title: Kinetics of release of heparin from alginate hydrogel.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiology, Indiana University Hospital Indianapolis 46202, USA. gmclenna@iupui.edu
authors.forename: G
authors.initials: G
authors.lastname: McLennan
authors.forename: M S
authors.initials: MS
authors.lastname: Johnson
authors.forename: K R
authors.initials: KR
authors.lastname: Stookey
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: W K
authors.initials: WK
authors.lastname: Fife
mesh_terms: D000464:Alginates / Q000737:chemistry; D002125:Calcium Gluconate / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D016503:Drug Delivery Systems; D020723:Glucuronic Acid; D006493:Heparin / Q000737:chemistry* / Q000493:pharmacokinetics*; D006603:Hexuronic Acids; D020100:Hydrogels / Q000737:chemistry*; D007700:Kinetics; D016014:Linear Models
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; D020100:Hydrogels; D020723:Glucuronic Acid; D006493:Heparin; D002125:Calcium Gluconate