Advances and Perspectives in Dental Pulp Stem Cell Based Neuroregeneration Therapies

Human dental pulp stem cells (hDPSCs) are some of the most promising stem cell types for regenerative therapies given their ability to grow in the absence of serum and their realistic possibility to be used in autologous grafts. In this review, we describe the particular advantages of hDPSCs for neuroregenerative cell therapies. We thoroughly discuss the knowledge about their embryonic origin and characteristics of their postnatal niche, as well as the current status of cell culture protocols to maximize their multilineage differentiation potential, highlighting some common issues when assessing neuronal differentiation fates of hDPSCs. We also review the recent progress on neuroprotective and immunomodulatory capacity of hDPSCs and their secreted extracellular vesicles, as well as their combination with scaffold materials to improve their functional integration on the injured central nervous system (CNS) and peripheral nervous system (PNS). Finally, we offer some perspectives on the current and possible future applications of hDPSCs in neuroregenerative cell therapies.     

Influence of the processing parameters and composition on the thermal stability of PLA/nanoclay bio‐nanocomposites

Poly(lactic acid) (PLA) is one the most promising bio‐based and biodegradable polymer. However, its low thermal stability limits the range of applications and complicates its transformation via the most industrial common processes. The novelty of this work is studying the thermal stability of PLA and PLA/clay nanocomposites during use, as a function of the composition and using a wide range of extrusion and injection moulding processing parameters. To improve the thermal stability of the PLA, laminar silicates containing different organomodifications have been added (Cloisite 20A and Cloisite 30B). The results show that the processing conditions and composition define the morphology of the bio‐nanocomposites, which plays key role in defining final thermal properties of the material. In general, clays improve the thermal stability of the processed material, increasing the degradation temperature and decreasing the degradation rate under a wide range of processing conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40747.     

Preparation of water-borne dispersions of polyolefins: new systems for the study of homogeneous nucleation of polymers

Very stable water-borne dispersions of homogeneous ethylene-1-octene (EO) copolymers and of maleic anhydride grafted polypropylene (PP-g-MA) were prepared. A Haake blender was used for dispersing the EO copolymers in water, and for the first time (in case of ‘normal’ molar mass) the use of a non-ionic surfactant turned out to be feasible. A stirred pressure vessel was used for dispersing the PP-g-MA in water beyond its boiling point. Particles having sizes down to submicrometer scale were generated in a controlled way and in large quantities. A study of crystallization of the dispersed particles by DSC reveals a correlation between particle size distribution and crystallization mode. Dispersions of PP-g-MA of sizes from 100 to 200 μm down to sizes below 0.04 μm show heterogeneous, fractionated and homogeneous modes of crystallization and mixtures thereof, respectively, partly under confined conditions. The lowest crystallization peak temperature and the largest extra supercooling ever observed for PP in analogous experiments, 33 and 77 °C, respectively, were realized.     

Quantitative evaluation of fractionated and homogeneous nucleation of polydisperse distributions of water-dispersed maleic anhydride-grafted-polypropylene micro- and nano-sized droplets

The nucleation processes in waterborne Maleic Anhydride-grafted-Polypropylene micro- and nano-droplet suspensions have been studied. Compared to a previous report on this topic, an extended set of samples in combination with improved particle size distribution data of the samples have been used, which are both essential for the advancement of the analysis.Self-nucleation was utilized to ensure that the observed lowered fractionated crystallization (peak) temperatures – down to the extremely low value of 34 °C – are due to a lack of seeds in the droplets, which seeds for the polypropylene system used are normally active at the heterogeneous crystallization temperature of approximately 110 °C. An unusual self-nucleation behavior was observed in case of samples having a large amount of small droplets, requiring an extremely low self-nucleation temperature in order to suppress all crystallization at the lowest temperatures. Such behavior was observed for block copolymers but has not been reported so far for droplets dispersed in an immiscible matrix, polymeric or not. Another unusual behavior was observed for some self-nucleation temperatures for which apparently two different populations of self-nuclei are created that are suggestive of the α₁ and α₂ crystal structures of isotactic polypropylene.Next, two new methods are presented to quantify various crucial parameters of the nucleation process: one estimates the density of nucleants acting at different temperatures from the combination of dynamic DSC data and particle size distribution (PSD) data, and the other one focuses on the nature of the nucleation mechanism using both isothermal DSC data and PSD data, quantifying the nucleation rate at different temperatures. For the present MA-g-PP dispersions the latter method leads to the conclusion that the lowest crystallization temperatures reflect sporadic nucleation, probably by way of volume (homogeneous) nucleation.In the field of polymer crystallization, polymer dispersions are usually treated as being monodisperse, even though that is rarely the case. This simplification is inadequate for the present calculations, which is why polydispersity has been taken into account in order to quantify the density of nucleants and the kinetics of nucleation. Though in the present study DSC data are used for the calculations, the methods developed can be easily adapted to other techniques like time-resolved X-ray, rheometry and dilatometry.     

Influence of the modification with MWCNT on the interlaminar fracture properties of long carbon fiber composites

This paper reports the processing of a carbon fiber reinforced epoxy composite with carbon nanotube integration and examines the potential improvement on the interlaminar toughness. Carbon nanotube enhanced composites were fabricated by spreading a solution of reinforcing nanoparticles between prepreg layers with the aid of an airbrush. The influence of MWCNTs incorporation has been studied by the End Notched Flexure (ENF) test by means of a new test methodology named “Beam Theory including Bending Rotation effects” (BTBR) proposed recently. This method allows the determination of the critical energy release rate at each point of the test when stable crack advance occurs, obtaining the R-curve. A maximum increase of 22% in initiation fracture toughness was observed in the samples with functionalized CNTs. Moreover, the propagation fracture toughness increased 14%.