Table 1 Overview on the NP treatment approach from the materials engineering perspective

1

Accessing the NP is only possible through the AF, leaving fissures that increase probability of herniation appearance.

Injectable material – so that only the area of the needle’s section of the AF is wounded.

[42]

2

The material cannot be polymerised before implantation, if it needs to be injected.

Material able to polymerize in vivo, by pH, ion interaction, temperature, light, or another possible factor.

[43, 44]

3

The NP tissue of a degenerated IVD tends to be a hostile environment for cells.

The material’s mechanical properties should be as close as possible with the mechanical properties of a healthy NP tissue. Hence, re-establishing IVD height and biomechanical function.

[45]

4

Cells injected in the NP of degenerated IVDs tend to lose the desired phenotype, due to the lack of hydrophilic molecules.

The material must be able to absorb a lot of water, at least 80%, just as a healthy NP matrix.

[5]

5

Non-degradable materials do not create or limit the space for new healthy tissue to grow.

The degradability rate must match the tissue’s rate of regeneration, not being at the expense of the mechanical properties.

[46]