Abstract
Hydroxyapatite (HA) nanoparticle-reinforced chitosan composites are biocompatible and biodegradable structural materials that are used as biomaterials in tissue engineering. However, in order for these materials to function effectively as intended, e.g., to provide adequate structural support for repairing damaged tissues, it is necessary to analyse and optimise the material processing parameters that affect the relevant mechanical properties. Here we are concerned with the strength, stiffness and toughness of wet-spun HA-reinforced chitosan fibres. Unlike previous studies which have addressed each of these parameters as singly applied treatments, we have carried out an experiment designed using a two-factor analysis of variance to study the main effects of two key material processing parameters, namely HA concentration and crystallization temperature, and their interactions on the respective mechanical properties of the composite fibres. The analysis reveals that significant interaction occurs between the crystallization temperature and HA concentration. Starting at a low HA concentration level, the magnitude of the respective mechanical properties decreases significantly with increasing HA concentration until a critical HA concentration is reached, at around 0.20–0.30 (HA mass fraction), beyond which the magnitude of the mechanical properties increases significantly with HA concentration. The sensitivity of the mechanical properties to crystallization temperature is masked by the interaction between the two parameters—further analysis reveals that the dependence on crystallization temperature is significant in at least some levels of HA concentration. The magnitude of the mechanical properties of the chitosan composite fibre corresponding to 40 °C is higher than that at 100 °C at low HA concentration; the reverse applies at high HA concentration. In conclusion, the elasticity of the HA nanoparticle-reinforced chitosan composite fibre is sensitive to HA concentration and crystallization temperature, and there exists a critical concentration level whereby the magnitude of the mechanical property is a minimum.
Highlights
Hydroxyapatite is a calcium phosphate salt (Ca10(PO4)6(OH)2; HA) which occurs naturally in vertebrate tissues such as bones and teeth [1]
Zhang et al [12] found that HA/chitosan composite fibre could encourage the growth of cells residing on it; the population of cells increased by 43% (10 days) and 110% (15 days) in scaffolds made from electrospun HA/chitosan fibres
There exists a HA concentration that leads to a minimum value for the mechanical properties such that any increase in HA concentration thereafter would result in an increase in the stiffness, strength and toughness; in all the cases, it is shown that the critical HA concentration appears at around 0.30–0.40
Summary
Hydroxyapatite is a calcium phosphate salt (Ca10(PO4)6(OH); HA) which occurs naturally in vertebrate tissues such as bones and teeth [1]. We note that there are two key characteristics of HA which make it an ideal candidate for blending into and reinforcing the chitosan matrix for applications in tissue engineering [3,4,5]: (1) mechanical stability (when synthesized into the form of nanoparticles with size of 100 nm or less) [6,7] and (2) an affinity to biopolymers [8]. To this end, HA-reinforced chitosan composites in the form of fibres—especially with hierarchical architectures [9]. The study of Lai et al [13] reveals that seeding hMSCs in an HA-reinforced chitosan fibrous scaffold has potential for bone regeneration, and such a scaffold may be used for bone tissue engineering
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