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: