MICROFLUIDICS IN MEDICAL DIAGNOSIS MICROFLUIDICS IN MEDICAL DIAGNOSIS

BY MOLECULAR IMAGINGBY MOLECULAR IMAGING

Oana Tatiana Nedelcu1), Catalin Tibeica1), Jean-Luc Morelle2),

Irina Codreanu1), Adina Bragaru1)

1) National Institute for Research & Development in Microtechnologies

2) Trasis SA, Liege, Belgium

ROMANIAN ACADEMY DECEMBER 6, 2006

INTRODUCTION

The application of microfluidic technologies and devices has

been steadily increasing for the last decade. Microfluidics are

integrated into a broad range of applications, such as industrial

marking, biotechnology, drug discovery and medical diagnostics,

pharmaco-genomics, polymer synthesis, combinatorial drug

synthesis and chemical processing and analysis.

It is expected that microfluidics will revolutionize the fields of

chemistry and biology in many applications, since is a key toward

the development of micro-synthesis, micro-separations and labs-

on-a-chip. Additional possible benefits of devices based on

microfluidics include automation, reduced waste, improved

precision and accuracy, and disposability.

ABOUT MOLECULAR IMAGING

“Molecular imaging“ concept is part of a domain at the

intersection between molecular biochemistry and medical imaging.

In the past decades, the medical imaging was based on

radioisotopes such as Tl, I, Ga, Tc, incorporated into specific

compounds.

Lately, the variety, specificity and complexity of the labelled

compounds increased. The preparation of these compounds was

designed to be as simple as possible, consisting mainly in mixing

the radioactive reagent, as extracted from its generator, with an

appropriately designed compound usually provided as a kit in

freezed-dried form.

In the late 70, PET (Positron Emission Tomography) appeared

as a new imaging modality that allowed the use of a different kind of

isotopes: the positron emitters. These isotopes include species such

as carbon and 18F fluorine that are more appropriate to tag organic

molecules than those used in the past. This drastically widened the

range of labelling possibilities and consequently, the range of diseases

that could potentially be imaged.

Among the compounds identified in that period, FDG (Fluoro-

Deoxy-Glucose) became in the late '90s one of the standards in

nuclear medicine, due to its wide range of diagnostic indications in the

fields of oncology, cardiology and neurology.

The FDG (2-Deoxy-2-fluoro-D-glucose or fluorodeoxyglucose ) is a

labeled version of the sugar glucose and it is used for medical

imaging technology by positron emission tomography (PET).

A microfluidic chip for implementig the production of FDG at

microscale consists of interconected fluid channels, valves,

micropumps, reaction chambers, etc… that allow to perform

multiple chemical operations, synthesizing molecules and

labeling them with radioisotopes.

2-Deoxy-2-fluoro-D-glucose molecule (FDG)

The steps of FDG production:

A. F18 solution comes from a cyclotron, where 18F fluoride is produced via the 18O(p, n) 18F nuclear reaction in 18O enriched water.

B. The five sequential processes should be implemented onto the chip:

1. recovery of the 18F radioisotope from a very dilute solution

2. reformulation of 18F (transfer from water to an organic solvent)

3. labelling 18F (reaction with the precursor)

4. deprotection reaction (hydrolytic deprotection)

5. remove solvent back to water

6*. eventually purification of the remaining product (if the result is toxic)

A dose of labeled FDG in solution, with typically 5 to 10 milliCuries

radioactivity, is ready to be injected!

It must be rapidly used because the 18F has a half-life of only 109.8

minutes!

Applications:

FDG-PET can be used for diagnosis, staging, and monitoring

treatment of cancers, particularly in Hodgkin’s disease, non-

Hodgkin’s lymphoma, and lung cancer. It has also been approved for

use in diagnosing Alzheimer’s disease.

Bibliography

" Chung-Chen Lee, et al. "Multistep Synthesis of a Radiolabeled Imaging Probe

Using Integrated Microfluidics, Science, December 16, 2005, pp. 1793–1797

MAJOR KEYS FOR FUTURE DEVELOPMENT

• The production of PET radiopharmaceuticals involves multiple reaction

step organic chemistry processes.

• These processes must be carried out in a time reasonably short with

respect to the half lives of these positron emitters

• The ability to rapidly implement pharmaceutically acceptable production

methods for newly identified and validated compounds is another major

key to the growing application of PET.

• The high ratio of unlabelled to labelled fractions in the compounds, due to

the macroscopic amounts of reagents involved in currently available

production instruments, sets severe limitations to the range of applications,

many of which will require purities higher by several orders of magnitude

than achieved today with FDG.

The next big step in the design of production instruments for

advanced molecular imaging agents resides in the implementation

of technologies addressing these technical, cost, and timely delivery

to the market matters.

Microfabrication technologies appear as the only way.

The future instruments must include micro-fluidic disposable

consumables, ready-for-use, with most of reagents embedded,

some of which could be linked on functionalised surfaces or could

even be chemically generated within the system. These techniques

are not operational today.

CHALLENGES IN MICROFLUIDIC TECHNOLOGY

Radiopharmaceuticals involve nano-molar quantities of active

ingredients, which make the current radio-synthetic methods and

device mostly inadequate to produce them. The availability of

instruments scaled down to dimensions matching these quantities

will be a major breakthrough.

In order to implement radio-pharmaceutical production processes in

a "lab-on-chip" system, new functions must be developed, the chip

must be mass producible at low cost, materials compatible with the

reagents and the manufacturing techniques need to be identified.

Such materials must allow the purity and specific activity levels

required.

Microfluidic functions should be designed to allow the implementation of

discontinuous, sequential processes. Besides "basic" functionalities such

as valves, pumps, reservoirs, mixers, filters, heaters, for which successful

concepts have been demonstrated, specific functionalities such as specific

detectors, connectors, electro-chemical structures, isolation diaphragms,

chemically functionalised high specific area channels, reagent filling and

containment structures need to be developed.

The manufacturability is a challenge in itself. Main design options have to

be identified to allow such different functions, and consequently different

manufacturing techniques to be merged onto a single component.

Specific Objectives to be taken into account

• Reducing quantities of consumable materials involved;

• Improving the purity of products and intermediates;

• Reducing the manufacturing costs of consumables;

• Reducing the size of the instruments;

The challenge is to develop all the chemical and physical functionalities

needed for the process and combine them into a mass producible single

component, and to develop the actuation and control interface to pilot the

process inside the component and monitor and record the parameters. In

addition to the higher purity requirement needed for MI tracers, yields similar

or higher than obtained in conventional systems should be obtained.

MICROFLUIDIC COMPONENTS

Basic components in microfluidic devices are: separation, mixing, reaction,

sample preparation, sample injection, sample collection, detection, pumping,

transport (through channels), flow control, reservoirs.

Fluid Control Components can be based on a set of actuation principles, such as

thermal actuation, piezoelectric actuation, electrostatic actuation, electromagnetic

actuation, pneumatic actuation.

Valveless pumps can be also used, such as electro-hydrodynamic (EHD) pumps,

diffuser pumps, electro-osmotic (electrokinetic) pumps, bubble pumps. Electro-

osmotic pumping requires materials with surface charge such as glasses and

many polymers having permanent negative surface charge. Electro-osmotic

pumps are attractive in fluidic microsystems for polar liquids because they have no

moving parts and can be integrated easily.

Another type of actuation by electrokinesis is electrophoresis: an electric

field influences the movement of charged molecules in fluids moving

through the micro-channels. Electrophoresis can be used to move

molecules in solution or to separate molecules with very subtle differences.

Carbon fibres can be used as alternative method for separation processes;

in this case, heating component must be added to perform the separation

process.

Mixing is also essential in many of the microfluidic systems targeted for use

in biochemistry analysis, drug delivery, and sequencing or synthesis of

nucleic acids, among. Biological processes involve reactions that require

mixing of reactants for initiation.

MICROFLUIDIC FUNCTIONS

TO BE IMPLEMENTED IN MOLECULAR IMAGING

- Fluid handling (micropumps, active / passive valves;

microchannels);

- Recovery functions;

- Labelling functions;

- Reagent storage and release;

- Heating function;

- Purification functions

Finally, mass production techniques involve micro physical studies

for:

- Temperature effects on fluids in the channels;

- The filling of the chip with micro volumes of liquids

NEW KNOWLEDGE TO BE CREATED

• Chemical /electro-chemical recovery of radioactive ions species at the micro scale.

• New synthesis organic chemistry methods intrinsically selective to the labelled

species (ex. selective to FDG vs un-labelled glucose and by-products) via

µreactors, tailored ionic liquids, molecular imprinting, fluorous technologies.

• Solutions to the problems created by the interaction between reagents and

surfaces of the fluid pathways.

• Purification/ separation/ reformulation techniques within microfluidic components.

• Method for pre-loading and storing liquids or solid reagents into µfluidic

component.

• Merging of all the functionalities on one chip; manufacturability with a common and

limited set of techniques despite the wide range of different functionalities.

• Behaviour of the chemical process and components at high radioactivity

concentration levels due to reduced size.