project based lab 2 final college projectdraft.docx
1. EFFECT OF VARYING POROSITY ON THE
MECHANICAL PROPERTIES OF HA /
PMMA COMPOSITE BONE SCAFFOLD
A report submitted
In Fulfilment of Project Based Lab
for the Degree of
BACHELOR OF TECHNOLOGY
In
MECHANICAL ENGINEERING
Submitted by:
DHEERAJ KUMAR MANDVI (211116243)
NIKHIL DWIVEDI (211116255)
VIPLAV AWASTHI (21116257)
Under the Guidance of:
Dr. EMON BARUA
DEPARTMENT OF MECHANICAL ENGINEERING
MAULANA AZAD NATIONAL INSTITUTE OF
TECHNOLOGY BHOPAL (M.P.) 462003
2. DECLARATION
We the undersigned declare that this project report titled “Effect of varying porosity
on the mechanical properties of HA/PMMA composite bone scaffold” submitted in partial
fulfilment of the degree of B.Tech in Mechanical Engineering is a record of original work
carried out by us under the supervision of “Dr. Emon Barua”. We assert that the statements
made and conclusions drawn are an outcome of the project work. We further declare that to the
best of my knowledge and belief that the project report does not contain any part of any work
which has been submitted for the award of any other degree/diploma/certificate in this University
or any other University.
Ms Suman Chabha -2211601141
Anya Yadav -2211601159
Harshit Rathore – 2211601160
Sahil Singh - 2211601168
Dr. Emon Barua
Assistant Professor
MANIT Bhopal
4. INTRODUCTION
A segmental bone defect refers to the loss or absence of a section of bone that has been caused by
injury, infection, tumour resection, or certain medical conditions. Unlike hairline fractures,
where the bone maintains its continuity and can typically heal through natural processes (with or
without intervention), a segmental defect involves a gap or void in the bone of 13 to 15mm that
cannot repair itself without medical intervention.
The gap in the bone, often described as a bone defect, can vary in size, location, and the causes
behind its formation. The primary challenge with segmental bone defects is the lack of a natural
healing pathway, as there is no intact bone structure to stimulate normal bone regeneration. In
these cases, medical interventions are necessary to promote bone healing, restore function, and
prevent complications.
Treatment Options for Segmental Bone Defects
Several treatment options exist for managing segmental bone defects, and the choice of method
depends on the size of the defect, its location, the patient's health, and the underlying cause.
Some common treatments include:
1. Bone Grafting:
As mentioned, bone grafting (autograft, allograft, or synthetic bone) is one of the
most commonly used methods for treating segmental bone defects. The graft
serves as a scaffold for new bone growth, and in some cases, it may also be
combined with growth factors or stem cells to enhance healing.
5. 2. Bone Substitutes:
In some cases, synthetic bone substitutes, such as calcium phosphate ceramics,
hydroxyapatite, or biodegradable polymers, can be used to fill the bone defect.
These materials mimic the natural bone structure and can gradually be resorbed
by the body as the bone heals.
3. Stem Cell Therapy:
Stem cells have shown promise in regenerative medicine for bone repair. By
using stem cells (either autologous or from a donor source), the body’s natural
healing mechanisms can be enhanced to promote new bone formation and repair
in the defect site
Bone grafting is used nowadays, and the failure rate is high. Bone grafting uses transplanted bone to
repair and rebuild diseased or damaged bones. In the last decade, tissue engineering and
regenerative medicine have opened a new pathway for the traditional techniques used. Lately,
the role has been taken up primarily due to an increasing need for transplantation and the scarcity
of donors. Scaffolds were developed as a result of tissue engineering. The scaffolds were made
by mimicking the extracellular matrix physical properties in order to facilitate the cells
recruitment, adhesion, proliferation and differentiation. A bone scaffold is a highly porous for
cell growth and transport of nutrients and metabolic waste. It is biocompatible for matching the
replacement of tissue and has enough channel to promote vascular integration. A scaffold
structure is made up of two layers: inner layer and the outer layer. The inner layer has a central
channel with micro channels along the plane surface which provide site for osteogenesis and also
compressive strength. The outer portion has channels which provide for cell proliferation,
vascular integration and torsional and bending strength. The layers are made from
microfilaments mesh.
6. The different types of bone scaffolds are:1) Composite scaffolds 2) Ceramic scaffolds 3)
Metallic scaffolds 4) Polymeric scaffolds.
Ceramic Scaffolds
These are scaffolds made of calcium phosphate (CaP) based material like Hydroxyapatite (HA),
tricalcium phosphate (TCP) and their combination as biphasic and amorphous calcium
phosphates (BCPs and ACPs). These scaffolds are known for their osteoconductive and
osteoinductive properties with excellent mechanical properties like compressive and bending
strength. However, their tensile and torsional strength as well as the fracture toughness are less
than that of human cortical bone. Moreover, they lack controllability in their physico-chemical
properties.
Polymeric scaffolds
Polymeric scaffolds are scaffolds made of biocompatible and biodegradable polymers which may
be synthetic-based like poly(lactic-acid) (PLA), poly(glycolic- acid) (PGA), and
poly(caprolactone) (PCL), etc. or, naturally derived like collagen, alginate, chitosan, etc.
Polymeric scaffolds have the advantage of having good controllability on physiochemical
characteristics. However, they lack mechanical strength compared to ceramic scaffolds.
Metallic scaffolds
These scaffolds are made of biocompatible metals like iron (Fe), magnesium (Mg), zinc (Zn),
titanium (Ti) etc. Metallic scaffolds are light-weight, mechanically strong, biocompatible and
osteoconductive, but they are non-biodegradable, shows poor osseointegration with the
surrounding bone due to the stiffness difference and release of toxic ions by corrosion which may
cause inflammatory responses.
7. Composite scaffolds
Composite scaffolds are made by combining two or more different materials like HA, TCP (CaP
based) reinforced with polymers like (PLLA, collagen, gelatin, etc.). Even oxides of metals like
zinc oxide (ZnO) or magnesium oxide (MgO) and HA are reinforced with polymers to develop
composite scaffolds with much-enhanced properties. Composite scaffolds show much improved
mechanical properties and osteoconductivity with controlled degradation for tissue engineering
applications.
Properties required for bone scaffold
Concerning to the functionalities assigned to a bone scaffold, it is expected to fulfil the following
requirements:
Bio functionality, or the ability of the scaffold to meet the requirement of restoring the
functions of the replaced tissue for which it was designed.
Biocompatibility with facility to promote cell attachment with negligible immune and
toxic reaction.
Biodegradability with controlled degradation kinetics to allow cells to produce their own
extracellular matrix and eventually replace the implanted scaffold.
Porous structure of about 65-90% porosity with interconnected macropores of sizes 100-
300 µm and micropores of sizes 20 μm for efficient nutrient transport, tissue infiltration
˂
and vascularization.
Adequate mechanical properties with a minimum compressive strength of 1- 10 MPa to
obtain positive pre- and post-implantation outcomes.
Lastly, it should be easy to manufacture with consistency in all the mentioned properties and
should be able to withstand the sterilization process without loss of properties.
8. LITERATURE REVIEW
Title Author Conclusion
Scaffolds in tissue
engineering bone and
cartilage
Dietmar W.
Hutmacher
It can be concluded that the ideal scaffold and
matrix material for tissue engineering bone and
cartilage has not yet been developed.
Recent advances in
bone tissue
engineering scaffolds
Susmita Bose, Mangal
Roy and Amit
Bandyopadhyay
One of the drawbacks of porous scaffolds is that,
independent of composition, it is mechanically
weak. Porosity in most of these scaffolds is
uniformly distributed throughout the scaffold
dimension. We also need to develop new material
combinations that are strong but can have timed
bioresorption.
Cartilage and Bone
Regeneration— How
Close Are We to
Bedside?
Raphaël F. Canadas*,
Sandra Pina*,
Alexandra P.
Marques, Joaquim M.
Oliveira, Rui L. Reis
It is known that tissue-engineered technologies can
take up to 20 years for reaching the market, and
despite progress in many fields, this time frame has
yet to be shorten. Cell therapy strategies, as well as
its first allogeneic stem cell therapy products, have
been successfully applied for only few applications.
9. RESEARCH GAP
Exploration of Novel Materials: Investigate the use of unconventional materials in
bone scaffold fabrication to fill the existing research gap.
Customization of Scaffold Architecture: Introduce a methodology to vary scaffold
architecture to enhance biocompatibility and tissue integration.
There is no existing research on the fatigue strength of PMMA and HA composites. The
combined effects of these materials on fatigue behavior, considering factors like
microstructure, surface treatments, and environmental conditions, have not been
investigated. This presents a significant research gap in understanding their performance,
particularly in biomedical applications.
NOVELTY
In present work, the mechanical properties of HA and PMMA are studied and its variation in
porosity percentage is determined, which is not found in the literature so far.
PROBLEM STATEMENT
Impact of varying porosity on the mechanical properties ( compressive strength , fatigue strength )
of HA and PMMA composite bone scaffold.
12. OBJECTIVES
1. To create a 3D CAD model of a composite bone scaffold
2. To assign material properties for the composite scaffold
3. To generate a 3D mesh of the bone scaffold
4. To investigate the effect of varying porosity on the mechanical properties
Objective 1: To create a 3D CAD model of a composite bone scaffold
In order to obtain a 3D CAD model to begin the simulation, a porous cube model is created
with size of 10 mm with various pore diameter at ANSYS software for 70%, 74%, 75%
porosities. Afterwards this model was selected for static structural analysis and for the
simulation.
36% porous model 46% porous model
13. 50% porous model 58% porous model
Objective 2: To assign material properties for the composite scaffold
Required material properties were assigned for the Hydroxyapatite and PMMA ( Poly methyle meta
acrylate) composite.
Properties of filler material (Hydroxyapatite)
Young’s modulus (E) = 1.35e11 Pa Density = 3
gm/cm3
Poisson’s ratio for HA:0.27
Properties of matrix material (PMMA-polymer)
Young’s modulus (E) = 3e9 Pa
Density = 1.2 gm/cm3
Poisson’s
ratio for PMMA:0.38
Volume percentage of the pores in the composite = 70%
Therefore, volume percentage of the filler material (hydroxyapatite) in the composite =
36.4%
14. Objective 3: To generate a 3D mesh of the bone scaffold
36% porous mesh 46% porous mesh
50% porous mesh 58% porous mesh
15. Objective 4: To investigate the effect of varying porosity on the mechanical properties
The simulation for HA and PMMA bone scaffolds was carried out for varying porosity. The
porosity was changed for the composite HA and PMMA bone scaffold.
The results from the simulation were then compared by plotting graph, enabling a visual
comparison of the different scaffold models. This approach allowed for the assessment of how
varying the porosity impacted the scaffold’s performance in terms of mechanical strength,
deformation, and stress distribution.
20. Results: The graphs of Normal stress and compressive modulus against porosity percentage were
plotted.
Porosity v/s Normal Stress
Porosity v/s Compressive Modulus
21. CONCLUSION
When you increase the porosity of a porous cube, the material's compressive strength will
typically decrease. This happens because increased porosity reduces the effective load-bearing
area, leading to higher stress concentrations in the remaining solid matrix, making it weaker.
However, calculating the new compressive strength of a porous material directly from an
increase in porosity is complex and typically requires empirical relationships or material models
that take porosity into account. Consequently, achieving an optimal balance between porosity
percent and mechanical strength is paramount in the design and fabrication of porous materials
for biomedical applications. While larger number of pores enhance cell infiltration and tissue
regeneration, they compromise the material's mechanical properties. Conversely, reducing
porosity improves mechanical strength but may hinder cell migration and tissue integration.
Therefore, the development of biomaterials involves careful consideration of various factors,
including porosity, material composition, and mechanical performance, to ensure an optimal
compromise between structural integrity and biological functionality.
22. SCOPE FOR FUTURE WORK
The current analysis is not highly realistic in mimicking a real bone scaffold. A 3D particle
reinforced composite with modelled particles could enhance the study of scaffolds. Future
studies in bone scaffold development could focus on conducting fatigue, bending, and torsional
tests to evaluate mechanical performance under dynamic loading conditions. These tests would
provide valuable insights into scaffold durability and resistance to mechanical stresses
encountered in the body. By systematically analysing the relationship between porosity and
strength, researchers can refine scaffold designs to enhance both biomechanical properties and
tissue regeneration capabilities.
