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Morphological differences in BMP-2-induced ectopic bone between solid and crushed hyaluronan hydrogel templates
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Biomedical Radiation Sciences.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics.
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2013 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 24, no 5, 1201-1209 p.Article in journal (Refereed) Published
Abstract [en]

The possibility to affect bone formation by using crushed versus solid hydrogels as carriers for bone morphogenetic protein 2 (BMP-2) was studied. Hydrogels, based on chemical crosslinking between hyaluronic acid and poly(vinyl alcohol) derivatives, were loaded with BMP-2 and hydroxyapatite. Crushed and solid forms of the gels were analyzed both in vitro via a release study using I-125 radioactive labeling of BMP-2, and in vivo in a subcutaneous ectopic bone model in rats. Dramatically different morphologies were observed for the ectopic bone formed in vivo in the two types of gels, even though virtually identical release profiles were observed in vitro. Solid hydrogels induced formation of a dense bone shell around non-degraded hydrogel, while crushed hydrogels demonstrated a uniform bone formation throughout the entire sample. These results suggest that by crushing the hydrogel, the construct's three-dimensional network becomes disrupted. This could expose unreacted functional groups, making the fragment's surfaces reactive and enable limited chemical fusion between the crushed hydrogel fragments, leading to similar in vitro release profiles. However, in vivo these interactions could be broken by enzymatic activity, creating a macroporous structure that allows easier cell infiltration, thus, facilitating bone formation.

Place, publisher, year, edition, pages
2013. Vol. 24, no 5, 1201-1209 p.
National Category
Engineering and Technology Natural Sciences Medical and Health Sciences
URN: urn:nbn:se:uu:diva-201244DOI: 10.1007/s10856-013-4877-6ISI: 000318510200008OAI: oai:DiVA.org:uu-201244DiVA: diva2:626857
Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2015-02-03Bibliographically approved
In thesis
1. Bone Regeneration with Cell-free Injectable Scaffolds
Open this publication in new window or tab >>Bone Regeneration with Cell-free Injectable Scaffolds
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bone is a remarkable multifunctional tissue with the ability to regenerate and remodel without generating any scar tissue. However, bone loss due to injury or diseases can be a great challenge and affect the patient significantly. Transplanting bone graft from one site in the patient to the site of fracture or bone void, i.e. autologous bone grafting is commonly used throughout the world. The transplanted bone not only fills voids, but is also bone inductive, housing the particular cells that are needed for bone regeneration. Nevertheless, a regenerative complement to autograft is of great interest and importance because the benefits from an off-the-shelf product with as good of healing capacity as autograft will circumvent most of the drawbacks with autograft. With a regenerative-medicine approach, the use of biomaterials loaded with bioactive molecules can avoid donor site morbidity and the problem of limited volume of material. Two such regenerative products that utilize bone morphogenetic protein 7 and 2 have been used for more than a decade in the clinic. However, some severe side effects have been reported, such as severe swelling due to inflammation and ectopic bone formation. Additionally, the products require open surgery, use of supra physiological doses of the BMPs due to poor localization and retention of the growth factors. The purpose of this thesis was to harness the strong inductive capability of the BMP-2 by optimizing the carrier of this bioactive protein, thereby minimizing the side effects that are associated with the clinical products and facilitating safe and localized bone regeneration at the desired site. We focused on an injectable hyaluronan-based carrier. The strategy was to use the body’s own regenerative pathway to stimulate and enhance bone healing in a manner similar to the natural bone-healing process. The hyaluronan-based carrier has a similar composition to the natural extracellular matrix and is degraded by resident hyaluronidase enzymes. Earlier studies have shown a more controlled release and improved mechanical properties when adding a weight of 25 percent of hydroxyapatite, a calcium phosphate that constitutes the inorganic part of the bone matrix. In Paper I, the aim was to improve the carrier by adding other forms of calcium phosphate. The results indicated that the bone formation was enhanced when using nano-sized hydroxyapatite. We wished to further develop the carrier system but were lacking an animal model with high output and easy access. We also wanted to provide paired data and were committed to the 3 Rs of refinement, reduction and replacement. To meet these challenges, we developed and refined an animal model, and this is described in Paper II. In Paper III, we characterized and optimized the handling properties of the carrier. In Paper IV, we discovered the importance of crushing the material, thus enhancing permeability and enlarging the surface area. In Paper V, we sought to further optimize biomaterial properties of the hydrogel through covalently bonding of bisphosphonates to the hyaluronan hydrogel. The results demonstrated exceptional retention of the growth factor BMP-2. In Paper VI, the in vivo response related to the release of the growth factor was examined by combining a SPECT/PET/µCT imaging method to visualize both the retention of the drug, and the in-vivo response in terms of mineralization.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 64 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1050
bone tissue engineering, hydrogel, computed tomography, positron emission tomography, large femoral bone defect, rat model, hydrogel, in vivo, osteogenesis, bone regeneration, 3R, single-photon emission computed tomography, bone morphogenetic protein 2, calcium phosphates, injectable, bisphosphonate
National Category
Biological Sciences Polymer Chemistry Other Medical Sciences Other Medical Sciences not elsewhere specified
Research subject
Medical Science; Biology; Chemistry with specialization in Polymer Chemistry; Orthopaedics
urn:nbn:se:uu:diva-234846 (URN)978-91-554-9093-5 (ISBN)
Public defence
2014-12-12, Enghofs salen, ingång 50 Akademiska sjukhuset, Uppsala, 09:15 (Swedish)
EU, FP7, Seventh Framework Programme, EUFP7-NMP.20102.3-1; Grant 262948
Available from: 2014-11-21 Created: 2014-10-24 Last updated: 2015-02-03

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