Upload
joseph-bates
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
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
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
• 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.