Both Tough and Soft Double Network Hydrogel Nanocomposite Based on O-Carboxymethyl Chitosan/Poly(vinyl alcohol) and Graphene Oxide: A Promising Alternative for Tissue Engineering
POLYMER ENGINEERING AND SCIENCE
Authors: Pourjavadi, Ali; Tehrani, Zahra Mazaheri; Salami, Hamid; Seidi, Farzad; Motamedi, Anahita; Amanzadi, Amirhossein; Zayerzadeh, Ehsan; Shabanian, Meisam
Abstract
A reinforced double network (DN) hydrogel as a candidate for skin scaffold was prepared. It consists of O-carboxymethyl chitosan, polyvinyl alcohol, honey, CaCl2, and graphene oxide. The various concentrations of CaCl2, namely, 30, 45, and 60 wt% were investigated. Besides, the GO content was studied as 3, 5, and 10 wt%. The structure of the DN was characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, energy dispersive X-ray and Brunauer-Emmett-Teller were evaluated. The mechanical properties were studied, too. It showed that the DN with 45 wt% CaCl2 was optimized. Also, swelling mechanism was investigated. Moreover, with the increase in GO content, the mechanical strength was increased. The cytotoxicity was evaluated and it was indicated that DN with 45% CaCl2 and 5% GO had an acceptable level of biocompatibility. Moreover, scanning electron microscopy images showed the porous structure of the DN nanocomposite. Thus, the DN has the potential to be applied in tissue engineering as a skin scaffold. POLYM. ENG. SCI., 2020. (c) 2020 Society of Plastics Engineers
The effect of moisture on the nonlinearly viscoelastic behavior of an epoxy
MECHANICS OF TIME-DEPENDENT MATERIALS
Authors: Vieira de Mattos, Daniel Ferreira; Huang, Rui; Liechti, Kenneth M.
Abstract
The shear and bulk relaxation moduli required to characterize a homogeneous, isotropic, and linearly viscoelastic material were determined using a confined compression experiment and by introducing a new iterative scheme that accounts for the fact that the hoop and radial strains are not step functions. In addition, the coefficients of thermal and hygral expansion of the epoxy being considered were determined along with its diffusive behavior. Fickian diffusion of moisture was confirmed by coupling radial diffusion in an epoxy disk with optical interference measurements of the out-of-plane displacements. These properties are essential components of the modified free-volume model of nonlinear viscoelasticity established by Popelar and Liechti (J. Eng. Mater. Technol. 119:205-210, 1997, Mech. Time-Depend. Mater. 7(2):89-141, 2003). For the nonlinear component of the model, its distortional parameters were evaluated from Arcan pure shear test results at one strain rate and temperature/humidity state. The nonlinear viscoelasticity model was then used to predict the shear stress-strain response under other conditions. The dilatational parameters were extracted from uniaxial tensile test results at one strain rate and temperature humidity state and predictions under other conditions compared favorably with the results from experiments. This exercise adds to a growing list of glassy polymers whose nonlinear stress-strain behavior can be modeled by this modified free-volume model.