Cerium Doped Hydroxyapatite

FINAL YEAR PROJECT 2 (Semester1, Academic Year 2008/2009)

Title :

Sintering Behaviour of Cerium-doped Hydroxyapatite Bioceramics Prepared by:

KELVIN HOH CHEE WAI (ME075719) Project Supervisor: Assoc. Prof. Ir. Dr. Ramesh Singh

Department of Mechanical Engineering Universiti Tenaga Nasional (UNITEN)

CONTENTS • • • • • • •

Introduction Objective Methodology Experimental techniques Experimental testing methods Results & Discussions Conclusion

INTRODUCTION • Hydroxyapatite (HA), Ca10(PO4)6(OH)2, exhibits excellent biocompatibility due to its chemistry similarity with the mineral portions of hard tissues. • However, its mechanical properties limit the usage of HA in clinical application. • Several approaches have been proposed to improve the mechanical properties of HA, such as:

INTRODUCTION Control of sintering temperature & atmosphere. Manipulation of processing parameters. Addition of sintering additives (i.e. dopants) into the HA powder.

OBJECTIVE • To investigate the effects of adding small amounts of Cerium Oxide (CeO 2 ) on the sinterability of nanocrystalline HA powder.

METHODOLOGY Literature Review

FYP 1

Preparation of Cerium-doped HA powder Powder Characterization Body Preparation Consolidation Process Mechanical Testing & Evaluation Report preparation & presentation

FYP 2

Experimental Techniques • Synthesized HA powder which is produced by wet chemical precipitation method was used and mixed with CeO2 ranging from 0.1 wt% - 1.0 wt% using wet milling method. • The powder was uniaxially pressed into discs and rectangular bars and subsequently cold isostatically pressed at 200 MPa. • The compacted samples were sintered at temperature ranging from 1100C to 1300C. • Sintered samples were polished to 1m finish prior to testing.

Experimental Testing Methods • Phase analysis

 X-Ray Diffraction (XRD).

• Bulk density

 Water Immersion Technique.

• Young’s modulus

 Sonic Resonance Method.

• Hardness

 Vicker’s Indentation Method.

• Fracture Toughness  Vicker’s Indentation Method.

RESULTS & DISCUSSIONS (XRD Analysis) • Ceria Peaks @ 1 wt%

Fig 1: XRD patterns for CeO2-doped HA sintered at 1300 C. (a) undoped HA, (b) 0.1 wt%, (c) 0.5 wt%, (d) 1.0 wt% CeO2, respectively.

XRD analysis revealed that the doped & undoped HA phase stability were not dis r upt ed r egardless of dopant additions and sintering temperature.

BULK DENSITY •

In general, the bulk density variation of all the composition studied exhibited a similar trend with increasing sintering temperature.

•

All the samples attained above 98% of theoretical density when sintered above 1100ºC.

Bulk Density (g/cm 3)

3.14 3.13 3.12 3.11

0wt% 0.1wt% 0.5wt% 1.0wt%

3.1 3.09 1100

1200

1300

Sintering Tem perature (ºC)

Fig 2: The effects of CeO2 addition on the bulk density of synthesized HA.

Young's modulus (GPa)

YOUNG’S MODULUS 126 125 124 123

The relationship between the Young’s modulus of the sintered body, sintering temperature and CeO2 additions are shown in Fig 3.

•

The inclusion of CeO2 in HA reduces the Young’s modulus.

•

However, the Young’s modulus of natural bone is reported to be between 11 GPa to 29 GPa.

undoped 0.1 wt% 0.5 wt% 1.0 wt%

122 121 120 119 118 117 1050

•

1100

1150

1200

1250

1300

1350

Sintering Tem perature (°C)

Fig 3: The effects of CeO2 addition on the Young’s modulus of synthesized HA.

YOUNG’S MODULUS

Fig 4: Fracture toughness versus Young’s modulus of present biomaterials and human bone.

VICKER’S HARNESS •

A general observation shows measured hardness of all the samples revealed a similar trend.

•

The results also revealed that the addition of 1 wt% CeO2 was beneficial as samples exhibited higher hardness value in the sintering regime employed as compared to undoped HA.

•

The highest hardness value of 6.19 GPa was obtained for HA doped with 1 wt% CeO2 and when sintered at 1200ºC.

7 Hardness (Gpa)

6 5 4

undoped 0.1wt% 0.5wt% 1.0wt%

3 2 1 0 1100

1200

1300

Sintering Temperature (°C)

Fig 5: The effects of CeO2 addition on the Vicker’s Hardness of synthesized HA.

Fracture Toughness (MPam1/2)

FRACTURE TOUGHNESS 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1100

•

The results also show that the addition of CeO2 was effective in enhancing the fracture toughness (KIc) of the synthesized HA, particularly when sintered at 1100ºC.

•

The 1 wt% cerium-doped HA samples exhibited the highest fracture toughness of 0.82 MPam1/2 as compared to 0.73 MPam1/2 measured for the undoped HA.

Undoped 0.1wt% 0.5wt% 1.0wt% 1200

1300

Sintering Temperature (°C)

Fig 5: The effects of CeO2 addition on the fracture toughness of synthesized HA.

CONCLUSIONS • Incorporation of small amount of cerium oxide can be beneficial in enhancing the mechanical properties without affecting the HA phase stability even when sintered at 1300ºC. • The addition of 1 wt% CeO2 and when sintered at 1100ºC was found to be most beneficial as the HA samples exhibited the moderate Young’s modulus of 120.53 GPa, enhanced hardness of 6.19 GPa and fracture toughness of 0.82 MPa.m1/2.

FURTHER WORK SUGGESTIONS