Strontium-doped hydroxyapatite polysaccharide materials effect on ectopic bone formation.

Previous studies performed using polysaccharide-based matrices supplemented with hydroxyapatite (HA) particles showed their ability to form in subcutaneous and intramuscular sites a mineralized and osteoid tissue. Our objectives are to optimize the HA content in the matrix and to test the combination of HA with strontium (Sr-HA) to increase the matrix bioactivity. First, non-doped Sr-HA powders were combined to the matrix at three different ratios and were implanted subcutaneously for 2 and 4 weeks. Interestingly, matrices showed radiolucent properties before implantation. Quantitative analysis of micro-CT data evidenced a significant increase of mineralized tissue formed ectopically with time of implantation and allowed us to select the best ratio of HA to polysaccharides of 30% (w/w). Then, two Sr-substitution of 8% and 50% were incorporated in the HA powders (8Sr-HA and 50Sr-HA). Both Sr-HA were chemically characterized and dispersed in matrices. In vitro studies performed with human mesenchymal stem cells (MSCs) demonstrated the absence of cytotoxicity of the Sr-doped matrices whatever the amount of incorporated Sr. They also supported osteoblastic differentiation and activated the expression of one late osteoblastic marker involved in the mineralization process i.e. osteopontin. In vivo, subcutaneous implantation of these Sr-doped matrices induced osteoid tissue and blood vessels formation.

In vitro assessment of a collagen/alginate composite scaffold for regenerative endodontics.

AIM: To develop a biological scaffold that could be moulded to reproduce the geometry of a gutta-percha point with precision and allow the differentiation of mesenchymal stem cells into osteoblasts to be used as a regenerative endodontic material. METHODOLOGY: A collagen/alginate composite scaffold was cast into a sodium alginate mould to produce a gutta-percha point-like cone. Prior to gelation, the cone was seeded with human stem cells from the apical papilla (SCAPs) to evaluate cell/scaffold interactions. The reconstructed tissue was characterized after 8 days in culture. Elastic modulus, tissue compaction and cell differentiation were assessed. Student t-tests and the Mann-Whitney U test were performed. RESULTS: The fabrication method developed enabled the shape of a gutta-percha point to be mimicked with great accuracy and reproducibility (P = 0.31). Stem cells seeded into this composite scaffold were able to spread, survive and proliferate (P < 0.001). Moreover, they were able to differentiate into osteoblasts and produce calcified osseous extracellular matrix (P < 0.001). The construct showed no significant contraction after 8 days, preserving its shape and tip diameter (P = 0.58). CONCLUSIONS: The composite scaffold could present substantial benefits compared to synthetic materials. It could provide a favourable healing environment in the root canal conducive for regenerative endodontics and is therefore appropriate to be evaluated in vivo in further studies.