Abstract
The repair of bone defects is of particular interest for orthopedic, oral, maxillofacial, and dental surgery. Bone loss requiring reconstruction is conventionally addressed through bone grafting. Depending on the size and the location of the defect, this method has limits and risks. Biomaterials can offer an alternative and have features supporting bone repair. Here, we propose to evaluate the cellular penetration and bone formation of new macroporous beads based on pullulan/dextran that has been supplemented with nanocrystalline hydroxyapatite in a rat model. Cross-linked beads of 300–500 µm diameters were used in a lateral femoral condyle defect and analyzed by magnetic resonance imaging, micro-computed tomography, and histology in comparison to the empty defects 15, 30, and 70 days after implantation. Inflammation was absent for both conditions. For empty defects, cellularisation and mineralization started from the periphery of the defect. For the defects containing beads, cellular structures filling out the spaces between the scaffolds with increasing interconnectivity and trabecular-like organization were observed over time. The analysis of calcified sections showed increased mineralization over time for both conditions, but was more pronounced for the samples containing beads. Bone Mineral Density and Bone Mineral Content were both significantly higher at day 70 for the beads in comparison to empty defects as well as compared with earlier time points. Analysis of newly formed tissue around the beads showed an increase of osteoid tissue, measured as percentage of the defect surface. This study suggests that the use of beads for the repair of small size defects in bone may be expanded on to meet the clinical need for a ready-to-use fill-up material that can favor bone formation and mineralization, as well as promote vessel ingrowth into the defect site.
Highlights
The repair of bone defects caused by trauma, surgery or due to cancer treatment is of particular interest for surgeons
Bone substitute biomaterials are often based on calcium phosphates like hydroxyapatite (HA) [13], tricalcium phosphate (TCP) [13,14,15], biphasic calcium phosphates (BCP) [13,16,17], or coral [18] because of their biocompatibility due to a composition similar to mature bone, and their osteoconductive properties [2]
Chemical cross-linking with sodium trimetaphosphate of an alkaline solution containing NaCl as a porogen, nanocrystalline hydroxyapatite (nHA) and a polysaccharide blend dispersed into canola oil under mechanical stirring allowed obtaining the beads
Summary
The repair of bone defects caused by trauma, surgery or due to cancer treatment is of particular interest for surgeons. Other groups of bone substitute biomaterials that promote vessel ingrowth are mainly based on polymers. Some polymers have little affinity with bone, but can be associated with cells or growth factors to promote bone tissue regeneration with angiogenic potential in vivo [28,29,30,31,32]. Composite materials in different shape and sizes of scaffolds have been used in numerous in vivo investigations to promote bone healing [34,35,36,37,38,39], and can be associated with cells or growth factors to enhance osteoinductive and/or osteoconductive properties [40,41]. The use of composite beads seems preferable for some clinical applications, because they could be injectable and easy to handle and adapt to the morphology of any defect [42], as seen previously in a clinical trial [43]
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