Epoxy resin composites with different weight fractions of TiO 2 microparticles (1%, 5%, 10%, 15%, 20%) and of TiO 2 nanoparticles (0.5%, 1%, 2%, 3%) were prepared. The particle size of the nanoparticles was averaged around 21 nm while the particle size of the micro TiO 2 particles was averaged around 0.2 µm. The morphology of the manufactured particulate composites was studied by means of scanning electron microscopy (SEM). The mechanical properties of both nanocomposites (21 nm) and microcomposites (0.2 µm) were investigated and compared through flexural testing. Furthermore, the effect of displacement-rate on the viscoelastic behavior of composite materials was investigated. The flexural tests were carried out at different filler weight fractions and different displacement-rates (0.5, 5, 10, 50 mm/min). The influence of TiO 2 micro-and nanoparticles on the mechanical response of the manufactured composites was studied. For micro TiO 2 composites, a maximum increase in flexural modulus on the order of 23% was achieved, while, in the nanocomposites, plastification of the epoxy matrix due to the presence of TiO 2 nanoparticles was observed. Both behaviors were predicted by the Property Prediction Model (PPM), and a fair agreement between experimental results and theoretical predictions was observed.Polymers 2020, 12, 22 2 of 13 in improving the mechanical properties of the composite. The lower the filler diameter, the higher the filler surface/contact area is. Thus, in case of micron sized particles, the size of the low-density interfacial region of the pure polymer surrounding the inclusion is higher, so that the contribution of the filler is reduced, concluding that the mechanical properties of the composite will not be improved that much [6]. On the contrary, the nanoparticles can fill up the weak regions within the epoxy resin, and thus increasing the filler-matrix interaction force. The increase of the extent interfacial region can significantly improve the mechanical properties of the epoxy/nanocomposite. However, the nanoparticles have a difficulty to disperse into the matrix, so it is crucial to find the proper manufacturing technique to improve particle dispersion within the matrix material. A technique that is commonly applied is the ultrasonic homogenization; however, as every technique has its disadvantages. More precisely, this technique decreases the gelling time of the epoxy resin [7][8][9][10][11].The mechanical response of particulate reinforced composites also depends on the rate of deformation. It was found that particulates increase the strain rate sensitivity concerning tensile modulus, but this sensitivity decreases when measuring yield strength [12]. The effect of strain rate on the flexural properties of some polymer matrix composites has been studied and, as it was found, the flexural modulus and flexural strength both increase linearly with the logarithm of the strain rate [13]. Furthermore, the strain-rate sensitivity seems to be slightly more pronounced in shear than in tension and comp...

Recent decades have seen a plethora of regenerating new tissues in order to treat a multitude of cardiovascular diseases. Autografts, xenografts and bioengineered extracellular matrices have been employed in this endeavor. However, current limitations of xenografts and exogenous scaffolds to acquire sustainable cell viability, anti-inflammatory and non-cytotoxic effects with anti-thrombogenic properties underline the requirement for alternative bioengineered scaffolds. Herein, we sought to encompass the methods of biofabricated scaffolds via 3D printing and bioprinting, the biomaterials and bioinks recruited to create biomimicked tissues of cardiac valves and vascular networks. Experimental and computational designing approaches have also been included. Moreover, the in vivo applications of the latest studies on the treatment of cardiovascular diseases have been compiled and rigorously discussed.

No abstract

Computational methods were combined with an experimental setup in order to investigate the response of human umbilical cord stem cells to 3D electrospun and printed scaffolds, when dynamically stimulated in a bioreactor. Key parameters associated to bioreactor working conditions were computationally investigated using Comsol software to use the output for the planned experimental setup. Based on the theoretical observations, the influence of the inlet velocity, cell number, and exposure time in the bioreactor were analyzed and the in vitro parameters were adjusted accordingly. MSCs were seeded in different numbers in the 3D porous scaffolds and stimulated in the bioreactor (0.5 and 2 h duration, 3 and 6 mm/s inlet velocity). Polycaprolactone 3D electrospun, and polyurethane and polylactic acid 3D-printed scaffolds were fabricated and fibronectin-coated. The computational study predicted initial events in the process of cells deposition and attachment. Total protein, osteopontin, and osteocalcin levels in cells deposited in scaffolds were investigated; SEM and confocal imaging confirmed the biomarker analysis. MSCs proliferated well in PCL. Polyurethane enabled extremely rapid proliferation followed by differentiation, while PLA induced a moderate proliferation and parallel mineralization. The scaffolds stiffness has been found as the key enabling parameter decisive for cells feedback.