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A uni-cortical femoral defect model in the rat: evaluation using injectable hyaluronan hydrogel as a carrier for bone morphogenetic protein-2
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics. (Sune Larsson)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry. (Jöns Hilborn)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics. (Sune Larsson)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry. (Jöns Hilborn)
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2015 (English)In: Journal of Tissue Engineering and Regenerative Medicine, ISSN 1932-6254, E-ISSN 1932-7005, Vol. 9, no 7, 799-807 p.Article in journal (Refereed) Published
Abstract [en]

The development of biomaterial for bone regeneration requires animal models that are reliable and designed to mimic clinically relevant situations. We have previously investigated hydrogels comprised of modified hyaluronic acid and polyvinyl alcohol in models of ectopic bone formation. This hydrogel induces bone regeneration when loaded with bone morphogenetic proteins (BMPs). To allow further optimization of hydrogels, we developed a new, femoral, non-critical-sized cortical defect model. In the rat femur, we drilled standardized, elongated unilateral cortical defects that did not require stabilization and that could be created bilaterally to allow paired comparisons of biomaterials. After optimizing the defect size, subsequent stress fractures occurred in only 8% and the defect healed partially over the 40 day study period. In a time-course experiment, we treated bone defects with the previously studied hyaluronan hydrogel loaded with 10 µg hydroxyapatite and 6 µg BMP-2. The shape of the defect allowed controlled containment of the material within the defect. The defect in the right leg was left untreated, while the left defect was filled with 40 µl of the BMP hydrogel. As determined by pQCT analysis, the treated defects had a higher bone mineral content, bone area and bone density than control defects. The relative difference was greatest between the groups at 10 and 20 days and diminished as the defect healed in the untreated legs. We conclude that this animal model allows facile and rapid screening of biomaterials for bone regeneration in cortical femoral defects without requiring external fixation.

Place, publisher, year, edition, pages
2015. Vol. 9, no 7, 799-807 p.
National Category
Other Natural Sciences Other Medical Sciences not elsewhere specified
Identifiers
URN: urn:nbn:se:uu:diva-189868DOI: 10.1002/term.1655ISI: 000357881900006PubMedID: 23225778OAI: oai:DiVA.org:uu-189868DiVA: diva2:582523
Available from: 2013-01-04 Created: 2013-01-04 Last updated: 2017-12-06Bibliographically 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
2017 (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. Autologous bone grafting is commonly used throughout the world. Autograft both fills the void and is bone inductive, housing the particular cells that are needed for bone regeneration. However, a regenerative complement to autograft is of great interest as the use of biomaterials loaded with bioactive molecules can avoid donor site morbidity and the problem of a limited volume of material. Two such regenerative products that utilise bone morphogenetic protein (BMP)-7 and -2 have been used for more than a decade clinically. Unfortunately, several side effects have been reported, such as severe swelling due to inflammation and ectopic bone formation. Additionally, the products require open surgery and use of supra physiological doses of the BMPs due to poor localisation and retention of the growth factor. The purpose of this thesis was to harness the strong inductive capacity of the BMP-2 by optimising the carrier of this bioactive protein, thereby minimising the side effects that are associated with the clinical products and facilitating safe and localised bone regeneration. We focused on an injectable hyaluronan-based carrier developed through polymer chemistry at the University of Uppsala. 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 enzymes. Earlier studies have shown improved properties when adding 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 bone formation was enhanced when using nano-sized hydroxyapatite. In Paper II, we discovered the importance of crushing the material, thus enhancing permeability and enlarging the surface area. We wished to further develop the carrier system, but were lacking an animal model with relatively high throughput, facilitated access, paired data, and we were also committed to the 3Rs of refinement, reduction, and replacement. To meet these challenges, we developed and refined an animal model, and this is described in Paper III. In Paper IV, we sought to further optimise the biomaterial properties of the hydrogel through covalent bonding of bisphosphonates to the hyaluronan hydrogel. This resulted in exceptional retention of the growth factor BMP-2. In Paper V, SPECT/PET/µCT was combined as a tri-modal imaging method to allow visualisation of the biomaterial’s in situ action, in terms of drug retention, osteoblast activity and mineralisation. Finally, in Paper VI the correlation between existing in vitro results with in vivo outcomes was observed for an array of biomaterials. The study identified a surprisingly poor correlation between in vitro and in vivo assessment of biomaterials for osteogenesis.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1287
Keyword
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
Biomaterials Science Orthopedics
Identifiers
urn:nbn:se:uu:diva-310312 (URN)978-91-554-9786-6 (ISBN)
Public defence
2017-02-24, Enghoffsalen, Akademiska sjukhuset, ingång 50, Uppsala, 09:15 (Swedish)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, EUFP7-NMP.20102.3-1; Grant 262948
Available from: 2017-02-02 Created: 2016-12-13 Last updated: 2017-02-07

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Hulsart-Billström, GryAndersson, BrittmarieHilborn, JönsLarsson, SuneJonsson, Kenneth B

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