Regulating in vivo calcification of alginate microbeads

• Type of Material: Article
• Authors: Christopher S.D. Lee, Georgia Institute of Technology; Hunter Moyer, Emory University; Rolando A. Gittens, Georgia Institute of Technology; Joseph Williams, Emory University; Adele L. Boskey, Hospital for Special Surgery; Barbara D. Boyan, Georgia Institute of Technology; Zvi Schwartz, Georgia Institute of Technology
• Language: English
• Date: 2010-06-01
• Publisher: Elsevier
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2010 Elsevier Ltd.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/j.biomaterials.2010.03.001
• Title of Journal or Parent Work: Biomaterials
• ISSN: 0142-9612
• Volume: 31
• Issue: 18
• Start Page: 4926
• End Page: 4934
• Grant/Funding Information: This research was also supported in part by NIH grant DE04141 (Boskey).; This study was funded in part by the National Science Foundation Graduate Research Program (Lee), the Department of Defense, and Children’s Healthcare of Atlanta.
• Keywords: Calcification; BEADS; MOLECULAR-WEIGHT DISTRIBUTION; Science & Technology; Engineering; Engineering, Biomedical; HYDROGELS; Bone tissue engineering; CARTILAGE; Technology; BONE-FORMATION; Materials Science, Biomaterials; TISSUE; Microencapsulation; MINERALIZATION; Alginate; STEM-CELLS; MICROCAPSULES; DEGRADATION; Adipose stem cell microbeads; Materials Science
• Research Categories: Engineering, Biomedical

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 m. m 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.