Hip Implant -Thin Film Improved-

Ahmed, NoumanHirvonen, SaaraLavanti, Kimmo

Lehikoinen, LottaMultaharju, Miikka

Key Issues

• What can we do to improve hip implants

• Structural construction

• Bone growth enhancement

• Low friction coating

• Surface testing and analysis imaging

• Integrated sensoring system

Improvement areas

• Loosening of the stem

• Dislocation of the joint

• Detached particles from the surfaces

• The right time for replacement

• Easy replacement

• Proper testing

Acetabulum and femoral head

DISADVANTAGES of using this structure

• Metallosis

• Heavy metal poisoning

• Metal sensitivity

• Bone deterioration

• Tissue damage

• Particles entering the blood stream and in soft tissues

Risk of displacement

• A small head size increase the risk of dislocation

• With a large head the risk of dislocation after same traveled distance is reduced

• Cup displacement affects the clearance and can increase the risk of wear which can be reduced by maintaining the fluid film interface

Possible Solutions

• Hydrophilic coating to facilitate the state of fluid film lubrication

• Bearings are fully separated and the load fully supported by the lubricant films

• Different taper (attachment) options as requirement for better fit and usability

Fixed hip implant with skeleton

Old Patients• Top of femur is sawn off and

replace with artificial new head

• Hip bone is shaved down to accommodate man made socket

• Bone cement use for attachment

Young Patients• Due to continuous bone

growth cement can crack off• Introduction of cup with

porous exterior • Porous exterior allows bone

to grow in and secure the implant in place

Bone growth enhancement

• Implant stem and cup attachment to the bone

– Uncemented stems for good quality bone

– Cemented devices for poor quality bone (risk of fracture during stem insertion)

• Uncemented stems can cause pain during the first year after, as the bone adapts to the device

• Porosity and surface coatings can stimulate bone growth and bond to the implant

Bone growth enhancementAcetabular Cup• Modular cup– The shell is made of metal– The outside has a porous coating

Femoral Component• Fits to the femur: anatomic

medullary locking• Porous coating promote

bone ingrowth

http://www.zimmer.com/fi-FI/hcp/hip/product/zimmer-mmc-cup.jspx

http://machinedesign.com/archive/high-performance-hips

Bone growth enhancementPorous coatings• Titanium plasma spray

coating– encourage bone on-growth

and in-growth– 34 % porosity

• Titanium sintered metal beads– stability and long-term

fixation– 35 % porosity

• Direct metal laser sintering– 70 % porosity

http://www.exac.com/products/hip/resource-library/titanium-plasma-spray

http://www.businesswire.com/news/home/20131010005166/en/Initiative Combines-Industrial-3D-Printing-Free-Medical-Implant

Bone growth enhancement

• Bone growth can be more enhanced with coatings• Calcium phosphate ceramics coatings on orthopedic

implants• Stimulate osseous apposition to the implant surface• Hydroxyapatite HA, “bone mineral”

– Increased of the mechanical fixation and bone ongrowth

– Plasma-spray

– Electrochemical-assisted deposition

• Porous AND bone growth enhancing coating

→ shorter healing time

Coatings against wear and friction

• Overall image of the case

• Two different coating methods to the top side of the hip implant

• DLC and ceramic thin film

Coatings against wear and friction

• Diamond-like carbon (DLC) coating deposited using saddle field source deposition system

• Deposition directly onto austenitic stainless stell

• Biocompatibily accepted

• Significantly lower level of wear

Coatings against wear and friction

• Ceramic thin films, many different alternatives like

TiN, ZrN, NbN, VN and HfN

• Usually several layers and these at top

• Used for their features of high hardness, electrochemical immunity and biocompatibility

• Deposited using reactive magneto sputtering

Coatings against wear and friction

• Using a lubricant in the hip joint increases its time-in-use

• This is done by rendering the surface more hydrophilic

• That way lubricant is more efficient and the friction drops down

Methods of examining the film

• SEM to investigate surface structure and wear patterns

• Optical white light interferometry to study the surface roughness

• Optical microscopy

Methods of examining the film

Example of optical interferometry data

(Haubold et al., 2010)

Methods of examining the film

• Electrochemical investigation to determine implant corrosion, e.g. electrochemical impedance spectroscopy

• Energy dispersive X-ray spectroscopy to determine the chemical composition

Methods of examining the film

• Hardness testing• Friction testing

Example of friction testing equipment

(Taposh et al., 2014)

MEMS acoustic emission(AE) transducer

• Capacitance change as transduction principle

• Integration of high- and low-frequency

• Better response & sensitivity (than piezoelectric)

• Well defined waveform signature

• Source location identification, with an array

• Optimized geometry for certain frequencies

Microfabrication of the AE MEMS• Thin film layers

– Silicon oxide (2 layers)– Silicon nitride (1+1 layer)– Doped polysilicon electrode (fixed)– Sacrificial SiO2

– Anchor/plating base metal– Electroplated nickel – Gold coating (contactivity+corrosion

resistance)

• Metal layer is patterned to form a spring and mass system

• The sacrificial layer is etched under the metal layer

• Individual elements are mounted in ceramic package with epoxy

H. Saboonchi , D. Ozevin. MEMS acoustic emission transducers designed with high aspect ratio geometry. Smart Mater. Struct. 22 (2013) 095006 (14pp). DOI:10.1088/0964-1726/22/9/095006

Measuring of acoustic emissions

• Parameters

– Ringdown count

– Event ”length”

– Peak amplitude

• Can detect the growth of subsurface cracks

N. Tandon & A. Choudhury. A review of vibration and acoustic measurement methods for the detection of defects in rolling element bearings Original Research Article Tribology International. Volume 32, Issue 8, August 1999, Pages 469-480.

Thank you!

Any questions?