MICROFLUIDICS IN MEDICAL DIAGNOSIS

1
MICROFLUIDICS IN MEDICAL DIAGNOSIS BY 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
2
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.
3
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.
4
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.
5
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.
6
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)
7
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 Hodgkins disease,
non-Hodgkins lymphoma, and lung cancer. It has
also been approved for use in diagnosing
Alzheimers disease. Bibliography " Chung-Chen
Lee, et al. "Multistep Synthesis of a
Radiolabeled Imaging Probe Using Integrated
Microfluidics, Science, December 16, 2005, pp.
17931797
8

• 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.

9
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.
10
CHALLENGES IN MICROFLUIDIC TECHNOLOGY Radiopharma
ceuticals 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.
11
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.
12

• 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.
13
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.
14
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.
15

• 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
16

• 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.