Scientific Method / Science & Exploration

Near-liquid CO2 gives a boost to cell scaffolds

Biocompatible cellular scaffold materials are the backbone of tissue …

Biomaterials research has mainly focused on moving away inorganic, man-made materials for reconstructive procedures (although we have seen continuing work there as well) and towards biocompatible scaffolds that can facilitate the regrowth of natural body structures. Mimicking the body’s unique mix of biocompatibility, mechanical integrity, and channels for moving nutrients and waste is a difficult task, and often one feature will come at the expense of another. Researchers have been experimenting with high pressure gases for hydrogel cellular scaffold material growth, with promising results.

Hydrogels are a natural choice for a soft-tissue scaffold—after all, they, like us, are mostly water anyway. Their production typically includes a natural polymer, often derived from tissue, and a chemical agent to cross-link the polymer chains. Cross-linking is exactly as it sounds: chains of the natural polymer are bonded together at mid-points to form a mesh structure. The density of these cross links and the conditions that they form under are huge factors in defining both the mechanical integrity of the gel, as well as its pore structure, which cells will need to grow into.

Work has been progressing in running the cross-linking reactions in high-pressure gases, mainly CO2 due to its compatibility with the scaffold materials. High-pressure gases are held near the critical point, meaning that they flow and behave somewhat like a liquid. In some recent experiments, polymer α-elastin was used for the scaffold material, and experiments were carried out using the cross linking agent glutaraldehyde and various times and pressures of CO2.

Just during simple handling, it became clear that the hydrogels produced under high pressures were much more mechanically robust than those produced at atmospheric pressures. Electron microscopy showed that, even though the average pore size in the high-pressure hydrogels was smaller, the interconnectivity among pores was greatly improved—that's a key factor that influences cell ingrowth, as well as the movement oxygen, nutrients, and cell waste. Tests with the atmospheric pressure hydrogel showed that cells only attached to the surface, with poor penetration into the bulk of the material. The high-pressure variant had much more complete cell penetration, at least to the extent that was allowed by the relatively small pores.

Although researchers pointed out that this isn’t a perfect, sliver-bullet hydrogel cellular scaffold material, the preliminary work is very encouraging. There are many more scaffold materials currently being tested for all sorts of tissue regeneration applications, and this process modification may enable materials that are deficient in their cellular compatibility to be processed in a way that makes them more useful. Although development and testing of anything related to medicine is a rigorous and often arduous process, the recent breakthroughs in biomaterials are encouraging.

Biomaterials, 2008. DOI:10.1016/j.biomaterials.2008.09.031 

Expand full story

This article does not have a comment thread.