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UV-Photolithography Fabrication of Poly-Ethylene Glycol Hydrogels Encapsulated with Hepatocytes
The development of biomanufacturing technologies particularly, layered manufacturing has
advanced cell encapsulation processes in an effort to mimic the cellular microenvironment for invitro studies. This paper illustrates an inexpensive UV-photolithographic method for
encapsulation of human hepatocytes in three dimensional structures using poly-ethylene
diacrylate (PEGDA) hydrogels as candidate substrates. In order to further develop this
technology for layered fabrication, we have quantified the long-term effects of the photo-initiator
concentration and UV light exposure on the metabolic rates of encapsulated human hepatocytes
under a 21 day study. The photoinitator toxicity was observed immediately after polymerization
with no significant cytotoxicity on a long term basis. A cellular viability is examined and
reported for the UV photopolymerization process. Cell phenotype maintenance was observed by
measuring the amount of urea produced over a 1 week time period. This photo encapsulation
process may find use in the fabrication of spatially complex 3D scaffolds for tissue engineering
applications, elucidation of the 3D structure-pharmacokinetic response relationship and the
fabrication of complex multi-compartment liver tissue analog devices for drug screening
applications.Mechanical Engineerin
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Freeform Bioprinting of Liver Encapsulated in Alginate Hydrogels Tissue Constructs for Pharmacokinetic Study
An in vitro model that can be realistically and inexpensively used to predict human response to
various drug administration and toxic chemical exposure is needed. By fabricating a microscale
3D physiological tissue construct consisting of an array of channels and tissue-embedded
chambers, one can selectively develop various biomimicking mammalian tissues for a number of
pharmaceutical applications, for example, experimental pharmaceutical screening for drug
efficacy and toxicity along with apprehending the disposition and metabolic profile of a
candidate drug. This paper addresses issues relating to the development and implementation of a
bioprinting process for freeform fabrication of a 3D cell-encapsulated hydrogel-based tissue
construct, the direct integration onto a microfluidic device for pharmacokinetic study, and the
underlying engineering science for the fabrication of a 3D microscale tissue chamber as well as
its application in pharmacokinetic study. To this end, a prototype 3D microfluidic tissue chamber
embedded with liver cells encapsulated within a hydrogel matrix construct is bioprinted as a
physiological in vitro model for pharmacokinetic study. The developed fabrication processes are
further validated and parameters optimized by assessing cell viability and liver cell phenotype, in
which metabolic and synthetic liver functions are quantitated.Mechanical Engineerin
Integrated lake farming for fish and environmental management in large shallow Chinese lakes: a review
Large shallow lakes in the Pacific Drainage Basin of China are unique aquatic natural resources intensively exploited in recent years for integrated lake farming. This paper presents a general description and major components of this culture method and discusses potential concerns and effects of increased fishery production on aquatic environments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72470/1/j.1365-2109.1989.tb00371.x.pd
Quantum tunneling through planar p-n junctions in HgTe quantum wells
We demonstrate that a p-n junction created electrically in HgTe quantum wells
with inverted band-structure exhibits interesting intraband and interband
tunneling processes. We find a perfect intraband transmission for electrons
injected perpendicularly to the interface of the p-n junction. The opacity and
transparency of electrons through the p-n junction can be tuned by changing the
incidence angle, the Fermi energy and the strength of the Rashba spin-orbit
interaction. The occurrence of a conductance plateau due to the formation of
topological edge states in a quasi-one-dimensional p-n junction can be switched
on and off by tuning the gate voltage. The spin orientation can be
substantially rotated when the samples exhibit a moderately strong Rashba
spin-orbit interaction.Comment: 4 pages, 4 figure
Thermal transistor: Heat flux switching and modulating
Thermal transistor is an efficient heat control device which can act as a
heat switch as well as a heat modulator. In this paper, we study systematically
one-dimensional and two-dimensional thermal transistors. In particular, we show
how to improve significantly the efficiency of the one-dimensional thermal
transistor. The study is also extended to the design of two-dimensional thermal
transistor by coupling different anharmonic lattices such as the
Frenkel-Kontorova and the Fermi-Pasta-Ulam lattices. Analogy between anharmonic
lattices and single-walled carbon nanotube is drawn and possible experimental
realization with multi-walled nanotube is suggested.Comment: To appear in J. Phys. Soc. Jp
Effect of surface roughness on the microwave emission from soils
The effect of surface roughness on the brightness temperature of a moist terrain was studied through the modification of Fresnel reflection coefficient and using the radiative transfer equation. The modification involves introduction of a single parameter to characterize the roughness. It is shown that this parameter depends on both the surface height variance and the horizontal scale of the roughness. Model calculations are in good quantitative agreement with the observed dependence of the brightness temperature on the moisture content in the surface layer. Data from truck mounted and airborne radiometers are presented for comparison. The results indicate that the roughness effects are greatest for wet soils where the difference between smooth and rough surfaces can be as great as 50K
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