AN ENGINEERING INVESTIGATION OF BIO-POLYMERS

Abstract

The research focus on the recent advances and challenges in the mechanical testing of biodegradable materials. The research aims to synthesis PLA, extrude it form wires, 3D print parts using materials & perform various mechanical testing on them such as Tensile, hardness, flexural, XRD, FTIR, SEM, and TG/DTA to find out its various mechanical strengths. The printing process was carried out on the 3D printers: Fractal Works Julia Dual V2 and Prusa i3 (2 Nos.). According to test carried out the polymers are found to be amorphous and biodegradable. It is also seen that printed polymers tend to carry lateral load more easily than longitudinal load and also, they can carry more compressive load than tensile one. When the polymer is bought from the different manufacture it may show different properties. Even the plane and temperature of the printing play a very important role in the properties.

Full text

www.tjprc.org SCOPUS Indexed Journal editor@tjprc.org
AN ENGINEERING INVESTIGATION OF BIO-POLYMERS
SHREYAS V. BHAGWAT
1
, VISHAL V. SHUKLA
1
, MOHAN G. TRIVEDI
1
,
ALOK JHA
1
& PRAMOD PADOLE
2
1
Shri Ramdeobaba College of Engineering and Management, Nagpur, Maharashtra, India
2
Visvesvaraya National Institute of Technology, Nagpur, Maharashtra, India
ABSTRACT
The research focus on the recent advances and challenges in the mechanical testing of bio-degradable
materials. The research aims to synthesis PLA, extrude it form wires, 3D print parts using materials & perform various
mechanical testing on them such as Tensile, hardness, flexural, XRD, FTIR, SEM, and TG/DTA to find out its various
mechanical strengths. The printing process was carried out on the 3D printers: Fractal Works Julia Dual V2 and Prusa
i3 (2 Nos.). According to test carried out the polymers are found to be amorphous and biodegradable. It is also seen that
printed polymers tend to carry lateral load more easily than longitudinal load and also, they can carry more compressive
load than tensile one. When the polymer is bought from the different manufacture it may show different properties.
Even the plane and temperature of the printing play a very important role in the properties.
KEYWORDS: Bio-Polymers, Tensile Testing, Flexural Test, XRD, FTIR, TG/DTA Tests, PLA, PETG & 3D Printing
INTRODUCTION
Bone are organic tissues consisting of calcium which makes them stronger compared with other biological
tissues. Bonecontains Collagen matrix which is primarily responsible for the tensile strength of the bone. The
component imparting compressive strength to the bone tissue is calcium phosphate. From the engineering
perspective, bones are analyzed on the basis of strength (load carrying capacity) and geometry (nonlinear shapes).
In the two major categories of bones, cortical bones are found to have higher Modulus. Table 1, presents material
properties of bones found in the popular literature.
Table 1: Strength Parameters of Different bones [2,4].
Sr. No. Particular Range
1 Young’s modulus of cortical bone 17–20 GPa
2 Compressive strengthof cortical bone 131–224 MPa
3 Young’s modulus of cancellous bone 50–100 MPa
4 Compressive strengthof cancellous bone 5–10 MPa
Bone tissue may sometimes get damaged due to accidental impact and trauma leading to fracture [5,6].
The general traditional treatment undertaken by orthopaedic surgeons to repair the fractured bone is to deploy some
metal fixators. The metals used for this purpose are majorly stainless steel, titanium and its alloys.
However, the metal implants like plates or rods, often require a subsequent surgery to remove them from
the body. This additional or subsequent surgery to remove the implant mostly leads to increased risk and cost to
patients, it may further adds to the complications and infections. Also, there is considerable difference in the
strengths of the physical properties of metals and that of bones, which create variations in the load shared by them
individually. The optimum load must also be shared by bone so that there must be proper bone tissue remodelling
Original Article
International Journal of Mechanical and Production
Engineering Research and Development (IJMPERD)
ISSN (P): 2249-6890; ISSN (E): 2249-8001
Vol. 9, Special Issue, Jun 2019, 348-355
© TJPRC Pvt. Ltd
.

349 Shreyas V. Bhagwat, Vishal V. Shukla, Mohan G. Trivedi,
Alok Jha & Pramod Padole
Impact Factor (JCC): 7.6197 SCOPUS Indexed Journal NAAS Rating: 3.11
leading to rapid healing of the fractured bone. Thus, biodegradable polymers like PLA designed plates and screw are used
for the bone healing, fixation & repair.
Researchers across the globe have been trying to develop bio-compatible and bio-degradable polymers, However,
the major challenge still remains to be the desirable strength. Further, well-controlled and gradual loading minimizes the
stress shield effect [15,16]. There is a sufficient progress in the development of clinically approved biodegradable rods,
plates, pins, screws and suture anchors made of polymers, ceramics, and metals.
Clinically approved Biodegradable polymers consists of repeated substructures of covalently boned large
molecules and can be used for bone repair. Their well-regulated decay rates based on structural composition and
fabrication are highly advantageous for clinical applications [16]. Considering the present need of quantifying the strength
of bio-polymers, this paper presents the preparation of specimen of bio-polymer and reports about the observed strength of
these specimen by mechanical testing.
OBJECTIVES
The objective of this paper is to estimate the strength of the 3-D printed specimen of biopolymers by mechanical
testing.
There are several biodegradable polymers that are commercially available. Some of the important and easily
available biopolymers are PLA (Poly-Lactic Acid) and PET-G (Poly-ethylene Terephthalate Glycol). These bio-polymers
can be procured in the form of wires called filaments which are extruded from the bulk mass of bio-polymers. However,
unlike the in-house developed biopolymer, information related to these commercial biopolymers pertaining to the exact
compositions and the extent to which these commercial polymers can be used in human or animal for surgical interventions
is not known and hence cannot be guaranteed. But these commercially available bio-polymer filaments can surely be tested
for mechanical strength, if brought in some particular geometrical forms like testing specimen.
3-D printing refers to process in which material is joined or solidified under computer control to create 3-D object,
with materials being added together (such as liquid molecules, powder grains fused together). 3-D printing is used in both
rapid prototyping and additive manufacturing (AM). There are many different technologies, like fused deposition
modelling (FDM), Stereo-lithography (SLA) or Selective laser melting (SLM); the process used to 3D-printing of the
biodegradable polymers is well known.
RESULTS
The reports on tensile test, flexural test, and hardness test, XRD, FTIR and TG/DTA are presented and discussed
sequentially.
Tensile Test
PLA and PETG specimen are tested on Instron Servo Hydraulic test system to study the tensile behaviour of the
polymer materials. It is ensured that the specimen is tightly locked in the machine fixtures and a gradually increasing load
is applied in the axial direction till the PLA specimen breaks. A stress-strain curve generated in tensile test of PLA and
PETG are shown in Figure 1 and Figure 2 respectively.
The tensile properties of PLA and PETG are obtained from these curves.

An Engineering Investigation of Bio-Polymers 350
www.tjprc.org SCOPUS Indexed Journal editor@tjprc.org
Figure 1: Load (kN) v/s Displacement (mm) Curve for PLA Tensile Test
Figure 1 shows that the PLA tested is brittle in nature. It can sustain maximum 1575 N axial load before failure.
The % elongation is found to be 4.164 % and the tensile strength is 38.831 MPa. The Young’s modulus is calculated to be
1643.155 MPa.
Figure 2: Load (kN) v/s Displacement (mm) Curve for PETG Tensile Testing
This curve (Figure 2) shows that the PETG tested is brittle in nature. It can sustain the maximum axial load of 633
N before failure. % elongation is found to be 3.6 % and the tensile strength is 18.011 MPa. The Young’s modulus is
calculated to be 640.084 MPa.
Point Bending Test
The 3-Point bending test is carried out to find out the Flexural strength of the material. A cuboidal part is created
from the material. It is subjected to bending: two points are fixed and the third point at the centre is subjected to load until
failure. Instron 4486 is used to carry out the test on the part. A stress-strain curve is generated after this testing and the
flexural properties are derived from this curve. The curves shown in Figure 3 and Figure 4 represent the curves of PLA and
PETG respectively. The sudden deviation (peaks) in graph occur due to failure in one strand or layer of the test element.

351 Shreyas V. Bhagwat, Vishal V. Shukla, Mohan G. Trivedi,
Alok Jha & Pramod Padole
Impact Factor (JCC): 7.6197 SCOPUS Indexed Journal NAAS Rating: 3.11
Figure 3: Load (KN) v/s Displacement (mm) Curve for PLA Flexural Testing
The curve (Figure 3) depicts that the PLA tested is elastic in nature. The flexural strength is calculated to be 46.86
MPa.
Figure 4: Load (KN) v/s Displacement (mm) curve for PETG Flexural Testing
The curve (Figure 4) depicts that the PETG tested is elastic in nature. The flexural strength is calculated to be
53.80 MPa.
Hardness Test
It is a test carried out to measure the hardness of the material. Hardness is a measure of resistance to localised
plastic deformation induced by mechanical indentation. The instrument used to find out the hardness of a polymer is the
Shore Durometer. To perform this test, a cylindrical specimen is created, and mounted under the probe of durometer. The
probe applies a point load on the specimen and an indentation is created. Two scales of Shore hardness are used: “Shore A”
and “Shore D”. Shore A is used for soft materials while the Shore D is used for hard materials. Table 2 shows the readings
of hardness taken for PLA and PETG and the avg. hardness calculated.
Table 2: Readings of Hardness Values
Reading 1 Reading 2 Reading 3 Reading 4 Reading 5 Average Hardness Value
(Unit: Shore D)
PETG
79 75.5 76.5 78 77.5 77.3
PLA 86.5 85.5 88 86 82 85.6

An Engineering Investigation of Bio-Polymers 352
www.tjprc.org SCOPUS Indexed Journal editor@tjprc.org
X-Ray Crystallography (XRD)
X-Ray Crystallography also known as X-Ray Diffraction (XRD) is a very important non-destructive testing
method to analyse all kinds of matter. It is used for material characterisation and quality control. It is used for identification
of crystalline phases in a material. In case of polymer, it defines whether a polymer is highly crystalline, semi-crystalline or
amorphous in nature. The instrument used for XRD is a diffractometer. Intensity v/s position (2theta) graph is generated by
the Diffractometer. The nature of peaks and the number of peaks in the graph defines the crystallinity of the material.
Figure 5, illustrates the different types of graphs usually observed and how the crystallinity is defined.
Figure 5: Nature of XRD Curves
According to Figure 5, when there are less no. of peaks and the graph is smooth, then the material is amorphous in
nature. When there are more no. of peaks and the peaks are pointed then the material is semi-crystalline in nature and when
there are many highly pointed peaks, then the material is defined as highly crystalline material. The curves shown in Figure
6 and Figure 7 are the XRD curves of PLA and PETG respectively. The peaks occur when the rays are deflected by the
crystals present in the material to be tested.
Figure 6: XRD Curve of PLA
Comparing Figure 5 and Figure 6, it is seen that PLA falls in the category of amorphous materials. Amorphous
materials are non-crystalline materials with a non-organised lattice structure. Amorphous materials do not have a specific
melting point or temperature. There is always a range of temperature provided for melting such materials.

353 Shreyas V. Bhagwat, Vishal V. Shukla, Mohan G. Trivedi,
Alok Jha & Pramod Padole
Impact Factor (JCC): 7.6197 SCOPUS Indexed Journal NAAS Rating: 3.11
Figure 7: XRD Curve of PETG
Comparing Figure 5 and Figure 7, it is seen that PETG falls in the category of amorphous materials.
3.5 Simultaneous Thermal Analysis (STA)
Simultaneous Thermal Analysis (STA) also known as Thermogravimetric Differential Thermal Analysis
(TG/DTA) is the simultaneous application of Thermogravimetric Analysis (TGA) and Differential Thermal Analysis
(DTA) on one sample with the same instrument. It can characterise multiple thermal characteristics of a sample in a single
experiment. PerkinElmer STA 4000 is used with Pyris software to carry out this analysis. A crucible loaded with sample is
placed inside the Analyser where the weight of the sample is constantly measured. The TGA and DTA curves of PLA and
PETG are shown in Figure 8 and Figure 9 respectively.
Figure 8: TG/DTA of PLA
Figure 9: TG/DTA of PETG

An Engineering Investigation of Bio-Polymers 354
www.tjprc.org SCOPUS Indexed Journal editor@tjprc.org
In both graphs, dotted blue line represents TGA while the red solid line represents DTA. It is also seen that
temperature plays a very important role for PLA as it starts degrading at very low temperatures while PETG loses its
weight at higher temperature.
CONCLUSIONS
Four samples of each part were printed using two polymers: PLA and PETG. PLA and PETG are both amorphous
in nature. PLA and PETG are biodegradable and biocompatible materials. It is found that both polymers can carry lateral
loads better than longitudinal. Two Polymers from different manufacturers show different properties. It is also observed
that the same Polymers printed at different temperatures show different properties. If material is printed in different
orientation then they show different properties. Bio-degradable polymers may be used to heal the fractures of bones that
have low to mild load carrying capacity, since these polymers do not display the strength of the metals.
REFERENCES
1. Driessens, F.C. Probable phase composition of the mineral in bone. Z. Naturfor. Sect. C 1980, 35,357–362.
2. Athanasiou, K.A.; Zhu, C.; Lanctot, D.R.; Agrawal, C.M.; Wang, X. Fundamentals of biomechanics in tissue engineering of
bone. Tissue Eng. 2000, 6, 361–381.
3. Driessens, F.C.; van Dijk, J.W.; Borggreven, J.M. Biological calcium phosphates and their role in the physiology of bone and
dental tissues I. Composition and solubility of calcium phosphates. Calcif. Tissue Res. 1978, 26, 127–137
4. Yaszemski, M.J.; Payne, R.G.; Hayes, W.C.; Langer, R.; Mikos, A.G. Evolution of bone transplantation: Molecular, cellular
and tissue strategies to engineer human bone. Biomaterials1996, 17, 175–185.
5. Rabie, A.B.;Wong, R.W.; Hagg, U. Composite autogenous bone and demineralized bone matrices used to repair defects in the
parietal bone of rabbits. Br. J. Oral Maxillofac. Surg. 2000, 38,565–570.
6. Cavalcanti, S.C.; Pereira, C.L.; Mazzonetto, R.; de Moraes, M.; Moreira, R.W. Histological and histomorphometric analyses
of calcium phosphate cement in rabbit calvaria. J. Cranio Maxillo Facial Surg. 2008, 36, 354–359. Materials 2015, 8 5767
7. Goodrich, J.T.; Sandler, A.L.; Tepper, O. A review of reconstructive materials for use in craniofacial surgery bone fixation
materials, bone substitutes, and distractors. Child’s Nerv. Syst.2012, 28, 1577–1588.
8. Curtis, R.; Goldhahn, J.; Schwyn, R.; Regazzoni, P.; Suhm, N. Fixation principles in metaphyseal bone—A patent based
review. Osteoporos. Int. 2005, 16, S54–S64.
9. Eglin, D.; Alini, M. Degradable polymeric materials for osteo synthesis: Tutorial. Eur. Cell Mater.2008, 16, 80–91.
10. Christensen, F.B.; Dalstra, M.; Sejling, F.; Overgaard, S.; Bunger, C. Titanium-alloy enhances bone-pedicle screw fixation:
Mechanical and histomorphometrical results of titanium-alloy versus stainless steel. Eur. Spine J. 2000, 9, 97–103.
11. Eppley, B.L.; Sadove, A.M. A comparison of resorbable and metallic fixation in healing of calvarial bone grafts. Plast.
Reconstr. Surg. 1995, 96, 316–322.
12. Marti, C.; Imhoff, A.B.; Bahrs, C.; Romero, J. Metallic versus bio absorbable interference screw for fixation of bone-patellar
tendon-bone auto graft in arthroscopic anterior cruciate ligament reconstruction. A preliminary report. Knee Surg. Sports
Traumatol. Arthrosc. 1997, 5, 217–221.
13. Alexander, R.; Theodos, L. Fracture of the bone-grafted mandible secondary to stress shielding: Report of a case and review
of the literature. J. Oral Maxillofac. Surg. 1993, 51, 695–697.

355 Shreyas V. Bhagwat, Vishal V. Shukla, Mohan G. Trivedi,
Alok Jha & Pramod Padole
Impact Factor (JCC): 7.6197 SCOPUS Indexed Journal NAAS Rating: 3.11
14. Sumner, D.R. Long-term implant fixation and stress-shielding in total hip replacement. J.Biomech. 2015, 48, 797–800.
15. Chanlalit, C.; Shukla, D.R.; Fitzsimmons, J.S.; An, K.N.; O’Driscoll, S.W. Stress shielding around radial head prostheses. J.
Hand Surg. 2012, 37, 2118–2125.
16. Z. Sheikh, Najeeb, Z. Khurshid, V. Verma, H. Rashid and M. Glogauer. “Biodegradable materials for bone repair and tissue
engineering applications”, Materials 8, 2015:544-5794.
17. Moon, S-I., et al. “Melt/Solid polycondensation of L-lactic acid; an alternate route to poly(L-lactic acid) with higher
molecular weight.” Polymer, 44, 2000:5059-5062.