1. Hip Implant -Thin Film Improved-
Ahmed, Nouman
Hirvonen, Saara
Lavanti, Kimmo
Lehikoinen, Lotta
Multaharju, Miikka

2. 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

3. Improvement areas Loosening of the stem Dislocation of the joint
Detached particles from the surfaces
The right time for replacement
Easy replacement
Proper testing

4. Acetabulum and femoral head

5. DISADVANTAGES of using this structure
Metallosis
Heavy metal poisoning
Metal sensitivity
Bone deterioration
Tissue damage
Particles entering the blood stream and in soft tissues

6. 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

7. 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

8. Fixed hip implant with skeleton
Old Patients
Young 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
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

9. 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

10. Bone growth enhancement
Acetabular Cup
Femoral Component
Modular cup
The shell is made of metal
The outside has a porous coating
Fits to the femur: anatomic medullary locking
Porous coating promote bone ingrowth

11. Bone growth enhancement
Porous 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
Combines-Industrial-3D-Printing-Free-Medical-Implant

12. 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

13. 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

14. 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

15. 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

16. 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

17. Methods of examining the film
SEM to investigate surface structure and wear patterns
Optical white light interferometry to study the surface roughness
Optical microscopy

18. Methods of examining the film
Example of optical interferometry data
(Haubold et al., 2010)

19. 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

20. Methods of examining the film
Hardness testing
Friction testing
Example of friction testing equipment
(Taposh et al., 2014)

21. 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

22. 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) (14pp).
DOI: / /22/9/095006

23. 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

24. Thank you! Any questions?