A nano-solution to bone tissue engineering?

A team of chemical engineers have developed highly-porous, bioactive titania scaffolds that encourage bone tissue to regenerate itself, speeding up the healing process.

Repairing bones has long been a lengthy process – the damaged bone sections must first be realigned and then stabilized (typically using a cast), but then the patient must just wait for the healing process to happen. But today’s biomedical literature is full of materials that could speed this process up – bio-inspired scaffolds that can encourage bone tissue regeneration.

One material that has attracted particular attention is the ceramic, titanium dioxide (TiO₂). It is not only biocompatible, but porous structures made from it display excellent mechanical properties. However, questions have remained about its bioactivity, that is, its ability to bond to bone without the need for a secondary coating. A team of Latvian chemical engineers recently published work in Materials Letters [DOI: 10.1016/j.matlet.2015.07.017] to demonstrate that nano-TiO₂ might be the answer.

They took inspiration from the fact that all bioactive materials form a layer called “bonelike apatite” on their surfaces – it’s this that allows them to bond directly to native bone. Knowing that its formation is influenced by the surface (nanostructured surfaces stimulate more growth than microstructured) the team from Riga Technical University coated highly-porous TiO₂ ceramic scaffolds with TiO₂ nanopowder. The scaffolds were produced using polyurethane foams with fully interconnected pore structure as sacrificial templates. After removal of the template, some of the resulting TiO₂ scaffolds were additionally coated with a TiO₂ nanoparticles (average size 15nm).

The bioactivity of these scaffolds (coated and non-coated) was evaluated by immersing them in simulated body fluid (SBF) for 21 days – a well-established in vitro test method. The results showed that the surface microstructure of the uncoated TiO₂ scaffolds remained unchanged throughout the test. In contrast, after just seven days, agglomerates of white, spherical particles were observed on the coated scaffolds, and by Day 21, the particles formed a uniform layer across the entire structure. Further analysis showed this layer to comprise of calcium and phosphorus, indicating that it was, in fact apatite.

This work has confirmed that nanostructured TiO₂ scaffolds display in vitro bioactivity. It is hoped that such structures could find use in bone tissue regeneration applications.

D. Loca, I. Narkevica and J. Ozolins, Materials Letters (2015) 159, 309–312, “The effect of TiO₂ nanopowder coating on in-vitro bioactivity of porous TiO₂ scaffolds” DOI: 10.1016/j.matlet.2015.07.017