Biomedical Engineering Reference
In-Depth Information
formation of covalent bonds (usually involving electrostatic, capillary, van der Waals
forces, or hydrogen bonds).
shadow evaporation:
In microfabrication, a technique to produce microstructures based on
casting the shadow of a previously patterned microstructure (a line, a post, etc.); as a
material is evaporated from a source (usually a metal), it deposits over the patterned
microstructure(s) but not behind it, thus creating a shadow which may have a shape or
a thickness that is not accessible with traditional photolithography.
shear stress:
A measure of the transverse force (per unit area perpendicular to the force) acting
on a deformable body. For a Newtonian luid, the shear stress is proportional to the
velocity gradient and the proportionality constant is the dynamic viscosity of the luid.
single-stroke PDMS peristaltic micropumps:
Micropumps fabricated in PDMS that produce
peristaltic pumping (i.e., reproduce the undulatory movements of the digestive tract or
“peristalsis”) with pulses from a single control line; traditional peristaltic micropumps
achieve peristalsis with three or more microvalves actuated in sequence (requiring
three control lines).
skin grat:
A skin transplant; “grating” is the name of the surgical procedure that involves
transplanting tissue from one site of the body to another, or from another person,
without transplanting the blood vasculature (the grat becomes vascularized ater
transplantation).
SlipChip:
A microluidic multichamber strategy for moving and mixing luids that, paradoxi-
cally, does not require the use of microvalves; invented by Rustem Ismagilov's labora-
tory at the University of Chicago, it is based on sliding two silanized glass plates with
a lubricating layer of luorocarbon that facilitates the relative motion of the two plates;
etched wells on either plate can be selectively illed with a special pipettor and mix with
each other when they are overlapped.
smart polymer:
A polymer material that can undergo a reversible phase transition (such as a
change in volume or solubility) on application of a stimulus (such as a change in pH,
temperature, or light); as the state is reversed on removal of the stimulus, these poly-
mers can be used as a sensor for that particular stimulus.
sot lithography:
Family of microfabrication techniques that have in common the use of a
micromolded piece of the elastomer PDMS;
see
PDMS.
solid-binding peptides:
A class of synthetic polypeptides that selectively bind to solid supports
such as particular metals, semiconductors, and plastics.
SPM:
See
scanning probe microscope.
stencil patterning:
Method for depositing materials on surfaces that consists of temporarily
blocking the surface with a removable stencil; the material may be shadow-evaporated,
or if the stencil seals well against the surface (i.e., a PDMS stencil), the material may be
deposited from the liquid phase.
Stokes-Einstein relation:
Equation derived by Einstein in 1905 that expresses the difusion
coeicient
D
of spherical particles difusing through liquid with low Reynolds number
(Brownian motion). It expresses that
D
is proportional to temperature and inversely
proportional to the viscosity of the luid and to the radius of the particle.
stopped-low lithography:
Modality of microluidic patterning developed by Patrick Doyle's
laboratory (MIT) in which a photocurable polymer is introduced in the microchan-
nel and a pattern of light is projected into the microchannel to locally cure polymer
microstructures inside the microchannel; during exposure, the low of polymer is
stopped temporarily, hence the name of the technique.
stripe assay:
Biological assay for axon guidance developed by Friedrich Bonhoefer's labora-
tory in 1987 that utilized a PDMS microluidic device to hydrodynamically immobi-
lize stripes of cell membrane fragments onto a porous ilter; retinal temporal axons
were shown to be guided by the stripes whereas nasal axons did not obey the pattern.
Bonhoefer's device is the irst micromolded PDMS device in history.
