| Expanded-Bed
Protein Adsorption using Porous Surface-Modified Zirconia
Particles
The third major project is the development of porous zirconia
particles for process scale protein adsorption and desorption.
The use of robust, cleanable porous ceramic particles will
reduce purification coats for proteins manufactured on the
kilogram to hundreds of kilogram scale/yr.
The density, thermal, and chemical stability of zirconia make
it an ideal material for use in expanded-bed protein adsorption
(EBA), high temperature processes, or in processes where the
porous media needs to be able to be cleaned with harsh reagents
(for example strong base), depyrogenated, or steam sterilized.
Zirconia is more stable than silica, particularly at pH>8.5.
The disadvantages of zirconia are the limited pore size of
particles of 35µm to 75µm in diameter suitable
for process scale protein absorbers and their complex surface.
The surface of bare zirconia consists of a variety of hydroxyl
chemistries including both Lewis acid and Lewis base sites.
Sterilizable surface-modified porous zirconia particles are
being investigated modified for ligand exchange (fluoride-modified
zirconia, FmZr) and immobilized metal affinity chromatography
(IMAC). Our current focus in this project is to develop a
variety of cleanable, sterilizable IMAC surfaces for expanded-bed
adsorption of proteins.
Because the fluid-filled density of porous zirconia particles
is high, approximately 3g/cm3, these ceramic particles
are ideal for EBA in the presence of a high density of bacteria,
yeast, or in the milk of transgenic animals. Expanded bed
adsorption of human serum albumin (HAS) has been demonstrated
in the presence of up to 100 g/l of dry Saccharomyces
cerevisiae cell mass using FmZr particles.
Porous zirconia particles are also being investigated as supports
for thermal stable enzymes. These ceramic composite particles
may be useful for industrial biotransformation of viscous
biopolymers or carbohydrates using immobilized enzymes at
elevated temperature to reduce viscosity.
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