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ADDITIVE LAYER MANUFACTURING AS APPLIED TO POROUS SURFACES ON MEDICAL IMPLANTS

CHALLENGES ASSOCIATED WITH CLEANING AND PROCESSING

Julius Bonini P.E., Senior Metallurgical EngineerKaitlyn Calaluca, Metallurgical Engineer

Lucideon M+P, Schenectady, NY

ALM - Challenges Associated with Cleaning and Processing

1. ALM process as applied to porous coated devices

2. General cleaning issues associated with ALM specific to porous coated devices

3. Unfused Particle Shedding

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Tailored Porous Surface Structure

Additive Layer Manufacturing

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− ALM - Otherwise know as 3D printing

− Titanium Components− Electron Beam Melting (EBM) or− Direct Metal Laser Sintering (DMLS)

− Several metallurgical issues need to be resolved for medical implant applications− Complex microstructural issues (won’t be addressed here)− Cleaning and processing issues

Additive Layer Manufacturing

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Porous Surface Structures of Common Medical Implants

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Accurate measurements can be made and parameters established per ASTM 1854

Sintered Wire and BeadHave Definable Porous Structures

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ALM Structures Found to be Highly Variable

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Cross-Sections Show Deep Porous Structures

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Surface Porous Structures

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Advantages of ALM Technologies

− Cost?

− Create any porous structure you want− Depth− Tapered porosity through section− Pore Size− Pore Density

− Complete flexibility for improved osseointegration

Components Manufactured via ALM Technology

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Most Common Application of ALM Acetabular Cups

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− How do you keep components clean during processing?

− How do you eliminate residues and prevent entrapment?

− How do you remove all processing fluids from final product?

Cleanliness Issues Related to Components Manufactured via ALM Technology

First You Need to Understand the Life of a Typical Component

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The Life of an Acetabular CupConventional Porous CoatWire, Bead, Plasma Spray

ALM Porous CoatEBM, DMLS

Bar/Forging

Extensive Machining &Processing

Extensive Cleaning & Degreasing

Porous Coated

Final CleaningAnd Packaging

Coated Shell(porous)

Extensive Machining &Processing

Extensive Cleaning & Degreasing

Final CleaningAnd Packaging

Passivation

“Dirty” Parts

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As-Received(Clean)

After Processing(Dirty)

− In-house processing operations will contaminate parts− includes applied cleaning procedures

− Think of ALM structures as sponges− Rough surfaces pick up surface debris− Substructures act as a sponge and absorb fluids and

humidity from air

− Removal of all these residues, liquids and debris is a challenge

Very Complex Issue

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To remove these contaminates, you clean: Wash, Blast, Ultrasonics?

Debris Pick-up and Removal

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Effective Cleaning of Complex Porous Structures is a Challenge

− Liquid exposures can be problematic

− Ultrasonic cleaning, rinsing, passivation

− Cleaning solutions, caustics, acids

− Problem becomes effective removal of cleaning liquids

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Open Cell Structures Pose Less of a Challenge

Fluids In – Fluids Out

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• Open Cells

• Closed Cells

• Semi-Closed Cells?

Closed and Complex Cell StructuresAre a Real Challenge

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Processing Effects

− Thermal Effects

− Open (interconnected) cells stay open during all stages of processing− General problem that has to be dealt with− Any liquid exposure has to be effectively rinsed and dried

− Closed cells remain closed during all stages of processing− Shouldn’t be a problem

− Semi-closed – open when heated due to thermal expansion, then close upon cooling− Can be a very big issue

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Processing Effects – Open Cells

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− Typical Liquid Exposures

− Cutting fluids and coolants

− Solvents and cleaners used to remove above− May include ultrasonic with heat

− Rinse agents and water used to remove above

− Passivation

− All can be effectively removed with proper practice

Processing Effects – Semi-Closed Cells

− Semi-closed cells open at elevated temperature ( > 40 o C)

− Liquid infuses into now open cells at temperature

− Liquid remains trapped as cells close again upon cooling

− Liquid can be effectively rinsed from all open areas but not from now closed cells

− Subsequent thermal exposure can re-release liquid

− Particular concern during passivation step

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Passivation Effects – Semi-Closed Cells

− Semi-closed cells – open when heated then close upon cooling

− Nitric Acid Exposure

− Slowly oozes out over time

Fully Porous Augment

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Potential Solutions

− Effective dissolution and removal of all liquid agents

− Use of volatile alcohols

− Combined with ultrasonics + temperature to open those semi-open cells

− Followed by effective oven drying

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Unfused Powder ParticlesLong Term Problem for all ALM Materials

• Nature of the material – it all starts with fine Ti powder

• Unfused particles are cleaned off of manufactured parts by blast methods using the same media

• Levels of effectiveness – surfaces look good

• Below the surface may be a problem – remember the complex porosity issue

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Unfused Particles

Particles Collected fromCleaned Sample Surface

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With Additional Surface BlastingAs Normally Processed

Unfused Particles

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NoAdditionalBlasting

WithAdditionalBlasting

Conclusions

• A variety of particle cleanliness issues need to be addressed for evolving ALM components

• Stick your head in the sand?

• Test, evaluation and material standardizations specific to ALM material are needed

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Thank you

Contact Details

T (518) 382‐0082E Julius.Bonini@lucideon.comW www.lucideon.com

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