characterization and corrosion behavior of poly(ɛ-caprolactone)/hydroxyapatite composite coating...

Characterization and Corrosion Behavior of Poly(ɛ-caprolactone)/Hydroxyapatite Composite Coating on

Ti6Al4V Fabricated by Dip - Coating Technique

By :Mohd Faiz Mohd Yusoff

MW103004Main-Supervisor :

Prof. Ir. Dr. Mohammed Rafiq

Co-Supervisor :Dr. Rafaqat Hussain

GARDEN OF KNWOLEGDE AND VIRTUEGARDEN OF KNWOLEGDE AND VIRTUE

INSPRING CREATIVE AND INNOVATIVE MINDSINSPRING CREATIVE AND INNOVATIVE MINDS

:: IN THE NAME OF ALLAH, MOST GRACIOUS, MOST MERCIFUL :::: IN THE NAME OF ALLAH, MOST GRACIOUS, MOST MERCIFUL ::

Presentation Outlines

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1.0 INTRODUCTION1.0 INTRODUCTION

2.0 MATERIALS & METHODS2.0 MATERIALS & METHODS

1.1 Project Background1.2 Problem Statement1.3 Objectives1.4 Scope of Study1.5 Significance of study

3.0 RESULTS & DISCUSSIONS3.0 RESULTS & DISCUSSIONS

4.0 CONCLUSIONS4.0 CONCLUSIONS

5.0 RECOMMENDATION5.0 RECOMMENDATION

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Biomaterial

Biocompatibility

Bio-degradable Bio-inert

Natural or synthetic material that aims to replace part of living tissue or to restore a normal function in biological

environment

Does not initiate a positive response when introduced

to the living tissue

The acceptance of the implant material by the surrounding tissues without producing any undesirable

response from the body and vice versa [1,2]

Induce positive interaction with

surrounding tissue

Metal Polymer Ceramic Composite

Bio-activeThe ability of material to

dissolve in biological environment and gradually substituted by new tissue

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Metals in Biomedical Applications

Metallic biomaterials are most commonly used for load bearing implant and internal fixation device due to its featured characteristics such as :i.Excellent mechanical properties :

High tensile strength High yield strength Resistance to cyclic loading (fatigue) Resistance to time dependent deformation (creep)

ii.Biocompatibility (low cyto-toxicity)iii.High corrosion resistance

The most commonly used metals and alloys for medical devices application include :i.Ti and Ti6Al4Vii.316L Stainless Steels iii.Co-Cr-based alloys

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DentistryOrthopedic

Craniofacial Cardiovascular

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Limitations of Metallic Implants

Bio-inert :Do not promote the formation of apatite layer on its surface [3]

Release metallic ions :May combine with biomolecules and

cause adverse biological reaction [4,5]

Solution

Surface modification:Coating with bioactive material

• Accelerate bone healing and bonding of the coatings with bone [6,7,8]• Enhance the corrosion resistance of metallic implant where coating layer

will reduce the release of metallic ions by acting a barrier• Combine the mechanical benefits of metal alloys with bioactivity of bioactive

materials

Advantages

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Coating materials

Hydroxyapatite (HA)Hydroxyapatite (HA)

Chemical Formula : Ca10(PO4)6(OH)2

The most important calcium phosphate compounds found in natural hard tissues as mineral phase

Ca/P ratio : 1.67 (similar to the bone)

Act as reinforcement in hard tissue and responsible for the stiffness of bone, dentine, and enamel.

Osteconductive : Promote osteointegration & accelerate implant fixation

Bioactive ceramic materials

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Deposition Technique

Plasma Spray

CVD

EBDPVD

Dip-Coating

PLD Sol-Gel

Sputter Coater

Biomimetic

Advantages Disadvantages

Rapid deposition rateHigh processing temperature

induces decomposition of HA[9,10]

Non-uniform coating with cracks[11]

Good adhesion High cost equipment and demand elaborate setup

Commercial Technique

What is potential alternative technique

to fabricate HA coating?

What is potential alternative technique

to fabricate HA coating?

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Deposition Technique

Dip-Coating

Advantages Disadvantages

Inexpensive equipment & simple setup

Poor adhesion between the coatings and metallic substrates

Uniformity of deposition [12]

Low processing temperature

Ability to coat complex substrate [13]

Ability to control coating amount and thickess

Alternative Technique

Solution: Post heat treatment (sintering)

i.Improve the coating adhesionii.Densify coating layeriii.Eliminate porosity

Solution: Post heat treatment (sintering)

i.Improve the coating adhesionii.Densify coating layeriii.Eliminate porosity

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Effect of high sintering temperature during heat treatment :

Problem Statement

Sintered in air at 600°C for 1h

Cracks

Sintered in vacuum at 800°C for 1h

i. The formation of cracks on the surface due to the thermal expansion coefficient mismatch between the coatings and substrate during sintering and cooling [14,15]

Substrate expose to the high temperature

iii. Oxidation and impaired mechanical properties [17]

ii. Catalyze the decomposition of HA into non-crystalline which increased the in-vitro dissolution rate [16]

HOW TO SOLVE ?Electrochemical study of HA coatings on stainless steel substrate (Quihua Yuan, 2009)

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• Poly (ɛ-caprolactone) [PCL; (C6H10O2)n] is a semi crystalline aliphatic polyester that can be synthesised by ROP of monomeric unit "ɛ-caprolactone” with good biocompatibility, sustained biodegradability, and remarkable mechanical properties [18,19,20].

• The use of PCL as polymeric binder can help to improve HA coating and eliminate the need of sintering process to densify the coating layer.

Polymer Binder : Poly (ɛ-caprolactone) (PCL)

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i. To develop a polymer-ceramic composite coating for Ti6Al4V alloy substrate by using dip coating technique

ii. To study the effect of PCL concentration in HA coating on deposition technique parameters.

iii. To study the anti-corrosion properties of the PCL/HA coated Ti6Al4V alloy substrate.

Objectives

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Significance of Study

i. An alternative coating technique which is simple, cost effective yet gives clinically acceptable results will be developed.

ii. The problem related to the dip coating technique (poor bonding adhesion) is solved by using polymeric binder.

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Parameter Description

Metallic Substrate Ti6Al4V (Dimension : 10 mm x 10 mm x 10 mm)

Deposition Technique Dip Coating ( HTWL-01 Destop Dip Coater (MTI Cooperation, USA)

HA precursor Ca Precursor : Ca(NO3)2.4H2OP precursor : (NH4)2HPO4

Polymeric Binder Poly (ɛ-caprolactone) (PCL)

Characterization Analyses XRD, FTIR, SEM

Electrochemical test Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) test(VersaSTAT 3, Priceton Applied Research)

Scope of Study

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Materials

Name Formula Brand MW (g/mol)

Calcium nitrate tetra hydrate Ca(NO3)2.4H2O QRëCTM, AR grade 236.18

Diammonium hydrogen phosphate

(NH4)2HPO4 QRëCTM, AR grade 132.06

Ammonium hydroxide NH4OH QRëCTM, AR grade 35.04

Chloroform CH3Cl QRëCTM, AR grade 119.38

Poly (ɛ-caprolactone) pallets [C6H10O2]n Sigma Aldrich, UK -

Sodium chloride NaCl Sigma Aldrich, UK 58.44

Sodium bicarbonate NaHCO3 Sigma Aldrich, UK 84.00

Calcium chloride CaCl2 Sigma Aldrich, UK 110.98

Potassium chloride KCl Sigma Aldrich, UK 74.55

Dipotassium phosphate anhydrate

K2HPO4.3H2O Sigma Aldrich, UK 174.18

Magnesium chloride hexahydrate

MgCl2.6H2O Sigma Aldrich, UK 203.30

Sodium sulphate Na2SO4 Sigma Aldrich, UK 142.04

Table 2.1 List of reagent used in the experiment

Substrate Preparation

Grinding 150 - 1000 grit sized silicon

carbide (SiC) paper

CleaningUltrasonically clean in acetone for

15 min

DryingIn oven at 40 °C for 30 min

4 mm

12 mm

12 mm

Cutting

StorageDesiccator

Synthesis of HA powder : Microwave assisted co-precipitation method

Ca – Precursor[Ca] = 1.0 M

P - Precursor[P] = 0.6 M

Ca - P MixtureCa/P : 1.67

Precipitation pH above 10

Drop wise

RefluxingMicrowave oven

30 min ( 20 s ON and 20 s OFF)

Filtration & Washing

Drying 24 h (80°C)

Heat TreatmentMuffle Furnace

900 °C for 3h (heating rate 5°C)

CharacterizationXRD & FTIR

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Preparation of PCL/HA Suspension

Sample code

HA PCL Solvent Total volume

(ml)Weight

(g)% Weight

(g)%

i 1.35 90 0.15 10   

Chloroform

10ii 1.20 80 0.30 20iii 1.05 70 0.45 30

iv 0.90 60 0.60 40v 0.75 50 0.75 50

1. PCL pallets were dissolved in chloroform at room temperature for 15 min followed by the addition HA powder (sieved to 71 µm) as shown in Table 2.2.

2. The ratio of final concentration was 15 % (w/v).

3. Finally, the mixture was stirred at room temperature for 72 h.

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Dip – coating process

To investigate the effect of dip coating parameter on coating efficiency :

i.Withdrawal speed (mm/min): 40, 80, 120, 160, 200

ii.Number of dips: (1 -5)

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Characterization

Viscosity of the suspension :• Brookfield DV-II Pro Viscometer

Coating thickness :• Hitachi Tabletop Microscope, TM3000

Phase composition : • XRD (Bruker D-8 Advance diffractometer)

Functional group :• FTIR (ALPHA-T, Brucher)

Surface morphology : • SEM (JOEL JSM-6390 LV)

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Electrochemical Test

Parameter Description

Equipment Potentiodynamic/galvanostat (VersaSTAT 3, Priceton Applied Research)

Cell electrode Counter : Graphite Reference : Ag/AgClWorking : Ti4Al4V

Artificial body fluid Simulated body fluid (SBF)

Exposed surface area of working electrode

0.5 cm2

Potentiodynamic polarization test

Scan rate : 1 mV/sPotential range : -400 mV to +900 mV

Electrochemical Impedance Spectroscopy (EIS) test

Perturbation amplitude : 10 mVFrequency range : 105 Hz to 10-3 Hz

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Electrochemical Test

Tafel extrapolation method

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The effect of PCL concentration on coating properties

Deposition amount

Coating Thickness

PCL Concentration

(wt. %)

Viscosity,ƞ

(N.s.m-2)

0 0.03328

10 0.07274

20 0.09628

30 0.10716

40 0.13416

50 0.27122

No. of dips : 5; Withdrawal speed : 200 mm/min

SEM : Surface Morphology

The surface is not fully covered by HA coating

HAHA

10 % PCL/HA10 % PCL/HA

30 % PCL/HA30 % PCL/HA

50 % PCL/HA50 % PCL/HA

Surface level pores

Free cracks

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SEM : Cross Section

HAHA 10 % PCL/HA

10 % PCL/HA

30 % PCL/HA30 % PCL/HA 50 % PCL/HA

50 % PCL/HA

Coating layer Coating layer

Coating layer

Coating layer

Ti6Al4v Ti6Al4v

Ti6Al4v

Ti6Al4v

Thin and loosely packed coating

Thick and densely packed

coating

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30 % PCL/HA composite coating

SMSM

CSCS

For further investigationFor further

investigation

Surface level pores

Important for promoting osteointegration & nutrient diffusion

Important for promoting osteointegration & nutrient diffusion

Densely packed and intact coating

Indicate the bonding between coating and Ti6Al4V is enough to

resist the force during implantation process

Indicate the bonding between coating and Ti6Al4V is enough to

resist the force during implantation process

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The Effect of Withdrawal Speed and Number of Dips on Deposition Amount

30 % HA/PCL

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The Effect of Withdrawal Speed and Number of Dips on Coating Thickness

30 % HA/PCL

Landau-Levish equation :Landau-Levish equation :

h : thicknessȠ : viscosityv : withdrawal speedγ : liquid-vapour surface tensionρ : densityg : gravitational acceleration

The coating thickness increases as the withdrawal speed

increases

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XRD

HA

TCP

PCL

HA

30 % HA/PCL

Confirm the presence of PCL

Confirm the presence of PCL

Scherrer’s EquationCrystallite size of HA : 18 nm

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FTIR

HA

30 % HA/PCL

Confirm the presence of PCL Confirm the presence of PCL

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Sample Ecorr (mVSCE) icorr ( µA/cm2) Rp (MΩcm2)

Ti6Al4V -372.4 2.6827 x 10-7 0.9110

HA -229.1 6.2560 x 10-8 6.9498

30 % PCL/HA -79.24 7.6862 x10-9 15.0987

PPT

Noble direction

Lower current density

4 x

35 x

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EIS

Higher Z modulus at lower frequency displays a better corrosion resistance

on metal substrate

1.5 orders

2 orders

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Conclusion

I. In this study, we have demonstrated that dip coating technique can be used to obtained homogeneous crack-free coating of PCL/HA composite coating on Ti6Al4V.

II. Process parameters and polymer concentration were successfully manipulated to control the deposition amount and coating thickness.

III. The addition of 30 % PCL to HA considerably improved the adhesion of HA and resulted in densely packed coating which provide better corrosion protection when compared with HA coating making this combination a potential candidate for biomedical application.

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RECOMMENDATIONS

In vitro study : cell adhesion, proliferation and differentiation

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