الفهرس 
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Abstract
Summary
Large bony defects are serious complications that are most commonly caused by extensive trauma, tumor, infection, or congenital musculoskeletal disorders. If nonunion occurs, implantation for repairing bone defects with biomaterials developed as a defect filler, which can promote bone regeneration, is essential and challenging and the choice between using different degradable devices for maxillofacial applications must be carefully weighed to fulfill the need in specific applications as alveolar ridge augmentation, defect filling after tumor or cyst removal, ridge fixation or as carriers of cells for bone renewal.
The aim of this study was to develop a composite scaffold at which the rate of biodegradation could be controlled to meet different applications and various bone types, and to evaluate the effect of incorporation of hydroxyapatite (incorporated to enhance regeneration) on the degradation rate of scaffolds and evaluate the properties of scaffolds after treatment with different crosslinkers.
Chitosan gelatin scaffolds and hydroxyapatite containing chitosan gelatin scaffolds were prepared using the freezedrying method for fabrication and were further crosslinked with gluteraldehyde and genipin with the least cytotoxic concentrations (1% and 0.1% respectively).
Prepared scaffolds were then evaluated for their biodegradation rate, swelling behaviour, thermal stability, mechanical performance and their effect on cell viability and proliferation.
For biodegradation results we were able to control the rate of degradation to be compatible with different rates of bone formation according to the bone type using the two types of crosslinkers.
The swelling behaviour of the scaffolds was not compromised by various crosslinking protocols which was necessary for adhesion to the walls of the bony defect for TE. Moreover, the thermal behaviour of the polymeric scaffolds was also found to be enhanced using gluteraldehyde and genipin as crosslinkers.
Crosslinking had a pronounced effect on the compressive strength of the polymeric scaffolds together with the addition of the nanohydroxyapatite in a concentration of 10%, but the increase in the concentration of the hydroxyapatite up to 30% had several drawbacks on the mechanical properties, cell viability and proliferation.
Cell culture studies were performed to assess the effect of crosslinking agents that was assumed to have a cytotoxic effect on the cells in contact with the scaffolds, the natural crosslinker (genipin) was found to be more compatible and to enhance proliferation of cells after following an appropriate washing protocol to get rid of any cytotoxic residues.
But gluteraldehyde, even after the washing protocol, still was more cytotoxic to the cells and cell proliferation was not favoured on the gluteraldehyde crosslinked scaffolds as on genipin crosslinked ones but was still in the accepted range.
Conclusions
1. Properties of chitosan/gelatin scaffolds could be optimized by crosslinking and adjustment of the percentage of bioactive materials to match the conditions of bone growth in a bony defect.
2. Genipin crosslinked scaffolds could be a potential replacement of cartilage and spongy bone regarding the degradation rate and mechanical properties.
3. Gluteraldehyde crosslinked scaffolds were found to be appropriate for replacement of compact bone regarding the degradation rate.
4. The compressive strength of the highest group (chitosan/gelatin with 10% hydroxyapatite –cross-linked with gluteraldehyde) was still far from that needed for the cortical bone but near to that of spongy bone.
5. Addition of hydroxyapatite at a concentration of 10% improved the properties of the scaffolds and did not compromise the structural integrity of the polymer.
6. Cell viability and proliferation of the scaffolds are not affected by using the appropriate crosslinking protocols.