-printed guide plate-assisted percutaneous pedicle screw implantation on minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) surgery.MethodsOverall, 162 patients who underwent MIS-TLIF at Tai’an City Central Hospital were retrospectively reviewed. The studied variables included operative time, volume of intraoperative blood loss, fluoroscopy time, postoperative drainage volume, visual analogue scale (VAS) score, Oswestry disability Index (ODI) score (preoperatively and at 2 weeks, 3 months, 6 months, and 12 months after surgery), and intervertebral fusion rate at 6 months after surgery.ResultsThe conventional group included 99 patients who underwent a conventional procedure, while the 3D printing group included 63 patients who underwent 3D-printed guide plate-assisted percutaneous pedicle screw implantation. The conventional group required more times of positioning needle punctures than the 3D printing group (22.2 ± 5.9 vs. 16.1 ± 4.9). The operation and fluoroscopy time were also longer in the former group (183.5 ± 51.1 min vs. 148.8 ± 40.3 min and 30.2 ± 5.9 s vs. 24.1 ± 4.9 s, respectively). In 3D printing group, lower back pain VAS scores and ODI scores at 2 weeks and 3 months after surgery were observed. There were no significant differences in terms of the volumes of intraoperative blood loss; postoperative lower limb pain VAS scores; and interbody fusion rate (P > 0.05).ConclusionThe novel 3D-printed guide plate-assisted percutaneous pedicle screw implantation can achieve better amelioration of back pain and recovery of function. It also reduced the times of positioning needle puncture and fluoroscopy time during percutaneous screw placement surgery and reduced the duration of surgery.

Introduction of the lowest printable (channel) characteristic length (LPCL) as a geometrical metric for the SLA 3D printing of embedded negative micro-structures

Introduction of the lowest printable (channel) characteristic length (LPCL) as a geometrical metric for the SLA 3D printing of embedded negative micro-structures