Processing and Characterization of Tricalcium Phosphate
with SrO and ZnO Dopants for Bone Grafts
Johanna Feuerstein, Shashwat Banerjee, Scott Rewinkel, Amit Bandyopadhyay and Susmita Bose
W. M. Keck Biomedical Materials Research Laboratory
School of Mechanical and Materials Engineering
jdfeuerstein@gmail.com
Avstract:The purpose of this study is to develop a ceramic material with the proper strength degradation kinetics to be used as bone implants. Tricalcium phosphate (TCP) ceramics have gained a lot of attention over the past several years for their similarity to bone. However, they show poor mechanical strength and uncontrolled strength degradation. For this reason, various dopants and their
affect on the strength and strength degradation of TCP in-vitro- are being studied.In this study, three different TCP-based compounds were studied: (i) 0.25 wt% ZnO, (ii) 1 wt% SrO and (iii) binary dopants with 0.25wt% ZnO and 1 wt% SrO. The compounds were sintered at 1250° C. It was found that the binary dopants had the highest weight increase at both 14 and 28 days, indicating the most
hydroxycarbonate apatite (HCA) formation on the surface of the disks and the least amount of dissolution. The SrO is proving to have the most stable degradation kinetics. The binary dopant also seems to be the most bioactive as it has the most HCA formation.
.
Objective: To develop a ceramic material with adjustable degradation kinetics
In vitro Study:
Weight Change
Weight change is a
competition between
Hydroxycarbonate apatite
(HCA) formation and TCP
dissolution.
Weight Change
0.65000
 Tricalcium Phosphate (TCP) materials have recently
Weight Change (%)
gained attention and are being studied as biodegradable
materials and tissue engineering scaffolds.
Controlled degradation kinetics are necessary for these
Maxillofacial surgery:
3-6 months to repair.
biomaterials to have applications as implants for bones in
biodegradation times.
0.25000
0.05000
1% SrO
0.25% ZnO
TCP control indicates it is
dissolving at about the same
rate as the HCA formation.
Binary
Relative density of synthesized TCP as compared to the
theoretical density of TCP at 3.07 g/cm3 Calculated as total
mass over volume, taken after sintering.
ArchimedeanDensity
Why SrO and ZnO?
96
95
94
93
92
TCP Control
SrO
• Found in Natural Bone
•Shown to have effect on bone
regeneration
•Studying 0.25 wt% ZnO
• Found in Natural Bone
•Aids in osteoblast formation.
•Prevents osteoclast formation
•Studying 1 wt% SrO
1% SrO
0.25% ZnO
0.25 wt%
ZnO
60 ksi for 5 minutes
Sinter at
1250 C
750 mg powder
pressed at 58 MPa
for 1 minute
500 mg powder
pressed at 145 MPa
for 1 minute
.
40
60
80
100
Time (s)
TCP Con
SrO
ZnO
Bin
0.5
0.4
Binary dopants has the highest HCA formation, and a comparatively
small amount of dissolution.
SrO released the highest
total amount of Calcium.
0.2
0.1
Future Plans
0
Time (days)
20
Binary
SrO has the most controllable strength degradation kinetics up to this
point.
Calcium uptake occurs
when HCA is forming.
0.3
10
1 wt% SrO
 Addition of SrO and ZnO dopants did not increase the density.
Binary released one of the
lowest Ca concentrations.
30
 Carry SBF study out to 16 weeks
To determine the amount of TCP dissolution, used SBF solution was collected from
incubating samples every 3-4 days. Amounts were calculated as rates, and then added
to get total concentration. Volume change was assumed to be negligible.
Analyze XRD data to determine amounts of α- and β-TCP.
Cell culture studies to determine cell attachment to the surface of the
sample over time
In-vivo study (using rat model) to determine ion concentration using
atomic absorption spectrophotometer
CO32- was quantitatively
analyzed in the apatite layer on
the surface of the samples.
TCP control exhibited the
most intense phosphate peaks.
CO32-
TCP Control
1 wt% SrO
0.25 wt% ZnO
Binary
References:
PO44-
2200
2000
1800
1600
1400
1200
Wave Number (cm-1)
.
Binary
20
Conclusions
Calcium release is an
indicator of TCP dissolution.
Calcium AAS
2400
.
Control 0.25% ZnO 1% SrO
-200
0
Binary formed the most HCA, but had the finest size.
FTIR
2 shapes of ceramics were formed: cylinders and disks as
shown:
0
Scanning electron microscopy of samples after 4 weeks in SBF. Images taken at 5000x resolution.
4 weeks
Machine used for uniaxial
press.ing
4 weeks
200
50.00
TCP control
Atomic Absorption Spectroscopy
0
Place in Simulated
Body Fluid (SBF)
2 weeks
400
Binary
TCP control achieved the highest Archimedean density, while ZnO was the lowest.
Total [Ca2+] (μg/mL)
Cold Isostatic Press
0 weeks
87
Binary
Relative density of synthesized TCP as compared to the
theoretical density of TCP at 3.07 g/cm3 . Metal addition to
TCP was not calculated into the theoretical density due to
the relatively small concentrations.
0.6
Uniaxially
Pressed
600
89
TCP Control 1 wt% SrO
0.7
Wet Mixing on
Ball Mill
8 weeks
91
In vitro Study:
Synthesis and Formation of Ceramics
800
4 weeks
93
Binary has higher Archimedean density that either of the single dopants, but a lower bulk
density.
Binary - 1 wt% SrO + 0.25 wt% ZnO
2 weeks
200.00
95
91
ZnO
1000
Scanning Electron Microscopy
Bulk Density
Percent of Theoretical Density
degradation kinetics.
Percent of Theoretical Density
97
Spinal fusion:
9-12 months to repair.
1200
0 weeks
-25.00
Density
was not easy to be effectively varied or modulated.
Load vs. Time
275.00
125.00
-0.15000
Addition of certain metals can help to regulate the
SrO is degrading at a slow and
constant rate.
350.00
Binary exhibited the
highest percent weight
increase from its original
weight, indicating the most
HCA formation and least
amount of dissolution.
2 weeks
4 weeks
8 weeks
TCP Control
Despite extensive research, the biodegradation of TCP
425.00
0.45000
the body as different parts of the body require different
[2]
Compressive Strength
Load (kg)
Introduction
TCP control achieved the highest
strength, but is exhibiting
uncontrollable degradation kinetics.
Strength Degradation
Strength (MPa)
to be used as implants for bones in the body.
Results
1000
800
600
400
1. Amit Bandyopadhyay, Sheldon Bernard, Weichang Xue and Susmita Bose, “Feature Article: Calcium Phosphate Based Resorbable
Ceramics: Influence of MgO, ZnO and SiO2 Dopants,” J. Acer. Cer. Soc., 89 [9], pp. 2675-88 (2006).
2. Weichang Xue, Kelly Dahlquist, Ashis Banerjee, A. Bandyopadhyay and S. Bose, “Synthesis and characterization of Tricalcium phosphate
with Zn and Mg based dopants,” J. Mat. Sci.-Mat. in Med., 19 [7], pp. 2669-2677 (2008).
Acknowledgements: CIB Fellowship and National Institute of Health (Grant # NIH-R01-EB-007351) for Financial Support