In footprint, is quite linear and operates with a

In recent years, Micro electro-mechanical systems(MEMS) are
dominating the field of medical, optical acoustics and automotive
applications.  Based on MEMS technology
microgrippers is a developing technology plays an important role in micro
assembly and micromanipulation fields. 
It provides manipulating signal for nerves, tissues, cells and
micromechanical objects, etc.  In order
to manufacture microgrippers, microactuators are essential to control the
operations of microgrippers, 
Microactuators are developed using different actuation principles such
as shape memory alloys, electrostatic, electro thermal, piezoelectric,
pneumatic and electromagnetic approaches. 
Static model of the MEMS microgrippers can be developed by utilizing the
mechanics for the electrostatic actuation system(lateral comb drive) and
sensing systems(transverse comb drive) for testing the operation of the
device.  Electrostaically actuated
microgrippers with a post-assembly self-locking mechanism is the current trend
in MEMS microgrippers.  The arms are
driven by rotary comb actuators, enabling the microgripper to grip objects of
any size from 0 to 100µm.  It enables the
microgripper arms to grip for long periods without continuously applying the external
driving signal.  It significantly reduces
the effects and damage to the gripped objects caused by the external driving
signals. The electrothermal  microgripper
are also leading technique which is fabricated using the PolyMUMPs surface
micromachining process which gives high reliability, repeatability and
reproducibility of jaws gap.  The
electrothermal force sensor has a small footprint,  is quite linear and operates with a high
accuracy.  It is fabricated from
biocompatible material(silicon) with sufficiently long gripping arms.  These microgripper can be used to manipulate
living cells, tissues and other biologically relevant samples,  Hydrogel provide a wide range of actuatable
and self-folding microstructures where mechanical motion is derived from the
large and reversible swelling response of this cross linked hydrogel in varying
thermal or pH environmnets. 
Thermo-piezoelectric  actuator
based microgripper presents both a high range and a high positioning
resolution.  The principle of these
microgripper is based on the combination of the thermal actuation (for the coarse
positioning) and the piezoelectric actuation (for the fine positioning).  This paper presents an overview of recent
development in microgrippers for the actuators(electrostatic, electrothermal
and other actuators) and sensors (optical method, piezoresistive force sensor,
capacitive force sensor for different application in biomedical and biological
applications involves micro-manufacturing operation.