A Presentation on An Implantable Drug Delivery system based on shape Memory Alloy Micro Actuation

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A Presentation onAn Implantable Drug Delivery
system based on shape Memory Alloy Micro Actuation

• By Eluru Srinivasulu Nikitha

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Contents

• Shape Memory Alloys.
• Design of the liquid Drug Delivery Device.
• Design of the valve.
• Design of the Drug Delivery system.
• Testing of the Drug Delivery system.
• Conclusions.
• References.

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• An actuator is a mechanical device for moving or
  controlling a mechanism or system.
• In engineering, actuators are a subdivision of
  transducers. They are devices which transform an
  input signal (mainly an electrical signal) into
  motion.
• Specific examples are electric motors, pneumatic
  actuators, hydraulic pistons, relays, comb drive,
  piezo electric actuators, thermal bimorphs,
  Digital Micro mirror Devices and electro active
  polymers.

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• Shape memory alloys (SMAs) are metals that
  "remember" their original shapes.
• SMAs are useful for such things as actuators
  which are materials that "change shape,
  stiffness, position, natural frequency, and other
  mechanical characteristics in response to
  temperature or electromagnetic fields" .
• The potential uses for SMAs especially as
  actuators have broadened the spectrum of many
  scientific fields. The study of the history and
  development of SMAs can provide an insight into a
  material involved in cutting-edge technology.
• The diverse applications for these metals have
  made them increasingly important and visible to
  the world.

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History

• Nickel-titanium alloys have been found to be the
  most useful of all SMAs. Other shape memory
  alloys include copper-aluminum-nickel,
  copper-zinc-aluminum, and iron- manganese-silicon
  alloys) The generic name for the family of
  nickel-titanium alloys is Nitinol.
• In 1961, Nitinol, which stands for Nickel
  Titanium Naval Ordnance Laboratory, was
  discovered to possess the unique property of
  having shape memory.

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Manufacture

• There are various ways to manufacture Nitinol.
  Current techniques of producing nickel-titanium
  alloys include vacuum melting techniques such as
  electron-beam melting, vacuum arc melting or
  vacuum induction melting.
• There is also a process of cold working of Ni-Ti
  alloys. The procedure is similar to titanium wire
  fabrication. Carbide and diamond dies are used in
  the process to produce wires ranging from 0.075mm
  to 1.25mm in diameter.

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• This paper describes the design of an implantable
  drug delivery system based on shape memory alloy
  actuators.
• The proposed operating principle is based on a
  precisely controlled, discontinuous release from
  a pressurised reservoir using a shape memory
  alloy actuated microvalve-system.
• The volume of one dose can be controlled with an
  accuracy up to 5 microlitres.

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• The design of the valve is such that it can be
  mounted on a printed circuit board together with
  the other electrical components.
• Furthermore, the design is optimised towards
  aspects like biocompatibility, low cost
  production, lifetime safety, and minimal
  dimensions.
• The design is aiming at patients that need
  multiple injections per day over a long period of
  time
• .
• The current design could already reduce the
  number of injections by a factor of 200, but by
  further miniaturizations a factor of 3000 could
  be obtained.

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The main reasons to take SMA actuators instead of
other types of actuation are

• They have a higher energy density than other
  driving principles.
• Their construction is easy.
• They can directly be driven by an electric
  current using simple resistive heating .
• They are reliable over long periods of time.
• .

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• This paper discusses an actively controlled
  implantable drug delivery device. Its job is to
  deliver small amounts of drug on a daily basis
  such that the patient no longer needs to get an
  injection every day or week.
• Implantable drug delivery devices give a more
  constant drug level in the blood than injections.
  By the use of an active device instead of a
  passive, the drug level in the blood can be
  adapted to variations in physical activity,
  changes in temperature etc.
• In chemotherapy and similar treatments, the
  device can be implanted at the place where the
  drug is needed such that in the rest of the body
  the concentration of the drug is much lower. The
  device could also be useful for hormonal
  treatments and all other treatments where small
  amounts of drugs are needed.

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Design of a liquid drug delivery device

• The operating principle is based on a precisely
  controlled, discontinuous, release from a
  pressurized reservoir using a shape memory alloy
  actuated micro valve. The reservoir is
  pressurized using a two-phase fluid providing
  constant pressure at body temperature.
• The basic idea for the valve is a pincher placed
  on an elastic tube connected to the reservoir. In
  the normal state the pincher is pressing on the
  tube such that it is closed.
• To open the tube, the pincher can be opened by
  actuation of a SMA element.
• The dose can be controlled by use of a calibrated
  flow channel in the outlet. By calibrating this
  flow channel during production of the device, the
  delivered dose can be tuned to be constant for
  all produced dosing systems..
• Because of the limited size of the main reservoir
  (partially due to safety requirements), it must
  also be possible to refill it while implanted

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Design of the valve

• The basic idea for the valve is that of a small
  pincher placed on an elastic tube made of
  silicone rubber. That way, only the silicone
  rubber of the tube is in contact with the drug
  which is a substantial advantage for
  biocompatibility.
• The design is optimised towards dimensions,
  number of parts, and energy consumption. The
  valve is normally closed and opens when it is
  elastically deformed by actuating (heating) the
  SMA wire.
• When cooling the SMA, the valve closes again by
  the elasticity of the joint.
• The valve consists of only three parts a body, a
  screw, and a SMA wire. The reduction of parts is
  of extreme importance for both miniaturisation
  and production (cost) reasons.

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• The small dimensions allow to integrate the valve
  on a PCB with the electronics, simplifying the
  electrical connections.
• To allow the high strains in the elastic joints,
  plastic was chosen for the valve body.
• Additional advantages are a good electrical
  isolation of the wire, good machinability, and
  the possibility of mass production. The used
  plastic also gives the possibility to put
  electrical connections on the surface (like on a
  PCB). This technology also allows to integrate
  sensors to
• detect leakage or fracture of the device.

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Design of an integrated drug delivery system

• A prototype was developed incorporating the
  reservoir, tubing, valve system,housing, and a
  mock-up of the antenna. It uses an operating
  principle similar to the one discussed before,
  but features an improved accuracy and safety.
• Picture 2 shows a cross-section and a photograph
  of the device. It roughly has a diameter of 50 mm
  and a height of 15 mm. The injection port is a
  little bit elevated such that you can feel it
  through the skin. All reservoirs and tubing are
  made of silicone rubber.
• Stainless steel is used for the needle stop and
  the connection of the tubes. After tuning the
  valve system, it is glued on a printed circuit
  board and the SMA wire is soldered on the copper
  pads. As NiTi is normally not solderable, a
  copper layer was first deposited in an
  electrochemical way.

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Design of an integrated drug delivery system
Contd..

• This technique guarantees a good electrical
  connection but is not sufficient to serve as a
  mechanical connection.
• The housing is a thin metal shell of stainless
  steel or titanium.
• To facilitate the construction of the prototype,
  the depicted system has an aluminium housing.
  Also, the main reservoir is not pressurised by a
  two-phase fluid. Instead, the elasticity of the
  silicone rubber is used.

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Testing of the drug delivery system

• The valve remains closed at 2 bar, the maximum
  overpressure the tubes can withstand. A fatigue
  test of 10,000 cycles was performed on the
  valve-tube system at an overpressure of 1 bar. No
  leaks were found and the valve had not to be
  retuned. These 10,000 cycles correspond to 3
  injections a day, 9 years long, or 5 injections a
  day, 5 years long.
• Also the integrated system with refill port,
  reservoir and valve system was tested.
  Distillated water was injected through the
  silicone rubber stop of the refill system. After
  activating the valve system, one dose leaves the
  drug delivery device.

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Testing of the drug delivery system Contd..

• The main reservoir of the proposed prototype has
  a capacity of about 1 ml. Depending on the
  internal pressure, the dose leaving the system
  each cycle is 5 to 25 µl, allowing 40 to 200
  doses.
• Further miniaturization would allow to include a
  reservoir of 15 ml so that the total number of
  doses could be 3000.

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Conclusion

• The small dimensions allow to integrate the valve
  on a PCB with the electronics, simplifying the
  electrical connections.
• Tests showed no leakage and long lifetime (10,000
  cycles).
• The volume of one dose can be controlled with an
  accuracy up to 5 µl.
• Besides the valve system, the prototype contains
  also a main reservoir, a refill port, an antenna
  and a housing. The current design could already
  reduce the number of injections by a factor of
  200, but by further miniaturisation a factor of
  3000 could be obtained

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References

• 1 D. Reynaerts, and H. Van Brussel, Shape
  Memory Alloy based Electrical Actuation for
  Robotic Applications.
• 2 M. Kohl, K.D. Skrobanek, E. Quandt, P.
  Schlossmacher, A. Schuessler, and D.M. Allen,
  Development of Microactuators based on the Shape
  Memory Effect.
• 3 D. Reynaerts and H. van Brussel, "A SMA High
  Performance Actuator for Robot Hands.
• 4 D. Reynaerts, J. Peirs, and H. Van Brussel,
  Production of Shape Memory Alloys for
  Microactuation.
• 5 A.V. Shelyakov, V.A. Antonov, Yu.A. Bykovsky,
  and N.M. Matveeva, Optical devices based on
  Shape Memory Effect for Signal Processing.

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• Questions???

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• Thank you!!!