Computer-aided Designed Research Articles

Fabrication of 3D printed trabecular bone-templated scaffolds modified with rare earth europium (III)-based complex for enhancing mitochondrial function in bone regeneration

Bone defects have been a tough clinical challenge. The natural trabecular tissue reflects a balance between the minimal metabolic cost of maintenance and maximal network stability, with mitochondria being the energy suppliers for osteogenesis. Herein, a 3D printed trabecular bone-templated scaffold composed of polylactide (PLA) modified with europium (III)-organic ligands (polydopamine and chitooligosaccharide, PDA/COS@Eu) was fabricated (denoted as Tra-PLA/PDA/COS@Eu) to augment bone repair by facilitating mitochondrial function. First, the trabecular bone templated-scaffold provides superior mechanical performance and permeability in contrast to a computer aided designed (CAD) scaffold under a same volume fraction. Tra-PLA/PDA/COS@Eu scaffold up regulated PI3K/AKT/S6K/HIF-1α pathway and significantly promoted BMSCs proliferation and osteogenic differentiation. In addition, Tra-PLA/PDA/COS@Eu scaffold provided anti-inflammatory environment by promoting macrophages M2 polarization through COS, and significantly stimulated BMSCs osteogenesis with enhanced mitochondrial function and biosynthesis. Remarkably, Eu ions are the key ingredient in enhancing mitochondrial function and biosynthesis in BMSCs. Further studies showed that the above-mentioned facilitations in a rabbit bone defect model were found to be more significant with trabecular bone-templated scaffolds, as opposed to CAD scaffolds. In summary, this novel trabecular bone-templated scaffold targeting mitochondrial function has the potential to become an effective method in the treatment of large bone defects.

Computer-aided designed 3D-printed polymeric scaffolds for personalized reconstruction of maxillary and mandibular defects: a proof-of-concept study

PurposeTo investigate the potential reconstruction of complex maxillofacial defects using computer-aided design 3D-printed polymeric scaffolds by defining the production process, simulating the surgical procedure, and explore the feasibility and reproducibility of the whole algorithm.MethodsThis a preclinical study to investigate feasibility, reproducibility and efficacy of the reconstruction algorithm proposed. It encompassed 3 phases: (1) scaffold production (CAD and 3D-printing in polylactic acid); (2) surgical simulation on cadaver heads (navigation-guided osteotomies and scaffold fixation); (3) assessment of reconstruction (bone and occlusal morphological conformance, symmetry, and mechanical stress tests).ResultsSix cadaver heads were dissected. Six types of defects (3 mandibular and 3 maxillary) with different degree of complexity were tested. In all case the reconstruction algorithm could be successfully completed. Bone morphological conformance was optimal while the occlusal one was slightly higher. Mechanical stress tests were good (mean value, 318.6 and 286.4 N for maxillary and mandibular defects, respectively).ConclusionsOur reconstructive algorithm was feasible and reproducible in a preclinical setting. Functional and aesthetic outcomes were satisfactory independently of the complexity of the defect.

Enhanced Precision in Genioplasty: A Novel Intraoperative Spatial Repositioning Using Computer-Aided Design and Manufacturing Technology and a Holographic Mixed Reality Application

Genioplasty is performed for the orthognathic surgical correction of dentofacial deformities. This article reports a safe and accurate method for genioplasty combining a novel three-dimensional (3D) device with mixed reality (MR)-assisted surgery using a registration marker and a head-mounted display. Four types of devices were designed based on the virtual operation: a surgical splint with a connector; an osteotomy device; a repositioning device; and a registration marker. Microsoft HoloLens 2 and Holoeyes MD were used to project holograms created using computed tomography (CT) data onto the surgical field to improve the accuracy of the computer-aided designed and manufactured (CAD/CAM) surgical guides. After making an incision on the oral vestibule, the splint was fitted on the teeth and the osteotomy device was mounted at the junction site, placed directly on the exposed mandible bone surface. Temporary screws were fixed into the screw hole. An ultrasonic cutting instrument was used for the osteotomy. After separating the bone, a repositioning device was connected to the splint junction and bone segment, and repositioning was performed. At the time of repositioning, the registration marker was connected to the splint junction, and mandible repositioning was confirmed three-dimensionally through HoloLens 2 into the position specified in the virtual surgery. The rate of overlay error between the preoperative virtual operation and one-month postoperative CT data within 2 mm was 100%. CAD/CAM combined with MR enabled accurate genioplasty.

Ti6Al4V lattice structures manufactured by electron beam powder bed fusion - Microstructural and mechanical characterization based on advanced in situ techniques

Powder bed fusion (PBF) processes enable the manufacturing of complex components in a time- and cost-efficient manner. Especially lattice structures are currently focused since they show varying mechanical properties, including different deformation and damage behaviors, which can be used to locally tailor the mechanical behavior. However, the present process-structure-property relationships are highly complex and have to be understood in detail in order to enable an implementation of PBF manufactured lattice structures in safety-relevant applications. Within the present work Ti6Al4V lattice structures were manufactured by electron beam powder bed fusion of metals (PBF-EB/M). Based on the classification of bending- and stretch-dominated deformation behavior, two different lattice types, i.e. body-centered cubic like (BCC-) and face-centered cubic like (F2CCZ) structures were selected. Microstructural features were detected to evaluate if potential different microstructures can occur due to different lattice types and to answer the question if microstructural features might contribute to the mechanical behavior shown in this work. Furthermore, X-ray microfocus computed tomography (μCT) analysis were carried out to enable a comparison between the computer-aided designed (CAD) and as-built geometry. For mechanical characterization, quasi-static and cyclic tests were used. In particular, the BCC lattice type showed a more ductile material behavior whereby higher stiffness and strength was determined for the F2CCZ lattice type. Additionally, different in-situ measurement techniques such as direct current potential drop system and digital image correlation could be deployed to describe the damage progress both under quasi-static and cyclic loading.

Accuracy of indirect bracket placement with medium-soft, transparent, broad-coverage transfer trays fabricated using computer-aided design and manufacturing: An in-vivo study

The objective of this study was to test the precision of in-vivo indirect bracket placement via medium-soft, transparent, broad-coverage, computer-aided designed and manufactured transfer trays using an automated digital method. Seventeen patients requiring vestibular fixed appliances were consecutively recruited, and bonding accuracy was measured at each bracket, evaluating 3 linear (mesiodistal, buccolingual, and vertical) and 3 angular measurements (torque, tip, and rotation) with an automated method involving digital superimposition of individual teeth. Mean and standard deviation values were calculated for both arches, single arch, and tooth type, and the percentages of single deviations over the thresholds of 0.25 mm and 1° were calculated, as well as maximum and minimum values for each deviation and directional bias. Correlations between each variable (arch, tooth type, and single tooth) and deviations were investigated through classification and regression trees (CART) predictive models. Neither mean nor single linear deviations ever exceeded the set cutoff value of 0.25 mm. Mean angular deviations never exceeded 1°, but some individual angular deviations did, specifically 8.31% of torque, 13.16% of tip, and 7.16% of rotation deviations. The highest percentage of deviation was recorded for rotation of the maxillary incisors (18.11%). No evident trend in directional deviation bias was found. Tooth type appears to influence mesiodistal and torque deviations, whereas the single tooth variable influenced the percentage of rotation deviations exceeding 1° (P<0.05). This computer-aided designed and manufactured medium-soft, transparent transfer tray provides accurate bracket placement and could be recommended for routinely fixed orthodontics.

Topology optimization and additive manufacturing in producing lightweight and low vibration gear body

Reducing gear vibration as well as its weight is a challenging field latterly. This research deals with the manufacturing of a gear having cellular lattice body structure by using Selective Laser Melting (SLM) technology. A cellular lattice design defines a complex structure which typically cannot be fabricated by conventional manufacturing technologies. On the other hand, the SLM technology enables the production of such complex cellular lattice structures directly from their computer-aided designed (CAD) models. The cellular gear body structure was designed and optimized by employing topology optimization software ProTOp and fabricated by SLM using Ti-6Al-4V alloy. The problems faced by the researchers and the solution which enabled the manufacturing of this gear by SLM are described in this paper. To estimate the performance of the gear during operation, the sound pressure was measured and compared to the results obtained with the gear having a solid body. The experimental results show that the investigated cellular lattice structure of the gear body is well capable to reduce the mass and vibration of the gear.

Optimization of Prosthodontic Computer-Aided Designed Models: A Virtual Evaluation of Mesh Quality Reduction Using Open Source Software.

Mesh optimization reduces the texture quality of 3D models in order to reduce storage file size and computational load on a personal computer. This study aims to explore mesh optimization using open source (free) software in the context of prosthodontic application. An auricular prosthesis, a complete denture, and anterior and posterior crowns were constructed using conventional methods and laser scanned to create computerized 3D meshes. The meshes were optimized independently by four computer-aided design software (Meshmixer, Meshlab, Blender, and SculptGL) to 100%, 90%, 75%, 50%, and 25% levels of original file size. Upon optimization, the following parameters were virtually evaluated and compared; mesh vertices, file size, mesh surface area (SA), mesh volume (V), interpoint discrepancies (geometric similarity based on virtual point overlapping), and spatial similarity (volumetric similarity based on shape overlapping). The influence of software and optimization on surface area and volume of each prosthesis was evaluated independently using multiple linear regression. There were clear observable differences in vertices, file size, surface area, and volume. The choice of software significantly influenced the overall virtual parameters of auricular prosthesis [SA: F(4,15) = 12.93, R2 = 0.67, p < 0.001. V: F(4,15) = 9.33, R2 = 0.64, p < 0.001] and complete denture [SA: F(4,15) = 10.81, R2 = 0.67, p < 0.001. V: F(4,15) = 3.50, R2 = 0.34, p = 0.030] across optimization levels. Interpoint discrepancies were however limited to <0.1mm and volumetric similarity was >97%. Open-source mesh optimization of smaller dental prostheses in this study produced minimal loss of geometric and volumetric details. SculptGL models were most influenced by the amount of optimization performed.

Retention Forces of Prosthetic Clasps over a Simulated Wearing Period of Six Years In-Vitro: Direct Metal Laser Melting Versus Dental Casting.

This study determinates the persistence of retention force in Akers-clasps for removable partial dentures made from Co-Cr alloy. Therefore, standardized computer-aided designed (CAD) clasp #1 specimens were made by direct metal laser melting (DMLM, n = 10) and by lost-wax dental casting (DC) of computer-aided manufactured (CAM) replicas (n = 10, DC) from two comparable Co-Cr alloys. The retention force was tested after manufacturing for 9000 cycles of setting and removal from a molar tooth crown analog made from zirconia; simulating in-vitro a duration of six years in service. The first and last 360 cycles (T0 and T1, 3 months each) of all specimens were selected for comparison of retention forces between the materials. A constant decrease of 6% from the initial retention force (T0 = 4.86 N, SD = 0.077; T1 = 4.57 N, SD = 0.037) was detected at the DC specimens, and an increase of 4% in DMLM specimens (T0 = 5.69 N, SD = 0.078; T1 = 5.92 N, SD = 0.077); all differences were statistically significant (p < 0.0001). Even if these deviations are not of clinical relevance, further studies and applications should investigate the fatigue behavior of laser melted Co-Cr-alloys for dental application.

Manufacturing of silicon – Bioactive glass scaffolds by selective laser melting for bone tissue engineering

The irruption of additive manufacturing techniques opens the possibility to develop three-dimensional structures with complex geometries and high precision. In the current investigation a newly designed composite combining silicon (30, 40 and 50 wt%) with a bioactive glass and printed into scaffolds was obtained, using a direct selective laser melting (SLM) approach for the first time. Samples were computer-aided designed (CAD) to have cylindrical pores of 400 μm in diameter in order to be used as biomaterials for bone replacement. X – Ray diffraction was used to characterize the appearance of a new phase of pseudowollastonite precipitated by the partial devitrification of the glassy phase after the incidence of laser radiation. The mechanical behaviour of each composition was studied trough stress-strain curves, obtaining higher values of compressive strength as the silicon content increases. Scanning electron microscopy coupled to energy dispersive X – Ray spectroscopy (SEM-EDS) and Raman spectroscopy were used to study the bioactivity of each composite after soaking in the simulated body fluid (SBF) for 7 days, confirming this behaviour.

Use of Miniature Step Gauges to Assess the Performance of 3D Optical Scanners and to Evaluate the Accuracy of a Novel Additive Manufacture Process.

In this work, we show how miniature step gauges featuring unidirectional and bidirectional lengths can be used to assess the performance of 3D optical scanners as well as the accuracy of novel Additive Manufacturing (AM) processes. A miniature step gauge made of black polyphenylene sulfide (PPS) was used for the performance verification of three different optical scanners: a structured light scanner (SLS), a laser line scanner (LLS), and a photogrammetry-based scanner (PSSRT), having comparable resolutions and working volumes. Results have shown a good agreement between the involved scanners, with errors below 5 μm and expanded uncertainties below 10 μm. The step gauge geometry due to the bidirectional lengths, highlights that there is a different interaction between the optical properties of the step gauge under measurement and each optical instrument involved and this aspect has to be considered in the uncertainty budget. The same geometry, due to its great significance in the detection of systematic errors, was used, as a novelty, to evaluate the accuracy of Lithography-based Ceramics Manufacturing (LCM), a proprietary additive manufacturing technology used for the fabrication of medical implants. In particular, two miniature step gauges made of Tricalcium Phosphate (TCP) were produced. Measurements conducted with the SLS scanner were characterized by a negligible error and by an uncertainty of about 5 μm. Deviations of the manufactured step gauges with respect to the Computer Aided Designed (CAD) model were comprised between ±50 μm, with positive deviations in the order of 100 μm on vertical sides. Differences in the order of 50 μm between the two step gauges were registered.

An In Vitro Comparative Study to Assess Minimal Thickness Required for Monolithic Zirconia Crowns to Resist Fracture under Load on Rapid Prototyped Models

To evaluate and validate minimal thickness required for computer-aided designed (CAD) and computer-aided manufactured (CAM) monolithic zirconia crowns to withstand occlusal load. The study compares two systems. Forty-eight rapid prototype die models with varying occlusal reductions were fabricated. Group I samples had an axial wall height of 7.0 mm with occlusal reduction of 0.5 mm, group II had axial wall height 6.5 mm with occlusal reduction 1.0 mm, group III had axial wall height 6.0 mm with occlusal reduction of 1.5 mm. Control group IV had axial wall height 5.5 mm with occlusal reduction of 2.0 mm. Laboratories A (Czar) and B (3M) were provided with 24 samples each, 6 samples in each group for fabricating CAD/CAM monolithic zirconia crowns of 0.5, 1.0, 1.5, and 2 mm occlusal thickness, respectively, and cemented using resin-modified glass ionomer cement over the die models. Samples were loaded on a universal testing machine for fracture testing. Surface topography analysis of fractured specimens was done under the scanning electron microscope (SEM). The results were subjected to one-way analysis of variance (ANOVA) and honestly significant difference (HSD) Tukey test to analyze statistical significance at 0.05 levels. Samples of laboratory A performed superior to laboratory B. The t test showed fracture resistance of group AI (0.5 mm) > group BII (1.0 mm) and also group AIII (1.5 mm) > control of Lab B (2 mm). Monolithic zirconia crowns showed a favorable mechanical property to withstand occlusal load with minimal tooth preparation. The occlusal thickness of Czar with 0.5 mm is found to resist fracture under physiological masticatory load. Scanning electron microscope revealed increased voids in the microstructure of 3M, which lead to decreased fracture resistance. Preservation of tooth structure can be considered using monolithic crowns with minimal thickness of 1 mm.

A compartmental 3D scaffold fabrication and alignment device for neurovascular co-culture and tri-culture

Tissue engineers seek for the practical and affordable fabrication methods to be able to create the best biomimicking scaffold. The aim of the study was to create an easy-to use device to fabricate precisely designed 3D hydrogel scaffolds for co-culturing, tri-culturing and multi-culturing practices. In this study, gelatin methacryloyl (GelMA) was synthesized and textured three-dimensional hydrogel scaffolds were fabricated via photopolymerization using compartmental fabrication device. This device allowed fabricating computer aided designed (CAD) geometries precisely and encapsulating different cells in different hydrogel posts while building a whole geometry. The hydrogel texture characterization was performed using colored hydrogel solutions and it is observed that the device keep the distinct posts in contact precisely. A neural tissue model was created using neural, epithelial and endothelial cells as a proof of concept. Cell distribution was evaluated using cell trackers. The viability and the proliferation assays were also performed and the viability was above 80% while a positive proliferation was been observing. Overall findings showed that this device offers a practical way to fabricate and align precisely designed three-dimensional hydrogel scaffolds which allows modelling various types of tissues and organs and it tis promising for further applications in many fields.

RF02 ANOMALOUS AORTIC CORONARY ARTERY ORIGIN: A PARAMETRIC STRUCTURAL FINITE ELEMENT ANALYSIS AND COMPUTATIONAL SIMULATION.

Background and aim: In anomalous aortic origin of coronary arteries (AAOCA) underlying ischemic mechanism during high stress conditions have still to be elucidated. The study aims to understand the biomechanics of such a condition and in particular how the lumen of the AAOCA may narrow during aortic expansion. Methods: We create a parametric computer-aided designed (CAD) model of the aortic root and AAOCA origin and perform a static finite element analysis (FEA) on 10 models with different angles of take-off and intramural penetration at three different loading conditions (i.e. stress condition). The model is defined by twenty-three parameters describing aortic root geometry and allows to vary coronary position, take-off angle, degree of intramural penetration, and length of the intramural course to simulate the pathological conditions of AAOCA. Results: We show that the AAOCAs experience a reduced luminal expansion (LE) (LE = 1.85%, 5.98%, 10.42%) compared to the healthy ones (LE = 11.9%, 22.43%, 36.66%,) at 120-150-180 mmHg of aortic root pressure respectively. Acute angles of take-off lead to elongated ostia, with an eccentricity (e) that increases with aortic expansion (i.e. e = 0.72-0.69-0.66 at 120-150-180 mmHg, take-off angle = 35’ and 50% penetration). Conclusions: The study describes for the first time an idealized geometrical model as a proof of concept for static structural finite element simulations to assess the role of specific geometrical features on AAOCA physiopathology. The possible mechanism of lumen reduction in AAOCA can rely on biomechanical reasons and computational simulations may allow patient specific predictive model in future.

Human Bone Inspired Design of an Mg Alloy-Based Foam

As an initial step of this research, open cell magnesium foams were obtained by infiltration casting using a preform of salt particles with irregular morphology. Despite this metallic foam was a successful approach to bone replacement scaffold, the properties of a metal foam need to be improved to meet the requirements by accurately adjusting the porous geometry. The tissue scaffold structure should be submissive biologically as well as mechanically and should at best mimic the natural properties of bone to act as an accurate bone substitute. The architectural and mechanical bone scaffold parameters determine the biological outcome.This work aims to design and manufacture an ordered foam with mechanical and architectural properties similar to those of the bone using an Mg alloy as a base material. Accordingly, representative features were identified to generate computer-aided designed (CAD) unit cells. Then, a set of the selected cells was assembled to obtain a specified architecture for bone replacement. Finite element method analysis was applied to calculate the mechanical response. The architectural parameters were varied to match the elastic properties of human bone concerning suitable exposed area, volume, and pore size. The best architecture was determined by compression loading acting on the assembly. Finally, polymeric stamps with sets of truncated octahedrons will be printed from the CAD model and were replicated in a clay made with a combination of salt and flour. Infiltration casting will obtain last of all, open cell magnesium foams.

Aortic Expansion Induces Lumen Narrowing in Anomalous Coronary Arteries: A Parametric Structural Finite Element Analysis.

Anomalous aortic origin of coronary arteries (AAOCA) is a congenital disease that can lead to cardiac ischemia during intense physical activity. Although AAOCA is responsible for sudden cardiac death (SCD) among young athletes and soldiers, the mechanisms underlying the coronary occlusion during physical effort still have to be clarified. The present study investigates the correlation between geometric features of the anomaly and coronary lumen narrowing under aortic root dilatations. Idealized parametric computer-aided designed (CAD) models of the aortic root with anomalous and normal coronaries are created and static finite element (FE) simulations of increasing aortic root expansions are carried out. Different coronary take-off angles and intramural penetrations are investigated to assess their role on coronary lumen narrowing. Results show that increasing aortic and coronary pressures lead to lumen expansion in normal coronaries, particularly in the proximal tract, while the expansion of the anomalous coronaries is impaired especially at the ostium. Concerning the geometric features of the anomaly, acute take-off angles cause elongated coronary ostia, with an eccentricity increasing with aortic expansion; the impact of the coronary intramural penetration on the lumen narrowing is limited. The present study provides a proof of concept of the biomechanical reasons underlying the lumen narrowing in AAOCA during aortic expansion, promoting the role of computational simulations as a tool to assess the mechanisms of this pathology.

Statistical analysis of dimensional accuracy in additive manufacturing considering STL model properties

Additive manufacturing (AM) is a technology that produces a part layer by layer based on the computer-aided designed (CAD) model. Each AM process is defined by a set of parameters and materials. The laser power, scan spacing and speed, preheating and bed temperatures, hatch length, pulse frequency, and part placement (coordinates of a part placed in the build) are among the most studied process parameters reported in the literature. Recent attention to improving part quality is caused by the possibility of using AM for manufacturing, but the inconsistency of results’ repeatability is the main challenge that is not solved yet. This work attempts to improve the dimensional accuracy by predicting dimensional features of the part, namely length, width, and thickness. Data is collected from two identical runs done on EOS P395 polymer laser sintering system. By identical runs is meant that build layout, material and process parameters were kept constant in both runs. Pearson correlation test is used to identify whether the new parameters (the number of mesh triangles, surface, and volume of CAD model) are significantly correlated to dimensional features. Based on the correlation results, linear regression models are developed to predict dimensional features (compensate shrinkage effect). The obtained results are the following: models for thickness (in XZY orientation), length (in ZYX orientation), and length and thickness (in Angle orientation) can already be used to predict dimensional features (to minimize shrinkage effect by proposing scaling ratio for each specimen in the build separately).

Observation of Shape and Dimensional Accuracy Changing of Parts in Time Intervals Manufactured by Additive Method Fused Deposition Modeling

This article deals with the observation of shape and dimensional accuracy of parts after manufacturing in certain time intervals. The parts was manufactured by additive manufacturing method Fused Deposition Modeling (FDM). The shape and chosen dimension changes due to material shrinkage was observed on materials, namely Polylactic Acid (PLA) and Polyethylene Terephthalate Glycol (PET-G). These materials rank among health-conscious and usable in some medical applications. The parts were measured by using coordinate measuring machine (CMM) in certain time intervals and the shape and chosen dimensions was compared with the reference computer aided designed (CAD) model.

The effect of different geometric shapes and angles on the fracture strength of IPS e.max computer-aided designed ceramic onlays: An in vitro study.

Statement of Problem:The current ceramic onlay preparation techniques for cuspal areas involve the reduction of cusps following the cuspal anatomy and the removal of all sharp angulations. However, there is little research literature studying the effect of occlusal preparation angles. Furthermore, there is no recent literature on the effect of angulations on IPS e.max computer-aided designed (CAD) (e.max) ceramic onlays.Purpose:The purpose of this study is to investigate the effect of geometric cuspal angulation and different internal preparation angles on the fracture strength of e.max CAD ceramic onlays.Materials and Methods:Sharp (33° and 22°) and round (33° and 22°) preparations were tested, each group having 10 specimens. e.max ceramic onlays were milled, sintered, glazed, and then bonded onto geometric tooth models. Fracture strength was measured at the initial fracture with a universal testing machine. The load was applied laterally to the central fossa (2-point contact) and vertically to the cusp peak (1-point contact).Results:A reduced cuspal angulation of 22° resulted in a stronger ceramic onlay than a 33° angulation when laterally loaded (P = 0.001). The presence of sharp angles weakened the ceramic significantly for both the 22° preparation (P = 0.0013) and 33° preparation (P = 0.0304).Conclusion:This in vitro study found that preparation angles of 22° resulted in superior fracture strength during central fossa loading and that rounding the preparation resulted in significantly higher fracture strength when a cusp peak load was applied. When the cusp tip loading is applied, the preparation angle does not appear to influence the fracture strength.

New fabrication method using additive manufacturing technologies for the pattern of pressed lithium disilicate onlay restorations

There are 7 categories for the additive manufacturing (AM) technologies and a wide variety of materials that can be used to build a computer aided designed (CAD) 3-Dimensional (3D) object. The present article reviews the main AM processes for polymers for dental applications: stereolithography (SLA), direct light processing (DLP), material jetting (MJ) and material extrusion (ME). The manufacturing process, accuracy and precision of these methods will be reviewed, as well as, their prosthodontic applications. Keywords: 3D printing; Additive manufacturing technologies; Direct light processing; Fused deposition modelling; Material extrusion; Material jetting; Multijet printing; Prosthodontics; Stereolitography.

Microscale Numerical Simulation of Non-Darcy Flow of Coalbed Methane

To obtain the real physical model characterizing the pore structure of coal rocks and further explore the rules governing the flow of coalbed methane (CBM) using numerical simulation, we proposed a sequential method from real coal model to computer-aided designed (CAD) coal model to finite element coal model. First, six different coal samples were scanned using $$\upmu $$ CT225kVFCB CT system. The obtained CT data were subject to threshold segmentation using the compensated digital terrain model and a coal model in STL format was established. Then, we elaborated a reverse engineering method to convert the coal model into a CAD coal model. Lastly, we obtained the finite element coal model after setting the boundary conditions with CFX software, numerically simulated CBM flow at 30 different pressure gradients based on the finite element coal model and analyzed the impacts of effective porosity on permeability and seepage velocity of CBM. The results showed that (1) at the microscale ( $${<}100\,\upmu \hbox {m}$$ ), the seepage velocity and pressure gradient were in agreement with the Forchheimer law of high-speed nonlinear seepage; (2) permeability of CBM shows a fluctuating, but not absolute increase with effective porosity increasing; (3) at the same pressure gradient, the overall seepage velocity of CBM increases with the effective porosity increasing, but declines with non-Darcy flow coefficient increasing; (4) the non-Darcy flow coefficient reduces with both effective porosity and permeability increasing. Fitting to power function analysis shows that compared with permeability, the effective porosity has more significant impact on the non-Darcy flow coefficient.