High-pressure size-exclusion chromatography of anticoagulant materials

Kinetics of release of heparin from alginate hydrogel

PURPOSE

Injected sodium alginate may be a useful perivascular drug delivery vehicle. This study was performed to determine the release rates of heparin from sodium alginate hydrogels cross-linked with varying amounts of calcium gluconate.

MATERIALS AND METHODS

Six hydrogels, composed of 0.16 mEq sodium alginate and 4,000 units unfractionated heparin, were cross-linked with calcium gluconate to yield ion equivalence (IE) ratios (calcium:alginate) of 0.2, 0.4, 0.58, 0.8, 1.0, or 1.2. Two milliliters of normal saline was placed on top of each gel and allowed to remain in contact for up to 10 days. At set time intervals, the amount of heparin in the eluent was determined with use of high-performance liquid chromatography.

RESULTS

Gels with 0.2 and 0.4 IE were partially liquid at 24 hours; the other gels solidified within 10 minutes. The 0.58 IE gel was slowest to solidify but immobilized the most heparin and released heparin slowest over 10 days. At 10 days, between 5.5% and 9.8% of the heparin immobilized was retained in the gel.

CONCLUSION

This hydrogel shows promise as a vehicle for in vivo perivascular heparin delivery. The 0.58:1 IE ratio hydrogel has slowest release rate and the greatest immobilization despite its longer cross-linking time.

Development and validation of a size exclusion chromatography method for determination of molecular masses and molecular mass distribution in low molecular weight heparin

A precise and rugged high performance size exclusion chromatography (HPSEC) method for determination of peak maximum molecular mass (Mp), weight average molecular mass (Mw), number average molecular mass (Mn), and molecular mass distribution (MMD) in Low Molecular Weight heparin (LMW heparin) has been developed and validated on two Ultrahydrogel 250 (ID 7, 8 mm, length 30 cm) columns in series at three laboratories using different equipment. The calibration is based on four local laboratory heparin standards with relatively narrow molecular mass distribution and Mp covering the range from 3,000 to 17,000 Da. The calibration curve describing the logarithm of the molecular mass versus retention time is linear in the range 3,000 to 17,000 Da. The precision (relative standard deviation) within-run and between-run is better than 2%. The between-laboratory variation is below 5%, 3% and 8% for Mp, Mw and Mn, respectively. This method is reproducible, rugged, and fast and is suited for the determination of average molecular masses and molecular mass distribution of LMW heparins on a routine basis.