Developing Bio-Ceramic Orthopedic Screws

UNC Charlotte Senior Design Page 1 of 19
Project: UNCC BIOCE Final Report
Author: Quelle Kollie, Sutherland Zee Date: 2014-12-06
Cover Letter of Transmittal
UNCC BIOCE Team
9201 University City Blvd.
Charlotte, NC 28223
December 06, 2014
Senior Design Committee
9201 University City Blvd.
Charlotte, NC 28223
Dear Senior Design Committee,
The purpose of this documentation is to describe the progress that has been made thus far
towards the completion of the UNCC BIOCE project for Senior Design. The project is the
development of two processing techniques used to fabricate bio-ceramic orthopedic screws. The
new protocols will serve to reduce cost while maintaining the quality and productivity of
standard processes currently being used. Currently orthopedic screws are made of titanium or
stainless steel; these metals causes side effects. Accumulation of ions and wear debris from the
metal is toxic to the body and can cause implant failure. The modulus of elasticity of the metal
implants is higher than the bone thus leading to the weakening of the surrounding bone, also
known as stress shielding. The metal implants have poor fixation due to the micro-motion
caused by fibrous encapsulation of the orthopedic screw. The ceramic used in the processing
techniques was silica calcium phosphate nano-composite (SCPC). This ceramic was chosen
because it is bioactive, allowing better fixation as it has similar composition to that of bone. Due
to the similar composition of SCPC and bone bonds are form. After much research the student
team chose to utilize powder metallurgy and ceramic casting for developing the orthopedic
screws. The techniques would be compared to determine the effects of the processing protocols
on the mechanical properties and dimensional changes of the SCPC50 after sintering.
The processing techniques that will be implemented are powder metallurgy and ceramic
casting of a slurry composition. Powder metallurgy is a technique where the powder is pressed
into a cylinder at a constant pressure, thereafter the cylinder is heat treated to improve the
mechanical properties. Ceramic casting is a technique where the bio-ceramic screws are made
from molds. A slurry mixture is made and pour into the mold where it will then solidify after a
period of time. The hardened screw is then heat treated to increase the mechanical strength.
The slurry is made from silica calcium phosphate nano-composite 50 (SCPC50). The
SCPC50 will first need to be made. It was estimated that overall about 500grams of SCPC50
was use for the experiments that were conducted. The size of SCPC50 needs to be in
nanometers; therefore a manual grinding was needed as well. The Planetary Ball Mill is the
apparatus that was to use to crush the ceramic to nano-size. After the samples were fabricated,

they were compared to determine the effects of the processing protocols on the mechanical
properties and dimensional changes.
The UNCC BIOCE team did some preliminary testing to learn how equipment worked.
Heavy research was done through various research papers written by both the mentor and
previous graduate students. The team was confident in achieving and surpassing all objectives
successfully. The team were also on schedule for the duration of the project. Presented samples
created from various trials at the expo for Senior Design II.
A directory containing all relevant project deliverables for the Senior Design II course
was placed into a zip file and burned to two DVD’s. One DVD was delivered to our grading
instructor, and the other to the designated member of the ISL. The folder name on the DVD that
contains all files is BIOCE_Comprehensive_Submission_SD2. This zip file was also submitted
to the Comprehensive Document Submission assignment on Moodle. A list of all files contained
on the DVD should be displayed in the table below.
Deliverable File Name
Summary of Project Description, Initial Performance Specification UNCC_BIOCE_InitialSpecification.pdf
Document and Project Questions
Statement of Work Document UNCC_BIOCE_SOW.pdf
Project Specification Document UNCC_BIOCE_PerformanceSpec.pdf
Project Plan UNCC_BIOCE_IProjectPlan_Original.mmp.pdf
Mold Model CAD Drawings UNCC_BIOCE_Mold.zip
Progress Report # 1 UNCC_BIOCE_ProgressReport1-1.pdf
Progress Report # 2 UNCC_BIOCE_ProgressReport2.pdf
Prototype Status Review Presentation (PSR) UNCC_BIOCE_PSR
Prototype Review Presentation (PRP) UNCC_BIOCE_PRP
Final Timesheet (Senior II) UNCC_BIOCE_TIMESHEET5.xlsx
Project Summary UNCC_BIOCE_ProjectSummary.pdf
Final Project Report UNCC_BIOCE_FinalReport.pdf
Comprehensive Package UNCC_BIOCE_SD2
Final Poster_Senior II UNCC_BIOCE_Poster.pdf

BIOCE Project – Final Design Package – Senior Design II
Table of Contents
Overview of this Document...……………………………………………………………..4
Project Overview/ Statement of Work Summary…………………………………………4
Specifications……………………………………………………………………………..5
Design Narrative……………………………………………………………………….…6
Impact…………………………………………………………………………………….9
Conclusions…………………………………………………………………………….....9
References…………………………………………………………………………...........11
Appendices…………………………………………………………………………….....12
Date Revision Author Comments
2014-12-06 QK,SZ Original Document

Overview of this Document
The objective of this project was to develop protocols for making bio-ceramic orthopedic
screws. The new protocols will serve to reduce cost while maintaining the quality and
productivity of standard processes currently being used. Currently orthopedic screws are made of
titanium or stainless steel; these metals causes side effects. Accumulation of ions and wear debris
from the metal is toxic to the body and can cause implant failure. The modulus of elasticity of
the metal implants is higher than the bone thus leading to the weakening of the surrounding
bone, also known as stress shielding. The metal implants have poor fixation due to the micro-
motion caused by fibrous encapsulation of the orthopedic screw. The ceramic used in the
processing techniques was silica calcium phosphate nano-composite (SCPC). This ceramic was
chosen because it is bioactive, allowing better fixation as it has similar composition to that of
bone. Due to the similar composition of SCPC and bone bonds are form. After much research the
student team chose to utilize powder metallurgy and ceramic casting for developing the
orthopedic screws. The techniques were compared to determine the effects of the processing
protocols on the mechanical properties and dimensional changes of the SCPC after sintering.
This document will briefly describe the work completed as well as issues that were addressed,
recommendations for future research, and lastly a brief overview of the communications
between the team, mentors, and faculty advisor.
Quelle Kollie, who is identified as the Project Lead, is responsible for the maintenance of this
document.
Project Overview/ Statement of Work Summary
Mission Statement
The objective of this project is to develop protocols for making bio-ceramic orthopedic
screws using two processing techniques, powder metallurgy and ceramic casting of a
slurry composition. The orthopedic screws would be made of silica calcium phosphate
nano-composite (SCPC). The techniques will be compared to determine the effects of
the processing procedures on the mechanical properties and dimensional changes of the
SCPC screws.
The project requires fabrication of two plastic molds, polypropylene and rapid prototype
(RP). The molds will model using computer aided designing (CAD) programs such as Creo
Parametric and SolidWorks. After creating the model using the CAD program the RP mold
will be fabricated. The polypropylene mold be fabricated using a mill and the band saw in
the machine shop. The SCPC50 in its powder form will be transform into a slurry
composition. The slurry will be composed of 60% SCPC50 and 40% deionized water. The
slurry will then be used in the molds to cast the screws. Upon solidification the screws will
be removed from the molds and heat treated at various temperatures to allow the gain
structures to merge, thereby increasing the mechanical properties. Image analysis and
mechanical property testing will be conducted to verify the screws prototype
performance specifications.

Specifications
General Requirements
REQ1: Knowledge in chemistry will be needed for the synthesis of the slurry and
SCPC bio-ceramic cylinder.
REQ2: Skills in Creo Parametric will be needed as well as the ability to change to
the file to STI
REQ3: Knowledge of the Instron Tensile testing machine and SEM machine will
be required
REQ4: Knowledge of the Planetary Ball Mill is required
REQ5: Machining skills and knowledge of proper mold making will be required
for fabrication of the molds
Performance Specifications
PS1: Make Molds (Polypropylene and RP)
PS2: Inner wall of the mold must have a good surface finish
PS3: Test slurry methods by median and suspension (change particles size)
PS4: The slurry must be able to harden easy
PS5: Upon removal from the mold, the screws must not have deformations.
PS6: Thermal treatment (correlate heat treatment versus mechanical properties
and dimensional changes)
PS7: After heating in the furnace, the screws must be easy to remove
PS8: The screws will need to be a desirable size for it to be used in the Instron
Machine
PS9: Should slurry casting method not work, the alternative will be to create
cylinders by press then machining to desired dimensions
PS10: The modulus of elasticity of the screws will need to be similar to bone.
Depending on where in the body, the modulus of elasticity will differ;
high modulus may cause stress shielding and too low will lead to failure

Performance Verification
V1: A working mold will be made to verify PS1
V2: The inner wall of the mold will be inspected to verify PS2
V3: The slurry will be inspected for its viscosity and solidification rate to verify PS3
V4: After slurry is in place, a timer will be used to verify PS4
V5: Upon removal from the mold, the screws will be inspected for deformations to
verify PS5
V6: The prototype will be subjected to heat treatment via an oven to verify PS6
V7: The cylinder will be fitted inside the Instron Machine to verify PS7
V8: A ruler will be used to verify the dimensions to verify PS8
V9: The casted screws will be tested after heat treating to verify PS9
V10: The screws will be measured using the Instron Tensile testing machine to
verify PS10
Design Narrative
The following will describe the bioactive ceramic orthopedic screw and the processes
needed to complete the requirements and goals. Description of the overall design intent
and description of each method and component rationale for choices made are included in
this section.
SCPC Preparation
Silica Calcium Phosphate Nano-composite (SCPC) is the ceramic that was used in
creating the orthopedic screws. The primary properties that makes SCPC a great material to be
used as fixation devices is that it is bioactive and it has a similar composition to bone. SCPC
allows for implants compose of this material to bond directly to bone and stimulate the formation
of bone and soft tissue. To create the SCPC 200 grams of calcium phosphate dibasic dihydrate
was mixed with 200 grams of sodium metasilicate nonahydrate in a roller mixer for 24 hours.
The mixture was then sintered at 850 degrees Celsius for one hour. The 400 grams of SCPC50
were crushed to 450 microns using a mortar and pestle. Next, using the planetary ball mill the
SCPC50 was further crushed to nano-size.

Ceramic Casting Method
Polypropylene Mold
Ceramic casting is a manufacturing process that utilizes a mold and slurry to create
components. Ceramic casting was used to create the bioactive ceramic screws. The mold that
was use was created from a polymer, polypropylene. The team chose to use polypropylene
mainly because it has a high chemical resistance. This property of polypropylene was necessary
for our project because once in the mold the sample would not become contaminated. A reason
the team chose polypropylene is because it is relatively inexpensive compare to other polymers
on the market. The polypropylene mold was created using the band saw and the mill machine.
First, using the vertical band saw a 4 inch by 3 inch section was cut from a stock of
polypropylene. Next, using the mill machine four 3/16 inch holes were drilled through on the
side of the 4 inch by 3 inch section that was cut off. These holes were used to secure the two
halves of the mold together. Again, using the mill three 27/64 inch holes were drilled on the top
of the 4 inch by 3 inch section, the holes were drilled to a depth of 1.5 inches. These holes were
used to hold the slurry, allowing it to solidify. The thread pattern in the mold was created using a
½ -13 Tap. Next, using the vertical saw the polypropylene section was cut in half. After
machining the polypropylene mold sandpaper with 400 and 600 grits were used to improve the
surfaces that were cut using the band saw.
Wooden Mold
Next, the team chose to attempt casting the SCPC50 screws using a wooden mold.
Similar to the polypropylene mold, the polypropylene mold was created using the band saw and
the mill machine. First, using the vertical band saw a 4 inch by 3 inch section was cut from a
stock of plywood. Next, using the mill machine, four 3/16 inch holes were drilled through on the
side of the 4 inch by 3 inch section that was cut off. These holes were used to secure the two
halves of the mold together. Again, using the mill three 27/64 inch holes were drilled on the top
of the 4 inch by 3 inch section, the holes were drilled to a depth of 1.5 inches. These holes were
used to hold the slurry, allowing it to solidify. The thread pattern in the mold was created using a
½ -13 Tap. The thought behind choosing a wooden mold was that the wood would absorb the
water.
Plaster of Paris Mold
Another material we chose to experiment with was Plaster of Paris. Also known as
gypsum plaster, Plaster of Paris is similar to clay in that it is easily shaped when wet. The
formability of the Plaster of Paris made it possible create a two piece mold. First one half of a
medical screw model was embedded in clay and the mold is poured and allowed to fully solidify.
The mold was then turned over and the clay was removed. Next, a release agent was applied to
prevent bonding and the second half of the mold was poured. The mold was then allowed to fully
dry before de-molding. The fact that this material was used in the past to make classic plaster
orthopedic casts made it stand out to be a very promising material.

Acrylonitrile butadiene styrene (ABS) Rapid Prototype (RP) Mold
With the RP the team would be able to control the parameters for creating the mold. A
model of the mold was created using a 3D modeling software called Creo Parametric. This
method was chosen because it would allow for better surface finish. Another advantage of the RP
mold is that it was more precise and it can be easily created, modified, and improved. Additional
features could be easily added as well, such as a screw and cylinder that will apply additional
pressure. In addition to the RP mold, a “burnout” ABS mold was created. The burnout mold will be
simple as it does not require two pieces. As the ABS burns off, the screw would also sinter therefore
saving time with one less process. It is advantageous to have thinner walls for the burnout mold, as
when the ABS melts it deforms the screw with its weight.
The slurry that was poured into the mold was created using 60% SCPC50 and 40%
deionized water. The slurry was poured into the mold and allowed to solidify in ambient
temperature for one day. Next, the mold was place in the oven at 100 degrees Celsius for two
days to evaporate the remaining water from the samples. After the two days the mold was
removed from the oven and the samples were taken out of the mold. Next, the samples were put
in the furnace to be further heat treated. The heat treatment cycle was started from ambient
temperature and increased at a rate of two degrees Celsius per minute to 120 degree Celsius
where it was held for one hour. Next, the temperature was increased at a rate of two degrees
Celsius per minute to 800 degree Celsius where it was held for one hour. Upon completion of the
heat treatment cycle, the samples were left in the furnace for one day to allow them to cool
properly. The samples will be removed and their mechanical properties and dimensional changes
would be compared.
Metallurgy Method
Powder metallurgy is a manufacturing process that uses pressure to press fine powder
materials into a desired shape, and then the compressed material is heated in a controlled
environment (sintering). For this project the powder metallurgy technique will be used to create
the orthopedic screws of SCPC. The powder SCPC will be placed in a die where it will be
pressed at a constant pressure of 30 MPa for three hours. The samples will then be sintered at
800 degrees Celsius for two hours using the furnace. After sintering, threads were machined on
the samples using the manual lathe; single point turning thread. Upon machining the threads the
samples will be sintered once more at 900 degrees Celsius for two hours. The samples will be
removed and the mechanical properties and dimensional changes would be compared.

Impact
The project has a significant scientific impact on the medical and bioengineering society
as well as anyone who needs or already has medical screws in their body. Currently orthopedic
screws have been made from titanium or stainless steel. The human body rejects foreign
materials and responds by encapsulating the material with fibrous material. Fibrous
Encapsulation causes the metal screws to have a limited fixture on the bone; encapsulation
promotes micro movements which can lead to failure of the screw. Metals inside the body will
also give off metal ions, which are toxic to the body. Bio-active ceramic screws will eliminate
the adverse effects that metal screws tend to have. Bioactive means the body accepts this
material, therefore the screw will start forming bonds to the bone and soft tissue; and because
there is no fibrous encapsulation, the screw will have a “snug” fit into the bone. The ions
released from the SCPC screw is bone minerals that help regenerate bone.
Conclusions
The project required knowledge of not only mechanical engineering but also of biology
and chemistry. Heavy research in the two fields yielded many of the ideas that were
implemented. The research in slurry’s and ceramic casting helped the team in choosing the
design of the mold as well as the ratio for the water to solid in the slurry. A preliminary test mold
made with polypropylene was made and tested using a small batch the project required
knowledge of not only mechanical engineering but also of biology and chemistry. Heavy
research in the two fields yielded many of the ideas that were implemented. The research in
slurry’s and ceramic casting helped the team in choosing the design of the mold as well as the
ratio for the water to solid in the slurry. A preliminary test mold made with polypropylene was
made and tested using a small batch of SCPC50 sample we made. The results from these
experiments varied. The first experiment we made yielded a sample that had obvious surface
cracks and as we opened the mold, the sample broke in two. The second experiment we
improved, as this time lubrication was added while the rest was constant. This yielded a smooth
cylinder that had small surface cracks. Because we heated the cylinder with half of the mold
exposed, one side of the cylinder had more heat transfer therefore drying faster than the other
side. This caused the cylinder to warp. The third experiment we made came from the mold we
made that had the holes tapped, giving the mold threads on the inside. This yielded ceramic
screws but the screws had a small amount of air bubbles as well as fractures at two points.
In the fourth experiment we tried to solve the air bubble problems by having a runner system on
the bottom of the mold. This yielded a completely opposite effect in which we hoped as the
screws were covered in air bubbles.

Based on the research conducted by the team, it has been concluded that:
• Ceramic Casting
o Ceramic casting is quick and economical manufacturing method; further research
needs to be performed regarding preprocessing of SCPC50 slurry as well as
casting methods
o Further research should be conducted into applying distributed pressure on the
slurry while it dries
o A proper parting material that is uniformly distributed is essential for good mold
separation
o Smooth surface finish is vital for a good separation
o To ensure exact alignment of molds, studs and guiding holes are imperative
• Powder Metallurgy
o Powder Metallurgy seems to be a more precise process, however it is more time
consuming
o High pressure use to compress the cylinders ensures that the SCPC50 particles are
tightly packed
o Machining threads on the SCPC50 cylinder is problematic due to its brittleness
In the near future the team will need to improve mold configuration, decrease the
presence of air bubbles, investigate surface cracks and fractures, make the mold easier to open
upon dry heating, improve the metallurgy fabrication process, practice single point turning thread
on the SCPC50 cylinders made from metallurgy process. It would be ideal if the team is able to
perform mechanical properties test and image analysis, and eventually calculate the necessary
screw calculations based on the results of the mechanical testing.

References
1. El-Ghannam, Ahmed. Interview by author. Personal interview. Duke Centennial
Hall, January 8, 2014.
2. Sparnell, Amie. "Machining of a bioactive nanocomposite orthopedic fixation
device.” Society for Biomaterials 1 (2012): 1-11.
3. "Project Summary/InitialPerformance Specifications Document Template." UNC
Charlotte: Login to the site. https://moodle2.uncc.edu/course/view.php?id=58851
(accessed January 16, 2014).
4. Ohtsu, Naofumi. "Calcium-hydroxide slurry processing for bioactive calcium-
titanate coating." Surface & Coatings Technology 1 (2008): 1-6. Print.
5. Stampfl, Jurgen. "Rapid prototyping and manufacturing by gelcasting of
metallic." Materials Science and Engineering A334 1 (2001): 1-6. Print.

Appendices
All raw data, spec sheets, tables, plots, CAD drawings, schematics, computer code,
budgets, bill of materials, etc., that are not specifically included in the narrative. Note that
all material in appendices must be referred to in the narrative and each type of material
should have a separate appendix with a unique title. These supporting documents in the
native file format should be included in the Comprehensive Document Submission
assignment (see sample SD2 Final Design Package report posted on Moodle).
Ceramic Casting

Powder Metallurgy

Figure 17: Rapid Prototype Molds
Figure 18: Rapid Prototype Mold Revision A

Figure 19: Rapid Prototype Mold Revision B
Figure 20: Rapid Prototype Mold Revision C

Figure 21: Rapid Prototype Mold Revision D; Runner system added
Figure 22: Burn-out Mold Figure 23: Burn-out Mold Revision A
Figure 24: Burn-out Mold Revision B Figure 25: Burn-out Mold Revision C

Figure 26: Results from RP mold and burnout mold
Figure 27: Power Metallurgy pressing

Figure 28: Single point threading
Figure 29: Powder Metallurgy Results

Developing Bio-Ceramic Orthopedic Screws

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