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Laser light produces synthetic tissue for regenerative medicine

Tissue engineering pursues the aim of replacing natural tissue after injuries and illnesses with implants, which enable the body to regenerate itself with the patient’s own cells. So that tissue can be produced to replicate the body’s natural tissue, knowledge of the interaction between cells in a three-dimensional framework and the growth conditions for complete regeneration is essential. Using a special laser technique, research scientists at the Fraunhofer Institute for Laser Technology ILT and other Fraunhofer Institutes have succeeded in producing hybrid biomimetic matrices. These serve as a basis for scaffold and implant structures on which the cells can grow effectively.

If tissue has been badly damaged by disease or due to an accident or if parts of the tissue have been completely removed, the body is often unable to regenerate this tissue itself. What’s more, in many cases no endogenous material is available for transplants. As a result, demand in the medical field is increasing for implants that enable complete regeneration to take place. But the current artificially-produced implants are often not adequately adapted to the environment in the patient’s body and are therefore of limited use as a tissue replacement. The main reason for this lack is the missing knowledge on how cells react to a three-dimensional environment.

Scientists at Fraunhofer ILT in cooperation with other Fraunhofer Institutes, however, have developed a process for producing biomimetic scaffolds, which closely emulates the endogenous tissue. This process allows the fabrication of specialised model systems for the study of three-dimensional cell growth, for the future generation of optimal conditions for the cells to colonise and grow. For this purpose the Aachen-based research scientists have transferred the rapid prototyping technique to endogenous materials. They combine organic substances with polymers and produce three-dimensional structures, which are suitable for building artificial tissue.

As the basis the research scientists use dissolved proteins and polymers, which are irradiated with laser light and crosslinked by photolytic processes. For this they deploy specially developed laser systems, which by means of ultra-short laser pulses trigger multiphoton processes that lead to polymerisation in the volume. In contrast to conventional processes, innovative and low-cost microchip lasers with pulse durations in the picosecond range are used at Fraunhofer ILT, which render the technique affordable for any laboratory. The key factors in the process are the extremely short pulse durations and the high laser-beam intensities. The short pulse duration leads to almost no damage by heat to the material. Ultra-fast pulses in the megawatt range drive a massive amount of protons into the laser focus in an extremely short time, triggering a non-linear effect.

The molecules in the liquid absorb several photons simultaneously, causing free radicals to form which trigger a chemical reaction between the surrounding molecules. As a result of this process of multiphoton polymerisation, solids form from the liquid. On the basis of CAD data the system controls the position of the laser beam through a microscope with a precision of a few hundred nanometers in such a way that micrometer-fine, stable volume elements of crosslinked material gradually form.

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