Summary

Hydrogel based systems are currently viewed as the best candidates for tissue engineering applications, however due to the lack of appropriate mechanical properties, researchers have developed fibre reinforced hydrogels to improve the mechanical properties. Fibre reinforced hydrogel scaffolds not only improve the mechanical stability, but also mimic the morphological features of the natural ECM. The addition of nano-sized fibres embedded in the hydrogel increases biocompatibility, as a large surface area is beneficial for cell attachment. The use of bioreactor systems, which promotes tissue growth via nutrient provision and mechanical stimulation, helps to develop nanofibre composites for tissue engineering. As a growing research field, especially in the field of load-bearing tissue engineering, much care should be taken to characterisation and analysis of mechanical properties of the scaffold. Indeed there is need to optimise higher throughput production methods and analysis in realistic load-bearing conditions to evaluate their in vivo efficacy and expanding potential clinical application.

Fibre reinforced calcium phosphate cements are a new class of biomaterials that are attracting and growing attention as a replacement for conventional calcium phosphate cements. The main purpose of fibre reinforced calcium phosphate cements is to overcome the brittle nature of conventional calcium phosphate cements by improve their mechanical properties and biological activity. Inclusion of fibres not only improves the fracture toughness, but also creates porosity within the cement microstructure that can potentially help cell ingrowth for new native tissue formation. The success of fibre reinforced calcium phosphate cements mainly depends on the relationship between the different constituents that form the composite and the orientation of the fibres. To improve mechanical stability, fibre reinforced calcium phosphate cements have been developed containing resorbable fibres and fibrous constructs such as yarns, nonwoven, woven and knitted fabrics. Many publications have focused on the mechanical properties of these fibre reinforced cements - however there is still considerable work required to understand the dominant factors affecting the mechanical properties and fracture mechanism of fibre reinforced composites. As these fibres reinforced cements are still in the early stages of development - there is still significant scope to understand the mechanical and biological behaviour of these materials with respect to improving adhesion between fibre and matrix and the mechanical stability after implantation and during the bone remodeling process.

For tissue regeneration, scaffold reinforced with fibres have been growing due to their high mechanical properties. These properties are depend on various factors such as volume fraction, fibre diameter, direction of alignment, bond between matrix and fibres, method of loading either grafting or cross-link and chemical compatibility of these material. Therefore, while designing a composite for particular application, one should consider these properties. Also, the processing technique plays an important role, which determines the orientation of the fibres, improve the bond between fibre and matrix which ultimately produces homogeneous structure.

The addition of fibres to a scaffold not only improves the mechanical properties but also helps to improve the biocompatibility and biodegradability of the composite. For example, chitin fibres reinforced with PLA helps to maintain the pH during degradation, which helps for cell attachment and proliferation [132].

Tissue engineering is a very broad field that can be an effective tool for variety of composites that include fibre reinforced hydrogels and/or fibre reinforced calcium phosphate cements. As we have attempted to describe mechanical properties of fibres in some detail for tissue repair, as such there is no standard protocol developed for various composites. Innovation in the fabrication of fibre structures and characterisation continues to drive research for tissue repair and regeneration.

 
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