The effect of polyacrylonitrile nanofibrous interlaminar layers on the impact properties of unidirectional and woven carbon fabric (CF)-reinforced epoxy (EP) matrix composites was investigated. The nanofibers were produced directly on the surface of carbon fabrics by a needleless electrospinning method, and composites were then prepared by vacuum-assisted impregnation. Interlaminar shear stress tests, three-point bending, Charpy-impact and instrumented falling weight tests were carried out. The fracture surfaces were analyzed by scanning electron microscopy. Due to the nano-sized reinforcements, the interlaminar shear strength of the woven and unidirectional fiber-reinforced composites was enhanced by 7 and 11%, respectively. In the case of the falling weight impact tests carried out on woven reinforced composites, the nanofibers increased the absorbed energy to maximum force by 64% compared to that measured for the neat composite. The Charpy impact tests indicated that the nanofiber interleaves also led to a significant increase in the initiation and total break energies. Based on the results, it can be concluded that the presence of nanofibers can effectively increase the impact properties of composites without compromising their in-plane properties because the thickness of the composites was not altered by the presence of interleaves. The improvement of the impact properties can be explained by the good load distribution behavior of the nanofibers

Platelet-rich fibrin (PRF) membrane is a three-dimensional biodegradable biopolymer, which consists of platelet derived growth factors enhancing cell adhesion and proliferation. It is widely used in soft and hard tissue regeneration, however, there are unresolved problems with its clinical application. Its preparation needs open handling of the membranes, it degrades easily, and it has a low tensile strength which does not hold a suture blocking wider clinical applications of PRF. Our aim was to produce a sterile, suturable, reproducible PRF membrane suitable for surgical intervention. We compared the biological and mechanical properties of PRF membranes created by the classical glass-tube and those that were created in a single-syringe closed system (hypACT Inject), which allowed aseptic preparation. HypACT Inject device produces a PRF membrane with better handling characteristics without compromising biological properties. Freeze-thawing resulted in significantly higher tensile strength and higher cell adhesion at a lower degradation rate of the membranes. Mesenchymal stem cells seeded onto PRF membranes readily proliferated on the surface of fresh, but even better on freeze/thawed or freeze-dried membranes. These data show that PRF membranes can be made sterile, more uniform and significantly stronger which makes it possible to use them as suturable surgical membranes.

Crystalline properties of semicrystalline polymers are very important parameters that can influence the application area. The internal structure, like the mentioned crystalline properties, of polymers can be influenced by the production technology itself and by changing technology parameters. The present work is devoted to testing of electrospun and centrifugal spun fibrous and nanofibrous materials and compare them to foils and granules made from the same raw polymer. The test setup reveals the structural differences caused by the production technology. Effects of average molecular weight are also exhibited. The applied biodegradable and biocompatible polymer is polycaprolactone (PCL) as it is a widespread material for medical purposes. The crystallinity of PCL has significant effect on rate of degradation that is an important parameter for a biodegradable material and determines the applicability. The results of differential scanning calorimetry (DSC) showed that, at the degree of crystallinity, there is a minor difference between the electrospun and centrifugal spun fibrous materials. However, the significant influence of polymer molecular weight was exhibited. The morphology of the fibrous materials, represented by fiber diameter, also did not demonstrate any connection to final measured crystallinity degree of the tested materials.