Diabetes_Sensor

Integrated sensing and drug delivery for diabetes management

Applications of MEMS technology to Drug Delivery

-Shantanu Sood

Regularly monitor the levels of

glucose manually

If the glucose levels are not in

the normal range

Inject insulin one to two times a day

• Number of diabetes patients in 1985: 30 million• Number of diabetes patients worldwide: 285 million• Expected number of diabetes patients in 2030 according to IDF (International Diabetes Federation) : 435 million

Current technologies for diabetes managementWhat is diabetes?

Statistics

Future TechnologyArtificial kidneys, which is our dialysis

technology. Artificial heart

Artificial Pancreas for Diabetes management?

External GSII (Glucose sensing and insulin injection)

C o m p o n e nt s

S u b sy st e mSy st e m

GSII

SENSOR

GLUCOSE SENSOR

FLOW SENSOR

MICROVALVE

ACTUATOR

PDMS MICROCHANNEL

S-SHAPED MICROPUMP

Component Design Materials Processing

GLUCOSE SENSOR

Blood flows into the hollow areas inside the sensor.

Component Design Materials Working

Glucose Sensor

Pt working electrode

Pt counterelectrode

Pyrrole is deposited Blood enters

Then the electrochemical process takes place with 0.7 volt of voltage applied to the electrodes

To Flow sensor

Ag referenceelectrode

Three sensing electrodes, including a working (platinum, Pt), a counter (Pt), and a reference (silver, Ag) electrode, were designed and fabricated by using thin-film deposition process.

A constant current (2.483 μA) was applied to electropolymerized pyrrole and used to entrap glucose oxidase on the surface of working electrode for electrochemical sensing of glucose.


H2O2 → 0.7 V Pt with Ag/AgCl → 2H+ + O2 + 2e−

(GOD Glucose oxidase )

Glucose Oxidase was used to react with the blood glucose to electrochemically measure reaction currents

Then, the operation of the glucose sensor is based on electrochemical oxidation of hydrogen peroxide to regenerate oxygen, which thus completes the enzymatic cycle.

The amperometric method is used to convert this second chemical reaction

into a current signal

And this current signal has a threshold which drives the micro pump in the insulin reservoir

**reference 7

Photolithography

Step 1: Heated, to remove any water on the surface and then oxidised to form silicon dioxide.

Step 2: Wafer is coated with photoresist by spin coating

Why SU-8?

• A very viscous polymer that can be spun or spread over a thickness ranging from 0.1micrometer up to 2 millimeters.• Can easily be processed using contact lithography• Has high aspect ratio(>20)• Highly transparent in UV region allowing fabrication of relatively thick structures

Step 3: Wafer is exposed to UV light through a photomask

Step 4: Photoresist can now be stripped off and the oxide layer can be etched away using a suitable etchent

Step 5: Now the photoresist is no longer needed and can be removed using a liquid resist stripper


(1) Photoresist patterning

(2) Ag/Cr layer deposition

(3) Photoresist lift off


(5) Pt/Cr deposition



(8) Au/Ti deposition


Glucose Sensor


Flow Sensor

The temperature sensitive flow sensors can detect the flow rate based on their resistance change.

Flow sensors were composed of Pt and Au (gold) materialswith a resistance of 120.

1. Based on hot-film anemometry.

2. Platinum thin-film resistor is used for detecting the varying amounts of current flowing through the chip.

3. The resistors are located in the centre of the oxidised porous silicon diaphragm and the rim of the chip, respectively.

4. When the current is able to overcome the resistance then the flow sensors let the fluid flow.


Microfluidic PDMS based microchannel

SU-8

PDMS

Why Polydimethylsiloxane (PDMS)

Basis of the upper microfluidic control module consists of micropumps, microvalves and microchannels is a molecule called

polydimethylsiloxane (PDMS)

5

6

PDMS is a resilient material, it is an ideal choice for the currentpneumatic micropumps, in which the application of compressedair causes the PDMS membranes to deflect peristaltically, hencedriving the sample through the microchannel.

A Viscoelastic materials

At high Temperature At low Temperature


Microfluidic PDMS based microchannel

A) SU-8 photoresist is deposited over a pre treated and etched Silicon subsrate.

E) Finally the silicon substrate is removed

B) PDMS layer is then deposited

C) Silicon substrate is removed

D) Then this pneumatic chip is spread over the silicon substrate, the substrate is lined with PDMS


Actuator Device

S-shape pneumatic microchannel intersects the fluidic microchannel at various points along its length. Thin PDMS membranes are located at each intersection and are deflected as compressed air travels through the S-shape microchannel.

Compressed air travels along the lower S-shape microchannel and causes the PDMS to deflect

The time-phased deflection of neighboring membranes induces a peristaltic effect which drives the fluid along the microfluidic microchannel.


Actuator Device

(1) Spin-on of SU-8

(2) photolithography

(3) PDMS casting

(4) oxygen plasma treatment and bonding

(5) bonding of PDMS and sensor electrodes.


S-shaped micropump

(1) The SU-8 negative thick PR is spun-coated on a silicon wafer.(2) A standard lithography process is used to form the SU-8 structured mold.

(3) PDMS is poured on the SU-8 microstructure mold and then cured.

(4) PDMS inverse structures are formed and mechanically peeled off the mold. (5) A microflow sensor is formed using the standard lithography and E-beam evaporation processes. (6) Oxygen plasma treatment is performed prior to bonding PDMS layers and the glass substrate to form the completed S-shape micropump.

Glass

Glucose SensorBlood Inlet

Microvalve

Flow Sensors

Insulin Reservoir

Microvalve

Micropump

Insulin Outlet

Micro-channel

Summing everything together

Questions?

Health & Medicine

Diabetes_Sensor