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Current Landscape of SMART Technology in Orthopaedics
Mark G. Allen
Moore Professor of Electrical and Systems Engineering; andDirector, Singh Center for Nanotechnology
University of [email protected]
http://mems.seas.upenn.edu
Microsensor and Microactuator Laboratory
Goals for this presentation
• What I hope to achieve in this presentation/discussion– A brief historical foray as to why right now is the right
time– How miniaturized sensor (MEMS) technologies might
be are applicable to SMART orthopedics• What I purposely am not going to try and do in
this presentation– Give an exhaustive list of specific innovative devices
that people have developed or are developing
Microsensor and Microactuator Laboratory
Medical Microsystems/MEMS
Microsystems based on the use of microfabrication and nanofabrication
techniques to create mechanical structures, sensors, and actuators that can interface with parts of the human body, either in-vitro or in-
vivo, to diagnose or treat disease
Microsensor and Microactuator Laboratory
A Few Observations…
• People are living longer and longer• Maintaining quality of life and independence as
average age increases is demanded• Disease states are becoming more complex (a
consequence of success?)
• More information is required for cost-effective prevention and treatment of disease
Can medical microsystems help?
Microsensor and Microactuator Laboratory
Implantable Sensors for Physiological Parameter Measurement: The Promise
C. Collins, IEEE Trans. Biomedical Engineering April, 1967
Microsensor and Microactuator Laboratory
Implant Fabrication
• ‘Substrate’: Short (1-2mm), thin-walled (250 µm) glass tube
• Flat spiral coil hand-wound on teflon sheet and shellac used to hold in place
• Coils transferred to studs and mounted on mylar diaphragms
• Coil-bearing diaphragms stretched across glass tube
• Heat-sealing with polyethylene tubing
Implantable Sensors for Physiological Parameter Measurement: The Promise
Microsensor and Microactuator Laboratory
So Why Wasn’t This Adopted?Issues in Long-Term Human Implantation of Sensors
• Stability– Hermetic sealing of pressure reference– Overgrowth of tissue on sensor affecting calibration– Corrosion and Fatigue
• Biocompatibility– restricts materials set
• Readout Distance– Some applications require sensors deep within body (30
cm requires 10x improvement)– Attenuation by lossy medium of surrounding tissue
• But: something has happened…
Microsensor and Microactuator Laboratory
Why Now? The Technology Convergence
MEMS Fabrication TechnologyNew materials for MEMSReasonable manufacturing precisionMicromanufacturing infrastructure
Wireless Electronics TechnologyMiniaturization of communication technologyUnprecedented sensitivity to signal levelsAdvanced signal processingGlobe-spanning net for information transfer
Low Power CircuitryA milliwatt is a lot!Energy harvestersAdvanced batteries
Wireless Implantable Medical Microsystems
Microsensor and Microactuator Laboratory
MEMS: Using Microfabrication to Produce Mechanical Structures and Transducers
microphones pressure sensorschemical sensors
accelerometers endovascular implantable wireless sensors
Microsensor and Microactuator Laboratory
How do MEMS gain their functional advantages?
• A large number of small devices can be co-located, resulting in a spatially complex, functionally homogeneous or heterogeneous system that may or may not be small overall (example: TI DMD), or;
• A device can be made so small that it gains a cost or performance advantage (example: iPhone acceleration sensor), or;
• A device can be made so small that it can find application where larger analogous devices can’t (example, biological microinterfaces), or;
• A larger-scale device may contain a single or a few small-scale subcomponents that completely enable system operation (example: microfluidic separation)
Microsensor and Microactuator Laboratory
Can we create biosenors that will allow us to detect inflammatory markers?
Microsensor and Microactuator Laboratory
Can knowledge of local oxygen concentration allow us to better understand bone healing?
Microsensor and Microactuator Laboratory
Can we monitor the strain environment of a healing bone, and use this to detect callus formation and/or guide therapy?
Microsensor and Microactuator Laboratory
Some additional issues we may see soon
• Some newer technologies coming on line we might want to look out for– Biodegradable/bioresorbable devices
(transient devices for a transient health condition)
– Multiple sensing modalities (physical, chemical, biochemical) combined in one
– Combinations of therapeutic and diagnostic devices (electrical stimulation, chemical stimulation, drug delivery)