Materials that belong to the bodyMaterials that belong to the body

Optimizing the Golden StandardNew PolyEthylene Technologies for HIP Arthroplasty

Leo SmitBusiness Director Implant Solutions

DSM Biomedical

One of the largest successes of the medical profession

>2 Million Hip and Knee replacements carried out annually

Multitude of innovations, total hip/knee, uni-knee, hip resurfacing

Many materials being used – polymers, metals, ceramics

Total Hip ArthroplastyTotal Hip Arthroplasty

Wear: the central theme in HIP ArthroplastyWear: the central theme in HIP Arthroplasty

• Teflon too soft UHMwPE• “Hit by friendly fire” : Macrophage attacks on PE wear particles cause

human biological/physiological responses leading to osteolysis.• Current artificial hip lifetimes are app 10 – 15 years

current demographics ask for more!

Picture from Gomez-Barena

Alternative material approachesAlternative material approaches…………..

CrosslinkingCrosslinking –– THE breakthrough in UHMwPETHE breakthrough in UHMwPE

Powder

ConsolidationM

achiningCleaning

Thermal treatm

ent

Crosslinking

PackagingSterilization

Implant

Stryker: Crossfire®X3TM

Zimmer: LongevityTMProlongTM

DePuy: MARATHONBiomet: ArCom® XLTS&N: XLPE

Stryker: Crossfire®X3TM

Zimmer: LongevityTMProlongTM

DePuy: MARATHONBiomet: ArCom® XLTS&N: XLPE

Picture: Zimmer

Laboratory and clinical results

0.00

0.25

0.50

0.75

1.00

0 20 40 60 80 100Radiation Dose (kGy)

Nor

mal

ized

Wea

r

Longevity (Ref. 12)Conventional (Ref. 12)Durasul (Ref. 12)Conventional (Ref. 12)Marathon (Ref. 12)Crossfire (Ref. 13)Duration (Ref. 11)Gamma-air (Ref 14)Eto (Ref 15)N2 Vac - LabArcom - LabDuration - Lab"Marathon" - Lab"Durasul" - LabCrossfire - Lab"Longevity" - LabX3 - Lab

Edge-Loading Wear of Metal-on-Metal and Metal-on-X3® Highly Crosslinked Polyethylene: Survival of the FittestAiguo Wang, Ph.D., VP, Reconstructive Technologies, Stryker Orthopaedics, Mahwah, New Jersey, USA.

Both in-vitro as well as in-vivo wearreduced as function of the Radiation Dose

Significant reduction in wear rateSignificant reduction in wear rate

Radicals form new challengeRadicals form new challenge

Macro-radicals are createdduring irradiation

Macro-radicals react with oxygen -causing oxidative degradation of thebearing material

RemeltingRemelting OROR AnnealingAnnealing

Additional stepAdditional step -- time consuming, coststime consuming, costs

Loss of mechanical propertiesLoss of mechanical properties

DiffusionDiffusion into the final Implant ORinto the final Implant OR PrePre--blendingblending with the polymerwith the polymer

Pre blended Vitamin EPre blended Vitamin E interferesinterferes with crosslinking process *Vitamin E isVitamin E is consumedconsumed in the crosslinking processin the crosslinking processMaterial turnsMaterial turns yellowyellow

Current radical removal optionsCurrent radical removal optionsTh

erm

al tr

eatm

ent

Vita

min

E s

tabi

lizat

ion

Vita

min

E s

tabi

lizat

ion

* (Oral, E et al, Biomaterials (2005), 26(33), 6657* (Oral, E et al, Biomaterials (2005), 26(33), 6657--6663)6663)

UHMwPE ParadigmUHMwPE Paradigm

Ideally:

• wear resistance

• oxidation resistance

• mechanical properties

REAL WORLD so far notideal – Wear optimizationcauses compromises

Gomez-Barrena, E et al. Acta Orthopaedica 2008, 79 (6), 832.

OXIDATIVESTABILITY

WEARRESISTANCE

MECHANICALPROPERTIES

Reduced wear debris Reduced osteolysis

DSM approaches to joint healthDSM approaches to joint health

i-flex – a joint health food supplement from DSM Nutritional Products, containingvitamins, carotenoids and galactolipids mixture that has been demonstrated in vitro tohave protective and even regenerative effects on human cartilage.

DSM is the world’s leading producer of Vitamin EEasy-XL – a novel family of UHMwPE grades with a

new molecular architecture toincrease crosslinking efficiency

HALS-UH – an Alternative Stabilizer that provides forstabilization of UHMwPE powder

Bionate® Poly Carbonate Urethane polymers for soft bearing applications

Alternative stabilizer : HALSAlternative stabilizer : HALS

HALS : Hindered Amine Light Stabilizer

No radical scavenging during radiation

no interference with the crosslinking process

Regenerative - Less stabilizer needed

No yellowing (consistent color) because no degradationcomponents are formed

HALS : Crosslinking improvementHALS : Crosslinking improvementHigher crosslink

density for HALSthan for Vitamin Estabilized UHMwPE

• Tested 0.05 and 0.15 wt.% Vitamin Eversus 0.05 and 0.15 wt.% HALS

• No significant differences between0.05 and 0.15 wt.% HALS

• No influence type of HALS

Vitamin E: higher swellratio =lower XL density

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

0 20 40 60 80 100 120 140 160Irradiation dosage (kGy)

Swel

l rat

io (%

)

Reference 500 ppm Vit E1500 ppm Vit E 500 ppm HALS-1 1500 ppm HALS-1

GUR 1020 UHMwPE

HALSHALS--UH shows effective stabilizationUH shows effective stabilization

Change in Carbonyl Index as a result of ageing during 6 weeks at roomtemperature shows better stabilization compared to vitamin E

GUR 1020

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 20 40 60 80 100 120 140 160

Irradiation dose (kGy)

Del

ta C

arbo

nyl I

ndex

Reference500 ppm Vit E1500 ppm Vit E500 ppm HALS-11500 ppm HALS-1

(FTIR: Abs 1718 cm-1/ 2020 cm-1)

Hypothesis :

Incorporation of diene in UHMWPE will leave a pendantunsaturation which is believed to make

crosslinking more efficient.

This enables the use of lower radiation doses, soless radicals stay behind which will potentiallyreduce oxidative degradation.

Further by adapting molecular architecture wecan optimize mechanical properties

EasyEasy--XL : betterXL : better crosslinkablecrosslinkable UHMwPEUHMwPE

Growing polymer chain

M +

Incorporate dienes ingrowing PE chain:

+

Diene

Wear Factor versus irradation dosage

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 20 40 60 80

Irradiation dosage (kGy)

Wea

r fac

tor (

10-6

mm

3/N

m)

ConventionalUHMwPE(GUR1020, 1050and MG003)

DSM Nextgeneration

- 50 kGy

- 2 (10-6 mm3/N m)

EasyEasy--XL needs significantly less radiation for low wearXL needs significantly less radiation for low wear

Results show that 25 kGy irradiation (i.e. sterilization dose) resulted in awear resistance comparable to highly XL materials

Pin on Disk wear measurements.See Eva Wisse et.al. 4th International UHMWPE Meeting, Turin, 2009

Less remaining free radicals with Easy-XL

For both conventional UH and Easy-XL it was shown that 75 kGy radiationleaves behind 2-3 times higher radical content than 25 kGy

Easy-XL crosslinked material has much less residualradicals!

325 330 335 340 345 350

M325KGY1 M375KGY1

EPR

inte

nsity

[arb

.uni

ts]

Magnetic Field [mT]325 330 335 340 345 350

S2825KGY1 S2875KGY1

EPR

inte

nsity

[arb

.uni

ts]

Magnetic Field [mT]

25 kGy75 kGy

VNB, 12 C=C/100K C MG003 25 kGy75 kGy

electron spin resonance (ESR) spectroscopy

0

5

10

15

20

25

30

0 5 10 15 20

Strain [%]

Stre

ss [M

Pa]

3736 - 0kGyGUR 1020-0 kGy

Better Mechanical PropertiesBetter Mechanical Properties

Optimizing the MolecularArchitectureenables us to find a

new balance inmechanical properties.

Easy-XL is a stronger material:- 30% higher Yield Stress- 30% higher Crystallinity (better fatigue)

ConclusionConclusion –– will we break the paradigm?will we break the paradigm?

HALS-UH and Easy-XL,

separate or combined,form a strong vehicle to

break the paradigm,

creating novel polyethylenes for arthroplasty,having

better wear resistance,better mechanical properties

andbetter oxidative stability

all at the same time.

OXIDATIVESTABILITY

WEARRESISTANCE

MECHANICALPROPERTIES

Reduced wear debris Reduced osteolysis

AcknowledgementsAcknowledgements

In 2007 DSM Biomedical initiated a new R&D program to developnew polyethylene materials for use in Arthroplasty.

Our Team:

Eva WisseNilesh Kukalyekar

Jan StolkRob Janssen

Tim KiddMicha Mulders

Harold SmeltPieter Gijsman

Bill FullerMarc Hendriks

Materials that belong to the bodyMaterials that belong to the body

THANK YOULeo Smit

Business Director Implant Solutions

DSM Biomedical