Biology Reference
In-Depth Information
Table 4.2
Analytical Techniques for Alginate Characterization
Analytical Method
Purpose
Bulk Material Analysis
1
H-NMR
Uronic acid ratio (M:G). Critical for physical and
chemical stability of formed capsules.
SEC-MALLS
Weight-average molecular weight (M
w
) calculations
for overall chain length and sample homogeneity
(polydispersity).
Dynamic viscosity
Used to calculate intrinsic viscosity and molecular
weight. Useful for controlling droplet formation and
encapsulation procedure.
Protein concentration
Bulk quantification of alginate purity and potential
for degradation/host response.
FTIR
Alginate purity and comparison against a standard.
Useful for characterizing stability based on ratio of
alginate to polycation peaks.
Endotoxin
Quantification of endotoxin impurities per FDA
guidelines and to minimize tissue response.
Alginate-Polycation Microcapsules
Viability
Vital dye for determination of dosing, vitality, and
biomass of encapsulated product.
Diffusion
Predictor of isolation capability and pharmacokinetic
potential.
Burst
Bulk modulus of material and ultimate physical
strength of microcapsule.
Postencapsulation phenotype
Confirmation of potential cell functionality and
morphology.
Microbiology/virus screening
Screen for product acceptance and lot release.
Morphometry
Batch polydispersity and average size of capsules and
their respective wall thickness.
Fourier-transform infrared spectroscopy (FTIR), the surface of explanted capsules
(up to 6 months in the brain or peritoneum) was analyzed for the relative propor-
tion of alginate (outer coat) and PLO (middle coat). Using a mathematic relation-
ship between FTIR peaks related to these two material components, an index was
generated to compare the stability of the microcapsules. A notable difference was
observed: breakdown in the peritoneum was rapid, whereas identical alginate cap-
sules transplanted into the brain were completely stable for the duration of the six-
month study
[39,40]
.
