Download A droplets/capsules generator based on a piezoelectric actuator

A droplets/capsules generator based on a piezoelectric actuator Technion Reference RES‐1064 BACKGROUND Recently there has been a growing interest in droplet based microfluidic devices. These devices
generate thousands of micro droplets (usually aqueous) which flow in a continuous phase
(normally mineral oil). After their generation the droplets may be sorted, split, merged and
directed to desired locations on the microfluidic chip.
Usually, the droplets are generated passively, i.e. the continuous medium shears the aqueous
droplets separating them from the main flow. The frequency in which the droplets are generated
this way is a function of flow rate and so is their size and distance between them. Thus it is
impossible to control the three parameters (size, distance and rate) separately, furthermore
some flow rates are impractical therefore a range of parameter values cannot be obtained.
TECHNOLOGY The device comprises a piezoelectric actuator and a novel microfluidic design. The actuator
translates electric voltage into mechanical energy, thus by applying a certain voltage on the
actuator it will elongate by a precise length of several micro meters. The voltage is translated
linearly to extension in a precision of several nano meters.
As the actuator vibrates it pushes the membrane and thus a constant volume of fluid through
the microchannel and a droplet is generated. The actuator voltage signal applied by an amplifier
which is controlled via a signal generator. Different signals (pulse, sine wave, ramp etc.)
produce different droplet patterns. The duration of the pulse, wave length and frequency
determine the droplet size, generation rate and pattern (i.e. bursts of droplets).
As mentioned above, the actuator enables the precise control of droplet generation rate, highly
uniform droplet size and distance between droplets. Furthermore, it is possible to obtain bursts
of droplets with varying size which may be applicable to applications where parallelism is
required.
APPLICATIONS 1. FACS (fluorescence activated cell sorter) are able to sort and count different cells based
on their fluorescence emission. Fluorescence tagged cells flow in a stream and then
sprayed out in small droplets each one containing a cell. Droplets carrying the required
cells picked up by detectors are pulled away from he main stream by an electric field.
Present FACS machines are very expensive and complex. Researchers are trying to
develop a micro-FACS by encapsulating cells in micro-droplets using microfluidics and
then manipulating them on chip. However a reliable fully controlled droplet generator is
required.
2. Micro reactors in chemical kinetics, chemical amplification, chemical and biological
analysis and protein crystalization.
3. Particles fabrication: Several works and patents are written on the process of generating
micro polymer or gel particles. The method incorporates two or more sources of
droplets, each source contains a component in the chemical reaction (polymerization or
curring). When two droplets merge (or passed under UV) the reaction begins producing
a miature particle inplace of the former droplet.
4. Single cell diagnostic: single cells may be encapsulated in each droplet and then merged
to another droplet containing any kind of fluorescent marker/ growth factor/
hormone/drug and the result may be analyzed providing diagnostic information. This
method is the only one that enables the efficiently measuring of single cell attributes
instead of an average value obtained for a population of cells.