3D printing of materials has evolved rapidly during the last three decades to the point where desktop machines are now available at relatively low cost. These machines allow fabrication of almost any design that might be generated in a computer and now a team from Switzerland is using the system to create hierarchical components for tissue engineering.

Writing in the journal Acta Biomateriala [Béduer, A. et al. Acta Biomater. (2018); DOI: 10.1016/j.actbio.2018.05.056], Amélie Béduer of the University of Geneva and EPFL, Lausanne and the Lausanne University Hospital and colleagues explain how they have developed a way to manufacture in an additive manner free-form centimeter-scale biocompatible objects with a hierarchical structure. These objects can be used as scaffolds for tissue growth and could be implanted with only a minimally invasive procedure. The success of their approach pivots on the optimization of carboxymethylcellulose-based cryogel inks and their use in 3D printing on to a cryogenic substrate.

The researchers explain that their procedure with a basic commercial 3D printer allows them to fabricate highly porous and elastic cryogels structures that are biocompatible and have the added advantage of protecting the cells cultured within the component when it is compressed and injected into the host. Tests with mice have shown that such an implant can be readily injected under the skin. Once injected, the structure is quickly colonized by the animal's cells forming loose vascularized connective tissue with only minimal signs of inflammation. At three months following injection, the structure remains encapsulation-free.

It is possible to vary the local pore size simply by changing the temperatures of the substrate on to which the structure is cryogenically 3D printed, the team adds. This, they explain, allows them to control the overall cell seeding density of the structure at the local level as demonstrated by in vitro tests. This translates to control of the vascularization density in cell-free scaffolds in vivo.

The work circumvents the obvious problems of earlier approaches to the 3D printing of tissue engineering scaffolds in that the new structures are not bulky, are flexible, far less fragile than the products of other approaches, and can be injected under the skin. It also offers a way to exploit 3D printed hydrogels that was previously not possible and the system allows the use of multiple "inks" as well as being adaptable to most types of hydrogel.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".