Biomedical Engineering Reference
In-Depth Information
10.1
Introduction
Technological advances in molecular biology, tissue engineering, and medicine have been
paralleled by rapid and profound gains in microelectronics, smart materials research, and
information processing. The confluence of these emerging disciplines promises to bridge
the biotic (organism) and abiotic (environment) realms in unanticipated ways. The
dynamic coupling of organism and environment draws attention to those boundary struc-
tures that naturally allow flexible and adaptive sensory communication while simultane-
ously providing the physical barrier required for life outside the womb or ocean.
This review focuses on the unique biological boundary of the body manifested by the
surface of the human skin. Specifically, attention is drawn to the outermost layer of the
skin, the stratum corneum (SC), which as the terminally differentiated (dead) product of
epidermal differentiation forms the ultimate biopolymeric interface with the environment.
The SC, viewed through the lens of a materials engineer, is a multifunctional nanocom-
posite with all the hallmarks of a smart material. The strategic location of this highly
organized, thin (~20
m), bioengineered film places it in an optimal location to mediate
biotic/abiotic interactions. Improved sensor systems for noninvasive detection of physio-
logically relevant mechanical, electrical, or magnetic signatures at the surface of the body
(data beyond current electrocardiography or electroencephalography) require bridging to
the body via this complex but assessable biological structure.
The iterative development of such extended, noninvasive, bioengineered interfaces should
not ignore the body's own exquisite material solution to biotic/abiotic interface design.
Seamless coupling to the body surface requires a better understanding of the molecular archi-
tecture of the SC as a polymer film and the functional unit organization of the epidermis. This
challenge amounts to nothing less than an initial understanding of the boundary conditions
of the human body. This will necessitate integration of broad advances in a wide variety of
fields viz. microsystems, clinical medicine, cell and molecular biology, and information tech-
nology. Such extended interface systems would be typically freestanding, multifunctional,
multimode, microfluidics-based sensor systems (Figure 10.1) coupled to human skin for real-
time monitoring at global (physiological) and local (molecular) levels.
The scope of systems containing bioengineered microinterfaces goes beyond sampling
and extraction of high-quality distributed physiological data. Advanced systems hold the
Micro-fluidic interface
Remote
computing
Sensor array,
local computing,
communications
Response
Data
Man-made
Interface
20
µ
m
stratum
corneum
80 pm
living
epidermis
Biologica
l
Epidermis
Motor
Sensory
Invasive
Noninvasive
Brain
FIGURE 10.1
Bioengineered interface between analogous biological and MEMS-based systems.
