Lasers for nano scaffolds

Finnish researchers have developed a direct-write three-dimensional method of forming biomaterials into microscopic scaffolds that can be used to rebuild body tissue.

VTT Technical Research Centre of Finland, Tampere University of Technology and Nanofoot Finland developed the methodology which enables the fabrication of nano and micrometre scale structures that can be used as parts of tissue engineering scaffolds. The project is funded by the BioneXt Tampere Research Programme.

The new process is based on the use of visible light, ultra short pulse laser. When focused inside photopolymerisable material the radiation causes a reaction, where two photons are absorbed simultaneously, leading to the polymerisation of the material.

One of the advantages of this two-photon polymerisation process is that the fabrication occurs below the surface of liquid material, and the polymerisation is confined only to the point of focus whose diameter can be much less than one micrometre. Conventional ultraviolet light induced polymerisation causes hardening of the material along the entire path of the UV-beam, making it impossible to form very small three-dimensional features. The two photon polymerisation process requires no utilisation of special photolithographic masks since the structure is formed directly inside the liquid volume.

High accuracy biomaterial structures need to be used as tissue engineering scaffolds or cell culture platforms where the fine features have to follow the dimensions of the cultured cells. So far the smallest features achieved in this project have been about 700 nanometres wide. As a reference one can compare it to the epithelial cells, which have a diameter of 11,000 - 12,000 nm or viruses that range in size between 10 - 100nm. The fabricated structures can be made of biodegradable materials and thus are biocompatible. The process can also be used in manufacturing structures for other applications such as optical waveguides, photonic crystals, and microfluidic channels.

Another advantage of this process is the possibility to use an inexpensive, low-power laser. Other research has typically used very expensive femtosecond titanium-sapphire pulse lasers. A much cheaper laser that produces longer, picoseconds width pulses has been used in the project.

The project has been accomplished as an interdisciplinary collaboration. Research Scientist Sanna Peltola from the Institute of Biomaterials, Tampere University of Technology has been responsible of the development of materials, and the research group of Research Professor Jouko Viitanen from VTT has developed the laser system. The Tampere University researchers have specified the stem cell culturing requirements. Laser machining company Nanofoot Finland is commercialising the new process.