3D Printing Materials Research Articles

Systematic Review of the Quality of Stereolithographic Three-Dimensionally Printed Materials for Provisional Dental Restorations

Background and Objectives: The use of stereolithographic (SLA) 3D printing technology in dentistry has expanded, particularly for the fabrication of provisional dental restorations. Understanding the mechanical properties and quality of SLA 3D-printed materials is essential to ensure clinical success and patient safety. This systematic review aims to critically evaluate and summarize the available evidence on the mechanical properties and quality of SLA 3D-printed materials. Methods: A comprehensive literature search was conducted in PubMed, Scopus, Embase, Cochrane, and Web of Science up to October 2024. Studies comparing the mechanical properties of SLA 3D-printed provisional restoration materials with those of milled, conventional, or other additive manufacturing methods were included. Nine studies met the inclusion criteria. Data on flexural strength, hardness, fracture resistance, surface roughness, marginal adaptation, accuracy, cement film thickness, shear bond strength, and biofilm formation were extracted and analyzed. Results: The findings from the included studies indicate that SLA 3D-printed materials exhibit varied mechanical properties. Some studies reported that SLA 3D-printed resins had significantly lower flexural strength and hardness compared to milled PMMA and bis-acrylic resins. Other studies found that SLA 3D-printed resins showed clinically acceptable marginal adaptation, surface roughness, and fracture strength comparable to those fabricated by subtractive manufacturing and conventional methods. In terms of accuracy, build orientation influenced the dimensional accuracy of SLA-printed restorations. Studies assessing cement film thickness found that SLA-printed provisional restorations had higher cement film thickness compared to other materials. Regarding repairability and fatigue resistance, limitations were observed in some SLA resins. Conclusions: The mechanical properties and quality of SLA 3D-printed materials for provisional dental restorations vary among studies. While SLA technology holds promise for efficient fabrication of provisional restorations, inconsistencies in material properties suggest a need for further research to optimize materials and printing parameters. Standardization of protocols is necessary to ensure reliable clinical performance of SLA 3D-printed provisional restorations.

Resin Composite Depth of Cure Through Transparent Matrix Materials Used for Injection Molding.

The purpose of this study was to compare the curing light transmittance and depth of cure (DOC) of resin composite through clear polyvinyl siloxane (PVS) impression materials and 3D printed clear matrix materials at various thicknesses. Cylindrical specimens (n=6) of three clear PVS materials (Affinity Crystal, Clear Bite Matrix, Exaclear) were fabricated in Teflon molds, and two 3D-printed clear matrix materials (Filtek matrix, IDB 2) were printed into specimens of five different thicknesses (2 mm, 4 mm, 6 mm, 8 mm, 10 mm). To measure light irradiance transmittance, specimens were placed on a radiometer (CheckUp), allowing the transmitted irradiance from a light-curing unit (Elipar DeepCure-S, 1450 mW/cm2) to be recorded. DOC of resin composite specimens was measured by placing flowable composite (PVS and IDB 2) or heated conventional composite (Filtek Matrix) into a split metal die with a 4 mm diameter opening. The composite was cured through the different matrix specimens using the Elipar DeepCure-S curing light for the manufacturer's recommended curing time (10 seconds) or double the curing time (20 seconds). The DOC of the composite specimens was measured according to ISO 4049 7.8, and the percentage of total cure (%TC) was calculated by dividing by the total cure (DOC with no matrix and 10-second cure). The correlation between irradiance transmittance and %TC was analyzed with Pearson's coefficient. For each matrix material, the %TC was compared to the total cure of the material using a Dunnett's test. The compressive modulus of each material was measured and compared with a one-way ANOVA. There was a statistically significant, strong positive correlation between irradiance transmittance and %TC for 10 seconds (r=0.90 p<0.001) and 20 seconds (r=0.89 p<0.001). There was not a statistically different DOC for the total cure with Affinity (2 mm), Clear Bite (2 mm), Exaclear (2, 4, 6 mm), IDB2 (2, 4, 6, 8 mm), and Filtek Matrix (2,4 mm) if a 20-second cure was used. Decreased light irradiance from curing through clear matrix materials decreases the DOC of resin composites. Doubling the curing time when curing through some matrix materials at certain thicknesses allowed a total cure.

Interlaminar bonding assessment in vertical-oriented filament material extrusion bending specimens

Abstract Fused filament fabrication (FFF) is the leading 3D printing material extrusion process renowned for its versatility, affordability and easy production of complex components. Despite its advantages, the bonding quality between layers depends heavily on processing parameters and filament material properties. Using an orthogonal experimental design, this study investigates the effects of three nozzle-dependent variables—flow rate, temperature and speed. Poly(lactic) acid (PLA) specimens, built vertically, were evaluated via 3-point bending tests to assess flexural strength and surface roughness. The results showed that speed had an insignificant effect, while optimal performance was achieved at a 100% flow rate and 227 °C nozzle temperature across speeds of 50–70 mm/s, yielding ~ 67 MPa flexural strength and ~ 13-μm surface roughness. A reduced second-order regression model effectively captured these relationships. By focusing on bonding-related parameters, this work advances the understanding of FFF process optimization for enhanced component properties.

Application and progress of 3D printed biomaterials in osteoporosis

Osteoporosis results from a disruption in skeletal homeostasis caused by an imbalance between bone resorption and bone formation. Conventional treatments, such as pharmaceutical drugs and hormone replacement therapy, often yield suboptimal results and are frequently associated with side effects. Recently, biomaterial-based approaches have gained attention as promising alternatives for managing osteoporosis. This review summarizes the current advancements in 3D-printed biomaterials designed for osteoporosis treatment. The benefits of biomaterial-based approaches compared to traditional systemic drug therapies are discussed. These 3D-printed materials can be broadly categorized based on their functionalities, including promoting osteogenesis, reducing inflammation, exhibiting antioxidant properties, and inhibiting osteoclast activity. 3D printing has the advantages of speed, precision, personalization, etc. It is able to satisfy the requirements of irregular geometry, differentiated composition, and multilayered structure of articular osteochondral scaffolds with boundary layer structure. The limitations of existing biomaterials are critically analyzed and future directions for biomaterial-based therapies are considered.

Printability and Performance Metrics of New-Generation Multifunctional PMMA/Antibacterial Blend Nanocomposites in MEX Additive Manufacturing

Poly(methyl methacrylate) (PMMA) is a thermoplastic widely utilized in civilian-, defense-, and medicine-related applications. Therefore, inducing antibacterial properties is an additional asset when infection control is prioritized. To counter this, PMMA was mixed, for the first time, with antibacterial agents (antibacterial blend nanopowder, AP) to curb bacterial proliferation and therefore reduce the chances of infection. The reinforcing efficacy of the blend in PMMA was also assessed. Nanocomposites were developed with various nanopowder concentrations for 3D printing material extrusion (MEX). PMMA/AP nanocomposites were evaluated for their mechanical and rheological properties, thermal stability, morphological, structural, and chemical characteristics, and bacterial resistance (against Staphylococcus aureus and Escherichia coli (E. Coli) using the well diffusion method). The effect on quality metrics, such as the geometrical accuracy and pores of the 3D-printed structure was examined with micro-computed tomography. The modified PMMA had improved properties, such as increased tensile (~20% increase at 2 wt.%) and flexural strength (~10.8% at 4 wt.%), while also having strong antibacterial properties against Staphylococcus aureus and mild antibacterial properties against E. Coli. Such improvements add to the expanding portfolio of biomaterials, such as their use in the demanding defense sector and the medical field.

Influence of carboxyl content on the rheological properties and printability of oxidized starch for 3D printing applications.

With the rapid development of 3D printing technology, the development of starch gels based on 3D printing with excellent printing properties has attracted great attention. This study successfully prepared four types of oxidized starch (OMS) with varying carboxyl group contents (0.203%, 0.612%, 1.043%, and 1.278%) by controlling the amount of sodium hypochlorite. Rheological analysis of these OMS gels revealed typical shear-thinning behavior and excellent structural recovery during heating shear across various concentrations. As the concentration of OMS increased, key parameters such as consistency index (K), storage modulus (G'), yield stress (τy), and flow stress (τf) also increased, signifying enhanced molecular chain entanglement and densification with reduced digestibility. Conversely, at a constant concentration, increasing carboxyl group content led to decreased K, G', τy, and τf values due to molecular chain degradation, resulting in diminished aggregation and increased network pore size. Notably, OMS gels demonstrated favorable printability within a specific range of G' (4314.0-6690.0Pa), τy (1254.8-2697.5Pa), and τf (822.3-2296.3Pa). Meanwhile, oxidized starch (OMS2 and OMS3) gels exhibited exceptional printability, attributed to appropriate molecular chain length and carboxyl content, which promoted sufficient physical crosslinking. These findings provided theoretical insights and foundational data for developing 3D printable starch-based materials.

EDITORIAL| Special issues for “emerging materials for 3D printing in construction”

EDITORIAL| Special issues for “emerging materials for 3D printing in construction”

Experimental and numerical analysis of 3D-printed pure PLA and ceramic-reinforced PLA multilayered composites

Fused Deposition Modeling (FDM) is a remarkable manufacturing method that helps us to produce such complex structures without the need for extra components or parts as required by most other manufacturing processes. This research article has focused on 3D-printed multi-layered polymer composite materials for various kinds of biomedical applications. In this research investigation, polylactic acid (PLA) is considered an alternative to the existing material in biomedical applications. In addition, for further improvement of the mechanical performance of PLA composite structures, ceramic-reinforced PLA (CRPLA) filament materials have been utilized to be multilayered with pure PLA materials. Ceramic particles have proved to enhance the mechanical and thermal properties of polymer composites. The tensile, compression, and flexural strength of 3D-printed pure PLA, ceramic composite, and multilayered laminates were evaluated experimentally, which was validated by FE simulation analysis. The results concluded that the tensile, flexural, and compressive strengths of multilayered 3D-printed composite laminates were increased by 28.9%, 5.9%, and 16.3%, respectively, compared with pure PLA-printed laminates. Scanning electron microscopy (SEM) has been utilized to investigate the fractography analysis of multilayered composite laminates. Moreover, thermal characterization has been done by using differential scanning calorimetry (DSC) analysis.

Three-Dimensional-Printed Elements Based on Polymer and Composite Materials in Dentistry: A Narrative Review

Abstract 3D printing technologies are manufacturing technologies based on computer-designed digital models that allow fabrication of layered three-dimensional objects. This review aims to present a summary of the literature published on 3D-printed polymer and composite materials in dentistry. A literature search was performed using the PubMed database to identify eligible articles. In total 508 articles were identified based on the original search query, with 362 being eliminated based on the exclusion criteria and 146 articles were screened and based on their abstracts, 68 articles were studied in detail. Subsequently, these articles were divided into three groups based on the area of application: (1) restorative dentistry, which included 3D printed crowns, bridges, and veneers; (2) regenerative dentistry and tissue engineering, such as 3D printed scaffolds; (3) fabrication of oral guides and other appliances, such as surgical guides, dental implants, and surgical splints. In this review the 3D printing technology is described, including its benefits regarding working time, accuracy and overall design and fabrication of products. The review shows that the most studied area of application of printable polymers and composites is regenerative dentistry. Even though these materials are studied for their properties and the effects on the human body as well as the environment, novel materials with specific and revolutionary characteristics that have emerged in recent years are given special attention. However, more research is needed to ensure the safety of use and confirm the characteristics of novel materials in both in vivo and in vitro conditions.

Temperature‐Driven Topological Transformations in Prestressed Cellular Metamaterials

AbstractStimuli‐responsive materials are able to alter their physicochemical properties, e.g., shape, color, or stiffness, upon exposure to an external trigger, e.g., heat, light, or humidity, exhibiting environmental adaptability. Their capacity to undergo shape reconfiguration, pattern transformation, and property modulation enables multifunctionality. In this work, two strategies are harnessed, i.e., prestressed assembly and temperature‐dependent stiffness reversal, to introduce a class of temperature‐responsive metamaterials capable of undergoing topological transformations, endowing them with smart functionality. Through a combination of mechanics theory, numerical simulations, and thermomechanical experiments, the physical mechanisms underlying the temperature‐triggered topological transformations leading to pattern switches are first elucidated, and then the insights are leveraged to demonstrate tunable bandgaps and robotic capturers. These findings reveal the attainment of giant negative and positive values of coefficient of thermal expansion, accompanied by isotropic expansion and shrinkage under thermal actuation within a fairly rapid timeframe, below 6 s. The strategy here presented is versatile as it relies on a pair of off‐the‐shelf 3D printable materials, can be up‐ and down‐scaled, and can also be realized through other physical stimuli, e.g., light and moisture, paving the way for use in multifunctional applications, including stimulus‐triggered morphing devices, autonomous sensors and actuators, and reconfigurable soft robots.

Development of 4D-Printed Arterial Stents Utilizing Bioinspired Architected Auxetic Materials

The convergence of 3D printing and auxetic materials is paving the way for a new era of adaptive structures. Auxetic materials, known for their unique mechanical properties, such as a negative Poisson’s ratio, can be integrated into 3D-printed objects to enable them to morph or deform in a controlled manner, leading to the creation of 4D-printed structures. Since the first introduction of 4D printing, scientific interest has spiked in exploring its potential implementation in a wide range of applications, from deployable structures for space exploration to shape-adaptive biomechanical implants. In this context, the current paper aimed to develop 4D-printed arterial stents utilizing bioinspired architected auxetic materials made from biocompatible and biodegradable polymeric material. Specifically, three different auxetic materials were experimentally examined at different relative densities, under tensile and compression testing, to determine their mechanical behavior. Based on the extracted experimental data, non-linear hyperelastic finite element material models were developed in order to simulate the insertion of the stent into a catheter and its deployment in the aorta. The results demonstrated that among the three examined structures, the ‘square mode 3’ structure revealed the best performance in terms of strength, at the same time offering the necessary compressibility (diameter reduction) to allow insertion into a typical catheter for stent procedures.

Flexural Strength, Fatigue Behavior, and Microhardness of Three-Dimensional (3D)-Printed Resin Material for Indirect Restorations: A Systematic Review

The purpose of this systematic review was to evaluate three mechanical properties of 3D-printed resins for indirect restorations according to published scientific evidence. This systematic review was conducted according to the PRISMA statement (preferred reporting elements for systematic reviews and meta-analyses). The search was performed by two investigators, (DD) and (VB), and a third (AC) resolved disagreements. Articles were searched in four digital databases: PubMed, EBSCO, Lilacs, and Science Direct, starting on 18 February 2024. As 3D-printing technology has shown significant advances in the last 5 years, the review was conducted with a publication year range between 2019 and 2024, in English language and included in vitro articles on the mechanical properties of flexural strength, fatigue behavior, and microhardness of 3D-printed materials for temporary or definitive restorations. MeSH terms and free terms were used for the titles and abstracts of each article. Finally, the QUIN tool was used to assess the risk of bias. In the main search, 227 articles were found, of which 20 duplicates were excluded, leaving 207 articles; of these, titles and abstracts were read, and 181 that did not meet the eligibility criteria were eliminated; of the remaining 26 articles, 1 article was eliminated for not presenting quantitative results. Regarding publication bias, 6 of the 25 articles had a low risk of bias, 18 had a medium risk of bias, and 1 had a high risk of bias. It may be concluded that 3D-printed resins have lower flexural strength, fatigue behavior, and microhardness than other resin types used for the fabrication of temporary and permanent restorations. The type of 3D printer and polymerization time could be factors that significantly affect the flexural strength, fatigue behavior and microhardness of 3D-printed resins. Based on existing evidence, it should be considered that additive technology has promising future prospects for temporary and permanent dental restorations.

Three-Dimensional-Printed Photopolymer Resin Materials: A Narrative Review on Their Production Techniques and Applications in Dentistry

Additive manufacturing (3D printing) has transformed dentistry by providing solutions with high precision and accuracy achieved through digital workflows, which facilitate the creation of intricate and personalized structures. Additionally, 3D printing promotes cost efficiency by reducing material waste and errors while enabling on-demand production, minimizing the need for extensive inventories. Recent advancements in 3D-printed resin materials have enhanced their clinical applications by improving mechanical strength, biocompatibility, esthetics, and durability. These innovations have facilitated the fabrication of complex and patient-specific structures, such as dental prostheses, surgical guides, and orthodontic appliances, while significantly reducing production time and material waste. Ongoing research and innovation are expected to strengthen resin properties, including strength, translucency, and durability, broadening their clinical applications. The ongoing evolution of 3D printing technology is poised to play a critical role in driving personalized treatments, streamlining clinical workflows, and shaping the future of dental care. This narrative review comprehensively examines the production techniques and clinical applications of 3D-printed photopolymer resins across various dental specialties, including prosthodontics, orthodontics, pediatric dentistry, maxillofacial surgery, periodontology, endodontics, and conservative dentistry. Additionally, the review provides insight into the transformative impact of these technologies on patient care, highlights existing challenges, and suggests future directions for advancing resin properties and their integration into routine dental practice.

Correction: Głowacki et al. Change in the Low-Cycle Performance on the 3D-Printed Materials ABS, ASA, HIPS, and PLA Exposed to Mineral Oil. Polymers 2024, 16, 1120

Correction: Głowacki et al. Change in the Low-Cycle Performance on the 3D-Printed Materials ABS, ASA, HIPS, and PLA Exposed to Mineral Oil. Polymers 2024, 16, 1120

Polycarbonate–Acrylonitrile Butadiene Styrene Three Dimensional Printing Material Exhibits Biocompatibility and Enhances Osteogenesis and Gingival Tissue Formation with Human Cells

Three dimensional (3D) printing materials are widely used in dental applications, but their biocompatibility and interactions with human cells require evaluation. This study aimed to identify materials meeting biocompatibility, mechanical strength, and tissue-forming requirements for safe dental applications. We assessed the cytotoxicity of resins and thermoplastic filaments in human HaCaT keratinocytes, gingival fibroblasts (hGFs), and stem cells from human exfoliated deciduous teeth (SHED) using PrestoBlue assays. Three resins, including two types of surgical guide resins, exhibited strong cytotoxicity after 4–72 h, while 2 h exposure to an FDA-approved surgical guide resin did not affect SHED cell viability. In contrast, six thermoplastic filaments showed no significant cytotoxicity even after 72 h. Among these, polycarbonate–acrylonitrile butadiene styrene (PC-ABS) demonstrated excellent toughness, heat resistance, and surface quality at a low cost. SHED cells cultured on PC-ABS dishes and micro bone structures showed strong proliferation and osteogenic potential. Culture inserts made of PC-ABS also supported the growth of HaCaT keratinocytes and the hGFs formed gingival tissue, which was superior to that formed on commercially available PET inserts. In conclusion, PC-ABS is a promising 3D printing material for dental applications due to its biocompatibility, ability to promote osteogenesis, and support for gingival tissue formation, with no observed cytotoxicity.

Microbial Adhesion and Cytotoxicity of Heat-Polymerized and 3D-Printed Denture Base Materials when Modified with Dimethylaminohexadecyl Methacrylate and/or 2-Methacryloyloxyethyl Phosphorylcholine as Antimicrobial and Protein-Repellent Materials.

Polymethyl methacrylate (PMMA) is ideal for denture bases but is prone to biofilm accumulation, leading to denture stomatitis (DS), often involving Candida albicans. Dimethylaminohexadecyl methacrylate (DMAHDM) and 2-methacryloyloxyethyl phosphorylcholine (MPC) are introduced into dental materials for their antimicrobial and protein-repellent properties. This study investigates the effects of incorporating dimethylaminohexadecyl methacrylate (DMAHDM) and 2-methacryloyloxyethyl phosphorylcholine (MPC) into heat-polymerized (HP) and 3D-printed (3DP) denture base resins on microbial adhesion and cytotoxicity. HP and 3DP denture base specimens were prepared using varying concentrations of DMAHDM and MPC. Microbial adhesion was quantified using CFU counts of C. albicans, and cytotoxicity was assessed via an MTT assay using fibroblast cells after 24 h, 3 days, and 7 days. Both DMAHDM and MPC significantly reduced the CFU counts in both HP and 3DP materials; the combination of 1.5% DMAHDM and 3% MPC exhibited the most substantial antimicrobial effects. Cytotoxicity results varied between materials and time points; however, all treated groups maintained cell viability above the 70% threshold, indicating no significant cytotoxic effects. Incorporating DMAHDM and MPC into denture base resins can effectively reduce microbial adhesion while maintaining acceptable cytotoxicity levels.

Electrochemical Biosensors 3D Printed by Fused Deposition Modeling: Actualities, Trends, and Challenges.

The technology of 3D printing, particularly fused deposition modeling (FDM) 3D printing, has revolutionized the development of electrochemical biosensors, offering a versatile and cost-effective approach for clinical applications. This review explores the integration of FDM in fabricating biosensing platforms tailored for clinical diagnostics, emphasizing its role in detecting various biomarkers and viral pathogens. Advances in 3D printing materials, especially the emergence of bespoke conductive filaments, have allowed the production of highly customizable and efficient biosensors. A detailed discussion focuses on the design and application of these biosensors for viral detection, highlighting their potential to improve diagnostic accuracy. Furthermore, the review addresses current trends, including the push towards miniaturization and multianalyte detection, alongside challenges such as material optimization and regulatory hurdles. By providing a comprehensive overview, this work underscores the transformative impact of 3D-printed electrochemical biosensors in clinical diagnostics while also identifying critical areas for future research and development.

Recent Advances in Surface Functionalized 3D Electrocatalyst for Water Splitting

Hydrogen is gaining attention as a fossil fuel alternative due to its potential to meet global energy demands. Producing hydrogen from water splitting is promising as a clean and sustainable fuel pathway. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are crucial in electrocatalytic water splitting for energy conversion and storage. However, water electrolysis faces challenges in cost, efficiency, and scalability. Alternative transition metal electrocatalysts and emerging 2D materials advance electrolysis research, though transitioning from academia to industry remains challenging. The introduction of 3D‐printing technologies has revolutionized electrode fabrication for HER and OER. This review explores integrating 3D‐printing technologies and surface functionalization with non‐noble metal‐based electrocatalysts and emerging 2D materials. It focuses on surface‐functionalized 3D‐printed electrodes using technologies like selective laser melting, stereolithography, and fused deposition modeling with non‐noble metal electrocatalysts such as transition metal oxides, hydroxides, and emerging 2D materials like transition metal carbide/nitride (MXenes) and transition metal dichalcogenides (TMDCs). The review highlights the opportunities and challenges in scalable fabrication, long‐term durability, and cost‐efficiency for practical implementation. Future research directions include exploring new materials for 3D printing and alternative electrocatalysts alongside leveraging theoretical and machine‐learning approaches to accelerate the development of competitive materials for water electrolysis.

Particle Trajectory Simulation Facilitates the Development of an Efficient Sample Introduction System for Single-Particle ICP-MS Analysis.

Inductively coupled plasma mass spectrometry (ICP-MS) has demonstrated significant capabilities in the analysis of single events, such as single cells and particles. Researchers have been actively pursuing innovations in ICP-MS sample introduction systems to enhance their transport efficiency, as this is critical for ensuring the accuracy of single-event analysis. However, the majority of prior studies have relied heavily on empirical approaches, with limited attention given to the individual characteristics of particles from a theoretical perspective and a lack of efficient manufacturing tools for optimizing related components. Herein, we developed a high-efficiency sample introduction system for single-event ICP-MS analysis by integrating the computational simulation-aided design, precise 3D printing manufacturing, and rapid experimental testing process. For the first time, we simulated the transport trajectories of individual particles passing through the spray chamber, providing theoretical guidance for the design and optimization process. The statistical analysis of particle trajectories revealed that under the absorption boundary condition, particles between 20 and 100 nm achieved transport efficiencies exceeding 18.8%. In comparison, particles larger than 100 nm exhibited 0% transport efficiency due to increased deposition within the spray chamber. The spray chamber was fabricated in-house using a range of 3D printing technologies and materials, streamlining the process and reducing the cost for both manufacturing and validation. Further optimization of the operating parameters, including an increase in temperature, resulted in a notable transport efficiency of 61.1%. The workflow introduced in this study has the potential to transform the research and development of critical mass spectrometry components moving forward.

Research progress of polylactic acid/graphene composites and polylactic acid/ graphene oxide composites

The preparation of graphene/polylactic acid nanocomposites by modifying polylactic acid with graphene and its derivative graphene oxide is reviewed. It mainly includes solution method and melt blending method. Under different processing methods, the dispersion degree of nano fillers in the matrix is different, and the properties of the obtained materials are different. The choice of graphene and graphene oxide has a greater impact on the properties of the materials. The improvement of the mechanical properties of graphene /PLA composite materials has made the performance of PLA in packaging, textiles, biomedicine and other fields more excellent, while the gas isolation performance and electrical conductivity brought by graphene have opened up more new directions for graphene /PLA composite materials, such as 3d printing materials.