Hadi Goldansaz

Viscoelastic properties of linear associating poly(n-butyl acrylate) chains

The linear viscoelastic properties of entangled hydrolysed poly(n-butyl acrylate) PnBA copolymers, with varying density of functional moieties, i.e., acrylic acid (AA) groups, have been investigated both experimentally and theoretically using small amplitude oscillatory shear and a modified version of the time marching algorithm (TMA). A second, low frequency, plateau, the level of which depends on temperature and AA groups content, is evident in the storage modulus of these copolymers. It indicates that terminal flow, i.e., chain motion at large length scales, is highly suppressed within the experimental timescale. This slow relaxation process is attributed to long lifetime aggregates (sticky junctions) of AA groups. At intermediate frequencies, the dynamic moduli decay with a slope of 0.5 indicative of a Rouse-like relaxation process. This behavior is well captured by the model when constraint release Rouse motion of the strands that are trapped between successive AA junctions or/and trapped entanglements is considered. One new parameter, pst, the probability of a monomer to act as a sticky junction, is introduced in the TMA to account for the influence of the functional AA groups on the chain dynamics. The validation of this simple model is then achieved by comparing experimental and predicted viscoelastic data.

The type and composition of alginate and hyaluronic-based hydrogels influence the viability of stem cells of the apical papilla

OBJECTIVE The goal of the present work was to evaluate in vitro and in vivo the influence of various types and compositions of natural hydrogels on the viability and metabolic activity of SCAPs. METHODS Two alginate, three hyaluronic-based (Corgel™) hydrogel formulations and Matrigel were characterized for their mechanical, surface and microstructure properties using rheology, X-ray photoelectron spectroscopy and scanning electron microscopy, respectively. A characterized SCAP cell line (RP89 cells) was encapsulated in the different experimental hydrogel formulations. Cells were cultured in vitro, or implanted in cyclosporine treated mice. In vitro cell viability was evaluated using a Live/Dead assay and in vitro cellular metabolic activity was evaluated with a MTS assay. In vivo cell apoptosis was evaluated by a TUNEL test and RP89 cells were identified by human mitochondria immunostaining. RESULTS Hydrogel composition influenced their mechanical and surface properties, and their microstructure. In vitro cell viability was above 80% after 2 days but decreased significantly after 7 days (60-40%). Viability at day 7 was the highest in Matrigel (70%) and then in Corgel 1.5 (60%). Metabolic activity increased over time in all the hydrogels, excepted in alginate SLM. SCAPs survived after 1 week in vivo with low apoptosis (<1%). The highest number of RP89 cells was found in Corgel 5.5 (140cells/mm(2)). SIGNIFICANCE Collectively, these data demonstrate that SCAP viability was directly modulated by hydrogel composition and suggest that a commercially available hyaluronic acid-based formulation might be a suitable delivery vehicle for SCAP-based dental pulp regeneration strategies.