Through-thickness stress relaxation in bacterial cellulose hydrogel

Biphasic Properties of PVAH (Polyvinyl Alcohol Hydrogel) Reflecting Biomechanical Behavior of the Nucleus Pulposus of the Human Intervertebral Disc

PVAH is a mixture of solid and fluid, but its mechanical behavior has usually been described using solid material models. The purpose of this study was to obtain material properties that can reflect the mechanical behavior of polyvinyl alcohol hydrogel (PVAH) using finite element analysis, a biphasic continuum model, and to optimize the composition ratio of PVAH to replace the nucleus pulposus (NP) of the human intervertebral disc. Six types of PVAH specimens (3, 5, 7, 10, 15, 20 wt%) were prepared, then unconfined compression experiments were performed to acquire their material properties using the Holmes–Mow biphasic model. With an increasing weight percentage of PVA in PVAH, the Young’s modulus increased while the permeability parameter decreased. The Young’s modulus and permeability parameter were similar to those of the NP at 15 wt% and 20 wt%. The range of motion, facet joint force, and NP pressures measured from dynamic motional analysis of the lumbar segments with the NP model also exhibited similar values to those with 15~20 wt% PVAH models. Considering the structural stability and pain of the lumbar segments, it appears that 20 wt% PVAH is most suitable for replacing the NP.

Structural and mechanical characterization of bacterial cellulose-polyethylene glycol diacrylate composite gels

This study explores the structural and mechanical properties of bacterial cellulose-polyethylene glycol diacrylate (BC-PEGDA) composite gels. The molecular dynamics results obtained by solid-state ¹³C nuclear magnetic resonance analyses suggested that BC and PEGDA molecules were incompatible as composite gels, though BC fibers and PEGDA interact with each other. The mechanical strength of the gels depended on the amount of PEGDA, becoming softer and more stretchable when a tensile force was applied, but for a large amount of PEGDA, they became brittle. The BC-3% and 5% PEGDA gels had similar viscoelastic behaviors as a BC gel, and these composite gels could stick to human skin. Since BC-PEGDA composite gels are composed of BC and PEGDA-both of which are biocompatible, it is thought that these composite gels also have excellent biocompatibility. Taken together, we concluded that the BC-3% and 5% PEGDA gels have great potential for use in medical and cosmetic fields.