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Winning presentation of my PhD research at the DCU Research Day 2011 that featured 42 presentations from the Schools of Electronic Engineering, Mechanical Engineering and Computing. The research theme is thermal spraying of biodegradable polymers onto orthopaedic implants to act as a drug delivery system.
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Design of Experiments Analysis of Thermally Sprayed Biopolymer
Matrix for Orthopaedic Applications Ahmed Chebbi
Presentation LayoutTechnology background
The idea behind the project
Experimental set-up
Results
Conclusions
Next steps
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.
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)
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
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
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
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)
DoE Results
DoE Results
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.
Wetting PropertiesAverage contact angle ~ 53o for PHBV/PMMAHydrophilic surfaces are more osteogenic
than are hydrophobic surfaces
FTIR Study
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
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
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
This work is funded by:
