The new process is based on the use of visible light, ultra short pulse laser. When focused inside photopolymerizable material the radiation causes a reaction, where two photons are absorbed simultaneously, thus leading to the polymerization of the material. One of the advantages of this so called two-photon polymerization process is that the fabrication occurs below the surface of liquid material, and the polymerization is confined only to the point of focus whose diameter can be much less than 1 micrometer. The conventional ultraviolet light induced polymerization causes hardening of the material along the entire path of the UV-beam, thus making it impossible to form very small three dimensional features. The two photon polymerization process requires no utilization 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 nanometers wide. As a reference one can compare it to the epithelial cells, which have a diameter of 11000 - 12000 nm or viruses that range in size between 10 - 100 nm. The fabricated structures can be made of biodegradable materials and thus are biocompatible. The process can also be utilized in manufacturing structures for other applications, e.g. optical waveguides, photonic crystals, and microfluidic channels.
Another advantage of this process is the possibility to utilize an inexpensive, low-power laser. Other research groups have 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. As far as is known there is only one research group in the USA, that has previously succeeded in polymerizing biomaterials with a similar system.
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 stem cell culturing requirements have been specified by the researchers of the Tampere University. Nanofoot Finland Oy is commercializing the new process. The company offers versatile services in the area of laser machining.
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