American Ceramic Society Bulletin

advances in nanomaterials
Bioactive cement plaster: Bioengineering in action
For some time, it has been common
to use enzymes as biocatalysts. When
the enzymes required are difficult or
expensive to extract, the utilization of
microorganisms such as bacteria, yeast,
or fungi is an alternative.
Also from Berkeley Lab (see previous
story), we received word about
work there regarding spontaneous magnetization
in bismuth ferrite, another
multiferroic material.
What seems to have researchers
really excited is that they can turn this
magnetization on and off via an external
electric field at room temperature,
making the BFO a possible material
for spintronic applications.
In a news release from the lab,
Ramamoorthy Ramesh, the materials
scientist with the lab’s Materials Sciences
Division who led this research,
explains the novel approach taken. He
says, “[W]e’ve created a new magnetic
state in bismuth ferrite along with
the ability to electrically control this
magnetism at room temperature. An
enhanced magnetization arises in the
rhombohedral phases of our bismuth
ferrite self-assembled nanostructures.
This magnetization is strain-confined
between the tetragonal phases of the
material and can be erased by the
application of an electric field. The
magnetization is restored when the
polarity of the electric field is reversed.”
In 2009, Ramesh and his research
group looked at thin films of the BFO
and found that although bismuth ferrite
is an insulator, two of three domain
wall orientations in the material conduct
electricity. They subsequently
found that application of a large epitaxial
strain changes the BFO crystal
structure from a predominant rhombohedral
phase to a tetragonal phase.
Conversely, a partial strain reduction
produces a nanoscale mixed phase
For many applications, the living
cells are immobilized within a stable
matrix system. This prevents the
embedded cells against culture washout
and protects them from external
impact, such as shear forces, pH or sol-
Spintronics may get boost from enhanced magnetism in BFO films
AFM image of a mixed-phase bismuth
ferrite sample. The red and green areas
indicate phase regions oriented at 90
degrees to each other.
composed of the rhombohedral and
tetragonal phases. Ramesh says the
mixture can be stable, with the rhombohedral
phases mechanically confined
by regions of the tetragonal phases.
As a result of the interaction, a
different magnetic moment (30 to 40
electromagnetic units per cubic centimeter)
spontaneously arises within
the distorted rhombohedral phase, one
that is qualitatively stronger than the
magnetic moment of fully rhombohedral
BFO (6 to 8 electromagnetic units
per cubic centimeter).
Ramesh says these differences are
large enough to be put to use, and can
be manipulated using an external electrical
field rather than applying the
magnetic field used in conventional
memory devices.
The results of the group’s work
is published Nature Communications
(doi:10.1038/ncomms1221).
Visit: www.lbl.gov n
vents. Besides commonly used natural
polymers, some porous inorganic matrices
have become increasingly important
for immobilizing living cells.
Results of former studies have shown
that bacteria can be successfully embedded
within a very hard concrete matrix
and can remain viable for a period of
four months. This encouraged the R&D
organization GMBU and the company
InnoTERE (both Dresden, Germany) to
investigate the immobilization of microorganisms
in cements. The researchers
examined the viability and biocatalytic
applicability of the bacteria Rhodococcus
ruber and the yeast Saccharomyces
cerevisiae, in particular their dependence
on preparation conditions.
For their investigations, they used
magnesium phosphate cement, which
can be prepared easily by mixing hardburned
tribasic magnesium phosphate
powder and ammonium phosphate
solution. Because of the stiffness of the
cement matrix, bioactive MPC could
be very interesting for applications in
bioremediation, in biotechnology as
bulk material in large columns or reactive
walls, or as bioactive cement plaster
within sewers.
The results of the study, “Cements
with embedded living microorganisms:
A new class of biocatalytic composite
materials for application in bioremediation,
biotechnology” (doi:10.1002/
adem.201080040) revealed that the
bioactive composite material exhibits
good mechanical and chemical stability.
The embedded cells survived the
embedding within the cement matrix
even though the cements showed much
slower glucose and phenol consumption
in comparison with nonimmobilized
cells.
Combining a cement matrix with
living microorganisms is a promising
method to fabricate biocomposite materials
for application in biotechnology.
Visit: InnoTere, www.innotere.de;
and GMBU, www.gmbu.de n
16 American Ceramic Society Bulletin, Vol. 90, No. 4
(Credit: Ramesh Group; Berkeley Lab.)