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Mechanical Loading of Rigid Intramuscular Implants
Gerald E. Loeb, Raymond A. Peck, Jesse Singh, Young-Ho Kim+, Sudeep Deshpande and Lucinda L. Baker*
Alfred Mann Institute for Biomedical Engineering
*Dept. of Biokinesiology and Physical Therapy
University of Southern California +Dept. of Biomedical Engineering, Yonsei University, Korea
BION Implants for
Neuromuscular
Stimulation
16mm
2mm
Ir electrode
hermetic
glass
capsule
Ta capacitor
electrode
12 ga.
insertion tool
BION1 Clinical Trials Underway Study PATIENTS BIONs
Enrolled Withdrew Implanted Implanted Out of spec Explanted
Acute shoulder subluxation
Kingston, Canada 14 0 9 19 0 0
Knee osteoarthritis
Milan, Italy
5 0 5 10 0 1
Chronic shoulder subluxation
Downey, CA 14 0 10 22 8 0
Hand contractures
Downey, CA
16 1 10 25 7 0
Foot drop
Edmonton, Canada 1 0 1 4 1 0
Hand retraining
Los Angeles, CA
new IDE
Pressure ulcer prevention
Downey, CA
new IDE
TOTALS to date 50 1 35 80 16 1
4 fractured cases, all following long-term, intense exercise, no trauma
As implanted:
Initial x-ray:
5 mo. x-ray:
Wrist Extended
Wrist Flexed
◄hand
BION Capsule Strength
S2mmdiam.
2mmx8mmx0.3N/mm2=5Nmax
BION Impact Tests 10N
1N
1N
20ms
1 kg from 360 mmv = 2.66 m/s
E = 3.53 J
Loadcell
Center
Offset
2.20 N
1.24 N
1.21 N
0.62 N
12.5 mm
1.51 N 3.80 N
2.15 N0.26 N
25 mm
HIGH SPEED IMPACT CONDITIONS LOW SPEED IMPACT CONDITIONS
2.5 mm
10 mm
10 mm
10 mm
skin
muscle
v
vh
hmm
h=1.44 m
m=1 kg
v=5.32 m/s
E=14.13 J
h=0.36 m
m=0.5 kg
v=2.66 m/s
E=1.77 J
G=1.33 N s.G=5.32 N s.
Stress Repetitions
• ~0.8N bend 2 bend Fx @ 30kc
• ~1.2N bend 5 bend Fx @ 500c
• 7 bend + 0.1N shear Fx @ 30c
Requirement: 2h/d x 84d ÷ 5s/c = 121kc
Remediation: >4000kc (to date)
Fragmented glass
bead cracks
Loading Modes in vivo
Connective tissue
Muscle
Tendon
Tendon
Ir electrode
Ta
Electrode
Glass
Capsule
Loading Modes in vivo
Case 1&2 Case 3 Case 4
Connective tissue
Muscle
Tendon
Tendon
Tendon
Loading Modes in vivo
Case 1&2 Case 3 Case 4
Tendon
Muscle
Tendon
Ir electrode
Ta
Electrode
Glass
Capsule
Loading Modes in vivo
Case 1&2 Case 3 Case 4
Muscle
Tendon Ir electrode
Ta
Electrode
Glass
Capsule
y
x
L
l
c
),( dL
),( c01A
2AO
= -F = shear reaction force
between glass capsule and
electrode
y
x
L
c
1A
2AO
c
l
Uniformly Distributed Load 30N/cm2
-FA
L
Connective
Tissue
-FB
Case 1:
1.8N
Case 2:
?>1.8N
Case 3: 3.6N
(each end)
Redesign & Remediation
A
B
Fuse glass bead to Ta stem & sintered electrode
using vacuum furnace and carbon tooling
BION1 Hermetic Package Assembly
Nd-YAG laser welds:
2) PtIr Washer to Ta stem
4) Spring to Ta tube
7) Ta tube seal/cut & Ir Washer
CO2 laser welds:
3) Glass bead to Ta tube
5) Glass beads to capillary
Vacuum furnace seal:
1) Glass bead to Ta Electrode
6) He leak test
1)
2)
5)
4) 3)
5)
7)
ASIC
Capacitor
Wire bonds
Substrate
Ferrites Coil
Repetitive Loading Pattern
Applied Force
Glass capsule
Ta
Electrode
Ir
electrode
Saline @ 37C
>4,000,000 cycles @ 8N without failure
30 30
MPa
0
Clinical Status
Revised design now completing long-term validation testing
Revised IDE approved by FDA and IRBs
Clinical implantations resume in October
Risk Factors for Implanted Stimulators
Percutaneous implantation can result in unexpected mechanical configurations.
Chronic, strong electrical stimulation strengthens muscles.
Long term use produces large numbers of stress cycles.
Failures are accelerated synergistically by stress x repetitions x temperature x water
BION1 Hermetic Package Assembly
Nd-YAG laser welds:
2) PtIr Washer to Ta stem
4) Spring to Ta tube
7) Ta tube seal/cut & Ir Washer
CO2 laser welds:
3) Glass bead to Ta tube
5) Glass beads to capillary
Vacuum furnace seal:
1) Glass bead to Ta Electrode
6) He leak test
1)
2)
5)
4) 3)
5)
7)
ASIC
Capacitor
Wire bonds
Substrate
Ferrites Coil
BION Packaging Work Station
Y A G H e a d s
C O 2 L e n s
M i r r o r A s s e m b l y
V a c u u m
C h u c k
V B l o c k
X Y Z
T r a n s l a t i o n
S t a g e s
S y n c h r o n o u s
D r i v e
C O 2 B E A M
Y A G B E A M
Y A G H e a d s
C O 2 L e n s
M i r r o r A s s e m b l y
V a c u u m
C h u c k
V B l o c k
X Y Z
T r a n s l a t i o n
S t a g e s
S y n c h r o n o u s
D r i v e
C O 2 B E A M
Y A G B E A M
Electrochemistry of the BION
Capacitor Electrodes
BION1 Design Features
• Injectable through 12 ga. needle
• Fail-safe capacitive electrodes
– Anodized, sintered Ta
– Activated Ir
• Glass hermetic package
• Ceramic uPWB
• Water getter
• 2 MHz AM carrier
Hermeticity Test Requirement
LEAK
RATE
cc atm/s
VOLUME
cc
LIFE
TIME
s
BIONTM
1day 1mo. 1yr.
50% vol., 6% water vapor10% vol. getter
30yr.10yr.
mil
spec
typ.
prod.
max.
sens.
implantable
defibrillator
CLARIONTM
cochlear
implant
cardiac
pacemaker
102
101
100
10-1 10
-2
10-9
10-4
10-5
10-3
10-3
10-6
10-7
10-8
10-2
105
106
107
108
109
1010
10-11
10-12
10-13
10-10
trapped He detectorconventional bubble test
high pressure bomb - 100 atm
He mass spectrometer
Moisture Getter
• Natrasorb 900®: silica gel in machinable polymer
• Cylinder: 1.5mm od x 0.5mm id x 1mm = 1.1mg
• Slides over spring welded to tubular feedthrough
• Vacuum baked at 230C
• Potential water vapor absorption = 250 mm3
1.1mg • 18% • mole/18g • 22.4x106mm3/mole
• Capsule water vapor at dew point = 0.64 mm3
• Apparent package volume = 390X
• He leak testing sensitivity = 1 x 10-10 cc atm/s
• Minimum lifetime = 80 years
BION2 Assembly Sequence
To Helium Leak
Detector
A
D
C
E
A Wrist Extended
B Wrist Flexed
◄hand
Capsule Failure due to Repetitive Stress
peg (cannula handle peg)
cannula
cannula handle (inner handle)
probe handle (outer handle)
BIT v.5.4 (BIONTM Insertion Tool)
probe tip
BIONTM
rotate peg along track to release BIONTM
peg (cannula handle peg)
cannula
cannula handle (inner handle)
probe handle (outer handle)
BIT v.5.4 (BIONTM Insertion Tool)
probe tip
BIONTM
rotate peg along track to release BIONTM
RF-Powered BION