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A comparative study of nano-fillers to improve toughness and modulus of polymer-derived ceramics.

ABSTRACT: Brittleness is a major limitation of polymer-derived ceramics (PDCs). Different concentrations of three nanofillers (carbon nanotubes, Si₃N₄ and Al₂O₃ nanoparticles) were evaluated to improve both toughness and modulus of a commercial polysilazane (PSZ) PDC. The PSZs were thermally cross-linked and pyrolyzed under isostatic pressure in nitrogen. A combination of mechanical, chemical, density, and microscopy characterizations was used to determine the effects of these fillers. Si₃N₄ and Al₂O₃ nanoparticles (that were found to be active fillers) were more effective than nanotubes and improved the elastic modulus, hardness, and fracture toughness (J_IC) of the PDC by ~ 1.5 ×, ~ 3 ×, and ~ 2.5 ×, respectively. Nanotubes were also effective in maintaining the integrity of the samples during pyrolysis. The modulus and hardness of PDCs correlated positively with their apparent density; this can provide a fast way to assess future PDCs. The improvement in fracture toughness was attributed to crack deflection and bridging observed in the micro-indentation cracks in the modified PDCs. The specific toughness of the modified PDCs was 4 × higher than that of high-purity alumina, and its specific modulus reached that of commercially available technical ceramics. These PDCs can also easily take different shapes and therefore are of interest in protective armor, propulsion, thermal protection, device packaging and biomaterial systems.

SUBMITTER: Mirkhalaf M

PROVIDER: S-EPMC7997883 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Despite efforts to mature human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) for disease modeling and high throughput screening, cells remain immature and may not reflect adult biology. Recent advancements utilize electro-mechanical and paracrine stimulation to functionally mature cardiomyocytes, but the resulting engineered constructs continue to lack a microenvironment conducive to electrical signal propagation and maturity. Conductive polymers are attractive candidates to facilitate electrical communication between gaps in sparse hPSC-CM clusters or between hPSC-CMs to repair conduction defects. To create a conductive polymer platform for improved electrical signal propagation between hPSC-CMs and achieve electrical maturity, we electrospun poly(3,4-ethylendioxythiophene):polystyrene sulfonate (PEDOT:PSS) blended with 8% (w/v) poly(vinyl alcohol) (PVA). Matrix fiber structure remained stable over 4 weeks in buffer, stiffness remains near cardiac stiffness in vivo, and electrical conductivity scaled with PEDOT:PSS concentration. When fibroblasts were added to fibers, cells had higher initial attachment to PEDOT:PSS compared to PVA-only scaffolds, and after 5 days, over 90% of fibroblasts remained viable on PEDOT:PSS scaffolds compared to PVA-only scaffolds. Electrically excitable hPSC-CMs cultured on conductive substrates exhibited an upregulation of cardiac and muscle-related genes as opposed to non-conductive substrates. These cells further displayed increased desmoplakin (DP) localization on conductive scaffolds, indicating an improvement in the mechanical stability of our hPSC-CMs. Sarcomere organization also scaled with increasing PEDOT:PSS concentration, even in sub-monolayer cell densities, suggesting that improved organization of the contractile machinery in these cells was due to the electrical condition of the matrix. Calcium handling indicated higher calcium flux with a shorter time to peak, further suggesting improved electrical maturity, even when sub-confluent. Taken together, these data suggest that PEDOT:PSS/PVA scaffolds are stable, of a stiffness relevant to cardiomyocytes, and supportive of electrical coupling even in the absence of a monolayer, which may improve cardiac disease modeling and drug development.

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A comparative study of nano-fillers to improve toughness and modulus of polymer-derived ceramics.

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