Enhancement of periodontal tissue regeneration by locally controlled delivery of insulin-like growth factor-I from dextran–co-gelatin microspheres

The present work focused on the design of novel hydrogel microspheres based on both dextran- and gelatin-derived biomaterials, and discussed whether locally controlled delivery of IGF-I from dextran–co-gelatin hydrogel microspheres (DG-MP) was useful for periodontal regeneration enhancement. Microspheres were synthesized when gelatin was cooperating with glycidyl methacrylate (GMA) derivatized dextrans (Dex-GMA) and the resultant DG-MP with a hydrogel character of which the cross-linking density could be controlled by the degree of substitution (DS, the number of methacrylates per 100 glucopyranose residues) of Dex-GMA. In this study, three types of DG-MP (DG-MP4.7, DG-MP6.3 and DG-MP7.8) obtained from gelatin and Dex-GMA (differing in DS: 4.7, 6.3 and 7.8 respectively) were prepared and characterized by swelling and degradation properties, drug release kinetics and biological capability in promoting tissue regeneration. By swelling in aqueous positively charged IGF-I solutions, the protein could be encapsulated in DG-MP by polyionic complexation with negatively charged acidic gelatin. No obvious influence of Dex-GMA's DS on DG-MP's configuration and size was observed, and the release and degraded properties showed no significant difference between three types of DG-MP in PBS buffer either. However, high DS of Dex-GMA could lower microsphere's swelling, prolong its degraded time and minimize IGF-I burst release markedly in dextranase-containing PBS, where IGF-I release from a slow release type of microspheres (DG-MP7.8) could be maintained more than 28 days, and an effective protein release kinetics without a significant burst but a relevantly constant release after the initial burst was achieved. IGF-I in DG-MP resulted in more new bone formation in the periodontal defects within 4 or 8 weeks than IGF-I in blood clot directly did (P < 0.01). The observed newly formation of periodontal tissues including the height and percentage of new bone and new cementum on the denuded root surfaces of the furcation area in DG-MP7.8 group were more than that in other groups (P < 0.05). The adequate width of regenerative periodontal ligament (PDL), regular Sharpey's fibers and alveolar bone reconstruction could be observed only in DG-MP7.8 group. These combined results demonstrate that effective release kinetics can be realized by adjusting the DS of Dex-GMA and followed cross-linking density of DG-MP, and that locally controlled delivery of IGF-I from slow release type of DG-MP may serve as a novel therapeutic strategy for periodontal tissue regeneration.