Abstract
Reinforcing hydrogels with micro-fibre scaffolds obtained by a Melt-Electrospinning Writing (MEW) process has demonstrated great promise for developing tissue engineered (TE) constructs with mechanical properties compatible to native tissues. However, the mechanical performance and reinforcement mechanism of the micro-fibre reinforced hydrogels is not yet fully understood. In this study, FE models, implementing material properties measured experimentally, were used to explore the reinforcement mechanism of fibre-hydrogel composites. First, a continuum FE model based on idealized scaffold geometry was used to capture reinforcement effects related to the suppression of lateral gel expansion by the scaffold, while a second micro-FE model based on micro-CT images of the real construct geometry during compaction captured the effects of load transfer through the scaffold interconnections. Results demonstrate that the reinforcement mechanism at higher scaffold volume fractions was dominated by the load carrying-ability of the fibre scaffold interconnections, which was much higher than expected based on testing scaffolds alone because the hydrogel provides resistance against buckling of the scaffold. We propose that the theoretical understanding presented in this work will assist the design of more effective composite constructs with potential applications in a wide range of TE conditions.
Highlights
Soft tissues, e.g. articular cartilage or cardiac muscle, are complex composite materials consisting of collagen fibrils reinforcing a cell-containing proteoglycan gel-like matrix[1,2]
While the accurate fibre placement onto the collector enabled the formation of controlled squared fibre arrangements in two-dimensions (2D) (Fig. 1A–F), some fibre sagging occurred towards the middle of the fibre walls, which was more evident for scaffolds with larger fibre spacings (Fig. 1A–F)
We demonstrated that the reinforcement mechanism of the composite constructs is governed by two different mechanisms
Summary
E.g. articular cartilage or cardiac muscle, are complex composite materials consisting of collagen fibrils reinforcing a cell-containing proteoglycan gel-like matrix[1,2]. To mimic such natural composite structures, recent studies have highlighted the potential of developing composite constructs composed of hydrogels and fibrous materials[3,4,5] Hydrogels, with their highly hydrated polymer network, can provide the cells an environment that further resembles the natural extracellular matrix (ECM)[6], whilst the reinforcing fibres can provide the necessary mechanical properties, close to those of biological tissues[7]. This synergistic effect was assumed to be due to the fibres being pulled in tension when the construct was loaded in compression, i.e. a Poisson’s effect This assumption was supported by a relatively simple mathematical model that considered the hydrogel and fibre scaffolds as composed of an idealized geometry and linear elastic materials. By combing the simulation results with the experimental results, material parameters of the composite constituents are derived and the reinforcement mechanism of the fibres can be explained in detail
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