Winning presentation at the DCU Research Day 2011

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: