digital design of medical replicas via desktop systems: shape evaluation of colon parts.

by:INDUSTRIAL-MAN     2019-10-09
The prospect of complex shape manufacturing is a key factor that can bridge the manufacturing of additives (AM)
Medical application]1].
AM represents a small ideal
Mass customized production as the production of patients
The specific object is.
In fact, contrary to traditional manufacturing techniques, changes in nominal design may reduce the impact on AMplanning and related costs [2].
This applies not only to medical applications, but also to all cases where a high degree of customization is required, for example, in space applications [3].
So far, medical researchers and clinicians have limited access to process knowledge of 3D printing technology.
Now that this is changing rapidly, many surgeons and radiologists are starting to build their own 3D printing labs.
Understanding the advantages and limitations of various 3D printing technologies is a key factor in successful investment and expansion of 3D printing into the medical field.
In the literature, as [stated], many works relate to AM applications for medical purposes1].
They range from preoperative models to implants, surgical tools, and assistive devices.
AM is currently applied to face and orthopedics for custom implants and tools as well as coronary artery surgery [j [4, 5]. In [6]
, For rapid delivery of fracture skull models.
The effectiveness of using this model as a preoperative guide was shown. Time-
If a preoperative model of the fracture is provided, the surgical operation to reduce the fracture may be affected. In[7]
, AM is a new method for reducing fracture of the eye cavity.
The usual procedure is for the surgeon to manually plastic the metal platform based on what he found during the procedure.
The proposed method allows for the rapid delivery of the patient\'s skull model.
Based on this, an enhanced implant was designed to allow better fusion with adjacent bones.
The results showed that due to better surgical planning, the position of the artificial eye was improved and the operation time was shortened.
At the same time, it is also proved that the quality of the 3D model does not have a certain impact on the shape of the implant. In [8]
The geometric modeling problem was proposed to measure the fragments of the skull. In [9]
AM has been used to obtain a liver model.
Based on this, surgeons have a clearer idea of the postoperative incision in liver transplant surgery, helping to reduce the risk of donors.
These considerations were effectively and successfully implemented during liver transplant surgery.
By visual inspection and measurement carried out during the operation, comparing the copy with the real copy, the high accuracy of the copy can be displayed.
Similarly, the accuracy of the model is very important.
Inaccurate models are not able to plan a reliable surgical incision. In [10]
A workflow was proposed for fetal facial digital models to help diagnose cleft lip disease and to study the emotional impact on parents.
In AM technology, fuse manufacturing (FFF)
At present, most widely, in part, because the initial patent of Stratasys company expired in 2007, and Stratasys is the company that invented the technology, named melting deposition modeling (FDM).
This, along with the simplicity of the system, allows for low
Cost system, also called desktop system [11].
In order to provide a numerical example, we can consider that in 2015, the expensive business system and the low
Cost of desktop system (
That means less than $5000)
It\'s about 1: 20.
In addition to cost considerations, desktop systems can also be highly adaptable.
The selected materials can be selected in the materials of different suppliers.
Provides very limited limits on the set values available for process parameters.
On the contrary, this freedom does not guarantee any assurance from the supplier of quality, as it is generally applicable to more expensive solutions in materials, sizes, and shapes.
For a medical copy that can be used as a tool to manage surgical planning or better understand a particular patient, the desktop system seems desirableRelated aspects.
They can translate 2D qr easily and at low cost (
Digital imaging and communication in medicine)
Analysis of physical copies (
Also called [model]12])
Helps to correctly perceive the actual shape and length. In [13]
A medical replica of the skull and Chin made by a professional finite difference system was studied from a metrology perspective.
The authors applied a comparison between digital models and reproductions of different genders and ages, announcing excellent accuracy (
The overall average deviation is 0. 24%)
Limited difference technology compared to other fast prototyping technologies. In [14]
A low-cost FDMsystem is introduced and discussed for providing the performance of the jaw 3D model.
Although the performance is satisfactory, there is no discussion about the use of the system in terms of digital design.
A number of studies have shown that the spatial error of medical replicas is less than 1mm [15-17].
Generallyspeaking, medicalapplications related to shape and size inspection because it must (i)
[Quantification of gravity and evolution of deformity19]and (iii)
Interaction between organs and tools.
AM technology involves different sciences, almost every aspect of simulation in the literature [1]20, 21].
However, factors such as technology, process knowledge and robustness are not yet mature.
This lack of knowledge can lead to uncertainty that is still missing in manufacturing objects and standard tolerance control.
The digital design workflow requires data preprocessing, which requires specific skills in 3D modeling from opc;
Mosaic of slices;
Define process parameters according to functional and quality requirements [22].
Part of these topics requires new object-oriented methods and solutions, as they relate to [new] technologies23].
While these steps have become common skills in the engineering field, they are not always available in the medical field.
For these reasons, the most critical aspects are discussed in this paper (
Hardware, software and process parameters)
Digital design of medical replica through desktop system.
After their speech, a test
A case consisting of a portion of the colon, from the B-shaped colon to the rectum.
Its purpose is to provide an experimentaloverview replicascuracy process and quantitative evaluation, through a large number of experiments purchased by astrucured-light system.
For the experimental part, two low
Cost desktop systems, mobilbot and Tevo have been applied and compared-LittleMonster.
According to this goal, in section 2, we introduce the general workflow of digital design in terms of final precision;
Then, in section 3, we discuss the requirements set by the medical application;
Finally, we present and discuss the applications obtained and related experimental results. 2.
Regardless of the specific AM process, in the digital design workflow, we can differentiate the following steps [24]: (i)
Set the 3D model as the appropriate STLfile (ii)
Including the CAM settings for slicing and machining of component manufacturing (iii)
Post-processing related to removal of components from the manufacturing table and other operations required to remove external support and guarantee final shape and roughness (
Separation of adhesion of parts, surface treatment, etc. ).
Each step has its own workflow, which can be dedicated to specific application areas.
In Figure 1, some further details have been addressed according to the application of the medical copy.
Pre-processing begins with the capture of areas of interest in medical imaging (DICOM).
They can be obtained from different technologies, such as computed tomography (CT)
Electron emission tomography (PET), X-
Ray, ultrasonic, etc.
Medical images are two-dimensional images of the horizontal section of the human body.
These parts are usually done with a series of variable steps (
We assume the 3mm step, which in our specific case represents a good compromise between the time consumption and accuracy of the wide area scan).
They must be processed by segmentation to isolate the areas of interest from the rest of the body.
Then, a set of parts related to the quantity of interest (e. g.
Part of the organ)
Pile up to get a point, filter, and/or smooth 3D Cloud to achieve an appropriate description of the 3D model.
In most cases, especially in X-
Ray, a specific algorithm must be used [25].
In this step, errors may be wrong segmentation due to wrong pixel classification;
Due to the large scanning steps, the accuracy is insufficient;
And the 3D cloud of points with holes, so the segmentation is not accurate.
Must be checked according to the law (
Non-intersection or non-intersection
Multiple triangles should exist)and integrity.
If not, appropriate repair functions, such as optimization of shape triangles and filling of holes, must be applied.
If this step is not available, it may result in an object that is incorrectly manufactured, or an error interruption of the AM process [2].
After the examination, if a specific function must be provided, for example, the ability to open a part of the organ for an internal examination, the modeling steps can be considered.
Cam setting and machining (CAM)
Includes slices related to selecting the direction of the layer, as well as subdividing the 3D model into a set of slices called slices.
In this step, it is also necessary to assess the need to divide the copy into parts.
This may be due to the presence of open details that allow inspection or visibility, or it may be due to other manufacturing restrictions (e. g.
, Print the volume of the camera).
The result of the slice is an approximate 3D object given by the stack of 2D slices.
Their height is equal to the user-defined layer-
Thickness parameters.
The outer surface that is not aligned with the vertical direction will inevitably show
Called stair effect
The thickness of the layer affects this approximation.
The normal direction of the tilt represents the direction of the process.
It also affects the strength of the filling and support to avoid the collapse of the unsolidified bottom or unsupported slices.
Supports the reduction of the final quality of the surface and requires post-processing work to be carried out with care to remove the surface.
Regarding the definition of process parameters, it is related to the technology adopted.
The FFF allows the fabrication of slices by squeezing the melt aggregate filament through the nozzle.
The material usually used is acrylic acid-Ding benzene (ABS)
And lactic acid (PLA)
In the form of loose filament coils.
They are mainly used for rapid prototyping and do not cost. 2, 26].
As a basic component of any FFF hardware, the liquid nozzle (
The diameter is generally from 0. 2 to 2 mm)
Allow to melt the filament by reaching the temperature (
Within the scope of 100 【degrees]-200[degrees]
C, forABS and PLA).
Once liquefied, due to the pressure applied on the solid filament, the polymer flows out through the nozzle.
It is driven by a clamping roller mechanism.
The polymer is deposited on a printed plate or on a previously constructed layer.
When the heat is lost in the surrounding environment, the polymer melts and freezes.
The head through which the material passes can be moved along the print bed plane, I. e. , x-
Ydirections, because this can be moved independently along the height direction (zdirection).
Through this mechanism, 3D objects can be printed out.
In order to discuss the process in depth, as well as the country-of-the-
Modeling of Art Science, readers can refer to the review paper [20, 21].
A major disadvantage of this setup is related to the temperature gradient in the deposition process.
If it occurs suddenly, uneven cooling conditions may occur inside the manufactured part, resulting in residual stress (shrinkage).
In order to reduce the shrinkage, the chamber temperature should be guaranteed.
For desktop systems that normally do not have a closure and control room, a heated printed plate may help to achieve better conditions.
In addition, in the process of CAM pretreatment, correction factors can be applied to compensate for shrinkage as a function of the selected material.
Other problems that may affect this process are the Filament Extrusion conditions at the nozzle.
At the nominal value, the thickness of the layer may be uneven and stable.
Due to a problem with the mechanism of the material supply vector to the nozzle, or due to friction, it may change
Heat non-continuity in nozzle.
These aspects may be the most important for desktop systems, as they are not guaranteed or optimized in all process variables, as is the case with commercial systems [E. G. 27-29].
Regarding the post-processing steps, it is necessary to remove the part from the manufacturing platform and possibly support it.
Through proper operation, the surface finish can be improved, thus improving the residue of the support and stair non-continuity.
They can be mechanically operated or low
Cost chemical solutions such as acetone steam bath.
Very effective solution for chemistry [30]
But they only apply to certain materials.
For example, acetone bath is not suitable for lactic acid (PLA). 3.
Digital design requirements for surgeons to use medical replicas of tangible life
For preoperative planning, to explain the procedure of surgery to the patient and the dimensional model of the individual anatomy during the procedure as a reference.
Compared with traditional manufacturing technology, 3D printing has advantages.
In a clinical setting, a personalized single model can be created as needed, and the cost is relatively low in a fairly short period of time.
The medical needs of digital design can be summarized as follows :(1)
Areas of interest :(i)
Selection of a single organ/segment or multiple organs (ii)
Location of the area of interest (
Internal area, external area and internal and external area)(2)
Provide pins and positioning elements for the exhibition :(i)
Used to install parts in it (ii)
Open/close interesting areas (3)
Good size and shape accuracy these requirements constrain the pre-processing and the CAM steps shown in figure 2.
In more detail, the first requirement comes directly from dicomsegmation, which may have an impact on material selection (
Multiple Materials/colors can be selected if multiple organs are copied [9]).
The existence of the internal details of the organ requires a replica to be opened.
It will affect the copy modeling steps, requirements (a)
Modeling the separation of parts in coincident segments; and (b)
Modeling closed pins.
The necessity of the part that must be opened will also affect the manufacturing step, because in the case of complex shapes, it usually requires support during the slicing process.
For rapid prototyping, support must be highlighted in order to avoid post-processing issues.
Therefore, the shape of the surface to be opened is defined by a standard that provides a trade-off between the internal area size maximization, visibility and operability, and the minimum support, perfection and aesthetics.
The second requirement (
Provide pin and positioning elements for the exhibition)
Requires the addition of surface details embedded in the region of interest split, or external volumes built to repair the copy.
In any case, it may introduce local modifications to the model, thus affecting the process settings.
Positioning elements can also be designed separately from the copy.
The complex shape of a medical replica is typical free of charge
A surface characterized by curvature and curvature in different directions.
In the case of the colon, no cross section is equal to any other cross section in terms of length and morphology (Figure 3).
To ensure accuracy, the most stringent manufacturing limitation is to reduce the bracket.
The bracket must be removed mechanically, which will inevitably lead to a decrease in surface quality of the two structures combined [2].
In addition, cracks may be induced by mechanical action [31]
, Hidden under a roughly defined surface.
In order to avoid these problems, it is necessary to subdivide the axes in the straight section so that each subpart has an appropriate slice direction, suitable for minimizing stair effects and bracket requirements.
Figure 4 shows the assignment of this concept applied to the colon shown in figure 3. In Figure 4(a), its slicing (green)
The simulation is performed in the direction that it is possible to minimize the height of the bracket and remove difficulties. In Figure 4(b)
Although the brackets are more concentrated, their height is more relevant and protrude inside the folds, so there may be significant difficulties in the removal process.
Obviously, the solution in figure 4 (a)
, The small area bracket attached to the bracket will be badly affected after removal.
However, in Figure 4 (a)
In order to improve the finishing, it is easier to complete the solution, post-processing operations than Figure 4 (b)case.
For better surface accuracy, longitudinal cuts divided into two parts can be defined.
In this case, the correct inclination direction means finding the plane of the section along the center axis of the segment considered, which includes the projection of the overall half volume of the segment.
By doing so, the segment will be subdivided into two subparts with the smallest height and the largest interior
So that the volume can besupporting.
In this case, the department will require the parts to be bonded after processing, but it avoids the need for rough surfaces and post-processing, as well as factors that may reduce the accuracy of shape and size.
The test cases described in the next section will apply this solution to minimize post-processing work.
Finally, Figure 5 summarizes the concepts behind this reasoning from the sources of errors and the necessary efforts in the digital design workflow CAM steps. 4. Application 4. 1. Test-
Case description.
The proposed workflow has been applied to the evaluation of a replica of the colon and its final rectal part (Figure 3).
In the latter, abnormal growth and polyps are visible both inside and outside.
This proves two different manufacturing strategies.
Since there is no interest in indicating the internal part of the colon, this will be constructed as a dense part.
Instead, the final rectum will be built to create a hollow part, paying attention to polyps and abnormal growth.
Their shape and location, as well as the specific shape of the colon fold, are fundamental to the surgeon and, ultimately, they justify the manufacture of a medical replica.
Parts are copied through two different desktop systems: razbot and Tevo-
The little monster, from now on, is called DS1 and ds2 respectively.
Table 1 shows an overview of the Board values they declare.
In more detail, DS1 and ds2 replicate the B-shaped colon, and ds2 prints the final rectal.
Figure 6 shows the final copy, the red part is related to DS1, and the brown part is related to ds2.
In both cases, the materials used are the PLA.
For DS1, the selected parameter is the height of 0.
15mm, except for the first floor (0. 30 mm)
, Starting with a filament diameter of 1. 75 mm.
Nozzle temperature is 230 [degrees]
C. in disk 60 【degrees]C.
We choose to follow the shape of 3 perimeter in each layer, then, fill the inner part by the honeycomb 2D structure squeezed in the z direction.
For DS2, the diameter of the filament is 1.
75mm, height 0. 16 mm.
Nozzle temperature is 230 [degrees]
C. in plateau 80 [degrees]C.
The outer perimeter is made at a speed of 40 mm/s, otherwise higher, up to 650 mm/s for non-printable areas.
In this case, we choose to follow the shape of 4 perimeter in each layer, and then, as before, fill the interior through the honeycomb 2d structure and squeeze in the Z direction.
A honeycomb filling pattern with a density of 15% was selected.
Support is the same in both cases.
To evaluate the quality of the replica, measurements have been made and compared with the 3D model.
They have been acquired through caliber and reverse engineering by a structured
Light business system (Scan in a Box-FX)
Accuracy of declaration 0.
04mm, the minimum resolution is 0. 062 mm. 4. 2.
Pretreatment and manufacturing.
As described in section 3, good accuracy can be achieved by reducing external support and reducing the number of individual fragments.
The subdivision in the fragment is mainly due to the complexity of the shape, and there are different maximum surface projection planes along its axis.
In addition, because of the use of a very simple desktop system, the subdivision program is necessary to use a nozzle.
Therefore, the components to be printed must be the same material as those, if present.
Therefore, the mechanical removal of the bracket may also lead to the fracture and fracture of the components.
Otherwise, other removal techniques and procedures can be developed if there are multiple nozzles in the system.
Figure 7 shows the final fragment breakdown of the test with different colorscase.
The 5 fragments obtained, 4 of the B-shaped colon, and the last segment of the rectal ampulla are the result of the mid-axis positioning and segmentation into parts that can minimize the external stent.
The four colon segments were separated again during two surgeries.
This limits the inaccuracy of the outer surface and provides a flat contact area with the printed plate without involving the outer surface.
In addition, the cutting plane was selected to maximize the normal projection of the area of the part envelope.
In this way, we can also apply the cutting direction that is orthogonal to the cutting plane, so as to minimize or completely avoid the bottom cutting, especially the folds, thus minimizing the support.
Figure 8 shows the details of the subdivision in two sections of the first colon fragment at the top of the 3D model.
Obviously, in this case, there is no need to support given the internal volume of the filling structure filling. Figure 7(b)
Shows the breakdown adopted in the last segment associated with the rectum.
Contrary to expanded colon fragments, they are thin-
Wall volume that must be opened for internal inspection.
Because of their freedom.
Shape shape, the bracket is necessary to avoid the collapse of the inner surface and part of the protruding detail from the bottom height, as shown in Figure 9.
Also in this case, depending on the internal area of interest that must be displayed, it is found that the cutting plane can minimize the height, thus supporting the need to open a specific volume.
Axis analysis, fragment segmentation and slice positioning were performed interactively in the CAD environment.
Regarding the optimization of minimizing the bracket, the additional volume of the bracket has been checked iteratively. 5.
The experimental results and discussions of all the planning sections were successful.
Through some reverse engineering acquisitions, a quantitative comparison of the AM copy with the mosaic obtained from cdr was obtained.
They are associated with the first paragraph of the upper part of the colon.
Since there may be light reflection on the acquired surface, during the acquisition process, the structure-
Powder is covered on the lighting system.
Align with embedded software to get each fragment in multiple views (IDEA)
Through the best accessories.
After that, the point cloud is superimposed into the 3D model and measured by distance analysis.
The acquisition consists of more than 480x103 points, which were analyzed after selective filtering based on curvature analysis, which left about 91x103 points.
Figure 10 shows the results of the color chart.
In both cases, the deviation range is less [+ or -]1mm.
Specifically, more than 95% of the points are included between + 0 in each case. 48 mm and -0. 40mm.
In DS1 and DS2, the average deviation is very close to zero, showing a negative value (-0. 04 mm).
Shrinkagecan is therefore considered to be controlled, although it exists in a narrow blue area (small entity).
This result is consistent with the results already found in the literature (
A value with a deviation of less than 0.
1mm defined as non-shrinkage or controllable shrinkage)[13].
Due to the limitation of the adopted system, the stair effect and the thickness of the filament cannot be seen;
Otherwise, along the profile of the bonded part, the continuity is clearly displayed in DS2 (Figure 10(b)).
In the case of DS1, the system position of the blue area and the small value of the mean deviation are realized. let us say that in the process of alignment or acquisition, thistrend may depend on possible inaccuracies, rather than relying on the existence of shrinkage or errors in the manufacturing process.
With regard to the rectal ampulla section, sections that can be opened have been evaluated for thickness by caliber.
It confirms that the average value is 1mm, equal to the average value specified in the digital design.
These experimental evidence confirm that good shape accuracy can be achieved by using a low precision method
The cost desktop system is also very complex-form shapes.
Pay attention to minimize the presence of support and avoid serious contamination of materials (e. g.
, Increase the speed of deposition on the outer surface)
A good copy of all fragments is allowed without the need for surface post-processing.
On the contrary, the necessity of bonding a single part cannot be reduced.
Nevertheless, the experimental results show that it results in an error of less than 1mm. 6.
Conclusion This paper analyzes the digital design workflow of medical replicas and applies them to most of the replication of the colon. Twolow-
Cost desktop systems, shared robots and Tevo-
Little Monsters are used to make replicas of PLA.
Requirements for data preprocessing of this digital approachedaccording (a)
Make the copy part open and (b)
Surface post-treatment is limited due to support removal.
The open area is the rectal area, which is obtained as an athin-
Wall segment with a removable housing.
Instead, other parts are filled with honeycomb-in at 15%.
Complex freedom
Avoiding or limiting surface post-treatment mainly means minimizing the presence of the support, thereby optimizing the direction of the slice.
According to this, the center axis of the entire surface is divided into 5 segments, which is suitable to reproduce the related surface in the best slice direction.
Found a plane through the center axis of the line segment and was able to define two self
Support volumes, thus avoiding local support for printed tables on complex surfaces.
In order to ensure the visibility and accessibility of the inner surface, paragraph 5 (
About therectum)
It must be provided in a sparse volume, so some support must be provided.
This pre-processing step represents the most time-consuming part of the workflow, and while the cutting plane may be provided automatically, the current overall assessment of how many segments must be used for partitioning is based on integrated products, this is still a manual step. process skills.
After getting copies of all the clips, they are glued together.
The final shape of the first colon segment, contrary to the rectum, has been structured-light system.
The deviation analysis with the experimental results showed that the shape error was slower than 1mm and the experimental point exceeding 95% was less than 0. 5 mm.
The statistical distribution of points does not exist (
Or high limit)
Contraction effect, the distribution of deviations is almost symmetrical (
Average of less than 0. 1mm).
Finally, this paper shows that the desktop system can be used as a quick solution for medical replicas, showing good accuracy in the replication of complex shapes.
In terms of simplicity of the workflow, geometric design standards have been defined to ensure that surface treatment is completed by reducing support, minimizing post-processing work.
However, without proper automation of the processing of 3D models to set up clips, pre-processing is still a bottleneck for medical autonomous applications without the need for additional skills in the engineering field.
As a future work, the algorithm that provides process automation will be analyzed and developed.
In addition, this study will turn to the possibility of promoting and re-applying on other different types of organs.
This paper includes reverse engineering data and manufacturing parameters used to support the results of this study.
Upon request, the corresponding authors provide input data and all other data used to support the results of this study.
Conflict of Interest authors state that there is no conflict of interest in publishing this paper.
The study was funded by the University of Sapienza and received the following :(i)
University of Sapienza no.
Rm11715c7cbb72 24,207, \"3D tissue modeling with finite element analysis (FEA)
Model for surgical simulation and anatomical education \"; (ii)
University of Sapienza no.
Archos 1550284399b, 2016, \"CAD-
CAE tools for designing additional components \"; (iii)
University of Sapienza no.
C26J15ENS7, 2015, \"3D prototyping: additional manufacturing techniques and applications from micro to macro dimensions. Selective laser sintering/melting in China, macchinananotopoli
PDTA di vetettura \"; and (iv)
University of Sapienza no.
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Michelle beach, Cardinal valario, Marco yugini, Robinson Guachi, Fabiano biini, Francesca Campana (iD)
Marinozzi, Franco (iD)
, Dipartimento di PaoloGaudenzi ingneria Meccanica nazaerospaziale, sapienzauniverita Rome, by the Eudossiana decree, Rome 00184, Italian correspondence should be addressed to Francesca camparna; francesca.
Campana @ uniroma1.
Received on July 27, 2018;
Accepted on October 23, 2018;
Guest Editor Published in November 14, 2018: Michelle Cali Title: Figure 1: digital design workflow for medical reproductions and related error sources.
Description: Figure 2: Details of the sub-steps of pre-processing of medical replicas.
Picture Description: Figure 3: a 3D model of a descending/B-shaped colon and rectum, reconstructed by 3D segmentation and 3D point surface.
Description: Figure 4 :(a)
Slice simulation is performed according to the optimized direction to minimize the height of the bracket. (b)
Slice simulation in different directions.
Description: Figure 5: constraints on the CAM steps in the medical replica digital design workflow.
Description: Figure 6: final copy of DS1 (red)
And DS2 finalreplicas (brown): (a)
Model of final assembly; (b)
Replication of the first segment of the B-shaped colon.
Description: Figure 7: Subdivision of 3D model (
One color per production part): (a)
Segments of the spine; (b)
See the rectal subdivision of the inner surface (
The part to open (
Expressed in green)).
Title: Figure 8: First colon segment :(a)
Divided into two parts and (b, c)
Related slice simulation.
Description: Figure 9: Rectal segment :(a)
Section of the part connected to the colon; (b)
Slice of the part to be opened.
Description: Figure 10: analysis of the relevant deviation of the experimental results between the 3D model and the obtained copy :(a)DS1; (b)DS2.
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