Winning presentation at the DCU Research Day 2011
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Transcript of Winning presentation at the DCU Research Day 2011
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Design of Experiments Analysis of Thermally Sprayed Biopolymer
Matrix for Orthopaedic Applications Ahmed Chebbi
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Presentation LayoutTechnology background
The idea behind the project
Experimental set-up
Results
Conclusions
Next steps
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Orthopaedic implants: present technologyTo provide for an adequate range of
motion To transfer the joint load onto the
boneOsseointegration properties of some
materials (Hydroxyapatite) elicit a specific biological response at the interface of the material
Results in the formation of bond between the tissues and material.
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Orthopaedic implants: Limitations and ChallengesThermal spraying used to deposit coatings for
enhanced mechanical behaviour
Mechanically related limitation such as implant loosening
Biologically related limitations such as post-operative infections
Solution: Localised Drug Delivery System (DDS)
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Idea behind the projectBiocompatible polymers (PMMA , PLLA, etc.) are
widely used as drug delivery systemAdvantage: Biocompatible polymers were successfully
thermally sprayed to obtain coating with enhanced mechanical properties
Drawback: A second operation to remove carrierBiodegradable polymer offer a solution but were not
thoroughly investigated with thermal sprayingThermal spraying of biodegradable polymers for:A drug delivery purposeA structural (mechanical) purpose
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Flame spraying
Flame spraying used to melt polymer powder and form coatings on titanium substrates
Temperature generated up to 3000o C Jet velocity up to 100 m/s
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Experimental set-up and spraying parameters
Biopolymers: Polymethylmethacrylate (PMMA)Biodegradable biopolymer: Polyhydroxybutyrate 98%/
Polyhydroxyvalerate 2% (PHB/PHV)screening stage. The experimental design used was the
3-level factorial design (33) with 5 midpoint repeats
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BiopolymersPMMA:Good mechanical properties and
biocompatibilityPHBV: Superior piezoelectricity
properties, no undesirable chronic inflammatory response after implantation, its mechanical properties can be changed by varying the ratio of the respective monomers (PHBV)
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DoE Results
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DoE Results
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Thickness/Roughness/AdhesionThickness levels affect the degradation rate
in vivo. Crucial to control thickness in order to
control the amount of drug releasedRoughness affects the degree of cell
attachments.Bare Titanium disk: Ra~3.1 microns =>
Polymer coating: Ra~2.61 microns Understanding how adhesion is affected by
process parameters in order to obtain the highest levels of adhesion.
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Wetting PropertiesAverage contact angle ~ 53o for PHBV/PMMAHydrophilic surfaces are more osteogenic
than are hydrophobic surfaces
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FTIR Study
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Cell Proliferation Study
Reference PHB/PHV PCL Titanium0
0.1
0.2
0.3
0.4
0.5
0.6
OD
at
450m
m 3 Days
5 Days
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ConclusionsFully covered substrates were obtained
Sample roughness was not considerably reduced and remained within advisable levels
Excellent wetting properties =>precursor of good cell attachment
Minor chemical degradation
Polymer biocompatibility maintained
Better understanding of responses variation in relation to process factors
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Next StepsDoE for another biodegradable polymer:
PolycaprolactoneSpray optimised parameters for polymer matrix
on titanium Plasma spray HA coatingsSpray optimised parameters for polymer matrix
on titanium Conduct weight loss, ph, and conductivity testsMore thorough biological assessment:
flueorescent microscopy, alkaline phophatase, cell proliferation
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This work is funded by: