title: Delivery vehicle effects on bone regeneration and heterotopic ossification induced by high dose BMP-2.
abstract: Bone morphogenetic protein-2 (BMP-2), delivered on absorbable collagen sponge, is frequently used to treat bone defects. However, supraphysiological BMP-2 doses are common and often associated with complications such as heterotopic ossification and inflammation, causing pain and impaired mobility. This has prompted investigations into strategies to spatially control bone regeneration, for example growth factor delivery in appropriate scaffolds. Our objective was to investigate the spatiotemporal effects of high dose BMP-2 on bone regeneration as a function of the delivery vehicle. We hypothesized that an alginate delivery system would spatially restrict bone formation compared to a collagen sponge delivery system. In vitro, BMP-2 release was accelerated from collagen sponge compared to alginate constructs. In vivo, bone regeneration was evaluated over 12weeks in critically sized rat femoral segmental defects treated with 30μg rhBMP-2 in alginate hydrogel or collagen sponge, surrounded by perforated nanofiber meshes. Total bone volume, calculated from micro-CT reconstructions, was higher in the alginate group at 12weeks. Though bone volume within the central defect region was greater in the alginate group at 8 and 12weeks, heterotopic bone volume was similar between groups. Likewise, mechanical properties from ex vivo torsional testing were comparable between groups. Histology corroborated these findings and revealed heterotopic mineralization at 2weeks post-surgery in both groups. Overall, this study recapitulated the heterotopic ossification associated with high dose BMP-2 delivery, and demonstrated that the amount and spatial pattern of bone formation was dependent on the delivery matrix.
  
  
  
  Alginate hydrogel-based BMP-2 delivery has induced better spatiotemporal bone regeneration in animals, compared to clinically used collagen sponge, at lower BMP-2 doses. Lack of clear dose-response relationships for BMP-2 vis-à-vis bone regeneration has contributed to the use of higher doses clinically. We investigated the potential of the alginate system, with comparatively favorable BMP-2 release-kinetics, to reduce heterotopic ossification and promote bone regeneration, when used with a high BMP-2 dose. While defect mineralization improved with alginate hydrogel, the initial high-release phase and likely early tissue exposure to BMP-2 appeared sufficient to induce heterotopic ossification. The characterization presented here should provide the framework for future evaluations of strategies to optimize bone formation and minimize adverse effects of high dose BMP-2 therapy.
authors.affiliation: Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA.
authors.forename: Laxminarayanan
authors.initials: L
authors.lastname: Krishnan
authors.affiliation: Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA; Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Drive NW, Atlanta, GA 30332, USA.
authors.forename: Lauren B
authors.initials: LB
authors.lastname: Priddy
authors.affiliation: Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA.
authors.forename: Camden
authors.initials: C
authors.lastname: Esancy
authors.affiliation: Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA; George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive NW, Atlanta, GA 30332, USA.
authors.forename: Brett S
authors.initials: BS
authors.lastname: Klosterhoff
authors.affiliation: George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive NW, Atlanta, GA 30332, USA.
authors.forename: Hazel Y
authors.initials: HY
authors.lastname: Stevens
authors.affiliation: Department of Surgery, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Tran
authors.affiliation: Parker H. Petit Institute for Bioengineering & Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, USA; George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive NW, Atlanta, GA 30332, USA. Electronic address: robert.guldberg@me.gatech.edu.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Guldberg
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology*; D001861:Bone Regeneration / Q000187:drug effects*; D002460:Cell Line; D016503:Drug Delivery Systems; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000187:drug effects / Q000473:pathology; D020342:Finite Element Analysis; D006801:Humans; D007700:Kinetics; D051379:Mice; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000473:pathology*; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D055114:X-Ray Microtomography
chemical_list: D055396:Bone Morphogenetic Protein 2; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D000469:Alkaline Phosphatase
keywords: Heterotopic ossification; High dose BMP-2; Segmental defect