ArticlePDF Available

Abstract and Figures

Given the production method used in additive manufacturing (successive layers build-up) anisotropy is to be expected. This study is oriented on the anisotropy of the mechanical properties in compression for 3D printed parts made of PLA that are used for medical applications. The ratio of elastic modulus on longitudinal to the transverse direction was found to be 0.48 and 0.59 for the yield strength, showing that an accentuated anisotropy appears. Thermal processing was performed in order to ameliorate the anisotropy and the ratio value was risen to 0.73 for the elastic modulus and 0.86 for the yield strength.
Content may be subject to copyright.
U.P.B. Sci. Bull., Series B, Vol. 81, Iss. 4, 2019 ISSN 1454-2331
ANALYSIS OF THE ANISOTROPY FOR 3D PRINTED PLA
PARTS USABLE IN MEDICINE
Sebastian GRADINARU
1
, Diana TABARAS
2
, Dan GHEORGHE2*, Daniela
GHEORGHITA2, Raluca ZAMFIR2, Marius VASILESCU2, Mircea
DOBRESCU2, Gabriel GRIGORESCU2, Ioan CRISTESCU
3
Given the production method used in additive manufacturing (successive
layers build-up) anisotropy is to be expected. This study is oriented on the
anisotropy of the mechanical properties in compression for 3D printed parts made
of PLA that are used for medical applications. The ratio of elastic modulus on
longitudinal to the transverse direction was found to be 0.48 and 0.59 for the yield
strength, showing that an accentuated anisotropy appears.
Thermal processing was performed in order to ameliorate the anisotropy and
the ratio value was risen to 0.73 for the elastic modulus and 0.86 for the yield
strength.
Keywords: 3D printing, anisotropy, mechanical properties
1. Introduction
Additive manufacturing (AM) is used to describe a process where a part or
even a whole system is rapidly created. The basic principle of this technology is
that a model created using a Computer Aided Design (CAD) software can be
fabricated directly by successive material addition. Initially the model was used
solely for visualization purposes and current technology and material
improvement allows the output to be suitable for end use.
Current AM technologies specified by ASTM F2792 are binder jetting,
directed energy deposition, material extrusion, material jetting, powder bed
fusion, sheet lamination and Vat polymerization, each with its own targeted fields.
In the medical field AM is an emerging technology [1] with wide use in
personalized implant design and manufacture [2,3].
Of widespread in medical implant fabrication are extrusion-based systems
that use the extrusion process to form parts.
1
"Carol Davila" University of Medicine and Pharmacy Bucharest, Romania
2
University POLITEHNICA of Bucharest, Romania, e-mail: dan.gheorghe@upb.ro
3
Department of Orthopaedy & Traumatology, Clinical Emergency Hospital, Bucharest, Romania
314 Dan Gheorghe & co
The basic stages for the extrusion-based systems, as described in Fig.1,
are: filament material loading using a
feeding system, its liquefaction in a
liquefier chamber then moved under
pressure through a nozzle, extrusion
and plotting in a controlled manner
on a specified path. The extruded
material bonds to itself or other
materials and forms a coherent
structure.
The properties of filament
materials need to comply to the
manufacturing process as well as to
finished product requirements. For
medical applications the copolymers
of polyglicolic acid (PGA) and
polylactic acid (PLA) are most used
given their history in use for sutures,
scaffolds and biodegradable fixation materials [4-7], while new emerging
composites (scaffolds of absorbable polymers with cell and osteo-inductive
agents) usable as filament materials are developed [8-16].
PLA are biodegradable thermoplastic aliphatic polyesters, semi-crystalline
in nature with melting temperatures of 200-205°C and a glass transition
temperature of approximately 58°C. Their ultimate tensile strength is 25-50MPa
with a low elastic modulus of circa 4GPa [17] when processed by injection
molding.
Polymer processing methods and their parameters are known to alter their
characteristics [18-20], thus a study regarding the printed and processed PLA is
required, especially when its use is for structural applications.
2.Materials and methods
The generic additive manufacturing stages employed for sample
fabrication are shown in Fig. 2. A CAD model is required then it is converted into
a STL file which is manipulated and transferred to the machine where the part is
built, removed, post-processed (usually de-burred) and prepared for application.
Fig. 1. The principle of 3D printing
Analysis of the anisotropy for 3D printed PLA parts usable in medicine 315
Fig. 2 Sample processing route
In this study the test samples were obtained by 3D printing using a
CuraBCN3D Sigma 3D printer using as filament
poly-lactic acid (PLA). Printing parameters were
kept constant for all samples: the infill was set to
100% with a rectilinear pattern with ±45° infill
angles, 5 top and bottom solid layers and 3
perimeter outlines, as depicted schematically in
Fig. 3. In total 40 test samples shaped as cubes
(10x10x10mm) were printed using the above-
mentioned 3D printer parameters. The CAD
model and a finished 3D printed sample are
shown in Fig. 4along a detail during 3D printing.
a.
b.
c.
Fig. 3 Machine set-up parameters
and tool-head travel during sample
printing
316 Dan Gheorghe & co
The obtained test samples were then separated into 4 batches, each
comprising 10 specimens. One batch was used as reference, two were thermally
processed by heating at 90°C in boiling water and in an electric furnace, held at
this temperature for 60min and air cooled while the last was melted at the surface
using a heat gun until individual layers were no longer visible. Sample coding
along the processing parameters are mentioned in Table 1.
Table 1
Sample coding and processing
Sample coding
Processing
R
As printed, no processing
TP1
Water heating at 90°C/held 60min at 90°C/air cooling
TP2
Furnace heating at 90°C/held 60min at 90°C/air cooling
TP3
Superficial melting using a heat gun/air cooling
On the samples a dimensional analysis was performed by measuring the
dimensions of a sample using a digital caliper with ±0.01mm resolution. One
sample was randomly extracted from each batch and 18 length measurements
were performed. The data was processed statistically and comparison against the
reference sample was performed.
Using an Olympus BX51 light microscope the sample surface was studied.
Using the microscope proprietary software layer thickness measurements were
performed on randomly extracted samples and comparison was performed against
the reference. The samples from TP3 batch was excluded from this investigation
since the superficial melting process obscured individual layers.
Compression tests were performed using a hydraulic universal testing
machine Walter+Bai LFV 300. The samples from each batch were devised in two
subsets depending on the 3D printing direction (material build-up): parallel or
perpendicular. The resulting force-displacement curves were processed in order to
determine the mechanical characteristics (elastic modulus and yield strength in
compression). An anisotropy coefficient was computed by dividing the property
determined in one direction against the one determined on the perpendicular
direction.
3. Results and discussion
3.1. Dimensional analysis of samples
On a random extracted sample from each batch 18 length measurements
were performed using a digital caliper, this procedure being similar to a
computerized dimensional analysis performed by Pantea [21] on connector
diameters for fixed partial dentures. The results were recorded and processed, the
box-plot presented in Fig. 5 shows the results.
Analysis of the anisotropy for 3D printed PLA parts usable in medicine 317
Fig. 5 Box-plot showing the spread of data for the
dimensional analysis
From Fig. 5 it can be seen that reference sample R has the lowest while the
surface melted sample TP3 has the greatest dataspread, still within acceptable
tolerances for most applications.
A t-Test for two sample assuming unequal variances was performed with a
null hypothesized mean difference using α=0.05. The test was performed in pairs
by comparing R with TP1, R with TP2 and R with TP3.The results are shown in
Table 2. Table 2
The results of the t-Test
Pair
Hypothesized
mean difference
t-Statistic
Significance
R-TP1
0
1.64
0.114
R-TP2
0
2.57
0.016
R-TP3
0
0.54
0.597
Statistical significant differences do not appear in the case of R-TP1 and
R-TP3, thus dimensional variation does not appear when processing is performed
in boiling water and superficial melting using a heat gun. Significant dimensional
variations in sample dimensions, from statistical point of view, appear when
heating is performed in an electric furnace.
3.2 Study of layer thickness
Using the Olympus BX51 light microscope images on the surfaces of a
random extracted sample were obtained, a selection being presented in Fig. 6. The
heat gun treated samples were not included in this test since individual layers
could no longer be distinguished.
318 Dan Gheorghe & co
a.
b.
c.
Fig. 6 Light microscopy image showing layers in the 3D printed material for a. R, b. TP1 and c.
TP3 samples
Individual layers can be observed, fused together generating a structure
similar to a multi-ply composite. Also, a discoloration of sample TP1 can be
noticed which could alter biologic performance [22].
Using the proprietary software of the light microscope 10 layer thickness
measurements were performed on random regions of the micrograph. In Table 3
the descriptive statistics parameters are presented for the gathered data. Table 3
Descriptive statistics parameters regarding the layer thickness
Sample
N
Mean
m]
Standard deviation
[µm]
Confidence interval of the mean
[µm]
R
10
20.93
1.78
1.10
TP1
10
19.95
2.25
1.39
TP2
10
21.55
3.56
2.21
At first glance the results obtained showed a layer thickness reduction
when heating was performed in water (sample TP1) and an increase when the
furnace was used (sample TP2). Still, given the large standard deviation a t-Test
for two samples assuming unequal variances was performed with a null
hypothesized mean difference using α=0.05. The t-Test results are shown in Table
4. Table 4
The results of the t-Test
Pair
Hypothesized mean
difference
t-Statistic
Significance
R-TP1
0
0.763
0.457
R-TP2
0
-0.924
0.372
The results of the t-Test reveal that there are not statistically significant
differences between the means, it cannot be assumed that layer thickness is
influenced by thermal processing.
Analysis of the anisotropy for 3D printed PLA parts usable in medicine 319
3.3 Compression tests
Compression tests were performed on a hydraulic universal testing
machine Walter+Bai LFV 300
using a crosshead speed of
5mm/min.
In respect to material
buildup during 3D printing
process "Direction 1" was
chosen to be the same as
buildup direction and
"Direction 2" was taken
perpendicular as described in
Fig. 7. The samples in each
batch were divided in two to obtain 5 samples per direction to be tested in
compression. Post testing the load-displacement curves were processed in order to
determine the elastic modulus and yield strength in compression. The elastic
modulus was determined by linear regression on the initial region of the stress-
strain curve and the yield strength in compression was determined using the same
procedure as the conventional yield strength in tension. In Fig. 8 the mediated
stress - strain curves in compression for the 4 batches are presented.
0 5 10 15 20 25 30 35 40 45 50
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Stress (MPa)
Strain (%)
R - Direction 1
R - Direction 2
0 5 10 15 20 25 30 35 40 45 50 55
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
Stress (MPa)
Strain (%)
TP1 - Direction 1
TP1 - Direction2
a.
b.
0 5 10 15 20 25 30 35 40 45 50 55
0
10
20
30
40
50
60
70
80
90
100
110
120
Stress (MPa)
Strain (%)
TP2 - Direction 1
TP2 - Direction 2
0 5 10 15 20 25 30 35 40 45 50 55
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
Stress (MPa)
Strain (%)
TP3 - Direction 1
TP3 - Direction 2
c.
d.
Fig. 8 Mean stress - strain curves in compression for samples from a. R, b. TP1, c.TP2 and d. TP3
batch
a.
b.
Fig. 7 Sampling direction choice based upon a. material
buildup and b. 3D printing process
320 Dan Gheorghe & co
The curves suggest a malleable material with direction dependant
behavior. It can be seen on the stress-strain curves in compression when the
specimen is oriented on "Direction 1" that after reaching the first maxima a
steeper decrease appears when compared with the specimen tested on "Direction
2." Perpendicular layers on the load direction are compressed, slide against
each other, the sample barrels and fails by separation of layers. When the load is
parallel with the layers failure occurs by buckling of the perimeter layers (the
outer ones) and the rectilinear infill oriented at ±45° significantly increase shear
strength. Thermal processing appears to have an influence on the behavior, the
difference between first maxima decreases when compared with the reference
samples.
In case of specimens from TP3 batch it can be seen that the drop beyond
the first maxima on "Direction 1" almost disappears, the outer layers are fused
together and failure occurs in this case mainly by buckling.
In Fig. 9 comparisons between elastic moduli and yield strengths in
compression are shown.
a.
b.
Fig. 9 Comparison of a. elastic moduli and b. yield strength in compression
Analyzing the results from Fig. 9 it can be seen that the elastic modulus for
the reference R samples in direction 2 is by 51.51% higher than the one on
direction 1, for the samples TP1 the elastic modulus on direction 2 is by 26.84%
higher than for direction 1, for samples TP2 the elastic modulus on direction 1 is
by 38.24% higher than for direction 2 and for samples TP3 on direction 1 the
elastic modulus is by 47.02% higher than the one in direction 2. For yield
strengths the same pattern is observed, in direction 2 higher values are observed,
for R samples direction 2 shows a value by 41.24% higher, for sample TP1 is by
Analysis of the anisotropy for 3D printed PLA parts usable in medicine 321
13.98% higher, for samples TP2 by 22.30% higher and for samples TP3 by
40.58% higher.
It also can be stated that thermal processing clearly alters the structure of
the 3D printed material, but the mechanisms were not studied. It was inferred that
either adhesion between layers was improved or a change in the crystallinity
degree of the polymer could be responsible. Using the furnace showed best results
when the yield strength is in question and noteworthy is that the improvement on
direction 1 is more pronounced than on direction 2, suggesting that processes at
the interface of the layers is a stronger influence factor.
Using the heating gun for superficial melting of the samples did not yield
good results; the process was performed using visual appreciation without specific
process parameters. The process was halted when no more layers were observed
on the surface thus process optimization is required for repeatability and
reproducibility. The behavior during deformation associated with the mechanical
characteristics values determined showed that 3D printed materials show
anisotropy induced by the production characteristics, layer by layer build-up.
To appreciate the anisotropy and thermal processing influence on this
aspect an anisotropy coefficient was determined by dividing the property value
obtained on "Direction 1" to the one in "Direction 2", exemplified in eq. (1) for
the yield strength:
(1)
A comparison of the anisotropy coefficient for the elastic moduli and yield
strengths in compression is shown in Fig. 10.
a.
b.
Fig. 10 Anisotropy coefficient for a. elastic moduli and b. yield strengths in compression
322 Dan Gheorghe & co
For an isotropic material the value of this coefficient should be 1 in theory
and very close to 1 using experimental data while in the case of 3D printed
materials it is 0.49 for the elastic modulus and 0.59 for the yield strength in
compression. Thermal processing improves the values for this coefficient getting
it closer to 1 and highest values were obtained for sample TP1, processed in
boiling water.
Several studies [23, 24, 25]reportslight variations of the elastic modulus in
tension in XY plane (the transverse plane), with anisotropy coefficients ranging
0.92 to 0.98 as computed using the published values. Using this information
associated with current results it can be assumed that 3D printed PLA is
transversely isotropic, the strength and stiffness are greater when the samples are
loaded perpendicular than when load is applied parallel in respect to the build-up
direction.
3. Conclusions
This study was focused mainly on the mechanical characteristics of 3D
printed materials targeted for medical applications. Samples made of PLA were
printed using a commercial dual head extruder machine and processed by heating
in boiling water, in a furnace and using a heating gun. Comparing sample
dimensions, it was found that when using treatment in boiling water and using a
heating gun no statistical significant differences between the their dimensions and
the reference samples appear, while furnace heating generates dimensional
variation. Using the same procedure layer thickness measurements were
performed on optical micrographs and slight layer thickness decrease when using
water for heating and thickness increase when using the electric furnace were
observed, but no statistical significant differences were found.
The compression tests were performed on samples oriented perpendicular
and parallel to the build-up directions of the 3D printed part. The compression test
results confirmed that 3D printed materials are anisotropic and thermal post-
processing can reduce anisotropy. In this study it was observed that when heating
in performed in water the anisotropy is reduced, but not the best mechanical
characteristics are achieved - furnace heating gave best mechanical characteristics.
Material anisotropy should not be regarded as an inconvenient (it depends
upon the final application and sometimes anisotropy is desired). Careful planning
before 3D printing should be performed to align the part with the direction that
gives best mechanical characteristics for the application.
Analysis of the anisotropy for 3D printed PLA parts usable in medicine 323
R E F E R E N C E S
[1] Salmi, M.; Paloheimo, K. S.; Tuomi, J.; Wolff, J.; Makitie, A.: Accuracy of medical models
made by additive manufacturing (rapid manufacturing). J CranioMaxillSurg2013, 41, 603-
609
[2] Paun, M. A.; Frunza, A.; Stanciulescu, E. L.; Munteanu, T. C.; Cristescu, I.; Grama, S.;
Chiotoroiu, A.; Ene, A.; Mihai, C.: The use of collagen-coated polypropylene meshes for
nasal reconstructive surgery. IndTextila2019, 70, 242-247
[3] Antoniac IV, Stoia DI, Ghiban B, Tecu C, Miculescu F, Vigaru C, Saceleanu V.: Failure
Analysis of a Humeral Shaft Locking Compression PlateSurface Investigation and
Simulation by Finite Element Method. Materials. 2019; 12(7):1128
[4] Lasprilla, A. J. R., Martinez, G. A. R., Lunelli, B. H., Jardini, A. L., &Filho, R. M. (2012).
Poly-lactic acid synthesis for application in biomedical devices - A review. Biotechnology
Advances. https://doi.org/10.1016/j.biotechadv.2011.06.019
[5] Raquez, J. M., Habibi, Y., Murariu, M., & Dubois, P. (2013). Polylactide (PLA)-based
nanocomposites. Progress in Polymer Science.
https://doi.org/10.1016/j.progpolymsci.2013.05.014
[6] Elsawy, M. A., Kim, K. H., Park, J. W., & Deep, A. (2017). Hydrolytic degradation of
polylactic acid (PLA) and its composites.Renewable and Sustainable Energy Reviews.
https://doi.org/10.1016/j.rser.2017.05.143
[7] Vilcioiu, J. D.; Zamfirescu, D. G.; Cristescu, I.; Ursache, A.; Popescu, S. A.; Creanga, C. A.;
Lascar, I.: The interdisciplinary approach of an aggressive giant cell tumor of bone
complicated with a fracture of the distal femur. Rom J Morphol Embryo2016, 57, 567-572
[8] Petreus, T.; Stoica, B. A.; Petreus, O.; Goriuc, A.; Cotrutz, C. E.; Antoniac, I. V.; Barbu-
Tudoran, L.: Preparation and cytocompatibility evaluation for hydrosoluble phosphorous
acid-derivatized cellulose as tissue engineering scaffold material. J Mater Sci-Mater
M2014, 25, 1115-1127
[9] Guazzo, R.; Gardin, C.; Bellin, G.; Sbricoli, L.; Ferroni, L.; Ludovichetti, F. S.; Piattelli, A.;
Antoniac, I.; Bressan, E.; Zavan, B.: Graphene-Based Nanomaterials for Tissue
Engineering in the Dental Field. Nanomaterials-Basel2018, 8
[10] Rau, J. V.; Antoniac, I.; Cama, G.; Komlev, V. S.; Ravaglioli, A.: Bioactive Materials for
Bone Tissue Engineering. Biomed Res Int2016
[11] Tecu, C.; Antoniac, I.; Goller, G.; Yavas, B.; Gheorghe, D.; Antoniac, A.; Ciuca, I.;
Semenescu, A.; Raiciu, A. D.; Cristescu, I.: The Sintering Behaviour and Mechanical
Properties of Hydroxyapatite - Based Composites for Bone Tissue Regeneration. Mater
Plast2019, 56, 644-648
[12] Antoniac, I.; Popescu, D.; Zapciu, A.; Antoniac, A.; Miculescu, F.; Moldovan, H.:
Magnesium Filled Polylactic Acid (PLA) Material for Filament Based 3D Printing.
Materials2019, 12
[13] Niculescu, M.; Antoniac, A.; Vasile, E.; Semenescu, A.; Trante, O.; Sohaciu, M.; Musetescu,
A.: Evaluation of Biodegradability of Surgical Synthetic Absorbable Suture Materials: An
In Vitro Study. Mater Plast2016, 53, 642-645
[14] Titorencu, I.; Albu, M. G.; Giurginca, M.; Jinga, V.; Antoniac, I.; Trandafir, V.; Cotrut, C.;
Miculescu, F.; Simionescu, M.: In Vitro Biocompatibility of Human Endothelial Cells with
Collagen-Doxycycline Matrices. MolCrystLiqCryst2010, 523, 82-96
[15] Ionescu, M. A.; Ionescu, C.; Ciocoiu, R. C.; Ciuca, I.: Parylene-N a Better Candidate for
Medical Substrate Coating than Parylene-C. Rev Chim-Bucharest2015, 66, 1925-1928
[16] Dascalu, C. A.; Maidaniuc, A.; Pandele, A. M.; Voicu, S. I.; Machedon-Pisu, T.; Stan, G. E.;
Cimpean, A.; Mitran, V.; Antoniac, I. V.; Miculescu, F.: Synthesis and characterization of
324 Dan Gheorghe & co
biocompatible polymer-ceramic film structures as favorable interface in guided bone
regeneration. Appl Surf Sci2019, 494, 335-352
[17] Senatov, F. S., Niaza, K. V., Zadorozhnyy, M. Y., Maksimkin, A. V., Kaloshkin, S. D., &
Estrin, Y. Z. (2016). Mechanical properties and shape memory effect of 3D-printed PLA-
based porous scaffolds. Journal of the Mechanical Behavior of Biomedical Materials.
https://doi.org/10.1016/j.jmbbm.2015.11.036
[18] Moldovan, M.; Balazsi, R.; Soanca, A.; Roman, A.; Sarosi, C.; Prodan, D.; Vlassa, M.;
Cojocaru, I.; Saceleanu, V.; Cristescu, I.: Evaluation of the Degree of Conversion,
Residual Monomers and Mechanical Properties of Some Light-Cured Dental Resin
Composites. Materials2019, 12,
[19] Rivis, M.; Pricop, M.; Talpos, S.; Ciocoiu, R.; Antoniac, I.; Gheorghita, D.; Trante, O.;
Moldovan, H.; Grigorescu, G.; Seceleanu, V.; Mohan, A.: Influence of the Bone Cements
Processing on the Mechanical Properties in Cranioplasty. Rev Chim-Bucharest2018, 69,
990-993
[20] Bolcu, D.; Stanescu, M. M.; Ciuca, I.; Trante, O.; Mihai, B.: New Relations for the Calculus
of Elastical and Mechanical Characteristics of Polyester Composites Reinforced with
Randomly Dispersed Fibers. Mater Plast2009, 46, 206-210
[21] Pantea, M.; Antoniac, I.; Trante, O.; Ciocoiu, R.; Fischer, C. A.; Traistaru, T.: Correlations
between connector geometry and strength of zirconia-based fixed partial dentures. Mater
Chem Phys2019, 222, 96-109
[22] Antoniac, I.; Sinescu, C.; Antoniac, A.: Adhesion aspects in biomaterials and medical devices.
J AdhesSciTechnol2016, 30, 1711-1715
[23] T. Letcher, M. Waystanek, Material property testing of 3D-printed specimen in PLA on an
entry-level 3D printer, ASME 2014 International Mechanical Engineering
Congress&Exposition, ISBN 978-0-7918-4643-8, 2015
[24] Tymrak, B. M.; Kreiger, M.; Pearce, J. M.: Mechanical properties of components fabricated
with open-source 3-D printers under realistic environmental conditions. Mater Design2014,
58, 242-246
[25] Serra, T.; Planell, J. A.; Navarro, M.: High-resolution PLA-based composite scaffolds via 3-
D printing technology. ActaBiomater2013, 9, 5521-5530
... The transition between these two loads perpendicular to each other can be affected by many factors, but it can be said that it varies proportionally. For example, the authors have compared these directions for tensile [17][18][19] and compression [20][21][22] resistance. For the test, the authors printed samples from PLA material using Fused Deposition Modeling (FDM) technology, which as they mentioned, has a particularly big resulting anisotropy compared to the other technologies. ...
... Therefore, as a first step, the relevant measurement data about the tensile test results were collected to test the procedure. The results of three independent research works have been used [17][18][19][20][21][22], each of them obtained the anisotropic behavior of the samples printed from PLA raw material utilizing the FDM technique. ...
Article
Full-text available
As Additive Manufacturing technology is excellent for the production of function-based optimized parts. By choosing the right printing orientation, the dimensional accuracy and surface quality of the parts can be improved. But also possible to achieve improvement of the mechanical properties by the proper orientation. An algorithm has been developed, which can determine the optimal build orientation based on a numerical simulation for a given load case. The adverse and favourable load directions can be defined according to the layer's position by knowing the anisotropic behavior of the printed parts. The optimal print orientation has been found for four investigated geometries, according to the No-Preference and Weighted Sum multiple-objective optimization methods, and therefore the expected mechanical performance was increased. The algorithm was able to reduce the amount of unfavourable stresses by 100 % for simple beam geometries with longitudinal tensile and compression loads, while the more complex geometries were improved to the best possible extent.
... In this case using PLA, the working temperature will be 210 ° C [8]; ➢ Printing the prosthetic cup and checking the dimensions, by testing by the patient. If there is a need for adjustment, it will be done with metallographic paper. ...
Article
Full-text available
This study was aimed to observe, by comparison with conventional PLA, if embedding of silver particles can alter the printed parts surface characteristics. The studies performed include scanning electron microscopy and image analysis, Fourier transform infrared spectroscopy and surface wetting on 3D printed samples made of commercial and PLA with silver particles added for antibacterial properties. According to the results it was observed that by silver particle addition an uneven layer thickness in the structure of the part occurs and no noticeable changes in surface morphology and chemistry.
... Failure analysis is of great importance not only for orthopedics [1][2][3][4][5], but also for other various medical areas such as general surgery [6][7][8][9], gynecology [10][11][12], cranioplasty [13,14], ophthalmology [15], and dentistry [16,17], as the investigation of retrieved implants offers insight into implant failure mechanisms and how to prevent such cases. Physiologic forces are transmitted to intact human bone under normal conditions without exceeding its ultimate strength. ...
Article
Full-text available
Failure of osteosynthesis implants is an intricate matter with challenging management that calls for efficient investigation and prevention. Using implant retrieval analysis combined with standard radiological examination, we evaluated the main causes for osteosynthesis implant breakdown and the relations among them for a series of cases. Twenty-one patients diagnosed with implant failure were assessed for this work. For metallurgical analysis, microscopy techniques such as scanning electron microscopy (SEM), stereomicroscopy, and optical microscopy were employed. The results showed that material structural deficiencies (nine patients) and faulty surgical techniques (eight patients) were the main causes for failure. An important number of patients presented with material structural deficiencies superimposed on an imperfect osteosynthesis technique (six patients). Consequently, the importance of failure retrieval analysis should not be overlooked, and in combination with other investigational techniques, must provide information for both implant manufacturing and design improvement, as well as osteosynthesis technique optimization.
Chapter
The chapter discusses the basic principles of design for additive manufacturing (AM). It explains the concept of a digital model and introduces the reader to modeling software and the process of preparing a design for AM with respect to the chosen technology. In addition, the chapter discusses in detail the design limitations that occur for the most commonly used AM techniques, and also highlights the requirements in the finishing processes applied after printing. Besides, the study defines the principles of preparing files for AM. Moreover, it points out the importance of the orientation of the model in the machine during the printing process for various AM technologies and the influence of the orientation on the properties of the finished 3D object.
Article
Full-text available
The developement and regeneration of healthy bone tissue is a complex process that includes the interaction of different cell types and requires a set of coordinated processes. The loss of bone tissue may occur due to various reasons: surgical removal, bone trauma (i.e., fractures) or systemic bone loss (i.e., osteoporosis). When the natural bone tissue is destroyed, the regeneration capacity of the bone is not always satisfactory. The result consists therefore in many functional and structural aberrations. In order to improve and accelerate the healing process, bone substitutes have been developed. Hydroxyapatite has been widely used in bone applications due to its excellent biocompatibility, osteoconductivity and bioactivity [1,2]. The objective of this research is to obtain a new composite biomaterial that can be used as bone substitute. In this study, bovine hydroxyapatite obtained from freshly calcined bovine femur was used. The objective of this research is to obtain a new composite biomaterial that can be used as bone substitute. The experimental composite samples were obtained using bovine hydroxyapatite as matrix and tricalcium phosphate, respectively, magnesium oxide as reinforcement materials. The synthesis process of these new biomaterial composites, the effect of chemical composition, surface structure, chemical and phase composition as well as mechanical features have been investigated.
Article
Full-text available
Reconstructive surgery of the abdominal and thoracic wall frequently utilizes various materials in order to repair large defects. Polypropylene meshes are an example. In nasal reconstructive surgery they are rarely used for cartilage restoration. The purpose of this paper is to demonstrate the utility of the collagen-coated polypropylene meshes in nasal reconstructive surgery, as they are easy-to-use materials, with reduced incidence of foreign body reactions and with a very small price compared with other compounds. We conducted a literature review on the usage of the collagen-coated polypropylene meshes which also includes a comparison with other types of materials applied for nasal cartilage reconstruction. Moreover, we performed a retrospec - tive study, on the patients hospitalized in the Plastic Surgery Department of the Clinical Emergency Hospital, Bucharest. The best option and in the same time the gold standard for nasal cartilage reconstruction is considered to be autologous cartilage transplantation. In our clinic we observed good results when autologous septalor auricular cartilage grafts were used. Polypropylene is seldom used in nasal reconstructive surgery, having been conducted so far, a limited number of studies related to benefits and disadvantages of this type of material in the accomplishment of the medical devices used as a nasal implant. Polypropylene meshes are largely used in abdominal wall reconstruction and in the surgery for pelvic organ prolapse. In this surgical field, collagen-coated polypropylene meshes are also used, but future studies will demonstrate if they are effective enough in the nasal reconstructive surgery as well.
Article
Full-text available
The novelty of this study consists in the formulation and characterization of three experimental dental composites (PM, P14M, P2S) for cervical dental lesion restoration compared to the commercial composites Enamel plus HRi® - En (Micerium S.p.A, Avengo, Ge, Italy), G-ænial Anterior® - Ge, (GC Europe N.V., Leuven, Belgium), Charisma® - Ch (Heraeus Kulzer, Berkshire, UK). The physio-chemical properties were studied, like the degree of conversion and the residual monomers in cured samples using FTIR-ATR (attenuated total reflectance) and HPLC-UV (ultraviolet detection), as well as the evaluation of the mechanical properties of the materials. The null hypothesis was that there would be no differences between experimental and commercial resin composites regarding the evaluated parameters. Statistical analysis revealed that water and saliva storage induced significant modifications of all mechanical parameters after three months for all tested materials, except for a few comparisons for each type of material. Storage medium seemed not to alter the values of mechanical parameters in comparison with the initial ones for: diametral tensile strength (DTS-saliva for Ge and PM, compressive strength (CS)-water for Ch, DTS-water and Young’s modulus YM-saliva for P14M and YM-water/ saliva for P2S (p > 0.05). Two of the experimental materials showed less than 1% residual monomers, which sustains good polymerization efficiency. Experimental resin composites have good mechanical properties, which makes them recommendable for the successful use in load-bearing surfaces of posterior teeth.
Article
Full-text available
A case study of a failed humeral shaft locking compression plate is presented, starting with a clinical case where failure occurred and an implant replacement was required. This study uses finite element method (FEM) in order to determine the failure modes for the clinical case. Four loading scenarios that simulate daily life activities were considered for determining the stress distribution in a humeral shaft locking compression plate (LCP). Referring to the simulation results, the failure analysis was performed on the explant. Using fracture surface investigation methods, stereomicroscopy and scanning electron microscopy (SEM), a mixed mode failure was determined. An initial fatigue failure occurred followed by a sudden failure of the plate implant as a consequence of patient’s fall. The fracture morphology was mostly masked by galling; the fractured components were in a sliding contact. Using information from simulations, the loading was inferred and correlated with fracture site and surface features.
Article
Full-text available
The main objective of this research is to prove the viability of obtaining magnesium (Mg) filled polylactic acid (PLA) biocomposites as filament feedstock for material extrusion-based additive manufacturing (AM). These materials can be used for medical applications, thus benefiting of all the advantages offered by AM technology in terms of design freedom and product customization. Filaments were produced from two PLA + magnesium + vitamin E (α-tocopherol) compositions and then used for manufacturing test samples and ACL (anterior cruciate ligament) screws on a low-cost 3D printer. Filaments and implant screws were characterized using SEM (scanning electron microscopy), FTIR (fourier transform infrared spectrometry), and DSC (differential scanning calorimetry) analysis. Although the filament manufacturing process could not ensure a uniform distribution of Mg particles within the PLA matrix, a good integration was noticed, probably due to the use of vitamin E as a precursor. The results also show that the composite biomaterials can ensure and maintain implant screws structural integrity during the additive manufacturing process.
Article
Full-text available
The aim of this study is to observe the time of mixing influence on the properties of commercially available PMMA bone cement, widely used in cranioplasty. The studied bone cement is provided in the form of a solid powder (the copolymer) and a liquid monomer. The increase of the mixing phase duration and the use of two mixing methods (manual and mechanical) effect on surface and mechanical characteristics were studied. The samples were prepared as if in the operation room. Surface characteristics were studied by means of contact angle measurements, morphology by scanning electron microscopy (SEM) and mechanical characteristics determined by flexural tests in a three point bending configuration. The conclusion of this study is that by using a mechanical mixing method and increasing mixing time higher flexural strength can be achieved by reducing pore content within bone cement.
Article
Full-text available
Giant cell tumor of bone (GCTB) represents one of the commonest bone tumors encountered by an orthopedic surgeon. The giant-cell tumor is generally classified as benign but the fast growing rhythm and the aggressive soft-tissue invasion may in some cases demonstrate a malign potential of the tumor. We present the case of an aggressive giant cell tumor in a young patient that was first diagnosed in our emergency department with a fracture of the distal femur after a low energy trauma. With further examinations, we discovered that the tumor was invading the both femoral condyles and was vascularized by three major arterial pedicles. The onset of his problems was the femoral fracture and the changes on the major vessels, muscles and nerves. After an interdisciplinary approach of the patient and a meticulous preoperative planning, we decided to make an extensive total resection of the tumor followed by a complex reconstruction surgery for the bone. A very stable fixation of a vascularized graft allowed the bone to heal even if the surrounded soft-tissue was almost completely invaded by the tumor and removed during the excision. The follow-up of this case demonstrated that using an interdisciplinary approach of the patient with the Plastic Surgery team, we manage to remove the tumor within oncological limits and achieved bone healing with good stability of the distal femur.
Article
The bone regeneration field targeted lately the development of new products based on precursors of natural origin. This study aimed to obtain the optimal design of polymer-ceramic composites for guided bone regeneration application from cellulose acetate (CA) and hydroxyapatite (HA) by varying three relevant parameters: the amount of HA powder added to the CA matrix (in the 20–40 wt% range), the HA particles size (max. 20 μm vs. max. 40 μm) and the homogenization time required for HA powder dispersion in the CA matrix (1 min vs. 4 min). For polymer-ceramic film structures preparation, the phase inversion by immersion in water method was used. This involved the deposition of composite solution (i.e. CA with 20–40 wt% HA) on a glass support, followed by sizing it at a thickness of 0.2 mm. The obtained film structures were investigated in terms of morpho-compositional and structural properties. The surface features evaluation was achieved by surface wettability, roughness, water permeation, protein retention and in vitro evaluation of MC3T3-E1 morphology and viability. Further, ceramic particle distribution throughout samples volume was provided by computed tomography methods. These investigations targeted the validation of the prepared composite film structures as viable solutions for guided bone regeneration.
Article
Biodegradable polymers are seen as a potential solution to the environmental problems generated by plastic waste. In particular, the renewable aliphatic polyesters of poly(hydroxyacid)-type homopolymers and copolymers consisting of polylactic acid (PLA), poly(glycolic acid) (PGA), and poly(e-caprolactone) (PCL) constitute the most promising bioresorbable materials for applications in biomedical and consumer applications. Among those polymers, PLA has attracted particular attention as a substitute for conventional petroleum-based plastics. PLA is synthesized by the fermentation of renewable agricultural sources, including corn, cellulose, and other polysaccharides. Although some of its characteristics are disadvantageous (e.g., poor melt properties, mechanical brittleness, low heat resistance, and slow crystallization), there exist potential routes to resolve these shortcomings. These include copolymerization, blending, plasticization modification, or the addition of reinforcing phases (e.g., chitosan (Cs), cellulose, and starch). In this review, we discuss the degradation mechanisms of PLA and its modified form in the environment, current issues that hinder the achievement of good Cs/PLA combination, and ways to overcome some of these problems. Furthermore, our discussion is extended to cover the subjects of hydrolytic degradation and weathering effects with different Cs/PLA blends.
Article
The biomaterial - tissue interface plays a key role in implant success. The advantage of using parylene-C a class VI FDA approved polymer for implants is well known. Parylene-N and parylene-C thin films deposited via polymer vapor deposition (PVD) on Si(111) were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The surface of parylene-C is smooth, while for parylene - N bundles of fibrils are clearly observed by SEM. XRD showed that parylene-N is more packed than parylene-C thus should withstand better to moisture. The kinetics of the two is different; parylene-C has a greater deposition rate than parylene-N but the last one has a greater penetration to small crevices than parylene-C. Therefore we hypothesize that parylene-N could be more suitable as protective coating for medical instruments (not for implantable devices though) than parylene-C.