The viscoelastic response of electrospun poly(vinyl alcohol) mats.

Native biological tissues are viscoelastic materials that undergo time-dependent loading in vivo. It is therefore crucial to ensure that biomedical materials have a suitable viscoelastic response for a given application. In this study, the viscoelastic properties of electrospun poly(vinyl alcohol) are investigated using tensile load relaxation testing. A five-parameter generalised Maxwell constitutive model is found to characterise the experimental response. The effect of polymer concentration and electrospinning voltage on model parameters is investigated in detail. The stiffness coefficients for the relaxation process appear to be dependent on the electrospinning conditions used whereas the time constants remain relatively unchanged. It is also observed that the stiffness parameters are linearly correlated with the equilibrium modulus, indicating that a single underlying material property dictates the relaxation moduli. Lastly, it is found that the viscoelastic model parameters are not predicted by the fibre diameter. These results provide an important understanding in designing electrospun mats with desired time-dependent properties.

Systematic mechanical evaluation of electrospun gelatin meshes.

Electrospinning is a simple and efficient process for producing sub-micron fibres. However, the process has many variables, and their effects on the non-woven mesh of fibres is complex. In particular, the effects on the mechanical properties of the fibre meshes are poorly understood. This paper conducts a parametric study, where the concentration and bloom strength of the gelatin solutions are varied, while all electrospinning process parameters are held constant. The effects on the fibrous meshes are monitored using scanning electron microscopy and mechanical testing under uniaxial tension. Mesh mechanical properties are relatively consistent, despite changes to the solutions, demonstrating the robustness of electrospinning. The gel strength of the solution is shown to have a statistically significant effect on the morphology, stiffness and strength of the meshes, while the fibre diameter has surprisingly little influence on the stiffness of the meshes. This experimental finding is supported by finite element analysis, demonstrating that the stiffness of the meshes is controlled by the volume fraction, rather than fibre diameter. Our results demonstrate the importance of understanding how electrospinning parameters influence the pore size of the meshes, as controlling fibre diameter alone is insufficient for consistent mechanical properties.

Strong and tough nanofibrous hydrogel composites based on biomimetic principles.

Mechanically robust hydrogels are required for many tissue engineering applications to serve as cell-supporting structures. Unlike natural tissues, the majority of existing tough hydrogels lack ordered microstructures organized to withstand specific loading conditions. In this work, electrospun gelatin nanofibres, mimicking the collagen network in native tissues, are used to strengthen and resist crack propagation in brittle alginate hydrogels. Aligned nanofibre reinforcement enhances the tensile strength of the hydrogels by up to two orders of magnitude. The nanofibres can be arranged as multilayer laminates with varying orientations, which increases the toughness by two orders of magnitude compared with the unreinforced hydrogel. This work demonstrates a two-part strategy of fibre reinforcement and composite lamination in manufacturing strong and tough hydrogels with flexible microstructures to suit different mechanical and biomedical requirements.

Nanofibrous hydrogel composites as mechanically robust tissue engineering scaffolds.

Hydrogels closely resemble the extracellular matrix (ECM) and can support cell proliferation while new tissue is formed, making them materials of choice as tissue engineering scaffolds. However, their sometimes-poor mechanical properties can hinder their application. The addition of meshes of nanofibers embedded in their matrix forms a composite that draws from the advantages of both components. Given that these materials are still in the early stages of development, there is a lack of uniformity across methods for characterizing their mechanical properties. Here, we propose a simple metric to enable comparisons between materials. The fibrous constituent improves the mechanical properties of the hydrogel, while the biocompatibility and functionality of the gels are maintained or even improved.