Composite hydrogels for nucleus pulposus tissue engineering

Tissue engineering offers a paradigm shift in the treatment of back pain. Engineered intervertebral discs could replace degenerated tissue and overcome the limitations of current treatments, which substantially alter the biomechanical properties of the spine. The centre of the disc, the nucleus pulposus, is an amorphous gel with a large bound water content and it can resist substantial compressive loads. Due to similarities in their compositions, hydrogels have frequently been considered as substitutes for the nucleus pulposus. However, there has been limited work characterising the time-dependent mechanical behaviour of hydrogel scaffolds for nucleus pulposus tissue engineering. Poroelastic behaviour, which plays a key role in nutrient transport, is of particular importance. Here, we investigate the time-dependent mechanical properties of gelatin and agar hydrogels and of gelatin-agar composites. The time-dependent properties of these hydrogels are explored using viscoelastic and poroelastic frameworks. Several gel formulations demonstrate comparable equilibrium elastic behaviour to the nucleus pulposus under unconfined compression, but permeability values that are much greater than those of the native tissue. A range of time-dependent responses are observed in the composite gels examined, presenting the opportunity for targeted design of custom hydrogels with combinations of mechanical properties optimized for tissue engineering applications. © 2011 Elsevier Ltd.

A family of simple benzene 1,3,5-tricarboxamide (BTA) aromatic carboxylic acid hydrogels.

We present the characterisation of a hydrogel forming family of benzene 1,3,5-tricarboxamide (BTA) aromatic carboxylic acid derivatives. The simple, easy to synthesise compounds presented here exhibit consistent gel formation at low concentrations through the use of a pH trigger.

Separating poroviscoelastic deformation mechanisms in hydrogels

Hydrogels have applications in drug delivery, mechanical actuation, and regenerative medicine. When hydrogels are deformed, load-relaxation arising from fluid flow - poroelasticity - and from rearrangement of the polymer network - viscoelasticity - is observed. The physical mechanisms are different in that poroelastic relaxation varies with experimental length-scale while viscoelastic does not. Here, we show that poroviscoelastic load-relaxation is the product of the two individual responses. The difference in length-scale dependence of the two mechanisms can be exploited to uniquely determine poroviscoelastic properties from simultaneous analysis of multi-scale indentation experiments, providing insight into hydrogel physical behavior. © 2013 American Institute of Physics.

Mechanical behaviour of electrospun fibre-reinforced hydrogels.

Mechanically robust and biomimicking scaffolds are needed for structural engineering of tissues such as the intervertebral disc, which are prone to failure and incapable of natural healing. Here, the formation of thick, randomly aligned polycaprolactone electrospun fibre structures infiltrated with alginate is reported. The composites are characterised using both indentation and tensile testing and demonstrate substantially different tensile and compressive moduli. The composites are mechanically robust and exhibit large strains-to-failure, exhibiting toughening mechanisms observed in other composite material systems. The method presented here provides a way to create large-scale biomimetic scaffolds that more closely mimic the composite structure of natural tissue, with tuneable tensile and compressive properties via the fibre and matrix phases, respectively.