title: Regulating in vivo calcification of alginate microbeads.
abstract: Alginate calcification has been previously reported clinically and during animal implantation; however no study has investigated the mechanism, extensively characterized the mineral, or evaluated multiple methods to regulate or eliminate mineralization. In the present study, alginate calcification was first studied in vitro: calcium-crosslinked alginate beads sequestered surrounding phosphate while forming traces of hydroxyapatite. Calcification in vivo was then examined in nude mice using alginate microbeads with and without adipose stem cells (ASCs). Variables included the delivery method, site of delivery, sex of the animal, time in vivo, crosslinking solution, and method of storage prior to delivery. Calcium-crosslinked alginate microbeads mineralized when injected subcutaneously or implanted intramuscularly after 1-6 months. More extensive analysis with histology, microCT, FTIR, XRD, and EDS showed calcium phosphate deposits throughout the microbeads with surface mineralization that closely matched hydroxyapatite found in bone. Incorporating 25 mm bisphosphonate reduced alginate calcification whereas using barium chloride eliminated mineralization. Buffering the crosslinking solution with HEPES at pH 7.3 while washing and storing samples in basal media prior to implantation also eliminated calcification in vivo. This study shows that alginate processing prior to implantation can significantly influence bulk hydroxyapatite formation and presents a method to regulate alginate calcification.
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering and Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332-0363, USA.
authors.forename: Christopher S D
authors.initials: CS
authors.lastname: Lee
authors.forename: Hunter R
authors.initials: HR
authors.lastname: Moyer
authors.forename: Rolando A I
authors.initials: RA
authors.lastname: Gittens
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Williams
authors.forename: Adele L
authors.initials: AL
authors.lastname: Boskey
authors.forename: Barbara D
authors.initials: BD
authors.lastname: Boyan
authors.forename: Zvi
authors.initials: Z
authors.lastname: Schwartz
mesh_terms: D000273:Adipose Tissue / Q000166:cytology; D000293:Adolescent; D000464:Alginates / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002113:Calcification, Physiologic; D002118:Calcium / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D017886:Durapatite / Q000378:metabolism; D005260:Female; D020723:Glucuronic Acid / Q000737:chemistry / Q000378:metabolism; D006603:Hexuronic Acids / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D020007:Implants, Experimental; D008297:Male; D051379:Mice; D008819:Mice, Nude; D013234:Stem Cells / Q000166:cytology; D023822:Tissue Engineering
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; D020723:Glucuronic Acid; D017886:Durapatite; D002118:Calcium