Silvia Agnelli

Facile fabrication of shape memory poly(ε-caprolactone) non-woven mat by combining electrospinning and sol–gel reaction

Poly(e-caprolactone)-based non-woven fibrous mats showing excellent one-way shape memory properties were obtained through a straightforward approach by combining electrospinning process and sol–gel reaction. A solution of partially crosslinked α,ω-triethoxysilane-terminated poly(e-caprolactone) was used to obtain bead-free fibers through electrospinning. Non-woven mats with different crosslinking degrees have been prepared and the effect of the different crosslinking extent and of the microfibrous structure were correlated to the mechanical and shape memory properties of the material. The evolution of fiber architecture within the non-woven mat following deformation and shape memory cycles was also investigated.

Preparation and properties of high performance gelatin-based hydrogels with chitosan or hydroxyethyl cellulose for tissue engineering applications

ABSTRACT High performance gelatin-based biocompatible hybrid hydrogels are developed using functionalized polyethylene glycol as a cross-linker in presence of chitosan or hydroxyethyl cellulose. Tensile test shows robust and tunable mechanical properties and reveals non-linear and J-shaped stress-strain curves similar to those found for native extracellular matrix. Degradation study demonstrates that the mass loss and change in mechanical properties are dependent on hydrogel composition and cross-linking density. Structural features of the hydrogels are confirmed by infrared spectroscopy. A preliminary biological evaluation is carried out using rat myoblasts and human fibroblasts cell lines. The results show that all hydrogels allow cell adhesion and proliferation during four days culture, hence, they might have a great potential for use in the biomedical applications. GRAPHICAL ABSTRACT

Hybrid filler systems in rubber nanocomposites

Abstract In this chapter, hybrid filler systems in rubber nanocomposites are discussed, starting from the definition of a hybrid system. In particular, the chapter is dedicated to systems based on the combination of nano- and nanostructured fillers, that have been largely investigated in the literature and have, in some cases, found commercial applications. They are those based on either organoclay or carbon nanotubes or nanographite as the nanofillers and either carbon black or silica as the nanostructured fillers. Structure and aspects of the nanocomposites, such as curing, tensile, and dynamic-mechanical properties, tear and abrasion resistance, electrical and thermal conductivity, and impermeability, are discussed. Synergistic effects by the nanofillers on the nanocomposites properties are presented, attempting a rationalization on the basis of the available data.

Two-Way Shape Memory Behavior of Electrospun Non-Woven Mats Prepared from Sol-Gel Crosslinked Poly(ε-Caprolactone)

Non-woven fibrous mats based on semicrystalline networks were prepared starting from poly(ε-caprolactone) and by combining electrospinning process and sol-gel crosslinking reaction. The mats were subjected to proper thermo-mechanical cycles to investigate their two-way shape memory capabilities (i.e. the possibility to change between two distinguished shapes upon heating and cooling), and an improvement of the two-way behaviour was researched through the application of a training cycle. An ex-situ SEM analysis described the microstructural evolution accompanying the two-way shape memory cyclic response.

Novel nanobiocomposite hydrogels based on gelatin/chitosan and functionalized graphene

Composites of gelatin, chitosan and graphene layers functionalized with serinol pyrrole, containing hydroxyl groups, were prepared to create electrically conductive, mechanically robust and biodegradable hydrogels. The incorporation of hydrophilic graphene layers (up to 1% mass in wet condition) into the polymer matrix significantly improved mechanical and electrical properties. These composite hydrogels are promising candidates for use as conducting substrates for the growth of electro-responsive cells in tissue engineering.

High performance gelatin/polyethylene glycol macroporous hydrogels for biomedical applications

Hydrogel has been bourgeoning in recent years as a scaffold in the tissue engineering thanks to its excellent ability to mimic natural extracellular matrix (ECM). Driven by enormous potential of hydrogels, we have developed a green, facile and simple synthesis approach to fabricate gelatin/polyethylene glycol (G/PEG) macroporous hydrogels by three steps process consist of gelation, lyophilization and post curing. Poly(ethylene glycol) diglycydyl ether (PEGDGE) was used as a crosslinking agent. The effect of altering the composition on hydrogel structure, mechanical properties, swelling and degradation resistance was evaluated by adding hydroxyethyl cellulose (HEC) into G/PEG system. Structural features and crosslinking interaction of the hydrogels were confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The morphology of the porous hydrogels was studied by scanning electron microscopy. Mechanical properties were measured by uniaxial tensile tests, and the characterization revealed non-linear and J-shaped stress-strain curves for all hydrogels, similar to those found for native ECM. The mechanical integrity of the hydrogels was monitored during hydrolytic degradation over time.Hydrogel has been bourgeoning in recent years as a scaffold in the tissue engineering thanks to its excellent ability to mimic natural extracellular matrix (ECM). Driven by enormous potential of hydrogels, we have developed a green, facile and simple synthesis approach to fabricate gelatin/polyethylene glycol (G/PEG) macroporous hydrogels by three steps process consist of gelation, lyophilization and post curing. Poly(ethylene glycol) diglycydyl ether (PEGDGE) was used as a crosslinking agent. The effect of altering the composition on hydrogel structure, mechanical properties, swelling and degradation resistance was evaluated by adding hydroxyethyl cellulose (HEC) into G/PEG system. Structural features and crosslinking interaction of the hydrogels were confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The morphology of the porous hydrogels was studied by scanning electron microscopy. Mechanical properties were measured by uniaxial tensile tests, and the characte...

Mechanical reinforcement in a polyisoprene rubber by hybrid nanofillers

Melt blending of hybrid nanofillers with rubber matrices could make rubber nanocomposites more attractive for industrial applications. In this work, the low-amplitude dynamic shear modulus of polyisoprene rubber filled with carbon nanotubes or nano-graphite, individually or in combination with carbon black, was measured. A rationalisation of the results highlighted interactive effects of carbon allotropes on the mechanical reinforcement of rubber nanocomposites. The filler–matrix interfacial area was identified as a parameter able to correlate the moduli values of different fillers, by reducing them to a common master curve.

Macroporous hydrogels with tailored morphology and mechanical properties

In this work it is shown that hydroxyethylcellulose (HEC) can be employed for preparing macroporous polyacrylamide (PAAm) hydrogels with tailored morphology and mechanical properties. By changing the HEC content in the reaction mixture hydrogels with different pore sizes and degrees of interconnectivity can be synthesized. The equilibrium swelling ratio in 0.1 M NaCl increases with the amount of HEC employed. Tensile tests run on equilibrated hydrogels show that these materials behave as rubber-like materials. Their mechanical stiffness decreases regularly as the amount of HEC, and therefore their porosity, is increased. A more complex trend is observed for elongation and stress at break, which display a maximum at intermediate contents of HEC.

Interactive effects between carbon allotropes on the mechanical reinforcement of nanocomposites based on poly(1,4-cis-isoprene)

Interactive effects of carbon allotropes on the mechanical reinforcement of polymer nanocomposites were investigated by using, as the polymer matrix, poly(1,4-cis-isoprene) (PI) samples from industrial synthesis and from natural sources. Carbon nanotubes (CNT) and nano-graphite with high shape anisotropy (nanoG) were melt blended with PI, as the only fillers or in combination with carbon black (CB), measuring the shear modulus at low strain amplitudes. The nanofiller was found to increase the low amplitude storage modulus of the matrix, with or without CB, by a factor depending on nanofiller type and content. The filler-polymer interfacial area was able to correlate modulus data of composites with CNT, CB and with the hybrid filler system, leading to the construction of a common master curve. The filler networking phenomenon was found to be affected by type and amount of low molecular mass products of PI from natural sources. The correlation between chemical composition, dynamic mechanical and ultimate pr...

The load separation criterion in elastic-plastic fracture mechanics: Rate and temperature dependence of the material plastic deformation function in an ABS resin

This work is aimed at analyzing the effects of temperature and loading rate on the plastic deformation behavior of an acrylonitrile-butadiene-styrene (ABS) resin during a fracture process. According to the load separation criterion, the plastic deformation behavior during the fracture process of an elastic-plastic material is described by a plastic deformation function. For the ABS here examined, the material plastic deformation function was constructed at different temperatures and loading rates, by single edge notched in bending (SEB) tests on blunt notched specimens. Both low and moderately high (impact) loading rates were explored. For the various conditions of temperature and loading rate the material yield stress was also measured by uniaxial tensile tests. The relationships between material deformation function and yield stress were researched and discussed.